From 64f77827d2ab6711efabb423a08933f289dbce5e Mon Sep 17 00:00:00 2001 From: nsz Date: Sun, 24 Jul 2011 14:05:47 +0200 Subject: [PATCH] remove old c1x draft (n1548) --- n1548.html | 34498 --------------------------------------------------- n1548.txt | 26321 --------------------------------------- 2 files changed, 60819 deletions(-) delete mode 100644 n1548.html delete mode 100644 n1548.txt diff --git a/n1548.html b/n1548.html deleted file mode 100644 index 6502e1f..0000000 --- a/n1548.html +++ /dev/null @@ -1,34498 +0,0 @@ -N1548 December 2, 2010 ISO/IEC 9899:201x -

-N1548                    Committee Draft -- December 2, 2010          ISO/IEC 9899:201x
-
-
-
-
-INTERNATIONAL STANDARD                         (C)ISO/IEC              ISO/IEC 9899:201x
-
-
-
-
-
- -

Contents -

Programming languages -- C

-
-
-
-                                       ABSTRACT
-
-
-
-                     (Cover sheet to be provided by ISO Secretariat.)
-
-This International Standard specifies the form and establishes the interpretation of
-programs expressed in the programming language C. Its purpose is to promote
-portability, reliability, maintainability, and efficient execution of C language programs on
-a variety of computing systems.
-
-Clauses are included that detail the C language itself and the contents of the C language
-execution library. Annexes summarize aspects of both of them, and enumerate factors
-that influence the portability of C programs.
-
-Although this International Standard is intended to guide knowledgeable C language
-programmers as well as implementors of C language translation systems, the document
-itself is not designed to serve as a tutorial.
-
-Recipients of this draft are invited to submit, with their comments, notification of any
-relevant patent rights of which they are aware and to provide supporting documentation.
-
-Changes from the previous draft (N1256) are indicated by ''diff marks'' in the right
-margin: deleted text is marked with ''*'', new or changed text with '' ''.
-
-
-
- -

Contents -

Contents

- - -

Contents -

Foreword

-

- ISO (the International Organization for Standardization) and IEC (the International - Electrotechnical Commission) form the specialized system for worldwide - standardization. National bodies that are member of ISO or IEC participate in the - development of International Standards through technical committees established by the - respective organization to deal with particular fields of technical activity. ISO and IEC - technical committees collaborate in fields of mutual interest. Other international - organizations, governmental and non-governmental, in liaison with ISO and IEC, also - take part in the work. -

- International Standards are drafted in accordance with the rules given in the ISO/IEC - Directives, Part 2. This International Standard was drafted in accordance with the fifth - edition (2004). -

- In the field of information technology, ISO and IEC have established a joint technical - committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical - committee are circulated to national bodies for voting. Publication as an International - Standard requires approval by at least 75% of the national bodies casting a vote. -

- Attention is drawn to the possibility that some of the elements of this document may be - the subject of patent rights. ISO and IEC shall not be held responsible for identifying any - or all such patent rights. -

- This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1, - Information technology, Subcommittee SC 22, Programming languages, their - environments and system software interfaces. The Working Group responsible for this - standard (WG 14) maintains a site on the World Wide Web at http://www.open- - std.org/JTC1/SC22/WG14/ containing additional information relevant to this - standard such as a Rationale for many of the decisions made during its preparation and a - log of Defect Reports and Responses. -

- This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as - corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and - ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include: -

-

- Major changes in the second edition included: -

-

- Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, * - I, J, the bibliography, and the index are for information only. In accordance with Part 2 of - the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples - are also for information only. - - -

Contents -

Introduction

-

- With the introduction of new devices and extended character sets, new features may be - added to this International Standard. Subclauses in the language and library clauses warn - implementors and programmers of usages which, though valid in themselves, may - conflict with future additions. -

- Certain features are obsolescent, which means that they may be considered for - withdrawal in future revisions of this International Standard. They are retained because - of their widespread use, but their use in new implementations (for implementation - features) or new programs (for language [6.11] or library features [7.30]) is discouraged. -

- This International Standard is divided into four major subdivisions: -

-

- Examples are provided to illustrate possible forms of the constructions described. - Footnotes are provided to emphasize consequences of the rules described in that - subclause or elsewhere in this International Standard. References are used to refer to - other related subclauses. Recommendations are provided to give advice or guidance to - implementors. Annexes provide additional information and summarize the information - contained in this International Standard. A bibliography lists documents that were - referred to during the preparation of the standard. -

- The language clause (clause 6) is derived from ''The C Reference Manual''. -

- The library clause (clause 7) is based on the 1984 /usr/group Standard. - - - -

Contents -

Programming languages -- C

- - - - -

Contents -

1. Scope

-

- This International Standard specifies the form and establishes the interpretation of - programs written in the C programming language.1) It specifies -

-

- This International Standard does not specify -

- -

Footnotes -

1) This International Standard is designed to promote the portability of C programs among a variety of - data-processing systems. It is intended for use by implementors and programmers. - - -

Contents -

2. Normative references

-

- The following referenced documents are indispensable for the application of this - document. For dated references, only the edition cited applies. For undated references, - the latest edition of the referenced document (including any amendments) applies. -

- ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for - use in the physical sciences and technology. -

- ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information - interchange. -

- ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental - terms. -

- ISO 4217, Codes for the representation of currencies and funds. -

- ISO 8601, Data elements and interchange formats -- Information interchange -- - Representation of dates and times. -

- ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded - Character Set (UCS). -

- IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously - designated IEC 559:1989). - - -

Contents -

3. Terms, definitions, and symbols

-

- For the purposes of this International Standard, the following definitions apply. Other - terms are defined where they appear in italic type or on the left side of a syntax rule. - Terms explicitly defined in this International Standard are not to be presumed to refer - implicitly to similar terms defined elsewhere. Terms not defined in this International - Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not - defined in this International Standard are to be interpreted according to ISO 31-11. - -

Contents -

3.1

-

- access
- <execution-time action> to read or modify the value of an object -

- NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used. - -

- NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value. - -

- NOTE 3 Expressions that are not evaluated do not access objects. - - -

Contents -

3.2

-

- alignment
- requirement that objects of a particular type be located on storage boundaries with - addresses that are particular multiples of a byte address - -

Contents -

3.3

-

- argument
- actual argument - actual parameter (deprecated) - expression in the comma-separated list bounded by the parentheses in a function call - expression, or a sequence of preprocessing tokens in the comma-separated list bounded - by the parentheses in a function-like macro invocation - -

Contents -

3.4

-

- behavior
- external appearance or action - -

Contents -

3.4.1

-

- implementation-defined behavior
- unspecified behavior where each implementation documents how the choice is made -

- EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit - when a signed integer is shifted right. - - -

Contents -

3.4.2

-

- locale-specific behavior
- behavior that depends on local conventions of nationality, culture, and language that each - implementation documents - -

- EXAMPLE An example of locale-specific behavior is whether the islower function returns true for - characters other than the 26 lowercase Latin letters. - - -

Contents -

3.4.3

-

- undefined behavior
- behavior, upon use of a nonportable or erroneous program construct or of erroneous data, - for which this International Standard imposes no requirements -

- NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable - results, to behaving during translation or program execution in a documented manner characteristic of the - environment (with or without the issuance of a diagnostic message), to terminating a translation or - execution (with the issuance of a diagnostic message). - -

- EXAMPLE An example of undefined behavior is the behavior on integer overflow. - - -

Contents -

3.4.4

-

- unspecified behavior
- use of an unspecified value, or other behavior where this International Standard provides - two or more possibilities and imposes no further requirements on which is chosen in any - instance -

- EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are - evaluated. - - -

Contents -

3.5

-

- bit
- unit of data storage in the execution environment large enough to hold an object that may - have one of two values -

- NOTE It need not be possible to express the address of each individual bit of an object. - - -

Contents -

3.6

-

- byte
- addressable unit of data storage large enough to hold any member of the basic character - set of the execution environment -

- NOTE 1 It is possible to express the address of each individual byte of an object uniquely. - -

- NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation- - defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order - bit. - - -

Contents -

3.7

-

- character
- <abstract> member of a set of elements used for the organization, control, or - representation of data - -

Contents -

3.7.1

-

- character
- single-byte character - <C> bit representation that fits in a byte - - -

Contents -

3.7.2

-

- multibyte character
- sequence of one or more bytes representing a member of the extended character set of - either the source or the execution environment -

- NOTE The extended character set is a superset of the basic character set. - - -

Contents -

3.7.3

-

- wide character
- bit representation that fits in an object of type wchar_t, capable of representing any - character in the current locale - -

Contents -

3.8

-

- constraint
- restriction, either syntactic or semantic, by which the exposition of language elements is - to be interpreted - -

Contents -

3.9

-

- correctly rounded result
- representation in the result format that is nearest in value, subject to the current rounding - mode, to what the result would be given unlimited range and precision - -

Contents -

3.10

-

- diagnostic message
- message belonging to an implementation-defined subset of the implementation's message - output - -

Contents -

3.11

-

- forward reference
- reference to a later subclause of this International Standard that contains additional - information relevant to this subclause - -

Contents -

3.12

-

- implementation
- particular set of software, running in a particular translation environment under particular - control options, that performs translation of programs for, and supports execution of - functions in, a particular execution environment - -

Contents -

3.13

-

- implementation limit
- restriction imposed upon programs by the implementation - -

Contents -

3.14

-

- memory location
- either an object of scalar type, or a maximal sequence of adjacent bit-fields all having - nonzero width - -

- NOTE 1 Two threads of execution can update and access separate memory locations without interfering - with each other. - -

- NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same - applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the - two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member - declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all - members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those - intervening bit-fields happen to be. - -

- EXAMPLE A structure declared as -

-          struct {
-                char a;
-                int b:5, c:11, :0, d:8;
-                struct { int ee:8; } e;
-          }
-
- contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate - memory locations, and can be modified concurrently without interfering with each other. The bit-fields b - and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently - modified, but b and a, for example, can be. - - -

Contents -

3.15

-

- object
- region of data storage in the execution environment, the contents of which can represent - values -

- NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1. - - -

Contents -

3.16

-

- parameter
- formal parameter - formal argument (deprecated) - object declared as part of a function declaration or definition that acquires a value on - entry to the function, or an identifier from the comma-separated list bounded by the - parentheses immediately following the macro name in a function-like macro definition - -

Contents -

3.17

-

- recommended practice
- specification that is strongly recommended as being in keeping with the intent of the - standard, but that may be impractical for some implementations - -

Contents -

3.18

-

- runtime-constraint
- requirement on a program when calling a library function -

- NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and - need not be diagnosed at translation time. - -

- NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime- - constraints for a library function are not violated by the program; see K.3.1.4. - - -

Contents -

3.19

-

- value
- precise meaning of the contents of an object when interpreted as having a specific type - -

Contents -

3.19.1

-

- implementation-defined value
- unspecified value where each implementation documents how the choice is made - -

Contents -

3.19.2

-

- indeterminate value
- either an unspecified value or a trap representation - -

Contents -

3.19.3

-

- unspecified value
- valid value of the relevant type where this International Standard imposes no - requirements on which value is chosen in any instance -

- NOTE An unspecified value cannot be a trap representation. - - -

Contents -

3.19.4

-

- trap representation
- an object representation that need not represent a value of the object type - -

Contents -

3.19.5

-

- perform a trap
- interrupt execution of the program such that no further operations are performed -

- NOTE In this International Standard, when the word ''trap'' is not immediately followed by - ''representation'', this is the intended usage.2) - - -

Footnotes -

2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap - representation might perform a trap but is not required to (see 6.2.6.1). - - -

Contents -

3.20

-

- [^ x^]
- ceiling of x: the least integer greater than or equal to x -

- EXAMPLE [^2.4^] is 3, [^-2.4^] is -2. - - -

Contents -

3.21

-

- [_ x_]
- floor of x: the greatest integer less than or equal to x -

- EXAMPLE [_2.4_] is 2, [_-2.4_] is -3. - - - - - - -

Contents -

4. Conformance

-

- In this International Standard, ''shall'' is to be interpreted as a requirement on an - implementation or on a program; conversely, ''shall not'' is to be interpreted as a - prohibition. -

- If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime- - constraint is violated, the behavior is undefined. Undefined behavior is otherwise - indicated in this International Standard by the words ''undefined behavior'' or by the - omission of any explicit definition of behavior. There is no difference in emphasis among - these three; they all describe ''behavior that is undefined''. -

- A program that is correct in all other aspects, operating on correct data, containing - unspecified behavior shall be a correct program and act in accordance with 5.1.2.3. -

- The implementation shall not successfully translate a preprocessing translation unit - containing a #error preprocessing directive unless it is part of a group skipped by - conditional inclusion. -

- A strictly conforming program shall use only those features of the language and library - specified in this International Standard.3) It shall not produce output dependent on any - unspecified, undefined, or implementation-defined behavior, and shall not exceed any - minimum implementation limit. -

- The two forms of conforming implementation are hosted and freestanding. A conforming - hosted implementation shall accept any strictly conforming program. A conforming - freestanding implementation shall accept any strictly conforming program that does not - use complex types and in which the use of the features specified in the library clause - (clause 7) is confined to the contents of the standard headers <float.h>, - <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>, - <stddef.h>, and <stdint.h>. A conforming implementation may have extensions - (including additional library functions), provided they do not alter the behavior of any - strictly conforming program.4) - - - - -

- A conforming program is one that is acceptable to a conforming implementation.5) -

- An implementation shall be accompanied by a document that defines all implementation- - defined and locale-specific characteristics and all extensions. -

Forward references: conditional inclusion (6.10.1), error directive (6.10.5), - characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h> - (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15), - variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h> - (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20). - - - - - - -

Footnotes -

3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded - by an appropriate conditional inclusion preprocessing directive using the related macro. For example: - -

-         #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
-            /* ... */
-            fesetround(FE_UPWARD);
-            /* ... */
-         #endif
-
- - -

4) This implies that a conforming implementation reserves no identifiers other than those explicitly - reserved in this International Standard. - -

5) Strictly conforming programs are intended to be maximally portable among conforming - implementations. Conforming programs may depend upon nonportable features of a conforming - implementation. - - -

Contents -

5. Environment

-

- An implementation translates C source files and executes C programs in two data- - processing-system environments, which will be called the translation environment and - the execution environment in this International Standard. Their characteristics define and - constrain the results of executing conforming C programs constructed according to the - syntactic and semantic rules for conforming implementations. -

Forward references: In this clause, only a few of many possible forward references - have been noted. - -

Contents -

5.1 Conceptual models

- -

Contents -

5.1.1 Translation environment

- -

Contents -

5.1.1.1 Program structure
-

- A C program need not all be translated at the same time. The text of the program is kept - in units called source files, (or preprocessing files) in this International Standard. A - source file together with all the headers and source files included via the preprocessing - directive #include is known as a preprocessing translation unit. After preprocessing, a - preprocessing translation unit is called a translation unit. Previously translated translation - units may be preserved individually or in libraries. The separate translation units of a - program communicate by (for example) calls to functions whose identifiers have external - linkage, manipulation of objects whose identifiers have external linkage, or manipulation - of data files. Translation units may be separately translated and then later linked to - produce an executable program. -

Forward references: linkages of identifiers (6.2.2), external definitions (6.9), - preprocessing directives (6.10). - -

Contents -

5.1.1.2 Translation phases
-

- The precedence among the syntax rules of translation is specified by the following - phases.6) -

    -
  1. Physical source file multibyte characters are mapped, in an implementation- - defined manner, to the source character set (introducing new-line characters for - end-of-line indicators) if necessary. Trigraph sequences are replaced by - corresponding single-character internal representations. - - - - -
  2. Each instance of a backslash character (\) immediately followed by a new-line - character is deleted, splicing physical source lines to form logical source lines. - Only the last backslash on any physical source line shall be eligible for being part - of such a splice. A source file that is not empty shall end in a new-line character, - which shall not be immediately preceded by a backslash character before any such - splicing takes place. -
  3. The source file is decomposed into preprocessing tokens7) and sequences of - white-space characters (including comments). A source file shall not end in a - partial preprocessing token or in a partial comment. Each comment is replaced by - one space character. New-line characters are retained. Whether each nonempty - sequence of white-space characters other than new-line is retained or replaced by - one space character is implementation-defined. -
  4. Preprocessing directives are executed, macro invocations are expanded, and - _Pragma unary operator expressions are executed. If a character sequence that - matches the syntax of a universal character name is produced by token - concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing - directive causes the named header or source file to be processed from phase 1 - through phase 4, recursively. All preprocessing directives are then deleted. -
  5. Each source character set member and escape sequence in character constants and - string literals is converted to the corresponding member of the execution character - set; if there is no corresponding member, it is converted to an implementation- - defined member other than the null (wide) character.8) -
  6. Adjacent string literal tokens are concatenated. -
  7. White-space characters separating tokens are no longer significant. Each - preprocessing token is converted into a token. The resulting tokens are - syntactically and semantically analyzed and translated as a translation unit. -
  8. All external object and function references are resolved. Library components are - linked to satisfy external references to functions and objects not defined in the - current translation. All such translator output is collected into a program image - which contains information needed for execution in its execution environment. -
-

Forward references: universal character names (6.4.3), lexical elements (6.4), - preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9). - - - - - -

Footnotes -

6) Implementations shall behave as if these separate phases occur, even though many are typically folded - together in practice. Source files, translation units, and translated translation units need not - necessarily be stored as files, nor need there be any one-to-one correspondence between these entities - and any external representation. The description is conceptual only, and does not specify any - particular implementation. - -

7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is - context-dependent. For example, see the handling of < within a #include preprocessing directive. - -

8) An implementation need not convert all non-corresponding source characters to the same execution - character. - - -

Contents -

5.1.1.3 Diagnostics
-

- A conforming implementation shall produce at least one diagnostic message (identified in - an implementation-defined manner) if a preprocessing translation unit or translation unit - contains a violation of any syntax rule or constraint, even if the behavior is also explicitly - specified as undefined or implementation-defined. Diagnostic messages need not be - produced in other circumstances.9) -

- EXAMPLE An implementation shall issue a diagnostic for the translation unit: -

-          char i;
-          int i;
-
- because in those cases where wording in this International Standard describes the behavior for a construct - as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed. - - -

Footnotes -

9) The intent is that an implementation should identify the nature of, and where possible localize, each - violation. Of course, an implementation is free to produce any number of diagnostics as long as a - valid program is still correctly translated. It may also successfully translate an invalid program. - - -

Contents -

5.1.2 Execution environments

-

- Two execution environments are defined: freestanding and hosted. In both cases, - program startup occurs when a designated C function is called by the execution - environment. All objects with static storage duration shall be initialized (set to their - initial values) before program startup. The manner and timing of such initialization are - otherwise unspecified. Program termination returns control to the execution - environment. -

Forward references: storage durations of objects (6.2.4), initialization (6.7.9). - -

Contents -

5.1.2.1 Freestanding environment
-

- In a freestanding environment (in which C program execution may take place without any - benefit of an operating system), the name and type of the function called at program - startup are implementation-defined. Any library facilities available to a freestanding - program, other than the minimal set required by clause 4, are implementation-defined. -

- The effect of program termination in a freestanding environment is implementation- - defined. - -

Contents -

5.1.2.2 Hosted environment
-

- A hosted environment need not be provided, but shall conform to the following - specifications if present. - - - - - - -

Contents -

5.1.2.2.1 Program startup
-

- The function called at program startup is named main. The implementation declares no - prototype for this function. It shall be defined with a return type of int and with no - parameters: -

-         int main(void) { /* ... */ }
-
- or with two parameters (referred to here as argc and argv, though any names may be - used, as they are local to the function in which they are declared): -
-         int main(int argc, char *argv[]) { /* ... */ }
-
- or equivalent;10) or in some other implementation-defined manner. -

- If they are declared, the parameters to the main function shall obey the following - constraints: -

- -

Footnotes -

10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as - char ** argv, and so on. - - -

Contents -

5.1.2.2.2 Program execution
-

- In a hosted environment, a program may use all the functions, macros, type definitions, - and objects described in the library clause (clause 7). - - - - - - -

Contents -

5.1.2.2.3 Program termination
-

- If the return type of the main function is a type compatible with int, a return from the - initial call to the main function is equivalent to calling the exit function with the value - returned by the main function as its argument;11) reaching the } that terminates the - main function returns a value of 0. If the return type is not compatible with int, the - termination status returned to the host environment is unspecified. -

Forward references: definition of terms (7.1.1), the exit function (7.22.4.4). - -

Footnotes -

11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main - will have ended in the former case, even where they would not have in the latter. - - -

Contents -

5.1.2.3 Program execution
-

- The semantic descriptions in this International Standard describe the behavior of an - abstract machine in which issues of optimization are irrelevant. -

- Accessing a volatile object, modifying an object, modifying a file, or calling a function - that does any of those operations are all side effects,12) which are changes in the state of - the execution environment. Evaluation of an expression in general includes both value - computations and initiation of side effects. Value computation for an lvalue expression - includes determining the identity of the designated object. -

- Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations - executed by a single thread, which induces a partial order among those evaluations. - Given any two evaluations A and B, if A is sequenced before B, then the execution of A - shall precede the execution of B. (Conversely, if A is sequenced before B, then B is - sequenced after A.) If A is not sequenced before or after B, then A and B are - unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced - either before or after B, but it is unspecified which.13) The presence of a sequence point - between the evaluation of expressions A and B implies that every value computation and - side effect associated with A is sequenced before every value computation and side effect - associated with B. (A summary of the sequence points is given in annex C.) -

- In the abstract machine, all expressions are evaluated as specified by the semantics. An - actual implementation need not evaluate part of an expression if it can deduce that its - value is not used and that no needed side effects are produced (including any caused by - - - calling a function or accessing a volatile object). -

- When the processing of the abstract machine is interrupted by receipt of a signal, the - values of objects that are neither lock-free atomic objects nor of type volatile - sig_atomic_t are unspecified, and the value of any object that is modified by the - handler that is neither a lock-free atomic object nor of type volatile - sig_atomic_t becomes undefined. -

- The least requirements on a conforming implementation are: -

- This is the observable behavior of the program. -

- What constitutes an interactive device is implementation-defined. -

- More stringent correspondences between abstract and actual semantics may be defined by - each implementation. -

- EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual - semantics: at every sequence point, the values of the actual objects would agree with those specified by the - abstract semantics. The keyword volatile would then be redundant. -

- Alternatively, an implementation might perform various optimizations within each translation unit, such - that the actual semantics would agree with the abstract semantics only when making function calls across - translation unit boundaries. In such an implementation, at the time of each function entry and function - return where the calling function and the called function are in different translation units, the values of all - externally linked objects and of all objects accessible via pointers therein would agree with the abstract - semantics. Furthermore, at the time of each such function entry the values of the parameters of the called - function and of all objects accessible via pointers therein would agree with the abstract semantics. In this - type of implementation, objects referred to by interrupt service routines activated by the signal function - would require explicit specification of volatile storage, as well as other implementation-defined - restrictions. - -

- EXAMPLE 2 In executing the fragment -

-          char c1, c2;
-          /* ... */
-          c1 = c1 + c2;
-
- the ''integer promotions'' require that the abstract machine promote the value of each variable to int size - and then add the two ints and truncate the sum. Provided the addition of two chars can be done without - overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only - produce the same result, possibly omitting the promotions. - -

- EXAMPLE 3 Similarly, in the fragment -

-          float f1, f2;
-          double d;
-          /* ... */
-          f1 = f2 * d;
-
- the multiplication may be executed using single-precision arithmetic if the implementation can ascertain - that the result would be the same as if it were executed using double-precision arithmetic (for example, if d - were replaced by the constant 2.0, which has type double). - -

- EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate - semantics. Values are independent of whether they are represented in a register or in memory. For - example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load - is required to round to the precision of the storage type. In particular, casts and assignments are required to - perform their specified conversion. For the fragment -

-          double d1, d2;
-          float f;
-          d1 = f = expression;
-          d2 = (float) expression;
-
- the values assigned to d1 and d2 are required to have been converted to float. - -

- EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in - precision as well as range. The implementation cannot generally apply the mathematical associative rules - for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of - overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to - rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real - numbers are often not valid (see F.9). -

-          double x, y, z;
-          /* ... */
-          x = (x * y) * z;            //   not equivalent to x   *= y * z;
-          z = (x - y) + y ;           //   not equivalent to z   = x;
-          z = x + x * y;              //   not equivalent to z   = x * (1.0 + y);
-          y = x / 5.0;                //   not equivalent to y   = x * 0.2;
-
- -

- EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment -

-          int a, b;
-          /* ... */
-          a = a + 32760 + b + 5;
-
- the expression statement behaves exactly the same as -
-          a = (((a + 32760) + b) + 5);
-
- due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is - next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in - which overflows produce an explicit trap and in which the range of values representable by an int is - [-32768, +32767], the implementation cannot rewrite this expression as -
-          a = ((a + b) + 32765);
-
- since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap - while the original expression would not; nor can the expression be rewritten either as - -
-          a = ((a + 32765) + b);
-
- or -
-          a = (a + (b + 32765));
-
- since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine - in which overflow silently generates some value and where positive and negative overflows cancel, the - above expression statement can be rewritten by the implementation in any of the above ways because the - same result will occur. - -

- EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the - following fragment -

-          #include <stdio.h>
-          int sum;
-          char *p;
-          /* ... */
-          sum = sum * 10 - '0' + (*p++ = getchar());
-
- the expression statement is grouped as if it were written as -
-          sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
-
- but the actual increment of p can occur at any time between the previous sequence point and the next - sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned - value. - -

Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the - signal function (7.14), files (7.21.3). - -

Footnotes -

12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status - flags and control modes. Floating-point operations implicitly set the status flags; modes affect result - values of floating-point operations. Implementations that support such floating-point state are - required to regard changes to it as side effects -- see annex F for details. The floating-point - environment library <fenv.h> provides a programming facility for indicating when these side - effects matter, freeing the implementations in other cases. - -

13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations - cannot interleave, but can be executed in any order. - - -

Contents -

5.1.2.4 Multi-threaded executions and data races
-

- Under a hosted implementation, a program can have more than one thread of execution - (or thread) running concurrently. The execution of each thread proceeds as defined by - the remainder of this standard. The execution of the entire program consists of an - execution of all of its threads.14) Under a freestanding implementation, it is - implementation-defined whether a program can have more than one thread of execution. -

- The value of an object visible to a thread T at a particular point is the initial value of the - object, a value stored in the object by T , or a value stored in the object by another thread, - according to the rules below. -

- NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by - the desire to support atomic operations with explicit and detailed visibility constraints. However, it also - implicitly supports a simpler view for more restricted programs. - -

- Two expression evaluations conflict if one of them modifies a memory location and the - other one reads or modifies the same memory location. - - - - - -

- The library defines a number of atomic operations (7.17) and operations on mutexes - (7.25.4) that are specially identified as synchronization operations. These operations play - a special role in making assignments in one thread visible to another. A synchronization - operation on one or more memory locations is either an acquire operation, a release - operation, both an acquire and release operation, or a consume operation. A - synchronization operation without an associated memory location is a fence and can be - either an acquire fence, a release fence, or both an acquire and release fence. In addition, - there are relaxed atomic operations, which are not synchronization operations, and - atomic read-modify-write operations, which have special characteristics. -

- NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations - composing the mutex. Correspondingly, a call that releases the same mutex will perform a release - operation on those same locations. Informally, performing a release operation on A forces prior side effects - on other memory locations to become visible to other threads that later perform an acquire or consume - operation on A. We do not include relaxed atomic operations as synchronization operations although, like - synchronization operations, they cannot contribute to data races. - -

- All modifications to a particular atomic object M occur in some particular total order, - called the modification order of M. If A and B are modifications of an atomic object M, - and A happens before B, then A shall precede B in the modification order of M, which is - defined below. -

- NOTE 3 This states that the modification orders must respect the ''happens before'' relation. - -

- NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be - combined into a single total order for all objects. In general this will be impossible since different threads - may observe modifications to different variables in inconsistent orders. - -

- A release sequence on an atomic object M is a maximal contiguous sub-sequence of side - effects in the modification order of M, where the first operation is a release and every - subsequent operation either is performed by the same thread that performed the release or - is an atomic read-modify-write operation. -

- Certain library calls synchronize with other library calls performed by another thread. In - particular, an atomic operation A that performs a release operation on an object M - synchronizes with an atomic operation B that performs an acquire operation on M and - reads a value written by any side effect in the release sequence headed by A. -

- NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as - described below. Such a requirement would sometimes interfere with efficient implementation. - -

- NOTE 6 The specifications of the synchronization operations define when one reads the value written by - another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total - order. Each mutex acquisition ''reads the value written'' by the last mutex release. - -

- An evaluation A carries a dependency 15) to an evaluation B if: - - - -

-

- An evaluation A is dependency-ordered before16) an evaluation B if: -

-

- An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A - is dependency-ordered before B, or, for some evaluation X: -

-

- NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced - before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The - first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed - by ''sequenced before''. The reason for this limitation is that a consume operation participating in a - ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this - consume operation actually carries a dependency. The reason that this limitation applies only to the end of - such a concatenation is that any subsequent release operation will provide the required ordering for a prior - consume operation. The second exception is that a concatenation is not permitted to consist entirely of - ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be - transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships - consisting entirely of ''sequenced before''. - -

- An evaluation A happens before an evaluation B if A is sequenced before B or A inter- - thread happens before B. - - - - -

- A visible side effect A on an object M with respect to a value computation B of M - satisfies the conditions: -

- The value of a non-atomic scalar object M, as determined by evaluation B, shall be the - value stored by the visible side effect A. -

- NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data - race and the behavior is undefined. - -

- NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually - detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable - restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent) - execution. - -

- The visible sequence of side effects on an atomic object M, with respect to a value - computation B of M, is a maximal contiguous sub-sequence of side effects in the - modification order of M, where the first side effect is visible with respect to B, and for - every subsequent side effect, it is not the case that B happens before it. The value of an - atomic object M, as determined by evaluation B, shall be the value stored by some - operation in the visible sequence of M with respect to B. Furthermore, if a value - computation A of an atomic object M happens before a value computation B of M, and - the value computed by A corresponds to the value stored by side effect X, then the value - computed by B shall either equal the value computed by A, or be the value stored by side - effect Y , where Y follows X in the modification order of M. -

- NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if - both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee - provided by most hardware available to C atomic operations. - -

- NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the - values observed by loads of atomics, which we are restricting here. The intended reading is that there must - exist an association of atomic loads with modifications they observe that, together with suitably chosen - modification orders and the ''happens before'' relation derived as described above, satisfy the resulting - constraints as imposed here. - -

- The execution of a program contains a data race if it contains two conflicting actions in - different threads, at least one of which is not atomic, and neither happens before the - other. Any such data race results in undefined behavior. -

- NOTE 12 It can be shown that programs that correctly use simple mutexes and - memory_order_seq_cst operations to prevent all data races, and use no other synchronization - operations, behave as though the operations executed by their constituent threads were simply interleaved, - with each value computation of an object being the last value stored in that interleaving. This is normally - referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data- - race-free programs cannot observe most program transformations that do not change single-threaded - program semantics. In fact, most single-threaded program transformations continue to be allowed, since - any program that behaves differently as a result must contain undefined behavior. - -

- NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location - that would not be modified by the abstract machine are generally precluded by this standard, since such an - assignment might overwrite another assignment by a different thread in cases in which an abstract machine - execution would not have encountered a data race. This includes implementations of data member - assignment that overwrite adjacent members in separate memory locations. We also generally preclude - reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the - "visible sequence" rules. - -

- NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may - not preserve the semantics of the program as defined in this standard, since they potentially introduce a data - race. However, they are typically valid in the context of an optimizing compiler that targets a specific - machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that - is not tolerant of races or provides hardware race detection. - - -

Footnotes -

14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of - atomic operations, for example, allow executions inconsistent with a simple interleaving as described - below. - -

15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly - strictly intra-thread. - -

16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses - release/consume in place of release/acquire. - - -

Contents -

5.2 Environmental considerations

- -

Contents -

5.2.1 Character sets

-

- Two sets of characters and their associated collating sequences shall be defined: the set in - which source files are written (the source character set), and the set interpreted in the - execution environment (the execution character set). Each set is further divided into a - basic character set, whose contents are given by this subclause, and a set of zero or more - locale-specific members (which are not members of the basic character set) called - extended characters. The combined set is also called the extended character set. The - values of the members of the execution character set are implementation-defined. -

- In a character constant or string literal, members of the execution character set shall be - represented by corresponding members of the source character set or by escape - sequences consisting of the backslash \ followed by one or more characters. A byte with - all bits set to 0, called the null character, shall exist in the basic execution character set; it - is used to terminate a character string. -

- Both the basic source and basic execution character sets shall have the following - members: the 26 uppercase letters of the Latin alphabet -

-         A    B   C      D   E   F    G    H    I    J    K    L   M
-         N    O   P      Q   R   S    T    U    V    W    X    Y   Z
-
- the 26 lowercase letters of the Latin alphabet -
-         a    b   c      d   e   f    g    h    i    j    k    l   m
-         n    o   p      q   r   s    t    u    v    w    x    y   z
-
- the 10 decimal digits -
-         0    1   2      3   4   5    6    7    8    9
-
- the following 29 graphic characters -
-         !    "   #      %   &   '    (    )    *    +    ,    -   .    /    :
-         ;    <   =      >   ?   [    \    ]    ^    _    {    |   }    ~
-
- the space character, and control characters representing horizontal tab, vertical tab, and - form feed. The representation of each member of the source and execution basic - character sets shall fit in a byte. In both the source and execution basic character sets, the - value of each character after 0 in the above list of decimal digits shall be one greater than - the value of the previous. In source files, there shall be some way of indicating the end of - each line of text; this International Standard treats such an end-of-line indicator as if it - were a single new-line character. In the basic execution character set, there shall be - control characters representing alert, backspace, carriage return, and new line. If any - other characters are encountered in a source file (except in an identifier, a character - constant, a string literal, a header name, a comment, or a preprocessing token that is never - - converted to a token), the behavior is undefined. -

- A letter is an uppercase letter or a lowercase letter as defined above; in this International - Standard the term does not include other characters that are letters in other alphabets. -

- The universal character name construct provides a way to name other characters. -

Forward references: universal character names (6.4.3), character constants (6.4.4.4), - preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1). - -

Contents -

5.2.1.1 Trigraph sequences
-

- Before any other processing takes place, each occurrence of one of the following - sequences of three characters (called trigraph sequences17)) is replaced with the - corresponding single character. -

-        ??=      #                       ??)      ]                       ??!     |
-        ??(      [                       ??'      ^                       ??>     }
-        ??/      \                       ??<      {                       ??-     ~
-
- No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed - above is not changed. -

- EXAMPLE 1 -

-           ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
-
- becomes -
-           #define arraycheck(a, b) a[b] || b[a]
-
- -

- EXAMPLE 2 The following source line -

-           printf("Eh???/n");
-
- becomes (after replacement of the trigraph sequence ??/) -
-           printf("Eh?\n");
-
- - -

Footnotes -

17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as - described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set. - - -

Contents -

5.2.1.2 Multibyte characters
-

- The source character set may contain multibyte characters, used to represent members of - the extended character set. The execution character set may also contain multibyte - characters, which need not have the same encoding as for the source character set. For - both character sets, the following shall hold: -

-

- For source files, the following shall hold: -

- -

Contents -

5.2.2 Character display semantics

-

- The active position is that location on a display device where the next character output by - the fputc function would appear. The intent of writing a printing character (as defined - by the isprint function) to a display device is to display a graphic representation of - that character at the active position and then advance the active position to the next - position on the current line. The direction of writing is locale-specific. If the active - position is at the final position of a line (if there is one), the behavior of the display device - is unspecified. -

- Alphabetic escape sequences representing nongraphic characters in the execution - character set are intended to produce actions on display devices as follows: - \a (alert) Produces an audible or visible alert without changing the active position. - \b (backspace) Moves the active position to the previous position on the current line. If -

-    the active position is at the initial position of a line, the behavior of the display
-    device is unspecified.
-
- \f ( form feed) Moves the active position to the initial position at the start of the next -
-    logical page.
-
- \n (new line) Moves the active position to the initial position of the next line. - \r (carriage return) Moves the active position to the initial position of the current line. - \t (horizontal tab) Moves the active position to the next horizontal tabulation position -
-    on the current line. If the active position is at or past the last defined horizontal
-    tabulation position, the behavior of the display device is unspecified.
-
- \v (vertical tab) Moves the active position to the initial position of the next vertical - -
-    tabulation position. If the active position is at or past the last defined vertical
-      tabulation position, the behavior of the display device is unspecified.
-
-

- Each of these escape sequences shall produce a unique implementation-defined value - which can be stored in a single char object. The external representations in a text file - need not be identical to the internal representations, and are outside the scope of this - International Standard. -

Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3). - -

Contents -

5.2.3 Signals and interrupts

-

- Functions shall be implemented such that they may be interrupted at any time by a signal, - or may be called by a signal handler, or both, with no alteration to earlier, but still active, - invocations' control flow (after the interruption), function return values, or objects with - automatic storage duration. All such objects shall be maintained outside the function - image (the instructions that compose the executable representation of a function) on a - per-invocation basis. - -

Contents -

5.2.4 Environmental limits

-

- Both the translation and execution environments constrain the implementation of - language translators and libraries. The following summarizes the language-related - environmental limits on a conforming implementation; the library-related limits are - discussed in clause 7. - -

Contents -

5.2.4.1 Translation limits
-

- The implementation shall be able to translate and execute at least one program that - contains at least one instance of every one of the following limits:18) -

- -

Footnotes -

18) Implementations should avoid imposing fixed translation limits whenever possible. - -

19) See ''future language directions'' (6.11.3). - - -

Contents -

5.2.4.2 Numerical limits
-

- An implementation is required to document all the limits specified in this subclause, - which are specified in the headers <limits.h> and <float.h>. Additional limits are - specified in <stdint.h>. -

Forward references: integer types <stdint.h> (7.20). - -

Contents -

5.2.4.2.1 Sizes of integer types <limits.h>
-

- The values given below shall be replaced by constant expressions suitable for use in #if - preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the - following shall be replaced by expressions that have the same type as would an - expression that is an object of the corresponding type converted according to the integer - promotions. Their implementation-defined values shall be equal or greater in magnitude - - - - (absolute value) to those shown, with the same sign. -

-

- If the value of an object of type char is treated as a signed integer when used in an - expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the - value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of - CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of - UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1. -

Forward references: representations of types (6.2.6), conditional inclusion (6.10.1). - -

Footnotes -

20) See 6.2.5. - - -

Contents -

5.2.4.2.2 Characteristics of floating types <float.h>
-

- The characteristics of floating types are defined in terms of a model that describes a - representation of floating-point numbers and values that provide information about an - implementation's floating-point arithmetic.21) The following parameters are used to - define the model for each floating-point type: -

-        s          sign ((+-)1)
-        b          base or radix of exponent representation (an integer > 1)
-        e          exponent (an integer between a minimum emin and a maximum emax )
-        p          precision (the number of base-b digits in the significand)
-         fk        nonnegative integers less than b (the significand digits)
-
-

- A floating-point number (x) is defined by the following model: -

-                    p
-        x = sb e   (Sum) f k b-k ,
-                   k=1
-                                 emin <= e <= emax
-
- -

- In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be - able to contain other kinds of floating-point numbers, such as subnormal floating-point - numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0, - e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and - NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates - through almost every arithmetic operation without raising a floating-point exception; a - signaling NaN generally raises a floating-point exception when occurring as an - - - - arithmetic operand.22) -

- An implementation may give zero and values that are not floating-point numbers (such as - infinities and NaNs) a sign or may leave them unsigned. Wherever such values are - unsigned, any requirement in this International Standard to retrieve the sign shall produce - an unspecified sign, and any requirement to set the sign shall be ignored. -

- The minimum range of representable values for a floating type is the most negative finite - floating-point number representable in that type through the most positive finite floating- - point number representable in that type. In addition, if negative infinity is representable - in a type, the range of that type is extended to all negative real numbers; likewise, if - positive infinity is representable in a type, the range of that type is extended to all positive - real numbers. -

- The accuracy of the floating-point operations (+, -, *, /) and of the library functions in - <math.h> and <complex.h> that return floating-point results is implementation- - defined, as is the accuracy of the conversion between floating-point internal - representations and string representations performed by the library functions in - <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the - accuracy is unknown. -

- All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant - expressions suitable for use in #if preprocessing directives; all floating values shall be - constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, - and FLT_ROUNDS have separate names for all three floating-point types. The floating- - point model representation is provided for all values except FLT_EVAL_METHOD and - FLT_ROUNDS. -

- The rounding mode for floating-point addition is characterized by the implementation- - defined value of FLT_ROUNDS:23) -

-       -1      indeterminable
-        0      toward zero
-        1      to nearest
-        2      toward positive infinity
-        3      toward negative infinity
-
- All other values for FLT_ROUNDS characterize implementation-defined rounding - behavior. - - - -

- Except for assignment and cast (which remove all extra range and precision), the values - yielded by operators with floating operands and values subject to the usual arithmetic - conversions and of floating constants are evaluated to a format whose range and precision - may be greater than required by the type. The use of evaluation formats is characterized - by the implementation-defined value of FLT_EVAL_METHOD:24) -

-        -1         indeterminable;
-          0        evaluate all operations and constants just to the range and precision of the
-                   type;
-          1        evaluate operations and constants of type float and double to the
-                   range and precision of the double type, evaluate long double
-                   operations and constants to the range and precision of the long double
-                   type;
-          2        evaluate all operations and constants to the range and precision of the
-                   long double type.
-
- All other negative values for FLT_EVAL_METHOD characterize implementation-defined - behavior. -

- The presence or absence of subnormal numbers is characterized by the implementation- - defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and - LDBL_HAS_SUBNORM: -

-        -1       indeterminable25)
-         0       absent26) (type does not support subnormal numbers)
-         1       present (type does support subnormal numbers)
-
-

- The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater or equal in magnitude (absolute value) to - those shown, with the same sign: -

-

- The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater than or equal to those shown: -

-

- The values given in the following list shall be replaced by constant expressions with - implementation-defined (positive) values that are less than or equal to those shown: -

-

Recommended practice -

- Conversion from (at least) double to decimal with DECIMAL_DIG digits and back - should be the identity function. -

- EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum - requirements of this International Standard, and the appropriate values in a <float.h> header for type - float: -

-                    6
-       x = s16e    (Sum) f k 16-k ,
-                   k=1
-                                   -31 <= e <= +32
-
- -
-         FLT_RADIX                                    16
-         FLT_MANT_DIG                                  6
-         FLT_EPSILON                     9.53674316E-07F
-         FLT_DECIMAL_DIG                               9
-         FLT_DIG                                       6
-         FLT_MIN_EXP                                 -31
-         FLT_MIN                         2.93873588E-39F
-         FLT_MIN_10_EXP                              -38
-         FLT_MAX_EXP                                 +32
-         FLT_MAX                         3.40282347E+38F
-         FLT_MAX_10_EXP                              +38
-
- -

- EXAMPLE 2 The following describes floating-point representations that also meet the requirements for - single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a - <float.h> header for types float and double: -

-                   24
-       x f = s2e   (Sum) f k 2-k ,
-                   k=1
-                                  -125 <= e <= +128
-
- -
-                   53
-       x d = s2e   (Sum) f k 2-k ,
-                   k=1
-                                  -1021 <= e <= +1024
-
- -
-         FLT_RADIX                                     2
-         DECIMAL_DIG                                  17
-         FLT_MANT_DIG                                 24
-         FLT_EPSILON                     1.19209290E-07F // decimal constant
-         FLT_EPSILON                            0X1P-23F // hex constant
-         FLT_DECIMAL_DIG                               9
-
- - - -
-         FLT_DIG                             6
-         FLT_MIN_EXP                      -125
-         FLT_MIN               1.17549435E-38F               //   decimal constant
-         FLT_MIN                     0X1P-126F               //   hex constant
-         FLT_TRUE_MIN          1.40129846E-45F               //   decimal constant
-         FLT_TRUE_MIN                0X1P-149F               //   hex constant
-         FLT_HAS_SUBNORM                     1
-         FLT_MIN_10_EXP                    -37
-         FLT_MAX_EXP                      +128
-         FLT_MAX               3.40282347E+38F               // decimal constant
-         FLT_MAX               0X1.fffffeP127F               // hex constant
-         FLT_MAX_10_EXP                    +38
-         DBL_MANT_DIG                       53
-         DBL_EPSILON    2.2204460492503131E-16               // decimal constant
-         DBL_EPSILON                   0X1P-52               // hex constant
-         DBL_DECIMAL_DIG                    17
-         DBL_DIG                            15
-         DBL_MIN_EXP                     -1021
-         DBL_MIN      2.2250738585072014E-308                //   decimal constant
-         DBL_MIN                     0X1P-1022               //   hex constant
-         DBL_TRUE_MIN 4.9406564584124654E-324                //   decimal constant
-         DBL_TRUE_MIN                0X1P-1074               //   hex constant
-         DBL_HAS_SUBNORM                     1
-         DBL_MIN_10_EXP                   -307
-         DBL_MAX_EXP                     +1024
-         DBL_MAX      1.7976931348623157E+308                // decimal constant
-         DBL_MAX        0X1.fffffffffffffP1023               // hex constant
-         DBL_MAX_10_EXP                   +308
-
- If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For - example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of - precision), then DECIMAL_DIG would be 21. - -

Forward references: conditional inclusion (6.10.1), complex arithmetic - <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h> - (7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h> - (7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12). - - -

Footnotes -

21) The floating-point model is intended to clarify the description of each floating-point characteristic and - does not require the floating-point arithmetic of the implementation to be identical. - -

22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support - IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with - similar behavior. - -

23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through - the function fesetround in <fenv.h>. - -

24) The evaluation method determines evaluation formats of expressions involving all floating types, not - just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float - _Complex operands is represented in the double _Complex format, and its parts are evaluated to - double. - -

25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret - subnormal representations as zero, nor as nonzero. - -

26) Characterization as absent is intended if no floating-point operations produce subnormal results from - non-subnormal inputs, even if the type format includes representations of subnormal numbers. - -

27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a - positive number no greater than the minimum normalized positive number for the type. - -

28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent - limits are one less than shown here. - - -

Contents -

6. Language

- -

Contents -

6.1 Notation

-

- In the syntax notation used in this clause, syntactic categories (nonterminals) are - indicated by italic type, and literal words and character set members (terminals) by bold - type. A colon (:) following a nonterminal introduces its definition. Alternative - definitions are listed on separate lines, except when prefaced by the words ''one of''. An - optional symbol is indicated by the subscript ''opt'', so that -

-          { expressionopt }
-
- indicates an optional expression enclosed in braces. -

- When syntactic categories are referred to in the main text, they are not italicized and - words are separated by spaces instead of hyphens. -

- A summary of the language syntax is given in annex A. - -

Contents -

6.2 Concepts

- -

Contents -

6.2.1 Scopes of identifiers

-

- An identifier can denote an object; a function; a tag or a member of a structure, union, or - enumeration; a typedef name; a label name; a macro name; or a macro parameter. The - same identifier can denote different entities at different points in the program. A member - of an enumeration is called an enumeration constant. Macro names and macro - parameters are not considered further here, because prior to the semantic phase of - program translation any occurrences of macro names in the source file are replaced by the - preprocessing token sequences that constitute their macro definitions. -

- For each different entity that an identifier designates, the identifier is visible (i.e., can be - used) only within a region of program text called its scope. Different entities designated - by the same identifier either have different scopes, or are in different name spaces. There - are four kinds of scopes: function, file, block, and function prototype. (A function - prototype is a declaration of a function that declares the types of its parameters.) -

- A label name is the only kind of identifier that has function scope. It can be used (in a - goto statement) anywhere in the function in which it appears, and is declared implicitly - by its syntactic appearance (followed by a : and a statement). -

- Every other identifier has scope determined by the placement of its declaration (in a - declarator or type specifier). If the declarator or type specifier that declares the identifier - appears outside of any block or list of parameters, the identifier has file scope, which - terminates at the end of the translation unit. If the declarator or type specifier that - declares the identifier appears inside a block or within the list of parameter declarations in - a function definition, the identifier has block scope, which terminates at the end of the - associated block. If the declarator or type specifier that declares the identifier appears - - within the list of parameter declarations in a function prototype (not part of a function - definition), the identifier has function prototype scope, which terminates at the end of the - function declarator. If an identifier designates two different entities in the same name - space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end - strictly before the scope of the other entity (the outer scope). Within the inner scope, the - identifier designates the entity declared in the inner scope; the entity declared in the outer - scope is hidden (and not visible) within the inner scope. -

- Unless explicitly stated otherwise, where this International Standard uses the term - ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the - entity in the relevant name space whose declaration is visible at the point the identifier - occurs. -

- Two identifiers have the same scope if and only if their scopes terminate at the same - point. -

- Structure, union, and enumeration tags have scope that begins just after the appearance of - the tag in a type specifier that declares the tag. Each enumeration constant has scope that - begins just after the appearance of its defining enumerator in an enumerator list. Any - other identifier has scope that begins just after the completion of its declarator. -

- As a special case, a type name (which is not a declaration of an identifier) is considered to - have a scope that begins just after the place within the type name where the omitted - identifier would appear were it not omitted. -

Forward references: declarations (6.7), function calls (6.5.2.2), function definitions - (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3), - source file inclusion (6.10.2), statements (6.8). - -

Contents -

6.2.2 Linkages of identifiers

-

- An identifier declared in different scopes or in the same scope more than once can be - made to refer to the same object or function by a process called linkage.29) There are - three kinds of linkage: external, internal, and none. -

- In the set of translation units and libraries that constitutes an entire program, each - declaration of a particular identifier with external linkage denotes the same object or - function. Within one translation unit, each declaration of an identifier with internal - linkage denotes the same object or function. Each declaration of an identifier with no - linkage denotes a unique entity. -

- If the declaration of a file scope identifier for an object or a function contains the storage- - class specifier static, the identifier has internal linkage.30) - - - - -

- For an identifier declared with the storage-class specifier extern in a scope in which a - prior declaration of that identifier is visible,31) if the prior declaration specifies internal or - external linkage, the linkage of the identifier at the later declaration is the same as the - linkage specified at the prior declaration. If no prior declaration is visible, or if the prior - declaration specifies no linkage, then the identifier has external linkage. -

- If the declaration of an identifier for a function has no storage-class specifier, its linkage - is determined exactly as if it were declared with the storage-class specifier extern. If - the declaration of an identifier for an object has file scope and no storage-class specifier, - its linkage is external. -

- The following identifiers have no linkage: an identifier declared to be anything other than - an object or a function; an identifier declared to be a function parameter; a block scope - identifier for an object declared without the storage-class specifier extern. -

- If, within a translation unit, the same identifier appears with both internal and external - linkage, the behavior is undefined. -

Forward references: declarations (6.7), expressions (6.5), external definitions (6.9), - statements (6.8). - -

Footnotes -

29) There is no linkage between different identifiers. - -

30) A function declaration can contain the storage-class specifier static only if it is at file scope; see - 6.7.1. - -

31) As specified in 6.2.1, the later declaration might hide the prior declaration. - - -

Contents -

6.2.3 Name spaces of identifiers

-

- If more than one declaration of a particular identifier is visible at any point in a - translation unit, the syntactic context disambiguates uses that refer to different entities. - Thus, there are separate name spaces for various categories of identifiers, as follows: -

-

Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), - structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags - (6.7.2.3), the goto statement (6.8.6.1). - - - -

Footnotes -

32) There is only one name space for tags even though three are possible. - - -

Contents -

6.2.4 Storage durations of objects

-

- An object has a storage duration that determines its lifetime. There are four storage - durations: static, thread, automatic, and allocated. Allocated storage is described in - 7.22.3. -

- The lifetime of an object is the portion of program execution during which storage is - guaranteed to be reserved for it. An object exists, has a constant address,33) and retains - its last-stored value throughout its lifetime.34) If an object is referred to outside of its - lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when - the object it points to (or just past) reaches the end of its lifetime. -

- An object whose identifier is declared without the storage-class specifier - _Thread_local, and either with external or internal linkage or with the storage-class - specifier static, has static storage duration. Its lifetime is the entire execution of the - program and its stored value is initialized only once, prior to program startup. -

- An object whose identifier is declared with the storage-class specifier _Thread_local - has thread storage duration. Its lifetime is the entire execution of the thread for which it - is created, and its stored value is initialized when the thread is started. There is a distinct - object per thread, and use of the declared name in an expression refers to the object - associated with the thread evaluating the expression. The result of attempting to - indirectly access an object with thread storage duration from a thread other than the one - with which the object is associated is implementation-defined. -

- An object whose identifier is declared with no linkage and without the storage-class - specifier static has automatic storage duration, as do some compound literals. The - result of attempting to indirectly access an object with automatic storage duration from a - thread other than the one with which the object is associated is implementation-defined. -

- For such an object that does not have a variable length array type, its lifetime extends - from entry into the block with which it is associated until execution of that block ends in - any way. (Entering an enclosed block or calling a function suspends, but does not end, - execution of the current block.) If the block is entered recursively, a new instance of the - object is created each time. The initial value of the object is indeterminate. If an - initialization is specified for the object, it is performed each time the declaration or - compound literal is reached in the execution of the block; otherwise, the value becomes - indeterminate each time the declaration is reached. - - - - -

- For such an object that does have a variable length array type, its lifetime extends from - the declaration of the object until execution of the program leaves the scope of the - declaration.35) If the scope is entered recursively, a new instance of the object is created - each time. The initial value of the object is indeterminate. -

- A non-lvalue expression with structure or union type, where the structure or union - contains a member with array type (including, recursively, members of all contained - structures and unions) refers to an object with automatic storage duration and temporary - lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the - value of the expression. Its lifetime ends when the evaluation of the containing full - expression or full declarator ends. Any attempt to modify an object with temporary - lifetime results in undefined behavior. -

Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators - (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8). - -

Footnotes -

33) The term ''constant address'' means that two pointers to the object constructed at possibly different - times will compare equal. The address may be different during two different executions of the same - program. - -

34) In the case of a volatile object, the last store need not be explicit in the program. - -

35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an - embedded block prior to the declaration, leaves the scope of the declaration. - -

36) The address of such an object is taken implicitly when an array member is accessed. - - -

Contents -

6.2.5 Types

-

- The meaning of a value stored in an object or returned by a function is determined by the - type of the expression used to access it. (An identifier declared to be an object is the - simplest such expression; the type is specified in the declaration of the identifier.) Types - are partitioned into object types (types that describe objects) and function types (types - that describe functions). At various points within a translation unit an object type may be - incomplete (lacking sufficient information to determine the size of objects of that type) or - complete (having sufficient information).37) -

- An object declared as type _Bool is large enough to store the values 0 and 1. -

- An object declared as type char is large enough to store any member of the basic - execution character set. If a member of the basic execution character set is stored in a - char object, its value is guaranteed to be nonnegative. If any other character is stored in - a char object, the resulting value is implementation-defined but shall be within the range - of values that can be represented in that type. -

- There are five standard signed integer types, designated as signed char, short - int, int, long int, and long long int. (These and other types may be - designated in several additional ways, as described in 6.7.2.) There may also be - implementation-defined extended signed integer types.38) The standard and extended - signed integer types are collectively called signed integer types.39) - - -

- An object declared as type signed char occupies the same amount of storage as a - ''plain'' char object. A ''plain'' int object has the natural size suggested by the - architecture of the execution environment (large enough to contain any value in the range - INT_MIN to INT_MAX as defined in the header <limits.h>). -

- For each of the signed integer types, there is a corresponding (but different) unsigned - integer type (designated with the keyword unsigned) that uses the same amount of - storage (including sign information) and has the same alignment requirements. The type - _Bool and the unsigned integer types that correspond to the standard signed integer - types are the standard unsigned integer types. The unsigned integer types that - correspond to the extended signed integer types are the extended unsigned integer types. - The standard and extended unsigned integer types are collectively called unsigned integer - types.40) -

- The standard signed integer types and standard unsigned integer types are collectively - called the standard integer types, the extended signed integer types and extended - unsigned integer types are collectively called the extended integer types. -

- For any two integer types with the same signedness and different integer conversion rank - (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a - subrange of the values of the other type. -

- The range of nonnegative values of a signed integer type is a subrange of the - corresponding unsigned integer type, and the representation of the same value in each - type is the same.41) A computation involving unsigned operands can never overflow, - because a result that cannot be represented by the resulting unsigned integer type is - reduced modulo the number that is one greater than the largest value that can be - represented by the resulting type. -

- There are three real floating types, designated as float, double, and long - double.42) The set of values of the type float is a subset of the set of values of the - type double; the set of values of the type double is a subset of the set of values of the - type long double. - - - -

- There are three complex types, designated as float _Complex, double - _Complex, and long double _Complex.43) (Complex types are a conditional - feature that implementations need not support; see 6.10.8.3.) The real floating and - complex types are collectively called the floating types. -

- For each floating type there is a corresponding real type, which is always a real floating - type. For real floating types, it is the same type. For complex types, it is the type given - by deleting the keyword _Complex from the type name. -

- Each complex type has the same representation and alignment requirements as an array - type containing exactly two elements of the corresponding real type; the first element is - equal to the real part, and the second element to the imaginary part, of the complex - number. -

- The type char, the signed and unsigned integer types, and the floating types are - collectively called the basic types. The basic types are complete object types. Even if the - implementation defines two or more basic types to have the same representation, they are - nevertheless different types.44) -

- The three types char, signed char, and unsigned char are collectively called - the character types. The implementation shall define char to have the same range, - representation, and behavior as either signed char or unsigned char.45) -

- An enumeration comprises a set of named integer constant values. Each distinct - enumeration constitutes a different enumerated type. -

- The type char, the signed and unsigned integer types, and the enumerated types are - collectively called integer types. The integer and real floating types are collectively called - real types. -

- Integer and floating types are collectively called arithmetic types. Each arithmetic type - belongs to one type domain: the real type domain comprises the real types, the complex - type domain comprises the complex types. -

- The void type comprises an empty set of values; it is an incomplete object type that - cannot be completed. - - - - -

- Any number of derived types can be constructed from the object and function types, as - follows: -

- These methods of constructing derived types can be applied recursively. -

- Arithmetic types and pointer types are collectively called scalar types. Array and - structure types are collectively called aggregate types.46) -

- An array type of unknown size is an incomplete type. It is completed, for an identifier of - that type, by specifying the size in a later declaration (with internal or external linkage). - A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete - - - - type. It is completed, for all declarations of that type, by declaring the same structure or - union tag with its defining content later in the same scope. -

- A type has known constant size if the type is not incomplete and is not a variable length - array type. -

- Array, function, and pointer types are collectively called derived declarator types. A - declarator type derivation from a type T is the construction of a derived declarator type - from T by the application of an array-type, a function-type, or a pointer-type derivation to - T. -

- A type is characterized by its type category, which is either the outermost derivation of a - derived type (as noted above in the construction of derived types), or the type itself if the - type consists of no derived types. -

- Any type so far mentioned is an unqualified type. Each unqualified type has several - qualified versions of its type,47) corresponding to the combinations of one, two, or all - three of the const, volatile, and restrict qualifiers. The qualified or unqualified - versions of a type are distinct types that belong to the same type category and have the - same representation and alignment requirements.48) A derived type is not qualified by the - qualifiers (if any) of the type from which it is derived. -

- Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier - designates an atomic type. The size, representation, and alignment of an atomic type - need not be the same as those of the corresponding unqualified type. Therefore, this - Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the - atomic version of a type is permitted along with the other qualified versions of a type. - The phrase ''qualified or unqualified type'', without specific mention of atomic, does not - include the atomic types. -

- A pointer to void shall have the same representation and alignment requirements as a - pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of - compatible types shall have the same representation and alignment requirements. All - pointers to structure types shall have the same representation and alignment requirements - as each other. All pointers to union types shall have the same representation and - alignment requirements as each other. Pointers to other types need not have the same - representation or alignment requirements. -

- EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is - pointer, not a floating type. The const-qualified version of this type is designated as ''float * const'' - whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const- - - - - qualified float'' and is a pointer to a qualified type. - -

- EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to - function returning struct tag''. The array has length five and the function has a single parameter of type - float. Its type category is array. - -

Forward references: compatible type and composite type (6.2.7), declarations (6.7). - -

Footnotes -

37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at - different points within a translation unit. - -

38) Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - -

39) Therefore, any statement in this Standard about signed integer types also applies to the extended - signed integer types. - -

40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended - unsigned integer types. - -

41) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - -

42) See ''future language directions'' (6.11.1). - -

43) A specification for imaginary types is in annex G. - -

44) An implementation may define new keywords that provide alternative ways to designate a basic (or - any other) type; this does not violate the requirement that all basic types be different. - Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - -

45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be - used to distinguish the two options. Irrespective of the choice made, char is a separate type from the - other two and is not compatible with either. - -

46) Note that aggregate type does not include union type because an object with union type can only - contain one member at a time. - -

47) See 6.7.3 regarding qualified array and function types. - -

48) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - - -

Contents -

6.2.6 Representations of types

- -

Contents -

6.2.6.1 General
-

- The representations of all types are unspecified except as stated in this subclause. -

- Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, - the number, order, and encoding of which are either explicitly specified or - implementation-defined. -

- Values stored in unsigned bit-fields and objects of type unsigned char shall be - represented using a pure binary notation.49) -

- Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT - bits, where n is the size of an object of that type, in bytes. The value may be copied into - an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is - called the object representation of the value. Values stored in bit-fields consist of m bits, - where m is the size specified for the bit-field. The object representation is the set of m - bits the bit-field comprises in the addressable storage unit holding it. Two values (other - than NaNs) with the same object representation compare equal, but values that compare - equal may have different object representations. -

- Certain object representations need not represent a value of the object type. If the stored - value of an object has such a representation and is read by an lvalue expression that does - not have character type, the behavior is undefined. If such a representation is produced - by a side effect that modifies all or any part of the object by an lvalue expression that - does not have character type, the behavior is undefined.50) Such a representation is called - a trap representation. -

- When a value is stored in an object of structure or union type, including in a member - object, the bytes of the object representation that correspond to any padding bytes take - unspecified values.51) The value of a structure or union object is never a trap - - - - representation, even though the value of a member of the structure or union object may be - a trap representation. -

- When a value is stored in a member of an object of union type, the bytes of the object - representation that do not correspond to that member but do correspond to other members - take unspecified values. -

- Where an operator is applied to a value that has more than one object representation, - which object representation is used shall not affect the value of the result.52) Where a - value is stored in an object using a type that has more than one object representation for - that value, it is unspecified which representation is used, but a trap representation shall - not be generated. -

- Loads and stores of objects with atomic types are done with - memory_order_seq_cst semantics. -

Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function - designators (6.3.2.1), order and consistency (7.17.3). - -

Footnotes -

49) A positional representation for integers that uses the binary digits 0 and 1, in which the values - represented by successive bits are additive, begin with 1, and are multiplied by successive integral - powers of 2, except perhaps the bit with the highest position. (Adapted from the American National - Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of - type unsigned char range from 0 to 2 - -

-                                           CHAR_BIT
-                                                     - 1.
-
- -

50) Thus, an automatic variable can be initialized to a trap representation without causing undefined - behavior, but the value of the variable cannot be used until a proper value is stored in it. - -

51) Thus, for example, structure assignment need not copy any padding bits. - -

52) It is possible for objects x and y with the same effective type T to have the same value when they are - accessed as objects of type T, but to have different values in other contexts. In particular, if == is - defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0. - Furthermore, x == y does not necessarily imply that x and y have the same value; other operations - on values of type T may distinguish between them. - - -

Contents -

6.2.6.2 Integer types
-

- For unsigned integer types other than unsigned char, the bits of the object - representation shall be divided into two groups: value bits and padding bits (there need - not be any of the latter). If there are N value bits, each bit shall represent a different - power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of - representing values from 0 to 2 N - 1 using a pure binary representation; this shall be - known as the value representation. The values of any padding bits are unspecified.53) -

- For signed integer types, the bits of the object representation shall be divided into three - groups: value bits, padding bits, and the sign bit. There need not be any padding bits; - signed char shall not have any padding bits. There shall be exactly one sign bit. - Each bit that is a value bit shall have the same value as the same bit in the object - representation of the corresponding unsigned type (if there are M value bits in the signed - type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect - - - the resulting value. If the sign bit is one, the value shall be modified in one of the - following ways: -

- Which of these applies is implementation-defined, as is whether the value with sign bit 1 - and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones' - complement), is a trap representation or a normal value. In the case of sign and - magnitude and ones' complement, if this representation is a normal value it is called a - negative zero. -

- If the implementation supports negative zeros, they shall be generated only by: -

- It is unspecified whether these cases actually generate a negative zero or a normal zero, - and whether a negative zero becomes a normal zero when stored in an object. -

- If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<, - and >> operators with operands that would produce such a value is undefined. -

- The values of any padding bits are unspecified.54) A valid (non-trap) object representation - of a signed integer type where the sign bit is zero is a valid object representation of the - corresponding unsigned type, and shall represent the same value. For any integer type, - the object representation where all the bits are zero shall be a representation of the value - zero in that type. -

- The precision of an integer type is the number of bits it uses to represent values, - excluding any sign and padding bits. The width of an integer type is the same but - including any sign bit; thus for unsigned integer types the two values are the same, while - for signed integer types the width is one greater than the precision. - - - - - - -

Footnotes -

53) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow, and this cannot occur - with unsigned types. All other combinations of padding bits are alternative object representations of - the value specified by the value bits. - -

54) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow. All other - combinations of padding bits are alternative object representations of the value specified by the value - bits. - - -

Contents -

6.2.7 Compatible type and composite type

-

- Two types have compatible type if their types are the same. Additional rules for - determining whether two types are compatible are described in 6.7.2 for type specifiers, - in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure, - union, or enumerated types declared in separate translation units are compatible if their - tags and members satisfy the following requirements: If one is declared with a tag, the - other shall be declared with the same tag. If both are completed anywhere within their - respective translation units, then the following additional requirements apply: there shall - be a one-to-one correspondence between their members such that each pair of - corresponding members are declared with compatible types; if one member of the pair is - declared with an alignment specifier, the other is declared with an equivalent alignment - specifier; and if one member of the pair is declared with a name, the other is declared - with the same name. For two structures, corresponding members shall be declared in the - same order. For two structures or unions, corresponding bit-fields shall have the same - widths. For two enumerations, corresponding members shall have the same values. -

- All declarations that refer to the same object or function shall have compatible type; - otherwise, the behavior is undefined. -

- A composite type can be constructed from two types that are compatible; it is a type that - is compatible with both of the two types and satisfies the following conditions: -

- These rules apply recursively to the types from which the two types are derived. -

- For an identifier with internal or external linkage declared in a scope in which a prior - declaration of that identifier is visible,56) if the prior declaration specifies internal or - external linkage, the type of the identifier at the later declaration becomes the composite - type. -

Forward references: array declarators (6.7.6.2). -

- EXAMPLE Given the following two file scope declarations: -

-          int f(int (*)(), double (*)[3]);
-          int f(int (*)(char *), double (*)[]);
-
- The resulting composite type for the function is: -
-          int f(int (*)(char *), double (*)[3]);
-
- - -

Footnotes -

55) Two types need not be identical to be compatible. - -

56) As specified in 6.2.1, the later declaration might hide the prior declaration. - - -

Contents -

6.2.8 Alignment of objects

-

- Complete object types have alignment requirements which place restrictions on the - addresses at which objects of that type may be allocated. An alignment is an - implementation-defined integer value representing the number of bytes between - successive addresses at which a given object can be allocated. An object type imposes an - alignment requirement on every object of that type: stricter alignment can be requested - using the _Alignas keyword. -

- A fundamental alignment is represented by an alignment less than or equal to the greatest - alignment supported by the implementation in all contexts, which is equal to - alignof(max_align_t). -

- An extended alignment is represented by an alignment greater than - alignof(max_align_t). It is implementation-defined whether any extended - alignments are supported and the contexts in which they are supported. A type having an - extended alignment requirement is an over-aligned type.57) -

- Alignments are represented as values of the type size_t. Valid alignments include only - those values returned by an alignof expression for fundamental types, plus an - additional implementation-defined set of values, which may be empty. Every valid - alignment value shall be a nonnegative integral power of two. - - - -

- Alignments have an order from weaker to stronger or stricter alignments. Stricter - alignments have larger alignment values. An address that satisfies an alignment - requirement also satisfies any weaker valid alignment requirement. -

- The alignment requirement of a complete type can be queried using an alignof - expression. The types char, signed char, and unsigned char shall have the - weakest alignment requirement. -

- Comparing alignments is meaningful and provides the obvious results: -

- -

Footnotes -

57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended - alignment has been applied. - - -

Contents -

6.3 Conversions

-

- Several operators convert operand values from one type to another automatically. This - subclause specifies the result required from such an implicit conversion, as well as those - that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes - the conversions performed by most ordinary operators; it is supplemented as required by - the discussion of each operator in 6.5. -

- Conversion of an operand value to a compatible type causes no change to the value or the - representation. -

Forward references: cast operators (6.5.4). - -

Contents -

6.3.1 Arithmetic operands

- -

Contents -

6.3.1.1 Boolean, characters, and integers
-

- Every integer type has an integer conversion rank defined as follows: -

-

- The following may be used in an expression wherever an int or unsigned int may - be used: - -

- If an int can represent all values of the original type (as restricted by the width, for a - bit-field), the value is converted to an int; otherwise, it is converted to an unsigned - int. These are called the integer promotions.58) All other types are unchanged by the - integer promotions. -

- The integer promotions preserve value including sign. As discussed earlier, whether a - ''plain'' char is treated as signed is implementation-defined. -

Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers - (6.7.2.1). - -

Footnotes -

58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain - argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the - shift operators, as specified by their respective subclauses. - - -

Contents -

6.3.1.2 Boolean type
-

- When any scalar value is converted to _Bool, the result is 0 if the value compares equal - to 0; otherwise, the result is 1.59) - -

Footnotes -

59) NaNs do not compare equal to 0 and thus convert to 1. - - -

Contents -

6.3.1.3 Signed and unsigned integers
-

- When a value with integer type is converted to another integer type other than _Bool, if - the value can be represented by the new type, it is unchanged. -

- Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or - subtracting one more than the maximum value that can be represented in the new type - until the value is in the range of the new type.60) -

- Otherwise, the new type is signed and the value cannot be represented in it; either the - result is implementation-defined or an implementation-defined signal is raised. - -

Footnotes -

60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression. - - -

Contents -

6.3.1.4 Real floating and integer
-

- When a finite value of real floating type is converted to an integer type other than _Bool, - the fractional part is discarded (i.e., the value is truncated toward zero). If the value of - the integral part cannot be represented by the integer type, the behavior is undefined.61) - - - -

- When a value of integer type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - -

Footnotes -

61) The remaindering operation performed when a value of integer type is converted to unsigned type - need not be performed when a value of real floating type is converted to unsigned type. Thus, the - range of portable real floating values is (-1, Utype_MAX+1). - - -

Contents -

6.3.1.5 Real floating types
-

- When a value of real floating type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - -

Contents -

6.3.1.6 Complex types
-

- When a value of complex type is converted to another complex type, both the real and - imaginary parts follow the conversion rules for the corresponding real types. - -

Contents -

6.3.1.7 Real and complex
-

- When a value of real type is converted to a complex type, the real part of the complex - result value is determined by the rules of conversion to the corresponding real type and - the imaginary part of the complex result value is a positive zero or an unsigned zero. -

- When a value of complex type is converted to a real type, the imaginary part of the - complex value is discarded and the value of the real part is converted according to the - conversion rules for the corresponding real type. - -

Contents -

6.3.1.8 Usual arithmetic conversions
-

- Many operators that expect operands of arithmetic type cause conversions and yield result - types in a similar way. The purpose is to determine a common real type for the operands - and result. For the specified operands, each operand is converted, without change of type - domain, to a type whose corresponding real type is the common real type. Unless - explicitly stated otherwise, the common real type is also the corresponding real type of - the result, whose type domain is the type domain of the operands if they are the same, - and complex otherwise. This pattern is called the usual arithmetic conversions: - -

-       First, if the corresponding real type of either operand is long double, the other
-       operand is converted, without change of type domain, to a type whose
-        corresponding real type is long double.
-        Otherwise, if the corresponding real type of either operand is double, the other
-        operand is converted, without change of type domain, to a type whose
-        corresponding real type is double.
-        Otherwise, if the corresponding real type of either operand is float, the other
-        operand is converted, without change of type domain, to a type whose
-        corresponding real type is float.62)
-        Otherwise, the integer promotions are performed on both operands. Then the
-        following rules are applied to the promoted operands:
-               If both operands have the same type, then no further conversion is needed.
-               Otherwise, if both operands have signed integer types or both have unsigned
-               integer types, the operand with the type of lesser integer conversion rank is
-               converted to the type of the operand with greater rank.
-               Otherwise, if the operand that has unsigned integer type has rank greater or
-               equal to the rank of the type of the other operand, then the operand with
-               signed integer type is converted to the type of the operand with unsigned
-               integer type.
-               Otherwise, if the type of the operand with signed integer type can represent
-               all of the values of the type of the operand with unsigned integer type, then
-               the operand with unsigned integer type is converted to the type of the
-               operand with signed integer type.
-               Otherwise, both operands are converted to the unsigned integer type
-               corresponding to the type of the operand with signed integer type.
-
-

- The values of floating operands and of the results of floating expressions may be - represented in greater precision and range than that required by the type; the types are not - changed thereby.63) - - - - - - -

Footnotes -

62) For example, addition of a double _Complex and a float entails just the conversion of the - float operand to double (and yields a double _Complex result). - -

63) The cast and assignment operators are still required to remove extra range and precision. - - -

Contents -

6.3.2 Other operands

- -

Contents -

6.3.2.1 Lvalues, arrays, and function designators
-

- An lvalue is an expression (with an object type other than void) that potentially - designates an object;64) if an lvalue does not designate an object when it is evaluated, the - behavior is undefined. When an object is said to have a particular type, the type is - specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that - does not have array type, does not have an incomplete type, does not have a const- - qualified type, and if it is a structure or union, does not have any member (including, - recursively, any member or element of all contained aggregates or unions) with a const- - qualified type. -

- Except when it is the operand of the sizeof operator, the unary & operator, the ++ - operator, the -- operator, or the left operand of the . operator or an assignment operator, - an lvalue that does not have array type is converted to the value stored in the designated - object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has - qualified type, the value has the unqualified version of the type of the lvalue; additionally, - if the lvalue has atomic type, the value has the non-atomic version of the type of the - lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete - type and does not have array type, the behavior is undefined. If the lvalue designates an - object of automatic storage duration that could have been declared with the register - storage class (never had its address taken), and that object is uninitialized (not declared - with an initializer and no assignment to it has been performed prior to use), the behavior - is undefined. -

- Except when it is the operand of the sizeof operator or the unary & operator, or is a - string literal used to initialize an array, an expression that has type ''array of type'' is - converted to an expression with type ''pointer to type'' that points to the initial element of - the array object and is not an lvalue. If the array object has register storage class, the - behavior is undefined. -

- A function designator is an expression that has function type. Except when it is the - operand of the sizeof operator65) or the unary & operator, a function designator with - type ''function returning type'' is converted to an expression that has type ''pointer to - - - - function returning type''. -

Forward references: address and indirection operators (6.5.3.2), assignment operators - (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3). - -

Footnotes -

64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left - operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an - object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described - as the ''value of an expression''. - An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary - expression that is a pointer to an object, *E is an lvalue that designates the object to which E points. - -

65) Because this conversion does not occur, the operand of the sizeof operator remains a function - designator and violates the constraint in 6.5.3.4. - - -

Contents -

6.3.2.2 void
-

- The (nonexistent) value of a void expression (an expression that has type void) shall not - be used in any way, and implicit or explicit conversions (except to void) shall not be - applied to such an expression. If an expression of any other type is evaluated as a void - expression, its value or designator is discarded. (A void expression is evaluated for its - side effects.) - -

Contents -

6.3.2.3 Pointers
-

- A pointer to void may be converted to or from a pointer to any object type. A pointer to - any object type may be converted to a pointer to void and back again; the result shall - compare equal to the original pointer. -

- For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to - the q-qualified version of the type; the values stored in the original and converted pointers - shall compare equal. -

- An integer constant expression with the value 0, or such an expression cast to type - void *, is called a null pointer constant.66) If a null pointer constant is converted to a - pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal - to a pointer to any object or function. -

- Conversion of a null pointer to another pointer type yields a null pointer of that type. - Any two null pointers shall compare equal. -

- An integer may be converted to any pointer type. Except as previously specified, the - result is implementation-defined, might not be correctly aligned, might not point to an - entity of the referenced type, and might be a trap representation.67) -

- Any pointer type may be converted to an integer type. Except as previously specified, the - result is implementation-defined. If the result cannot be represented in the integer type, - the behavior is undefined. The result need not be in the range of values of any integer - type. - - - - - -

- A pointer to an object type may be converted to a pointer to a different object type. If the - resulting pointer is not correctly aligned68) for the referenced type, the behavior is - undefined. Otherwise, when converted back again, the result shall compare equal to the - original pointer. When a pointer to an object is converted to a pointer to a character type, - the result points to the lowest addressed byte of the object. Successive increments of the - result, up to the size of the object, yield pointers to the remaining bytes of the object. -

- A pointer to a function of one type may be converted to a pointer to a function of another - type and back again; the result shall compare equal to the original pointer. If a converted - pointer is used to call a function whose type is not compatible with the referenced type, - the behavior is undefined. -

Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types - capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1). - - - - - - -

Footnotes -

66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19. - -

67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to - be consistent with the addressing structure of the execution environment. - -

68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a - pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is - correctly aligned for a pointer to type C. - - -

Contents -

6.4 Lexical elements

-

Syntax -

-

-          token:
-                   keyword
-                   identifier
-                   constant
-                   string-literal
-                   punctuator
-          preprocessing-token:
-                 header-name
-                 identifier
-                 pp-number
-                 character-constant
-                 string-literal
-                 punctuator
-                 each non-white-space character that cannot be one of the above
-
-

Constraints -

- Each preprocessing token that is converted to a token shall have the lexical form of a - keyword, an identifier, a constant, a string literal, or a punctuator. -

Semantics -

- A token is the minimal lexical element of the language in translation phases 7 and 8. The - categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. - A preprocessing token is the minimal lexical element of the language in translation - phases 3 through 6. The categories of preprocessing tokens are: header names, - identifiers, preprocessing numbers, character constants, string literals, punctuators, and - single non-white-space characters that do not lexically match the other preprocessing - token categories.69) If a ' or a " character matches the last category, the behavior is - undefined. Preprocessing tokens can be separated by white space; this consists of - comments (described later), or white-space characters (space, horizontal tab, new-line, - vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances - during translation phase 4, white space (or the absence thereof) serves as more than - preprocessing token separation. White space may appear within a preprocessing token - only as part of a header name or between the quotation characters in a character constant - or string literal. - - - - -

- If the input stream has been parsed into preprocessing tokens up to a given character, the - next preprocessing token is the longest sequence of characters that could constitute a - preprocessing token. There is one exception to this rule: header name preprocessing - tokens are recognized only within #include preprocessing directives and in - implementation-defined locations within #pragma directives. In such contexts, a - sequence of characters that could be either a header name or a string literal is recognized - as the former. -

- EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a - valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex - might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program - fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or - not E is a macro name. - -

- EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on - increment operators, even though the parse x ++ + ++ y might yield a correct expression. - -

Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5), - floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals - (6.4.5). - -

Footnotes -

69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot - occur in source files. - - -

Contents -

6.4.1 Keywords

-

Syntax -

-

-          keyword: one of
-                alignof                         goto                         union
-                auto                            if                           unsigned
-                break                           inline                       void
-                case                            int                          volatile
-                char                            long                         while
-                const                           register                     _Alignas
-                continue                        restrict                     _Atomic
-                default                         return                       _Bool
-                do                              short                        _Complex
-                double                          signed                       _Generic
-                else                            sizeof                       _Imaginary
-                enum                            static                       _Noreturn
-                extern                          struct                       _Static_assert
-                float                           switch                       _Thread_local
-                for                             typedef
-
-

Semantics -

- The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as - keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for - - specifying imaginary types.70) - -

Footnotes -

70) One possible specification for imaginary types appears in annex G. - - -

Contents -

6.4.2 Identifiers

- -

Contents -

6.4.2.1 General
-

Syntax -

-

-          identifier:
-                 identifier-nondigit
-                 identifier identifier-nondigit
-                 identifier digit
-          identifier-nondigit:
-                 nondigit
-                 universal-character-name
-                 other implementation-defined characters
-          nondigit: one of
-                 _ a b            c    d    e    f     g    h    i    j     k    l    m
-                     n o          p    q    r    s     t    u    v    w     x    y    z
-                     A B          C    D    E    F     G    H    I    J     K    L    M
-                     N O          P    Q    R    S     T    U    V    W     X    Y    Z
-          digit: one of
-                 0 1        2     3    4    5    6     7    8    9
-
-

Semantics -

- An identifier is a sequence of nondigit characters (including the underscore _, the - lowercase and uppercase Latin letters, and other characters) and digits, which designates - one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. - There is no specific limit on the maximum length of an identifier. -

- Each universal character name in an identifier shall designate a character whose encoding - in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character - shall not be a universal character name designating a character whose encoding falls into - one of the ranges specified in D.2. An implementation may allow multibyte characters - that are not part of the basic source character set to appear in identifiers; which characters - and their correspondence to universal character names is implementation-defined. - - - - -

- When preprocessing tokens are converted to tokens during translation phase 7, if a - preprocessing token could be converted to either a keyword or an identifier, it is converted - to a keyword. -

Implementation limits -

- As discussed in 5.2.4.1, an implementation may limit the number of significant initial - characters in an identifier; the limit for an external name (an identifier that has external - linkage) may be more restrictive than that for an internal name (a macro name or an - identifier that does not have external linkage). The number of significant characters in an - identifier is implementation-defined. -

- Any identifiers that differ in a significant character are different identifiers. If two - identifiers differ only in nonsignificant characters, the behavior is undefined. -

Forward references: universal character names (6.4.3), macro replacement (6.10.3). - -

Footnotes -

71) On systems in which linkers cannot accept extended characters, an encoding of the universal character - name may be used in forming valid external identifiers. For example, some otherwise unused - character or sequence of characters may be used to encode the \u in a universal character name. - Extended characters may produce a long external identifier. - - -

Contents -

6.4.2.2 Predefined identifiers
-

Semantics -

- The identifier __func__ shall be implicitly declared by the translator as if, - immediately following the opening brace of each function definition, the declaration -

-          static const char __func__[] = "function-name";
-
- appeared, where function-name is the name of the lexically-enclosing function.72) -

- This name is encoded as if the implicit declaration had been written in the source - character set and then translated into the execution character set as indicated in translation - phase 5. -

- EXAMPLE Consider the code fragment: -

-          #include <stdio.h>
-          void myfunc(void)
-          {
-                printf("%s\n", __func__);
-                /* ... */
-          }
-
- Each time the function is called, it will print to the standard output stream: -
-          myfunc
-
- -

Forward references: function definitions (6.9.1). - - - - - - -

Footnotes -

72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other - identifier is explicitly declared using the name __func__, the behavior is undefined. - - -

Contents -

6.4.3 Universal character names

-

Syntax -

-

-          universal-character-name:
-                 \u hex-quad
-                 \U hex-quad hex-quad
-          hex-quad:
-                 hexadecimal-digit hexadecimal-digit
-                              hexadecimal-digit hexadecimal-digit
-
-

Constraints -

- A universal character name shall not specify a character whose short identifier is less than - 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through - DFFF inclusive.73) -

Description -

- Universal character names may be used in identifiers, character constants, and string - literals to designate characters that are not in the basic character set. -

Semantics -

- The universal character name \Unnnnnnnn designates the character whose eight-digit - short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal - character name \unnnn designates the character whose four-digit short identifier is nnnn - (and whose eight-digit short identifier is 0000nnnn). - - - - - - -

Footnotes -

73) The disallowed characters are the characters in the basic character set and the code positions reserved - by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by - UTF-16). - - -

74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997. - - -

Contents -

6.4.4 Constants

-

Syntax -

-

-          constant:
-                 integer-constant
-                 floating-constant
-                 enumeration-constant
-                 character-constant
-
-

Constraints -

- Each constant shall have a type and the value of a constant shall be in the range of - representable values for its type. -

Semantics -

- Each constant has a type, determined by its form and value, as detailed later. - -

Contents -

6.4.4.1 Integer constants
-

Syntax -

- -

-          integer-constant:
-                  decimal-constant integer-suffixopt
-                  octal-constant integer-suffixopt
-                  hexadecimal-constant integer-suffixopt
-          decimal-constant:
-                nonzero-digit
-                decimal-constant digit
-          octal-constant:
-                 0
-                 octal-constant octal-digit
-          hexadecimal-constant:
-                hexadecimal-prefix hexadecimal-digit
-                hexadecimal-constant hexadecimal-digit
-          hexadecimal-prefix: one of
-                0x 0X
-          nonzero-digit: one of
-                 1 2 3 4          5     6     7   8    9
-          octal-digit: one of
-                  0 1 2 3         4     5     6   7
-         hexadecimal-digit:   one of
-               0 1 2           3 4     5    6   7     8   9
-               a b c           d e     f
-               A B C           D E     F
-         integer-suffix:
-                 unsigned-suffix long-suffixopt
-                 unsigned-suffix long-long-suffix
-                 long-suffix unsigned-suffixopt
-                 long-long-suffix unsigned-suffixopt
-         unsigned-suffix: one of
-                u U
-         long-suffix: one of
-                l L
-         long-long-suffix: one of
-                ll LL
-
-

Description -

- An integer constant begins with a digit, but has no period or exponent part. It may have a - prefix that specifies its base and a suffix that specifies its type. -

- A decimal constant begins with a nonzero digit and consists of a sequence of decimal - digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the - digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed - by a sequence of the decimal digits and the letters a (or A) through f (or F) with values - 10 through 15 respectively. -

Semantics -

- The value of a decimal constant is computed base 10; that of an octal constant, base 8; - that of a hexadecimal constant, base 16. The lexically first digit is the most significant. -

- The type of an integer constant is the first of the corresponding list in which its value can - be represented. - -

-                                                                  Octal or Hexadecimal
-
- Suffix Decimal Constant Constant - - none int int -
-                     long int                               unsigned int
-                     long long int                          long int
-                                                            unsigned long int
-                                                            long long int
-                                                            unsigned long long int
-
- - u or U unsigned int unsigned int -
-                     unsigned long int                      unsigned long int
-                     unsigned long long int                 unsigned long long int
-
- - l or L long int long int -
-                     long long int                          unsigned long int
-                                                            long long int
-                                                            unsigned long long int
-
- - Both u or U unsigned long int unsigned long int - and l or L unsigned long long int unsigned long long int - - ll or LL long long int long long int -
-                                                            unsigned long long int
-
- - Both u or U unsigned long long int unsigned long long int - and ll or LL -

- If an integer constant cannot be represented by any type in its list, it may have an - extended integer type, if the extended integer type can represent its value. If all of the - types in the list for the constant are signed, the extended integer type shall be signed. If - all of the types in the list for the constant are unsigned, the extended integer type shall be - unsigned. If the list contains both signed and unsigned types, the extended integer type - may be signed or unsigned. If an integer constant cannot be represented by any type in - its list and has no extended integer type, then the integer constant has no type. - - -

Contents -

6.4.4.2 Floating constants
-

Syntax -

- -

-          floating-constant:
-                 decimal-floating-constant
-                 hexadecimal-floating-constant
-          decimal-floating-constant:
-                fractional-constant exponent-partopt floating-suffixopt
-                digit-sequence exponent-part floating-suffixopt
-          hexadecimal-floating-constant:
-                hexadecimal-prefix hexadecimal-fractional-constant
-                               binary-exponent-part floating-suffixopt
-                hexadecimal-prefix hexadecimal-digit-sequence
-                               binary-exponent-part floating-suffixopt
-          fractional-constant:
-                  digit-sequenceopt . digit-sequence
-                  digit-sequence .
-          exponent-part:
-                e signopt digit-sequence
-                E signopt digit-sequence
-          sign: one of
-                 + -
-          digit-sequence:
-                  digit
-                  digit-sequence digit
-          hexadecimal-fractional-constant:
-                hexadecimal-digit-sequenceopt .
-                               hexadecimal-digit-sequence
-                hexadecimal-digit-sequence .
-          binary-exponent-part:
-                 p signopt digit-sequence
-                 P signopt digit-sequence
-          hexadecimal-digit-sequence:
-                hexadecimal-digit
-                hexadecimal-digit-sequence hexadecimal-digit
-          floating-suffix: one of
-                 f l F L
-
-

Description -

- A floating constant has a significand part that may be followed by an exponent part and a - suffix that specifies its type. The components of the significand part may include a digit - sequence representing the whole-number part, followed by a period (.), followed by a - digit sequence representing the fraction part. The components of the exponent part are an - e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. - Either the whole-number part or the fraction part has to be present; for decimal floating - constants, either the period or the exponent part has to be present. -

Semantics -

- The significand part is interpreted as a (decimal or hexadecimal) rational number; the - digit sequence in the exponent part is interpreted as a decimal integer. For decimal - floating constants, the exponent indicates the power of 10 by which the significand part is - to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 - by which the significand part is to be scaled. For decimal floating constants, and also for - hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either - the nearest representable value, or the larger or smaller representable value immediately - adjacent to the nearest representable value, chosen in an implementation-defined manner. - For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is - correctly rounded. -

- An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has - type float. If suffixed by the letter l or L, it has type long double. -

- Floating constants are converted to internal format as if at translation-time. The - conversion of a floating constant shall not raise an exceptional condition or a floating- - point exception at execution time. All floating constants of the same source form75) shall - convert to the same internal format with the same value. -

Recommended practice -

- The implementation should produce a diagnostic message if a hexadecimal constant - cannot be represented exactly in its evaluation format; the implementation should then - proceed with the translation of the program. -

- The translation-time conversion of floating constants should match the execution-time - conversion of character strings by library functions, such as strtod, given matching - inputs suitable for both conversions, the same result format, and default execution-time - rounding.76) - - - -

Footnotes -

75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not - convert to the same internal format and value. - -

76) The specification for the library functions recommends more accurate conversion than required for - floating constants (see 7.22.1.3). - - -

Contents -

6.4.4.3 Enumeration constants
-

Syntax -

-

-          enumeration-constant:
-                identifier
-
-

Semantics -

- An identifier declared as an enumeration constant has type int. -

Forward references: enumeration specifiers (6.7.2.2). - -

Contents -

6.4.4.4 Character constants
-

Syntax -

- -

-          character-constant:
-                 ' c-char-sequence '
-                 L' c-char-sequence '
-                 u' c-char-sequence '
-                 U' c-char-sequence '
-          c-char-sequence:
-                 c-char
-                 c-char-sequence c-char
-          c-char:
-                    any member of the source character set except
-                                 the single-quote ', backslash \, or new-line character
-                    escape-sequence
-          escape-sequence:
-                 simple-escape-sequence
-                 octal-escape-sequence
-                 hexadecimal-escape-sequence
-                 universal-character-name
-          simple-escape-sequence: one of
-                 \' \" \? \\
-                 \a \b \f \n \r                  \t    \v
-          octal-escape-sequence:
-                  \ octal-digit
-                  \ octal-digit octal-digit
-                  \ octal-digit octal-digit octal-digit
-        hexadecimal-escape-sequence:
-              \x hexadecimal-digit
-              hexadecimal-escape-sequence hexadecimal-digit
-
-

Description -

- An integer character constant is a sequence of one or more multibyte characters enclosed - in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the - letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are - any members of the source character set; they are mapped in an implementation-defined - manner to members of the execution character set. -

- The single-quote ', the double-quote ", the question-mark ?, the backslash \, and - arbitrary integer values are representable according to the following table of escape - sequences: -

-       single quote '            \'
-       double quote "            \"
-       question mark ?           \?
-       backslash \               \\
-       octal character           \octal digits
-       hexadecimal character     \x hexadecimal digits
-
-

- The double-quote " and question-mark ? are representable either by themselves or by the - escape sequences \" and \?, respectively, but the single-quote ' and the backslash \ - shall be represented, respectively, by the escape sequences \' and \\. -

- The octal digits that follow the backslash in an octal escape sequence are taken to be part - of the construction of a single character for an integer character constant or of a single - wide character for a wide character constant. The numerical value of the octal integer so - formed specifies the value of the desired character or wide character. -

- The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape - sequence are taken to be part of the construction of a single character for an integer - character constant or of a single wide character for a wide character constant. The - numerical value of the hexadecimal integer so formed specifies the value of the desired - character or wide character. -

- Each octal or hexadecimal escape sequence is the longest sequence of characters that can - constitute the escape sequence. -

- In addition, characters not in the basic character set are representable by universal - character names and certain nongraphic characters are representable by escape sequences - consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, - and \v.77) - -

Constraints -

- The value of an octal or hexadecimal escape sequence shall be in the range of - representable values for the corresponding type: -

-        Prefix      Corresponding Type
-        none       unsigned char
-        L          the unsigned type corresponding to wchar_t
-        u          char16_t
-        U          char32_t
-
-

Semantics -

- An integer character constant has type int. The value of an integer character constant - containing a single character that maps to a single-byte execution character is the - numerical value of the representation of the mapped character interpreted as an integer. - The value of an integer character constant containing more than one character (e.g., - 'ab'), or containing a character or escape sequence that does not map to a single-byte - execution character, is implementation-defined. If an integer character constant contains - a single character or escape sequence, its value is the one that results when an object with - type char whose value is that of the single character or escape sequence is converted to - type int. -

- A wide character constant prefixed by the letter L has type wchar_t, an integer type - defined in the <stddef.h> header; a wide character constant prefixed by the letter u or - U has type char16_t or char32_t, respectively, unsigned integer types defined in the - <uchar.h> header. The value of a wide character constant containing a single - multibyte character that maps to a single member of the extended execution character set - is the wide character corresponding to that multibyte character, as defined by the - mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an - implementation-defined current locale. The value of a wide character constant containing - more than one multibyte character or a single multibyte character that maps to multiple - members of the extended execution character set, or containing a multibyte character or - escape sequence not represented in the extended execution character set, is - implementation-defined. -

- EXAMPLE 1 The construction '\0' is commonly used to represent the null character. - -

- EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight - bits for objects that have type char. In an implementation in which type char has the same range of - values as signed char, the integer character constant '\xFF' has the value -1; if type char has the - same range of values as unsigned char, the character constant '\xFF' has the value +255. - - - - - -

- EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123' - specifies an integer character constant containing only one character, since a hexadecimal escape sequence - is terminated only by a non-hexadecimal character. To specify an integer character constant containing the - two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal - escape sequence is terminated after three octal digits. (The value of this two-character integer character - constant is implementation-defined.) - -

- EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction - L'\1234' specifies the implementation-defined value that results from the combination of the values - 0123 and '4'. - -

Forward references: common definitions <stddef.h> (7.19), the mbtowc function - (7.22.7.2), Unicode utilities <uchar.h> (7.27). - -

Footnotes -

77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, - the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4). - - -

Contents -

6.4.5 String literals

-

Syntax -

-

-          string-literal:
-                  encoding-prefixopt " s-char-sequenceopt "
-          encoding-prefix:
-                 u8
-                 u
-                 U
-                 L
-          s-char-sequence:
-                 s-char
-                 s-char-sequence s-char
-          s-char:
-                    any member of the source character set except
-                                 the double-quote ", backslash \, or new-line character
-                    escape-sequence
-
-

Constraints -

- A sequence of adjacent string literal tokens shall not include both a wide string literal and - a UTF-8 string literal. -

Description -

- A character string literal is a sequence of zero or more multibyte characters enclosed in - double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8. - A wide string literal is the same, except prefixed by the letter L, u, or U. -

- The same considerations apply to each element of the sequence in a string literal as if it - were in an integer character constant (for a character or UTF-8 string literal) or a wide - character constant (for a wide string literal), except that the single-quote ' is - representable either by itself or by the escape sequence \', but the double-quote " shall - - be represented by the escape sequence \". -

Semantics -

- In translation phase 6, the multibyte character sequences specified by any sequence of - adjacent character and identically-prefixed string literal tokens are concatenated into a - single multibyte character sequence. If any of the tokens has an encoding prefix, the - resulting multibyte character sequence is treated as having the same prefix; otherwise, it - is treated as a character string literal. Whether differently-prefixed wide string literal - tokens can be concatenated and, if so, the treatment of the resulting multibyte character - sequence are implementation-defined. -

- In translation phase 7, a byte or code of value zero is appended to each multibyte - character sequence that results from a string literal or literals.78) The multibyte character - sequence is then used to initialize an array of static storage duration and length just - sufficient to contain the sequence. For character string literals, the array elements have - type char, and are initialized with the individual bytes of the multibyte character - sequence. For UTF-8 string literals, the array elements have type char, and are - initialized with the characters of the multibyte character sequence, as encoded in UTF-8. - For wide string literals prefixed by the letter L, the array elements have type wchar_t - and are initialized with the sequence of wide characters corresponding to the multibyte - character sequence, as defined by the mbstowcs function with an implementation- - defined current locale. For wide string literals prefixed by the letter u or U, the array - elements have type char16_t or char32_t, respectively, and are initialized with the - sequence of wide characters corresponding to the multibyte character sequence, as - defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for - its type, with an implementation-defined current locale. The value of a string literal - containing a multibyte character or escape sequence not represented in the execution - character set is implementation-defined. -

- It is unspecified whether these arrays are distinct provided their elements have the - appropriate values. If the program attempts to modify such an array, the behavior is - undefined. -

- EXAMPLE 1 This pair of adjacent character string literals -

-          "\x12" "3"
-
- produces a single character string literal containing the two characters whose values are '\x12' and '3', - because escape sequences are converted into single members of the execution character set just prior to - adjacent string literal concatenation. - -

- EXAMPLE 2 Each of the sequences of adjacent string literal tokens - - - - -

-          "a" "b" L"c"
-          "a" L"b" "c"
-          L"a" "b" L"c"
-          L"a" L"b" L"c"
-
- is equivalent to the string literal -
-          L"abc"
-
- Likewise, each of the sequences -
-          "a" "b" u"c"
-          "a" u"b" "c"
-          u"a" "b" u"c"
-          u"a" u"b" u"c"
-
- is equivalent to -
-          u"abc"
-
- -

Forward references: common definitions <stddef.h> (7.19), the mbstowcs - function (7.22.8.1), Unicode utilities <uchar.h> (7.27). - -

Footnotes -

78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a - \0 escape sequence. - - -

Contents -

6.4.6 Punctuators

-

Syntax -

-

-          punctuator: one of
-                 [ ] ( ) { } . ->
-                 ++ -- & * + - ~ !
-                 / % << >> < > <= >=                         ==    !=    ^    |   &&   ||
-                 ? : ; ...
-                 = *= /= %= += -= <<=                        >>=    &=       ^=   |=
-                 , # ##
-                 <: :> <% %> %: %:%:
-
-

Semantics -

- A punctuator is a symbol that has independent syntactic and semantic significance. - Depending on context, it may specify an operation to be performed (which in turn may - yield a value or a function designator, produce a side effect, or some combination thereof) - in which case it is known as an operator (other forms of operator also exist in some - contexts). An operand is an entity on which an operator acts. - -

- In all aspects of the language, the six tokens79) -

-          <:    :>      <%    %>     %:     %:%:
-
- behave, respectively, the same as the six tokens -
-          [     ]       {     }      #      ##
-
- except for their spelling.80) -

Forward references: expressions (6.5), declarations (6.7), preprocessing directives - (6.10), statements (6.8). - -

Footnotes -

79) These tokens are sometimes called ''digraphs''. - -

80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely - interchanged. - - -

Contents -

6.4.7 Header names

-

Syntax -

-

-          header-name:
-                 < h-char-sequence >
-                 " q-char-sequence "
-          h-char-sequence:
-                 h-char
-                 h-char-sequence h-char
-          h-char:
-                    any member of the source character set except
-                                 the new-line character and >
-          q-char-sequence:
-                 q-char
-                 q-char-sequence q-char
-          q-char:
-                    any member of the source character set except
-                                 the new-line character and "
-
-

Semantics -

- The sequences in both forms of header names are mapped in an implementation-defined - manner to headers or external source file names as specified in 6.10.2. -

- If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters, - the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the - - - - - - sequence between the " delimiters, the behavior is undefined.81) Header name - preprocessing tokens are recognized only within #include preprocessing directives and - in implementation-defined locations within #pragma directives.82) -

- EXAMPLE The following sequence of characters: -

-          0x3<1/a.h>1e2
-          #include <1/a.h>
-          #define const.member@$
-
- forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited - by a { on the left and a } on the right). -
-          {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
-          {#}{include} {<1/a.h>}
-          {#}{define} {const}{.}{member}{@}{$}
-
- -

Forward references: source file inclusion (6.10.2). - -

Footnotes -

81) Thus, sequences of characters that resemble escape sequences cause undefined behavior. - -

82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9. - - -

Contents -

6.4.8 Preprocessing numbers

-

Syntax -

-

-          pp-number:
-                digit
-                . digit
-                pp-number       digit
-                pp-number       identifier-nondigit
-                pp-number       e sign
-                pp-number       E sign
-                pp-number       p sign
-                pp-number       P sign
-                pp-number       .
-
-

Description -

- A preprocessing number begins with a digit optionally preceded by a period (.) and may - be followed by valid identifier characters and the character sequences e+, e-, E+, E-, - p+, p-, P+, or P-. -

- Preprocessing number tokens lexically include all floating and integer constant tokens. -

Semantics -

- A preprocessing number does not have type or a value; it acquires both after a successful - conversion (as part of translation phase 7) to a floating constant token or an integer - constant token. - - - - -

Contents -

6.4.9 Comments

-

- Except within a character constant, a string literal, or a comment, the characters /* - introduce a comment. The contents of such a comment are examined only to identify - multibyte characters and to find the characters */ that terminate it.83) -

- Except within a character constant, a string literal, or a comment, the characters // - introduce a comment that includes all multibyte characters up to, but not including, the - next new-line character. The contents of such a comment are examined only to identify - multibyte characters and to find the terminating new-line character. -

- EXAMPLE -

-          "a//b"                             //   four-character string literal
-          #include "//e"                     //   undefined behavior
-          // */                              //   comment, not syntax error
-          f = g/**//h;                       //   equivalent to f = g / h;
-          //\
-          i();                               // part of a two-line comment
-          /\
-          / j();                             // part of a two-line comment
-          #define glue(x,y) x##y
-          glue(/,/) k();                     // syntax error, not comment
-          /*//*/ l();                        // equivalent to l();
-          m = n//**/o
-             + p;                            // equivalent to m = n + p;
-
- - - - - - -

Footnotes -

83) Thus, /* ... */ comments do not nest. - - -

Contents -

6.5 Expressions

-

- An expression is a sequence of operators and operands that specifies computation of a - value, or that designates an object or a function, or that generates side effects, or that - performs a combination thereof. The value computations of the operands of an operator - are sequenced before the value computation of the result of the operator. -

- If a side effect on a scalar object is unsequenced relative to either a different side effect - on the same scalar object or a value computation using the value of the same scalar - object, the behavior is undefined. If there are multiple allowable orderings of the - subexpressions of an expression, the behavior is undefined if such an unsequenced side - effect occurs in any of the orderings.84) -

- The grouping of operators and operands is indicated by the syntax.85) Except as specified - later, side effects and value computations of subexpressions are unsequenced.86) * -

- Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, - collectively described as bitwise operators) are required to have operands that have - integer type. These operators yield values that depend on the internal representations of - integers, and have implementation-defined and undefined aspects for signed types. -

- If an exceptional condition occurs during the evaluation of an expression (that is, if the - result is not mathematically defined or not in the range of representable values for its - type), the behavior is undefined. - - - - -

- The effective type of an object for an access to its stored value is the declared type of the - object, if any.87) If a value is stored into an object having no declared type through an - lvalue having a type that is not a character type, then the type of the lvalue becomes the - effective type of the object for that access and for subsequent accesses that do not modify - the stored value. If a value is copied into an object having no declared type using - memcpy or memmove, or is copied as an array of character type, then the effective type - of the modified object for that access and for subsequent accesses that do not modify the - value is the effective type of the object from which the value is copied, if it has one. For - all other accesses to an object having no declared type, the effective type of the object is - simply the type of the lvalue used for the access. -

- An object shall have its stored value accessed only by an lvalue expression that has one of - the following types:88) -

-

- A floating expression may be contracted, that is, evaluated as though it were a single - operation, thereby omitting rounding errors implied by the source code and the - expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a - way to disallow contracted expressions. Otherwise, whether and how expressions are - contracted is implementation-defined.90) -

Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2). - - - - -

Footnotes -

84) This paragraph renders undefined statement expressions such as - -

-           i = ++i + 1;
-           a[i++] = i;
-
- while allowing - -
-           i = i + 1;
-           a[i] = i;
-
- - -

85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same - as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the - expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in - 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators - (6.5.3), and an operand contained between any of the following pairs of operators: grouping - parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and - the conditional operator ? : (6.5.15). - Within each major subclause, the operators have the same precedence. Left- or right-associativity is - indicated in each subclause by the syntax for the expressions discussed therein. - -

86) In an expression that is evaluated more than once during the execution of a program, unsequenced and - indeterminately sequenced evaluations of its subexpressions need not be performed consistently in - different evaluations. - -

87) Allocated objects have no declared type. - -

88) The intent of this list is to specify those circumstances in which an object may or may not be aliased. - -

89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and - range, while the final operation is rounded to the format determined by the expression evaluation - method. A contracted expression might also omit the raising of floating-point exceptions. - -

90) This license is specifically intended to allow implementations to exploit fast machine instructions that - combine multiple C operators. As contractions potentially undermine predictability, and can even - decrease accuracy for containing expressions, their use needs to be well-defined and clearly - documented. - - -

Contents -

6.5.1 Primary expressions

-

Syntax -

-

-          primary-expression:
-                 identifier
-                 constant
-                 string-literal
-                 ( expression )
-                 generic-selection
-
-

Semantics -

- An identifier is a primary expression, provided it has been declared as designating an - object (in which case it is an lvalue) or a function (in which case it is a function - designator).91) -

- A constant is a primary expression. Its type depends on its form and value, as detailed in - 6.4.4. -

- A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5. -

- A parenthesized expression is a primary expression. Its type and value are identical to - those of the unparenthesized expression. It is an lvalue, a function designator, or a void - expression if the unparenthesized expression is, respectively, an lvalue, a function - designator, or a void expression. -

Forward references: declarations (6.7). - -

Footnotes -

91) Thus, an undeclared identifier is a violation of the syntax. - - -

Contents -

6.5.1.1 Generic selection
-

Syntax -

-

-          generic-selection:
-                 _Generic ( assignment-expression , generic-assoc-list )
-          generic-assoc-list:
-                 generic-association
-                 generic-assoc-list , generic-association
-          generic-association:
-                 type-name : assignment-expression
-                 default : assignment-expression
-
-

Constraints -

- A generic selection shall have no more than one default generic association. The type - name in a generic association shall specify a complete object type other than a variably - - - modified type. No two generic associations in the same generic selection shall specify - compatible types. The controlling expression of a generic selection shall have type - compatible with at most one of the types named in its generic association list. If a - generic selection has no default generic association, its controlling expression shall - have type compatible with exactly one of the types named in its generic association list. -

Semantics -

- The controlling expression of a generic selection is not evaluated. If a generic selection - has a generic association with a type name that is compatible with the type of the - controlling expression, then the result expression of the generic selection is the - expression in that generic association. Otherwise, the result expression of the generic - selection is the expression in the default generic association. None of the expressions - from any other generic association of the generic selection is evaluated. -

- The type and value of a generic selection are identical to those of its result expression. It - is an lvalue, a function designator, or a void expression if its result expression is, - respectively, an lvalue, a function designator, or a void expression. -

- EXAMPLE The cbrt type-generic macro could be implemented as follows: -

-          #define cbrt(X) _Generic((X),                                      \
-                                  long double: cbrtl,                        \
-                                  default: cbrt,                             \
-                                  float: cbrtf                               \
-                                  )(X)
-
- - -

Contents -

6.5.2 Postfix operators

-

Syntax -

- -

-          postfix-expression:
-                 primary-expression
-                 postfix-expression [ expression ]
-                 postfix-expression ( argument-expression-listopt )
-                 postfix-expression . identifier
-                 postfix-expression -> identifier
-                 postfix-expression ++
-                 postfix-expression --
-                 ( type-name ) { initializer-list }
-                 ( type-name ) { initializer-list , }
-          argument-expression-list:
-                assignment-expression
-                argument-expression-list , assignment-expression
-
- -

Contents -

6.5.2.1 Array subscripting
-

Constraints -

- One of the expressions shall have type ''pointer to complete object type'', the other - expression shall have integer type, and the result has type ''type''. -

Semantics -

- A postfix expression followed by an expression in square brackets [] is a subscripted - designation of an element of an array object. The definition of the subscript operator [] - is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that - apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the - initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th - element of E1 (counting from zero). -

- Successive subscript operators designate an element of a multidimensional array object. - If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as - other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with - dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or - implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional - array, which itself is converted into a pointer if used as other than an lvalue. It follows - from this that arrays are stored in row-major order (last subscript varies fastest). -

- EXAMPLE Consider the array object defined by the declaration -

-          int x[3][5];
-
- Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an - array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to - a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually - entails multiplying i by the size of the object to which the pointer points, namely an array of five int - objects. The results are added and indirection is applied to yield an array of five ints. When used in the - expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j] - yields an int. - -

Forward references: additive operators (6.5.6), address and indirection operators - (6.5.3.2), array declarators (6.7.6.2). - -

Contents -

6.5.2.2 Function calls
-

Constraints -

- The expression that denotes the called function92) shall have type pointer to function - returning void or returning a complete object type other than an array type. -

- If the expression that denotes the called function has a type that includes a prototype, the - number of arguments shall agree with the number of parameters. Each argument shall - - - - have a type such that its value may be assigned to an object with the unqualified version - of the type of its corresponding parameter. -

Semantics -

- A postfix expression followed by parentheses () containing a possibly empty, comma- - separated list of expressions is a function call. The postfix expression denotes the called - function. The list of expressions specifies the arguments to the function. -

- An argument may be an expression of any complete object type. In preparing for the call - to a function, the arguments are evaluated, and each parameter is assigned the value of the - corresponding argument.93) -

- If the expression that denotes the called function has type pointer to function returning an - object type, the function call expression has the same type as that object type, and has the - value determined as specified in 6.8.6.4. Otherwise, the function call has type void. * -

- If the expression that denotes the called function has a type that does not include a - prototype, the integer promotions are performed on each argument, and arguments that - have type float are promoted to double. These are called the default argument - promotions. If the number of arguments does not equal the number of parameters, the - behavior is undefined. If the function is defined with a type that includes a prototype, and - either the prototype ends with an ellipsis (, ...) or the types of the arguments after - promotion are not compatible with the types of the parameters, the behavior is undefined. - If the function is defined with a type that does not include a prototype, and the types of - the arguments after promotion are not compatible with those of the parameters after - promotion, the behavior is undefined, except for the following cases: -

-

- If the expression that denotes the called function has a type that does include a prototype, - the arguments are implicitly converted, as if by assignment, to the types of the - corresponding parameters, taking the type of each parameter to be the unqualified version - of its declared type. The ellipsis notation in a function prototype declarator causes - argument type conversion to stop after the last declared parameter. The default argument - promotions are performed on trailing arguments. - - - - -

- No other conversions are performed implicitly; in particular, the number and types of - arguments are not compared with those of the parameters in a function definition that - does not include a function prototype declarator. -

- If the function is defined with a type that is not compatible with the type (of the - expression) pointed to by the expression that denotes the called function, the behavior is - undefined. -

- There is a sequence point after the evaluations of the function designator and the actual - arguments but before the actual call. Every evaluation in the calling function (including - other function calls) that is not otherwise specifically sequenced before or after the - execution of the body of the called function is indeterminately sequenced with respect to - the execution of the called function.94) -

- Recursive function calls shall be permitted, both directly and indirectly through any chain - of other functions. -

- EXAMPLE In the function call -

-          (*pf[f1()]) (f2(), f3() + f4())
-
- the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before - the function pointed to by pf[f1()] is called. - -

Forward references: function declarators (including prototypes) (6.7.6.3), function - definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1). - -

Footnotes -

92) Most often, this is the result of converting an identifier that is a function designator. - -

93) A function may change the values of its parameters, but these changes cannot affect the values of the - arguments. On the other hand, it is possible to pass a pointer to an object, and the function may - change the value of the object pointed to. A parameter declared to have array or function type is - adjusted to have a pointer type as described in 6.9.1. - -

94) In other words, function executions do not ''interleave'' with each other. - - -

Contents -

6.5.2.3 Structure and union members
-

Constraints -

- The first operand of the . operator shall have an atomic, qualified, or unqualified - structure or union type, and the second operand shall name a member of that type. -

- The first operand of the -> operator shall have type ''pointer to atomic, qualified, or - unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the - second operand shall name a member of the type pointed to. -

Semantics -

- A postfix expression followed by the . operator and an identifier designates a member of - a structure or union object. The value is that of the named member,95) and is an lvalue if - the first expression is an lvalue. If the first expression has qualified type, the result has - the so-qualified version of the type of the designated member. - - -

- A postfix expression followed by the -> operator and an identifier designates a member - of a structure or union object. The value is that of the named member of the object to - which the first expression points, and is an lvalue.96) If the first expression is a pointer to - a qualified type, the result has the so-qualified version of the type of the designated - member. -

- Accessing a member of an atomic structure or union object results in undefined - behavior.97) -

- One special guarantee is made in order to simplify the use of unions: if a union contains - several structures that share a common initial sequence (see below), and if the union - object currently contains one of these structures, it is permitted to inspect the common - initial part of any of them anywhere that a declaration of the completed type of the union - is visible. Two structures share a common initial sequence if corresponding members - have compatible types (and, for bit-fields, the same widths) for a sequence of one or more - initial members. -

- EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or - union, f().x is a valid postfix expression but is not an lvalue. - -

- EXAMPLE 2 In: -

-          struct s { int i; const int ci; };
-          struct s s;
-          const struct s cs;
-          volatile struct s vs;
-
- the various members have the types: -
-          s.i          int
-          s.ci         const int
-          cs.i         const int
-          cs.ci        const int
-          vs.i         volatile int
-          vs.ci        volatile const int
-
- - - - - -

- EXAMPLE 3 The following is a valid fragment: -

-          union {
-                  struct {
-                        int      alltypes;
-                  } n;
-                  struct {
-                        int      type;
-                        int      intnode;
-                  } ni;
-                  struct {
-                        int      type;
-                        double doublenode;
-                  } nf;
-          } u;
-          u.nf.type = 1;
-          u.nf.doublenode = 3.14;
-          /* ... */
-          if (u.n.alltypes == 1)
-                  if (sin(u.nf.doublenode) == 0.0)
-                        /* ... */
-
- The following is not a valid fragment (because the union type is not visible within function f): -
-          struct t1 { int m; };
-          struct t2 { int m; };
-          int f(struct t1 *p1, struct t2 *p2)
-          {
-                if (p1->m < 0)
-                        p2->m = -p2->m;
-                return p1->m;
-          }
-          int g()
-          {
-                union {
-                        struct t1 s1;
-                        struct t2 s2;
-                } u;
-                /* ... */
-                return f(&u.s1, &u.s2);
-          }
-
- -

Forward references: address and indirection operators (6.5.3.2), structure and union - specifiers (6.7.2.1). - - -

Footnotes -

95) If the member used to read the contents of a union object is not the same as the member last used to - store a value in the object, the appropriate part of the object representation of the value is reinterpreted - as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type - punning''). This might be a trap representation. - -

96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to - its operand), the expression (&E)->MOS is the same as E.MOS. - -

97) For example, a data race would occur if access to the entire structure or union in one thread conflicts - with access to a member from another thread, where at least one access is a modification. Members - can be safely accessed using a non-atomic object which is assigned to or from the atomic object. - - -

Contents -

6.5.2.4 Postfix increment and decrement operators
-

Constraints -

- The operand of the postfix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. -

Semantics -

- The result of the postfix ++ operator is the value of the operand. As a side effect, the - value of the operand object is incremented (that is, the value 1 of the appropriate type is - added to it). See the discussions of additive operators and compound assignment for - information on constraints, types, and conversions and the effects of operations on - pointers. The value computation of the result is sequenced before the side effect of - updating the stored value of the operand. With respect to an indeterminately-sequenced - function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object - with atomic type is a read-modify-write operation with memory_order_seq_cst - memory order semantics.98) -

- The postfix -- operator is analogous to the postfix ++ operator, except that the value of - the operand is decremented (that is, the value 1 of the appropriate type is subtracted from - it). -

Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - -

Footnotes -

98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence - where T is the type of E: - -

-          T tmp;
-          T result = E;
-          do {
-                 tmp = result + 1;
-          } while (!atomic_compare_exchange_strong(&E, &result, tmp));
-
- with result being the result of the operation. - - -

Contents -

6.5.2.5 Compound literals
-

Constraints -

- The type name shall specify a complete object type or an array of unknown size, but not a - variable length array type. -

- All the constraints for initializer lists in 6.7.9 also apply to compound literals. -

Semantics -

- A postfix expression that consists of a parenthesized type name followed by a brace- - enclosed list of initializers is a compound literal. It provides an unnamed object whose - value is given by the initializer list.99) - - - -

- If the type name specifies an array of unknown size, the size is determined by the - initializer list as specified in 6.7.9, and the type of the compound literal is that of the - completed array type. Otherwise (when the type name specifies an object type), the type - of the compound literal is that specified by the type name. In either case, the result is an - lvalue. -

- The value of the compound literal is that of an unnamed object initialized by the - initializer list. If the compound literal occurs outside the body of a function, the object - has static storage duration; otherwise, it has automatic storage duration associated with - the enclosing block. -

- All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100) -

- String literals, and compound literals with const-qualified types, need not designate - distinct objects.101) -

- EXAMPLE 1 The file scope definition -

-          int *p = (int []){2, 4};
-
- initializes p to point to the first element of an array of two ints, the first having the value two and the - second, four. The expressions in this compound literal are required to be constant. The unnamed object - has static storage duration. - -

- EXAMPLE 2 In contrast, in -

-          void f(void)
-          {
-                int *p;
-                /*...*/
-                p = (int [2]){*p};
-                /*...*/
-          }
-
- p is assigned the address of the first element of an array of two ints, the first having the value previously - pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The - unnamed object has automatic storage duration. - -

- EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects - created using compound literals can be passed to functions without depending on member order: -

-          drawline((struct point){.x=1, .y=1},
-                (struct point){.x=3, .y=4});
-
- Or, if drawline instead expected pointers to struct point: - - - - -
-          drawline(&(struct point){.x=1, .y=1},
-                &(struct point){.x=3, .y=4});
-
- -

- EXAMPLE 4 A read-only compound literal can be specified through constructions like: -

-          (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
-
- -

- EXAMPLE 5 The following three expressions have different meanings: -

-          "/tmp/fileXXXXXX"
-          (char []){"/tmp/fileXXXXXX"}
-          (const char []){"/tmp/fileXXXXXX"}
-
- The first always has static storage duration and has type array of char, but need not be modifiable; the last - two have automatic storage duration when they occur within the body of a function, and the first of these - two is modifiable. - -

- EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory - and can even be shared. For example, -

-          (const char []){"abc"} == "abc"
-
- might yield 1 if the literals' storage is shared. - -

- EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly - linked object. For example, there is no way to write a self-referential compound literal that could be used - as the function argument in place of the named object endless_zeros below: -

-          struct int_list { int car; struct int_list *cdr; };
-          struct int_list endless_zeros = {0, &endless_zeros};
-          eval(endless_zeros);
-
- -

- EXAMPLE 8 Each compound literal creates only a single object in a given scope: -

-          struct s { int i; };
-          int f (void)
-          {
-                struct s *p = 0, *q;
-                int j = 0;
-          again:
-                    q = p, p = &((struct s){ j++ });
-                    if (j < 2) goto again;
-                    return p == q && q->i == 1;
-          }
-
- The function f() always returns the value 1. -

- Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the - lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would - have an indeterminate value, which would result in undefined behavior. - -

Forward references: type names (6.7.7), initialization (6.7.9). - - -

Footnotes -

99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types - or void only, and the result of a cast expression is not an lvalue. - -

100) For example, subobjects without explicit initializers are initialized to zero. - -

101) This allows implementations to share storage for string literals and constant compound literals with - the same or overlapping representations. - - -

Contents -

6.5.3 Unary operators

-

Syntax -

-

-          unary-expression:
-                 postfix-expression
-                 ++ unary-expression
-                 -- unary-expression
-                 unary-operator cast-expression
-                 sizeof unary-expression
-                 sizeof ( type-name )
-                 alignof ( type-name )
-          unary-operator: one of
-                 & * + - ~             !
-
- -

Contents -

6.5.3.1 Prefix increment and decrement operators
-

Constraints -

- The operand of the prefix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. -

Semantics -

- The value of the operand of the prefix ++ operator is incremented. The result is the new - value of the operand after incrementation. The expression ++E is equivalent to (E+=1). - See the discussions of additive operators and compound assignment for information on - constraints, types, side effects, and conversions and the effects of operations on pointers. -

- The prefix -- operator is analogous to the prefix ++ operator, except that the value of the - operand is decremented. -

Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - -

Contents -

6.5.3.2 Address and indirection operators
-

Constraints -

- The operand of the unary & operator shall be either a function designator, the result of a - [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is - not declared with the register storage-class specifier. -

- The operand of the unary * operator shall have pointer type. -

Semantics -

- The unary & operator yields the address of its operand. If the operand has type ''type'', - the result has type ''pointer to type''. If the operand is the result of a unary * operator, - neither that operator nor the & operator is evaluated and the result is as if both were - omitted, except that the constraints on the operators still apply and the result is not an - - lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor - the unary * that is implied by the [] is evaluated and the result is as if the & operator - were removed and the [] operator were changed to a + operator. Otherwise, the result is - a pointer to the object or function designated by its operand. -

- The unary * operator denotes indirection. If the operand points to a function, the result is - a function designator; if it points to an object, the result is an lvalue designating the - object. If the operand has type ''pointer to type'', the result has type ''type''. If an - invalid value has been assigned to the pointer, the behavior of the unary * operator is - undefined.102) -

Forward references: storage-class specifiers (6.7.1), structure and union specifiers - (6.7.2.1). - -

Footnotes -

102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is - always true that if E is a function designator or an lvalue that is a valid operand of the unary & - operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of - an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. - Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an - address inappropriately aligned for the type of object pointed to, and the address of an object after the - end of its lifetime. - - -

Contents -

6.5.3.3 Unary arithmetic operators
-

Constraints -

- The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, - integer type; of the ! operator, scalar type. -

Semantics -

- The result of the unary + operator is the value of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -

- The result of the unary - operator is the negative of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -

- The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, - each bit in the result is set if and only if the corresponding bit in the converted operand is - not set). The integer promotions are performed on the operand, and the result has the - promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent - to the maximum value representable in that type minus E. -

- The result of the logical negation operator ! is 0 if the value of its operand compares - unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. - The expression !E is equivalent to (0==E). - - - - - -

Contents -

6.5.3.4 The sizeof and alignof operators
-

Constraints -

- The sizeof operator shall not be applied to an expression that has function type or an - incomplete type, to the parenthesized name of such a type, or to an expression that - designates a bit-field member. The alignof operator shall not be applied to a function - type or an incomplete type. -

Semantics -

- The sizeof operator yields the size (in bytes) of its operand, which may be an - expression or the parenthesized name of a type. The size is determined from the type of - the operand. The result is an integer. If the type of the operand is a variable length array - type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an - integer constant. -

- The alignof operator yields the alignment requirement of its operand type. The result - is an integer constant. When applied to an array type, the result is the alignment - requirement of the element type. -

- When sizeof is applied to an operand that has type char, unsigned char, or - signed char, (or a qualified version thereof) the result is 1. When applied to an - operand that has array type, the result is the total number of bytes in the array.103) When - applied to an operand that has structure or union type, the result is the total number of - bytes in such an object, including internal and trailing padding. -

- The value of the result of both operators is implementation-defined, and its type (an - unsigned integer type) is size_t, defined in <stddef.h> (and other headers). -

- EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage - allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to - allocate and return a pointer to void. For example: -

-         extern void *alloc(size_t);
-         double *dp = alloc(sizeof *dp);
-
- The implementation of the alloc function should ensure that its return value is aligned suitably for - conversion to a pointer to double. - -

- EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array: -

-         sizeof array / sizeof array[0]
-
- -

- EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a - function: -

-         #include <stddef.h>
-
- - - - -
-          size_t fsize3(int n)
-          {
-                char b[n+3];                  // variable length array
-                return sizeof b;              // execution time sizeof
-          }
-          int main()
-          {
-                size_t size;
-                size = fsize3(10); // fsize3 returns 13
-                return 0;
-          }
-
- -

Forward references: common definitions <stddef.h> (7.19), declarations (6.7), - structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2). - -

Footnotes -

103) When applied to a parameter declared to have array or function type, the sizeof operator yields the - size of the adjusted (pointer) type (see 6.9.1). - - -

Contents -

6.5.4 Cast operators

-

Syntax -

-

-          cast-expression:
-                 unary-expression
-                 ( type-name ) cast-expression
-
-

Constraints -

- Unless the type name specifies a void type, the type name shall specify atomic, qualified, - or unqualified scalar type, and the operand shall have scalar type. -

- Conversions that involve pointers, other than where permitted by the constraints of - 6.5.16.1, shall be specified by means of an explicit cast. -

- A pointer type shall not be converted to any floating type. A floating type shall not be - converted to any pointer type. -

Semantics -

- Preceding an expression by a parenthesized type name converts the value of the - expression to the named type. This construction is called a cast.104) A cast that specifies - no conversion has no effect on the type or value of an expression. -

- If the value of the expression is represented with greater precision or range than required - by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the - type of the expression is the same as the named type and removes any extra range and - precision. -

Forward references: equality operators (6.5.9), function declarators (including - prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7). - - - -

Footnotes -

104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the - unqualified version of the type. - - -

Contents -

6.5.5 Multiplicative operators

-

Syntax -

-

-          multiplicative-expression:
-                  cast-expression
-                  multiplicative-expression * cast-expression
-                  multiplicative-expression / cast-expression
-                  multiplicative-expression % cast-expression
-
-

Constraints -

- Each of the operands shall have arithmetic type. The operands of the % operator shall - have integer type. -

Semantics -

- The usual arithmetic conversions are performed on the operands. -

- The result of the binary * operator is the product of the operands. -

- The result of the / operator is the quotient from the division of the first operand by the - second; the result of the % operator is the remainder. In both operations, if the value of - the second operand is zero, the behavior is undefined. -

- When integers are divided, the result of the / operator is the algebraic quotient with any - fractional part discarded.105) If the quotient a/b is representable, the expression - (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is - undefined. - -

Footnotes -

105) This is often called ''truncation toward zero''. - - -

Contents -

6.5.6 Additive operators

-

Syntax -

-

-          additive-expression:
-                 multiplicative-expression
-                 additive-expression + multiplicative-expression
-                 additive-expression - multiplicative-expression
-
-

Constraints -

- For addition, either both operands shall have arithmetic type, or one operand shall be a - pointer to a complete object type and the other shall have integer type. (Incrementing is - equivalent to adding 1.) -

- For subtraction, one of the following shall hold: - - - - - -

- (Decrementing is equivalent to subtracting 1.) -

Semantics -

- If both operands have arithmetic type, the usual arithmetic conversions are performed on - them. -

- The result of the binary + operator is the sum of the operands. -

- The result of the binary - operator is the difference resulting from the subtraction of the - second operand from the first. -

- For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -

- When an expression that has integer type is added to or subtracted from a pointer, the - result has the type of the pointer operand. If the pointer operand points to an element of - an array object, and the array is large enough, the result points to an element offset from - the original element such that the difference of the subscripts of the resulting and original - array elements equals the integer expression. In other words, if the expression P points to - the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and - (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of - the array object, provided they exist. Moreover, if the expression P points to the last - element of an array object, the expression (P)+1 points one past the last element of the - array object, and if the expression Q points one past the last element of an array object, - the expression (Q)-1 points to the last element of the array object. If both the pointer - operand and the result point to elements of the same array object, or one past the last - element of the array object, the evaluation shall not produce an overflow; otherwise, the - behavior is undefined. If the result points one past the last element of the array object, it - shall not be used as the operand of a unary * operator that is evaluated. -

- When two pointers are subtracted, both shall point to elements of the same array object, - or one past the last element of the array object; the result is the difference of the - subscripts of the two array elements. The size of the result is implementation-defined, - and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. - If the result is not representable in an object of that type, the behavior is undefined. In - other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of - an array object, the expression (P)-(Q) has the value i-j provided the value fits in an - - object of type ptrdiff_t. Moreover, if the expression P points either to an element of - an array object or one past the last element of an array object, and the expression Q points - to the last element of the same array object, the expression ((Q)+1)-(P) has the same - value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the - expression P points one past the last element of the array object, even though the - expression (Q)+1 does not point to an element of the array object.106) -

- EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types. -

-          {
-                   int n = 4, m = 3;
-                   int a[n][m];
-                   int (*p)[m] = a;            //   p == &a[0]
-                   p += 1;                     //   p == &a[1]
-                   (*p)[2] = 99;               //   a[1][2] == 99
-                   n = p - a;                  //   n == 1
-          }
-
-

- If array a in the above example were declared to be an array of known constant size, and pointer p were - declared to be a pointer to an array of the same known constant size (pointing to a), the results would be - the same. - -

Forward references: array declarators (6.7.6.2), common definitions <stddef.h> - (7.19). - -

Footnotes -

106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In - this scheme the integer expression added to or subtracted from the converted pointer is first multiplied - by the size of the object originally pointed to, and the resulting pointer is converted back to the - original type. For pointer subtraction, the result of the difference between the character pointers is - similarly divided by the size of the object originally pointed to. - When viewed in this way, an implementation need only provide one extra byte (which may overlap - another object in the program) just after the end of the object in order to satisfy the ''one past the last - element'' requirements. - - -

Contents -

6.5.7 Bitwise shift operators

-

Syntax -

-

-          shift-expression:
-                  additive-expression
-                  shift-expression << additive-expression
-                  shift-expression >> additive-expression
-
-

Constraints -

- Each of the operands shall have integer type. -

Semantics -

- The integer promotions are performed on each of the operands. The type of the result is - that of the promoted left operand. If the value of the right operand is negative or is - - - greater than or equal to the width of the promoted left operand, the behavior is undefined. -

- The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with - zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo - one more than the maximum value representable in the result type. If E1 has a signed - type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is - the resulting value; otherwise, the behavior is undefined. -

- The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type - or if E1 has a signed type and a nonnegative value, the value of the result is the integral - part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the - resulting value is implementation-defined. - -

Contents -

6.5.8 Relational operators

-

Syntax -

-

-          relational-expression:
-                  shift-expression
-                  relational-expression   <    shift-expression
-                  relational-expression   >    shift-expression
-                  relational-expression   <=   shift-expression
-                  relational-expression   >=   shift-expression
-
-

Constraints -

- One of the following shall hold: -

-

Semantics -

- If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. -

- For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -

- When two pointers are compared, the result depends on the relative locations in the - address space of the objects pointed to. If two pointers to object types both point to the - same object, or both point one past the last element of the same array object, they - compare equal. If the objects pointed to are members of the same aggregate object, - pointers to structure members declared later compare greater than pointers to members - declared earlier in the structure, and pointers to array elements with larger subscript - values compare greater than pointers to elements of the same array with lower subscript - - values. All pointers to members of the same union object compare equal. If the - expression P points to an element of an array object and the expression Q points to the - last element of the same array object, the pointer expression Q+1 compares greater than - P. In all other cases, the behavior is undefined. -

- Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= - (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is - false.107) The result has type int. - -

Footnotes -

107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it - means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''. - - -

Contents -

6.5.9 Equality operators

-

Syntax -

-

-          equality-expression:
-                 relational-expression
-                 equality-expression == relational-expression
-                 equality-expression != relational-expression
-
-

Constraints -

- One of the following shall hold: -

-

Semantics -

- The == (equal to) and != (not equal to) operators are analogous to the relational - operators except for their lower precedence.108) Each of the operators yields 1 if the - specified relation is true and 0 if it is false. The result has type int. For any pair of - operands, exactly one of the relations is true. -

- If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. Values of complex types are equal if and only if both their real parts are equal - and also their imaginary parts are equal. Any two values of arithmetic types from - different type domains are equal if and only if the results of their conversions to the - (complex) result type determined by the usual arithmetic conversions are equal. - - - - -

- Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a - null pointer constant, the null pointer constant is converted to the type of the pointer. If - one operand is a pointer to an object type and the other is a pointer to a qualified or - unqualified version of void, the former is converted to the type of the latter. -

- Two pointers compare equal if and only if both are null pointers, both are pointers to the - same object (including a pointer to an object and a subobject at its beginning) or function, - both are pointers to one past the last element of the same array object, or one is a pointer - to one past the end of one array object and the other is a pointer to the start of a different - array object that happens to immediately follow the first array object in the address - space.109) -

- For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. - -

Footnotes -

108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value. - -

109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or - adjacent members of a structure with no padding between them, or because the implementation chose - to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses - outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined - behavior. - - -

Contents -

6.5.10 Bitwise AND operator

-

Syntax -

-

-          AND-expression:
-                equality-expression
-                AND-expression & equality-expression
-
-

Constraints -

- Each of the operands shall have integer type. -

Semantics -

- The usual arithmetic conversions are performed on the operands. -

- The result of the binary & operator is the bitwise AND of the operands (that is, each bit in - the result is set if and only if each of the corresponding bits in the converted operands is - set). - - - - - - -

Contents -

6.5.11 Bitwise exclusive OR operator

-

Syntax -

-

-          exclusive-OR-expression:
-                  AND-expression
-                  exclusive-OR-expression ^ AND-expression
-
-

Constraints -

- Each of the operands shall have integer type. -

Semantics -

- The usual arithmetic conversions are performed on the operands. -

- The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit - in the result is set if and only if exactly one of the corresponding bits in the converted - operands is set). - -

Contents -

6.5.12 Bitwise inclusive OR operator

-

Syntax -

-

-          inclusive-OR-expression:
-                  exclusive-OR-expression
-                  inclusive-OR-expression | exclusive-OR-expression
-
-

Constraints -

- Each of the operands shall have integer type. -

Semantics -

- The usual arithmetic conversions are performed on the operands. -

- The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in - the result is set if and only if at least one of the corresponding bits in the converted - operands is set). - - -

Contents -

6.5.13 Logical AND operator

-

Syntax -

-

-          logical-AND-expression:
-                  inclusive-OR-expression
-                  logical-AND-expression && inclusive-OR-expression
-
-

Constraints -

- Each of the operands shall have scalar type. -

Semantics -

- The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it - yields 0. The result has type int. -

- Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation; - if the second operand is evaluated, there is a sequence point between the evaluations of - the first and second operands. If the first operand compares equal to 0, the second - operand is not evaluated. - -

Contents -

6.5.14 Logical OR operator

-

Syntax -

-

-          logical-OR-expression:
-                  logical-AND-expression
-                  logical-OR-expression || logical-AND-expression
-
-

Constraints -

- Each of the operands shall have scalar type. -

Semantics -

- The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it - yields 0. The result has type int. -

- Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the - second operand is evaluated, there is a sequence point between the evaluations of the first - and second operands. If the first operand compares unequal to 0, the second operand is - not evaluated. - - -

Contents -

6.5.15 Conditional operator

-

Syntax -

-

-          conditional-expression:
-                 logical-OR-expression
-                 logical-OR-expression ? expression : conditional-expression
-
-

Constraints -

- The first operand shall have scalar type. -

- One of the following shall hold for the second and third operands: -

-

Semantics -

- The first operand is evaluated; there is a sequence point between its evaluation and the - evaluation of the second or third operand (whichever is evaluated). The second operand - is evaluated only if the first compares unequal to 0; the third operand is evaluated only if - the first compares equal to 0; the result is the value of the second or third operand - (whichever is evaluated), converted to the type described below.110) * -

- If both the second and third operands have arithmetic type, the result type that would be - determined by the usual arithmetic conversions, were they applied to those two operands, - is the type of the result. If both the operands have structure or union type, the result has - that type. If both operands have void type, the result has void type. -

- If both the second and third operands are pointers or one is a null pointer constant and the - other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers - of the types referenced by both operands. Furthermore, if both operands are pointers to - compatible types or to differently qualified versions of compatible types, the result type is - a pointer to an appropriately qualified version of the composite type; if one operand is a - null pointer constant, the result has the type of the other operand; otherwise, one operand - is a pointer to void or a qualified version of void, in which case the result type is a - pointer to an appropriately qualified version of void. - - -

- EXAMPLE The common type that results when the second and third operands are pointers is determined - in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two - pointers have compatible types. -

- Given the declarations -

-           const void *c_vp;
-           void *vp;
-           const int *c_ip;
-           volatile int *v_ip;
-           int *ip;
-           const char *c_cp;
-
- the third column in the following table is the common type that is the result of a conditional expression in - which the first two columns are the second and third operands (in either order): -
-           c_vp    c_ip      const void *
-           v_ip    0         volatile int *
-           c_ip    v_ip      const volatile int *
-           vp      c_cp      const void *
-           ip      c_ip      const int *
-           vp      ip        void *
-
- - -

Footnotes -

110) A conditional expression does not yield an lvalue. - - -

Contents -

6.5.16 Assignment operators

-

Syntax -

-

-          assignment-expression:
-                 conditional-expression
-                 unary-expression assignment-operator assignment-expression
-          assignment-operator: one of
-                 = *= /= %= +=                       -=     <<=      >>=      &=     ^=     |=
-
-

Constraints -

- An assignment operator shall have a modifiable lvalue as its left operand. -

Semantics -

- An assignment operator stores a value in the object designated by the left operand. An - assignment expression has the value of the left operand after the assignment,111) but is not - an lvalue. The type of an assignment expression is the type the left operand would have - after lvalue conversion. The side effect of updating the stored value of the left operand is - sequenced after the value computations of the left and right operands. The evaluations of - the operands are unsequenced. - - - - - - -

Footnotes -

111) The implementation is permitted to read the object to determine the value but is not required to, even - when the object has volatile-qualified type. - - -

Contents -

6.5.16.1 Simple assignment
-

Constraints -

- One of the following shall hold:112) -

-

Semantics -

- In simple assignment (=), the value of the right operand is converted to the type of the - assignment expression and replaces the value stored in the object designated by the left - operand. -

- If the value being stored in an object is read from another object that overlaps in any way - the storage of the first object, then the overlap shall be exact and the two objects shall - have qualified or unqualified versions of a compatible type; otherwise, the behavior is - undefined. -

- EXAMPLE 1 In the program fragment - - - - - -

-         int f(void);
-         char c;
-         /* ... */
-         if ((c = f()) == -1)
-                 /* ... */
-
- the int value returned by the function may be truncated when stored in the char, and then converted back - to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of - values as unsigned char (and char is narrower than int), the result of the conversion cannot be - negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the - variable c should be declared as int. - -

- EXAMPLE 2 In the fragment: -

-         char c;
-         int i;
-         long l;
-         l = (c = i);
-
- the value of i is converted to the type of the assignment expression c = i, that is, char type. The value - of the expression enclosed in parentheses is then converted to the type of the outer assignment expression, - that is, long int type. - -

- EXAMPLE 3 Consider the fragment: -

-         const char **cpp;
-         char *p;
-         const char c = 'A';
-         cpp = &p;                  // constraint violation
-         *cpp = &c;                 // valid
-         *p = 0;                    // valid
-
- The first assignment is unsafe because it would allow the following valid code to attempt to change the - value of the const object c. - - -

Footnotes -

112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion - (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type - qualifiers that were applied to the type category of the expression (for example, it removes const but - not volatile from the type int volatile * const). - - -

Contents -

6.5.16.2 Compound assignment
-

Constraints -

- For the operators += and -= only, either the left operand shall be an atomic, qualified, or - unqualified pointer to a complete object type, and the right shall have integer type; or the - left operand shall have atomic, qualified, or unqualified arithmetic type, and the right - shall have arithmetic type. -

- For the other operators, the left operand shall have atomic, qualified, or unqualified - arithmetic type, and (considering the type the left operand would have after lvalue - conversion) each operand shall have arithmetic type consistent with those allowed by the - corresponding binary operator. -

Semantics -

- A compound assignment of the form E1 op = E2 is equivalent to the simple assignment - expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with - respect to an indeterminately-sequenced function call, the operation of a compound - - assignment is a single evaluation. If E1 has an atomic type, compound assignment is a - read-modify-write operation with memory_order_seq_cst memory order - semantics.113) - -

Footnotes -

113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence - where T is the type of E1: - -

-          T tmp = E1;
-          T result;
-          do {
-                result = tmp op (E2);
-          } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
-
- with result being the result of the operation. - - -

Contents -

6.5.17 Comma operator

-

Syntax -

-

-          expression:
-                 assignment-expression
-                 expression , assignment-expression
-
-

Semantics -

- The left operand of a comma operator is evaluated as a void expression; there is a - sequence point between its evaluation and that of the right operand. Then the right - operand is evaluated; the result has its type and value.114) * -

- EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot - appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists - of initializers). On the other hand, it can be used within a parenthesized expression or within the second - expression of a conditional operator in such contexts. In the function call -

-          f(a, (t=3, t+2), c)
-
- the function has three arguments, the second of which has the value 5. - -

Forward references: initialization (6.7.9). - - - - - - -

Footnotes -

114) A comma operator does not yield an lvalue. - - -

Contents -

6.6 Constant expressions

-

Syntax -

-

-          constant-expression:
-                 conditional-expression
-
-

Description -

- A constant expression can be evaluated during translation rather than runtime, and - accordingly may be used in any place that a constant may be. -

Constraints -

- Constant expressions shall not contain assignment, increment, decrement, function-call, - or comma operators, except when they are contained within a subexpression that is not - evaluated.115) -

- Each constant expression shall evaluate to a constant that is in the range of representable - values for its type. -

Semantics -

- An expression that evaluates to a constant is required in several contexts. If a floating - expression is evaluated in the translation environment, the arithmetic precision and range - shall be at least as great as if the expression were being evaluated in the execution - environment.116) -

- An integer constant expression117) shall have integer type and shall only have operands - that are integer constants, enumeration constants, character constants, sizeof - expressions whose results are integer constants, and floating constants that are the - immediate operands of casts. Cast operators in an integer constant expression shall only - convert arithmetic types to integer types, except as part of an operand to the sizeof - operator. -

- More latitude is permitted for constant expressions in initializers. Such a constant - expression shall be, or evaluate to, one of the following: -

-

- An arithmetic constant expression shall have arithmetic type and shall only have - operands that are integer constants, floating constants, enumeration constants, character - constants, and sizeof expressions. Cast operators in an arithmetic constant expression - shall only convert arithmetic types to arithmetic types, except as part of an operand to a - sizeof operator whose result is an integer constant. -

- An address constant is a null pointer, a pointer to an lvalue designating an object of static - storage duration, or a pointer to a function designator; it shall be created explicitly using - the unary & operator or an integer constant cast to pointer type, or implicitly by the use of - an expression of array or function type. The array-subscript [] and member-access . - and -> operators, the address & and indirection * unary operators, and pointer casts may - be used in the creation of an address constant, but the value of an object shall not be - accessed by use of these operators. -

- An implementation may accept other forms of constant expressions. -

- The semantic rules for the evaluation of a constant expression are the same as for - nonconstant expressions.118) -

Forward references: array declarators (6.7.6.2), initialization (6.7.9). - - - - - - -

Footnotes -

115) The operand of a sizeof operator is usually not evaluated (6.5.3.4). - -

116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in - the translation environment. - -

117) An integer constant expression is required in a number of contexts such as the size of a bit-field - member of a structure, the value of an enumeration constant, and the size of a non-variable length - array. Further constraints that apply to the integer constant expressions used in conditional-inclusion - preprocessing directives are discussed in 6.10.1. - -

118) Thus, in the following initialization, - -

-           static int i = 2 || 1 / 0;
-
- the expression is a valid integer constant expression with value one. - - -

Contents -

6.7 Declarations

-

Syntax -

-

-          declaration:
-                 declaration-specifiers init-declarator-listopt ;
-                 static_assert-declaration
-          declaration-specifiers:
-                 storage-class-specifier declaration-specifiersopt
-                 type-specifier declaration-specifiersopt
-                 type-qualifier declaration-specifiersopt
-                 function-specifier declaration-specifiersopt
-                 alignment-specifier declaration-specifiersopt
-          init-declarator-list:
-                  init-declarator
-                  init-declarator-list , init-declarator
-          init-declarator:
-                  declarator
-                  declarator = initializer
-
-

Constraints -

- A declaration other than a static_assert declaration shall declare at least a declarator - (other than the parameters of a function or the members of a structure or union), a tag, or - the members of an enumeration. -

- If an identifier has no linkage, there shall be no more than one declaration of the identifier - (in a declarator or type specifier) with the same scope and in the same name space, except - that a typedef name can be redefined to denote the same type as it currently does and tags - may be redeclared as specified in 6.7.2.3. -

- All declarations in the same scope that refer to the same object or function shall specify - compatible types. -

Semantics -

- A declaration specifies the interpretation and attributes of a set of identifiers. A definition - of an identifier is a declaration for that identifier that: -

-

- The declaration specifiers consist of a sequence of specifiers that indicate the linkage, - storage duration, and part of the type of the entities that the declarators denote. The init- - declarator-list is a comma-separated sequence of declarators, each of which may have - additional type information, or an initializer, or both. The declarators contain the - identifiers (if any) being declared. -

- If an identifier for an object is declared with no linkage, the type for the object shall be - complete by the end of its declarator, or by the end of its init-declarator if it has an - initializer; in the case of function parameters (including in prototypes), it is the adjusted - type (see 6.7.6.3) that is required to be complete. -

Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization - (6.7.9), type names (6.7.7), type qualifiers (6.7.3). - -

Footnotes -

119) Function definitions have a different syntax, described in 6.9.1. - - -

Contents -

6.7.1 Storage-class specifiers

-

Syntax -

-

-          storage-class-specifier:
-                 typedef
-                 extern
-                 static
-                 _Thread_local
-                 auto
-                 register
-
-

Constraints -

- At most, one storage-class specifier may be given in the declaration specifiers in a - declaration, except that _Thread_local may appear with static or extern.120) -

- In the declaration of an object with block scope, if the declaration specifiers include - _Thread_local, they shall also include either static or extern. If - _Thread_local appears in any declaration of an object, it shall be present in every - declaration of that object. -

Semantics -

- The typedef specifier is called a ''storage-class specifier'' for syntactic convenience - only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations - were discussed in 6.2.2 and 6.2.4. - - - - -

- A declaration of an identifier for an object with storage-class specifier register - suggests that access to the object be as fast as possible. The extent to which such - suggestions are effective is implementation-defined.121) -

- The declaration of an identifier for a function that has block scope shall have no explicit - storage-class specifier other than extern. -

- If an aggregate or union object is declared with a storage-class specifier other than - typedef, the properties resulting from the storage-class specifier, except with respect to - linkage, also apply to the members of the object, and so on recursively for any aggregate - or union member objects. -

Forward references: type definitions (6.7.8). - -

Footnotes -

120) See ''future language directions'' (6.11.5). - -

121) The implementation may treat any register declaration simply as an auto declaration. However, - whether or not addressable storage is actually used, the address of any part of an object declared with - storage-class specifier register cannot be computed, either explicitly (by use of the unary & - operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in - 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier - register is sizeof. - - -

Contents -

6.7.2 Type specifiers

-

Syntax -

-

-          type-specifier:
-                 void
-                 char
-                 short
-                 int
-                 long
-                 float
-                 double
-                 signed
-                 unsigned
-                 _Bool
-                 _Complex
-                 atomic-type-specifier
-                 struct-or-union-specifier
-                 enum-specifier
-                 typedef-name
-
-

Constraints -

- At least one type specifier shall be given in the declaration specifiers in each declaration, - and in the specifier-qualifier list in each struct declaration and type name. Each list of - - - - type specifiers shall be one of the following multisets (delimited by commas, when there - is more than one multiset per item); the type specifiers may occur in any order, possibly - intermixed with the other declaration specifiers. -

-

- The type specifier _Complex shall not be used if the implementation does not support - complex types (see 6.10.8.3). - -

Semantics -

- Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1 - through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The - characteristics of the other types are discussed in 6.2.5. -

- Each of the comma-separated multisets designates the same type, except that for bit- - fields, it is implementation-defined whether the specifier int designates the same type as - signed int or the same type as unsigned int. -

Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2), - structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8). - -

Contents -

6.7.2.1 Structure and union specifiers
-

Syntax -

-

-          struct-or-union-specifier:
-                  struct-or-union identifieropt { struct-declaration-list }
-                  struct-or-union identifier
-          struct-or-union:
-                  struct
-                  union
-          struct-declaration-list:
-                  struct-declaration
-                  struct-declaration-list struct-declaration
-          struct-declaration:
-                  specifier-qualifier-list struct-declarator-listopt ;
-                  static_assert-declaration
-          specifier-qualifier-list:
-                 type-specifier specifier-qualifier-listopt
-                 type-qualifier specifier-qualifier-listopt
-          struct-declarator-list:
-                  struct-declarator
-                  struct-declarator-list , struct-declarator
-          struct-declarator:
-                  declarator
-                  declaratoropt : constant-expression
-
-

Constraints -

- A struct-declaration that does not declare an anonymous structure or anonymous union - shall contain a struct-declarator-list. - -

- A structure or union shall not contain a member with incomplete or function type (hence, - a structure shall not contain an instance of itself, but may contain a pointer to an instance - of itself), except that the last member of a structure with more than one named member - may have incomplete array type; such a structure (and any union containing, possibly - recursively, a member that is such a structure) shall not be a member of a structure or an - element of an array. -

- The expression that specifies the width of a bit-field shall be an integer constant - expression with a nonnegative value that does not exceed the width of an object of the - type that would be specified were the colon and expression omitted.122) If the value is - zero, the declaration shall have no declarator. -

- A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed - int, unsigned int, or some other implementation-defined type. It is - implementation-defined whether atomic types are permitted. -

Semantics -

- As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose - storage is allocated in an ordered sequence, and a union is a type consisting of a sequence - of members whose storage overlap. -

- Structure and union specifiers have the same form. The keywords struct and union - indicate that the type being specified is, respectively, a structure type or a union type. -

- The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type, - within a translation unit. The struct-declaration-list is a sequence of declarations for the - members of the structure or union. If the struct-declaration-list contains no named - members, no anonymous structures, and no anonymous unions, the behavior is undefined. - The type is incomplete until immediately after the } that terminates the list, and complete - thereafter. -

- A member of a structure or union may have any complete object type other than a - variably modified type.123) In addition, a member may be declared to consist of a - specified number of bits (including a sign bit, if any). Such a member is called a - bit-field;124) its width is preceded by a colon. -

- A bit-field is interpreted as having a signed or unsigned integer type consisting of the - specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of - - - type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool - bit-field has the semantics of a _Bool. -

- An implementation may allocate any addressable storage unit large enough to hold a bit- - field. If enough space remains, a bit-field that immediately follows another bit-field in a - structure shall be packed into adjacent bits of the same unit. If insufficient space remains, - whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is - implementation-defined. The order of allocation of bit-fields within a unit (high-order to - low-order or low-order to high-order) is implementation-defined. The alignment of the - addressable storage unit is unspecified. -

- A bit-field declaration with no declarator, but only a colon and a width, indicates an - unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0 - indicates that no further bit-field is to be packed into the unit in which the previous bit- - field, if any, was placed. -

- An unnamed member of structure type with no tag is called an anonymous structure; an - unnamed member of union type with no tag is called an anonymous union. The members - of an anonymous structure or union are considered to be members of the containing - structure or union. This applies recursively if the containing structure or union is also - anonymous. -

- Each non-bit-field member of a structure or union object is aligned in an implementation- - defined manner appropriate to its type. -

- Within a structure object, the non-bit-field members and the units in which bit-fields - reside have addresses that increase in the order in which they are declared. A pointer to a - structure object, suitably converted, points to its initial member (or if that member is a - bit-field, then to the unit in which it resides), and vice versa. There may be unnamed - padding within a structure object, but not at its beginning. -

- The size of a union is sufficient to contain the largest of its members. The value of at - most one of the members can be stored in a union object at any time. A pointer to a - union object, suitably converted, points to each of its members (or if a member is a bit- - field, then to the unit in which it resides), and vice versa. -

- There may be unnamed padding at the end of a structure or union. -

- As a special case, the last element of a structure with more than one named member may - have an incomplete array type; this is called a flexible array member. In most situations, - - - - the flexible array member is ignored. In particular, the size of the structure is as if the - flexible array member were omitted except that it may have more trailing padding than - the omission would imply. However, when a . (or ->) operator has a left operand that is - (a pointer to) a structure with a flexible array member and the right operand names that - member, it behaves as if that member were replaced with the longest array (with the same - element type) that would not make the structure larger than the object being accessed; the - offset of the array shall remain that of the flexible array member, even if this would differ - from that of the replacement array. If this array would have no elements, it behaves as if - it had one element but the behavior is undefined if any attempt is made to access that - element or to generate a pointer one past it. -

- EXAMPLE 1 The following illustrates anonymous structures and unions: -

-          struct v {
-                union {      // anonymous union
-                       struct { int i, j; };    // anonymous structure
-                       struct { long k, l; } w;
-                };
-                int m;
-          } v1;
-          v1.i = 2;   // valid
-          v1.k = 3;   // invalid: inner structure is not anonymous
-          v1.w.k = 5; // valid
-
- -

- EXAMPLE 2 After the declaration: -

-          struct s { int n; double d[]; };
-
- the structure struct s has a flexible array member d. A typical way to use this is: -
-          int m = /* some value */;
-          struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
-
- and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if - p had been declared as: -
-          struct { int n; double d[m]; } *p;
-
- (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might - not be the same). -

- Following the above declaration: -

-          struct s t1 = { 0 };                         //   valid
-          struct s t2 = { 1, { 4.2 }};                 //   invalid
-          t1.n = 4;                                    //   valid
-          t1.d[0] = 4.2;                               //   might be undefined behavior
-
- The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not - contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that -
-          sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
-
- in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming - code. - -

- After the further declaration: -

-          struct ss { int n; };
-
- the expressions: -
-          sizeof (struct s) >= sizeof (struct ss)
-          sizeof (struct s) >= offsetof(struct s, d)
-
- are always equal to 1. -

- If sizeof (double) is 8, then after the following code is executed: -

-          struct s *s1;
-          struct s *s2;
-          s1 = malloc(sizeof (struct s) + 64);
-          s2 = malloc(sizeof (struct s) + 46);
-
- and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most - purposes, as if the identifiers had been declared as: -
-          struct { int n; double d[8]; } *s1;
-          struct { int n; double d[5]; } *s2;
-
-

- Following the further successful assignments: -

-          s1 = malloc(sizeof (struct s) + 10);
-          s2 = malloc(sizeof (struct s) + 6);
-
- they then behave as if the declarations were: -
-          struct { int n; double d[1]; } *s1, *s2;
-
- and: -
-          double *dp;
-          dp = &(s1->d[0]);          //   valid
-          *dp = 42;                  //   valid
-          dp = &(s2->d[0]);          //   valid
-          *dp = 42;                  //   undefined behavior
-
-

- The assignment: -

-          *s1 = *s2;
-
- only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes - of the structure, they might be copied or simply overwritten with indeterminate values. - -

Forward references: declarators (6.7.6), tags (6.7.2.3). - - -

Footnotes -

122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and - value bits) of a _Bool may be just 1 bit. - -

123) A structure or union cannot contain a member with a variably modified type because member names - are not ordinary identifiers as defined in 6.2.3. - -

124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to - or arrays of bit-field objects. - -

125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int, - then it is implementation-defined whether the bit-field is signed or unsigned. - -

126) An unnamed bit-field structure member is useful for padding to conform to externally imposed - layouts. - - -

Contents -

6.7.2.2 Enumeration specifiers
-

Syntax -

-

-          enum-specifier:
-                enum identifieropt { enumerator-list }
-                enum identifieropt { enumerator-list , }
-                enum identifier
-          enumerator-list:
-                enumerator
-                enumerator-list , enumerator
-          enumerator:
-                enumeration-constant
-                enumeration-constant = constant-expression
-
-

Constraints -

- The expression that defines the value of an enumeration constant shall be an integer - constant expression that has a value representable as an int. -

Semantics -

- The identifiers in an enumerator list are declared as constants that have type int and - may appear wherever such are permitted.127) An enumerator with = defines its - enumeration constant as the value of the constant expression. If the first enumerator has - no =, the value of its enumeration constant is 0. Each subsequent enumerator with no = - defines its enumeration constant as the value of the constant expression obtained by - adding 1 to the value of the previous enumeration constant. (The use of enumerators with - = may produce enumeration constants with values that duplicate other values in the same - enumeration.) The enumerators of an enumeration are also known as its members. -

- Each enumerated type shall be compatible with char, a signed integer type, or an - unsigned integer type. The choice of type is implementation-defined,128) but shall be - capable of representing the values of all the members of the enumeration. The - enumerated type is incomplete until immediately after the } that terminates the list of - enumerator declarations, and complete thereafter. - - - - - -

- EXAMPLE The following fragment: -

-          enum hue { chartreuse, burgundy, claret=20, winedark };
-          enum hue col, *cp;
-          col = claret;
-          cp = &col;
-          if (*cp != burgundy)
-                /* ... */
-
- makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a - pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }. - -

Forward references: tags (6.7.2.3). - -

Footnotes -

127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from - each other and from other identifiers declared in ordinary declarators. - -

128) An implementation may delay the choice of which integer type until all enumeration constants have - been seen. - - -

Contents -

6.7.2.3 Tags
-

Constraints -

- A specific type shall have its content defined at most once. -

- Where two declarations that use the same tag declare the same type, they shall both use - the same choice of struct, union, or enum. -

- A type specifier of the form -

-         enum identifier
-
- without an enumerator list shall only appear after the type it specifies is complete. -

Semantics -

- All declarations of structure, union, or enumerated types that have the same scope and - use the same tag declare the same type. Irrespective of whether there is a tag or what - other declarations of the type are in the same translation unit, the type is incomplete129) - until immediately after the closing brace of the list defining the content, and complete - thereafter. -

- Two declarations of structure, union, or enumerated types which are in different scopes or - use different tags declare distinct types. Each declaration of a structure, union, or - enumerated type which does not include a tag declares a distinct type. -

- A type specifier of the form - - - - - -

-          struct-or-union identifieropt { struct-declaration-list }
-
- or -
-          enum identifieropt { enumerator-list }
-
- or -
-          enum identifieropt { enumerator-list , }
-
- declares a structure, union, or enumerated type. The list defines the structure content, - union content, or enumeration content. If an identifier is provided,130) the type specifier - also declares the identifier to be the tag of that type. -

- A declaration of the form -

-          struct-or-union identifier ;
-
- specifies a structure or union type and declares the identifier as a tag of that type.131) -

- If a type specifier of the form -

-          struct-or-union identifier
-
- occurs other than as part of one of the above forms, and no other declaration of the - identifier as a tag is visible, then it declares an incomplete structure or union type, and - declares the identifier as the tag of that type.131) -

- If a type specifier of the form -

-          struct-or-union identifier
-
- or -
-          enum identifier
-
- occurs other than as part of one of the above forms, and a declaration of the identifier as a - tag is visible, then it specifies the same type as that other declaration, and does not - redeclare the tag. -

- EXAMPLE 1 This mechanism allows declaration of a self-referential structure. -

-          struct tnode {
-                int count;
-                struct tnode *left, *right;
-          };
-
- specifies a structure that contains an integer and two pointers to objects of the same type. Once this - declaration has been given, the declaration - - - - - -
-          struct tnode s, *sp;
-
- declares s to be an object of the given type and sp to be a pointer to an object of the given type. With - these declarations, the expression sp->left refers to the left struct tnode pointer of the object to - which sp points; the expression s.right->count designates the count member of the right struct - tnode pointed to from s. -

- The following alternative formulation uses the typedef mechanism: -

-          typedef struct tnode TNODE;
-          struct tnode {
-                int count;
-                TNODE *left, *right;
-          };
-          TNODE s, *sp;
-
- -

- EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential - structures, the declarations -

-          struct s1 { struct s2 *s2p; /* ... */ }; // D1
-          struct s2 { struct s1 *s1p; /* ... */ }; // D2
-
- specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already - declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in - D2. To eliminate this context sensitivity, the declaration -
-          struct s2;
-
- may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then - completes the specification of the new type. - -

Forward references: declarators (6.7.6), type definitions (6.7.8). - -

Footnotes -

129) An incomplete type may only by used when the size of an object of that type is not needed. It is not - needed, for example, when a typedef name is declared to be a specifier for a structure or union, or - when a pointer to or a function returning a structure or union is being declared. (See incomplete types - in 6.2.5.) The specification has to be complete before such a function is called or defined. - -

130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration - of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations - can make use of that typedef name to declare objects having the specified structure, union, or - enumerated type. - -

131) A similar construction with enum does not exist. - - -

Contents -

6.7.2.4 Atomic type specifiers
-

Syntax -

-

-          atomic-type-specifier:
-                 _Atomic ( type-name )
-
-

Constraints -

- Atomic type specifiers shall not be used if the implementation does not support atomic - types (see 6.10.8.3). -

- The type name in an atomic type specifier shall not refer to an array type, a function type, - an atomic type, or a qualified type. -

Semantics -

- The properties associated with atomic types are meaningful only for expressions that are - lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is - interpreted as a type specifier (with a type name), not as a type qualifier. - - -

Contents -

6.7.3 Type qualifiers

-

Syntax -

-

-          type-qualifier:
-                 const
-                 restrict
-                 volatile
-                 _Atomic
-
-

Constraints -

- Types other than pointer types whose referenced type is an object type shall not be - restrict-qualified. -

- The type modified by the _Atomic qualifier shall not be an array type or a function - type. -

Semantics -

- The properties associated with qualified types are meaningful only for expressions that - are lvalues.132) -

- If the same qualifier appears more than once in the same specifier-qualifier-list, either - directly or via one or more typedefs, the behavior is the same as if it appeared only - once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier- - list, the resulting type is the so-qualified atomic type. -

- If an attempt is made to modify an object defined with a const-qualified type through use - of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is - made to refer to an object defined with a volatile-qualified type through use of an lvalue - with non-volatile-qualified type, the behavior is undefined.133) -

- An object that has volatile-qualified type may be modified in ways unknown to the - implementation or have other unknown side effects. Therefore any expression referring - to such an object shall be evaluated strictly according to the rules of the abstract machine, - as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the - object shall agree with that prescribed by the abstract machine, except as modified by the - - - - - - unknown factors mentioned previously.134) What constitutes an access to an object that - has volatile-qualified type is implementation-defined. -

- An object that is accessed through a restrict-qualified pointer has a special association - with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to - that object use, directly or indirectly, the value of that particular pointer.135) The intended - use of the restrict qualifier (like the register storage class) is to promote - optimization, and deleting all instances of the qualifier from all preprocessing translation - units composing a conforming program does not change its meaning (i.e., observable - behavior). -

- If the specification of an array type includes any type qualifiers, the element type is so- - qualified, not the array type. If the specification of a function type includes any type - qualifiers, the behavior is undefined.136) -

- For two qualified types to be compatible, both shall have the identically qualified version - of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers - does not affect the specified type. -

- EXAMPLE 1 An object declared -

-          extern const volatile int real_time_clock;
-
- may be modifiable by hardware, but cannot be assigned to, incremented, or decremented. - -

- EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers - modify an aggregate type: -

-          const struct s { int mem; } cs = { 1 };
-          struct s ncs; // the object ncs is modifiable
-          typedef int A[2][3];
-          const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
-          int *pi;
-          const int *pci;
-          ncs = cs;            //    valid
-          cs = ncs;            //    violates modifiable lvalue constraint for =
-          pi = &ncs.mem;       //    valid
-          pi = &cs.mem;        //    violates type constraints for =
-          pci = &cs.mem;       //    valid
-          pi = a[0];           //    invalid: a[0] has type ''const int *''
-
- - - - -

- EXAMPLE 3 The declaration -

-          _Atomic volatile int *p;
-
- specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type. - - -

Footnotes -

132) The implementation may place a const object that is not volatile in a read-only region of - storage. Moreover, the implementation need not allocate storage for such an object if its address is - never used. - -

133) This applies to those objects that behave as if they were defined with qualified types, even if they are - never actually defined as objects in the program (such as an object at a memory-mapped input/output - address). - -

134) A volatile declaration may be used to describe an object corresponding to a memory-mapped - input/output port or an object accessed by an asynchronously interrupting function. Actions on - objects so declared shall not be ''optimized out'' by an implementation or reordered except as - permitted by the rules for evaluating expressions. - -

135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this - association between the allocated object and the pointer. - -

136) Both of these can occur through the use of typedefs. - - -

Contents -

6.7.3.1 Formal definition of restrict
-

- Let D be a declaration of an ordinary identifier that provides a means of designating an - object P as a restrict-qualified pointer to type T. -

- If D appears inside a block and does not have storage class extern, let B denote the - block. If D appears in the list of parameter declarations of a function definition, let B - denote the associated block. Otherwise, let B denote the block of main (or the block of - whatever function is called at program startup in a freestanding environment). -

- In what follows, a pointer expression E is said to be based on object P if (at some - sequence point in the execution of B prior to the evaluation of E) modifying P to point to - a copy of the array object into which it formerly pointed would change the value of E.137) - Note that ''based'' is defined only for expressions with pointer types. -

- During each execution of B, let L be any lvalue that has &L based on P. If L is used to - access the value of the object X that it designates, and X is also modified (by any means), - then the following requirements apply: T shall not be const-qualified. Every other lvalue - used to access the value of X shall also have its address based on P. Every access that - modifies X shall be considered also to modify P, for the purposes of this subclause. If P - is assigned the value of a pointer expression E that is based on another restricted pointer - object P2, associated with block B2, then either the execution of B2 shall begin before - the execution of B, or the execution of B2 shall end prior to the assignment. If these - requirements are not met, then the behavior is undefined. -

- Here an execution of B means that portion of the execution of the program that would - correspond to the lifetime of an object with scalar type and automatic storage duration - associated with B. -

- A translator is free to ignore any or all aliasing implications of uses of restrict. -

- EXAMPLE 1 The file scope declarations -

-          int * restrict a;
-          int * restrict b;
-          extern int c[];
-
- assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the - program, then it is never accessed using either of the other two. - - - -

- EXAMPLE 2 The function parameter declarations in the following example -

-         void f(int n, int * restrict p, int * restrict q)
-         {
-               while (n-- > 0)
-                     *p++ = *q++;
-         }
-
- assert that, during each execution of the function, if an object is accessed through one of the pointer - parameters, then it is not also accessed through the other. -

- The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence - analysis of function f without examining any of the calls of f in the program. The cost is that the - programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the - second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through - both p and q. -

-          void g(void)
-          {
-                extern int d[100];
-                f(50, d + 50, d); // valid
-                f(50, d + 1, d); // undefined behavior
-          }
-
- -

- EXAMPLE 3 The function parameter declarations -

-         void h(int n, int * restrict p, int * restrict q, int * restrict r)
-         {
-               int i;
-               for (i = 0; i < n; i++)
-                      p[i] = q[i] + r[i];
-         }
-
- illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b - are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not - modified within function h. - -

- EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a - function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments - between restricted pointers declared in nested blocks have defined behavior. - -

-         {
-                  int * restrict p1;
-                  int * restrict q1;
-                  p1 = q1; // undefined behavior
-                  {
-                        int * restrict p2 = p1; // valid
-                        int * restrict q2 = q1; // valid
-                        p1 = q2;                // undefined behavior
-                        p2 = q2;                // undefined behavior
-                  }
-         }
-
-

- The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more - precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For - example, this permits new_vector to return a vector. -

-          typedef struct { int n; float * restrict v; } vector;
-          vector new_vector(int n)
-          {
-                vector t;
-                t.n = n;
-                t.v = malloc(n * sizeof (float));
-                return t;
-          }
-
- - -

Footnotes -

137) In other words, E depends on the value of P itself rather than on the value of an object referenced - indirectly through P. For example, if identifier p has type (int **restrict), then the pointer - expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer - expressions *p and p[1] are not. - - -

Contents -

6.7.4 Function specifiers

-

Syntax -

-

-          function-specifier:
-                 inline
-                 _Noreturn
-
-

Constraints -

- Function specifiers shall be used only in the declaration of an identifier for a function. -

- An inline definition of a function with external linkage shall not contain a definition of a - modifiable object with static or thread storage duration, and shall not contain a reference - to an identifier with internal linkage. -

- In a hosted environment, no function specifier(s) shall appear in a declaration of main. -

Semantics -

- A function specifier may appear more than once; the behavior is the same as if it - appeared only once. -

- A function declared with an inline function specifier is an inline function. Making a * - function an inline function suggests that calls to the function be as fast as possible.138) - The extent to which such suggestions are effective is implementation-defined.139) - - - - - -

- Any function with internal linkage can be an inline function. For a function with external - linkage, the following restrictions apply: If a function is declared with an inline - function specifier, then it shall also be defined in the same translation unit. If all of the - file scope declarations for a function in a translation unit include the inline function - specifier without extern, then the definition in that translation unit is an inline - definition. An inline definition does not provide an external definition for the function, - and does not forbid an external definition in another translation unit. An inline definition - provides an alternative to an external definition, which a translator may use to implement - any call to the function in the same translation unit. It is unspecified whether a call to the - function uses the inline definition or the external definition.140) -

- A function declared with a _Noreturn function specifier shall not return to its caller. -

Recommended practice -

- The implementation should produce a diagnostic message for a function declared with a - _Noreturn function specifier that appears to be capable of returning to its caller. -

- EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external - definition, or a definition available for use only within the translation unit. A file scope declaration with - extern creates an external definition. The following example shows an entire translation unit. -

-          inline double fahr(double t)
-          {
-                return (9.0 * t) / 5.0 + 32.0;
-          }
-          inline double cels(double t)
-          {
-                return (5.0 * (t - 32.0)) / 9.0;
-          }
-          extern double fahr(double);                  // creates an external definition
-          double convert(int is_fahr, double temp)
-          {
-                /* A translator may perform inline substitutions */
-                return is_fahr ? cels(temp) : fahr(temp);
-          }
-
-

- Note that the definition of fahr is an external definition because fahr is also declared with extern, but - the definition of cels is an inline definition. Because cels has external linkage and is referenced, an - external definition has to appear in another translation unit (see 6.9); the inline definition and the external - definition are distinct and either may be used for the call. - -

- EXAMPLE 2 - - - - - -

-          _Noreturn void f () {
-                abort(); // ok
-          }
-          _Noreturn void g (int i) { // causes undefined behavior if i <= 0
-                if (i > 0) abort();
-          }
-
- -

Forward references: function definitions (6.9.1). - -

Footnotes -

138) By using, for example, an alternative to the usual function call mechanism, such as ''inline - substitution''. Inline substitution is not textual substitution, nor does it create a new function. - Therefore, for example, the expansion of a macro used within the body of the function uses the - definition it had at the point the function body appears, and not where the function is called; and - identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a - single address, regardless of the number of inline definitions that occur in addition to the external - definition. - -

139) For example, an implementation might never perform inline substitution, or might only perform inline - substitutions to calls in the scope of an inline declaration. - -

140) Since an inline definition is distinct from the corresponding external definition and from any other - corresponding inline definitions in other translation units, all corresponding objects with static storage - duration are also distinct in each of the definitions. - - -

Contents -

6.7.5 Alignment specifier

-

Syntax -

-

-          alignment-specifier:
-                _Alignas ( type-name )
-                _Alignas ( constant-expression )
-
-

Constraints -

- An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or - a function, or a parameter, or an object declared with the register storage-class - specifier. -

- The constant expression shall be an integer constant expression. It shall evaluate to a - valid fundamental alignment, or to a valid extended alignment supported by the - implementation in the context in which it appears, or to zero. -

- The combined effect of all alignment attributes in a declaration shall not specify an - alignment that is less strict than the alignment that would otherwise be required for the - type of the object or member being declared. -

Semantics -

- The first form is equivalent to _Alignas(alignof(type-name)). -

- The alignment requirement of the declared object or member is taken to be the specified - alignment. An alignment specification of zero has no effect.141) When multiple - alignment specifiers occur in a declaration, the effective alignment requirement is the - strictest specified alignment. -

- If the definition of an object has an alignment specifier, any other declaration of that - object shall either specify equivalent alignment or have no alignment specifier. If the - definition of an object does not have an alignment specifier, any other declaration of that - object shall also have no alignment specifier. If declarations of an object in different - translation units have different alignment specifiers, the behavior is undefined. - - - - - -

Footnotes -

141) An alignment specification of zero also does not affect other alignment specifications in the same - declaration. - - -

Contents -

6.7.6 Declarators

-

Syntax -

-

-          declarator:
-                 pointeropt direct-declarator
-          direct-declarator:
-                  identifier
-                  ( declarator )
-                  direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
-                  direct-declarator [ static type-qualifier-listopt assignment-expression ]
-                  direct-declarator [ type-qualifier-list static assignment-expression ]
-                  direct-declarator [ type-qualifier-listopt * ]
-                  direct-declarator ( parameter-type-list )
-                  direct-declarator ( identifier-listopt )
-          pointer:
-                 * type-qualifier-listopt
-                 * type-qualifier-listopt pointer
-          type-qualifier-list:
-                 type-qualifier
-                 type-qualifier-list type-qualifier
-          parameter-type-list:
-                parameter-list
-                parameter-list , ...
-          parameter-list:
-                parameter-declaration
-                parameter-list , parameter-declaration
-          parameter-declaration:
-                declaration-specifiers declarator
-                declaration-specifiers abstract-declaratoropt
-          identifier-list:
-                 identifier
-                 identifier-list , identifier
-
-

Semantics -

- Each declarator declares one identifier, and asserts that when an operand of the same - form as the declarator appears in an expression, it designates a function or object with the - scope, storage duration, and type indicated by the declaration specifiers. -

- A full declarator is a declarator that is not part of another declarator. The end of a full - declarator is a sequence point. If, in the nested sequence of declarators in a full - - declarator, there is a declarator specifying a variable length array type, the type specified - by the full declarator is said to be variably modified. Furthermore, any type derived by - declarator type derivation from a variably modified type is itself variably modified. -

- In the following subclauses, consider a declaration -

-         T D1
-
- where T contains the declaration specifiers that specify a type T (such as int) and D1 is - a declarator that contains an identifier ident. The type specified for the identifier ident in - the various forms of declarator is described inductively using this notation. -

- If, in the declaration ''T D1'', D1 has the form -

-         identifier
-
- then the type specified for ident is T . -

- If, in the declaration ''T D1'', D1 has the form -

-         ( D )
-
- then ident has the type specified by the declaration ''T D''. Thus, a declarator in - parentheses is identical to the unparenthesized declarator, but the binding of complicated - declarators may be altered by parentheses. -

Implementation limits -

- As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and - function declarators that modify an arithmetic, structure, union, or void type, either - directly or via one or more typedefs. -

Forward references: array declarators (6.7.6.2), type definitions (6.7.8). - -

Contents -

6.7.6.1 Pointer declarators
-

Semantics -

- If, in the declaration ''T D1'', D1 has the form -

-         * type-qualifier-listopt D
-
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list - pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer. -

- For two pointer types to be compatible, both shall be identically qualified and both shall - be pointers to compatible types. -

- EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer - to a constant value'' and a ''constant pointer to a variable value''. - -

-          const int *ptr_to_constant;
-          int *const constant_ptr;
-
- The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer, - but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the - int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the - same location. -

- The declaration of the constant pointer constant_ptr may be clarified by including a definition for the - type ''pointer to int''. -

-          typedef int *int_ptr;
-          const int_ptr constant_ptr;
-
- declares constant_ptr as an object that has type ''const-qualified pointer to int''. - - -

Contents -

6.7.6.2 Array declarators
-

Constraints -

- In addition to optional type qualifiers and the keyword static, the [ and ] may delimit - an expression or *. If they delimit an expression (which specifies the size of an array), the - expression shall have an integer type. If the expression is a constant expression, it shall - have a value greater than zero. The element type shall not be an incomplete or function - type. The optional type qualifiers and the keyword static shall appear only in a - declaration of a function parameter with an array type, and then only in the outermost - array type derivation. -

- If an identifier is declared as having a variably modified type, it shall be an ordinary - identifier (as defined in 6.2.3), have no linkage, and have either block scope or function - prototype scope. If an identifier is declared to be an object with static or thread storage - duration, it shall not have a variable length array type. -

Semantics -

- If, in the declaration ''T D1'', D1 has one of the forms: -

-          D[ type-qualifier-listopt assignment-expressionopt ]
-          D[ static type-qualifier-listopt assignment-expression ]
-          D[ type-qualifier-list static assignment-expression ]
-          D[ type-qualifier-listopt * ]
-
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142) - (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.) -

- If the size is not present, the array type is an incomplete type. If the size is * instead of - being an expression, the array type is a variable length array type of unspecified size, - which can only be used in declarations or type names with function prototype scope;143) - - - such arrays are nonetheless complete types. If the size is an integer constant expression - and the element type has a known constant size, the array type is not a variable length - array type; otherwise, the array type is a variable length array type. (Variable length - arrays are a conditional feature that implementations need not support; see 6.10.8.3.) -

- If the size is an expression that is not an integer constant expression: if it occurs in a - declaration at function prototype scope, it is treated as if it were replaced by *; otherwise, - each time it is evaluated it shall have a value greater than zero. The size of each instance - of a variable length array type does not change during its lifetime. Where a size - expression is part of the operand of a sizeof operator and changing the value of the - size expression would not affect the result of the operator, it is unspecified whether or not - the size expression is evaluated. -

- For two array types to be compatible, both shall have compatible element types, and if - both size specifiers are present, and are integer constant expressions, then both size - specifiers shall have the same constant value. If the two array types are used in a context - which requires them to be compatible, it is undefined behavior if the two size specifiers - evaluate to unequal values. -

- EXAMPLE 1 -

-          float fa[11], *afp[17];
-
- declares an array of float numbers and an array of pointers to float numbers. - -

- EXAMPLE 2 Note the distinction between the declarations -

-          extern int *x;
-          extern int y[];
-
- The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size - (an incomplete type), the storage for which is defined elsewhere. - -

- EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types. -

-          extern int n;
-          extern int m;
-          void fcompat(void)
-          {
-                int a[n][6][m];
-                int (*p)[4][n+1];
-                int c[n][n][6][m];
-                int (*r)[n][n][n+1];
-                p = a;       // invalid: not compatible because 4 != 6
-                r = c;       // compatible, but defined behavior only if
-                             // n == 6 and m == n+1
-          }
-
- - - - - -

- EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or - function prototype scope. Array objects declared with the _Thread_local, static, or extern - storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with - the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all - identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of - structures or unions. -

-         extern int n;
-         int A[n];                                           // invalid: file scope VLA
-         extern int (*p2)[n];                                // invalid: file scope VM
-         int B[100];                                         // valid: file scope but not VM
-         void fvla(int m, int C[m][m]);                      // valid: VLA with prototype scope
-         void fvla(int m, int C[m][m])                       // valid: adjusted to auto pointer to VLA
-         {
-               typedef int VLA[m][m];                        // valid: block scope typedef VLA
-                  struct tag {
-                        int (*y)[n];                         // invalid: y not ordinary identifier
-                        int z[n];                            // invalid: z not ordinary identifier
-                  };
-                  int D[m];                                  //   valid: auto VLA
-                  static int E[m];                           //   invalid: static block scope VLA
-                  extern int F[m];                           //   invalid: F has linkage and is VLA
-                  int (*s)[m];                               //   valid: auto pointer to VLA
-                  extern int (*r)[m];                        //   invalid: r has linkage and points to VLA
-                  static int (*q)[m] = &B;                   //   valid: q is a static block pointer to VLA
-         }
-
- -

Forward references: function declarators (6.7.6.3), function definitions (6.9.1), - initialization (6.7.9). - -

Footnotes -

142) When several ''array of'' specifications are adjacent, a multidimensional array is declared. - -

143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3). - - -

Contents -

6.7.6.3 Function declarators (including prototypes)
-

Constraints -

- A function declarator shall not specify a return type that is a function type or an array - type. -

- The only storage-class specifier that shall occur in a parameter declaration is register. -

- An identifier list in a function declarator that is not part of a definition of that function - shall be empty. -

- After adjustment, the parameters in a parameter type list in a function declarator that is - part of a definition of that function shall not have incomplete type. -

Semantics -

- If, in the declaration ''T D1'', D1 has the form - -

-        D( parameter-type-list )
-
- or -
-        D( identifier-listopt )
-
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list function returning - T ''. -

- A parameter type list specifies the types of, and may declare identifiers for, the - parameters of the function. -

- A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to - type'', where the type qualifiers (if any) are those specified within the [ and ] of the - array type derivation. If the keyword static also appears within the [ and ] of the - array type derivation, then for each call to the function, the value of the corresponding - actual argument shall provide access to the first element of an array with at least as many - elements as specified by the size expression. -

- A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to - function returning type'', as in 6.3.2.1. -

- If the list terminates with an ellipsis (, ...), no information about the number or types - of the parameters after the comma is supplied.144) -

- The special case of an unnamed parameter of type void as the only item in the list - specifies that the function has no parameters. -

- If, in a parameter declaration, an identifier can be treated either as a typedef name or as a - parameter name, it shall be taken as a typedef name. -

- If the function declarator is not part of a definition of that function, parameters may have - incomplete type and may use the [*] notation in their sequences of declarator specifiers - to specify variable length array types. -

- The storage-class specifier in the declaration specifiers for a parameter declaration, if - present, is ignored unless the declared parameter is one of the members of the parameter - type list for a function definition. -

- An identifier list declares only the identifiers of the parameters of the function. An empty - list in a function declarator that is part of a definition of that function specifies that the - function has no parameters. The empty list in a function declarator that is not part of a - definition of that function specifies that no information about the number or types of the - parameters is supplied.145) - - - - -

- For two function types to be compatible, both shall specify compatible return types.146) - Moreover, the parameter type lists, if both are present, shall agree in the number of - parameters and in use of the ellipsis terminator; corresponding parameters shall have - compatible types. If one type has a parameter type list and the other type is specified by a - function declarator that is not part of a function definition and that contains an empty - identifier list, the parameter list shall not have an ellipsis terminator and the type of each - parameter shall be compatible with the type that results from the application of the - default argument promotions. If one type has a parameter type list and the other type is - specified by a function definition that contains a (possibly empty) identifier list, both shall - agree in the number of parameters, and the type of each prototype parameter shall be - compatible with the type that results from the application of the default argument - promotions to the type of the corresponding identifier. (In the determination of type - compatibility and of a composite type, each parameter declared with function or array - type is taken as having the adjusted type and each parameter declared with qualified type - is taken as having the unqualified version of its declared type.) -

- EXAMPLE 1 The declaration -

-          int f(void), *fip(), (*pfi)();
-
- declares a function f with no parameters returning an int, a function fip with no parameter specification - returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an - int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the - declaration suggests, and the same construction in an expression requires, the calling of a function fip, - and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the - extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function - designator, which is then used to call the function; it returns an int. -

- If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the - declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either - internal or external linkage (depending on what file scope declarations for these identifiers are visible), and - the identifier of the pointer pfi has block scope and no linkage. - -

- EXAMPLE 2 The declaration -

-          int (*apfi[3])(int *x, int *y);
-
- declares an array apfi of three pointers to functions returning int. Each of these functions has two - parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and - go out of scope at the end of the declaration of apfi. - -

- EXAMPLE 3 The declaration -

-          int (*fpfi(int (*)(long), int))(int, ...);
-
- declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two - parameters: a pointer to a function returning an int (with one parameter of type long int), and an int. - The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more - - - - additional arguments of any type. - -

- EXAMPLE 4 The following prototype has a variably modified parameter. -

-           void addscalar(int n, int m,
-                 double a[n][n*m+300], double x);
-           int main()
-           {
-                 double b[4][308];
-                 addscalar(4, 2, b, 2.17);
-                 return 0;
-           }
-           void addscalar(int n, int m,
-                 double a[n][n*m+300], double x)
-           {
-                 for (int i = 0; i < n; i++)
-                       for (int j = 0, k = n*m+300; j < k; j++)
-                             // a is a pointer to a VLA with n*m+300 elements
-                             a[i][j] += x;
-           }
-
- -

- EXAMPLE 5 The following are all compatible function prototype declarators. -

-           double    maximum(int       n,   int   m,   double   a[n][m]);
-           double    maximum(int       n,   int   m,   double   a[*][*]);
-           double    maximum(int       n,   int   m,   double   a[ ][*]);
-           double    maximum(int       n,   int   m,   double   a[ ][m]);
-
- as are: -
-           void   f(double     (* restrict a)[5]);
-           void   f(double     a[restrict][5]);
-           void   f(double     a[restrict 3][5]);
-           void   f(double     a[restrict static 3][5]);
-
- (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a - non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.) - -

Forward references: function definitions (6.9.1), type names (6.7.7). - - -

Footnotes -

144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that - correspond to the ellipsis. - -

145) See ''future language directions'' (6.11.6). - -

146) If both function types are ''old style'', parameter types are not compared. - - -

Contents -

6.7.7 Type names

-

Syntax -

-

-          type-name:
-                 specifier-qualifier-list abstract-declaratoropt
-          abstract-declarator:
-                 pointer
-                 pointeropt direct-abstract-declarator
-          direct-abstract-declarator:
-                  ( abstract-declarator )
-                  direct-abstract-declaratoropt [ type-qualifier-listopt
-                                 assignment-expressionopt ]
-                  direct-abstract-declaratoropt [ static type-qualifier-listopt
-                                 assignment-expression ]
-                  direct-abstract-declaratoropt [ type-qualifier-list static
-                                 assignment-expression ]
-                  direct-abstract-declaratoropt [ * ]
-                  direct-abstract-declaratoropt ( parameter-type-listopt )
-
-

Semantics -

- In several contexts, it is necessary to specify a type. This is accomplished using a type - name, which is syntactically a declaration for a function or an object of that type that - omits the identifier.147) -

- EXAMPLE The constructions -

-          (a)      int
-          (b)      int   *
-          (c)      int   *[3]
-          (d)      int   (*)[3]
-          (e)      int   (*)[*]
-          (f)      int   *()
-          (g)      int   (*)(void)
-          (h)      int   (*const [])(unsigned int, ...)
-
- name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an - array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function - with no parameter specification returning a pointer to int, (g) pointer to function with no parameters - returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one - parameter that has type unsigned int and an unspecified number of other parameters, returning an - int. - - - - - - -

Footnotes -

147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no - parameter specification'', rather than redundant parentheses around the omitted identifier. - - -

Contents -

6.7.8 Type definitions

-

Syntax -

-

-          typedef-name:
-                 identifier
-
-

Constraints -

- If a typedef name specifies a variably modified type then it shall have block scope. -

Semantics -

- In a declaration whose storage-class specifier is typedef, each declarator defines an - identifier to be a typedef name that denotes the type specified for the identifier in the way - described in 6.7.6. Any array size expressions associated with variable length array - declarators are evaluated each time the declaration of the typedef name is reached in the - order of execution. A typedef declaration does not introduce a new type, only a - synonym for the type so specified. That is, in the following declarations: -

-          typedef T type_ident;
-          type_ident D;
-
- type_ident is defined as a typedef name with the type specified by the declaration - specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator- - type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A - typedef name shares the same name space as other identifiers declared in ordinary - declarators. -

- EXAMPLE 1 After -

-          typedef int MILES, KLICKSP();
-          typedef struct { double hi, lo; } range;
-
- the constructions -
-          MILES distance;
-          extern KLICKSP *metricp;
-          range x;
-          range z, *zp;
-
- are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no - parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to - such a structure. The object distance has a type compatible with any other int object. - -

- EXAMPLE 2 After the declarations -

-          typedef struct s1 { int x; } t1, *tp1;
-          typedef struct s2 { int x; } t2, *tp2;
-
- type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct - s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int. - -

- EXAMPLE 3 The following obscure constructions -

-          typedef signed int t;
-          typedef int plain;
-          struct tag {
-                unsigned t:4;
-                const t:5;
-                plain r:5;
-          };
-
- declare a typedef name t with type signed int, a typedef name plain with type int, and a structure - with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const- - qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or - [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15]. - (The choice of range is implementation-defined.) The first two bit-field declarations differ in that - unsigned is a type specifier (which forces t to be the name of a structure member), while const is a - type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed - in an inner scope by -
-          t f(t (t));
-          long t;
-
- then a function f is declared with type ''function returning signed int with one unnamed parameter - with type pointer to function returning signed int with one unnamed parameter with type signed - int'', and an identifier t with type long int. - -

- EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the - following declarations of the signal function specify exactly the same type, the first without making use - of any typedef names. -

-          typedef void fv(int), (*pfv)(int);
-          void (*signal(int, void (*)(int)))(int);
-          fv *signal(int, fv *);
-          pfv signal(int, pfv);
-
- -

- EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the - time the typedef name is defined, not each time it is used: - -

-          void copyt(int n)
-          {
-                typedef int B[n];   //               B is n ints, n evaluated now
-                n += 1;
-                B a;                //               a is n ints, n without += 1
-                int b[n];           //               a and b are different sizes
-                for (int i = 1; i < n;               i++)
-                      a[i-1] = b[i];
-          }
-
- -

Contents -

6.7.9 Initialization

-

Syntax -

-

-          initializer:
-                   assignment-expression
-                   { initializer-list }
-                   { initializer-list , }
-          initializer-list:
-                   designationopt initializer
-                   initializer-list , designationopt initializer
-          designation:
-                 designator-list =
-          designator-list:
-                 designator
-                 designator-list designator
-          designator:
-                 [ constant-expression ]
-                 . identifier
-
-

Constraints -

- No initializer shall attempt to provide a value for an object not contained within the entity - being initialized. -

- The type of the entity to be initialized shall be an array of unknown size or a complete - object type that is not a variable length array type. -

- All the expressions in an initializer for an object that has static or thread storage duration - shall be constant expressions or string literals. -

- If the declaration of an identifier has block scope, and the identifier has external or - internal linkage, the declaration shall have no initializer for the identifier. -

- If a designator has the form -

-          [ constant-expression ]
-
- then the current object (defined below) shall have array type and the expression shall be - an integer constant expression. If the array is of unknown size, any nonnegative value is - valid. -

- If a designator has the form -

-          . identifier
-
- then the current object (defined below) shall have structure or union type and the - identifier shall be the name of a member of that type. - -

Semantics -

- An initializer specifies the initial value stored in an object. -

- Except where explicitly stated otherwise, for the purposes of this subclause unnamed - members of objects of structure and union type do not participate in initialization. - Unnamed members of structure objects have indeterminate value even after initialization. -

- If an object that has automatic storage duration is not initialized explicitly, its value is - indeterminate. If an object that has static or thread storage duration is not initialized - explicitly, then: -

-

- The initializer for a scalar shall be a single expression, optionally enclosed in braces. The - initial value of the object is that of the expression (after conversion); the same type - constraints and conversions as for simple assignment apply, taking the type of the scalar - to be the unqualified version of its declared type. -

- The rest of this subclause deals with initializers for objects that have aggregate or union - type. -

- The initializer for a structure or union object that has automatic storage duration shall be - either an initializer list as described below, or a single expression that has compatible - structure or union type. In the latter case, the initial value of the object, including - unnamed members, is that of the expression. -

- An array of character type may be initialized by a character string literal or UTF-8 string - literal, optionally enclosed in braces. Successive bytes of the string literal (including the - terminating null character if there is room or if the array is of unknown size) initialize the - elements of the array. -

- An array with element type compatible with a qualified or unqualified version of - wchar_t may be initialized by a wide string literal, optionally enclosed in braces. - Successive wide characters of the wide string literal (including the terminating null wide - character if there is room or if the array is of unknown size) initialize the elements of the - array. -

- Otherwise, the initializer for an object that has aggregate or union type shall be a brace- - enclosed list of initializers for the elements or named members. - -

- Each brace-enclosed initializer list has an associated current object. When no - designations are present, subobjects of the current object are initialized in order according - to the type of the current object: array elements in increasing subscript order, structure - members in declaration order, and the first named member of a union.148) In contrast, a - designation causes the following initializer to begin initialization of the subobject - described by the designator. Initialization then continues forward in order, beginning - with the next subobject after that described by the designator.149) -

- Each designator list begins its description with the current object associated with the - closest surrounding brace pair. Each item in the designator list (in order) specifies a - particular member of its current object and changes the current object for the next - designator (if any) to be that member.150) The current object that results at the end of the - designator list is the subobject to be initialized by the following initializer. -

- The initialization shall occur in initializer list order, each initializer provided for a - particular subobject overriding any previously listed initializer for the same subobject;151) - all subobjects that are not initialized explicitly shall be initialized implicitly the same as - objects that have static storage duration. -

- If the aggregate or union contains elements or members that are aggregates or unions, - these rules apply recursively to the subaggregates or contained unions. If the initializer of - a subaggregate or contained union begins with a left brace, the initializers enclosed by - that brace and its matching right brace initialize the elements or members of the - subaggregate or the contained union. Otherwise, only enough initializers from the list are - taken to account for the elements or members of the subaggregate or the first member of - the contained union; any remaining initializers are left to initialize the next element or - member of the aggregate of which the current subaggregate or contained union is a part. -

- If there are fewer initializers in a brace-enclosed list than there are elements or members - of an aggregate, or fewer characters in a string literal used to initialize an array of known - size than there are elements in the array, the remainder of the aggregate shall be - initialized implicitly the same as objects that have static storage duration. - - - - -

- If an array of unknown size is initialized, its size is determined by the largest indexed - element with an explicit initializer. The array type is completed at the end of its - initializer list. -

- The evaluations of the initialization list expressions are indeterminately sequenced with - respect to one another and thus the order in which any side effects occur is - unspecified.152) -

- EXAMPLE 1 Provided that <complex.h> has been #included, the declarations -

-          int i = 3.5;
-          double complex c = 5 + 3 * I;
-
- define and initialize i with the value 3 and c with the value 5.0 + i3.0. - -

- EXAMPLE 2 The declaration -

-          int x[] = { 1, 3, 5 };
-
- defines and initializes x as a one-dimensional array object that has three elements, as no size was specified - and there are three initializers. - -

- EXAMPLE 3 The declaration -

-          int y[4][3] =         {
-                { 1, 3,         5 },
-                { 2, 4,         6 },
-                { 3, 5,         7 },
-          };
-
- is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object - y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and - y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have - been achieved by -
-          int y[4][3] = {
-                1, 3, 5, 2, 4, 6, 3, 5, 7
-          };
-
- The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the - next three are taken successively for y[1] and y[2]. - -

- EXAMPLE 4 The declaration -

-          int z[4][3] = {
-                { 1 }, { 2 }, { 3 }, { 4 }
-          };
-
- initializes the first column of z as specified and initializes the rest with zeros. - -

- EXAMPLE 5 The declaration -

-          struct { int a[3], b; } w[] = { { 1 }, 2 };
-
- is a definition with an inconsistently bracketed initialization. It defines an array with two element - - - - - structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero. - -

- EXAMPLE 6 The declaration -

-           short q[4][3][2] = {
-                 { 1 },
-                 { 2, 3 },
-                 { 4, 5, 6 }
-           };
-
- contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array - object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize - q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for - q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is - only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers - for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their - respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a - diagnostic message would have been issued. The same initialization result could have been achieved by: -
-           short q[4][3][2] = {
-                 1, 0, 0, 0, 0, 0,
-                 2, 3, 0, 0, 0, 0,
-                 4, 5, 6
-           };
-
- or by: -
-           short q[4][3][2] = {
-                 {
-                       { 1 },
-                 },
-                 {
-                       { 2, 3 },
-                 },
-                 {
-                       { 4, 5 },
-                       { 6 },
-                 }
-           };
-
- in a fully bracketed form. -

- Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to - cause confusion. - -

- EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the - declaration -

-           typedef int A[];          // OK - declared with block scope
-
- the declaration -
-           A a = { 1, 2 }, b = { 3, 4, 5 };
-
- is identical to -
-           int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
-
- due to the rules for incomplete types. - -

- EXAMPLE 8 The declaration -

-          char s[] = "abc", t[3] = "abc";
-
- defines ''plain'' char array objects s and t whose elements are initialized with character string literals. - This declaration is identical to -
-          char s[] = { 'a', 'b', 'c', '\0' },
-               t[] = { 'a', 'b', 'c' };
-
- The contents of the arrays are modifiable. On the other hand, the declaration -
-          char *p = "abc";
-
- defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char'' - with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to - modify the contents of the array, the behavior is undefined. - -

- EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using - designators: -

-          enum { member_one,           member_two };
-          const char *nm[] =           {
-                [member_two]           = "member two",
-                [member_one]           = "member one",
-          };
-
- -

- EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order: -

-          div_t answer = { .quot = 2, .rem = -1 };
-
- -

- EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists - might be misunderstood: -

-          struct { int a[3], b; } w[] =
-                { [0].a = {1}, [1].a[0] = 2 };
-
- -

- EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator: -

-          int a[MAX] = {
-                1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
-          };
-
-

- In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less - than ten, some of the values provided by the first five initializers will be overridden by the second five. - -

- EXAMPLE 13 Any member of a union can be initialized: -

-          union { /* ... */ } u = { .any_member = 42 };
-
- -

Forward references: common definitions <stddef.h> (7.19). - - -

Footnotes -

148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its - subobjects are initialized as usual, but the subaggregate or contained union does not become the - current object: current objects are associated only with brace-enclosed initializer lists. - -

149) After a union member is initialized, the next object is not the next member of the union; instead, it is - the next subobject of an object containing the union. - -

150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with - the surrounding brace pair. Note, too, that each separate designator list is independent. - -

151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might - not be evaluated at all. - -

152) In particular, the evaluation order need not be the same as the order of subobject initialization. - - -

Contents -

6.7.10 Static assertions

-

Syntax -

-

-          static_assert-declaration:
-                  _Static_assert ( constant-expression , string-literal ) ;
-
-

Constraints -

- The constant expression shall compare unequal to 0. -

Semantics -

- The constant expression shall be an integer constant expression. If the value of the - constant expression compares unequal to 0, the declaration has no effect. Otherwise, the - constraint is violated and the implementation shall produce a diagnostic message that - includes the text of the string literal, except that characters not in the basic source - character set are not required to appear in the message. -

Forward references: diagnostics (7.2). - - -

Contents -

6.8 Statements and blocks

-

Syntax -

-

-          statement:
-                 labeled-statement
-                 compound-statement
-                 expression-statement
-                 selection-statement
-                 iteration-statement
-                 jump-statement
-
-

Semantics -

- A statement specifies an action to be performed. Except as indicated, statements are - executed in sequence. -

- A block allows a set of declarations and statements to be grouped into one syntactic unit. - The initializers of objects that have automatic storage duration, and the variable length - array declarators of ordinary identifiers with block scope, are evaluated and the values are - stored in the objects (including storing an indeterminate value in objects without an - initializer) each time the declaration is reached in the order of execution, as if it were a - statement, and within each declaration in the order that declarators appear. -

- A full expression is an expression that is not part of another expression or of a declarator. - Each of the following is a full expression: an initializer that is not part of a compound - literal; the expression in an expression statement; the controlling expression of a selection - statement (if or switch); the controlling expression of a while or do statement; each - of the (optional) expressions of a for statement; the (optional) expression in a return - statement. There is a sequence point between the evaluation of a full expression and the - evaluation of the next full expression to be evaluated. -

Forward references: expression and null statements (6.8.3), selection statements - (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4). - -

Contents -

6.8.1 Labeled statements

-

Syntax -

-

-          labeled-statement:
-                 identifier : statement
-                 case constant-expression : statement
-                 default : statement
-
-

Constraints -

- A case or default label shall appear only in a switch statement. Further - constraints on such labels are discussed under the switch statement. - -

- Label names shall be unique within a function. -

Semantics -

- Any statement may be preceded by a prefix that declares an identifier as a label name. - Labels in themselves do not alter the flow of control, which continues unimpeded across - them. -

Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2). - -

Contents -

6.8.2 Compound statement

-

Syntax -

-

-          compound-statement:
-                { block-item-listopt }
-          block-item-list:
-                  block-item
-                  block-item-list block-item
-          block-item:
-                  declaration
-                  statement
-
-

Semantics -

- A compound statement is a block. - -

Contents -

6.8.3 Expression and null statements

-

Syntax -

-

-          expression-statement:
-                 expressionopt ;
-
-

Semantics -

- The expression in an expression statement is evaluated as a void expression for its side - effects.153) -

- A null statement (consisting of just a semicolon) performs no operations. -

- EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the - discarding of its value may be made explicit by converting the expression to a void expression by means of - a cast: -

-          int p(int);
-          /* ... */
-          (void)p(0);
-
- - - - -

- EXAMPLE 2 In the program fragment -

-          char *s;
-          /* ... */
-          while (*s++ != '\0')
-                  ;
-
- a null statement is used to supply an empty loop body to the iteration statement. - -

- EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound - statement. -

-          while (loop1) {
-                /* ... */
-                while (loop2) {
-                        /* ... */
-                        if (want_out)
-                                goto end_loop1;
-                        /* ... */
-                }
-                /* ... */
-          end_loop1: ;
-          }
-
- -

Forward references: iteration statements (6.8.5). - -

Footnotes -

153) Such as assignments, and function calls which have side effects. - - -

Contents -

6.8.4 Selection statements

-

Syntax -

-

-          selection-statement:
-                  if ( expression ) statement
-                  if ( expression ) statement else statement
-                  switch ( expression ) statement
-
-

Semantics -

- A selection statement selects among a set of statements depending on the value of a - controlling expression. -

- A selection statement is a block whose scope is a strict subset of the scope of its - enclosing block. Each associated substatement is also a block whose scope is a strict - subset of the scope of the selection statement. - -

Contents -

6.8.4.1 The if statement
-

Constraints -

- The controlling expression of an if statement shall have scalar type. -

Semantics -

- In both forms, the first substatement is executed if the expression compares unequal to 0. - In the else form, the second substatement is executed if the expression compares equal - - to 0. If the first substatement is reached via a label, the second substatement is not - executed. -

- An else is associated with the lexically nearest preceding if that is allowed by the - syntax. - -

Contents -

6.8.4.2 The switch statement
-

Constraints -

- The controlling expression of a switch statement shall have integer type. -

- If a switch statement has an associated case or default label within the scope of an - identifier with a variably modified type, the entire switch statement shall be within the - scope of that identifier.154) -

- The expression of each case label shall be an integer constant expression and no two of - the case constant expressions in the same switch statement shall have the same value - after conversion. There may be at most one default label in a switch statement. - (Any enclosed switch statement may have a default label or case constant - expressions with values that duplicate case constant expressions in the enclosing - switch statement.) -

Semantics -

- A switch statement causes control to jump to, into, or past the statement that is the - switch body, depending on the value of a controlling expression, and on the presence of a - default label and the values of any case labels on or in the switch body. A case or - default label is accessible only within the closest enclosing switch statement. -

- The integer promotions are performed on the controlling expression. The constant - expression in each case label is converted to the promoted type of the controlling - expression. If a converted value matches that of the promoted controlling expression, - control jumps to the statement following the matched case label. Otherwise, if there is - a default label, control jumps to the labeled statement. If no converted case constant - expression matches and there is no default label, no part of the switch body is - executed. -

Implementation limits -

- As discussed in 5.2.4.1, the implementation may limit the number of case values in a - switch statement. - - - - - -

- EXAMPLE In the artificial program fragment -

-          switch (expr)
-          {
-                int i = 4;
-                f(i);
-          case 0:
-                i = 17;
-                /* falls through into default code */
-          default:
-                printf("%d\n", i);
-          }
-
- the object whose identifier is i exists with automatic storage duration (within the block) but is never - initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will - access an indeterminate value. Similarly, the call to the function f cannot be reached. - - -

Footnotes -

154) That is, the declaration either precedes the switch statement, or it follows the last case or - default label associated with the switch that is in the block containing the declaration. - - -

Contents -

6.8.5 Iteration statements

-

Syntax -

-

-          iteration-statement:
-                  while ( expression ) statement
-                  do statement while ( expression ) ;
-                  for ( expressionopt ; expressionopt ; expressionopt ) statement
-                  for ( declaration expressionopt ; expressionopt ) statement
-
-

Constraints -

- The controlling expression of an iteration statement shall have scalar type. -

- The declaration part of a for statement shall only declare identifiers for objects having - storage class auto or register. -

Semantics -

- An iteration statement causes a statement called the loop body to be executed repeatedly - until the controlling expression compares equal to 0. The repetition occurs regardless of - whether the loop body is entered from the iteration statement or by a jump.155) -

- An iteration statement is a block whose scope is a strict subset of the scope of its - enclosing block. The loop body is also a block whose scope is a strict subset of the scope - of the iteration statement. -

- An iteration statement whose controlling expression is not a constant expression,156) that - performs no input/output operations, does not access volatile objects, and performs no - synchronization or atomic operations in its body, controlling expression, or (in the case of - - - a for statement) its expression-3, may be assumed by the implementation to - terminate.157) - -

Footnotes -

155) Code jumped over is not executed. In particular, the controlling expression of a for or while - statement is not evaluated before entering the loop body, nor is clause-1 of a for statement. - -

156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression. - -

157) This is intended to allow compiler transformations such as removal of empty loops even when - termination cannot be proven. - - -

Contents -

6.8.5.1 The while statement
-

- The evaluation of the controlling expression takes place before each execution of the loop - body. - -

Contents -

6.8.5.2 The do statement
-

- The evaluation of the controlling expression takes place after each execution of the loop - body. - -

Contents -

6.8.5.3 The for statement
-

- The statement -

-          for ( clause-1 ; expression-2 ; expression-3 ) statement
-
- behaves as follows: The expression expression-2 is the controlling expression that is - evaluated before each execution of the loop body. The expression expression-3 is - evaluated as a void expression after each execution of the loop body. If clause-1 is a - declaration, the scope of any identifiers it declares is the remainder of the declaration and - the entire loop, including the other two expressions; it is reached in the order of execution - before the first evaluation of the controlling expression. If clause-1 is an expression, it is - evaluated as a void expression before the first evaluation of the controlling expression.158) -

- Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a - nonzero constant. - -

Footnotes -

158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in - the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration, - such that execution of the loop continues until the expression compares equal to 0; and expression-3 - specifies an operation (such as incrementing) that is performed after each iteration. - - -

Contents -

6.8.6 Jump statements

-

Syntax -

-

-          jump-statement:
-                 goto identifier ;
-                 continue ;
-                 break ;
-                 return expressionopt ;
-
- - - - - -

Semantics -

- A jump statement causes an unconditional jump to another place. - -

Contents -

6.8.6.1 The goto statement
-

Constraints -

- The identifier in a goto statement shall name a label located somewhere in the enclosing - function. A goto statement shall not jump from outside the scope of an identifier having - a variably modified type to inside the scope of that identifier. -

Semantics -

- A goto statement causes an unconditional jump to the statement prefixed by the named - label in the enclosing function. -

- EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The - following outline presents one possible approach to a problem based on these three assumptions: -

    -
  1. The general initialization code accesses objects only visible to the current function. -
  2. The general initialization code is too large to warrant duplication. -
  3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by - continue statements, for example.) - -
    -    /* ... */
-    goto first_time;
-    for (;;) {
-            // determine next operation
-            /* ... */
-            if (need to reinitialize) {
-                    // reinitialize-only code
-                    /* ... */
-            first_time:
-                    // general initialization code
-                    /* ... */
-                    continue;
-            }
-            // handle other operations
-            /* ... */
-    }
-
    -
-

- EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably - modified types. A jump within the scope, however, is permitted. -

-         goto lab3;                         // invalid: going INTO scope of VLA.
-         {
-               double a[n];
-               a[j] = 4.4;
-         lab3:
-               a[j] = 3.3;
-               goto lab4;                   // valid: going WITHIN scope of VLA.
-               a[j] = 5.5;
-         lab4:
-               a[j] = 6.6;
-         }
-         goto lab4;                         // invalid: going INTO scope of VLA.
-
- - -

Contents -

6.8.6.2 The continue statement
-

Constraints -

- A continue statement shall appear only in or as a loop body. -

Semantics -

- A continue statement causes a jump to the loop-continuation portion of the smallest - enclosing iteration statement; that is, to the end of the loop body. More precisely, in each - of the statements - while (/* ... */) { do { for (/* ... */) { -

-    /* ... */                            /* ... */                            /* ... */
-    continue;                            continue;                            continue;
-    /* ... */                            /* ... */                            /* ... */
-
- contin: ; contin: ; contin: ; - } } while (/* ... */); } - unless the continue statement shown is in an enclosed iteration statement (in which - case it is interpreted within that statement), it is equivalent to goto contin;.159) - -

Footnotes -

159) Following the contin: label is a null statement. - - -

Contents -

6.8.6.3 The break statement
-

Constraints -

- A break statement shall appear only in or as a switch body or loop body. -

Semantics -

- A break statement terminates execution of the smallest enclosing switch or iteration - statement. - - - - - -

Contents -

6.8.6.4 The return statement
-

Constraints -

- A return statement with an expression shall not appear in a function whose return type - is void. A return statement without an expression shall only appear in a function - whose return type is void. -

Semantics -

- A return statement terminates execution of the current function and returns control to - its caller. A function may have any number of return statements. -

- If a return statement with an expression is executed, the value of the expression is - returned to the caller as the value of the function call expression. If the expression has a - type different from the return type of the function in which it appears, the value is - converted as if by assignment to an object having the return type of the function.160) -

- EXAMPLE In: -

-         struct s { double i; } f(void);
-         union {
-               struct {
-                     int f1;
-                     struct s f2;
-               } u1;
-               struct {
-                     struct s f3;
-                     int f4;
-               } u2;
-         } g;
-         struct s f(void)
-         {
-               return g.u1.f2;
-         }
-         /* ... */
-         g.u2.f3 = f();
-
- there is no undefined behavior, although there would be if the assignment were done directly (without using - a function call to fetch the value). - - - - - - -

Footnotes -

160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not - apply to the case of function return. The representation of floating-point values may have wider range - or precision than implied by the type; a cast may be used to remove this extra range and precision. - - -

Contents -

6.9 External definitions

-

Syntax -

-

-          translation-unit:
-                  external-declaration
-                  translation-unit external-declaration
-          external-declaration:
-                 function-definition
-                 declaration
-
-

Constraints -

- The storage-class specifiers auto and register shall not appear in the declaration - specifiers in an external declaration. -

- There shall be no more than one external definition for each identifier declared with - internal linkage in a translation unit. Moreover, if an identifier declared with internal - linkage is used in an expression (other than as a part of the operand of a sizeof - operator whose result is an integer constant), there shall be exactly one external definition - for the identifier in the translation unit. -

Semantics -

- As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit, - which consists of a sequence of external declarations. These are described as ''external'' - because they appear outside any function (and hence have file scope). As discussed in - 6.7, a declaration that also causes storage to be reserved for an object or a function named - by the identifier is a definition. -

- An external definition is an external declaration that is also a definition of a function - (other than an inline definition) or an object. If an identifier declared with external - linkage is used in an expression (other than as part of the operand of a sizeof operator - whose result is an integer constant), somewhere in the entire program there shall be - exactly one external definition for the identifier; otherwise, there shall be no more than - one.161) - - - - - - -

Footnotes -

161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no - external definition for it. - - -

Contents -

6.9.1 Function definitions

-

Syntax -

-

-          function-definition:
-                 declaration-specifiers declarator declaration-listopt compound-statement
-          declaration-list:
-                 declaration
-                 declaration-list declaration
-
-

Constraints -

- The identifier declared in a function definition (which is the name of the function) shall - have a function type, as specified by the declarator portion of the function definition.162) -

- The return type of a function shall be void or a complete object type other than array - type. -

- The storage-class specifier, if any, in the declaration specifiers shall be either extern or - static. -

- If the declarator includes a parameter type list, the declaration of each parameter shall - include an identifier, except for the special case of a parameter list consisting of a single - parameter of type void, in which case there shall not be an identifier. No declaration list - shall follow. -

- If the declarator includes an identifier list, each declaration in the declaration list shall - have at least one declarator, those declarators shall declare only identifiers from the - identifier list, and every identifier in the identifier list shall be declared. An identifier - declared as a typedef name shall not be redeclared as a parameter. The declarations in the - declaration list shall contain no storage-class specifier other than register and no - initializations. - - - - -

Semantics -

- The declarator in a function definition specifies the name of the function being defined - and the identifiers of its parameters. If the declarator includes a parameter type list, the - list also specifies the types of all the parameters; such a declarator also serves as a - function prototype for later calls to the same function in the same translation unit. If the - declarator includes an identifier list,163) the types of the parameters shall be declared in a - following declaration list. In either case, the type of each parameter is adjusted as - described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object - type. -

- If a function that accepts a variable number of arguments is defined without a parameter - type list that ends with the ellipsis notation, the behavior is undefined. -

- Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout - of the storage for parameters is unspecified. -

- On entry to the function, the size expressions of each variably modified parameter are - evaluated and the value of each argument expression is converted to the type of the - corresponding parameter as if by assignment. (Array expressions and function - designators as arguments were converted to pointers before the call.) -

- After all parameters have been assigned, the compound statement that constitutes the - body of the function definition is executed. -

- If the } that terminates a function is reached, and the value of the function call is used by - the caller, the behavior is undefined. -

- EXAMPLE 1 In the following: -

-          extern int max(int a, int b)
-          {
-                return a > b ? a : b;
-          }
-
- extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the - function declarator; and -
-          { return a > b ? a : b; }
-
- is the function body. The following similar definition uses the identifier-list form for the parameter - declarations: - - - - - -
-          extern int max(a, b)
-          int a, b;
-          {
-                return a > b ? a : b;
-          }
-
- Here int a, b; is the declaration list for the parameters. The difference between these two definitions is - that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls - to the function, whereas the second form does not. - -

- EXAMPLE 2 To pass one function to another, one might say -

-                      int f(void);
-                      /* ... */
-                      g(f);
-
- Then the definition of g might read -
-          void g(int (*funcp)(void))
-          {
-                /* ... */
-                (*funcp)(); /* or funcp(); ...                    */
-          }
-
- or, equivalently, -
-          void g(int func(void))
-          {
-                /* ... */
-                func(); /* or (*func)(); ...                   */
-          }
-
- - -

Footnotes -

162) The intent is that the type category in a function definition cannot be inherited from a typedef: - -

-          typedef int F(void);                          //   type F is ''function with no parameters
-                                                        //                  returning int''
-          F f, g;                                       //   f and g both have type compatible with F
-          F f { /* ... */ }                             //   WRONG: syntax/constraint error
-          F g() { /* ... */ }                           //   WRONG: declares that g returns a function
-          int f(void) { /* ... */ }                     //   RIGHT: f has type compatible with F
-          int g() { /* ... */ }                         //   RIGHT: g has type compatible with F
-          F *e(void) { /* ... */ }                      //   e returns a pointer to a function
-          F *((e))(void) { /* ... */ }                  //   same: parentheses irrelevant
-          int (*fp)(void);                              //   fp points to a function that has type F
-          F *Fp;                                        //   Fp points to a function that has type F
-
- -

163) See ''future language directions'' (6.11.7). - -

164) A parameter identifier cannot be redeclared in the function body except in an enclosed block. - - -

Contents -

6.9.2 External object definitions

-

Semantics -

- If the declaration of an identifier for an object has file scope and an initializer, the - declaration is an external definition for the identifier. -

- A declaration of an identifier for an object that has file scope without an initializer, and - without a storage-class specifier or with the storage-class specifier static, constitutes a - tentative definition. If a translation unit contains one or more tentative definitions for an - identifier, and the translation unit contains no external definition for that identifier, then - the behavior is exactly as if the translation unit contains a file scope declaration of that - identifier, with the composite type as of the end of the translation unit, with an initializer - equal to 0. -

- If the declaration of an identifier for an object is a tentative definition and has internal - linkage, the declared type shall not be an incomplete type. - -

- EXAMPLE 1 -

-          int i1 = 1;                    // definition, external linkage
-          static int i2 = 2;             // definition, internal linkage
-          extern int i3 = 3;             // definition, external linkage
-          int i4;                        // tentative definition, external linkage
-          static int i5;                 // tentative definition, internal linkage
-          int   i1;                      // valid tentative definition, refers to previous
-          int   i2;                      // 6.2.2 renders undefined, linkage disagreement
-          int   i3;                      // valid tentative definition, refers to previous
-          int   i4;                      // valid tentative definition, refers to previous
-          int   i5;                      // 6.2.2 renders undefined, linkage disagreement
-          extern    int   i1;            // refers to previous, whose linkage is external
-          extern    int   i2;            // refers to previous, whose linkage is internal
-          extern    int   i3;            // refers to previous, whose linkage is external
-          extern    int   i4;            // refers to previous, whose linkage is external
-          extern    int   i5;            // refers to previous, whose linkage is internal
-
- -

- EXAMPLE 2 If at the end of the translation unit containing -

-          int i[];
-
- the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to - zero on program startup. - - -

Contents -

6.10 Preprocessing directives

-

Syntax -

- -

-          preprocessing-file:
-                 groupopt
-          group:
-                   group-part
-                   group group-part
-          group-part:
-                 if-section
-                 control-line
-                 text-line
-                 # non-directive
-          if-section:
-                   if-group elif-groupsopt else-groupopt endif-line
-          if-group:
-                  # if     constant-expression new-line groupopt
-                  # ifdef identifier new-line groupopt
-                  # ifndef identifier new-line groupopt
-          elif-groups:
-                  elif-group
-                  elif-groups elif-group
-          elif-group:
-                  # elif       constant-expression new-line groupopt
-          else-group:
-                  # else       new-line groupopt
-          endif-line:
-                  # endif      new-line
-          control-line:
-                 # include pp-tokens new-line
-                 # define identifier replacement-list new-line
-                 # define identifier lparen identifier-listopt )
-                                                 replacement-list new-line
-                 # define identifier lparen ... ) replacement-list new-line
-                 # define identifier lparen identifier-list , ... )
-                                                 replacement-list new-line
-                 # undef   identifier new-line
-                 # line    pp-tokens new-line
-                 # error   pp-tokensopt new-line
-                 # pragma pp-tokensopt new-line
-                 #         new-line
-          text-line:
-                  pp-tokensopt new-line
-          non-directive:
-                 pp-tokens new-line
-          lparen:
-                    a ( character not immediately preceded by white-space
-          replacement-list:
-                 pp-tokensopt
-          pp-tokens:
-                 preprocessing-token
-                 pp-tokens preprocessing-token
-          new-line:
-                 the new-line character
-
-

Description -

- A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the - following constraints: The first token in the sequence is a # preprocessing token that (at - the start of translation phase 4) is either the first character in the source file (optionally - after white space containing no new-line characters) or that follows white space - containing at least one new-line character. The last token in the sequence is the first new- - line character that follows the first token in the sequence.165) A new-line character ends - the preprocessing directive even if it occurs within what would otherwise be an - - - invocation of a function-like macro. -

- A text line shall not begin with a # preprocessing token. A non-directive shall not begin - with any of the directive names appearing in the syntax. -

- When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any - sequence of preprocessing tokens to occur between the directive name and the following - new-line character. -

Constraints -

- The only white-space characters that shall appear between preprocessing tokens within a - preprocessing directive (from just after the introducing # preprocessing token through - just before the terminating new-line character) are space and horizontal-tab (including - spaces that have replaced comments or possibly other white-space characters in - translation phase 3). -

Semantics -

- The implementation can process and skip sections of source files conditionally, include - other source files, and replace macros. These capabilities are called preprocessing, - because conceptually they occur before translation of the resulting translation unit. -

- The preprocessing tokens within a preprocessing directive are not subject to macro - expansion unless otherwise stated. -

- EXAMPLE In: -

-           #define EMPTY
-           EMPTY # include <file.h>
-
- the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not - begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been - replaced. - - -

Footnotes -

165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic - significance, as all white space is equivalent except in certain situations during preprocessing (see the - # character string literal creation operator in 6.10.3.2, for example). - - -

Contents -

6.10.1 Conditional inclusion

-

Constraints -

- The expression that controls conditional inclusion shall be an integer constant expression - except that: identifiers (including those lexically identical to keywords) are interpreted as * - described below;166) and it may contain unary operator expressions of the form -

-      defined identifier
-
- or -
-      defined ( identifier )
-
- which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is - - - - predefined or if it has been the subject of a #define preprocessing directive without an - intervening #undef directive with the same subject identifier), 0 if it is not. -

- Each preprocessing token that remains (in the list of preprocessing tokens that will - become the controlling expression) after all macro replacements have occurred shall be in - the lexical form of a token (6.4). -

Semantics -

- Preprocessing directives of the forms -

-    # if   constant-expression new-line groupopt
-    # elif constant-expression new-line groupopt
-
- check whether the controlling constant expression evaluates to nonzero. -

- Prior to evaluation, macro invocations in the list of preprocessing tokens that will become - the controlling constant expression are replaced (except for those macro names modified - by the defined unary operator), just as in normal text. If the token defined is - generated as a result of this replacement process or use of the defined unary operator - does not match one of the two specified forms prior to macro replacement, the behavior is - undefined. After all replacements due to macro expansion and the defined unary - operator have been performed, all remaining identifiers (including those lexically - identical to keywords) are replaced with the pp-number 0, and then each preprocessing - token is converted into a token. The resulting tokens compose the controlling constant - expression which is evaluated according to the rules of 6.6. For the purposes of this - token conversion and evaluation, all signed integer types and all unsigned integer types - act as if they have the same representation as, respectively, the types intmax_t and - uintmax_t defined in the header <stdint.h>.167) This includes interpreting - character constants, which may involve converting escape sequences into execution - character set members. Whether the numeric value for these character constants matches - the value obtained when an identical character constant occurs in an expression (other - than within a #if or #elif directive) is implementation-defined.168) Also, whether a - single-character character constant may have a negative value is implementation-defined. - - - - - -

- Preprocessing directives of the forms -

-    # ifdef identifier new-line groupopt
-    # ifndef identifier new-line groupopt
-
- check whether the identifier is or is not currently defined as a macro name. Their - conditions are equivalent to #if defined identifier and #if !defined identifier - respectively. -

- Each directive's condition is checked in order. If it evaluates to false (zero), the group - that it controls is skipped: directives are processed only through the name that determines - the directive in order to keep track of the level of nested conditionals; the rest of the - directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the - group. Only the first group whose control condition evaluates to true (nonzero) is - processed. If none of the conditions evaluates to true, and there is a #else directive, the - group controlled by the #else is processed; lacking a #else directive, all the groups - until the #endif are skipped.169) -

Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest - integer types (7.20.1.5). - -

Footnotes -

166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers - either are or are not macro names -- there simply are no keywords, enumeration constants, etc. - -

167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant - 0x8000 is signed and positive within a #if expression even though it would be unsigned in - translation phase 7. - -

168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to - evaluate to the same value in these two contexts. - #if 'z' - 'a' == 25 - if ('z' - 'a' == 25) - -

169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive - before the terminating new-line character. However, comments may appear anywhere in a source file, - including within a preprocessing directive. - - -

Contents -

6.10.2 Source file inclusion

-

Constraints -

- A #include directive shall identify a header or source file that can be processed by the - implementation. -

Semantics -

- A preprocessing directive of the form -

-    # include <h-char-sequence> new-line
-
- searches a sequence of implementation-defined places for a header identified uniquely by - the specified sequence between the < and > delimiters, and causes the replacement of that - directive by the entire contents of the header. How the places are specified or the header - identified is implementation-defined. -

- A preprocessing directive of the form -

-    # include "q-char-sequence" new-line
-
- causes the replacement of that directive by the entire contents of the source file identified - by the specified sequence between the " delimiters. The named source file is searched - - - - for in an implementation-defined manner. If this search is not supported, or if the search - fails, the directive is reprocessed as if it read -
-    # include <h-char-sequence> new-line
-
- with the identical contained sequence (including > characters, if any) from the original - directive. -

- A preprocessing directive of the form -

-    # include pp-tokens new-line
-
- (that does not match one of the two previous forms) is permitted. The preprocessing - tokens after include in the directive are processed just as in normal text. (Each - identifier currently defined as a macro name is replaced by its replacement list of - preprocessing tokens.) The directive resulting after all replacements shall match one of - the two previous forms.170) The method by which a sequence of preprocessing tokens - between a < and a > preprocessing token pair or a pair of " characters is combined into a - single header name preprocessing token is implementation-defined. -

- The implementation shall provide unique mappings for sequences consisting of one or - more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The - first character shall not be a digit. The implementation may ignore distinctions of - alphabetical case and restrict the mapping to eight significant characters before the - period. -

- A #include preprocessing directive may appear in a source file that has been read - because of a #include directive in another file, up to an implementation-defined - nesting limit (see 5.2.4.1). -

- EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following: -

-          #include <stdio.h>
-          #include "myprog.h"
-
- - - - - -

- EXAMPLE 2 This illustrates macro-replaced #include directives: -

-           #if VERSION == 1
-                 #define INCFILE          "vers1.h"
-           #elif VERSION == 2
-                 #define INCFILE          "vers2.h"        // and so on
-           #else
-                  #define INCFILE         "versN.h"
-           #endif
-           #include INCFILE
-
- -

Forward references: macro replacement (6.10.3). - -

Footnotes -

170) Note that adjacent string literals are not concatenated into a single string literal (see the translation - phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive. - - -

Contents -

6.10.3 Macro replacement

-

Constraints -

- Two replacement lists are identical if and only if the preprocessing tokens in both have - the same number, ordering, spelling, and white-space separation, where all white-space - separations are considered identical. -

- An identifier currently defined as an object-like macro shall not be redefined by another - #define preprocessing directive unless the second definition is an object-like macro - definition and the two replacement lists are identical. Likewise, an identifier currently - defined as a function-like macro shall not be redefined by another #define - preprocessing directive unless the second definition is a function-like macro definition - that has the same number and spelling of parameters, and the two replacement lists are - identical. -

- There shall be white-space between the identifier and the replacement list in the definition - of an object-like macro. -

- If the identifier-list in the macro definition does not end with an ellipsis, the number of - arguments (including those arguments consisting of no preprocessing tokens) in an - invocation of a function-like macro shall equal the number of parameters in the macro - definition. Otherwise, there shall be more arguments in the invocation than there are - parameters in the macro definition (excluding the ...). There shall exist a ) - preprocessing token that terminates the invocation. -

- The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like - macro that uses the ellipsis notation in the parameters. -

- A parameter identifier in a function-like macro shall be uniquely declared within its - scope. -

Semantics -

- The identifier immediately following the define is called the macro name. There is one - name space for macro names. Any white-space characters preceding or following the - replacement list of preprocessing tokens are not considered part of the replacement list - - for either form of macro. -

- If a # preprocessing token, followed by an identifier, occurs lexically at the point at which - a preprocessing directive could begin, the identifier is not subject to macro replacement. -

- A preprocessing directive of the form -

-    # define identifier replacement-list new-line
-
- defines an object-like macro that causes each subsequent instance of the macro name171) - to be replaced by the replacement list of preprocessing tokens that constitute the - remainder of the directive. The replacement list is then rescanned for more macro names - as specified below. -

- A preprocessing directive of the form -

-    # define identifier lparen identifier-listopt ) replacement-list new-line
-    # define identifier lparen ... ) replacement-list new-line
-    # define identifier lparen identifier-list , ... ) replacement-list new-line
-
- defines a function-like macro with parameters, whose use is similar syntactically to a - function call. The parameters are specified by the optional list of identifiers, whose scope - extends from their declaration in the identifier list until the new-line character that - terminates the #define preprocessing directive. Each subsequent instance of the - function-like macro name followed by a ( as the next preprocessing token introduces the - sequence of preprocessing tokens that is replaced by the replacement list in the definition - (an invocation of the macro). The replaced sequence of preprocessing tokens is - terminated by the matching ) preprocessing token, skipping intervening matched pairs of - left and right parenthesis preprocessing tokens. Within the sequence of preprocessing - tokens making up an invocation of a function-like macro, new-line is considered a normal - white-space character. -

- The sequence of preprocessing tokens bounded by the outside-most matching parentheses - forms the list of arguments for the function-like macro. The individual arguments within - the list are separated by comma preprocessing tokens, but comma preprocessing tokens - between matching inner parentheses do not separate arguments. If there are sequences of - preprocessing tokens within the list of arguments that would otherwise act as - preprocessing directives,172) the behavior is undefined. -

- If there is a ... in the identifier-list in the macro definition, then the trailing arguments, - including any separating comma preprocessing tokens, are merged to form a single item: - - - - the variable arguments. The number of arguments so combined is such that, following - merger, the number of arguments is one more than the number of parameters in the macro - definition (excluding the ...). - -

Footnotes -

171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens, - not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they - are never scanned for macro names or parameters. - -

172) Despite the name, a non-directive is a preprocessing directive. - - -

Contents -

6.10.3.1 Argument substitution
-

- After the arguments for the invocation of a function-like macro have been identified, - argument substitution takes place. A parameter in the replacement list, unless preceded - by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is - replaced by the corresponding argument after all macros contained therein have been - expanded. Before being substituted, each argument's preprocessing tokens are - completely macro replaced as if they formed the rest of the preprocessing file; no other - preprocessing tokens are available. -

- An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it - were a parameter, and the variable arguments shall form the preprocessing tokens used to - replace it. - -

Contents -

6.10.3.2 The # operator
-

Constraints -

- Each # preprocessing token in the replacement list for a function-like macro shall be - followed by a parameter as the next preprocessing token in the replacement list. -

Semantics -

- If, in the replacement list, a parameter is immediately preceded by a # preprocessing - token, both are replaced by a single character string literal preprocessing token that - contains the spelling of the preprocessing token sequence for the corresponding - argument. Each occurrence of white space between the argument's preprocessing tokens - becomes a single space character in the character string literal. White space before the - first preprocessing token and after the last preprocessing token composing the argument - is deleted. Otherwise, the original spelling of each preprocessing token in the argument - is retained in the character string literal, except for special handling for producing the - spelling of string literals and character constants: a \ character is inserted before each " - and \ character of a character constant or string literal (including the delimiting " - characters), except that it is implementation-defined whether a \ character is inserted - before the \ character beginning a universal character name. If the replacement that - results is not a valid character string literal, the behavior is undefined. The character - string literal corresponding to an empty argument is "". The order of evaluation of # and - ## operators is unspecified. - - -

Contents -

6.10.3.3 The ## operator
-

Constraints -

- A ## preprocessing token shall not occur at the beginning or at the end of a replacement - list for either form of macro definition. -

Semantics -

- If, in the replacement list of a function-like macro, a parameter is immediately preceded - or followed by a ## preprocessing token, the parameter is replaced by the corresponding - argument's preprocessing token sequence; however, if an argument consists of no - preprocessing tokens, the parameter is replaced by a placemarker preprocessing token - instead.173) -

- For both object-like and function-like macro invocations, before the replacement list is - reexamined for more macro names to replace, each instance of a ## preprocessing token - in the replacement list (not from an argument) is deleted and the preceding preprocessing - token is concatenated with the following preprocessing token. Placemarker - preprocessing tokens are handled specially: concatenation of two placemarkers results in - a single placemarker preprocessing token, and concatenation of a placemarker with a - non-placemarker preprocessing token results in the non-placemarker preprocessing token. - If the result is not a valid preprocessing token, the behavior is undefined. The resulting - token is available for further macro replacement. The order of evaluation of ## operators - is unspecified. -

- EXAMPLE In the following fragment: -

-         #define     hash_hash # ## #
-         #define     mkstr(a) # a
-         #define     in_between(a) mkstr(a)
-         #define     join(c, d) in_between(c hash_hash d)
-         char p[] = join(x, y); // equivalent to
-                                // char p[] = "x ## y";
-
- The expansion produces, at various stages: -
-         join(x, y)
-         in_between(x hash_hash y)
-         in_between(x ## y)
-         mkstr(x ## y)
-         "x ## y"
-
- In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but - this new token is not the ## operator. - - - - -

Footnotes -

173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that - exist only within translation phase 4. - - -

Contents -

6.10.3.4 Rescanning and further replacement
-

- After all parameters in the replacement list have been substituted and # and ## - processing has taken place, all placemarker preprocessing tokens are removed. The - resulting preprocessing token sequence is then rescanned, along with all subsequent - preprocessing tokens of the source file, for more macro names to replace. -

- If the name of the macro being replaced is found during this scan of the replacement list - (not including the rest of the source file's preprocessing tokens), it is not replaced. - Furthermore, if any nested replacements encounter the name of the macro being replaced, - it is not replaced. These nonreplaced macro name preprocessing tokens are no longer - available for further replacement even if they are later (re)examined in contexts in which - that macro name preprocessing token would otherwise have been replaced. -

- The resulting completely macro-replaced preprocessing token sequence is not processed - as a preprocessing directive even if it resembles one, but all pragma unary operator - expressions within it are then processed as specified in 6.10.9 below. - -

Contents -

6.10.3.5 Scope of macro definitions
-

- A macro definition lasts (independent of block structure) until a corresponding #undef - directive is encountered or (if none is encountered) until the end of the preprocessing - translation unit. Macro definitions have no significance after translation phase 4. -

- A preprocessing directive of the form -

-    # undef identifier new-line
-
- causes the specified identifier no longer to be defined as a macro name. It is ignored if - the specified identifier is not currently defined as a macro name. -

- EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in -

-         #define TABSIZE 100
-         int table[TABSIZE];
-
- -

- EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments. - It has the advantages of working for any compatible types of the arguments and of generating in-line code - without the overhead of function calling. It has the disadvantages of evaluating one or the other of its - arguments a second time (including side effects) and generating more code than a function if invoked - several times. It also cannot have its address taken, as it has none. -

-         #define max(a, b) ((a) > (b) ? (a) : (b))
-
- The parentheses ensure that the arguments and the resulting expression are bound properly. - -

- EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence -

-          #define   x         3
-          #define   f(a)      f(x * (a))
-          #undef    x
-          #define   x         2
-          #define   g         f
-          #define   z         z[0]
-          #define   h         g(~
-          #define   m(a)      a(w)
-          #define   w         0,1
-          #define   t(a)      a
-          #define   p()       int
-          #define   q(x)      x
-          #define   r(x,y)    x ## y
-          #define   str(x)    # x
-          f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
-          g(x+(3,4)-w) | h 5) & m
-                (f)^m(m);
-          p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
-          char c[2][6] = { str(hello), str() };
-
- results in -
-          f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
-          f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
-          int i[] = { 1, 23, 4, 5, };
-          char c[2][6] = { "hello", "" };
-
- -

- EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the - sequence -

-          #define str(s)      # s
-          #define xstr(s)     str(s)
-          #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
-                                  x ## s, x ## t)
-          #define INCFILE(n) vers ## n
-          #define glue(a, b) a ## b
-          #define xglue(a, b) glue(a, b)
-          #define HIGHLOW     "hello"
-          #define LOW         LOW ", world"
-          debug(1, 2);
-          fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
-                == 0) str(: @\n), s);
-          #include xstr(INCFILE(2).h)
-          glue(HIGH, LOW);
-          xglue(HIGH, LOW)
-
- results in - -
-          printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
-          fputs(
-            "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
-            s);
-          #include "vers2.h"    (after macro replacement, before file access)
-          "hello";
-          "hello" ", world"
-
- or, after concatenation of the character string literals, -
-          printf("x1= %d, x2= %s", x1, x2);
-          fputs(
-            "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
-            s);
-          #include "vers2.h"    (after macro replacement, before file access)
-          "hello";
-          "hello, world"
-
- Space around the # and ## tokens in the macro definition is optional. - -

- EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence -

-          #define t(x,y,z) x ## y ## z
-          int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
-                     t(10,,), t(,11,), t(,,12), t(,,) };
-
- results in -
-          int j[] = { 123, 45, 67, 89,
-                      10, 11, 12, };
-
- -

- EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid. -

-          #define      OBJ_LIKE      (1-1)
-          #define      OBJ_LIKE      /* white space */ (1-1) /* other */
-          #define      FUNC_LIKE(a)   ( a )
-          #define      FUNC_LIKE( a )( /* note the white space */ \
-                                       a /* other stuff on this line
-                                           */ )
-
- But the following redefinitions are invalid: -
-          #define      OBJ_LIKE    (0)     // different token sequence
-          #define      OBJ_LIKE    (1 - 1) // different white space
-          #define      FUNC_LIKE(b) ( a ) // different parameter usage
-          #define      FUNC_LIKE(b) ( b ) // different parameter spelling
-
- -

- EXAMPLE 7 Finally, to show the variable argument list macro facilities: - -

-          #define debug(...)       fprintf(stderr, __VA_ARGS__)
-          #define showlist(...)    puts(#__VA_ARGS__)
-          #define report(test, ...) ((test)?puts(#test):\
-                      printf(__VA_ARGS__))
-          debug("Flag");
-          debug("X = %d\n", x);
-          showlist(The first, second, and third items.);
-          report(x>y, "x is %d but y is %d", x, y);
-
- results in -
-          fprintf(stderr, "Flag" );
-          fprintf(stderr, "X = %d\n", x );
-          puts( "The first, second, and third items." );
-          ((x>y)?puts("x>y"):
-                      printf("x is %d but y is %d", x, y));
-
- - -

Contents -

6.10.4 Line control

-

Constraints -

- The string literal of a #line directive, if present, shall be a character string literal. -

Semantics -

- The line number of the current source line is one greater than the number of new-line - characters read or introduced in translation phase 1 (5.1.1.2) while processing the source - file to the current token. -

- A preprocessing directive of the form -

-    # line digit-sequence new-line
-
- causes the implementation to behave as if the following sequence of source lines begins - with a source line that has a line number as specified by the digit sequence (interpreted as - a decimal integer). The digit sequence shall not specify zero, nor a number greater than - 2147483647. -

- A preprocessing directive of the form -

-    # line digit-sequence "s-char-sequenceopt" new-line
-
- sets the presumed line number similarly and changes the presumed name of the source - file to be the contents of the character string literal. -

- A preprocessing directive of the form -

-    # line pp-tokens new-line
-
- (that does not match one of the two previous forms) is permitted. The preprocessing - tokens after line on the directive are processed just as in normal text (each identifier - currently defined as a macro name is replaced by its replacement list of preprocessing - tokens). The directive resulting after all replacements shall match one of the two - previous forms and is then processed as appropriate. - - -

Contents -

6.10.5 Error directive

-

Semantics -

- A preprocessing directive of the form -

-    # error pp-tokensopt new-line
-
- causes the implementation to produce a diagnostic message that includes the specified - sequence of preprocessing tokens. - -

Contents -

6.10.6 Pragma directive

-

Semantics -

- A preprocessing directive of the form -

-    # pragma pp-tokensopt new-line
-
- where the preprocessing token STDC does not immediately follow pragma in the - directive (prior to any macro replacement)174) causes the implementation to behave in an - implementation-defined manner. The behavior might cause translation to fail or cause the - translator or the resulting program to behave in a non-conforming manner. Any such - pragma that is not recognized by the implementation is ignored. -

- If the preprocessing token STDC does immediately follow pragma in the directive (prior - to any macro replacement), then no macro replacement is performed on the directive, and - the directive shall have one of the following forms175) whose meanings are described - elsewhere: -

-    #pragma STDC FP_CONTRACT on-off-switch
-    #pragma STDC FENV_ACCESS on-off-switch
-    #pragma STDC CX_LIMITED_RANGE on-off-switch
-    on-off-switch: one of
-                ON     OFF           DEFAULT
-
-

Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma - (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4). - - - - - - -

Footnotes -

174) An implementation is not required to perform macro replacement in pragmas, but it is permitted - except for in standard pragmas (where STDC immediately follows pragma). If the result of macro - replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still - implementation-defined; an implementation is permitted to behave as if it were the standard pragma, - but is not required to. - -

175) See ''future language directions'' (6.11.8). - - -

Contents -

6.10.7 Null directive

-

Semantics -

- A preprocessing directive of the form -

-    # new-line
-
- has no effect. - -

Contents -

6.10.8 Predefined macro names

-

- The values of the predefined macros listed in the following subclauses176) (except for - __FILE__ and __LINE__) remain constant throughout the translation unit. -

- None of these macro names, nor the identifier defined, shall be the subject of a - #define or a #undef preprocessing directive. Any other predefined macro names - shall begin with a leading underscore followed by an uppercase letter or a second - underscore. -

- The implementation shall not predefine the macro __cplusplus, nor shall it define it - in any standard header. -

Forward references: standard headers (7.1.2). - -

Footnotes -

176) See ''future language directions'' (6.11.9). - - -

Contents -

6.10.8.1 Mandatory macros
-

- The following macro names shall be defined by the implementation: - __DATE__ The date of translation of the preprocessing translation unit: a character -

-            string literal of the form "Mmm dd yyyy", where the names of the
-            months are the same as those generated by the asctime function, and the
-            first character of dd is a space character if the value is less than 10. If the
-            date of translation is not available, an implementation-defined valid date
-            shall be supplied.
-
- __FILE__ The presumed name of the current source file (a character string literal).177) - __LINE__ The presumed line number (within the current source file) of the current -
-            source line (an integer constant).177)
-
- __STDC__ The integer constant 1, intended to indicate a conforming implementation. - __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted -
-           implementation or the integer constant 0 if it is not.
-
- - - - - - __STDC_VERSION__ The integer constant 201ymmL.178) - __TIME__ The time of translation of the preprocessing translation unit: a character -
-            string literal of the form "hh:mm:ss" as in the time generated by the
-            asctime function. If the time of translation is not available, an
-            implementation-defined valid time shall be supplied.
-
-

Forward references: the asctime function (7.26.3.1). - -

Footnotes -

177) The presumed source file name and line number can be changed by the #line directive. - -

178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in - ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will - remain an integer constant of type long int that is increased with each revision of this International - Standard. - - -

Contents -

6.10.8.2 Environment macros
-

- The following macro names are conditionally defined by the implementation: - __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example, -

-           199712L). If this symbol is defined, then every character in the Unicode
-           required set, when stored in an object of type wchar_t, has the same
-           value as the short identifier of that character. The Unicode required set
-           consists of all the characters that are defined by ISO/IEC 10646, along with
-           all amendments and technical corrigenda, as of the specified year and
-           month. If some other encoding is used, the macro shall not be defined and
-           the actual encoding used is implementation-defined.
-
- __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in -
-           the encoding for wchar_t, a member of the basic character set need not
-           have a code value equal to its value when used as the lone character in an
-           integer character constant.
-
- __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type -
-           char16_t are UTF-16 encoded. If some other encoding is used, the
-           macro shall not be defined and the actual encoding used is implementation-
-           defined.
-
- __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type -
-           char32_t are UTF-32 encoded. If some other encoding is used, the
-           macro shall not be defined and the actual encoding used is implementation-
-           defined.
-
-

Forward references: common definitions (7.19), unicode utilities (7.27). - - - - - - -

Contents -

6.10.8.3 Conditional feature macros
-

- The following macro names are conditionally defined by the implementation: - __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to -

-           the specifications in annex L (Analyzability).
-
- __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the -
-           specifications in annex F (IEC 60559 floating-point arithmetic).
-
- __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate -
-           adherence to the specifications in annex G (IEC 60559 compatible complex
-           arithmetic).
-
- __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support -
-           for the extensions defined in annex K (Bounds-checking interfaces).179)
-
- __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the -
-           implementation does not support complex types or the <complex.h>
-           header.
-
- __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the -
-           implementation does not support atomic types (including the _Atomic
-           type qualifier and the <stdatomic.h> header) or the <threads.h>
-           header.
-
- __STDC_NO_VLA__ The integer constant 1, intended to indicate that the -
-           implementation does not support variable length arrays or variably
-           modified types.
-
-

- An implementation that defines __STDC_NO_COMPLEX__ shall not define - __STDC_IEC_559_COMPLEX__. - -

Footnotes -

179) The intention is that this will remain an integer constant of type long int that is increased with - each revision of this International Standard. - - -

Contents -

6.10.9 Pragma operator

-

Semantics -

- A unary operator expression of the form: -

-    _Pragma ( string-literal )
-
- is processed as follows: The string literal is destringized by deleting the L prefix, if - present, deleting the leading and trailing double-quotes, replacing each escape sequence - \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The - resulting sequence of characters is processed through translation phase 3 to produce - preprocessing tokens that are executed as if they were the pp-tokens in a pragma - - - - directive. The original four preprocessing tokens in the unary operator expression are - removed. -

- EXAMPLE A directive of the form: -

-           #pragma listing on "..\listing.dir"
-
- can also be expressed as: -
-           _Pragma ( "listing on \"..\\listing.dir\"" )
-
- The latter form is processed in the same way whether it appears literally as shown, or results from macro - replacement, as in: - -
-           #define LISTING(x) PRAGMA(listing on #x)
-           #define PRAGMA(x) _Pragma(#x)
-           LISTING ( ..\listing.dir )
-
- -

Contents -

6.11 Future language directions

- -

Contents -

6.11.1 Floating types

-

- Future standardization may include additional floating-point types, including those with - greater range, precision, or both than long double. - -

Contents -

6.11.2 Linkages of identifiers

-

- Declaring an identifier with internal linkage at file scope without the static storage- - class specifier is an obsolescent feature. - -

Contents -

6.11.3 External names

-

- Restriction of the significance of an external name to fewer than 255 characters - (considering each universal character name or extended source character as a single - character) is an obsolescent feature that is a concession to existing implementations. - -

Contents -

6.11.4 Character escape sequences

-

- Lowercase letters as escape sequences are reserved for future standardization. Other - characters may be used in extensions. - -

Contents -

6.11.5 Storage-class specifiers

-

- The placement of a storage-class specifier other than at the beginning of the declaration - specifiers in a declaration is an obsolescent feature. - -

Contents -

6.11.6 Function declarators

-

- The use of function declarators with empty parentheses (not prototype-format parameter - type declarators) is an obsolescent feature. - -

Contents -

6.11.7 Function definitions

-

- The use of function definitions with separate parameter identifier and declaration lists - (not prototype-format parameter type and identifier declarators) is an obsolescent feature. - -

Contents -

6.11.8 Pragma directives

-

- Pragmas whose first preprocessing token is STDC are reserved for future standardization. - -

Contents -

6.11.9 Predefined macro names

-

- Macro names beginning with __STDC_ are reserved for future standardization. - - -

Contents -

7. Library

- -

Contents -

7.1 Introduction

- -

Contents -

7.1.1 Definitions of terms

-

- A string is a contiguous sequence of characters terminated by and including the first null - character. The term multibyte string is sometimes used instead to emphasize special - processing given to multibyte characters contained in the string or to avoid confusion - with a wide string. A pointer to a string is a pointer to its initial (lowest addressed) - character. The length of a string is the number of bytes preceding the null character and - the value of a string is the sequence of the values of the contained characters, in order. -

- The decimal-point character is the character used by functions that convert floating-point - numbers to or from character sequences to denote the beginning of the fractional part of - such character sequences.180) It is represented in the text and examples by a period, but - may be changed by the setlocale function. -

- A null wide character is a wide character with code value zero. -

- A wide string is a contiguous sequence of wide characters terminated by and including - the first null wide character. A pointer to a wide string is a pointer to its initial (lowest - addressed) wide character. The length of a wide string is the number of wide characters - preceding the null wide character and the value of a wide string is the sequence of code - values of the contained wide characters, in order. -

- A shift sequence is a contiguous sequence of bytes within a multibyte string that - (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a - corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte - character.181) -

Forward references: character handling (7.4), the setlocale function (7.11.1.1). - - - - - - -

Footnotes -

180) The functions that make use of the decimal-point character are the numeric conversion functions - (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2). - -

181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large - enough to count all the bytes in any complete multibyte character plus at least one adjacent shift - sequence of maximum length. Whether these counts provide for more than one shift sequence is the - implementation's choice. - - -

Contents -

7.1.2 Standard headers

-

- Each library function is declared, with a type that includes a prototype, in a header,182) - whose contents are made available by the #include preprocessing directive. The - header declares a set of related functions, plus any necessary types and additional macros - needed to facilitate their use. Declarations of types described in this clause shall not - include type qualifiers, unless explicitly stated otherwise. -

- The standard headers are183) -

-        <assert.h>             <iso646.h>              <stdarg.h>              <string.h>
-        <complex.h>            <limits.h>              <stdatomic.h>           <tgmath.h>
-        <ctype.h>              <locale.h>              <stdbool.h>             <threads.h>
-        <errno.h>              <math.h>                <stddef.h>              <time.h>
-        <fenv.h>               <setjmp.h>              <stdint.h>              <uchar.h>
-        <float.h>              <signal.h>              <stdio.h>               <wchar.h>
-        <inttypes.h>           <stdalign.h>            <stdlib.h>              <wctype.h>
-
-

- If a file with the same name as one of the above < and > delimited sequences, not - provided as part of the implementation, is placed in any of the standard places that are - searched for included source files, the behavior is undefined. -

- Standard headers may be included in any order; each may be included more than once in - a given scope, with no effect different from being included only once, except that the - effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If - used, a header shall be included outside of any external declaration or definition, and it - shall first be included before the first reference to any of the functions or objects it - declares, or to any of the types or macros it defines. However, if an identifier is declared - or defined in more than one header, the second and subsequent associated headers may be - included after the initial reference to the identifier. The program shall not have any - macros with names lexically identical to keywords currently defined prior to the - inclusion. -

- Any definition of an object-like macro described in this clause shall expand to code that is - fully protected by parentheses where necessary, so that it groups in an arbitrary - expression as if it were a single identifier. -

- Any declaration of a library function shall have external linkage. - - - - - -

- A summary of the contents of the standard headers is given in annex B. -

Forward references: diagnostics (7.2). - -

Footnotes -

182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names - necessarily valid source file names. - -

183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that - implementations need not support; see 6.10.8.3. - - -

Contents -

7.1.3 Reserved identifiers

-

- Each header declares or defines all identifiers listed in its associated subclause, and - optionally declares or defines identifiers listed in its associated future library directions - subclause and identifiers which are always reserved either for any use or for use as file - scope identifiers. -

-

- No other identifiers are reserved. If the program declares or defines an identifier in a - context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved - identifier as a macro name, the behavior is undefined. -

- If the program removes (with #undef) any macro definition of an identifier in the first - group listed above, the behavior is undefined. - - - - - - -

Footnotes -

184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp, - va_copy, and va_end. - - -

Contents -

7.1.4 Use of library functions

-

- Each of the following statements applies unless explicitly stated otherwise in the detailed - descriptions that follow: If an argument to a function has an invalid value (such as a value - outside the domain of the function, or a pointer outside the address space of the program, - or a null pointer, or a pointer to non-modifiable storage when the corresponding - parameter is not const-qualified) or a type (after promotion) not expected by a function - with variable number of arguments, the behavior is undefined. If a function argument is - described as being an array, the pointer actually passed to the function shall have a value - such that all address computations and accesses to objects (that would be valid if the - pointer did point to the first element of such an array) are in fact valid. Any function - declared in a header may be additionally implemented as a function-like macro defined in - the header, so if a library function is declared explicitly when its header is included, one - of the techniques shown below can be used to ensure the declaration is not affected by - such a macro. Any macro definition of a function can be suppressed locally by enclosing - the name of the function in parentheses, because the name is then not followed by the left - parenthesis that indicates expansion of a macro function name. For the same syntactic - reason, it is permitted to take the address of a library function even if it is also defined as - a macro.185) The use of #undef to remove any macro definition will also ensure that an - actual function is referred to. Any invocation of a library function that is implemented as - a macro shall expand to code that evaluates each of its arguments exactly once, fully - protected by parentheses where necessary, so it is generally safe to use arbitrary - expressions as arguments.186) Likewise, those function-like macros described in the - following subclauses may be invoked in an expression anywhere a function with a - compatible return type could be called.187) All object-like macros listed as expanding to - - - - integer constant expressions shall additionally be suitable for use in #if preprocessing - directives. -

- Provided that a library function can be declared without reference to any type defined in a - header, it is also permissible to declare the function and use it without including its - associated header. -

- There is a sequence point immediately before a library function returns. -

- The functions in the standard library are not guaranteed to be reentrant and may modify - objects with static or thread storage duration.188) -

- Unless explicitly stated otherwise in the detailed descriptions that follow, library - functions shall prevent data races as follows: A library function shall not directly or - indirectly access objects accessible by threads other than the current thread unless the - objects are accessed directly or indirectly via the function's arguments. A library - function shall not directly or indirectly modify objects accessible by threads other than - the current thread unless the objects are accessed directly or indirectly via the function's - non-const arguments.189) Implementations may share their own internal objects between - threads if the objects are not visible to users and are protected against data races. -

- Unless otherwise specified, library functions shall perform all operations solely within the - current thread if those operations have effects that are visible to users.190) -

- EXAMPLE The function atoi may be used in any of several ways: -

- -

Footnotes -

185) This means that an implementation shall provide an actual function for each library function, even if it - also provides a macro for that function. - -

186) Such macros might not contain the sequence points that the corresponding function calls do. - -

187) Because external identifiers and some macro names beginning with an underscore are reserved, - implementations may provide special semantics for such names. For example, the identifier - _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the - appropriate header could specify - -

-           #define abs(x) _BUILTIN_abs(x)
-
- for a compiler whose code generator will accept it. - In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine - function may write - -
-           #undef abs
-
- whether the implementation's header provides a macro implementation of abs or a built-in - implementation. The prototype for the function, which precedes and is hidden by any macro - definition, is thereby revealed also. - -

188) Thus, a signal handler cannot, in general, call standard library functions. - -

189) This means, for example, that an implementation is not permitted to use a static object for internal - purposes without synchronization because it could cause a data race even in programs that do not - explicitly share objects between threads. - -

190) This allows implementations to parallelize operations if there are no visible side effects. - - -

Contents -

7.2 Diagnostics <assert.h>

-

- The header <assert.h> defines the assert and static_assert macros and - refers to another macro, -

-         NDEBUG
-
- which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the - point in the source file where <assert.h> is included, the assert macro is defined - simply as -
-         #define assert(ignore) ((void)0)
-
- The assert macro is redefined according to the current state of NDEBUG each time that - <assert.h> is included. -

- The assert macro shall be implemented as a macro, not as an actual function. If the - macro definition is suppressed in order to access an actual function, the behavior is - undefined. -

- The macro -

-         static_assert
-
- expands to _Static_assert. - -

Contents -

7.2.1 Program diagnostics

- -

Contents -

7.2.1.1 The assert macro
-

Synopsis -

-

-         #include <assert.h>
-         void assert(scalar expression);
-
-

Description -

- The assert macro puts diagnostic tests into programs; it expands to a void expression. - When it is executed, if expression (which shall have a scalar type) is false (that is, - compares equal to 0), the assert macro writes information about the particular call that - failed (including the text of the argument, the name of the source file, the source line - number, and the name of the enclosing function -- the latter are respectively the values of - the preprocessing macros __FILE__ and __LINE__ and of the identifier - __func__) on the standard error stream in an implementation-defined format.191) It - then calls the abort function. - - - - -

Returns -

- The assert macro returns no value. -

Forward references: the abort function (7.22.4.1). - - -

Footnotes -

191) The message written might be of the form: - Assertion failed: expression, function abc, file xyz, line nnn. - - -

Contents -

7.3 Complex arithmetic <complex.h>

- -

Contents -

7.3.1 Introduction

-

- The header <complex.h> defines macros and declares functions that support complex - arithmetic.192) -

- Implementations that define the macro __STDC_NO_COMPLEX__ need not provide - this header nor support any of its facilities. -

- Each synopsis specifies a family of functions consisting of a principal function with one - or more double complex parameters and a double complex or double return - value; and other functions with the same name but with f and l suffixes which are - corresponding functions with float and long double parameters and return values. -

- The macro -

-          complex
-
- expands to _Complex; the macro -
-          _Complex_I
-
- expands to a constant expression of type const float _Complex, with the value of - the imaginary unit.193) -

- The macros -

-          imaginary
-
- and -
-          _Imaginary_I
-
- are defined if and only if the implementation supports imaginary types;194) if defined, - they expand to _Imaginary and a constant expression of type const float - _Imaginary with the value of the imaginary unit. -

- The macro -

-          I
-
- expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not - defined, I shall expand to _Complex_I. -

- Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then - redefine the macros complex, imaginary, and I. - - -

Forward references: IEC 60559-compatible complex arithmetic (annex G). - -

Footnotes -

192) See ''future library directions'' (7.30.1). - -

193) The imaginary unit is a number i such that i 2 = -1. - -

194) A specification for imaginary types is in informative annex G. - - -

Contents -

7.3.2 Conventions

-

- Values are interpreted as radians, not degrees. An implementation may set errno but is - not required to. - -

Contents -

7.3.3 Branch cuts

-

- Some of the functions below have branch cuts, across which the function is - discontinuous. For implementations with a signed zero (including all IEC 60559 - implementations) that follow the specifications of annex G, the sign of zero distinguishes - one side of a cut from another so the function is continuous (except for format - limitations) as the cut is approached from either side. For example, for the square root - function, which has a branch cut along the negative real axis, the top of the cut, with - imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with - imaginary part -0, maps to the negative imaginary axis. -

- Implementations that do not support a signed zero (see annex F) cannot distinguish the - sides of branch cuts. These implementations shall map a cut so the function is continuous - as the cut is approached coming around the finite endpoint of the cut in a counter - clockwise direction. (Branch cuts for the functions specified here have just one finite - endpoint.) For example, for the square root function, coming counter clockwise around - the finite endpoint of the cut along the negative real axis approaches the cut from above, - so the cut maps to the positive imaginary axis. - -

Contents -

7.3.4 The CX_LIMITED_RANGE pragma

-

Synopsis -

-

-        #include <complex.h>
-        #pragma STDC CX_LIMITED_RANGE on-off-switch
-
-

Description -

- The usual mathematical formulas for complex multiply, divide, and absolute value are - problematic because of their treatment of infinities and because of undue overflow and - underflow. The CX_LIMITED_RANGE pragma can be used to inform the - implementation that (where the state is ''on'') the usual mathematical formulas are - acceptable.195) The pragma can occur either outside external declarations or preceding all - explicit declarations and statements inside a compound statement. When outside external - declarations, the pragma takes effect from its occurrence until another - CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit. - When inside a compound statement, the pragma takes effect from its occurrence until - another CX_LIMITED_RANGE pragma is encountered (including within a nested - compound statement), or until the end of the compound statement; at the end of a - compound statement the state for the pragma is restored to its condition just before the - - compound statement. If this pragma is used in any other context, the behavior is - undefined. The default state for the pragma is ''off''. - -

Footnotes -

195) The purpose of the pragma is to allow the implementation to use the formulas: - -

-    (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
-    (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
-    | x + iy | = (sqrt) x 2 + y 2
-                 -----
-
- where the programmer can determine they are safe. - - -

Contents -

7.3.5 Trigonometric functions

- -

Contents -

7.3.5.1 The cacos functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex cacos(double complex z);
-         float complex cacosf(float complex z);
-         long double complex cacosl(long double complex z);
-
-

Description -

- The cacos functions compute the complex arc cosine of z, with branch cuts outside the - interval [-1, +1] along the real axis. -

Returns -

- The cacos functions return the complex arc cosine value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the - real axis. - -

Contents -

7.3.5.2 The casin functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex casin(double complex z);
-         float complex casinf(float complex z);
-         long double complex casinl(long double complex z);
-
-

Description -

- The casin functions compute the complex arc sine of z, with branch cuts outside the - interval [-1, +1] along the real axis. -

Returns -

- The casin functions return the complex arc sine value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] - - - along the real axis. - -

Contents -

7.3.5.3 The catan functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex catan(double complex z);
-        float complex catanf(float complex z);
-        long double complex catanl(long double complex z);
-
-

Description -

- The catan functions compute the complex arc tangent of z, with branch cuts outside the - interval [-i, +i] along the imaginary axis. -

Returns -

- The catan functions return the complex arc tangent value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] - along the real axis. - -

Contents -

7.3.5.4 The ccos functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex ccos(double complex z);
-        float complex ccosf(float complex z);
-        long double complex ccosl(long double complex z);
-
-

Description -

- The ccos functions compute the complex cosine of z. -

Returns -

- The ccos functions return the complex cosine value. - -

Contents -

7.3.5.5 The csin functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex csin(double complex z);
-        float complex csinf(float complex z);
-        long double complex csinl(long double complex z);
-
-

Description -

- The csin functions compute the complex sine of z. - -

Returns -

- The csin functions return the complex sine value. - -

Contents -

7.3.5.6 The ctan functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex ctan(double complex z);
-         float complex ctanf(float complex z);
-         long double complex ctanl(long double complex z);
-
-

Description -

- The ctan functions compute the complex tangent of z. -

Returns -

- The ctan functions return the complex tangent value. - -

Contents -

7.3.6 Hyperbolic functions

- -

Contents -

7.3.6.1 The cacosh functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex cacosh(double complex z);
-         float complex cacoshf(float complex z);
-         long double complex cacoshl(long double complex z);
-
-

Description -

- The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch - cut at values less than 1 along the real axis. -

Returns -

- The cacosh functions return the complex arc hyperbolic cosine value, in the range of a - half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the - imaginary axis. - -

Contents -

7.3.6.2 The casinh functions
-

Synopsis -

- -

-         #include <complex.h>
-         double complex casinh(double complex z);
-         float complex casinhf(float complex z);
-         long double complex casinhl(long double complex z);
-
-

Description -

- The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts - outside the interval [-i, +i] along the imaginary axis. -

Returns -

- The casinh functions return the complex arc hyperbolic sine value, in the range of a - strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] - along the imaginary axis. - -

Contents -

7.3.6.3 The catanh functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex catanh(double complex z);
-        float complex catanhf(float complex z);
-        long double complex catanhl(long double complex z);
-
-

Description -

- The catanh functions compute the complex arc hyperbolic tangent of z, with branch - cuts outside the interval [-1, +1] along the real axis. -

Returns -

- The catanh functions return the complex arc hyperbolic tangent value, in the range of a - strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] - along the imaginary axis. - -

Contents -

7.3.6.4 The ccosh functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex ccosh(double complex z);
-        float complex ccoshf(float complex z);
-        long double complex ccoshl(long double complex z);
-
-

Description -

- The ccosh functions compute the complex hyperbolic cosine of z. -

Returns -

- The ccosh functions return the complex hyperbolic cosine value. - - -

Contents -

7.3.6.5 The csinh functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex csinh(double complex z);
-         float complex csinhf(float complex z);
-         long double complex csinhl(long double complex z);
-
-

Description -

- The csinh functions compute the complex hyperbolic sine of z. -

Returns -

- The csinh functions return the complex hyperbolic sine value. - -

Contents -

7.3.6.6 The ctanh functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex ctanh(double complex z);
-         float complex ctanhf(float complex z);
-         long double complex ctanhl(long double complex z);
-
-

Description -

- The ctanh functions compute the complex hyperbolic tangent of z. -

Returns -

- The ctanh functions return the complex hyperbolic tangent value. - -

Contents -

7.3.7 Exponential and logarithmic functions

- -

Contents -

7.3.7.1 The cexp functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex cexp(double complex z);
-         float complex cexpf(float complex z);
-         long double complex cexpl(long double complex z);
-
-

Description -

- The cexp functions compute the complex base-e exponential of z. -

Returns -

- The cexp functions return the complex base-e exponential value. - - -

Contents -

7.3.7.2 The clog functions
-

Synopsis -

-

-        #include <complex.h>
-        double complex clog(double complex z);
-        float complex clogf(float complex z);
-        long double complex clogl(long double complex z);
-
-

Description -

- The clog functions compute the complex natural (base-e) logarithm of z, with a branch - cut along the negative real axis. -

Returns -

- The clog functions return the complex natural logarithm value, in the range of a strip - mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the - imaginary axis. - -

Contents -

7.3.8 Power and absolute-value functions

- -

Contents -

7.3.8.1 The cabs functions
-

Synopsis -

-

-        #include <complex.h>
-        double cabs(double complex z);
-        float cabsf(float complex z);
-        long double cabsl(long double complex z);
-
-

Description -

- The cabs functions compute the complex absolute value (also called norm, modulus, or - magnitude) of z. -

Returns -

- The cabs functions return the complex absolute value. - -

Contents -

7.3.8.2 The cpow functions
-

Synopsis -

- -

-        #include <complex.h>
-        double complex cpow(double complex x, double complex y);
-        float complex cpowf(float complex x, float complex y);
-        long double complex cpowl(long double complex x,
-             long double complex y);
-
-

Description -

- The cpow functions compute the complex power function xy , with a branch cut for the - first parameter along the negative real axis. -

Returns -

- The cpow functions return the complex power function value. - -

Contents -

7.3.8.3 The csqrt functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex csqrt(double complex z);
-         float complex csqrtf(float complex z);
-         long double complex csqrtl(long double complex z);
-
-

Description -

- The csqrt functions compute the complex square root of z, with a branch cut along the - negative real axis. -

Returns -

- The csqrt functions return the complex square root value, in the range of the right half- - plane (including the imaginary axis). - -

Contents -

7.3.9 Manipulation functions

- -

Contents -

7.3.9.1 The carg functions
-

Synopsis -

-

-         #include <complex.h>
-         double carg(double complex z);
-         float cargf(float complex z);
-         long double cargl(long double complex z);
-
-

Description -

- The carg functions compute the argument (also called phase angle) of z, with a branch - cut along the negative real axis. -

Returns -

- The carg functions return the value of the argument in the interval [-pi , +pi ]. - - -

Contents -

7.3.9.2 The cimag functions
-

Synopsis -

-

-        #include <complex.h>
-        double cimag(double complex z);
-        float cimagf(float complex z);
-        long double cimagl(long double complex z);
-
-

Description -

- The cimag functions compute the imaginary part of z.196) -

Returns -

- The cimag functions return the imaginary part value (as a real). - -

Footnotes -

196) For a variable z of complex type, z == creal(z) + cimag(z)*I. - - -

Contents -

7.3.9.3 The CMPLX macros
-

Synopsis -

-

-        #include <complex.h>
-        double complex CMPLX(double x, double y);
-        float complex CMPLXF(float x, float y);
-        long double complex CMPLXL(long double x, long double y);
-
-

Description -

- The CMPLX macros expand to an expression of the specified complex type, with the real - part having the (converted) value of x and the imaginary part having the (converted) - value of y. -

Recommended practice -

- The resulting expression should be suitable for use as an initializer for an object with - static or thread storage duration, provided both arguments are likewise suitable. -

Returns -

- The CMPLX macros return the complex value x + i y. -

- NOTE These macros act as if the implementation supported imaginary types and the definitions were: -

-       #define CMPLX(x, y)  ((double complex)((double)(x) + \
-                                     _Imaginary_I * (double)(y)))
-       #define CMPLXF(x, y) ((float complex)((float)(x) + \
-                                     _Imaginary_I * (float)(y)))
-       #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
-                                     _Imaginary_I * (long double)(y)))
-
- - - - - - -

Contents -

7.3.9.4 The conj functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex conj(double complex z);
-         float complex conjf(float complex z);
-         long double complex conjl(long double complex z);
-
-

Description -

- The conj functions compute the complex conjugate of z, by reversing the sign of its - imaginary part. -

Returns -

- The conj functions return the complex conjugate value. - -

Contents -

7.3.9.5 The cproj functions
-

Synopsis -

-

-         #include <complex.h>
-         double complex cproj(double complex z);
-         float complex cprojf(float complex z);
-         long double complex cprojl(long double complex z);
-
-

Description -

- The cproj functions compute a projection of z onto the Riemann sphere: z projects to - z except that all complex infinities (even those with one infinite part and one NaN part) - project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is - equivalent to -

-         INFINITY + I * copysign(0.0, cimag(z))
-
-

Returns -

- The cproj functions return the value of the projection onto the Riemann sphere. - -

Contents -

7.3.9.6 The creal functions
-

Synopsis -

-

-         #include <complex.h>
-         double creal(double complex z);
-         float crealf(float complex z);
-         long double creall(long double complex z);
-
-

Description -

- The creal functions compute the real part of z.197) - -

Returns -

- The creal functions return the real part value. - - - - - - -

Footnotes -

197) For a variable z of complex type, z == creal(z) + cimag(z)*I. - - -

Contents -

7.4 Character handling <ctype.h>

-

- The header <ctype.h> declares several functions useful for classifying and mapping - characters.198) In all cases the argument is an int, the value of which shall be - representable as an unsigned char or shall equal the value of the macro EOF. If the - argument has any other value, the behavior is undefined. -

- The behavior of these functions is affected by the current locale. Those functions that - have locale-specific aspects only when not in the "C" locale are noted below. -

- The term printing character refers to a member of a locale-specific set of characters, each - of which occupies one printing position on a display device; the term control character - refers to a member of a locale-specific set of characters that are not printing - characters.199) All letters and digits are printing characters. -

Forward references: EOF (7.21.1), localization (7.11). - -

Footnotes -

198) See ''future library directions'' (7.30.2). - -

199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those - whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose - values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL). - - -

Contents -

7.4.1 Character classification functions

-

- The functions in this subclause return nonzero (true) if and only if the value of the - argument c conforms to that in the description of the function. - -

Contents -

7.4.1.1 The isalnum function
-

Synopsis -

-

-          #include <ctype.h>
-          int isalnum(int c);
-
-

Description -

- The isalnum function tests for any character for which isalpha or isdigit is true. - -

Contents -

7.4.1.2 The isalpha function
-

Synopsis -

-

-          #include <ctype.h>
-          int isalpha(int c);
-
-

Description -

- The isalpha function tests for any character for which isupper or islower is true, - or any character that is one of a locale-specific set of alphabetic characters for which - - - - - none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale, - isalpha returns true only for the characters for which isupper or islower is true. - -

Footnotes -

200) The functions islower and isupper test true or false separately for each of these additional - characters; all four combinations are possible. - - -

Contents -

7.4.1.3 The isblank function
-

Synopsis -

-

-         #include <ctype.h>
-         int isblank(int c);
-
-

Description -

- The isblank function tests for any character that is a standard blank character or is one - of a locale-specific set of characters for which isspace is true and that is used to - separate words within a line of text. The standard blank characters are the following: - space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only - for the standard blank characters. - -

Contents -

7.4.1.4 The iscntrl function
-

Synopsis -

-

-         #include <ctype.h>
-         int iscntrl(int c);
-
-

Description -

- The iscntrl function tests for any control character. - -

Contents -

7.4.1.5 The isdigit function
-

Synopsis -

-

-         #include <ctype.h>
-         int isdigit(int c);
-
-

Description -

- The isdigit function tests for any decimal-digit character (as defined in 5.2.1). - -

Contents -

7.4.1.6 The isgraph function
-

Synopsis -

-

-         #include <ctype.h>
-         int isgraph(int c);
-
- - - - - -

Description -

- The isgraph function tests for any printing character except space (' '). - -

Contents -

7.4.1.7 The islower function
-

Synopsis -

-

-         #include <ctype.h>
-         int islower(int c);
-
-

Description -

- The islower function tests for any character that is a lowercase letter or is one of a - locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or - isspace is true. In the "C" locale, islower returns true only for the lowercase - letters (as defined in 5.2.1). - -

Contents -

7.4.1.8 The isprint function
-

Synopsis -

-

-         #include <ctype.h>
-         int isprint(int c);
-
-

Description -

- The isprint function tests for any printing character including space (' '). - -

Contents -

7.4.1.9 The ispunct function
-

Synopsis -

-

-         #include <ctype.h>
-         int ispunct(int c);
-
-

Description -

- The ispunct function tests for any printing character that is one of a locale-specific set - of punctuation characters for which neither isspace nor isalnum is true. In the "C" - locale, ispunct returns true for every printing character for which neither isspace - nor isalnum is true. - -

Contents -

7.4.1.10 The isspace function
-

Synopsis -

-

-         #include <ctype.h>
-         int isspace(int c);
-
-

Description -

- The isspace function tests for any character that is a standard white-space character or - is one of a locale-specific set of characters for which isalnum is false. The standard - - white-space characters are the following: space (' '), form feed ('\f'), new-line - ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the - "C" locale, isspace returns true only for the standard white-space characters. - -

Contents -

7.4.1.11 The isupper function
-

Synopsis -

-

-        #include <ctype.h>
-        int isupper(int c);
-
-

Description -

- The isupper function tests for any character that is an uppercase letter or is one of a - locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or - isspace is true. In the "C" locale, isupper returns true only for the uppercase - letters (as defined in 5.2.1). - -

Contents -

7.4.1.12 The isxdigit function
-

Synopsis -

-

-        #include <ctype.h>
-        int isxdigit(int c);
-
-

Description -

- The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1). - -

Contents -

7.4.2 Character case mapping functions

- -

Contents -

7.4.2.1 The tolower function
-

Synopsis -

-

-        #include <ctype.h>
-        int tolower(int c);
-
-

Description -

- The tolower function converts an uppercase letter to a corresponding lowercase letter. -

Returns -

- If the argument is a character for which isupper is true and there are one or more - corresponding characters, as specified by the current locale, for which islower is true, - the tolower function returns one of the corresponding characters (always the same one - for any given locale); otherwise, the argument is returned unchanged. - - -

Contents -

7.4.2.2 The toupper function
-

Synopsis -

-

-         #include <ctype.h>
-         int toupper(int c);
-
-

Description -

- The toupper function converts a lowercase letter to a corresponding uppercase letter. -

Returns -

- If the argument is a character for which islower is true and there are one or more - corresponding characters, as specified by the current locale, for which isupper is true, - the toupper function returns one of the corresponding characters (always the same one - for any given locale); otherwise, the argument is returned unchanged. - - -

Contents -

7.5 Errors <errno.h>

-

- The header <errno.h> defines several macros, all relating to the reporting of error - conditions. -

- The macros are -

-          EDOM
-          EILSEQ
-          ERANGE
-
- which expand to integer constant expressions with type int, distinct positive values, and - which are suitable for use in #if preprocessing directives; and -
-          errno
-
- which expands to a modifiable lvalue201) that has type int and thread local storage - duration, the value of which is set to a positive error number by several library functions. - If a macro definition is suppressed in order to access an actual object, or a program - defines an identifier with the name errno, the behavior is undefined. -

- The value of errno in the initial thread is zero at program startup (the initial value of - errno in other threads is an indeterminate value), but is never set to zero by any library - function.202) The value of errno may be set to nonzero by a library function call - whether or not there is an error, provided the use of errno is not documented in the - description of the function in this International Standard. -

- Additional macro definitions, beginning with E and a digit or E and an uppercase - letter,203) may also be specified by the implementation. - - - - - - -

Footnotes -

201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue - resulting from a function call (for example, *errno()). - -

202) Thus, a program that uses errno for error checking should set it to zero before a library function call, - then inspect it before a subsequent library function call. Of course, a library function can save the - value of errno on entry and then set it to zero, as long as the original value is restored if errno's - value is still zero just before the return. - -

203) See ''future library directions'' (7.30.3). - - -

Contents -

7.6 Floating-point environment <fenv.h>

-

- The header <fenv.h> defines several macros, and declares types and functions that - provide access to the floating-point environment. The floating-point environment refers - collectively to any floating-point status flags and control modes supported by the - implementation.204) A floating-point status flag is a system variable whose value is set - (but never cleared) when a floating-point exception is raised, which occurs as a side effect - of exceptional floating-point arithmetic to provide auxiliary information.205) A floating- - point control mode is a system variable whose value may be set by the user to affect the - subsequent behavior of floating-point arithmetic. -

- The floating-point environment has thread storage duration. The initial state for a - thread's floating-point environment is the current state of the floating-point environment - of the thread that creates it at the time of creation. -

- Certain programming conventions support the intended model of use for the floating- - point environment:206) -

-

- The type -

-         fenv_t
-
- represents the entire floating-point environment. -

- The type -

-         fexcept_t
-
- represents the floating-point status flags collectively, including any status the - implementation associates with the flags. - - - -

- Each of the macros -

-          FE_DIVBYZERO
-          FE_INEXACT
-          FE_INVALID
-          FE_OVERFLOW
-          FE_UNDERFLOW
-
- is defined if and only if the implementation supports the floating-point exception by - means of the functions in 7.6.2.207) Additional implementation-defined floating-point - exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also - be specified by the implementation. The defined macros expand to integer constant - expressions with values such that bitwise ORs of all combinations of the macros result in - distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in - zero.208) -

- The macro -

-          FE_ALL_EXCEPT
-
- is simply the bitwise OR of all floating-point exception macros defined by the - implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0. -

- Each of the macros -

-          FE_DOWNWARD
-          FE_TONEAREST
-          FE_TOWARDZERO
-          FE_UPWARD
-
- is defined if and only if the implementation supports getting and setting the represented - rounding direction by means of the fegetround and fesetround functions. - Additional implementation-defined rounding directions, with macro definitions beginning - with FE_ and an uppercase letter, may also be specified by the implementation. The - defined macros expand to integer constant expressions whose values are distinct - nonnegative values.209) -

- The macro - - - - -

-          FE_DFL_ENV
-
- represents the default floating-point environment -- the one installed at program startup - - <fenv.h> functions that manage the floating-point environment. -

- Additional implementation-defined environments, with macro definitions beginning with - FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may - also be specified by the implementation. - -

Footnotes -

204) This header is designed to support the floating-point exception status flags and directed-rounding - control modes required by IEC 60559, and other similar floating-point state information. It is also - designed to facilitate code portability among all systems. - -

205) A floating-point status flag is not an object and can be set more than once within an expression. - -

206) With these conventions, a programmer can safely assume default floating-point control modes (or be - unaware of them). The responsibilities associated with accessing the floating-point environment fall - on the programmer or program that does so explicitly. - -

207) The implementation supports a floating-point exception if there are circumstances where a call to at - least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not - necessary for all the functions to succeed all the time. - -

208) The macros should be distinct powers of two. - -

209) Even though the rounding direction macros may expand to constants corresponding to the values of - FLT_ROUNDS, they are not required to do so. - - -

Contents -

7.6.1 The FENV_ACCESS pragma

-

Synopsis -

-

-          #include <fenv.h>
-          #pragma STDC FENV_ACCESS on-off-switch
-
-

Description -

- The FENV_ACCESS pragma provides a means to inform the implementation when a - program might access the floating-point environment to test floating-point status flags or - run under non-default floating-point control modes.210) The pragma shall occur either - outside external declarations or preceding all explicit declarations and statements inside a - compound statement. When outside external declarations, the pragma takes effect from - its occurrence until another FENV_ACCESS pragma is encountered, or until the end of - the translation unit. When inside a compound statement, the pragma takes effect from its - occurrence until another FENV_ACCESS pragma is encountered (including within a - nested compound statement), or until the end of the compound statement; at the end of a - compound statement the state for the pragma is restored to its condition just before the - compound statement. If this pragma is used in any other context, the behavior is - undefined. If part of a program tests floating-point status flags, sets floating-point control - modes, or runs under non-default mode settings, but was translated with the state for the - FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or - ''off'') for the pragma is implementation-defined. (When execution passes from a part of - the program translated with FENV_ACCESS ''off'' to a part translated with - FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the - floating-point control modes have their default settings.) - - - - - -

- EXAMPLE -

-         #include <fenv.h>
-         void f(double x)
-         {
-               #pragma STDC FENV_ACCESS ON
-               void g(double);
-               void h(double);
-               /* ... */
-               g(x + 1);
-               h(x + 1);
-               /* ... */
-         }
-
-

- If the function g might depend on status flags set as a side effect of the first x + 1, or if the second - x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall - contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211) - - -

Footnotes -

210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag - tests and mode changes (e.g., global common subexpression elimination, code motion, and constant - folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default - modes are in effect and the flags are not tested. - -

211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other - hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is - ''off'', just one evaluation of x + 1 would suffice. - - -

Contents -

7.6.2 Floating-point exceptions

-

- The following functions provide access to the floating-point status flags.212) The int - input argument for the functions represents a subset of floating-point exceptions, and can - be zero or the bitwise OR of one or more floating-point exception macros, for example - FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these - functions is undefined. - -

Footnotes -

212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic - abstraction of flags that are either set or clear. An implementation may endow floating-point status - flags with more information -- for example, the address of the code which first raised the floating- - point exception; the functions fegetexceptflag and fesetexceptflag deal with the full - content of flags. - - -

Contents -

7.6.2.1 The feclearexcept function
-

Synopsis -

-

-         #include <fenv.h>
-         int feclearexcept(int excepts);
-
-

Description -

- The feclearexcept function attempts to clear the supported floating-point exceptions - represented by its argument. -

Returns -

- The feclearexcept function returns zero if the excepts argument is zero or if all - the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value. - - - - -

Contents -

7.6.2.2 The fegetexceptflag function
-

Synopsis -

-

-          #include <fenv.h>
-          int fegetexceptflag(fexcept_t *flagp,
-               int excepts);
-
-

Description -

- The fegetexceptflag function attempts to store an implementation-defined - representation of the states of the floating-point status flags indicated by the argument - excepts in the object pointed to by the argument flagp. -

Returns -

- The fegetexceptflag function returns zero if the representation was successfully - stored. Otherwise, it returns a nonzero value. - -

Contents -

7.6.2.3 The feraiseexcept function
-

Synopsis -

-

-          #include <fenv.h>
-          int feraiseexcept(int excepts);
-
-

Description -

- The feraiseexcept function attempts to raise the supported floating-point exceptions - represented by its argument.213) The order in which these floating-point exceptions are - raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function - additionally raises the ''inexact'' floating-point exception whenever it raises the - ''overflow'' or ''underflow'' floating-point exception is implementation-defined. -

Returns -

- The feraiseexcept function returns zero if the excepts argument is zero or if all - the specified exceptions were successfully raised. Otherwise, it returns a nonzero value. - - - - - - -

Footnotes -

213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations. - Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification - in F.8.6 is in the same spirit. - - -

Contents -

7.6.2.4 The fesetexceptflag function
-

Synopsis -

-

-         #include <fenv.h>
-         int fesetexceptflag(const fexcept_t *flagp,
-              int excepts);
-
-

Description -

- The fesetexceptflag function attempts to set the floating-point status flags - indicated by the argument excepts to the states stored in the object pointed to by - flagp. The value of *flagp shall have been set by a previous call to - fegetexceptflag whose second argument represented at least those floating-point - exceptions represented by the argument excepts. This function does not raise floating- - point exceptions, but only sets the state of the flags. -

Returns -

- The fesetexceptflag function returns zero if the excepts argument is zero or if - all the specified flags were successfully set to the appropriate state. Otherwise, it returns - a nonzero value. - -

Contents -

7.6.2.5 The fetestexcept function
-

Synopsis -

-

-         #include <fenv.h>
-         int fetestexcept(int excepts);
-
-

Description -

- The fetestexcept function determines which of a specified subset of the floating- - point exception flags are currently set. The excepts argument specifies the floating- - point status flags to be queried.214) -

Returns -

- The fetestexcept function returns the value of the bitwise OR of the floating-point - exception macros corresponding to the currently set floating-point exceptions included in - excepts. -

- EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set: - - - - - -

-         #include <fenv.h>
-         /* ... */
-         {
-                 #pragma STDC FENV_ACCESS ON
-                 int set_excepts;
-                 feclearexcept(FE_INVALID | FE_OVERFLOW);
-                 // maybe raise exceptions
-                 set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
-                 if (set_excepts & FE_INVALID) f();
-                 if (set_excepts & FE_OVERFLOW) g();
-                 /* ... */
-         }
-
- - -

Footnotes -

214) This mechanism allows testing several floating-point exceptions with just one function call. - - -

Contents -

7.6.3 Rounding

-

- The fegetround and fesetround functions provide control of rounding direction - modes. - -

Contents -

7.6.3.1 The fegetround function
-

Synopsis -

-

-         #include <fenv.h>
-         int fegetround(void);
-
-

Description -

- The fegetround function gets the current rounding direction. -

Returns -

- The fegetround function returns the value of the rounding direction macro - representing the current rounding direction or a negative value if there is no such - rounding direction macro or the current rounding direction is not determinable. - -

Contents -

7.6.3.2 The fesetround function
-

Synopsis -

-

-         #include <fenv.h>
-         int fesetround(int round);
-
-

Description -

- The fesetround function establishes the rounding direction represented by its - argument round. If the argument is not equal to the value of a rounding direction macro, - the rounding direction is not changed. -

Returns -

- The fesetround function returns zero if and only if the requested rounding direction - was established. - -

- EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the - rounding direction fails. -

-        #include <fenv.h>
-        #include <assert.h>
-        void f(int round_dir)
-        {
-              #pragma STDC FENV_ACCESS ON
-              int save_round;
-              int setround_ok;
-              save_round = fegetround();
-              setround_ok = fesetround(round_dir);
-              assert(setround_ok == 0);
-              /* ... */
-              fesetround(save_round);
-              /* ... */
-        }
-
- - -

Contents -

7.6.4 Environment

-

- The functions in this section manage the floating-point environment -- status flags and - control modes -- as one entity. - -

Contents -

7.6.4.1 The fegetenv function
-

Synopsis -

-

-        #include <fenv.h>
-        int fegetenv(fenv_t *envp);
-
-

Description -

- The fegetenv function attempts to store the current floating-point environment in the - object pointed to by envp. -

Returns -

- The fegetenv function returns zero if the environment was successfully stored. - Otherwise, it returns a nonzero value. - -

Contents -

7.6.4.2 The feholdexcept function
-

Synopsis -

-

-        #include <fenv.h>
-        int feholdexcept(fenv_t *envp);
-
-

Description -

- The feholdexcept function saves the current floating-point environment in the object - pointed to by envp, clears the floating-point status flags, and then installs a non-stop - (continue on floating-point exceptions) mode, if available, for all floating-point - exceptions.215) - -

Returns -

- The feholdexcept function returns zero if and only if non-stop floating-point - exception handling was successfully installed. - -

Footnotes -

215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap - handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For - such systems, the feholdexcept function can be used in conjunction with the feupdateenv - function to write routines that hide spurious floating-point exceptions from their callers. - - -

Contents -

7.6.4.3 The fesetenv function
-

Synopsis -

-

-         #include <fenv.h>
-         int fesetenv(const fenv_t *envp);
-
-

Description -

- The fesetenv function attempts to establish the floating-point environment represented - by the object pointed to by envp. The argument envp shall point to an object set by a - call to fegetenv or feholdexcept, or equal a floating-point environment macro. - Note that fesetenv merely installs the state of the floating-point status flags - represented through its argument, and does not raise these floating-point exceptions. -

Returns -

- The fesetenv function returns zero if the environment was successfully established. - Otherwise, it returns a nonzero value. - -

Contents -

7.6.4.4 The feupdateenv function
-

Synopsis -

-

-         #include <fenv.h>
-         int feupdateenv(const fenv_t *envp);
-
-

Description -

- The feupdateenv function attempts to save the currently raised floating-point - exceptions in its automatic storage, install the floating-point environment represented by - the object pointed to by envp, and then raise the saved floating-point exceptions. The - argument envp shall point to an object set by a call to feholdexcept or fegetenv, - or equal a floating-point environment macro. -

Returns -

- The feupdateenv function returns zero if all the actions were successfully carried out. - Otherwise, it returns a nonzero value. - - - - - -

- EXAMPLE Hide spurious underflow floating-point exceptions: - -

-       #include <fenv.h>
-       double f(double x)
-       {
-             #pragma STDC FENV_ACCESS ON
-             double result;
-             fenv_t save_env;
-             if (feholdexcept(&save_env))
-                   return /* indication of an environmental problem */;
-             // compute result
-             if (/* test spurious underflow */)
-                   if (feclearexcept(FE_UNDERFLOW))
-                            return /* indication of an environmental problem */;
-             if (feupdateenv(&save_env))
-                   return /* indication of an environmental problem */;
-             return result;
-       }
-
- -

Contents -

7.7 Characteristics of floating types <float.h>

-

- The header <float.h> defines several macros that expand to various limits and - parameters of the standard floating-point types. -

- The macros, their meanings, and the constraints (or restrictions) on their values are listed - in 5.2.4.2.2. - - -

Contents -

7.8 Format conversion of integer types <inttypes.h>

-

- The header <inttypes.h> includes the header <stdint.h> and extends it with - additional facilities provided by hosted implementations. -

- It declares functions for manipulating greatest-width integers and converting numeric - character strings to greatest-width integers, and it declares the type -

-          imaxdiv_t
-
- which is a structure type that is the type of the value returned by the imaxdiv function. - For each type declared in <stdint.h>, it defines corresponding macros for conversion - specifiers for use with the formatted input/output functions.216) -

Forward references: integer types <stdint.h> (7.20), formatted input/output - functions (7.21.6), formatted wide character input/output functions (7.28.2). - -

Footnotes -

216) See ''future library directions'' (7.30.4). - - -

Contents -

7.8.1 Macros for format specifiers

-

- Each of the following object-like macros expands to a character string literal containing a * - conversion specifier, possibly modified by a length modifier, suitable for use within the - format argument of a formatted input/output function when converting the corresponding - integer type. These macro names have the general form of PRI (character string literals - for the fprintf and fwprintf family) or SCN (character string literals for the - fscanf and fwscanf family),217) followed by the conversion specifier, followed by a - name corresponding to a similar type name in 7.20.1. In these names, N represents the - width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a - format string to print the value of an integer of type int_fast32_t. -

- The fprintf macros for signed integers are: -

-        PRIdN             PRIdLEASTN                PRIdFASTN          PRIdMAX             PRIdPTR
-        PRIiN             PRIiLEASTN                PRIiFASTN          PRIiMAX             PRIiPTR
-
-

- The fprintf macros for unsigned integers are: -

-        PRIoN             PRIoLEASTN                PRIoFASTN          PRIoMAX             PRIoPTR
-        PRIuN             PRIuLEASTN                PRIuFASTN          PRIuMAX             PRIuPTR
-        PRIxN             PRIxLEASTN                PRIxFASTN          PRIxMAX             PRIxPTR
-        PRIXN             PRIXLEASTN                PRIXFASTN          PRIXMAX             PRIXPTR
-
-

- The fscanf macros for signed integers are: - - - - -

-        SCNdN           SCNdLEASTN               SCNdFASTN              SCNdMAX             SCNdPTR
-        SCNiN           SCNiLEASTN               SCNiFASTN              SCNiMAX             SCNiPTR
-
-

- The fscanf macros for unsigned integers are: -

-        SCNoN           SCNoLEASTN               SCNoFASTN              SCNoMAX             SCNoPTR
-        SCNuN           SCNuLEASTN               SCNuFASTN              SCNuMAX             SCNuPTR
-        SCNxN           SCNxLEASTN               SCNxFASTN              SCNxMAX             SCNxPTR
-
-

- For each type that the implementation provides in <stdint.h>, the corresponding - fprintf macros shall be defined and the corresponding fscanf macros shall be - defined unless the implementation does not have a suitable fscanf length modifier for - the type. -

- EXAMPLE -

-         #include <inttypes.h>
-         #include <wchar.h>
-         int main(void)
-         {
-               uintmax_t i = UINTMAX_MAX;    // this type always exists
-               wprintf(L"The largest integer value is %020"
-                     PRIxMAX "\n", i);
-               return 0;
-         }
-
- - -

Footnotes -

217) Separate macros are given for use with fprintf and fscanf functions because, in the general case, - different format specifiers may be required for fprintf and fscanf, even when the type is the - same. - - -

Contents -

7.8.2 Functions for greatest-width integer types

- -

Contents -

7.8.2.1 The imaxabs function
-

Synopsis -

-

-         #include <inttypes.h>
-         intmax_t imaxabs(intmax_t j);
-
-

Description -

- The imaxabs function computes the absolute value of an integer j. If the result cannot - be represented, the behavior is undefined.218) -

Returns -

- The imaxabs function returns the absolute value. - - - - - - -

Footnotes -

218) The absolute value of the most negative number cannot be represented in two's complement. - - -

Contents -

7.8.2.2 The imaxdiv function
-

Synopsis -

-

-        #include <inttypes.h>
-        imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
-
-

Description -

- The imaxdiv function computes numer / denom and numer % denom in a single - operation. -

Returns -

- The imaxdiv function returns a structure of type imaxdiv_t comprising both the - quotient and the remainder. The structure shall contain (in either order) the members - quot (the quotient) and rem (the remainder), each of which has type intmax_t. If - either part of the result cannot be represented, the behavior is undefined. - -

Contents -

7.8.2.3 The strtoimax and strtoumax functions
-

Synopsis -

-

-        #include <inttypes.h>
-        intmax_t strtoimax(const char * restrict nptr,
-             char ** restrict endptr, int base);
-        uintmax_t strtoumax(const char * restrict nptr,
-             char ** restrict endptr, int base);
-
-

Description -

- The strtoimax and strtoumax functions are equivalent to the strtol, strtoll, - strtoul, and strtoull functions, except that the initial portion of the string is - converted to intmax_t and uintmax_t representation, respectively. -

Returns -

- The strtoimax and strtoumax functions return the converted value, if any. If no - conversion could be performed, zero is returned. If the correct value is outside the range - of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned - (according to the return type and sign of the value, if any), and the value of the macro - ERANGE is stored in errno. -

Forward references: the strtol, strtoll, strtoul, and strtoull functions - (7.22.1.4). - - -

Contents -

7.8.2.4 The wcstoimax and wcstoumax functions
-

Synopsis -

-

-         #include <stddef.h>           // for wchar_t
-         #include <inttypes.h>
-         intmax_t wcstoimax(const wchar_t * restrict nptr,
-              wchar_t ** restrict endptr, int base);
-         uintmax_t wcstoumax(const wchar_t * restrict nptr,
-              wchar_t ** restrict endptr, int base);
-
-

Description -

- The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll, - wcstoul, and wcstoull functions except that the initial portion of the wide string is - converted to intmax_t and uintmax_t representation, respectively. -

Returns -

- The wcstoimax function returns the converted value, if any. If no conversion could be - performed, zero is returned. If the correct value is outside the range of representable - values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the - return type and sign of the value, if any), and the value of the macro ERANGE is stored in - errno. -

Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions - (7.28.4.1.2). - - -

Contents -

7.9 Alternative spellings <iso646.h>

-

- The header <iso646.h> defines the following eleven macros (on the left) that expand - to the corresponding tokens (on the right): - -

-       and           &&
-       and_eq        &=
-       bitand        &
-       bitor         |
-       compl         ~
-       not           !
-       not_eq        !=
-       or            ||
-       or_eq         |=
-       xor           ^
-       xor_eq        ^=
-
- -

Contents -

7.10 Sizes of integer types <limits.h>

-

- The header <limits.h> defines several macros that expand to various limits and - parameters of the standard integer types. -

- The macros, their meanings, and the constraints (or restrictions) on their values are listed - in 5.2.4.2.1. - - -

Contents -

7.11 Localization <locale.h>

-

- The header <locale.h> declares two functions, one type, and defines several macros. -

- The type is -

-        struct lconv
-
- which contains members related to the formatting of numeric values. The structure shall - contain at least the following members, in any order. The semantics of the members and - their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have - the values specified in the comments. - -
-        char   *decimal_point;                 //   "."
-        char   *thousands_sep;                 //   ""
-        char   *grouping;                      //   ""
-        char   *mon_decimal_point;             //   ""
-        char   *mon_thousands_sep;             //   ""
-        char   *mon_grouping;                  //   ""
-        char   *positive_sign;                 //   ""
-        char   *negative_sign;                 //   ""
-        char   *currency_symbol;               //   ""
-        char   frac_digits;                    //   CHAR_MAX
-        char   p_cs_precedes;                  //   CHAR_MAX
-        char   n_cs_precedes;                  //   CHAR_MAX
-        char   p_sep_by_space;                 //   CHAR_MAX
-        char   n_sep_by_space;                 //   CHAR_MAX
-        char   p_sign_posn;                    //   CHAR_MAX
-        char   n_sign_posn;                    //   CHAR_MAX
-        char   *int_curr_symbol;               //   ""
-        char   int_frac_digits;                //   CHAR_MAX
-        char   int_p_cs_precedes;              //   CHAR_MAX
-        char   int_n_cs_precedes;              //   CHAR_MAX
-        char   int_p_sep_by_space;             //   CHAR_MAX
-        char   int_n_sep_by_space;             //   CHAR_MAX
-        char   int_p_sign_posn;                //   CHAR_MAX
-        char   int_n_sign_posn;                //   CHAR_MAX
-
-

- The macros defined are NULL (described in 7.19); and -

-          LC_ALL
-          LC_COLLATE
-          LC_CTYPE
-          LC_MONETARY
-          LC_NUMERIC
-          LC_TIME
-
- which expand to integer constant expressions with distinct values, suitable for use as the - first argument to the setlocale function.219) Additional macro definitions, beginning - with the characters LC_ and an uppercase letter,220) may also be specified by the - implementation. - -

Footnotes -

219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C. - -

220) See ''future library directions'' (7.30.5). - - -

Contents -

7.11.1 Locale control

- -

Contents -

7.11.1.1 The setlocale function
-

Synopsis -

-

-          #include <locale.h>
-          char *setlocale(int category, const char *locale);
-
-

Description -

- The setlocale function selects the appropriate portion of the program's locale as - specified by the category and locale arguments. The setlocale function may be - used to change or query the program's entire current locale or portions thereof. The value - LC_ALL for category names the program's entire locale; the other values for - category name only a portion of the program's locale. LC_COLLATE affects the - behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of - the character handling functions221) and the multibyte and wide character functions. - LC_MONETARY affects the monetary formatting information returned by the - localeconv function. LC_NUMERIC affects the decimal-point character for the - formatted input/output functions and the string conversion functions, as well as the - nonmonetary formatting information returned by the localeconv function. LC_TIME - affects the behavior of the strftime and wcsftime functions. -

- A value of "C" for locale specifies the minimal environment for C translation; a value - of "" for locale specifies the locale-specific native environment. Other - implementation-defined strings may be passed as the second argument to setlocale. - - -

- At program startup, the equivalent of -

-         setlocale(LC_ALL, "C");
-
- is executed. -

- A call to the setlocale function may introduce a data race with other calls to the - setlocale function or with calls to functions that are affected by the current locale. - The implementation shall behave as if no library function calls the setlocale function. -

Returns -

- If a pointer to a string is given for locale and the selection can be honored, the - setlocale function returns a pointer to the string associated with the specified - category for the new locale. If the selection cannot be honored, the setlocale - function returns a null pointer and the program's locale is not changed. -

- A null pointer for locale causes the setlocale function to return a pointer to the - string associated with the category for the program's current locale; the program's - locale is not changed.222) -

- The pointer to string returned by the setlocale function is such that a subsequent call - with that string value and its associated category will restore that part of the program's - locale. The string pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the setlocale function. -

Forward references: formatted input/output functions (7.21.6), multibyte/wide - character conversion functions (7.22.7), multibyte/wide string conversion functions - (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the - strftime function (7.26.3.5), the strxfrm function (7.23.4.5). - -

Footnotes -

221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and - isxdigit. - -

222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous - locale when category has the value LC_ALL. - - -

Contents -

7.11.2 Numeric formatting convention inquiry

- -

Contents -

7.11.2.1 The localeconv function
-

Synopsis -

-

-         #include <locale.h>
-         struct lconv *localeconv(void);
-
-

Description -

- The localeconv function sets the components of an object with type struct lconv - with values appropriate for the formatting of numeric quantities (monetary and otherwise) - according to the rules of the current locale. - - - - -

- The members of the structure with type char * are pointers to strings, any of which - (except decimal_point) can point to "", to indicate that the value is not available in - the current locale or is of zero length. Apart from grouping and mon_grouping, the - strings shall start and end in the initial shift state. The members with type char are - nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not - available in the current locale. The members include the following: - char *decimal_point -

-           The decimal-point character used to format nonmonetary quantities.
-
- char *thousands_sep -
-           The character used to separate groups of digits before the decimal-point
-           character in formatted nonmonetary quantities.
-
- char *grouping -
-           A string whose elements indicate the size of each group of digits in
-           formatted nonmonetary quantities.
-
- char *mon_decimal_point -
-           The decimal-point used to format monetary quantities.
-
- char *mon_thousands_sep -
-           The separator for groups of digits before the decimal-point in formatted
-           monetary quantities.
-
- char *mon_grouping -
-           A string whose elements indicate the size of each group of digits in
-           formatted monetary quantities.
-
- char *positive_sign -
-           The string used to indicate a nonnegative-valued formatted monetary
-           quantity.
-
- char *negative_sign -
-           The string used to indicate a negative-valued formatted monetary quantity.
-
- char *currency_symbol -
-           The local currency symbol applicable to the current locale.
-
- char frac_digits -
-           The number of fractional digits (those after the decimal-point) to be
-           displayed in a locally formatted monetary quantity.
-
- char p_cs_precedes - -
-           Set to 1 or 0 if the currency_symbol respectively precedes or
-           succeeds the value for a nonnegative locally formatted monetary quantity.
-
- char n_cs_precedes -
-           Set to 1 or 0 if the currency_symbol respectively precedes or
-           succeeds the value for a negative locally formatted monetary quantity.
-
- char p_sep_by_space -
-           Set to a value indicating the separation of the currency_symbol, the
-           sign string, and the value for a nonnegative locally formatted monetary
-           quantity.
-
- char n_sep_by_space -
-           Set to a value indicating the separation of the currency_symbol, the
-           sign string, and the value for a negative locally formatted monetary
-           quantity.
-
- char p_sign_posn -
-           Set to a value indicating the positioning of the positive_sign for a
-           nonnegative locally formatted monetary quantity.
-
- char n_sign_posn -
-           Set to a value indicating the positioning of the negative_sign for a
-           negative locally formatted monetary quantity.
-
- char *int_curr_symbol -
-           The international currency symbol applicable to the current locale. The
-           first three characters contain the alphabetic international currency symbol
-           in accordance with those specified in ISO 4217. The fourth character
-           (immediately preceding the null character) is the character used to separate
-           the international currency symbol from the monetary quantity.
-
- char int_frac_digits -
-           The number of fractional digits (those after the decimal-point) to be
-           displayed in an internationally formatted monetary quantity.
-
- char int_p_cs_precedes -
-           Set to 1 or 0 if the int_curr_symbol respectively precedes or
-           succeeds the value for a nonnegative internationally formatted monetary
-           quantity.
-
- char int_n_cs_precedes -
-           Set to 1 or 0 if the int_curr_symbol respectively precedes or
-           succeeds the value for a negative internationally formatted monetary
-           quantity.
-
- char int_p_sep_by_space - -
-           Set to a value indicating the separation of the int_curr_symbol, the
-           sign string, and the value for a nonnegative internationally formatted
-           monetary quantity.
-
- char int_n_sep_by_space -
-           Set to a value indicating the separation of the int_curr_symbol, the
-           sign string, and the value for a negative internationally formatted monetary
-           quantity.
-
- char int_p_sign_posn -
-           Set to a value indicating the positioning of the positive_sign for a
-           nonnegative internationally formatted monetary quantity.
-
- char int_n_sign_posn -
-           Set to a value indicating the positioning of the negative_sign for a
-           negative internationally formatted monetary quantity.
-
-

- The elements of grouping and mon_grouping are interpreted according to the - following: - CHAR_MAX No further grouping is to be performed. - 0 The previous element is to be repeatedly used for the remainder of the -

-               digits.
-
- other The integer value is the number of digits that compose the current group. -
-               The next element is examined to determine the size of the next group of
-               digits before the current group.
-
-

- The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space, - and int_n_sep_by_space are interpreted according to the following: - 0 No space separates the currency symbol and value. - 1 If the currency symbol and sign string are adjacent, a space separates them from the -

-     value; otherwise, a space separates the currency symbol from the value.
-
- 2 If the currency symbol and sign string are adjacent, a space separates them; -
-     otherwise, a space separates the sign string from the value.
-
- For int_p_sep_by_space and int_n_sep_by_space, the fourth character of - int_curr_symbol is used instead of a space. -

- The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and - int_n_sign_posn are interpreted according to the following: - 0 Parentheses surround the quantity and currency symbol. - 1 The sign string precedes the quantity and currency symbol. - 2 The sign string succeeds the quantity and currency symbol. - 3 The sign string immediately precedes the currency symbol. - 4 The sign string immediately succeeds the currency symbol. - -

- The implementation shall behave as if no library function calls the localeconv - function. -

Returns -

- The localeconv function returns a pointer to the filled-in object. The structure - pointed to by the return value shall not be modified by the program, but may be - overwritten by a subsequent call to the localeconv function. In addition, calls to the - setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may - overwrite the contents of the structure. -

- EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format - monetary quantities. -

-                               Local format                                     International format
-
- - Country Positive Negative Positive Negative - - Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56 - Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234 - Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56 - Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C -

- For these four countries, the respective values for the monetary members of the structure returned by - localeconv could be: -

-                                   Country1              Country2              Country3            Country4
-
- - mon_decimal_point "," "" "," "." - mon_thousands_sep "." "." "." "," - mon_grouping "\3" "\3" "\3" "\3" - positive_sign "" "" "" "" - negative_sign "-" "-" "-" "C" - currency_symbol "mk" "L." "\u0192" "SFrs." - frac_digits 2 0 2 2 - p_cs_precedes 0 1 1 1 - n_cs_precedes 0 1 1 1 - p_sep_by_space 1 0 1 0 - n_sep_by_space 1 0 2 0 - p_sign_posn 1 1 1 1 - n_sign_posn 1 1 4 2 - int_curr_symbol "FIM " "ITL " "NLG " "CHF " - int_frac_digits 2 0 2 2 - int_p_cs_precedes 1 1 1 1 - int_n_cs_precedes 1 1 1 1 - int_p_sep_by_space 1 1 1 1 - int_n_sep_by_space 2 1 2 1 - int_p_sign_posn 1 1 1 1 - int_n_sign_posn 4 1 4 2 - -

- EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members - affect the formatted value. -

-                                                               p_sep_by_space
-
- - p_cs_precedes p_sign_posn 0 1 2 - -
-                 0                    0         (1.25$)            (1.25 $)            (1.25$)
-                                      1         +1.25$             +1.25 $             + 1.25$
-                                      2         1.25$+             1.25 $+             1.25$ +
-                                      3         1.25+$             1.25 +$             1.25+ $
-                                      4         1.25$+             1.25 $+             1.25$ +
-
- - -
-                 1                    0         ($1.25)            ($ 1.25)            ($1.25)
-                                      1         +$1.25             +$ 1.25             + $1.25
-                                      2         $1.25+             $ 1.25+             $1.25 +
-                                      3         +$1.25             +$ 1.25             + $1.25
-                                      4         $+1.25             $+ 1.25             $ +1.25
-
- -

Contents -

7.12 Mathematics <math.h>

-

- The header <math.h> declares two types and many mathematical functions and defines - several macros. Most synopses specify a family of functions consisting of a principal - function with one or more double parameters, a double return value, or both; and - other functions with the same name but with f and l suffixes, which are corresponding - functions with float and long double parameters, return values, or both.223) - Integer arithmetic functions and conversion functions are discussed later. -

- The types -

-         float_t
-         double_t
-
- are floating types at least as wide as float and double, respectively, and such that - double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0, - float_t and double_t are float and double, respectively; if - FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals - 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are - otherwise implementation-defined.224) -

- The macro -

-         HUGE_VAL
-
- expands to a positive double constant expression, not necessarily representable as a - float. The macros -
-         HUGE_VALF
-         HUGE_VALL
-
- are respectively float and long double analogs of HUGE_VAL.225) -

- The macro -

-         INFINITY
-
- expands to a constant expression of type float representing positive or unsigned - infinity, if available; else to a positive constant of type float that overflows at - - - - - translation time.226) -

- The macro -

-          NAN
-
- is defined if and only if the implementation supports quiet NaNs for the float type. It - expands to a constant expression of type float representing a quiet NaN. -

- The number classification macros -

-          FP_INFINITE
-          FP_NAN
-          FP_NORMAL
-          FP_SUBNORMAL
-          FP_ZERO
-
- represent the mutually exclusive kinds of floating-point values. They expand to integer - constant expressions with distinct values. Additional implementation-defined floating- - point classifications, with macro definitions beginning with FP_ and an uppercase letter, - may also be specified by the implementation. -

- The macro -

-          FP_FAST_FMA
-
- is optionally defined. If defined, it indicates that the fma function generally executes - about as fast as, or faster than, a multiply and an add of double operands.227) The - macros -
-          FP_FAST_FMAF
-          FP_FAST_FMAL
-
- are, respectively, float and long double analogs of FP_FAST_FMA. If defined, - these macros expand to the integer constant 1. -

- The macros -

-          FP_ILOGB0
-          FP_ILOGBNAN
-
- expand to integer constant expressions whose values are returned by ilogb(x) if x is - zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or - -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN. - - - -

- The macros -

-         MATH_ERRNO
-         MATH_ERREXCEPT
-
- expand to the integer constants 1 and 2, respectively; the macro -
-         math_errhandling
-
- expands to an expression that has type int and the value MATH_ERRNO, - MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is - constant for the duration of the program. It is unspecified whether - math_errhandling is a macro or an identifier with external linkage. If a macro - definition is suppressed or a program defines an identifier with the name - math_errhandling, the behavior is undefined. If the expression - math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation - shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in - <fenv.h>. - -

Footnotes -

223) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments - and return values in wider format than the synopsis prototype indicates. - -

224) The types float_t and double_t are intended to be the implementation's most efficient types at - least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the - type float_t is the narrowest type used by the implementation to evaluate floating expressions. - -

225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that - supports infinities. - -

226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic. - -

227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented - directly with a hardware multiply-add instruction. Software implementations are expected to be - substantially slower. - - -

Contents -

7.12.1 Treatment of error conditions

-

- The behavior of each of the functions in <math.h> is specified for all representable - values of its input arguments, except where stated otherwise. Each function shall execute - as if it were a single operation without raising SIGFPE and without generating any of the - floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect - the result of the function. -

- For all functions, a domain error occurs if an input argument is outside the domain over - which the mathematical function is defined. The description of each function lists any - required domain errors; an implementation may define additional domain errors, provided - that such errors are consistent with the mathematical definition of the function.228) On a - domain error, the function returns an implementation-defined value; if the integer - expression math_errhandling & MATH_ERRNO is nonzero, the integer expression - errno acquires the value EDOM; if the integer expression math_errhandling & - MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised. -

- Similarly, a pole error (also known as a singularity or infinitary) occurs if the - mathematical function has an exact infinite result as the finite input argument(s) are - approached in the limit (for example, log(0.0)). The description of each function lists - any required pole errors; an implementation may define additional pole errors, provided - that such errors are consistent with the mathematical definition of the function. On a pole - error, the function returns an implementation-defined value; if the integer expression - - - - math_errhandling & MATH_ERRNO is nonzero, the integer expression errno - acquires the value ERANGE; if the integer expression math_errhandling & - MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised. -

- Likewise, a range error occurs if the mathematical result of the function cannot be - represented in an object of the specified type, due to extreme magnitude. -

- A floating result overflows if the magnitude of the mathematical result is finite but so - large that the mathematical result cannot be represented without extraordinary roundoff - error in an object of the specified type. If a floating result overflows and default rounding - is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or * - HUGE_VALL according to the return type, with the same sign as the correct value of the - function; if the integer expression math_errhandling & MATH_ERRNO is nonzero, - the integer expression errno acquires the value ERANGE; if the integer expression - math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating- - point exception is raised. -

- The result underflows if the magnitude of the mathematical result is so small that the - mathematical result cannot be represented, without extraordinary roundoff error, in an - object of the specified type.229) If the result underflows, the function returns an - implementation-defined value whose magnitude is no greater than the smallest - normalized positive number in the specified type; if the integer expression - math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the - value ERANGE is implementation-defined; if the integer expression - math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow'' - floating-point exception is raised is implementation-defined. -

- If a domain, pole, or range error occurs and the integer expression - math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to - the value corresponding to the error or left unmodified. If no such error occurs, errno - shall be left unmodified regardless of the setting of math_errhandling. - - - - - - -

Footnotes -

228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain - error if the mathematical domain of the function does not include the infinity. - -

229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and - also ''flush-to-zero'' underflow. - -

230) Math errors are being indicated by the floating-point exception flags rather than by errno. - - -

Contents -

7.12.2 The FP_CONTRACT pragma

-

Synopsis -

-

-          #include <math.h>
-          #pragma STDC FP_CONTRACT on-off-switch
-
-

Description -

- The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the - state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur - either outside external declarations or preceding all explicit declarations and statements - inside a compound statement. When outside external declarations, the pragma takes - effect from its occurrence until another FP_CONTRACT pragma is encountered, or until - the end of the translation unit. When inside a compound statement, the pragma takes - effect from its occurrence until another FP_CONTRACT pragma is encountered - (including within a nested compound statement), or until the end of the compound - statement; at the end of a compound statement the state for the pragma is restored to its - condition just before the compound statement. If this pragma is used in any other - context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is - implementation-defined. - -

Contents -

7.12.3 Classification macros

-

- In the synopses in this subclause, real-floating indicates that the argument shall be an - expression of real floating type. - -

Contents -

7.12.3.1 The fpclassify macro
-

Synopsis -

-

-          #include <math.h>
-          int fpclassify(real-floating x);
-
-

Description -

- The fpclassify macro classifies its argument value as NaN, infinite, normal, - subnormal, zero, or into another implementation-defined category. First, an argument - represented in a format wider than its semantic type is converted to its semantic type. - Then classification is based on the type of the argument.231) -

Returns -

- The fpclassify macro returns the value of the number classification macro - appropriate to the value of its argument. * - - - - -

Footnotes -

231) Since an expression can be evaluated with more range and precision than its type has, it is important to - know the type that classification is based on. For example, a normal long double value might - become subnormal when converted to double, and zero when converted to float. - - -

Contents -

7.12.3.2 The isfinite macro
-

Synopsis -

-

-         #include <math.h>
-         int isfinite(real-floating x);
-
-

Description -

- The isfinite macro determines whether its argument has a finite value (zero, - subnormal, or normal, and not infinite or NaN). First, an argument represented in a - format wider than its semantic type is converted to its semantic type. Then determination - is based on the type of the argument. -

Returns -

- The isfinite macro returns a nonzero value if and only if its argument has a finite - value. - -

Contents -

7.12.3.3 The isinf macro
-

Synopsis -

-

-         #include <math.h>
-         int isinf(real-floating x);
-
-

Description -

- The isinf macro determines whether its argument value is an infinity (positive or - negative). First, an argument represented in a format wider than its semantic type is - converted to its semantic type. Then determination is based on the type of the argument. -

Returns -

- The isinf macro returns a nonzero value if and only if its argument has an infinite - value. - -

Contents -

7.12.3.4 The isnan macro
-

Synopsis -

-

-         #include <math.h>
-         int isnan(real-floating x);
-
-

Description -

- The isnan macro determines whether its argument value is a NaN. First, an argument - represented in a format wider than its semantic type is converted to its semantic type. - Then determination is based on the type of the argument.232) - - - -

Returns -

- The isnan macro returns a nonzero value if and only if its argument has a NaN value. - -

Footnotes -

232) For the isnan macro, the type for determination does not matter unless the implementation supports - NaNs in the evaluation type but not in the semantic type. - - -

Contents -

7.12.3.5 The isnormal macro
-

Synopsis -

-

-         #include <math.h>
-         int isnormal(real-floating x);
-
-

Description -

- The isnormal macro determines whether its argument value is normal (neither zero, - subnormal, infinite, nor NaN). First, an argument represented in a format wider than its - semantic type is converted to its semantic type. Then determination is based on the type - of the argument. -

Returns -

- The isnormal macro returns a nonzero value if and only if its argument has a normal - value. - -

Contents -

7.12.3.6 The signbit macro
-

Synopsis -

-

-         #include <math.h>
-         int signbit(real-floating x);
-
-

Description -

- The signbit macro determines whether the sign of its argument value is negative.233) -

Returns -

- The signbit macro returns a nonzero value if and only if the sign of its argument value - is negative. - - - - - - -

Footnotes -

233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is - unsigned, it is treated as positive. - - -

Contents -

7.12.4 Trigonometric functions

- -

Contents -

7.12.4.1 The acos functions
-

Synopsis -

-

-         #include <math.h>
-         double acos(double x);
-         float acosf(float x);
-         long double acosl(long double x);
-
-

Description -

- The acos functions compute the principal value of the arc cosine of x. A domain error - occurs for arguments not in the interval [-1, +1]. -

Returns -

- The acos functions return arccos x in the interval [0, pi ] radians. - -

Contents -

7.12.4.2 The asin functions
-

Synopsis -

-

-         #include <math.h>
-         double asin(double x);
-         float asinf(float x);
-         long double asinl(long double x);
-
-

Description -

- The asin functions compute the principal value of the arc sine of x. A domain error - occurs for arguments not in the interval [-1, +1]. -

Returns -

- The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians. - -

Contents -

7.12.4.3 The atan functions
-

Synopsis -

-

-         #include <math.h>
-         double atan(double x);
-         float atanf(float x);
-         long double atanl(long double x);
-
-

Description -

- The atan functions compute the principal value of the arc tangent of x. - -

Returns -

- The atan functions return arctan x in the interval [-pi /2, +pi /2] radians. - -

Contents -

7.12.4.4 The atan2 functions
-

Synopsis -

-

-        #include <math.h>
-        double atan2(double y, double x);
-        float atan2f(float y, float x);
-        long double atan2l(long double y, long double x);
-
-

Description -

- The atan2 functions compute the value of the arc tangent of y/x, using the signs of both - arguments to determine the quadrant of the return value. A domain error may occur if - both arguments are zero. -

Returns -

- The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians. - -

Contents -

7.12.4.5 The cos functions
-

Synopsis -

-

-        #include <math.h>
-        double cos(double x);
-        float cosf(float x);
-        long double cosl(long double x);
-
-

Description -

- The cos functions compute the cosine of x (measured in radians). -

Returns -

- The cos functions return cos x. - -

Contents -

7.12.4.6 The sin functions
-

Synopsis -

-

-        #include <math.h>
-        double sin(double x);
-        float sinf(float x);
-        long double sinl(long double x);
-
-

Description -

- The sin functions compute the sine of x (measured in radians). - -

Returns -

- The sin functions return sin x. - -

Contents -

7.12.4.7 The tan functions
-

Synopsis -

-

-         #include <math.h>
-         double tan(double x);
-         float tanf(float x);
-         long double tanl(long double x);
-
-

Description -

- The tan functions return the tangent of x (measured in radians). -

Returns -

- The tan functions return tan x. - -

Contents -

7.12.5 Hyperbolic functions

- -

Contents -

7.12.5.1 The acosh functions
-

Synopsis -

-

-         #include <math.h>
-         double acosh(double x);
-         float acoshf(float x);
-         long double acoshl(long double x);
-
-

Description -

- The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain - error occurs for arguments less than 1. -

Returns -

- The acosh functions return arcosh x in the interval [0, +(inf)]. - -

Contents -

7.12.5.2 The asinh functions
-

Synopsis -

-

-         #include <math.h>
-         double asinh(double x);
-         float asinhf(float x);
-         long double asinhl(long double x);
-
-

Description -

- The asinh functions compute the arc hyperbolic sine of x. - -

Returns -

- The asinh functions return arsinh x. - -

Contents -

7.12.5.3 The atanh functions
-

Synopsis -

-

-        #include <math.h>
-        double atanh(double x);
-        float atanhf(float x);
-        long double atanhl(long double x);
-
-

Description -

- The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs - for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals - -1 or +1. -

Returns -

- The atanh functions return artanh x. - -

Contents -

7.12.5.4 The cosh functions
-

Synopsis -

-

-        #include <math.h>
-        double cosh(double x);
-        float coshf(float x);
-        long double coshl(long double x);
-
-

Description -

- The cosh functions compute the hyperbolic cosine of x. A range error occurs if the - magnitude of x is too large. -

Returns -

- The cosh functions return cosh x. - -

Contents -

7.12.5.5 The sinh functions
-

Synopsis -

-

-        #include <math.h>
-        double sinh(double x);
-        float sinhf(float x);
-        long double sinhl(long double x);
-
-

Description -

- The sinh functions compute the hyperbolic sine of x. A range error occurs if the - magnitude of x is too large. - -

Returns -

- The sinh functions return sinh x. - -

Contents -

7.12.5.6 The tanh functions
-

Synopsis -

-

-         #include <math.h>
-         double tanh(double x);
-         float tanhf(float x);
-         long double tanhl(long double x);
-
-

Description -

- The tanh functions compute the hyperbolic tangent of x. -

Returns -

- The tanh functions return tanh x. - -

Contents -

7.12.6 Exponential and logarithmic functions

- -

Contents -

7.12.6.1 The exp functions
-

Synopsis -

-

-         #include <math.h>
-         double exp(double x);
-         float expf(float x);
-         long double expl(long double x);
-
-

Description -

- The exp functions compute the base-e exponential of x. A range error occurs if the - magnitude of x is too large. -

Returns -

- The exp functions return ex . - -

Contents -

7.12.6.2 The exp2 functions
-

Synopsis -

-

-         #include <math.h>
-         double exp2(double x);
-         float exp2f(float x);
-         long double exp2l(long double x);
-
-

Description -

- The exp2 functions compute the base-2 exponential of x. A range error occurs if the - magnitude of x is too large. - -

Returns -

- The exp2 functions return 2x . - -

Contents -

7.12.6.3 The expm1 functions
-

Synopsis -

-

-         #include <math.h>
-         double expm1(double x);
-         float expm1f(float x);
-         long double expm1l(long double x);
-
-

Description -

- The expm1 functions compute the base-e exponential of the argument, minus 1. A range - error occurs if x is too large.234) -

Returns -

- The expm1 functions return ex - 1. - -

Footnotes -

234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1. - - -

Contents -

7.12.6.4 The frexp functions
-

Synopsis -

-

-         #include <math.h>
-         double frexp(double value, int *exp);
-         float frexpf(float value, int *exp);
-         long double frexpl(long double value, int *exp);
-
-

Description -

- The frexp functions break a floating-point number into a normalized fraction and an - integral power of 2. They store the integer in the int object pointed to by exp. -

Returns -

- If value is not a floating-point number or if the integral power of 2 is outside the range - of int, the results are unspecified. Otherwise, the frexp functions return the value x, - such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp . - If value is zero, both parts of the result are zero. - - - - - - -

Contents -

7.12.6.5 The ilogb functions
-

Synopsis -

-

-         #include <math.h>
-         int ilogb(double x);
-         int ilogbf(float x);
-         int ilogbl(long double x);
-
-

Description -

- The ilogb functions extract the exponent of x as a signed int value. If x is zero they - compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is - a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling - the corresponding logb function and casting the returned value to type int. A domain - error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside - the range of the return type, the numeric result is unspecified. -

Returns -

- The ilogb functions return the exponent of x as a signed int value. -

Forward references: the logb functions (7.12.6.11). - -

Contents -

7.12.6.6 The ldexp functions
-

Synopsis -

-

-         #include <math.h>
-         double ldexp(double x, int exp);
-         float ldexpf(float x, int exp);
-         long double ldexpl(long double x, int exp);
-
-

Description -

- The ldexp functions multiply a floating-point number by an integral power of 2. A - range error may occur. -

Returns -

- The ldexp functions return x x 2exp . - -

Contents -

7.12.6.7 The log functions
-

Synopsis -

- -

-         #include <math.h>
-         double log(double x);
-         float logf(float x);
-         long double logl(long double x);
-
-

Description -

- The log functions compute the base-e (natural) logarithm of x. A domain error occurs if - the argument is negative. A pole error may occur if the argument is zero. -

Returns -

- The log functions return loge x. - -

Contents -

7.12.6.8 The log10 functions
-

Synopsis -

-

-         #include <math.h>
-         double log10(double x);
-         float log10f(float x);
-         long double log10l(long double x);
-
-

Description -

- The log10 functions compute the base-10 (common) logarithm of x. A domain error - occurs if the argument is negative. A pole error may occur if the argument is zero. -

Returns -

- The log10 functions return log10 x. - -

Contents -

7.12.6.9 The log1p functions
-

Synopsis -

-

-         #include <math.h>
-         double log1p(double x);
-         float log1pf(float x);
-         long double log1pl(long double x);
-
-

Description -

- The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235) - A domain error occurs if the argument is less than -1. A pole error may occur if the - argument equals -1. -

Returns -

- The log1p functions return loge (1 + x). - - - - - - -

Footnotes -

235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x). - - -

Contents -

7.12.6.10 The log2 functions
-

Synopsis -

-

-         #include <math.h>
-         double log2(double x);
-         float log2f(float x);
-         long double log2l(long double x);
-
-

Description -

- The log2 functions compute the base-2 logarithm of x. A domain error occurs if the - argument is less than zero. A pole error may occur if the argument is zero. -

Returns -

- The log2 functions return log2 x. - -

Contents -

7.12.6.11 The logb functions
-

Synopsis -

-

-         #include <math.h>
-         double logb(double x);
-         float logbf(float x);
-         long double logbl(long double x);
-
-

Description -

- The logb functions extract the exponent of x, as a signed integer value in floating-point - format. If x is subnormal it is treated as though it were normalized; thus, for positive - finite x, -

-       1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
-
- A domain error or pole error may occur if the argument is zero. -

Returns -

- The logb functions return the signed exponent of x. - -

Contents -

7.12.6.12 The modf functions
-

Synopsis -

-

-         #include <math.h>
-         double modf(double value, double *iptr);
-         float modff(float value, float *iptr);
-         long double modfl(long double value, long double *iptr);
-
-

Description -

- The modf functions break the argument value into integral and fractional parts, each of - which has the same type and sign as the argument. They store the integral part (in - - floating-point format) in the object pointed to by iptr. -

Returns -

- The modf functions return the signed fractional part of value. - -

Contents -

7.12.6.13 The scalbn and scalbln functions
-

Synopsis -

-

-        #include <math.h>
-        double scalbn(double x, int n);
-        float scalbnf(float x, int n);
-        long double scalbnl(long double x, int n);
-        double scalbln(double x, long int n);
-        float scalblnf(float x, long int n);
-        long double scalblnl(long double x, long int n);
-
-

Description -

- The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not - normally by computing FLT_RADIXn explicitly. A range error may occur. -

Returns -

- The scalbn and scalbln functions return x x FLT_RADIXn . - -

Contents -

7.12.7 Power and absolute-value functions

- -

Contents -

7.12.7.1 The cbrt functions
-

Synopsis -

-

-        #include <math.h>
-        double cbrt(double x);
-        float cbrtf(float x);
-        long double cbrtl(long double x);
-
-

Description -

- The cbrt functions compute the real cube root of x. -

Returns -

- The cbrt functions return x1/3 . - - -

Contents -

7.12.7.2 The fabs functions
-

Synopsis -

-

-         #include <math.h>
-         double fabs(double x);
-         float fabsf(float x);
-         long double fabsl(long double x);
-
-

Description -

- The fabs functions compute the absolute value of a floating-point number x. -

Returns -

- The fabs functions return | x |. - -

Contents -

7.12.7.3 The hypot functions
-

Synopsis -

-

-         #include <math.h>
-         double hypot(double x, double y);
-         float hypotf(float x, float y);
-         long double hypotl(long double x, long double y);
-
-

Description -

- The hypot functions compute the square root of the sum of the squares of x and y, - without undue overflow or underflow. A range error may occur. -

-

Returns -

- The hypot functions return (sqrt)x2 + y2 . -

-                            -
-                            -----
-
- -

Contents -

7.12.7.4 The pow functions
-

Synopsis -

-

-         #include <math.h>
-         double pow(double x, double y);
-         float powf(float x, float y);
-         long double powl(long double x, long double y);
-
-

Description -

- The pow functions compute x raised to the power y. A domain error occurs if x is finite - and negative and y is finite and not an integer value. A range error may occur. A domain - error may occur if x is zero and y is zero. A domain error or pole error may occur if x is - zero and y is less than zero. - -

Returns -

- The pow functions return xy . - -

Contents -

7.12.7.5 The sqrt functions
-

Synopsis -

-

-        #include <math.h>
-        double sqrt(double x);
-        float sqrtf(float x);
-        long double sqrtl(long double x);
-
-

Description -

- The sqrt functions compute the nonnegative square root of x. A domain error occurs if - the argument is less than zero. -

Returns -

- The sqrt functions return (sqrt)x. -

-                           -
-                           -
-
- -

Contents -

7.12.8 Error and gamma functions

- -

Contents -

7.12.8.1 The erf functions
-

Synopsis -

-

-        #include <math.h>
-        double erf(double x);
-        float erff(float x);
-        long double erfl(long double x);
-
-

Description -

- The erf functions compute the error function of x. -

Returns -

-

-                                    2        x
-                                         (integral)       e-t dt.
-                                                   2
-
- The erf functions return erf x = -
-                                    (sqrt)pi
-                                    -
-                                    -    0
-
- - -

Contents -

7.12.8.2 The erfc functions
-

Synopsis -

-

-        #include <math.h>
-        double erfc(double x);
-        float erfcf(float x);
-        long double erfcl(long double x);
-
-

Description -

- The erfc functions compute the complementary error function of x. A range error - occurs if x is too large. - -

Returns -

-

-                                                     2       (inf)
-                                                         (integral)       e-t dt.
-                                                                   2
-
- The erfc functions return erfc x = 1 - erf x = -
-                                                  (sqrt)pi
-                                                  -
-                                                  -      x
-
- - -

Contents -

7.12.8.3 The lgamma functions
-

Synopsis -

-

-         #include <math.h>
-         double lgamma(double x);
-         float lgammaf(float x);
-         long double lgammal(long double x);
-
-

Description -

- The lgamma functions compute the natural logarithm of the absolute value of gamma of - x. A range error occurs if x is too large. A pole error may occur if x is a negative integer - or zero. -

Returns -

- The lgamma functions return loge | (Gamma)(x) |. - -

Contents -

7.12.8.4 The tgamma functions
-

Synopsis -

-

-         #include <math.h>
-         double tgamma(double x);
-         float tgammaf(float x);
-         long double tgammal(long double x);
-
-

Description -

- The tgamma functions compute the gamma function of x. A domain error or pole error - may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is - too large and may occur if the magnitude of x is too small. -

Returns -

- The tgamma functions return (Gamma)(x). - - -

Contents -

7.12.9 Nearest integer functions

- -

Contents -

7.12.9.1 The ceil functions
-

Synopsis -

-

-        #include <math.h>
-        double ceil(double x);
-        float ceilf(float x);
-        long double ceill(long double x);
-
-

Description -

- The ceil functions compute the smallest integer value not less than x. -

Returns -

- The ceil functions return [^x^], expressed as a floating-point number. - -

Contents -

7.12.9.2 The floor functions
-

Synopsis -

-

-        #include <math.h>
-        double floor(double x);
-        float floorf(float x);
-        long double floorl(long double x);
-
-

Description -

- The floor functions compute the largest integer value not greater than x. -

Returns -

- The floor functions return [_x_], expressed as a floating-point number. - -

Contents -

7.12.9.3 The nearbyint functions
-

Synopsis -

-

-        #include <math.h>
-        double nearbyint(double x);
-        float nearbyintf(float x);
-        long double nearbyintl(long double x);
-
-

Description -

- The nearbyint functions round their argument to an integer value in floating-point - format, using the current rounding direction and without raising the ''inexact'' floating- - point exception. - -

Returns -

- The nearbyint functions return the rounded integer value. - -

Contents -

7.12.9.4 The rint functions
-

Synopsis -

-

-         #include <math.h>
-         double rint(double x);
-         float rintf(float x);
-         long double rintl(long double x);
-
-

Description -

- The rint functions differ from the nearbyint functions (7.12.9.3) only in that the - rint functions may raise the ''inexact'' floating-point exception if the result differs in - value from the argument. -

Returns -

- The rint functions return the rounded integer value. - -

Contents -

7.12.9.5 The lrint and llrint functions
-

Synopsis -

-

-         #include <math.h>
-         long int lrint(double x);
-         long int lrintf(float x);
-         long int lrintl(long double x);
-         long long int llrint(double x);
-         long long int llrintf(float x);
-         long long int llrintl(long double x);
-
-

Description -

- The lrint and llrint functions round their argument to the nearest integer value, - rounding according to the current rounding direction. If the rounded value is outside the - range of the return type, the numeric result is unspecified and a domain error or range - error may occur. -

Returns -

- The lrint and llrint functions return the rounded integer value. - - -

Contents -

7.12.9.6 The round functions
-

Synopsis -

-

-        #include <math.h>
-        double round(double x);
-        float roundf(float x);
-        long double roundl(long double x);
-
-

Description -

- The round functions round their argument to the nearest integer value in floating-point - format, rounding halfway cases away from zero, regardless of the current rounding - direction. -

Returns -

- The round functions return the rounded integer value. - -

Contents -

7.12.9.7 The lround and llround functions
-

Synopsis -

-

-        #include <math.h>
-        long int lround(double x);
-        long int lroundf(float x);
-        long int lroundl(long double x);
-        long long int llround(double x);
-        long long int llroundf(float x);
-        long long int llroundl(long double x);
-
-

Description -

- The lround and llround functions round their argument to the nearest integer value, - rounding halfway cases away from zero, regardless of the current rounding direction. If - the rounded value is outside the range of the return type, the numeric result is unspecified - and a domain error or range error may occur. -

Returns -

- The lround and llround functions return the rounded integer value. - -

Contents -

7.12.9.8 The trunc functions
-

Synopsis -

- -

-        #include <math.h>
-        double trunc(double x);
-        float truncf(float x);
-        long double truncl(long double x);
-
-

Description -

- The trunc functions round their argument to the integer value, in floating format, - nearest to but no larger in magnitude than the argument. -

Returns -

- The trunc functions return the truncated integer value. - -

Contents -

7.12.10 Remainder functions

- -

Contents -

7.12.10.1 The fmod functions
-

Synopsis -

-

-          #include <math.h>
-          double fmod(double x, double y);
-          float fmodf(float x, float y);
-          long double fmodl(long double x, long double y);
-
-

Description -

- The fmod functions compute the floating-point remainder of x/y. -

Returns -

- The fmod functions return the value x - ny, for some integer n such that, if y is nonzero, - the result has the same sign as x and magnitude less than the magnitude of y. If y is zero, - whether a domain error occurs or the fmod functions return zero is implementation- - defined. - -

Contents -

7.12.10.2 The remainder functions
-

Synopsis -

-

-          #include <math.h>
-          double remainder(double x, double y);
-          float remainderf(float x, float y);
-          long double remainderl(long double x, long double y);
-
-

Description -

- The remainder functions compute the remainder x REM y required by IEC 60559.236) - - - - - -

Returns -

- The remainder functions return x REM y. If y is zero, whether a domain error occurs - or the functions return zero is implementation defined. - -

Footnotes -

236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the - mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever - | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for * - all implementations. - - -

Contents -

7.12.10.3 The remquo functions
-

Synopsis -

-

-        #include <math.h>
-        double remquo(double x, double y, int *quo);
-        float remquof(float x, float y, int *quo);
-        long double remquol(long double x, long double y,
-             int *quo);
-
-

Description -

- The remquo functions compute the same remainder as the remainder functions. In - the object pointed to by quo they store a value whose sign is the sign of x/y and whose - magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where - n is an implementation-defined integer greater than or equal to 3. -

Returns -

- The remquo functions return x REM y. If y is zero, the value stored in the object - pointed to by quo is unspecified and whether a domain error occurs or the functions - return zero is implementation defined. - -

Contents -

7.12.11 Manipulation functions

- -

Contents -

7.12.11.1 The copysign functions
-

Synopsis -

-

-        #include <math.h>
-        double copysign(double x, double y);
-        float copysignf(float x, float y);
-        long double copysignl(long double x, long double y);
-
-

Description -

- The copysign functions produce a value with the magnitude of x and the sign of y. - They produce a NaN (with the sign of y) if x is a NaN. On implementations that - represent a signed zero but do not treat negative zero consistently in arithmetic - operations, the copysign functions regard the sign of zero as positive. -

Returns -

- The copysign functions return a value with the magnitude of x and the sign of y. - - -

Contents -

7.12.11.2 The nan functions
-

Synopsis -

-

-         #include <math.h>
-         double nan(const char *tagp);
-         float nanf(const char *tagp);
-         long double nanl(const char *tagp);
-
-

Description -

- The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char- - sequence)", (char**) NULL); the call nan("") is equivalent to - strtod("NAN()", (char**) NULL). If tagp does not point to an n-char - sequence or an empty string, the call is equivalent to strtod("NAN", (char**) - NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof - and strtold. -

Returns -

- The nan functions return a quiet NaN, if available, with content indicated through tagp. - If the implementation does not support quiet NaNs, the functions return zero. -

Forward references: the strtod, strtof, and strtold functions (7.22.1.3). - -

Contents -

7.12.11.3 The nextafter functions
-

Synopsis -

-

-         #include <math.h>
-         double nextafter(double x, double y);
-         float nextafterf(float x, float y);
-         long double nextafterl(long double x, long double y);
-
-

Description -

- The nextafter functions determine the next representable value, in the type of the - function, after x in the direction of y, where x and y are first converted to the type of the - function.237) The nextafter functions return y if x equals y. A range error may occur - if the magnitude of x is the largest finite value representable in the type and the result is - infinite or not representable in the type. -

Returns -

- The nextafter functions return the next representable value in the specified format - after x in the direction of y. - - - - -

Footnotes -

237) The argument values are converted to the type of the function, even by a macro implementation of the - function. - - -

Contents -

7.12.11.4 The nexttoward functions
-

Synopsis -

-

-         #include <math.h>
-         double nexttoward(double x, long double y);
-         float nexttowardf(float x, long double y);
-         long double nexttowardl(long double x, long double y);
-
-

Description -

- The nexttoward functions are equivalent to the nextafter functions except that the - second parameter has type long double and the functions return y converted to the - type of the function if x equals y.238) - -

Footnotes -

238) The result of the nexttoward functions is determined in the type of the function, without loss of - range or precision in a floating second argument. - - -

Contents -

7.12.12 Maximum, minimum, and positive difference functions

- -

Contents -

7.12.12.1 The fdim functions
-

Synopsis -

-

-         #include <math.h>
-         double fdim(double x, double y);
-         float fdimf(float x, float y);
-         long double fdiml(long double x, long double y);
-
-

Description -

- The fdim functions determine the positive difference between their arguments: -

-       {x - y if x > y
-       {
-       {+0     if x <= y
-
- A range error may occur. -

Returns -

- The fdim functions return the positive difference value. - -

Contents -

7.12.12.2 The fmax functions
-

Synopsis -

-

-         #include <math.h>
-         double fmax(double x, double y);
-         float fmaxf(float x, float y);
-         long double fmaxl(long double x, long double y);
-
- - - - -

Description -

- The fmax functions determine the maximum numeric value of their arguments.239) -

Returns -

- The fmax functions return the maximum numeric value of their arguments. - -

Footnotes -

239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the - fmax functions choose the numeric value. See F.10.9.2. - - -

Contents -

7.12.12.3 The fmin functions
-

Synopsis -

-

-         #include <math.h>
-         double fmin(double x, double y);
-         float fminf(float x, float y);
-         long double fminl(long double x, long double y);
-
-

Description -

- The fmin functions determine the minimum numeric value of their arguments.240) -

Returns -

- The fmin functions return the minimum numeric value of their arguments. - -

Footnotes -

240) The fmin functions are analogous to the fmax functions in their treatment of NaNs. - - -

Contents -

7.12.13 Floating multiply-add

- -

Contents -

7.12.13.1 The fma functions
-

Synopsis -

-

-         #include <math.h>
-         double fma(double x, double y, double z);
-         float fmaf(float x, float y, float z);
-         long double fmal(long double x, long double y,
-              long double z);
-
-

Description -

- The fma functions compute (x x y) + z, rounded as one ternary operation: they compute - the value (as if) to infinite precision and round once to the result format, according to the - current rounding mode. A range error may occur. -

Returns -

- The fma functions return (x x y) + z, rounded as one ternary operation. - - - - - - -

Contents -

7.12.14 Comparison macros

-

- The relational and equality operators support the usual mathematical relationships - between numeric values. For any ordered pair of numeric values exactly one of the - relationships -- less, greater, and equal -- is true. Relational operators may raise the - ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a - numeric value, or for two NaNs, just the unordered relationship is true.241) The following - subclauses provide macros that are quiet (non floating-point exception raising) versions - of the relational operators, and other comparison macros that facilitate writing efficient - code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In - the synopses in this subclause, real-floating indicates that the argument shall be an - expression of real floating type242) (both arguments need not have the same type).243) - -

Footnotes -

241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if - the operands compare unordered, as an error indicator for programs written without consideration of - NaNs; the result in these cases is false. - -

242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is - undefined. - -

243) Whether an argument represented in a format wider than its semantic type is converted to the semantic - type is unspecified. - - -

Contents -

7.12.14.1 The isgreater macro
-

Synopsis -

-

-          #include <math.h>
-          int isgreater(real-floating x, real-floating y);
-
-

Description -

- The isgreater macro determines whether its first argument is greater than its second - argument. The value of isgreater(x, y) is always equal to (x) > (y); however, - unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point - exception when x and y are unordered. -

Returns -

- The isgreater macro returns the value of (x) > (y). - -

Contents -

7.12.14.2 The isgreaterequal macro
-

Synopsis -

-

-          #include <math.h>
-          int isgreaterequal(real-floating x, real-floating y);
-
- - - - - -

Description -

- The isgreaterequal macro determines whether its first argument is greater than or - equal to its second argument. The value of isgreaterequal(x, y) is always equal - to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does - not raise the ''invalid'' floating-point exception when x and y are unordered. -

Returns -

- The isgreaterequal macro returns the value of (x) >= (y). - -

Contents -

7.12.14.3 The isless macro
-

Synopsis -

-

-         #include <math.h>
-         int isless(real-floating x, real-floating y);
-
-

Description -

- The isless macro determines whether its first argument is less than its second - argument. The value of isless(x, y) is always equal to (x) < (y); however, - unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point - exception when x and y are unordered. -

Returns -

- The isless macro returns the value of (x) < (y). - -

Contents -

7.12.14.4 The islessequal macro
-

Synopsis -

-

-         #include <math.h>
-         int islessequal(real-floating x, real-floating y);
-
-

Description -

- The islessequal macro determines whether its first argument is less than or equal to - its second argument. The value of islessequal(x, y) is always equal to - (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise - the ''invalid'' floating-point exception when x and y are unordered. -

Returns -

- The islessequal macro returns the value of (x) <= (y). - - -

Contents -

7.12.14.5 The islessgreater macro
-

Synopsis -

-

-        #include <math.h>
-        int islessgreater(real-floating x, real-floating y);
-
-

Description -

- The islessgreater macro determines whether its first argument is less than or - greater than its second argument. The islessgreater(x, y) macro is similar to - (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise - the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x - and y twice). -

Returns -

- The islessgreater macro returns the value of (x) < (y) || (x) > (y). - -

Contents -

7.12.14.6 The isunordered macro
-

Synopsis -

-

-        #include <math.h>
-        int isunordered(real-floating x, real-floating y);
-
-

Description -

- The isunordered macro determines whether its arguments are unordered. -

Returns -

- The isunordered macro returns 1 if its arguments are unordered and 0 otherwise. - - -

Contents -

7.13 Nonlocal jumps <setjmp.h>

-

- The header <setjmp.h> defines the macro setjmp, and declares one function and - one type, for bypassing the normal function call and return discipline.244) -

- The type declared is -

-         jmp_buf
-
- which is an array type suitable for holding the information needed to restore a calling - environment. The environment of a call to the setjmp macro consists of information - sufficient for a call to the longjmp function to return execution to the correct block and - invocation of that block, were it called recursively. It does not include the state of the - floating-point status flags, of open files, or of any other component of the abstract - machine. -

- It is unspecified whether setjmp is a macro or an identifier declared with external - linkage. If a macro definition is suppressed in order to access an actual function, or a - program defines an external identifier with the name setjmp, the behavior is undefined. - -

Footnotes -

244) These functions are useful for dealing with unusual conditions encountered in a low-level function of - a program. - - -

Contents -

7.13.1 Save calling environment

- -

Contents -

7.13.1.1 The setjmp macro
-

Synopsis -

-

-         #include <setjmp.h>
-         int setjmp(jmp_buf env);
-
-

Description -

- The setjmp macro saves its calling environment in its jmp_buf argument for later use - by the longjmp function. -

Returns -

- If the return is from a direct invocation, the setjmp macro returns the value zero. If the - return is from a call to the longjmp function, the setjmp macro returns a nonzero - value. -

Environmental limits -

- An invocation of the setjmp macro shall appear only in one of the following contexts: -

-

- If the invocation appears in any other context, the behavior is undefined. - -

Contents -

7.13.2 Restore calling environment

- -

Contents -

7.13.2.1 The longjmp function
-

Synopsis -

-

-          #include <setjmp.h>
-          _Noreturn void longjmp(jmp_buf env, int val);
-
-

Description -

- The longjmp function restores the environment saved by the most recent invocation of - the setjmp macro in the same invocation of the program with the corresponding - jmp_buf argument. If there has been no such invocation, or if the function containing - the invocation of the setjmp macro has terminated execution245) in the interim, or if the - invocation of the setjmp macro was within the scope of an identifier with variably - modified type and execution has left that scope in the interim, the behavior is undefined. -

- All accessible objects have values, and all other components of the abstract machine246) - have state, as of the time the longjmp function was called, except that the values of - objects of automatic storage duration that are local to the function containing the - invocation of the corresponding setjmp macro that do not have volatile-qualified type - and have been changed between the setjmp invocation and longjmp call are - indeterminate. -

Returns -

- After longjmp is completed, program execution continues as if the corresponding - invocation of the setjmp macro had just returned the value specified by val. The - longjmp function cannot cause the setjmp macro to return the value 0; if val is 0, - the setjmp macro returns the value 1. -

- EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation - might cause memory associated with a variable length array object to be squandered. - - - - - - -

-         #include <setjmp.h>
-         jmp_buf buf;
-         void g(int n);
-         void h(int n);
-         int n = 6;
-         void f(void)
-         {
-               int x[n];          // valid: f is not terminated
-               setjmp(buf);
-               g(n);
-         }
-         void g(int n)
-         {
-               int a[n];          // a may remain allocated
-               h(n);
-         }
-         void h(int n)
-         {
-               int b[n];          // b may remain allocated
-               longjmp(buf, 2);   // might cause memory loss
-         }
-
- -

Footnotes -

245) For example, by executing a return statement or because another longjmp call has caused a - transfer to a setjmp invocation in a function earlier in the set of nested calls. - -

246) This includes, but is not limited to, the floating-point status flags and the state of open files. - - -

Contents -

7.14 Signal handling <signal.h>

-

- The header <signal.h> declares a type and two functions and defines several macros, - for handling various signals (conditions that may be reported during program execution). -

- The type defined is -

-          sig_atomic_t
-
- which is the (possibly volatile-qualified) integer type of an object that can be accessed as - an atomic entity, even in the presence of asynchronous interrupts. -

- The macros defined are -

-          SIG_DFL
-          SIG_ERR
-          SIG_IGN
-
- which expand to constant expressions with distinct values that have type compatible with - the second argument to, and the return value of, the signal function, and whose values - compare unequal to the address of any declarable function; and the following, which - expand to positive integer constant expressions with type int and distinct values that are - the signal numbers, each corresponding to the specified condition: -
-          SIGABRT abnormal termination, such as is initiated by the abort function
-          SIGFPE        an erroneous arithmetic operation, such as zero divide or an operation
-                        resulting in overflow
-          SIGILL        detection of an invalid function image, such as an invalid instruction
-          SIGINT        receipt of an interactive attention signal
-          SIGSEGV an invalid access to storage
-          SIGTERM a termination request sent to the program
-
-

- An implementation need not generate any of these signals, except as a result of explicit - calls to the raise function. Additional signals and pointers to undeclarable functions, - with macro definitions beginning, respectively, with the letters SIG and an uppercase - letter or with SIG_ and an uppercase letter,247) may also be specified by the - implementation. The complete set of signals, their semantics, and their default handling - is implementation-defined; all signal numbers shall be positive. - - - - - - -

Footnotes -

247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms - (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation, - and termination. - - -

Contents -

7.14.1 Specify signal handling

- -

Contents -

7.14.1.1 The signal function
-

Synopsis -

-

-         #include <signal.h>
-         void (*signal(int sig, void (*func)(int)))(int);
-
-

Description -

- The signal function chooses one of three ways in which receipt of the signal number - sig is to be subsequently handled. If the value of func is SIG_DFL, default handling - for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored. - Otherwise, func shall point to a function to be called when that signal occurs. An - invocation of such a function because of a signal, or (recursively) of any further functions - called by that invocation (other than functions in the standard library),248) is called a - signal handler. -

- When a signal occurs and func points to a function, it is implementation-defined - whether the equivalent of signal(sig, SIG_DFL); is executed or the - implementation prevents some implementation-defined set of signals (at least including - sig) from occurring until the current signal handling has completed; in the case of - SIGILL, the implementation may alternatively define that no action is taken. Then the - equivalent of (*func)(sig); is executed. If and when the function returns, if the - value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined - value corresponding to a computational exception, the behavior is undefined; otherwise - the program will resume execution at the point it was interrupted. -

- If the signal occurs as the result of calling the abort or raise function, the signal - handler shall not call the raise function. -

- If the signal occurs other than as the result of calling the abort or raise function, the - behavior is undefined if the signal handler refers to any object with static or thread - storage duration that is not a lock-free atomic object other than by assigning a value to an - object declared as volatile sig_atomic_t, or the signal handler calls any function - in the standard library other than the abort function, the _Exit function, the - quick_exit function, or the signal function with the first argument equal to the - signal number corresponding to the signal that caused the invocation of the handler. - Furthermore, if such a call to the signal function results in a SIG_ERR return, the - value of errno is indeterminate.249) - - - -

- At program startup, the equivalent of -

-        signal(sig, SIG_IGN);
-
- may be executed for some signals selected in an implementation-defined manner; the - equivalent of -
-        signal(sig, SIG_DFL);
-
- is executed for all other signals defined by the implementation. -

- The implementation shall behave as if no library function calls the signal function. -

Returns -

- If the request can be honored, the signal function returns the value of func for the - most recent successful call to signal for the specified signal sig. Otherwise, a value of - SIG_ERR is returned and a positive value is stored in errno. -

Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the - _Exit function (7.22.4.5), the quick_exit function (7.22.4.7). - -

Footnotes -

248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler - called via the abort function). - -

249) If any signal is generated by an asynchronous signal handler, the behavior is undefined. - - -

Contents -

7.14.2 Send signal

- -

Contents -

7.14.2.1 The raise function
-

Synopsis -

-

-        #include <signal.h>
-        int raise(int sig);
-
-

Description -

- The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a - signal handler is called, the raise function shall not return until after the signal handler - does. -

Returns -

- The raise function returns zero if successful, nonzero if unsuccessful. - - -

Contents -

7.15 Alignment <stdalign.h>

-

- The header <stdalign.h> defines two macros. -

- The macro -

-         alignas
-
- expands to _Alignas. -

- The remaining macro is suitable for use in #if preprocessing directives. It is -

-         __alignas_is_defined
-
- which expands to the integer constant 1. - - -

Contents -

7.16 Variable arguments <stdarg.h>

-

- The header <stdarg.h> declares a type and defines four macros, for advancing - through a list of arguments whose number and types are not known to the called function - when it is translated. -

- A function may be called with a variable number of arguments of varying types. As - described in 6.9.1, its parameter list contains one or more parameters. The rightmost - parameter plays a special role in the access mechanism, and will be designated parmN in - this description. -

- The type declared is -

-         va_list
-
- which is a complete object type suitable for holding information needed by the macros - va_start, va_arg, va_end, and va_copy. If access to the varying arguments is - desired, the called function shall declare an object (generally referred to as ap in this - subclause) having type va_list. The object ap may be passed as an argument to - another function; if that function invokes the va_arg macro with parameter ap, the - value of ap in the calling function is indeterminate and shall be passed to the va_end - macro prior to any further reference to ap.250) - -

Footnotes -

250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which - case the original function may make further use of the original list after the other function returns. - - -

Contents -

7.16.1 Variable argument list access macros

-

- The va_start and va_arg macros described in this subclause shall be implemented - as macros, not functions. It is unspecified whether va_copy and va_end are macros or - identifiers declared with external linkage. If a macro definition is suppressed in order to - access an actual function, or a program defines an external identifier with the same name, - the behavior is undefined. Each invocation of the va_start and va_copy macros - shall be matched by a corresponding invocation of the va_end macro in the same - function. - -

Contents -

7.16.1.1 The va_arg macro
-

Synopsis -

-

-         #include <stdarg.h>
-         type va_arg(va_list ap, type);
-
-

Description -

- The va_arg macro expands to an expression that has the specified type and the value of - the next argument in the call. The parameter ap shall have been initialized by the - va_start or va_copy macro (without an intervening invocation of the va_end - - - macro for the same ap). Each invocation of the va_arg macro modifies ap so that the - values of successive arguments are returned in turn. The parameter type shall be a type - name specified such that the type of a pointer to an object that has the specified type can - be obtained simply by postfixing a * to type. If there is no actual next argument, or if - type is not compatible with the type of the actual next argument (as promoted according - to the default argument promotions), the behavior is undefined, except for the following - cases: -

-

Returns -

- The first invocation of the va_arg macro after that of the va_start macro returns the - value of the argument after that specified by parmN . Successive invocations return the - values of the remaining arguments in succession. - -

Contents -

7.16.1.2 The va_copy macro
-

Synopsis -

-

-         #include <stdarg.h>
-         void va_copy(va_list dest, va_list src);
-
-

Description -

- The va_copy macro initializes dest as a copy of src, as if the va_start macro had - been applied to dest followed by the same sequence of uses of the va_arg macro as - had previously been used to reach the present state of src. Neither the va_copy nor - va_start macro shall be invoked to reinitialize dest without an intervening - invocation of the va_end macro for the same dest. -

Returns -

- The va_copy macro returns no value. - -

Contents -

7.16.1.3 The va_end macro
-

Synopsis -

-

-         #include <stdarg.h>
-         void va_end(va_list ap);
-
-

Description -

- The va_end macro facilitates a normal return from the function whose variable - argument list was referred to by the expansion of the va_start macro, or the function - containing the expansion of the va_copy macro, that initialized the va_list ap. The - va_end macro may modify ap so that it is no longer usable (without being reinitialized - - by the va_start or va_copy macro). If there is no corresponding invocation of the - va_start or va_copy macro, or if the va_end macro is not invoked before the - return, the behavior is undefined. -

Returns -

- The va_end macro returns no value. - -

Contents -

7.16.1.4 The va_start macro
-

Synopsis -

-

-         #include <stdarg.h>
-         void va_start(va_list ap, parmN);
-
-

Description -

- The va_start macro shall be invoked before any access to the unnamed arguments. -

- The va_start macro initializes ap for subsequent use by the va_arg and va_end - macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap - without an intervening invocation of the va_end macro for the same ap. -

- The parameter parmN is the identifier of the rightmost parameter in the variable - parameter list in the function definition (the one just before the , ...). If the parameter - parmN is declared with the register storage class, with a function or array type, or - with a type that is not compatible with the type that results after application of the default - argument promotions, the behavior is undefined. -

Returns -

- The va_start macro returns no value. -

- EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not - more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of - pointers is specified by the first argument to f1. - -

-         #include <stdarg.h>
-         #define MAXARGS   31
-         void f1(int n_ptrs, ...)
-         {
-               va_list ap;
-               char *array[MAXARGS];
-               int ptr_no = 0;
-                   if (n_ptrs > MAXARGS)
-                         n_ptrs = MAXARGS;
-                   va_start(ap, n_ptrs);
-                   while (ptr_no < n_ptrs)
-                         array[ptr_no++] = va_arg(ap, char *);
-                   va_end(ap);
-                   f2(n_ptrs, array);
-          }
-
- Each call to f1 is required to have visible the definition of the function or a declaration such as -
-          void f1(int, ...);
-
- -

- EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the - indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list - is gathered again and passed to function f4. - -

-          #include <stdarg.h>
-          #define MAXARGS 31
-          void f3(int n_ptrs, int f4_after, ...)
-          {
-                va_list ap, ap_save;
-                char *array[MAXARGS];
-                int ptr_no = 0;
-                if (n_ptrs > MAXARGS)
-                      n_ptrs = MAXARGS;
-                va_start(ap, f4_after);
-                while (ptr_no < n_ptrs) {
-                      array[ptr_no++] = va_arg(ap, char *);
-                      if (ptr_no == f4_after)
-                            va_copy(ap_save, ap);
-                }
-                va_end(ap);
-                f2(n_ptrs, array);
-                   // Now process the saved copy.
-                   n_ptrs -= f4_after;
-                   ptr_no = 0;
-                   while (ptr_no < n_ptrs)
-                         array[ptr_no++] = va_arg(ap_save, char *);
-                   va_end(ap_save);
-                   f4(n_ptrs, array);
-          }
-
- -

Contents -

7.17 Atomics <stdatomic.h>

- -

Contents -

7.17.1 Introduction

-

- The header <stdatomic.h> defines several macros and declares several types and - functions for performing atomic operations on data shared between threads. -

- Implementations that define the macro __STDC_NO_THREADS__ need not provide - this header nor support any of its facilities. -

- The macros defined are the atomic lock-free macros -

-        ATOMIC_CHAR_LOCK_FREE
-        ATOMIC_CHAR16_T_LOCK_FREE
-        ATOMIC_CHAR32_T_LOCK_FREE
-        ATOMIC_WCHAR_T_LOCK_FREE
-        ATOMIC_SHORT_LOCK_FREE
-        ATOMIC_INT_LOCK_FREE
-        ATOMIC_LONG_LOCK_FREE
-        ATOMIC_LLONG_LOCK_FREE
-        ATOMIC_ADDRESS_LOCK_FREE
-
- which indicate the lock-free property of the corresponding atomic types (both signed and - unsigned); and -
-        ATOMIC_FLAG_INIT
-
- which expands to an initializer for an object of type atomic_flag. -

- The types include -

-        memory_order
-
- which is an enumerated type whose enumerators identify memory ordering constraints; -
-        atomic_flag
-
- which is a structure type representing a lock-free, primitive atomic flag; -
-        atomic_bool
-
- which is a structure type representing the atomic analog of the type _Bool; -
-        atomic_address
-
- which is a structure type representing the atomic analog of a pointer type; and several - atomic analogs of integer types. -

- In the following operation definitions: -

-

- NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not - changed in the standard. This qualification means that volatility is preserved when applying these - operations to volatile objects. - - -

Contents -

7.17.2 Initialization

- -

Contents -

7.17.2.1 The ATOMIC_VAR_INIT macro
-

Synopsis -

-

-         #include <stdatomic.h>
-         #define ATOMIC_VAR_INIT(C value)
-
-

Description -

- The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an - atomic object of a type that is initialization-compatible with value. An atomic object - with automatic storage duration that is not explicitly initialized using - ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero) - initialization for objects with static or thread-local storage duration is guaranteed to - produce a valid state. -

- Concurrent access to the variable being initialized, even via an atomic operation, - constitutes a data race. -

- EXAMPLE -

-         atomic_int guide = ATOMIC_VAR_INIT(42);
-
- - -

Contents -

7.17.2.2 The atomic_init generic function
-

Synopsis -

-

-         #include <stdatomic.h>
-         void atomic_init(volatile A *obj, C value);
-
-

Description -

- The atomic_init generic function initializes the atomic object pointed to by obj to - the value value, while also initializing any additional state that the implementation - might need to carry for the atomic object. - -

- Although this function initializes an atomic object, it does not avoid data races; - concurrent access to the variable being initialized, even via an atomic operation, - constitutes a data race. -

Returns -

- The atomic_init generic function returns no value. -

- EXAMPLE -

-         atomic_int guide;
-         atomic_init(&guide, 42);
-
- - -

Contents -

7.17.3 Order and consistency

-

- The enumerated type memory_order specifies the detailed regular (non-atomic) - memory synchronization operations as defined in 5.1.2.4 and may provide for operation - ordering. Its enumeration constants are as follows: -

-         memory_order_relaxed
-         memory_order_consume
-         memory_order_acquire
-         memory_order_release
-         memory_order_acq_rel
-         memory_order_seq_cst
-
-

- For memory_order_relaxed, no operation orders memory. -

- For memory_order_release, memory_order_acq_rel, and - memory_order_seq_cst, a store operation performs a release operation on the - affected memory location. -

- For memory_order_acquire, memory_order_acq_rel, and - memory_order_seq_cst, a load operation performs an acquire operation on the - affected memory location. -

- For memory_order_consume, a load operation performs a consume operation on the - affected memory location. -

- For memory_order_seq_cst, there shall be a single total order S on all operations, - consistent with the ''happens before'' order and modification orders for all affected - locations, such that each memory_order_seq_cst operation that loads a value - observes either the last preceding modification according to this order S, or the result of - an operation that is not memory_order_seq_cst. -

- NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to - an order that does include lock and unlock operations, since the ordering between those is already included - in the ''happens before'' ordering. - -

- NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to - memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic - - object be indivisible with respect to all other atomic accesses to that object. - -

- For an atomic operation B that reads the value of an atomic object M, if there is a - memory_order_seq_cst fence X sequenced before B, then B observes either the - last memory_order_seq_cst modification of M preceding X in the total order S or - a later modification of M in its modification order. -

- For atomic operations A and B on an atomic object M, where A modifies M and B takes - its value, if there is a memory_order_seq_cst fence X such that A is sequenced - before X and B follows X in S, then B observes either the effects of A or a later - modification of M in its modification order. -

- For atomic operations A and B on an atomic object M, where A modifies M and B takes - its value, if there are memory_order_seq_cst fences X and Y such that A is - sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes - either the effects of A or a later modification of M in its modification order. -

- Atomic read-modify-write operations shall always read the last value (in the modification - order) stored before the write associated with the read-modify-write operation. -

- An atomic store shall only store a value that has been computed from constants and - program input values by a finite sequence of program evaluations, such that each - evaluation observes the values of variables as computed by the last prior assignment in - the sequence.251) The ordering of evaluations in this sequence shall be such that -

-

- NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when - relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this - sequence out of thread order. For example, with x and y initially zero, -

-          // Thread 1:
-          r1 = atomic_load_explicit(&y, memory_order_relaxed);
-          atomic_store_explicit(&x, r1, memory_order_relaxed);
-
- -
-          // Thread 2:
-          r2 = atomic_load_explicit(&x, memory_order_relaxed);
-          atomic_store_explicit(&y, 42, memory_order_relaxed);
-
- is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of: - - - - - -
-         atomic_store_explicit(&y, 42,               memory_order_relaxed);
-         r1 = atomic_load_explicit(&y,               memory_order_relaxed);
-         atomic_store_explicit(&x, r1,               memory_order_relaxed);
-         r2 = atomic_load_explicit(&x,               memory_order_relaxed);
-
- On the other hand, -
-         // Thread 1:
-         r1 = atomic_load_explicit(&y, memory_order_relaxed);
-         atomic_store_explicit(&x, r1, memory_order_relaxed);
-
- -
-         // Thread 2:
-         r2 = atomic_load_explicit(&x, memory_order_relaxed);
-         atomic_store_explicit(&y, r2, memory_order_relaxed);
-
- is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results - in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with - weaker than memory_order_acq_rel ordering, the second requirement has no impact. - -

Recommended practice -

- The requirements do not forbid r1 == 42 && r2 == 42 in the following example, - with x and y initially zero: -

-         // Thread 1:
-         r1 = atomic_load_explicit(&x, memory_order_relaxed);
-         if (r1 == 42)
-              atomic_store_explicit(&y, r1, memory_order_relaxed);
-
- -
-         // Thread 2:
-         r2 = atomic_load_explicit(&y, memory_order_relaxed);
-         if (r2 == 42)
-              atomic_store_explicit(&x, 42, memory_order_relaxed);
-
- However, this is not useful behavior, and implementations should not allow it. -

- Implementations should make atomic stores visible to atomic loads within a reasonable - amount of time. - -

Footnotes -

251) Among other implications, atomic variables shall not decay. - - -

Contents -

7.17.3.1 The kill_dependency macro
-

Synopsis -

-

-         #include <stdatomic.h>
-         type kill_dependency(type y);
-
-

Description -

- The kill_dependency macro terminates a dependency chain; the argument does not - carry a dependency to the return value. - -

Returns -

- The kill_dependency macro returns the value of y. - -

Contents -

7.17.4 Fences

-

- This subclause introduces synchronization primitives called fences. Fences can have - acquire semantics, release semantics, or both. A fence with acquire semantics is called - an acquire fence; a fence with release semantics is called a release fence. -

- A release fence A synchronizes with an acquire fence B if there exist atomic operations - X and Y , both operating on some atomic object M, such that A is sequenced before X, X - modifies M, Y is sequenced before B, and Y reads the value written by X or a value - written by any side effect in the hypothetical release sequence X would head if it were a - release operation. -

- A release fence A synchronizes with an atomic operation B that performs an acquire - operation on an atomic object M if there exists an atomic operation X such that A is - sequenced before X, X modifies M, and B reads the value written by X or a value written - by any side effect in the hypothetical release sequence X would head if it were a release - operation. -

- An atomic operation A that is a release operation on an atomic object M synchronizes - with an acquire fence B if there exists some atomic operation X on M such that X is - sequenced before B and reads the value written by A or a value written by any side effect - in the release sequence headed by A. - -

Contents -

7.17.4.1 The atomic_thread_fence function
-

Synopsis -

-

-         #include <stdatomic.h>
-         void atomic_thread_fence(memory_order order);
-
-

Description -

- Depending on the value of order, this operation: -

-

Returns -

- The atomic_thread_fence function returns no value. - -

Contents -

7.17.4.2 The atomic_signal_fence function
-

Synopsis -

-

-         #include <stdatomic.h>
-         void atomic_signal_fence(memory_order order);
-
-

Description -

- Equivalent to atomic_thread_fence(order), except that ''synchronizes with'' - relationships are established only between a thread and a signal handler executed in the - same thread. -

- NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions - performed by the thread become visible to the signal handler. - -

- NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with - atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would - have inserted are not emitted. - -

Returns -

- The atomic_signal_fence function returns no value. - -

Contents -

7.17.5 Lock-free property

-

- The atomic lock-free macros indicate the lock-free property of integer and address atomic - types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that - the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free. -

- NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same - memory location via two different addresses will communicate atomically. The implementation should not - depend on any per-process state. This restriction enables communication via memory mapped into a - process more than once and memory shared between two processes. - - -

Contents -

7.17.5.1 The atomic_is_lock_free generic function
-

Synopsis -

-

-         #include <stdatomic.h>
-         _Bool atomic_is_lock_free(atomic_type const volatile *obj);
-
-

Description -

- The atomic_is_lock_free generic function indicates whether or not the object - pointed to by obj is lock-free. atomic_type can be any atomic type. -

Returns -

- The atomic_is_lock_free generic function returns nonzero (true) if and only if the - object's operations are lock-free. The result of a lock-free query on one object cannot be - - inferred from the result of a lock-free query on another object. - -

Contents -

7.17.6 Atomic integer and address types

-

- For each line in the following table, the atomic type name is declared as the - corresponding direct type. - -

-            Atomic type name                              Direct type
-        atomic_char                           _Atomic    char
-        atomic_schar                          _Atomic    signed char
-        atomic_uchar                          _Atomic    unsigned char
-        atomic_short                          _Atomic    short
-        atomic_ushort                         _Atomic    unsigned short
-        atomic_int                            _Atomic    int
-        atomic_uint                           _Atomic    unsigned int
-        atomic_long                           _Atomic    long
-        atomic_ulong                          _Atomic    unsigned long
-        atomic_llong                          _Atomic    long long
-        atomic_ullong                         _Atomic    unsigned long long
-        atomic_char16_t                       _Atomic    char16_t
-        atomic_char32_t                       _Atomic    char32_t
-        atomic_wchar_t                        _Atomic    wchar_t
-        atomic_int_least8_t                   _Atomic    int_least8_t
-        atomic_uint_least8_t                  _Atomic    uint_least8_t
-        atomic_int_least16_t                  _Atomic    int_least16_t
-        atomic_uint_least16_t                 _Atomic    uint_least16_t
-        atomic_int_least32_t                  _Atomic    int_least32_t
-        atomic_uint_least32_t                 _Atomic    uint_least32_t
-        atomic_int_least64_t                  _Atomic    int_least64_t
-        atomic_uint_least64_t                 _Atomic    uint_least64_t
-        atomic_int_fast8_t                    _Atomic    int_fast8_t
-        atomic_uint_fast8_t                   _Atomic    uint_fast8_t
-        atomic_int_fast16_t                   _Atomic    int_fast16_t
-        atomic_uint_fast16_t                  _Atomic    uint_fast16_t
-        atomic_int_fast32_t                   _Atomic    int_fast32_t
-        atomic_uint_fast32_t                  _Atomic    uint_fast32_t
-        atomic_int_fast64_t                   _Atomic    int_fast64_t
-        atomic_uint_fast64_t                  _Atomic    uint_fast64_t
-        atomic_intptr_t                       _Atomic    intptr_t
-        atomic_uintptr_t                      _Atomic    uintptr_t
-        atomic_size_t                         _Atomic    size_t
-        atomic_ptrdiff_t                      _Atomic    ptrdiff_t
-        atomic_intmax_t                       _Atomic    intmax_t
-        atomic_uintmax_t                      _Atomic    uintmax_t
-
-

- The semantics of the operations on these types are defined in 7.17.7. -

- The atomic_bool type provides an atomic boolean. - -

- The atomic_address type provides atomic void * operations. The unit of - addition/subtraction shall be one byte. -

- NOTE The representation of atomic integer and address types need not have the same size as their - corresponding regular types. They should have the same size whenever possible, as it eases effort required - to port existing code. - - -

Contents -

7.17.7 Operations on atomic types

-

- There are only a few kinds of operations on atomic types, though there are many - instances of those kinds. This subclause specifies each general kind. - -

Contents -

7.17.7.1 The atomic_store generic functions
-

Synopsis -

-

-         #include <stdatomic.h>
-         void atomic_store(volatile A *object, C desired);
-         void atomic_store_explicit(volatile A *object,
-              C desired, memory_order order);
-
-

Description -

- The order argument shall not be memory_order_acquire, - memory_order_consume, nor memory_order_acq_rel. Atomically replace the - value pointed to by object with the value of desired. Memory is affected according - to the value of order. -

Returns -

- The atomic_store generic functions return no value. - -

Contents -

7.17.7.2 The atomic_load generic functions
-

Synopsis -

-

-         #include <stdatomic.h>
-         C atomic_load(volatile A *object);
-         C atomic_load_explicit(volatile A *object,
-              memory_order order);
-
-

Description -

- The order argument shall not be memory_order_release nor - memory_order_acq_rel. Memory is affected according to the value of order. -

Returns - Atomically returns the value pointed to by object. - - -

Contents -

7.17.7.3 The atomic_exchange generic functions
-

Synopsis -

-

-          #include <stdatomic.h>
-          C atomic_exchange(volatile A *object, C desired);
-          C atomic_exchange_explicit(volatile A *object,
-               C desired, memory_order order);
-
-

Description -

- Atomically replace the value pointed to by object with desired. Memory is affected - according to the value of order. These operations are read-modify-write operations - (5.1.2.4). -

Returns -

- Atomically returns the value pointed to by object immediately before the effects. - -

Contents -

7.17.7.4 The atomic_compare_exchange generic functions
-

Synopsis -

-

-          #include <stdatomic.h>
-          _Bool atomic_compare_exchange_strong(volatile A *object,
-               C *expected, C desired);
-          _Bool atomic_compare_exchange_strong_explicit(
-               volatile A *object, C *expected, C desired,
-               memory_order success, memory_order failure);
-          _Bool atomic_compare_exchange_weak(volatile A *object,
-               C *expected, C desired);
-          _Bool atomic_compare_exchange_weak_explicit(
-               volatile A *object, C *expected, C desired,
-               memory_order success, memory_order failure);
-
-

Description -

- The failure argument shall not be memory_order_release nor - memory_order_acq_rel. The failure argument shall be no stronger than the - success argument. Atomically, compares the value pointed to by object for equality - with that in expected, and if true, replaces the value pointed to by object with - desired, and if false, updates the value in expected with the value pointed to by - object. Further, if the comparison is true, memory is affected according to the value of - success, and if the comparison is false, memory is affected according to the value of - failure. These operations are atomic read-modify-write operations (5.1.2.4). -

- NOTE 1 The effect of the compare-and-exchange operations is - -

-          if (*object == *expected)
-                *object = desired;
-          else
-                *expected = *object;
-
- -

- The weak compare-and-exchange operations may fail spuriously, that is, return zero - while leaving the value pointed to by expected unchanged. -

- NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of - machines, e.g. load-locked store-conditional machines. - -

- EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will - be in a loop. -

-          exp = atomic_load(&cur);
-          do {
-                des = function(exp);
-          } while (!atomic_compare_exchange_weak(&cur, &exp, des));
-
- When a compare-and-exchange is in a loop, the weak version will yield better performance on some - platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the - strong one is preferable. - -

Returns -

- The result of the comparison. - -

Contents -

7.17.7.5 The atomic_fetch and modify generic functions
-

- The following operations perform arithmetic and bitwise computations. All of these - operations are applicable to an object of any atomic integer type. Only addition and - subtraction are applicable to atomic_address. None of these operations is applicable - to atomic_bool. The key, operator, and computation correspondence is: - key op computation - add + addition - sub - subtraction - or | bitwise inclusive or - xor ^ bitwise exclusive or - and & bitwise and -

Synopsis -

-

-          #include <stdatomic.h>
-          C atomic_fetch_key(volatile A *object, M operand);
-          C atomic_fetch_key_explicit(volatile A *object,
-               M operand, memory_order order);
-
-

Description -

- Atomically replaces the value pointed to by object with the result of the computation - applied to the value pointed to by object and the given operand. Memory is affected - according to the value of order. These operations are atomic read-modify-write - - operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's - complement representation with silent wrap-around on overflow; there are no undefined - results. For address types, the result may be an undefined address, but the operations - otherwise have no undefined behavior. -

Returns -

- Atomically, the value pointed to by object immediately before the effects. -

- NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the - operation of the corresponding op= compound assignment operators. The only differences are that the - compound assignment operators are not guaranteed to operate atomically, and the value yielded by a - compound assignment operator is the updated value of the object, whereas the value returned by the - atomic_fetch and modify generic functions is the previous value of the atomic object. - - -

Contents -

7.17.8 Atomic flag type and operations

-

- The atomic_flag type provides the classic test-and-set functionality. It has two - states, set and clear. -

- Operations on an object of type atomic_flag shall be lock free. -

- NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so - the atomic_flag type is the minimum hardware-implemented type needed to conform to this - International standard. The remaining types can be emulated with atomic_flag, though with less than - ideal properties. - -

- The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the - clear state. An atomic_flag that is not explicitly initialized with - ATOMIC_FLAG_INIT is initially in an indeterminate state. -

- EXAMPLE -

-         atomic_flag guard = ATOMIC_FLAG_INIT;
-
- - -

Contents -

7.17.8.1 The atomic_flag_test_and_set functions
-

Synopsis -

-

-         #include <stdatomic.h>
-         bool atomic_flag_test_and_set(
-              volatile atomic_flag *object);
-         bool atomic_flag_test_and_set_explicit(
-              volatile atomic_flag *object, memory_order order);
-
-

Description -

- Atomically sets the value pointed to by object to true. Memory is affected according - to the value of order. These operations are atomic read-modify-write operations - (5.1.2.4). - -

Returns -

- Atomically, the value of the object immediately before the effects. - -

Contents -

7.17.8.2 The atomic_flag_clear functions
-

Synopsis -

-

-         #include <stdatomic.h>
-         void atomic_flag_clear(volatile atomic_flag *object);
-         void atomic_flag_clear_explicit(
-              volatile atomic_flag *object, memory_order order);
-
-

Description -

- The order argument shall not be memory_order_acquire nor - memory_order_acq_rel. Atomically sets the value pointed to by object to false. - Memory is affected according to the value of order. -

Returns -

- The atomic_flag_clear functions return no value. - - -

Contents -

7.18 Boolean type and values <stdbool.h>

-

- The header <stdbool.h> defines four macros. -

- The macro -

-          bool
-
- expands to _Bool. -

- The remaining three macros are suitable for use in #if preprocessing directives. They - are -

-          true
-
- which expands to the integer constant 1, -
-          false
-
- which expands to the integer constant 0, and -
-          __bool_true_false_are_defined
-
- which expands to the integer constant 1. -

- Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then - redefine the macros bool, true, and false.252) - - - - - - -

Footnotes -

252) See ''future library directions'' (7.30.7). - - -

Contents -

7.19 Common definitions <stddef.h>

-

- The header <stddef.h> defines the following macros and declares the following types. - Some are also defined in other headers, as noted in their respective subclauses. -

- The types are -

-         ptrdiff_t
-
- which is the signed integer type of the result of subtracting two pointers; -
-         size_t
-
- which is the unsigned integer type of the result of the sizeof operator; -
-         max_align_t
-
- which is an object type whose alignment is as great as is supported by the implementation - in all contexts; and -
-         wchar_t
-
- which is an integer type whose range of values can represent distinct codes for all - members of the largest extended character set specified among the supported locales; the - null character shall have the code value zero. Each member of the basic character set - shall have a code value equal to its value when used as the lone character in an integer - character constant if an implementation does not define - __STDC_MB_MIGHT_NEQ_WC__. -

- The macros are -

-         NULL
-
- which expands to an implementation-defined null pointer constant; and -
-         offsetof(type, member-designator)
-
- which expands to an integer constant expression that has type size_t, the value of - which is the offset in bytes, to the structure member (designated by member-designator), - from the beginning of its structure (designated by type). The type and member designator - shall be such that given -
-         static type t;
-
- then the expression &(t.member-designator) evaluates to an address constant. (If the - specified member is a bit-field, the behavior is undefined.) -

Recommended practice -

- The types used for size_t and ptrdiff_t should not have an integer conversion rank - greater than that of signed long int unless the implementation supports objects - large enough to make this necessary. - -

Forward references: localization (7.11). - - -

Contents -

7.20 Integer types <stdint.h>

-

- The header <stdint.h> declares sets of integer types having specified widths, and - defines corresponding sets of macros.253) It also defines macros that specify limits of - integer types corresponding to types defined in other standard headers. -

- Types are defined in the following categories: -

- (Some of these types may denote the same type.) -

- Corresponding macros specify limits of the declared types and construct suitable - constants. -

- For each type described herein that the implementation provides,254) <stdint.h> shall - declare that typedef name and define the associated macros. Conversely, for each type - described herein that the implementation does not provide, <stdint.h> shall not - declare that typedef name nor shall it define the associated macros. An implementation - shall provide those types described as ''required'', but need not provide any of the others - (described as ''optional''). - -

Footnotes -

253) See ''future library directions'' (7.30.8). - -

254) Some of these types may denote implementation-defined extended integer types. - - -

Contents -

7.20.1 Integer types

-

- When typedef names differing only in the absence or presence of the initial u are defined, - they shall denote corresponding signed and unsigned types as described in 6.2.5; an - implementation providing one of these corresponding types shall also provide the other. -

- In the following descriptions, the symbol N represents an unsigned decimal integer with - no leading zeros (e.g., 8 or 24, but not 04 or 048). - - - - - - -

Contents -

7.20.1.1 Exact-width integer types
-

- The typedef name intN_t designates a signed integer type with width N , no padding - bits, and a two's complement representation. Thus, int8_t denotes such a signed - integer type with a width of exactly 8 bits. -

- The typedef name uintN_t designates an unsigned integer type with width N and no - padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of - exactly 24 bits. -

- These types are optional. However, if an implementation provides integer types with - widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a - two's complement representation, it shall define the corresponding typedef names. - -

Contents -

7.20.1.2 Minimum-width integer types
-

- The typedef name int_leastN_t designates a signed integer type with a width of at - least N , such that no signed integer type with lesser size has at least the specified width. - Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits. -

- The typedef name uint_leastN_t designates an unsigned integer type with a width - of at least N , such that no unsigned integer type with lesser size has at least the specified - width. Thus, uint_least16_t denotes an unsigned integer type with a width of at - least 16 bits. -

- The following types are required: -

-          int_least8_t                                      uint_least8_t
-          int_least16_t                                     uint_least16_t
-          int_least32_t                                     uint_least32_t
-          int_least64_t                                     uint_least64_t
-
- All other types of this form are optional. - -

Contents -

7.20.1.3 Fastest minimum-width integer types
-

- Each of the following types designates an integer type that is usually fastest255) to operate - with among all integer types that have at least the specified width. -

- The typedef name int_fastN_t designates the fastest signed integer type with a width - of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer - type with a width of at least N . - - - - - -

- The following types are required: -

-         int_fast8_t                                    uint_fast8_t
-         int_fast16_t                                   uint_fast16_t
-         int_fast32_t                                   uint_fast32_t
-         int_fast64_t                                   uint_fast64_t
-
- All other types of this form are optional. - -

Footnotes -

255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear - grounds for choosing one type over another, it will simply pick some integer type satisfying the - signedness and width requirements. - - -

Contents -

7.20.1.4 Integer types capable of holding object pointers
-

- The following type designates a signed integer type with the property that any valid - pointer to void can be converted to this type, then converted back to pointer to void, - and the result will compare equal to the original pointer: -

-         intptr_t
-
- The following type designates an unsigned integer type with the property that any valid - pointer to void can be converted to this type, then converted back to pointer to void, - and the result will compare equal to the original pointer: -
-         uintptr_t
-
- These types are optional. - -

Contents -

7.20.1.5 Greatest-width integer types
-

- The following type designates a signed integer type capable of representing any value of - any signed integer type: -

-         intmax_t
-
- The following type designates an unsigned integer type capable of representing any value - of any unsigned integer type: -
-         uintmax_t
-
- These types are required. - -

Contents -

7.20.2 Limits of specified-width integer types

-

- The following object-like macros specify the minimum and maximum limits of the types * - declared in <stdint.h>. Each macro name corresponds to a similar type name in - 7.20.1. -

- Each instance of any defined macro shall be replaced by a constant expression suitable - for use in #if preprocessing directives, and this expression shall have the same type as - would an expression that is an object of the corresponding type converted according to - the integer promotions. Its implementation-defined value shall be equal to or greater in - magnitude (absolute value) than the corresponding value given below, with the same sign, - except where stated to be exactly the given value. - - -

Contents -

7.20.2.1 Limits of exact-width integer types
-

-

- -

Contents -

7.20.2.2 Limits of minimum-width integer types
-

-

- -

Contents -

7.20.2.3 Limits of fastest minimum-width integer types
-

-

- -

Contents -

7.20.2.4 Limits of integer types capable of holding object pointers
-

-

- -

Contents -

7.20.2.5 Limits of greatest-width integer types
-

-

- -

Contents -

7.20.3 Limits of other integer types

-

- The following object-like macros specify the minimum and maximum limits of integer * - types corresponding to types defined in other standard headers. -

- Each instance of these macros shall be replaced by a constant expression suitable for use - in #if preprocessing directives, and this expression shall have the same type as would an - expression that is an object of the corresponding type converted according to the integer - promotions. Its implementation-defined value shall be equal to or greater in magnitude - (absolute value) than the corresponding value given below, with the same sign. An - implementation shall define only the macros corresponding to those typedef names it - actually provides.256) -

-

- If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of - SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX - shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer - type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of - SIG_ATOMIC_MAX shall be no less than 255. -

- If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN - shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127; - otherwise, wchar_t is defined as an unsigned integer type, and the value of - WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257) -

- If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall - be no greater than -32767 and the value of WINT_MAX shall be no less than 32767; - otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN - shall be 0 and the value of WINT_MAX shall be no less than 65535. - -

Footnotes -

256) A freestanding implementation need not provide all of these types. - -

257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended - character set. - - -

Contents -

7.20.4 Macros for integer constants

-

- The following function-like macros expand to integer constants suitable for initializing * - objects that have integer types corresponding to types defined in <stdint.h>. Each - macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5. -

- The argument in any instance of these macros shall be an unsuffixed integer constant (as - defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type. -

- Each invocation of one of these macros shall expand to an integer constant expression - suitable for use in #if preprocessing directives. The type of the expression shall have - the same type as would an expression of the corresponding type converted according to - the integer promotions. The value of the expression shall be that of the argument. - -

Contents -

7.20.4.1 Macros for minimum-width integer constants
-

- The macro INTN_C(value) shall expand to an integer constant expression - corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand - to an integer constant expression corresponding to the type uint_leastN_t. For - example, if uint_least64_t is a name for the type unsigned long long int, - then UINT64_C(0x123) might expand to the integer constant 0x123ULL. - - - - - - -

Contents -

7.20.4.2 Macros for greatest-width integer constants
-

- The following macro expands to an integer constant expression having the value specified - by its argument and the type intmax_t: -

-         INTMAX_C(value)
-
- The following macro expands to an integer constant expression having the value specified - by its argument and the type uintmax_t: - -
-         UINTMAX_C(value)
-
- -

Contents -

7.21 Input/output <stdio.h>

- -

Contents -

7.21.1 Introduction

-

- The header <stdio.h> defines several macros, and declares three types and many - functions for performing input and output. -

- The types declared are size_t (described in 7.19); -

-        FILE
-
- which is an object type capable of recording all the information needed to control a - stream, including its file position indicator, a pointer to its associated buffer (if any), an - error indicator that records whether a read/write error has occurred, and an end-of-file - indicator that records whether the end of the file has been reached; and -
-        fpos_t
-
- which is a complete object type other than an array type capable of recording all the - information needed to specify uniquely every position within a file. -

- The macros are NULL (described in 7.19); -

-        _IOFBF
-        _IOLBF
-        _IONBF
-
- which expand to integer constant expressions with distinct values, suitable for use as the - third argument to the setvbuf function; -
-        BUFSIZ
-
- which expands to an integer constant expression that is the size of the buffer used by the - setbuf function; -
-        EOF
-
- which expands to an integer constant expression, with type int and a negative value, that - is returned by several functions to indicate end-of-file, that is, no more input from a - stream; -
-        FOPEN_MAX
-
- which expands to an integer constant expression that is the minimum number of files that - the implementation guarantees can be open simultaneously; -
-        FILENAME_MAX
-
- which expands to an integer constant expression that is the size needed for an array of - char large enough to hold the longest file name string that the implementation - - guarantees can be opened;258) -
-         L_tmpnam
-
- which expands to an integer constant expression that is the size needed for an array of - char large enough to hold a temporary file name string generated by the tmpnam - function; -
-         SEEK_CUR
-         SEEK_END
-         SEEK_SET
-
- which expand to integer constant expressions with distinct values, suitable for use as the - third argument to the fseek function; -
-         TMP_MAX
-
- which expands to an integer constant expression that is the minimum number of unique - file names that can be generated by the tmpnam function; -
-         stderr
-         stdin
-         stdout
-
- which are expressions of type ''pointer to FILE'' that point to the FILE objects - associated, respectively, with the standard error, input, and output streams. -

- The header <wchar.h> declares a number of functions useful for wide character input - and output. The wide character input/output functions described in that subclause - provide operations analogous to most of those described here, except that the - fundamental units internal to the program are wide characters. The external - representation (in the file) is a sequence of ''generalized'' multibyte characters, as - described further in 7.21.3. -

- The input/output functions are given the following collective terms: -

-

Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the - tmpnam function (7.21.4.4), <wchar.h> (7.28). - -

Footnotes -

258) If the implementation imposes no practical limit on the length of file name strings, the value of - FILENAME_MAX should instead be the recommended size of an array intended to hold a file name - string. Of course, file name string contents are subject to other system-specific constraints; therefore - all possible strings of length FILENAME_MAX cannot be expected to be opened successfully. - - -

Contents -

7.21.2 Streams

-

- Input and output, whether to or from physical devices such as terminals and tape drives, - or whether to or from files supported on structured storage devices, are mapped into - logical data streams, whose properties are more uniform than their various inputs and - outputs. Two forms of mapping are supported, for text streams and for binary - streams.259) -

- A text stream is an ordered sequence of characters composed into lines, each line - consisting of zero or more characters plus a terminating new-line character. Whether the - last line requires a terminating new-line character is implementation-defined. Characters - may have to be added, altered, or deleted on input and output to conform to differing - conventions for representing text in the host environment. Thus, there need not be a one- - to-one correspondence between the characters in a stream and those in the external - representation. Data read in from a text stream will necessarily compare equal to the data - that were earlier written out to that stream only if: the data consist only of printing - characters and the control characters horizontal tab and new-line; no new-line character is - immediately preceded by space characters; and the last character is a new-line character. - Whether space characters that are written out immediately before a new-line character - appear when read in is implementation-defined. -

- A binary stream is an ordered sequence of characters that can transparently record - internal data. Data read in from a binary stream shall compare equal to the data that were - earlier written out to that stream, under the same implementation. Such a stream may, - however, have an implementation-defined number of null characters appended to the end - of the stream. -

- Each stream has an orientation. After a stream is associated with an external file, but - before any operations are performed on it, the stream is without orientation. Once a wide - character input/output function has been applied to a stream without orientation, the - - - - stream becomes a wide-oriented stream. Similarly, once a byte input/output function has - been applied to a stream without orientation, the stream becomes a byte-oriented stream. - Only a call to the freopen function or the fwide function can otherwise alter the - orientation of a stream. (A successful call to freopen removes any orientation.)260) -

- Byte input/output functions shall not be applied to a wide-oriented stream and wide - character input/output functions shall not be applied to a byte-oriented stream. The - remaining stream operations do not affect, and are not affected by, a stream's orientation, - except for the following additional restrictions: -

-

- Each wide-oriented stream has an associated mbstate_t object that stores the current - parse state of the stream. A successful call to fgetpos stores a representation of the - value of this mbstate_t object as part of the value of the fpos_t object. A later - successful call to fsetpos using the same stored fpos_t value restores the value of - the associated mbstate_t object as well as the position within the controlled stream. -

Environmental limits -

- An implementation shall support text files with lines containing at least 254 characters, - including the terminating new-line character. The value of the macro BUFSIZ shall be at - least 256. -

Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5), - mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function - (7.21.9.3). - - - - - - -

Footnotes -

259) An implementation need not distinguish between text streams and binary streams. In such an - implementation, there need be no new-line characters in a text stream nor any limit to the length of a - line. - -

260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup. - - -

Contents -

7.21.3 Files

-

- A stream is associated with an external file (which may be a physical device) by opening - a file, which may involve creating a new file. Creating an existing file causes its former - contents to be discarded, if necessary. If a file can support positioning requests (such as a - disk file, as opposed to a terminal), then a file position indicator associated with the - stream is positioned at the start (character number zero) of the file, unless the file is - opened with append mode in which case it is implementation-defined whether the file - position indicator is initially positioned at the beginning or the end of the file. The file - position indicator is maintained by subsequent reads, writes, and positioning requests, to - facilitate an orderly progression through the file. -

- Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text - stream causes the associated file to be truncated beyond that point is implementation- - defined. -

- When a stream is unbuffered, characters are intended to appear from the source or at the - destination as soon as possible. Otherwise characters may be accumulated and - transmitted to or from the host environment as a block. When a stream is fully buffered, - characters are intended to be transmitted to or from the host environment as a block when - a buffer is filled. When a stream is line buffered, characters are intended to be - transmitted to or from the host environment as a block when a new-line character is - encountered. Furthermore, characters are intended to be transmitted as a block to the host - environment when a buffer is filled, when input is requested on an unbuffered stream, or - when input is requested on a line buffered stream that requires the transmission of - characters from the host environment. Support for these characteristics is - implementation-defined, and may be affected via the setbuf and setvbuf functions. -

- A file may be disassociated from a controlling stream by closing the file. Output streams - are flushed (any unwritten buffer contents are transmitted to the host environment) before - the stream is disassociated from the file. The value of a pointer to a FILE object is - indeterminate after the associated file is closed (including the standard text streams). - Whether a file of zero length (on which no characters have been written by an output - stream) actually exists is implementation-defined. -

- The file may be subsequently reopened, by the same or another program execution, and - its contents reclaimed or modified (if it can be repositioned at its start). If the main - function returns to its original caller, or if the exit function is called, all open files are - closed (hence all output streams are flushed) before program termination. Other paths to - program termination, such as calling the abort function, need not close all files - properly. -

- The address of the FILE object used to control a stream may be significant; a copy of a - FILE object need not serve in place of the original. - -

- At program startup, three text streams are predefined and need not be opened explicitly -

- conventional output), and standard error (for writing diagnostic output). As initially - opened, the standard error stream is not fully buffered; the standard input and standard - output streams are fully buffered if and only if the stream can be determined not to refer - to an interactive device. -

- Functions that open additional (nontemporary) files require a file name, which is a string. - The rules for composing valid file names are implementation-defined. Whether the same - file can be simultaneously open multiple times is also implementation-defined. -

- Although both text and binary wide-oriented streams are conceptually sequences of wide - characters, the external file associated with a wide-oriented stream is a sequence of - multibyte characters, generalized as follows: -

-

- Moreover, the encodings used for multibyte characters may differ among files. Both the - nature and choice of such encodings are implementation-defined. -

- The wide character input functions read multibyte characters from the stream and convert - them to wide characters as if they were read by successive calls to the fgetwc function. - Each conversion occurs as if by a call to the mbrtowc function, with the conversion state - described by the stream's own mbstate_t object. The byte input functions read - characters from the stream as if by successive calls to the fgetc function. -

- The wide character output functions convert wide characters to multibyte characters and - write them to the stream as if they were written by successive calls to the fputwc - function. Each conversion occurs as if by a call to the wcrtomb function, with the - conversion state described by the stream's own mbstate_t object. The byte output - functions write characters to the stream as if by successive calls to the fputc function. -

- In some cases, some of the byte input/output functions also perform conversions between - multibyte characters and wide characters. These conversions also occur as if by calls to - the mbrtowc and wcrtomb functions. -

- An encoding error occurs if the character sequence presented to the underlying - mbrtowc function does not form a valid (generalized) multibyte character, or if the code - value passed to the underlying wcrtomb does not correspond to a valid (generalized) - - - - multibyte character. The wide character input/output functions and the byte input/output - functions store the value of the macro EILSEQ in errno if and only if an encoding error - occurs. -

Environmental limits -

- The value of FOPEN_MAX shall be at least eight, including the three standard text - streams. -

Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the - fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function - (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the - fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function - (7.28.6.3.2), the wcrtomb function (7.28.6.3.3). - -

Footnotes -

261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has - undefined behavior for a binary stream (because of possible trailing null characters) or for any stream - with state-dependent encoding that does not assuredly end in the initial shift state. - - -

Contents -

7.21.4 Operations on files

- -

Contents -

7.21.4.1 The remove function
-

Synopsis -

-

-        #include <stdio.h>
-        int remove(const char *filename);
-
-

Description -

- The remove function causes the file whose name is the string pointed to by filename - to be no longer accessible by that name. A subsequent attempt to open that file using that - name will fail, unless it is created anew. If the file is open, the behavior of the remove - function is implementation-defined. -

Returns -

- The remove function returns zero if the operation succeeds, nonzero if it fails. - -

Contents -

7.21.4.2 The rename function
-

Synopsis -

-

-        #include <stdio.h>
-        int rename(const char *old, const char *new);
-
-

Description -

- The rename function causes the file whose name is the string pointed to by old to be - henceforth known by the name given by the string pointed to by new. The file named - old is no longer accessible by that name. If a file named by the string pointed to by new - exists prior to the call to the rename function, the behavior is implementation-defined. - -

Returns -

- The rename function returns zero if the operation succeeds, nonzero if it fails,262) in - which case if the file existed previously it is still known by its original name. - -

Footnotes -

262) Among the reasons the implementation may cause the rename function to fail are that the file is open - or that it is necessary to copy its contents to effectuate its renaming. - - -

Contents -

7.21.4.3 The tmpfile function
-

Synopsis -

-

-         #include <stdio.h>
-         FILE *tmpfile(void);
-
-

Description -

- The tmpfile function creates a temporary binary file that is different from any other - existing file and that will automatically be removed when it is closed or at program - termination. If the program terminates abnormally, whether an open temporary file is - removed is implementation-defined. The file is opened for update with "wb+" mode. -

Recommended practice -

- It should be possible to open at least TMP_MAX temporary files during the lifetime of the - program (this limit may be shared with tmpnam) and there should be no limit on the - number simultaneously open other than this limit and any limit on the number of open - files (FOPEN_MAX). -

Returns -

- The tmpfile function returns a pointer to the stream of the file that it created. If the file - cannot be created, the tmpfile function returns a null pointer. -

Forward references: the fopen function (7.21.5.3). - -

Contents -

7.21.4.4 The tmpnam function
-

Synopsis -

-

-         #include <stdio.h>
-         char *tmpnam(char *s);
-
-

Description -

- The tmpnam function generates a string that is a valid file name and that is not the same - as the name of an existing file.263) The function is potentially capable of generating at - - - - least TMP_MAX different strings, but any or all of them may already be in use by existing - files and thus not be suitable return values. -

- The tmpnam function generates a different string each time it is called. -

- Calls to the tmpnam function with a null pointer argument may introduce data races with - each other. The implementation shall behave as if no library function calls the tmpnam - function. -

Returns -

- If no suitable string can be generated, the tmpnam function returns a null pointer. - Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an - internal static object and returns a pointer to that object (subsequent calls to the tmpnam - function may modify the same object). If the argument is not a null pointer, it is assumed - to point to an array of at least L_tmpnam chars; the tmpnam function writes its result - in that array and returns the argument as its value. -

Environmental limits -

- The value of the macro TMP_MAX shall be at least 25. - -

Footnotes -

263) Files created using strings generated by the tmpnam function are temporary only in the sense that - their names should not collide with those generated by conventional naming rules for the - implementation. It is still necessary to use the remove function to remove such files when their use - is ended, and before program termination. - - -

Contents -

7.21.5 File access functions

- -

Contents -

7.21.5.1 The fclose function
-

Synopsis -

-

-        #include <stdio.h>
-        int fclose(FILE *stream);
-
-

Description -

- A successful call to the fclose function causes the stream pointed to by stream to be - flushed and the associated file to be closed. Any unwritten buffered data for the stream - are delivered to the host environment to be written to the file; any unread buffered data - are discarded. Whether or not the call succeeds, the stream is disassociated from the file - and any buffer set by the setbuf or setvbuf function is disassociated from the stream - (and deallocated if it was automatically allocated). -

Returns -

- The fclose function returns zero if the stream was successfully closed, or EOF if any - errors were detected. - - -

Contents -

7.21.5.2 The fflush function
-

Synopsis -

-

-         #include <stdio.h>
-         int fflush(FILE *stream);
-
-

Description -

- If stream points to an output stream or an update stream in which the most recent - operation was not input, the fflush function causes any unwritten data for that stream - to be delivered to the host environment to be written to the file; otherwise, the behavior is - undefined. -

- If stream is a null pointer, the fflush function performs this flushing action on all - streams for which the behavior is defined above. -

Returns -

- The fflush function sets the error indicator for the stream and returns EOF if a write - error occurs, otherwise it returns zero. -

Forward references: the fopen function (7.21.5.3). - -

Contents -

7.21.5.3 The fopen function
-

Synopsis -

-

-         #include <stdio.h>
-         FILE *fopen(const char * restrict filename,
-              const char * restrict mode);
-
-

Description -

- The fopen function opens the file whose name is the string pointed to by filename, - and associates a stream with it. -

- The argument mode points to a string. If the string is one of the following, the file is - open in the indicated mode. Otherwise, the behavior is undefined.264) - r open text file for reading - w truncate to zero length or create text file for writing - wx create text file for writing - a append; open or create text file for writing at end-of-file - rb open binary file for reading - wb truncate to zero length or create binary file for writing - - - - wbx create binary file for writing - ab append; open or create binary file for writing at end-of-file - r+ open text file for update (reading and writing) - w+ truncate to zero length or create text file for update - w+x create text file for update - a+ append; open or create text file for update, writing at end-of-file - r+b or rb+ open binary file for update (reading and writing) - w+b or wb+ truncate to zero length or create binary file for update - w+bx or wb+x create binary file for update - a+b or ab+ append; open or create binary file for update, writing at end-of-file -

- Opening a file with read mode ('r' as the first character in the mode argument) fails if - the file does not exist or cannot be read. -

- Opening a file with exclusive mode ('x' as the last character in the mode argument) - fails if the file already exists or cannot be created. Otherwise, the file is created with - exclusive (also known as non-shared) access to the extent that the underlying system - supports exclusive access. -

- Opening a file with append mode ('a' as the first character in the mode argument) - causes all subsequent writes to the file to be forced to the then current end-of-file, - regardless of intervening calls to the fseek function. In some implementations, opening - a binary file with append mode ('b' as the second or third character in the above list of - mode argument values) may initially position the file position indicator for the stream - beyond the last data written, because of null character padding. -

- When a file is opened with update mode ('+' as the second or third character in the - above list of mode argument values), both input and output may be performed on the - associated stream. However, output shall not be directly followed by input without an - intervening call to the fflush function or to a file positioning function (fseek, - fsetpos, or rewind), and input shall not be directly followed by output without an - intervening call to a file positioning function, unless the input operation encounters end- - of-file. Opening (or creating) a text file with update mode may instead open (or create) a - binary stream in some implementations. -

- When opened, a stream is fully buffered if and only if it can be determined not to refer to - an interactive device. The error and end-of-file indicators for the stream are cleared. -

Returns -

- The fopen function returns a pointer to the object controlling the stream. If the open - operation fails, fopen returns a null pointer. -

Forward references: file positioning functions (7.21.9). - - -

Footnotes -

264) If the string begins with one of the above sequences, the implementation might choose to ignore the - remaining characters, or it might use them to select different kinds of a file (some of which might not - conform to the properties in 7.21.2). - - -

Contents -

7.21.5.4 The freopen function
-

Synopsis -

-

-         #include <stdio.h>
-         FILE *freopen(const char * restrict filename,
-              const char * restrict mode,
-              FILE * restrict stream);
-
-

Description -

- The freopen function opens the file whose name is the string pointed to by filename - and associates the stream pointed to by stream with it. The mode argument is used just - as in the fopen function.265) -

- If filename is a null pointer, the freopen function attempts to change the mode of - the stream to that specified by mode, as if the name of the file currently associated with - the stream had been used. It is implementation-defined which changes of mode are - permitted (if any), and under what circumstances. -

- The freopen function first attempts to close any file that is associated with the specified - stream. Failure to close the file is ignored. The error and end-of-file indicators for the - stream are cleared. -

Returns -

- The freopen function returns a null pointer if the open operation fails. Otherwise, - freopen returns the value of stream. - -

Footnotes -

265) The primary use of the freopen function is to change the file associated with a standard text stream - (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value - returned by the fopen function may be assigned. - - -

Contents -

7.21.5.5 The setbuf function
-

Synopsis -

-

-         #include <stdio.h>
-         void setbuf(FILE * restrict stream,
-              char * restrict buf);
-
-

Description -

- Except that it returns no value, the setbuf function is equivalent to the setvbuf - function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf - is a null pointer), with the value _IONBF for mode. - - - - - -

Returns -

- The setbuf function returns no value. -

Forward references: the setvbuf function (7.21.5.6). - -

Contents -

7.21.5.6 The setvbuf function
-

Synopsis -

-

-         #include <stdio.h>
-         int setvbuf(FILE * restrict stream,
-              char * restrict buf,
-              int mode, size_t size);
-
-

Description -

- The setvbuf function may be used only after the stream pointed to by stream has - been associated with an open file and before any other operation (other than an - unsuccessful call to setvbuf) is performed on the stream. The argument mode - determines how stream will be buffered, as follows: _IOFBF causes input/output to be - fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes - input/output to be unbuffered. If buf is not a null pointer, the array it points to may be - used instead of a buffer allocated by the setvbuf function266) and the argument size - specifies the size of the array; otherwise, size may determine the size of a buffer - allocated by the setvbuf function. The contents of the array at any time are - indeterminate. -

Returns -

- The setvbuf function returns zero on success, or nonzero if an invalid value is given - for mode or if the request cannot be honored. - - - - - - -

Footnotes -

266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed - before a buffer that has automatic storage duration is deallocated upon block exit. - - -

Contents -

7.21.6 Formatted input/output functions

-

- The formatted input/output functions shall behave as if there is a sequence point after the - actions associated with each specifier.267) - -

Footnotes -

267) The fprintf functions perform writes to memory for the %n specifier. - - -

Contents -

7.21.6.1 The fprintf function
-

Synopsis -

-

-          #include <stdio.h>
-          int fprintf(FILE * restrict stream,
-               const char * restrict format, ...);
-
-

Description -

- The fprintf function writes output to the stream pointed to by stream, under control - of the string pointed to by format that specifies how subsequent arguments are - converted for output. If there are insufficient arguments for the format, the behavior is - undefined. If the format is exhausted while arguments remain, the excess arguments are - evaluated (as always) but are otherwise ignored. The fprintf function returns when - the end of the format string is encountered. -

- The format shall be a multibyte character sequence, beginning and ending in its initial - shift state. The format is composed of zero or more directives: ordinary multibyte - characters (not %), which are copied unchanged to the output stream; and conversion - specifications, each of which results in fetching zero or more subsequent arguments, - converting them, if applicable, according to the corresponding conversion specifier, and - then writing the result to the output stream. -

- Each conversion specification is introduced by the character %. After the %, the following - appear in sequence: -

-

- As noted above, a field width, or precision, or both, may be indicated by an asterisk. In - this case, an int argument supplies the field width or precision. The arguments - specifying field width, or precision, or both, shall appear (in that order) before the - argument (if any) to be converted. A negative field width argument is taken as a - flag - followed by a positive field width. A negative precision argument is taken as if the - precision were omitted. -

- The flag characters and their meanings are: - - The result of the conversion is left-justified within the field. (It is right-justified if -

-         this flag is not specified.)
-
- + The result of a signed conversion always begins with a plus or minus sign. (It -
-         begins with a sign only when a negative value is converted if this flag is not
-         specified.)269)
-
- space If the first character of a signed conversion is not a sign, or if a signed conversion -
-       results in no characters, a space is prefixed to the result. If the space and + flags
-       both appear, the space flag is ignored.
-
- # The result is converted to an ''alternative form''. For o conversion, it increases -
-         the precision, if and only if necessary, to force the first digit of the result to be a
-         zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
-         conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
-         and G conversions, the result of converting a floating-point number always
-         contains a decimal-point character, even if no digits follow it. (Normally, a
-         decimal-point character appears in the result of these conversions only if a digit
-         follows it.) For g and G conversions, trailing zeros are not removed from the
-         result. For other conversions, the behavior is undefined.
-
- 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros -
-         (following any indication of sign or base) are used to pad to the field width rather
-         than performing space padding, except when converting an infinity or NaN. If the
-         0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
-
- - - -
-           conversions, if a precision is specified, the 0 flag is ignored. For other
-           conversions, the behavior is undefined.
-
-

- The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -

-               signed char or unsigned char argument (the argument will have
-               been promoted according to the integer promotions, but its value shall be
-               converted to signed char or unsigned char before printing); or that
-               a following n conversion specifier applies to a pointer to a signed char
-               argument.
-
- h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-               short int or unsigned short int argument (the argument will
-               have been promoted according to the integer promotions, but its value shall
-               be converted to short int or unsigned short int before printing);
-               or that a following n conversion specifier applies to a pointer to a short
-               int argument.
-
- l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-               long int or unsigned long int argument; that a following n
-               conversion specifier applies to a pointer to a long int argument; that a
-               following c conversion specifier applies to a wint_t argument; that a
-               following s conversion specifier applies to a pointer to a wchar_t
-               argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
-               specifier.
-
- ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-              long long int or unsigned long long int argument; or that a
-              following n conversion specifier applies to a pointer to a long long int
-              argument.
-
- j Specifies that a following d, i, o, u, x, or X conversion specifier applies to -
-               an intmax_t or uintmax_t argument; or that a following n conversion
-               specifier applies to a pointer to an intmax_t argument.
-
- z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-               size_t or the corresponding signed integer type argument; or that a
-               following n conversion specifier applies to a pointer to a signed integer type
-               corresponding to size_t argument.
-
- t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - -
-               ptrdiff_t or the corresponding unsigned integer type argument; or that a
-               following n conversion specifier applies to a pointer to a ptrdiff_t
-               argument.
-
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier -
-                applies to a long double argument.
-
- If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -

- The conversion specifiers and their meanings are: - d,i The int argument is converted to signed decimal in the style [-]dddd. The -

-              precision specifies the minimum number of digits to appear; if the value
-              being converted can be represented in fewer digits, it is expanded with
-              leading zeros. The default precision is 1. The result of converting a zero
-              value with a precision of zero is no characters.
-
- o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned -
-         decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
-         letters abcdef are used for x conversion and the letters ABCDEF for X
-         conversion. The precision specifies the minimum number of digits to appear;
-         if the value being converted can be represented in fewer digits, it is expanded
-         with leading zeros. The default precision is 1. The result of converting a
-         zero value with a precision of zero is no characters.
-
- f,F A double argument representing a floating-point number is converted to -
-              decimal notation in the style [-]ddd.ddd, where the number of digits after
-              the decimal-point character is equal to the precision specification. If the
-              precision is missing, it is taken as 6; if the precision is zero and the # flag is
-              not specified, no decimal-point character appears. If a decimal-point
-              character appears, at least one digit appears before it. The value is rounded to
-              the appropriate number of digits.
-              A double argument representing an infinity is converted in one of the styles
-              [-]inf or [-]infinity -- which style is implementation-defined. A
-              double argument representing a NaN is converted in one of the styles
-              [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
-              any n-char-sequence, is implementation-defined. The F conversion specifier
-              produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
-              respectively.270)
-
- e,E A double argument representing a floating-point number is converted in the -
-              style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
-              argument is nonzero) before the decimal-point character and the number of
-              digits after it is equal to the precision; if the precision is missing, it is taken as
-
- - - -
-               6; if the precision is zero and the # flag is not specified, no decimal-point
-               character appears. The value is rounded to the appropriate number of digits.
-               The E conversion specifier produces a number with E instead of e
-               introducing the exponent. The exponent always contains at least two digits,
-               and only as many more digits as necessary to represent the exponent. If the
-               value is zero, the exponent is zero.
-               A double argument representing an infinity or NaN is converted in the style
-               of an f or F conversion specifier.
-
- g,G A double argument representing a floating-point number is converted in -
-               style f or e (or in style F or E in the case of a G conversion specifier),
-               depending on the value converted and the precision. Let P equal the
-               precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
-               Then, if a conversion with style E would have an exponent of X:
-               -- if P > X >= -4, the conversion is with style f (or F) and precision
-                 P - (X + 1).
-               -- otherwise, the conversion is with style e (or E) and precision P - 1.
-               Finally, unless the # flag is used, any trailing zeros are removed from the
-               fractional portion of the result and the decimal-point character is removed if
-               there is no fractional portion remaining.
-               A double argument representing an infinity or NaN is converted in the style
-               of an f or F conversion specifier.
-
- a,A A double argument representing a floating-point number is converted in the -
-               style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
-               nonzero if the argument is a normalized floating-point number and is
-               otherwise unspecified) before the decimal-point character271) and the number
-               of hexadecimal digits after it is equal to the precision; if the precision is
-               missing and FLT_RADIX is a power of 2, then the precision is sufficient for
-               an exact representation of the value; if the precision is missing and
-               FLT_RADIX is not a power of 2, then the precision is sufficient to
-
- - - - - -
-               distinguish272) values of type double, except that trailing zeros may be
-               omitted; if the precision is zero and the # flag is not specified, no decimal-
-               point character appears. The letters abcdef are used for a conversion and
-               the letters ABCDEF for A conversion. The A conversion specifier produces a
-               number with X and P instead of x and p. The exponent always contains at
-               least one digit, and only as many more digits as necessary to represent the
-               decimal exponent of 2. If the value is zero, the exponent is zero.
-               A double argument representing an infinity or NaN is converted in the style
-               of an f or F conversion specifier.
-
- c If no l length modifier is present, the int argument is converted to an -
-               unsigned char, and the resulting character is written.
-               If an l length modifier is present, the wint_t argument is converted as if by
-               an ls conversion specification with no precision and an argument that points
-               to the initial element of a two-element array of wchar_t, the first element
-               containing the wint_t argument to the lc conversion specification and the
-               second a null wide character.
-
- s If no l length modifier is present, the argument shall be a pointer to the initial -
-               element of an array of character type.273) Characters from the array are
-               written up to (but not including) the terminating null character. If the
-               precision is specified, no more than that many bytes are written. If the
-               precision is not specified or is greater than the size of the array, the array shall
-               contain a null character.
-               If an l length modifier is present, the argument shall be a pointer to the initial
-               element of an array of wchar_t type. Wide characters from the array are
-               converted to multibyte characters (each as if by a call to the wcrtomb
-               function, with the conversion state described by an mbstate_t object
-               initialized to zero before the first wide character is converted) up to and
-               including a terminating null wide character. The resulting multibyte
-               characters are written up to (but not including) the terminating null character
-               (byte). If no precision is specified, the array shall contain a null wide
-               character. If a precision is specified, no more than that many bytes are
-               written (including shift sequences, if any), and the array shall contain a null
-               wide character if, to equal the multibyte character sequence length given by
-
- - -
-                the precision, the function would need to access a wide character one past the
-                end of the array. In no case is a partial multibyte character written.274)
-
- p The argument shall be a pointer to void. The value of the pointer is -
-                converted to a sequence of printing characters, in an implementation-defined
-                manner.
-
- n The argument shall be a pointer to signed integer into which is written the -
-                number of characters written to the output stream so far by this call to
-                fprintf. No argument is converted, but one is consumed. If the conversion
-                specification includes any flags, a field width, or a precision, the behavior is
-                undefined.
-
- % A % character is written. No argument is converted. The complete -
-                conversion specification shall be %%.
-
-

- If a conversion specification is invalid, the behavior is undefined.275) If any argument is - not the correct type for the corresponding conversion specification, the behavior is - undefined. -

- In no case does a nonexistent or small field width cause truncation of a field; if the result - of a conversion is wider than the field width, the field is expanded to contain the - conversion result. -

- For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded - to a hexadecimal floating number with the given precision. -

Recommended practice -

- For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly - representable in the given precision, the result should be one of the two adjacent numbers - in hexadecimal floating style with the given precision, with the extra stipulation that the - error should have a correct sign for the current rounding direction. -

- For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most - DECIMAL_DIG, then the result should be correctly rounded.276) If the number of - significant decimal digits is more than DECIMAL_DIG but the source value is exactly - representable with DECIMAL_DIG digits, then the result should be an exact - representation with trailing zeros. Otherwise, the source value is bounded by two - adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value - - - - of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that - the error should have a correct sign for the current rounding direction. -

Returns -

- The fprintf function returns the number of characters transmitted, or a negative value - if an output or encoding error occurred. -

Environmental limits -

- The number of characters that can be produced by any single conversion shall be at least - 4095. -

- EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal - places: -

-          #include <math.h>
-          #include <stdio.h>
-          /* ... */
-          char *weekday, *month;      // pointers to strings
-          int day, hour, min;
-          fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
-                  weekday, month, day, hour, min);
-          fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
-
- -

- EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the - members of the extended character set that consist of more than one byte each consist of exactly two bytes, - the first of which is denoted here by a and the second by an uppercase letter. -

- Given the following wide string with length seven, -

-          static wchar_t wstr[] = L" X Yabc Z W";
-
- the seven calls -
-          fprintf(stdout,          "|1234567890123|\n");
-          fprintf(stdout,          "|%13ls|\n", wstr);
-          fprintf(stdout,          "|%-13.9ls|\n", wstr);
-          fprintf(stdout,          "|%13.10ls|\n", wstr);
-          fprintf(stdout,          "|%13.11ls|\n", wstr);
-          fprintf(stdout,          "|%13.15ls|\n", &wstr[2]);
-          fprintf(stdout,          "|%13lc|\n", (wint_t) wstr[5]);
-
- will print the following seven lines: -
-          |1234567890123|
-          |   X Yabc Z W|
-          | X Yabc Z    |
-          |     X Yabc Z|
-          |   X Yabc Z W|
-          |      abc Z W|
-          |            Z|
-
- -

Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3). - - -

Footnotes -

268) Note that 0 is taken as a flag, not as the beginning of a field width. - -

269) The results of all floating conversions of a negative zero, and of negative values that round to zero, - include a minus sign. - -

270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning; - the # and 0 flag characters have no effect. - -

271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so - that subsequent digits align to nibble (4-bit) boundaries. - -

272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is - FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p - might suffice depending on the implementation's scheme for determining the digit to the left of the - decimal-point character. - -

273) No special provisions are made for multibyte characters. - -

274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding. - -

275) See ''future library directions'' (7.30.9). - -

276) For binary-to-decimal conversion, the result format's values are the numbers representable with the - given format specifier. The number of significant digits is determined by the format specifier, and in - the case of fixed-point conversion by the source value as well. - - -

Contents -

7.21.6.2 The fscanf function
-

Synopsis -

-

-         #include <stdio.h>
-         int fscanf(FILE * restrict stream,
-              const char * restrict format, ...);
-
-

Description -

- The fscanf function reads input from the stream pointed to by stream, under control - of the string pointed to by format that specifies the admissible input sequences and how - they are to be converted for assignment, using subsequent arguments as pointers to the - objects to receive the converted input. If there are insufficient arguments for the format, - the behavior is undefined. If the format is exhausted while arguments remain, the excess - arguments are evaluated (as always) but are otherwise ignored. -

- The format shall be a multibyte character sequence, beginning and ending in its initial - shift state. The format is composed of zero or more directives: one or more white-space - characters, an ordinary multibyte character (neither % nor a white-space character), or a - conversion specification. Each conversion specification is introduced by the character %. - After the %, the following appear in sequence: -

-

- The fscanf function executes each directive of the format in turn. When all directives - have been executed, or if a directive fails (as detailed below), the function returns. - Failures are described as input failures (due to the occurrence of an encoding error or the - unavailability of input characters), or matching failures (due to inappropriate input). -

- A directive composed of white-space character(s) is executed by reading input up to the - first non-white-space character (which remains unread), or until no more characters can - be read. -

- A directive that is an ordinary multibyte character is executed by reading the next - characters of the stream. If any of those characters differ from the ones composing the - directive, the directive fails and the differing and subsequent characters remain unread. - Similarly, if end-of-file, an encoding error, or a read error prevents a character from being - read, the directive fails. -

- A directive that is a conversion specification defines a set of matching input sequences, as - described below for each specifier. A conversion specification is executed in the - - following steps: -

- Input white-space characters (as specified by the isspace function) are skipped, unless - the specification includes a [, c, or n specifier.277) -

- An input item is read from the stream, unless the specification includes an n specifier. An - input item is defined as the longest sequence of input characters which does not exceed - any specified field width and which is, or is a prefix of, a matching input sequence.278) - The first character, if any, after the input item remains unread. If the length of the input - item is zero, the execution of the directive fails; this condition is a matching failure unless - end-of-file, an encoding error, or a read error prevented input from the stream, in which - case it is an input failure. -

- Except in the case of a % specifier, the input item (or, in the case of a %n directive, the - count of input characters) is converted to a type appropriate to the conversion specifier. If - the input item is not a matching sequence, the execution of the directive fails: this - condition is a matching failure. Unless assignment suppression was indicated by a *, the - result of the conversion is placed in the object pointed to by the first argument following - the format argument that has not already received a conversion result. If this object - does not have an appropriate type, or if the result of the conversion cannot be represented - in the object, the behavior is undefined. -

- The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -

-                to an argument with type pointer to signed char or unsigned char.
-
- h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-                to an argument with type pointer to short int or unsigned short
-                int.
-
- l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-                to an argument with type pointer to long int or unsigned long
-                int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
-                an argument with type pointer to double; or that a following c, s, or [
-                conversion specifier applies to an argument with type pointer to wchar_t.
-
- ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to long long int or unsigned
-              long long int.
-
- - - - - j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to intmax_t or uintmax_t.
-
- z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to size_t or the corresponding signed
-              integer type.
-
- t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to ptrdiff_t or the corresponding
-              unsigned integer type.
-
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier -
-              applies to an argument with type pointer to long double.
-
- If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -

- The conversion specifiers and their meanings are: - d Matches an optionally signed decimal integer, whose format is the same as -

-             expected for the subject sequence of the strtol function with the value 10
-             for the base argument. The corresponding argument shall be a pointer to
-             signed integer.
-
- i Matches an optionally signed integer, whose format is the same as expected -
-             for the subject sequence of the strtol function with the value 0 for the
-             base argument. The corresponding argument shall be a pointer to signed
-             integer.
-
- o Matches an optionally signed octal integer, whose format is the same as -
-             expected for the subject sequence of the strtoul function with the value 8
-             for the base argument. The corresponding argument shall be a pointer to
-             unsigned integer.
-
- u Matches an optionally signed decimal integer, whose format is the same as -
-             expected for the subject sequence of the strtoul function with the value 10
-             for the base argument. The corresponding argument shall be a pointer to
-             unsigned integer.
-
- x Matches an optionally signed hexadecimal integer, whose format is the same -
-             as expected for the subject sequence of the strtoul function with the value
-             16 for the base argument. The corresponding argument shall be a pointer to
-             unsigned integer.
-
- a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose - -
-         format is the same as expected for the subject sequence of the strtod
-         function. The corresponding argument shall be a pointer to floating.
-
- c Matches a sequence of characters of exactly the number specified by the field -
-               width (1 if no field width is present in the directive).279)
-               If no l length modifier is present, the corresponding argument shall be a
-               pointer to the initial element of a character array large enough to accept the
-               sequence. No null character is added.
-               If an l length modifier is present, the input shall be a sequence of multibyte
-               characters that begins in the initial shift state. Each multibyte character in the
-               sequence is converted to a wide character as if by a call to the mbrtowc
-               function, with the conversion state described by an mbstate_t object
-               initialized to zero before the first multibyte character is converted. The
-               corresponding argument shall be a pointer to the initial element of an array of
-               wchar_t large enough to accept the resulting sequence of wide characters.
-               No null wide character is added.
-
- s Matches a sequence of non-white-space characters.279) -
-               If no l length modifier is present, the corresponding argument shall be a
-               pointer to the initial element of a character array large enough to accept the
-               sequence and a terminating null character, which will be added automatically.
-               If an l length modifier is present, the input shall be a sequence of multibyte
-               characters that begins in the initial shift state. Each multibyte character is
-               converted to a wide character as if by a call to the mbrtowc function, with
-               the conversion state described by an mbstate_t object initialized to zero
-               before the first multibyte character is converted. The corresponding argument
-               shall be a pointer to the initial element of an array of wchar_t large enough
-               to accept the sequence and the terminating null wide character, which will be
-               added automatically.
-
- [ Matches a nonempty sequence of characters from a set of expected characters -
-               (the scanset).279)
-               If no l length modifier is present, the corresponding argument shall be a
-               pointer to the initial element of a character array large enough to accept the
-               sequence and a terminating null character, which will be added automatically.
-               If an l length modifier is present, the input shall be a sequence of multibyte
-               characters that begins in the initial shift state. Each multibyte character is
-               converted to a wide character as if by a call to the mbrtowc function, with
-               the conversion state described by an mbstate_t object initialized to zero
-
- - -
-                before the first multibyte character is converted. The corresponding argument
-                shall be a pointer to the initial element of an array of wchar_t large enough
-                to accept the sequence and the terminating null wide character, which will be
-                added automatically.
-                The conversion specifier includes all subsequent characters in the format
-                string, up to and including the matching right bracket (]). The characters
-                between the brackets (the scanlist) compose the scanset, unless the character
-                after the left bracket is a circumflex (^), in which case the scanset contains all
-                characters that do not appear in the scanlist between the circumflex and the
-                right bracket. If the conversion specifier begins with [] or [^], the right
-                bracket character is in the scanlist and the next following right bracket
-                character is the matching right bracket that ends the specification; otherwise
-                the first following right bracket character is the one that ends the
-                specification. If a - character is in the scanlist and is not the first, nor the
-                second where the first character is a ^, nor the last character, the behavior is
-                implementation-defined.
-
- p Matches an implementation-defined set of sequences, which should be the -
-                same as the set of sequences that may be produced by the %p conversion of
-                the fprintf function. The corresponding argument shall be a pointer to a
-                pointer to void. The input item is converted to a pointer value in an
-                implementation-defined manner. If the input item is a value converted earlier
-                during the same program execution, the pointer that results shall compare
-                equal to that value; otherwise the behavior of the %p conversion is undefined.
-
- n No input is consumed. The corresponding argument shall be a pointer to -
-                signed integer into which is to be written the number of characters read from
-                the input stream so far by this call to the fscanf function. Execution of a
-                %n directive does not increment the assignment count returned at the
-                completion of execution of the fscanf function. No argument is converted,
-                but one is consumed. If the conversion specification includes an assignment-
-                suppressing character or a field width, the behavior is undefined.
-
- % Matches a single % character; no conversion or assignment occurs. The -
-                complete conversion specification shall be %%.
-
-

- If a conversion specification is invalid, the behavior is undefined.280) -

- The conversion specifiers A, E, F, G, and X are also valid and behave the same as, - respectively, a, e, f, g, and x. - - - - -

- Trailing white space (including new-line characters) is left unread unless matched by a - directive. The success of literal matches and suppressed assignments is not directly - determinable other than via the %n directive. -

Returns -

- The fscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. -

- EXAMPLE 1 The call: -

-          #include <stdio.h>
-          /* ... */
-          int n, i; float x; char name[50];
-          n = fscanf(stdin, "%d%f%s", &i, &x, name);
-
- with the input line: -
-          25 54.32E-1 thompson
-
- will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -

- EXAMPLE 2 The call: -

-          #include <stdio.h>
-          /* ... */
-          int i; float x; char name[50];
-          fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
-
- with input: -
-          56789 0123 56a72
-
- will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the - sequence 56\0. The next character read from the input stream will be a. - -

- EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name: -

-          #include <stdio.h>
-          /* ... */
-          int count; float quant; char units[21], item[21];
-          do {
-                  count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
-                  fscanf(stdin,"%*[^\n]");
-          } while (!feof(stdin) && !ferror(stdin));
-
-

- If the stdin stream contains the following lines: - -

-          2 quarts of oil
-          -12.8degrees Celsius
-          lots of luck
-          10.0LBS     of
-          dirt
-          100ergs of energy
-
- the execution of the above example will be analogous to the following assignments: -
-           quant     =   2; strcpy(units, "quarts"); strcpy(item, "oil");
-           count     =   3;
-           quant     =   -12.8; strcpy(units, "degrees");
-           count     =   2; // "C" fails to match "o"
-           count     =   0; // "l" fails to match "%f"
-           quant     =   10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
-           count     =   3;
-           count     =   0; // "100e" fails to match "%f"
-           count     =   EOF;
-
- -

- EXAMPLE 4 In: -

-           #include <stdio.h>
-           /* ... */
-           int d1, d2, n1, n2, i;
-           i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
-
- the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value - of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i. - -

- EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the - members of the extended character set that consist of more than one byte each consist of exactly two bytes, - the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as - such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes - entry into the alternate shift state. -

- After the call: -

-           #include <stdio.h>
-           /* ... */
-           char str[50];
-           fscanf(stdin, "a%s", str);
-
- with the input line: -
-           a(uparrow) X Y(downarrow) bc
-
- str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte - characters, in the more general case) appears to be a single-byte white-space character. -

- In contrast, after the call: -

-           #include <stdio.h>
-           #include <stddef.h>
-           /* ... */
-           wchar_t wstr[50];
-           fscanf(stdin, "a%ls", wstr);
-
- with the same input line, wstr will contain the two wide characters that correspond to X and Y and a - terminating null wide character. -

- However, the call: - -

-         #include <stdio.h>
-         #include <stddef.h>
-         /* ... */
-         wchar_t wstr[50];
-         fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr);
-
- with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format - string. -

- Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte - character Y, after the call: -

-         #include <stdio.h>
-         #include <stddef.h>
-         /* ... */
-         wchar_t wstr[50];
-         fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr);
-
- with the same input line, zero will again be returned, but stdin will be left with a partially consumed - multibyte character. - -

Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the - strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state - (7.28.6), the wcrtomb function (7.28.6.3.3). - -

Footnotes -

277) These white-space characters are not counted against a specified field width. - -

278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences - that are acceptable to strtod, strtol, etc., are unacceptable to fscanf. - -

279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [ - conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The - resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state. - -

280) See ''future library directions'' (7.30.9). - - -

Contents -

7.21.6.3 The printf function
-

Synopsis -

-

-         #include <stdio.h>
-         int printf(const char * restrict format, ...);
-
-

Description -

- The printf function is equivalent to fprintf with the argument stdout interposed - before the arguments to printf. -

Returns -

- The printf function returns the number of characters transmitted, or a negative value if - an output or encoding error occurred. - -

Contents -

7.21.6.4 The scanf function
-

Synopsis -

-

-         #include <stdio.h>
-         int scanf(const char * restrict format, ...);
-
-

Description -

- The scanf function is equivalent to fscanf with the argument stdin interposed - before the arguments to scanf. - -

Returns -

- The scanf function returns the value of the macro EOF if an input failure occurs before - the first conversion (if any) has completed. Otherwise, the scanf function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. - -

Contents -

7.21.6.5 The snprintf function
-

Synopsis -

-

-         #include <stdio.h>
-         int snprintf(char * restrict s, size_t n,
-              const char * restrict format, ...);
-
-

Description -

- The snprintf function is equivalent to fprintf, except that the output is written into - an array (specified by argument s) rather than to a stream. If n is zero, nothing is written, - and s may be a null pointer. Otherwise, output characters beyond the n-1st are - discarded rather than being written to the array, and a null character is written at the end - of the characters actually written into the array. If copying takes place between objects - that overlap, the behavior is undefined. -

Returns -

- The snprintf function returns the number of characters that would have been written - had n been sufficiently large, not counting the terminating null character, or a negative - value if an encoding error occurred. Thus, the null-terminated output has been - completely written if and only if the returned value is nonnegative and less than n. - -

Contents -

7.21.6.6 The sprintf function
-

Synopsis -

-

-         #include <stdio.h>
-         int sprintf(char * restrict s,
-              const char * restrict format, ...);
-
-

Description -

- The sprintf function is equivalent to fprintf, except that the output is written into - an array (specified by the argument s) rather than to a stream. A null character is written - at the end of the characters written; it is not counted as part of the returned value. If - copying takes place between objects that overlap, the behavior is undefined. -

Returns -

- The sprintf function returns the number of characters written in the array, not - counting the terminating null character, or a negative value if an encoding error occurred. - - -

Contents -

7.21.6.7 The sscanf function
-

Synopsis -

-

-        #include <stdio.h>
-        int sscanf(const char * restrict s,
-             const char * restrict format, ...);
-
-

Description -

- The sscanf function is equivalent to fscanf, except that input is obtained from a - string (specified by the argument s) rather than from a stream. Reaching the end of the - string is equivalent to encountering end-of-file for the fscanf function. If copying - takes place between objects that overlap, the behavior is undefined. -

Returns -

- The sscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the sscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.21.6.8 The vfprintf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <stdio.h>
-        int vfprintf(FILE * restrict stream,
-             const char * restrict format,
-             va_list arg);
-
-

Description -

- The vfprintf function is equivalent to fprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfprintf function does not invoke the - va_end macro.281) -

Returns -

- The vfprintf function returns the number of characters transmitted, or a negative - value if an output or encoding error occurred. -

- EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine. - - - - - -

-         #include <stdarg.h>
-         #include <stdio.h>
-         void error(char *function_name, char *format, ...)
-         {
-               va_list args;
-               va_start(args, format);
-               // print out name of function causing error
-               fprintf(stderr, "ERROR in %s: ", function_name);
-               // print out remainder of message
-               vfprintf(stderr, format, args);
-               va_end(args);
-         }
-
- - -

Footnotes -

281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and - vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate. - - -

Contents -

7.21.6.9 The vfscanf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <stdio.h>
-         int vfscanf(FILE * restrict stream,
-              const char * restrict format,
-              va_list arg);
-
-

Description -

- The vfscanf function is equivalent to fscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfscanf function does not invoke the - va_end macro.281) -

Returns -

- The vfscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vfscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.21.6.10 The vprintf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <stdio.h>
-         int vprintf(const char * restrict format,
-              va_list arg);
-
-

Description -

- The vprintf function is equivalent to printf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - - possibly subsequent va_arg calls). The vprintf function does not invoke the - va_end macro.281) -

Returns -

- The vprintf function returns the number of characters transmitted, or a negative value - if an output or encoding error occurred. - -

Contents -

7.21.6.11 The vscanf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <stdio.h>
-        int vscanf(const char * restrict format,
-             va_list arg);
-
-

Description -

- The vscanf function is equivalent to scanf, with the variable argument list replaced - by arg, which shall have been initialized by the va_start macro (and possibly - subsequent va_arg calls). The vscanf function does not invoke the va_end - macro.281) -

Returns -

- The vscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.21.6.12 The vsnprintf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <stdio.h>
-        int vsnprintf(char * restrict s, size_t n,
-             const char * restrict format,
-             va_list arg);
-
-

Description -

- The vsnprintf function is equivalent to snprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsnprintf function does not invoke the - va_end macro.281) If copying takes place between objects that overlap, the behavior is - undefined. - -

Returns -

- The vsnprintf function returns the number of characters that would have been written - had n been sufficiently large, not counting the terminating null character, or a negative - value if an encoding error occurred. Thus, the null-terminated output has been - completely written if and only if the returned value is nonnegative and less than n. - -

Contents -

7.21.6.13 The vsprintf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <stdio.h>
-         int vsprintf(char * restrict s,
-              const char * restrict format,
-              va_list arg);
-
-

Description -

- The vsprintf function is equivalent to sprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsprintf function does not invoke the - va_end macro.281) If copying takes place between objects that overlap, the behavior is - undefined. -

Returns -

- The vsprintf function returns the number of characters written in the array, not - counting the terminating null character, or a negative value if an encoding error occurred. - -

Contents -

7.21.6.14 The vsscanf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <stdio.h>
-         int vsscanf(const char * restrict s,
-              const char * restrict format,
-              va_list arg);
-
-

Description -

- The vsscanf function is equivalent to sscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsscanf function does not invoke the - va_end macro.281) -

Returns -

- The vsscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vsscanf function - - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.21.7 Character input/output functions

- -

Contents -

7.21.7.1 The fgetc function
-

Synopsis -

-

-         #include <stdio.h>
-         int fgetc(FILE *stream);
-
-

Description -

- If the end-of-file indicator for the input stream pointed to by stream is not set and a - next character is present, the fgetc function obtains that character as an unsigned - char converted to an int and advances the associated file position indicator for the - stream (if defined). -

Returns -

- If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- - of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the - fgetc function returns the next character from the input stream pointed to by stream. - If a read error occurs, the error indicator for the stream is set and the fgetc function - returns EOF.282) - -

Footnotes -

282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. - - -

Contents -

7.21.7.2 The fgets function
-

Synopsis -

-

-         #include <stdio.h>
-         char *fgets(char * restrict s, int n,
-              FILE * restrict stream);
-
-

Description -

- The fgets function reads at most one less than the number of characters specified by n - from the stream pointed to by stream into the array pointed to by s. No additional - characters are read after a new-line character (which is retained) or after end-of-file. A - null character is written immediately after the last character read into the array. -

Returns -

- The fgets function returns s if successful. If end-of-file is encountered and no - characters have been read into the array, the contents of the array remain unchanged and a - null pointer is returned. If a read error occurs during the operation, the array contents are - indeterminate and a null pointer is returned. - - - -

Contents -

7.21.7.3 The fputc function
-

Synopsis -

-

-         #include <stdio.h>
-         int fputc(int c, FILE *stream);
-
-

Description -

- The fputc function writes the character specified by c (converted to an unsigned - char) to the output stream pointed to by stream, at the position indicated by the - associated file position indicator for the stream (if defined), and advances the indicator - appropriately. If the file cannot support positioning requests, or if the stream was opened - with append mode, the character is appended to the output stream. -

Returns -

- The fputc function returns the character written. If a write error occurs, the error - indicator for the stream is set and fputc returns EOF. - -

Contents -

7.21.7.4 The fputs function
-

Synopsis -

-

-         #include <stdio.h>
-         int fputs(const char * restrict s,
-              FILE * restrict stream);
-
-

Description -

- The fputs function writes the string pointed to by s to the stream pointed to by - stream. The terminating null character is not written. -

Returns -

- The fputs function returns EOF if a write error occurs; otherwise it returns a - nonnegative value. - -

Contents -

7.21.7.5 The getc function
-

Synopsis -

-

-         #include <stdio.h>
-         int getc(FILE *stream);
-
-

Description -

- The getc function is equivalent to fgetc, except that if it is implemented as a macro, it - may evaluate stream more than once, so the argument should never be an expression - with side effects. - -

Returns -

- The getc function returns the next character from the input stream pointed to by - stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and - getc returns EOF. If a read error occurs, the error indicator for the stream is set and - getc returns EOF. - -

Contents -

7.21.7.6 The getchar function
-

Synopsis -

-

-        #include <stdio.h>
-        int getchar(void);
-
-

Description -

- The getchar function is equivalent to getc with the argument stdin. -

Returns -

- The getchar function returns the next character from the input stream pointed to by - stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and - getchar returns EOF. If a read error occurs, the error indicator for the stream is set and - getchar returns EOF. * - -

Contents -

7.21.7.7 The putc function
-

Synopsis -

-

-        #include <stdio.h>
-        int putc(int c, FILE *stream);
-
-

Description -

- The putc function is equivalent to fputc, except that if it is implemented as a macro, it - may evaluate stream more than once, so that argument should never be an expression - with side effects. -

Returns -

- The putc function returns the character written. If a write error occurs, the error - indicator for the stream is set and putc returns EOF. - -

Contents -

7.21.7.8 The putchar function
-

Synopsis -

-

-        #include <stdio.h>
-        int putchar(int c);
-
-

Description -

- The putchar function is equivalent to putc with the second argument stdout. - -

Returns -

- The putchar function returns the character written. If a write error occurs, the error - indicator for the stream is set and putchar returns EOF. - -

Contents -

7.21.7.9 The puts function
-

Synopsis -

-

-         #include <stdio.h>
-         int puts(const char *s);
-
-

Description -

- The puts function writes the string pointed to by s to the stream pointed to by stdout, - and appends a new-line character to the output. The terminating null character is not - written. -

Returns -

- The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative - value. - -

Contents -

7.21.7.10 The ungetc function
-

Synopsis -

-

-         #include <stdio.h>
-         int ungetc(int c, FILE *stream);
-
-

Description -

- The ungetc function pushes the character specified by c (converted to an unsigned - char) back onto the input stream pointed to by stream. Pushed-back characters will be - returned by subsequent reads on that stream in the reverse order of their pushing. A - successful intervening call (with the stream pointed to by stream) to a file positioning - function (fseek, fsetpos, or rewind) discards any pushed-back characters for the - stream. The external storage corresponding to the stream is unchanged. -

- One character of pushback is guaranteed. If the ungetc function is called too many - times on the same stream without an intervening read or file positioning operation on that - stream, the operation may fail. -

- If the value of c equals that of the macro EOF, the operation fails and the input stream is - unchanged. -

- A successful call to the ungetc function clears the end-of-file indicator for the stream. - The value of the file position indicator for the stream after reading or discarding all - pushed-back characters shall be the same as it was before the characters were pushed - back. For a text stream, the value of its file position indicator after a successful call to the - ungetc function is unspecified until all pushed-back characters are read or discarded. - - For a binary stream, its file position indicator is decremented by each successful call to - the ungetc function; if its value was zero before a call, it is indeterminate after the - call.283) -

Returns -

- The ungetc function returns the character pushed back after conversion, or EOF if the - operation fails. -

Forward references: file positioning functions (7.21.9). - -

Footnotes -

283) See ''future library directions'' (7.30.9). - - -

Contents -

7.21.8 Direct input/output functions

- -

Contents -

7.21.8.1 The fread function
-

Synopsis -

-

-          #include <stdio.h>
-          size_t fread(void * restrict ptr,
-               size_t size, size_t nmemb,
-               FILE * restrict stream);
-
-

Description -

- The fread function reads, into the array pointed to by ptr, up to nmemb elements - whose size is specified by size, from the stream pointed to by stream. For each - object, size calls are made to the fgetc function and the results stored, in the order - read, in an array of unsigned char exactly overlaying the object. The file position - indicator for the stream (if defined) is advanced by the number of characters successfully - read. If an error occurs, the resulting value of the file position indicator for the stream is - indeterminate. If a partial element is read, its value is indeterminate. -

Returns -

- The fread function returns the number of elements successfully read, which may be - less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, - fread returns zero and the contents of the array and the state of the stream remain - unchanged. - - - - - - -

Contents -

7.21.8.2 The fwrite function
-

Synopsis -

-

-         #include <stdio.h>
-         size_t fwrite(const void * restrict ptr,
-              size_t size, size_t nmemb,
-              FILE * restrict stream);
-
-

Description -

- The fwrite function writes, from the array pointed to by ptr, up to nmemb elements - whose size is specified by size, to the stream pointed to by stream. For each object, - size calls are made to the fputc function, taking the values (in order) from an array of - unsigned char exactly overlaying the object. The file position indicator for the - stream (if defined) is advanced by the number of characters successfully written. If an - error occurs, the resulting value of the file position indicator for the stream is - indeterminate. -

Returns -

- The fwrite function returns the number of elements successfully written, which will be - less than nmemb only if a write error is encountered. If size or nmemb is zero, - fwrite returns zero and the state of the stream remains unchanged. - -

Contents -

7.21.9 File positioning functions

- -

Contents -

7.21.9.1 The fgetpos function
-

Synopsis -

-

-         #include <stdio.h>
-         int fgetpos(FILE * restrict stream,
-              fpos_t * restrict pos);
-
-

Description -

- The fgetpos function stores the current values of the parse state (if any) and file - position indicator for the stream pointed to by stream in the object pointed to by pos. - The values stored contain unspecified information usable by the fsetpos function for - repositioning the stream to its position at the time of the call to the fgetpos function. -

Returns -

- If successful, the fgetpos function returns zero; on failure, the fgetpos function - returns nonzero and stores an implementation-defined positive value in errno. -

Forward references: the fsetpos function (7.21.9.3). - - -

Contents -

7.21.9.2 The fseek function
-

Synopsis -

-

-        #include <stdio.h>
-        int fseek(FILE *stream, long int offset, int whence);
-
-

Description -

- The fseek function sets the file position indicator for the stream pointed to by stream. - If a read or write error occurs, the error indicator for the stream is set and fseek fails. -

- For a binary stream, the new position, measured in characters from the beginning of the - file, is obtained by adding offset to the position specified by whence. The specified - position is the beginning of the file if whence is SEEK_SET, the current value of the file - position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not - meaningfully support fseek calls with a whence value of SEEK_END. -

- For a text stream, either offset shall be zero, or offset shall be a value returned by - an earlier successful call to the ftell function on a stream associated with the same file - and whence shall be SEEK_SET. -

- After determining the new position, a successful call to the fseek function undoes any - effects of the ungetc function on the stream, clears the end-of-file indicator for the - stream, and then establishes the new position. After a successful fseek call, the next - operation on an update stream may be either input or output. -

Returns -

- The fseek function returns nonzero only for a request that cannot be satisfied. -

Forward references: the ftell function (7.21.9.4). - -

Contents -

7.21.9.3 The fsetpos function
-

Synopsis -

-

-        #include <stdio.h>
-        int fsetpos(FILE *stream, const fpos_t *pos);
-
-

Description -

- The fsetpos function sets the mbstate_t object (if any) and file position indicator - for the stream pointed to by stream according to the value of the object pointed to by - pos, which shall be a value obtained from an earlier successful call to the fgetpos - function on a stream associated with the same file. If a read or write error occurs, the - error indicator for the stream is set and fsetpos fails. -

- A successful call to the fsetpos function undoes any effects of the ungetc function - on the stream, clears the end-of-file indicator for the stream, and then establishes the new - parse state and position. After a successful fsetpos call, the next operation on an - - update stream may be either input or output. -

Returns -

- If successful, the fsetpos function returns zero; on failure, the fsetpos function - returns nonzero and stores an implementation-defined positive value in errno. - -

Contents -

7.21.9.4 The ftell function
-

Synopsis -

-

-         #include <stdio.h>
-         long int ftell(FILE *stream);
-
-

Description -

- The ftell function obtains the current value of the file position indicator for the stream - pointed to by stream. For a binary stream, the value is the number of characters from - the beginning of the file. For a text stream, its file position indicator contains unspecified - information, usable by the fseek function for returning the file position indicator for the - stream to its position at the time of the ftell call; the difference between two such - return values is not necessarily a meaningful measure of the number of characters written - or read. -

Returns -

- If successful, the ftell function returns the current value of the file position indicator - for the stream. On failure, the ftell function returns -1L and stores an - implementation-defined positive value in errno. - -

Contents -

7.21.9.5 The rewind function
-

Synopsis -

-

-         #include <stdio.h>
-         void rewind(FILE *stream);
-
-

Description -

- The rewind function sets the file position indicator for the stream pointed to by - stream to the beginning of the file. It is equivalent to -

-         (void)fseek(stream, 0L, SEEK_SET)
-
- except that the error indicator for the stream is also cleared. -

Returns -

- The rewind function returns no value. - - -

Contents -

7.21.10 Error-handling functions

- -

Contents -

7.21.10.1 The clearerr function
-

Synopsis -

-

-        #include <stdio.h>
-        void clearerr(FILE *stream);
-
-

Description -

- The clearerr function clears the end-of-file and error indicators for the stream pointed - to by stream. -

Returns -

- The clearerr function returns no value. - -

Contents -

7.21.10.2 The feof function
-

Synopsis -

-

-        #include <stdio.h>
-        int feof(FILE *stream);
-
-

Description -

- The feof function tests the end-of-file indicator for the stream pointed to by stream. -

Returns -

- The feof function returns nonzero if and only if the end-of-file indicator is set for - stream. - -

Contents -

7.21.10.3 The ferror function
-

Synopsis -

-

-        #include <stdio.h>
-        int ferror(FILE *stream);
-
-

Description -

- The ferror function tests the error indicator for the stream pointed to by stream. -

Returns -

- The ferror function returns nonzero if and only if the error indicator is set for - stream. - - -

Contents -

7.21.10.4 The perror function
-

Synopsis -

-

-         #include <stdio.h>
-         void perror(const char *s);
-
-

Description -

- The perror function maps the error number in the integer expression errno to an - error message. It writes a sequence of characters to the standard error stream thus: first - (if s is not a null pointer and the character pointed to by s is not the null character), the - string pointed to by s followed by a colon (:) and a space; then an appropriate error - message string followed by a new-line character. The contents of the error message - strings are the same as those returned by the strerror function with argument errno. -

Returns -

- The perror function returns no value. -

Forward references: the strerror function (7.23.6.2). - - -

Contents -

7.22 General utilities <stdlib.h>

-

- The header <stdlib.h> declares five types and several functions of general utility, and - defines several macros.284) -

- The types declared are size_t and wchar_t (both described in 7.19), -

-          div_t
-
- which is a structure type that is the type of the value returned by the div function, -
-          ldiv_t
-
- which is a structure type that is the type of the value returned by the ldiv function, and -
-          lldiv_t
-
- which is a structure type that is the type of the value returned by the lldiv function. -

- The macros defined are NULL (described in 7.19); -

-          EXIT_FAILURE
-
- and -
-          EXIT_SUCCESS
-
- which expand to integer constant expressions that can be used as the argument to the - exit function to return unsuccessful or successful termination status, respectively, to the - host environment; -
-          RAND_MAX
-
- which expands to an integer constant expression that is the maximum value returned by - the rand function; and -
-          MB_CUR_MAX
-
- which expands to a positive integer expression with type size_t that is the maximum - number of bytes in a multibyte character for the extended character set specified by the - current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX. - - - - - - -

Footnotes -

284) See ''future library directions'' (7.30.10). - - -

Contents -

7.22.1 Numeric conversion functions

-

- The functions atof, atoi, atol, and atoll need not affect the value of the integer - expression errno on an error. If the value of the result cannot be represented, the - behavior is undefined. - -

Contents -

7.22.1.1 The atof function
-

Synopsis -

-

-         #include <stdlib.h>
-         double atof(const char *nptr);
-
-

Description -

- The atof function converts the initial portion of the string pointed to by nptr to - double representation. Except for the behavior on error, it is equivalent to -

-         strtod(nptr, (char **)NULL)
-
-

Returns -

- The atof function returns the converted value. -

Forward references: the strtod, strtof, and strtold functions (7.22.1.3). - -

Contents -

7.22.1.2 The atoi, atol, and atoll functions
-

Synopsis -

-

-         #include <stdlib.h>
-         int atoi(const char *nptr);
-         long int atol(const char *nptr);
-         long long int atoll(const char *nptr);
-
-

Description -

- The atoi, atol, and atoll functions convert the initial portion of the string pointed - to by nptr to int, long int, and long long int representation, respectively. - Except for the behavior on error, they are equivalent to -

-         atoi: (int)strtol(nptr, (char **)NULL, 10)
-         atol: strtol(nptr, (char **)NULL, 10)
-         atoll: strtoll(nptr, (char **)NULL, 10)
-
-

Returns -

- The atoi, atol, and atoll functions return the converted value. -

Forward references: the strtol, strtoll, strtoul, and strtoull functions - (7.22.1.4). - - -

Contents -

7.22.1.3 The strtod, strtof, and strtold functions
-

Synopsis -

-

-        #include <stdlib.h>
-        double strtod(const char * restrict nptr,
-             char ** restrict endptr);
-        float strtof(const char * restrict nptr,
-             char ** restrict endptr);
-        long double strtold(const char * restrict nptr,
-             char ** restrict endptr);
-
-

Description -

- The strtod, strtof, and strtold functions convert the initial portion of the string - pointed to by nptr to double, float, and long double representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space characters (as specified by the isspace function), a - subject sequence resembling a floating-point constant or representing an infinity or NaN; - and a final string of one or more unrecognized characters, including the terminating null - character of the input string. Then, they attempt to convert the subject sequence to a - floating-point number, and return the result. -

- The expected form of the subject sequence is an optional plus or minus sign, then one of - the following: -

- The subject sequence is defined as the longest initial subsequence of the input string, - starting with the first non-white-space character, that is of the expected form. The subject - sequence contains no characters if the input string is not of the expected form. -

- If the subject sequence has the expected form for a floating-point number, the sequence of - characters starting with the first digit or the decimal-point character (whichever occurs - first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the - - decimal-point character is used in place of a period, and that if neither an exponent part - nor a decimal-point character appears in a decimal floating point number, or if a binary - exponent part does not appear in a hexadecimal floating point number, an exponent part - of the appropriate type with value zero is assumed to follow the last digit in the string. If - the subject sequence begins with a minus sign, the sequence is interpreted as negated.285) - A character sequence INF or INFINITY is interpreted as an infinity, if representable in - the return type, else like a floating constant that is too large for the range of the return - type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet - NaN, if supported in the return type, else like a subject sequence part that does not have - the expected form; the meaning of the n-char sequences is implementation-defined.286) A - pointer to the final string is stored in the object pointed to by endptr, provided that - endptr is not a null pointer. -

- If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the - value resulting from the conversion is correctly rounded. -

- In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -

- If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. -

Recommended practice -

- If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and - the result is not exactly representable, the result should be one of the two numbers in the - appropriate internal format that are adjacent to the hexadecimal floating source value, - with the extra stipulation that the error should have a correct sign for the current rounding - direction. -

- If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in - <float.h>) significant digits, the result should be correctly rounded. If the subject - sequence D has the decimal form and more than DECIMAL_DIG significant digits, - consider the two bounding, adjacent decimal strings L and U, both having - DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. - The result should be one of the (equal or adjacent) values that would be obtained by - correctly rounding L and U according to the current rounding direction, with the extra - - - stipulation that the error with respect to D should have a correct sign for the current - rounding direction.287) -

Returns -

- The functions return the converted value, if any. If no conversion could be performed, - zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), - plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the - return type and sign of the value), and the value of the macro ERANGE is stored in - errno. If the result underflows (7.12.1), the functions return a value whose magnitude is - no greater than the smallest normalized positive number in the return type; whether - errno acquires the value ERANGE is implementation-defined. - -

Footnotes -

285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two - methods may yield different results if rounding is toward positive or negative infinity. In either case, - the functions honor the sign of zero if floating-point arithmetic supports signed zeros. - -

286) An implementation may use the n-char sequence to determine extra information to be represented in - the NaN's significand. - -

287) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round - to the same internal floating value, but if not will round to adjacent values. - - -

Contents -

7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
-

Synopsis -

-

-         #include <stdlib.h>
-         long int strtol(
-              const char * restrict nptr,
-              char ** restrict endptr,
-              int base);
-         long long int strtoll(
-              const char * restrict nptr,
-              char ** restrict endptr,
-              int base);
-         unsigned long int strtoul(
-              const char * restrict nptr,
-              char ** restrict endptr,
-              int base);
-         unsigned long long int strtoull(
-              const char * restrict nptr,
-              char ** restrict endptr,
-              int base);
-
-

Description -

- The strtol, strtoll, strtoul, and strtoull functions convert the initial - portion of the string pointed to by nptr to long int, long long int, unsigned - long int, and unsigned long long int representation, respectively. First, - they decompose the input string into three parts: an initial, possibly empty, sequence of - white-space characters (as specified by the isspace function), a subject sequence - - - - resembling an integer represented in some radix determined by the value of base, and a - final string of one or more unrecognized characters, including the terminating null - character of the input string. Then, they attempt to convert the subject sequence to an - integer, and return the result. -

- If the value of base is zero, the expected form of the subject sequence is that of an - integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but - not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the - expected form of the subject sequence is a sequence of letters and digits representing an - integer with the radix specified by base, optionally preceded by a plus or minus sign, - but not including an integer suffix. The letters from a (or A) through z (or Z) are - ascribed the values 10 through 35; only letters and digits whose ascribed values are less - than that of base are permitted. If the value of base is 16, the characters 0x or 0X may - optionally precede the sequence of letters and digits, following the sign if present. -

- The subject sequence is defined as the longest initial subsequence of the input string, - starting with the first non-white-space character, that is of the expected form. The subject - sequence contains no characters if the input string is empty or consists entirely of white - space, or if the first non-white-space character is other than a sign or a permissible letter - or digit. -

- If the subject sequence has the expected form and the value of base is zero, the sequence - of characters starting with the first digit is interpreted as an integer constant according to - the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base - is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value - as given above. If the subject sequence begins with a minus sign, the value resulting from - the conversion is negated (in the return type). A pointer to the final string is stored in the - object pointed to by endptr, provided that endptr is not a null pointer. -

- In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -

- If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. -

Returns -

- The strtol, strtoll, strtoul, and strtoull functions return the converted - value, if any. If no conversion could be performed, zero is returned. If the correct value - is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, - LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type - and sign of the value, if any), and the value of the macro ERANGE is stored in errno. - - -

Contents -

7.22.2 Pseudo-random sequence generation functions

- -

Contents -

7.22.2.1 The rand function
-

Synopsis -

-

-         #include <stdlib.h>
-         int rand(void);
-
-

Description -

- The rand function computes a sequence of pseudo-random integers in the range 0 to - RAND_MAX.288) -

- The rand function is not required to avoid data races. The implementation shall behave - as if no library function calls the rand function. -

Returns -

- The rand function returns a pseudo-random integer. -

Environmental limits -

- The value of the RAND_MAX macro shall be at least 32767. - -

Footnotes -

288) There are no guarantees as to the quality of the random sequence produced and some implementations - are known to produce sequences with distressingly non-random low-order bits. Applications with - particular requirements should use a generator that is known to be sufficient for their needs. - - -

Contents -

7.22.2.2 The srand function
-

Synopsis -

-

-         #include <stdlib.h>
-         void srand(unsigned int seed);
-
-

Description -

- The srand function uses the argument as a seed for a new sequence of pseudo-random - numbers to be returned by subsequent calls to rand. If srand is then called with the - same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is - called before any calls to srand have been made, the same sequence shall be generated - as when srand is first called with a seed value of 1. -

- The implementation shall behave as if no library function calls the srand function. -

Returns -

- The srand function returns no value. - - - - - -

- EXAMPLE The following functions define a portable implementation of rand and srand. -

-         static unsigned long int next = 1;
-         int rand(void)   // RAND_MAX assumed to be 32767
-         {
-               next = next * 1103515245 + 12345;
-               return (unsigned int)(next/65536) % 32768;
-         }
-         void srand(unsigned int seed)
-         {
-               next = seed;
-         }
-
- - -

Contents -

7.22.3 Memory management functions

-

- The order and contiguity of storage allocated by successive calls to the - aligned_alloc, calloc, malloc, and realloc functions is unspecified. The - pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to - a pointer to any type of object with a fundamental alignment requirement and then used - to access such an object or an array of such objects in the space allocated (until the space - is explicitly deallocated). The lifetime of an allocated object extends from the allocation - until the deallocation. Each such allocation shall yield a pointer to an object disjoint from - any other object. The pointer returned points to the start (lowest byte address) of the - allocated space. If the space cannot be allocated, a null pointer is returned. If the size of - the space requested is zero, the behavior is implementation-defined: either a null pointer - is returned, or the behavior is as if the size were some nonzero value, except that the - returned pointer shall not be used to access an object. - -

Contents -

7.22.3.1 The aligned_alloc function
-

Synopsis -

-

-         #include <stdlib.h>
-         void *aligned_alloc(size_t alignment, size_t size);
-
-

Description -

- The aligned_alloc function allocates space for an object whose alignment is - specified by alignment, whose size is specified by size, and whose value is - indeterminate. The value of alignment shall be a valid alignment supported by the - implementation and the value of size shall be an integral multiple of alignment. -

Returns -

- The aligned_alloc function returns either a null pointer or a pointer to the allocated - space. - - -

Contents -

7.22.3.2 The calloc function
-

Synopsis -

-

-         #include <stdlib.h>
-         void *calloc(size_t nmemb, size_t size);
-
-

Description -

- The calloc function allocates space for an array of nmemb objects, each of whose size - is size. The space is initialized to all bits zero.289) -

Returns -

- The calloc function returns either a null pointer or a pointer to the allocated space. - -

Footnotes -

289) Note that this need not be the same as the representation of floating-point zero or a null pointer - constant. - - -

Contents -

7.22.3.3 The free function
-

Synopsis -

-

-         #include <stdlib.h>
-         void free(void *ptr);
-
-

Description -

- The free function causes the space pointed to by ptr to be deallocated, that is, made - available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if - the argument does not match a pointer earlier returned by a memory management - function, or if the space has been deallocated by a call to free or realloc, the - behavior is undefined. -

Returns -

- The free function returns no value. - -

Contents -

7.22.3.4 The malloc function
-

Synopsis -

-

-         #include <stdlib.h>
-         void *malloc(size_t size);
-
-

Description -

- The malloc function allocates space for an object whose size is specified by size and - whose value is indeterminate. - - - - - -

Returns -

- The malloc function returns either a null pointer or a pointer to the allocated space. - -

Contents -

7.22.3.5 The realloc function
-

Synopsis -

-

-         #include <stdlib.h>
-         void *realloc(void *ptr, size_t size);
-
-

Description -

- The realloc function deallocates the old object pointed to by ptr and returns a - pointer to a new object that has the size specified by size. The contents of the new - object shall be the same as that of the old object prior to deallocation, up to the lesser of - the new and old sizes. Any bytes in the new object beyond the size of the old object have - indeterminate values. -

- If ptr is a null pointer, the realloc function behaves like the malloc function for the - specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory - management function, or if the space has been deallocated by a call to the free or - realloc function, the behavior is undefined. If memory for the new object cannot be - allocated, the old object is not deallocated and its value is unchanged. -

Returns -

- The realloc function returns a pointer to the new object (which may have the same - value as a pointer to the old object), or a null pointer if the new object could not be - allocated. - -

Contents -

7.22.4 Communication with the environment

- -

Contents -

7.22.4.1 The abort function
-

Synopsis -

-

-         #include <stdlib.h>
-         _Noreturn void abort(void);
-
-

Description -

- The abort function causes abnormal program termination to occur, unless the signal - SIGABRT is being caught and the signal handler does not return. Whether open streams - with unwritten buffered data are flushed, open streams are closed, or temporary files are - removed is implementation-defined. An implementation-defined form of the status - unsuccessful termination is returned to the host environment by means of the function - call raise(SIGABRT). - -

Returns -

- The abort function does not return to its caller. - -

Contents -

7.22.4.2 The atexit function
-

Synopsis -

-

-        #include <stdlib.h>
-        int atexit(void (*func)(void));
-
-

Description -

- The atexit function registers the function pointed to by func, to be called without - arguments at normal program termination.290) -

Environmental limits -

- The implementation shall support the registration of at least 32 functions. -

Returns -

- The atexit function returns zero if the registration succeeds, nonzero if it fails. -

Forward references: the at_quick_exit function (7.22.4.3), the exit function - (7.22.4.4). - -

Footnotes -

290) The atexit function registrations are distinct from the at_quick_exit registrations, so - applications may need to call both registration functions with the same argument. - - -

Contents -

7.22.4.3 The at_quick_exit function
-

Synopsis -

-

-        #include <stdlib.h>
-        int at_quick_exit(void (*func)(void));
-
-

Description -

- The at_quick_exit function registers the function pointed to by func, to be called - without arguments should quick_exit be called.291) -

Environmental limits -

- The implementation shall support the registration of at least 32 functions. -

Returns -

- The at_quick_exit function returns zero if the registration succeeds, nonzero if it - fails. -

Forward references: the quick_exit function (7.22.4.7). - - - - -

Footnotes -

291) The at_quick_exit function registrations are distinct from the atexit registrations, so - applications may need to call both registration functions with the same argument. - - -

Contents -

7.22.4.4 The exit function
-

Synopsis -

-

-         #include <stdlib.h>
-         _Noreturn void exit(int status);
-
-

Description -

- The exit function causes normal program termination to occur. No functions registered - by the at_quick_exit function are called. If a program calls the exit function - more than once, or calls the quick_exit function in addition to the exit function, the - behavior is undefined. -

- First, all functions registered by the atexit function are called, in the reverse order of - their registration,292) except that a function is called after any previously registered - functions that had already been called at the time it was registered. If, during the call to - any such function, a call to the longjmp function is made that would terminate the call - to the registered function, the behavior is undefined. -

- Next, all open streams with unwritten buffered data are flushed, all open streams are - closed, and all files created by the tmpfile function are removed. -

- Finally, control is returned to the host environment. If the value of status is zero or - EXIT_SUCCESS, an implementation-defined form of the status successful termination is - returned. If the value of status is EXIT_FAILURE, an implementation-defined form - of the status unsuccessful termination is returned. Otherwise the status returned is - implementation-defined. -

Returns -

- The exit function cannot return to its caller. - -

Footnotes -

292) Each function is called as many times as it was registered, and in the correct order with respect to - other registered functions. - - -

Contents -

7.22.4.5 The _Exit function
-

Synopsis -

-

-         #include <stdlib.h>
-         _Noreturn void _Exit(int status);
-
-

Description -

- The _Exit function causes normal program termination to occur and control to be - returned to the host environment. No functions registered by the atexit function, the - at_quick_exit function, or signal handlers registered by the signal function are - called. The status returned to the host environment is determined in the same way as for - - - - the exit function (7.22.4.4). Whether open streams with unwritten buffered data are - flushed, open streams are closed, or temporary files are removed is implementation- - defined. -

Returns -

- The _Exit function cannot return to its caller. - -

Contents -

7.22.4.6 The getenv function
-

Synopsis -

-

-         #include <stdlib.h>
-         char *getenv(const char *name);
-
-

Description -

- The getenv function searches an environment list, provided by the host environment, - for a string that matches the string pointed to by name. The set of environment names - and the method for altering the environment list are implementation-defined. The - getenv function need not avoid data races with other threads of execution that modify - the environment list.293) -

- The implementation shall behave as if no library function calls the getenv function. -

Returns -

- The getenv function returns a pointer to a string associated with the matched list - member. The string pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the getenv function. If the specified name cannot - be found, a null pointer is returned. - -

Footnotes -

293) Many implementations provide non-standard functions that modify the environment list. - - -

Contents -

7.22.4.7 The quick_exit function
-

Synopsis -

-

-         #include <stdlib.h>
-         _Noreturn void quick_exit(int status);
-
-

Description -

- The quick_exit function causes normal program termination to occur. No functions - registered by the atexit function or signal handlers registered by the signal function - are called. If a program calls the quick_exit function more than once, or calls the - exit function in addition to the quick_exit function, the behavior is undefined. -

- The quick_exit function first calls all functions registered by the at_quick_exit - function, in the reverse order of their registration,294) except that a function is called after - - - - any previously registered functions that had already been called at the time it was - registered. If, during the call to any such function, a call to the longjmp function is - made that would terminate the call to the registered function, the behavior is undefined. -

- Then control is returned to the host environment by means of the function call - _Exit(status). -

Returns -

- The quick_exit function cannot return to its caller. - -

Footnotes -

294) Each function is called as many times as it was registered, and in the correct order with respect to - other registered functions. - - -

Contents -

7.22.4.8 The system function
-

Synopsis -

-

-         #include <stdlib.h>
-         int system(const char *string);
-
-

Description -

- If string is a null pointer, the system function determines whether the host - environment has a command processor. If string is not a null pointer, the system - function passes the string pointed to by string to that command processor to be - executed in a manner which the implementation shall document; this might then cause the - program calling system to behave in a non-conforming manner or to terminate. -

Returns -

- If the argument is a null pointer, the system function returns nonzero only if a - command processor is available. If the argument is not a null pointer, and the system - function does return, it returns an implementation-defined value. - -

Contents -

7.22.5 Searching and sorting utilities

-

- These utilities make use of a comparison function to search or sort arrays of unspecified - type. Where an argument declared as size_t nmemb specifies the length of the array - for a function, nmemb can have the value zero on a call to that function; the comparison - function is not called, a search finds no matching element, and sorting performs no - rearrangement. Pointer arguments on such a call shall still have valid values, as described - in 7.1.4. -

- The implementation shall ensure that the second argument of the comparison function - (when called from bsearch), or both arguments (when called from qsort), are - pointers to elements of the array.295) The first argument when called from bsearch - shall equal key. - - - - -

- The comparison function shall not alter the contents of the array. The implementation - may reorder elements of the array between calls to the comparison function, but shall not - alter the contents of any individual element. -

- When the same objects (consisting of size bytes, irrespective of their current positions - in the array) are passed more than once to the comparison function, the results shall be - consistent with one another. That is, for qsort they shall define a total ordering on the - array, and for bsearch the same object shall always compare the same way with the - key. -

- A sequence point occurs immediately before and immediately after each call to the - comparison function, and also between any call to the comparison function and any - movement of the objects passed as arguments to that call. - -

Footnotes -

295) That is, if the value passed is p, then the following expressions are always nonzero: - -

-          ((char *)p - (char *)base) % size == 0
-          (char *)p >= (char *)base
-          (char *)p < (char *)base + nmemb * size
-
- - - -

Contents -

7.22.5.1 The bsearch function
-

Synopsis -

-

-          #include <stdlib.h>
-          void *bsearch(const void *key, const void *base,
-               size_t nmemb, size_t size,
-               int (*compar)(const void *, const void *));
-
-

Description -

- The bsearch function searches an array of nmemb objects, the initial element of which - is pointed to by base, for an element that matches the object pointed to by key. The - size of each element of the array is specified by size. -

- The comparison function pointed to by compar is called with two arguments that point - to the key object and to an array element, in that order. The function shall return an - integer less than, equal to, or greater than zero if the key object is considered, - respectively, to be less than, to match, or to be greater than the array element. The array - shall consist of: all the elements that compare less than, all the elements that compare - equal to, and all the elements that compare greater than the key object, in that order.296) -

Returns -

- The bsearch function returns a pointer to a matching element of the array, or a null - pointer if no match is found. If two elements compare as equal, which element is - - - - matched is unspecified. - -

Footnotes -

296) In practice, the entire array is sorted according to the comparison function. - - -

Contents -

7.22.5.2 The qsort function
-

Synopsis -

-

-         #include <stdlib.h>
-         void qsort(void *base, size_t nmemb, size_t size,
-              int (*compar)(const void *, const void *));
-
-

Description -

- The qsort function sorts an array of nmemb objects, the initial element of which is - pointed to by base. The size of each object is specified by size. -

- The contents of the array are sorted into ascending order according to a comparison - function pointed to by compar, which is called with two arguments that point to the - objects being compared. The function shall return an integer less than, equal to, or - greater than zero if the first argument is considered to be respectively less than, equal to, - or greater than the second. -

- If two elements compare as equal, their order in the resulting sorted array is unspecified. -

Returns -

- The qsort function returns no value. - -

Contents -

7.22.6 Integer arithmetic functions

- -

Contents -

7.22.6.1 The abs, labs and llabs functions
-

Synopsis -

-

-         #include <stdlib.h>
-         int abs(int j);
-         long int labs(long int j);
-         long long int llabs(long long int j);
-
-

Description -

- The abs, labs, and llabs functions compute the absolute value of an integer j. If the - result cannot be represented, the behavior is undefined.297) -

Returns -

- The abs, labs, and llabs, functions return the absolute value. - - - - - - -

Footnotes -

297) The absolute value of the most negative number cannot be represented in two's complement. - - -

Contents -

7.22.6.2 The div, ldiv, and lldiv functions
-

Synopsis -

-

-          #include <stdlib.h>
-          div_t div(int numer, int denom);
-          ldiv_t ldiv(long int numer, long int denom);
-          lldiv_t lldiv(long long int numer, long long int denom);
-
-

Description -

- The div, ldiv, and lldiv, functions compute numer / denom and numer % - denom in a single operation. -

Returns -

- The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and - lldiv_t, respectively, comprising both the quotient and the remainder. The structures - shall contain (in either order) the members quot (the quotient) and rem (the remainder), - each of which has the same type as the arguments numer and denom. If either part of - the result cannot be represented, the behavior is undefined. - -

Contents -

7.22.7 Multibyte/wide character conversion functions

-

- The behavior of the multibyte character functions is affected by the LC_CTYPE category - of the current locale. For a state-dependent encoding, each function is placed into its - initial conversion state at program startup and can be returned to that state by a call for - which its character pointer argument, s, is a null pointer. Subsequent calls with s as - other than a null pointer cause the internal conversion state of the function to be altered as - necessary. A call with s as a null pointer causes these functions to return a nonzero value - if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE - category causes the conversion state of these functions to be indeterminate. - -

Footnotes -

298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide - character codes, but are grouped with an adjacent multibyte character. - - -

Contents -

7.22.7.1 The mblen function
-

Synopsis -

-

-          #include <stdlib.h>
-          int mblen(const char *s, size_t n);
-
-

Description -

- If s is not a null pointer, the mblen function determines the number of bytes contained - in the multibyte character pointed to by s. Except that the conversion state of the - mbtowc function is not affected, it is equivalent to - - - - -

-         mbtowc((wchar_t *)0, (const char *)0, 0);
-         mbtowc((wchar_t *)0, s, n);
-
-

- The implementation shall behave as if no library function calls the mblen function. -

Returns -

- If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the mblen function either returns 0 (if s points to the null character), - or returns the number of bytes that are contained in the multibyte character (if the next n - or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid - multibyte character). -

Forward references: the mbtowc function (7.22.7.2). - -

Contents -

7.22.7.2 The mbtowc function
-

Synopsis -

-

-         #include <stdlib.h>
-         int mbtowc(wchar_t * restrict pwc,
-              const char * restrict s,
-              size_t n);
-
-

Description -

- If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the value of the - corresponding wide character and then, if pwc is not a null pointer, stores that value in - the object pointed to by pwc. If the corresponding wide character is the null wide - character, the function is left in the initial conversion state. -

- The implementation shall behave as if no library function calls the mbtowc function. -

Returns -

- If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the mbtowc function either returns 0 (if s points to the null character), - or returns the number of bytes that are contained in the converted multibyte character (if - the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not - form a valid multibyte character). -

- In no case will the value returned be greater than n or the value of the MB_CUR_MAX - macro. - - -

Contents -

7.22.7.3 The wctomb function
-

Synopsis -

-

-        #include <stdlib.h>
-        int wctomb(char *s, wchar_t wc);
-
-

Description -

- The wctomb function determines the number of bytes needed to represent the multibyte - character corresponding to the wide character given by wc (including any shift - sequences), and stores the multibyte character representation in the array whose first - element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters - are stored. If wc is a null wide character, a null byte is stored, preceded by any shift - sequence needed to restore the initial shift state, and the function is left in the initial - conversion state. -

- The implementation shall behave as if no library function calls the wctomb function. -

Returns -

- If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the wctomb function returns -1 if the value of wc does not correspond - to a valid multibyte character, or returns the number of bytes that are contained in the - multibyte character corresponding to the value of wc. -

- In no case will the value returned be greater than the value of the MB_CUR_MAX macro. - -

Contents -

7.22.8 Multibyte/wide string conversion functions

-

- The behavior of the multibyte string functions is affected by the LC_CTYPE category of - the current locale. - -

Contents -

7.22.8.1 The mbstowcs function
-

Synopsis -

-

-        #include <stdlib.h>
-        size_t mbstowcs(wchar_t * restrict pwcs,
-             const char * restrict s,
-             size_t n);
-
-

Description -

- The mbstowcs function converts a sequence of multibyte characters that begins in the - initial shift state from the array pointed to by s into a sequence of corresponding wide - characters and stores not more than n wide characters into the array pointed to by pwcs. - No multibyte characters that follow a null character (which is converted into a null wide - character) will be examined or converted. Each multibyte character is converted as if by - a call to the mbtowc function, except that the conversion state of the mbtowc function is - - not affected. -

- No more than n elements will be modified in the array pointed to by pwcs. If copying - takes place between objects that overlap, the behavior is undefined. -

Returns -

- If an invalid multibyte character is encountered, the mbstowcs function returns - (size_t)(-1). Otherwise, the mbstowcs function returns the number of array - elements modified, not including a terminating null wide character, if any.299) - -

Footnotes -

299) The array will not be null-terminated if the value returned is n. - - -

Contents -

7.22.8.2 The wcstombs function
-

Synopsis -

-

-          #include <stdlib.h>
-          size_t wcstombs(char * restrict s,
-               const wchar_t * restrict pwcs,
-               size_t n);
-
-

Description -

- The wcstombs function converts a sequence of wide characters from the array pointed - to by pwcs into a sequence of corresponding multibyte characters that begins in the - initial shift state, and stores these multibyte characters into the array pointed to by s, - stopping if a multibyte character would exceed the limit of n total bytes or if a null - character is stored. Each wide character is converted as if by a call to the wctomb - function, except that the conversion state of the wctomb function is not affected. -

- No more than n bytes will be modified in the array pointed to by s. If copying takes place - between objects that overlap, the behavior is undefined. -

Returns -

- If a wide character is encountered that does not correspond to a valid multibyte character, - the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function - returns the number of bytes modified, not including a terminating null character, if - any.299) - - - - - - -

Contents -

7.23 String handling <string.h>

- -

Contents -

7.23.1 String function conventions

-

- The header <string.h> declares one type and several functions, and defines one - macro useful for manipulating arrays of character type and other objects treated as arrays - of character type.300) The type is size_t and the macro is NULL (both described in - 7.19). Various methods are used for determining the lengths of the arrays, but in all cases - a char * or void * argument points to the initial (lowest addressed) character of the - array. If an array is accessed beyond the end of an object, the behavior is undefined. -

- Where an argument declared as size_t n specifies the length of the array for a - function, n can have the value zero on a call to that function. Unless explicitly stated - otherwise in the description of a particular function in this subclause, pointer arguments - on such a call shall still have valid values, as described in 7.1.4. On such a call, a - function that locates a character finds no occurrence, a function that compares two - character sequences returns zero, and a function that copies characters copies zero - characters. -

- For all functions in this subclause, each character shall be interpreted as if it had the type - unsigned char (and therefore every possible object representation is valid and has a - different value). - -

Footnotes -

300) See ''future library directions'' (7.30.11). - - -

Contents -

7.23.2 Copying functions

- -

Contents -

7.23.2.1 The memcpy function
-

Synopsis -

-

-          #include <string.h>
-          void *memcpy(void * restrict s1,
-               const void * restrict s2,
-               size_t n);
-
-

Description -

- The memcpy function copies n characters from the object pointed to by s2 into the - object pointed to by s1. If copying takes place between objects that overlap, the behavior - is undefined. -

Returns -

- The memcpy function returns the value of s1. - - - - - - -

Contents -

7.23.2.2 The memmove function
-

Synopsis -

-

-         #include <string.h>
-         void *memmove(void *s1, const void *s2, size_t n);
-
-

Description -

- The memmove function copies n characters from the object pointed to by s2 into the - object pointed to by s1. Copying takes place as if the n characters from the object - pointed to by s2 are first copied into a temporary array of n characters that does not - overlap the objects pointed to by s1 and s2, and then the n characters from the - temporary array are copied into the object pointed to by s1. -

Returns -

- The memmove function returns the value of s1. - -

Contents -

7.23.2.3 The strcpy function
-

Synopsis -

-

-         #include <string.h>
-         char *strcpy(char * restrict s1,
-              const char * restrict s2);
-
-

Description -

- The strcpy function copies the string pointed to by s2 (including the terminating null - character) into the array pointed to by s1. If copying takes place between objects that - overlap, the behavior is undefined. -

Returns -

- The strcpy function returns the value of s1. - -

Contents -

7.23.2.4 The strncpy function
-

Synopsis -

-

-         #include <string.h>
-         char *strncpy(char * restrict s1,
-              const char * restrict s2,
-              size_t n);
-
-

Description -

- The strncpy function copies not more than n characters (characters that follow a null - character are not copied) from the array pointed to by s2 to the array pointed to by - - s1.301) If copying takes place between objects that overlap, the behavior is undefined. -

- If the array pointed to by s2 is a string that is shorter than n characters, null characters - are appended to the copy in the array pointed to by s1, until n characters in all have been - written. -

Returns -

- The strncpy function returns the value of s1. - -

Footnotes -

301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will - not be null-terminated. - - -

Contents -

7.23.3 Concatenation functions

- -

Contents -

7.23.3.1 The strcat function
-

Synopsis -

-

-          #include <string.h>
-          char *strcat(char * restrict s1,
-               const char * restrict s2);
-
-

Description -

- The strcat function appends a copy of the string pointed to by s2 (including the - terminating null character) to the end of the string pointed to by s1. The initial character - of s2 overwrites the null character at the end of s1. If copying takes place between - objects that overlap, the behavior is undefined. -

Returns -

- The strcat function returns the value of s1. - -

Contents -

7.23.3.2 The strncat function
-

Synopsis -

-

-          #include <string.h>
-          char *strncat(char * restrict s1,
-               const char * restrict s2,
-               size_t n);
-
-

Description -

- The strncat function appends not more than n characters (a null character and - characters that follow it are not appended) from the array pointed to by s2 to the end of - the string pointed to by s1. The initial character of s2 overwrites the null character at the - end of s1. A terminating null character is always appended to the result.302) If copying - - - takes place between objects that overlap, the behavior is undefined. -

Returns -

- The strncat function returns the value of s1. -

Forward references: the strlen function (7.23.6.3). - -

Footnotes -

302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is - strlen(s1)+n+1. - - -

Contents -

7.23.4 Comparison functions

-

- The sign of a nonzero value returned by the comparison functions memcmp, strcmp, - and strncmp is determined by the sign of the difference between the values of the first - pair of characters (both interpreted as unsigned char) that differ in the objects being - compared. - -

Contents -

7.23.4.1 The memcmp function
-

Synopsis -

-

-         #include <string.h>
-         int memcmp(const void *s1, const void *s2, size_t n);
-
-

Description -

- The memcmp function compares the first n characters of the object pointed to by s1 to - the first n characters of the object pointed to by s2.303) -

Returns -

- The memcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the object pointed to by s1 is greater than, equal to, or less than the object - pointed to by s2. - -

Footnotes -

303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are - indeterminate. Strings shorter than their allocated space and unions may also cause problems in - comparison. - - -

Contents -

7.23.4.2 The strcmp function
-

Synopsis -

-

-         #include <string.h>
-         int strcmp(const char *s1, const char *s2);
-
-

Description -

- The strcmp function compares the string pointed to by s1 to the string pointed to by - s2. -

Returns -

- The strcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the string pointed to by s1 is greater than, equal to, or less than the string - - - pointed to by s2. - -

Contents -

7.23.4.3 The strcoll function
-

Synopsis -

-

-        #include <string.h>
-        int strcoll(const char *s1, const char *s2);
-
-

Description -

- The strcoll function compares the string pointed to by s1 to the string pointed to by - s2, both interpreted as appropriate to the LC_COLLATE category of the current locale. -

Returns -

- The strcoll function returns an integer greater than, equal to, or less than zero, - accordingly as the string pointed to by s1 is greater than, equal to, or less than the string - pointed to by s2 when both are interpreted as appropriate to the current locale. - -

Contents -

7.23.4.4 The strncmp function
-

Synopsis -

-

-        #include <string.h>
-        int strncmp(const char *s1, const char *s2, size_t n);
-
-

Description -

- The strncmp function compares not more than n characters (characters that follow a - null character are not compared) from the array pointed to by s1 to the array pointed to - by s2. -

Returns -

- The strncmp function returns an integer greater than, equal to, or less than zero, - accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal - to, or less than the possibly null-terminated array pointed to by s2. - -

Contents -

7.23.4.5 The strxfrm function
-

Synopsis -

-

-        #include <string.h>
-        size_t strxfrm(char * restrict s1,
-             const char * restrict s2,
-             size_t n);
-
-

Description -

- The strxfrm function transforms the string pointed to by s2 and places the resulting - string into the array pointed to by s1. The transformation is such that if the strcmp - function is applied to two transformed strings, it returns a value greater than, equal to, or - - less than zero, corresponding to the result of the strcoll function applied to the same - two original strings. No more than n characters are placed into the resulting array - pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to - be a null pointer. If copying takes place between objects that overlap, the behavior is - undefined. -

Returns -

- The strxfrm function returns the length of the transformed string (not including the - terminating null character). If the value returned is n or more, the contents of the array - pointed to by s1 are indeterminate. -

- EXAMPLE The value of the following expression is the size of the array needed to hold the - transformation of the string pointed to by s. -

-         1 + strxfrm(NULL, s, 0)
-
- - -

Contents -

7.23.5 Search functions

- -

Contents -

7.23.5.1 The memchr function
-

Synopsis -

-

-         #include <string.h>
-         void *memchr(const void *s, int c, size_t n);
-
-

Description -

- The memchr function locates the first occurrence of c (converted to an unsigned - char) in the initial n characters (each interpreted as unsigned char) of the object - pointed to by s. The implementation shall behave as if it reads the characters sequentially - and stops as soon as a matching character is found. -

Returns -

- The memchr function returns a pointer to the located character, or a null pointer if the - character does not occur in the object. - -

Contents -

7.23.5.2 The strchr function
-

Synopsis -

-

-         #include <string.h>
-         char *strchr(const char *s, int c);
-
-

Description -

- The strchr function locates the first occurrence of c (converted to a char) in the - string pointed to by s. The terminating null character is considered to be part of the - string. - -

Returns -

- The strchr function returns a pointer to the located character, or a null pointer if the - character does not occur in the string. - -

Contents -

7.23.5.3 The strcspn function
-

Synopsis -

-

-        #include <string.h>
-        size_t strcspn(const char *s1, const char *s2);
-
-

Description -

- The strcspn function computes the length of the maximum initial segment of the string - pointed to by s1 which consists entirely of characters not from the string pointed to by - s2. -

Returns -

- The strcspn function returns the length of the segment. - -

Contents -

7.23.5.4 The strpbrk function
-

Synopsis -

-

-        #include <string.h>
-        char *strpbrk(const char *s1, const char *s2);
-
-

Description -

- The strpbrk function locates the first occurrence in the string pointed to by s1 of any - character from the string pointed to by s2. -

Returns -

- The strpbrk function returns a pointer to the character, or a null pointer if no character - from s2 occurs in s1. - -

Contents -

7.23.5.5 The strrchr function
-

Synopsis -

-

-        #include <string.h>
-        char *strrchr(const char *s, int c);
-
-

Description -

- The strrchr function locates the last occurrence of c (converted to a char) in the - string pointed to by s. The terminating null character is considered to be part of the - string. - -

Returns -

- The strrchr function returns a pointer to the character, or a null pointer if c does not - occur in the string. - -

Contents -

7.23.5.6 The strspn function
-

Synopsis -

-

-         #include <string.h>
-         size_t strspn(const char *s1, const char *s2);
-
-

Description -

- The strspn function computes the length of the maximum initial segment of the string - pointed to by s1 which consists entirely of characters from the string pointed to by s2. -

Returns -

- The strspn function returns the length of the segment. - -

Contents -

7.23.5.7 The strstr function
-

Synopsis -

-

-         #include <string.h>
-         char *strstr(const char *s1, const char *s2);
-
-

Description -

- The strstr function locates the first occurrence in the string pointed to by s1 of the - sequence of characters (excluding the terminating null character) in the string pointed to - by s2. -

Returns -

- The strstr function returns a pointer to the located string, or a null pointer if the string - is not found. If s2 points to a string with zero length, the function returns s1. - -

Contents -

7.23.5.8 The strtok function
-

Synopsis -

-

-         #include <string.h>
-         char *strtok(char * restrict s1,
-              const char * restrict s2);
-
-

Description -

- A sequence of calls to the strtok function breaks the string pointed to by s1 into a - sequence of tokens, each of which is delimited by a character from the string pointed to - by s2. The first call in the sequence has a non-null first argument; subsequent calls in the - sequence have a null first argument. The separator string pointed to by s2 may be - different from call to call. - -

- The first call in the sequence searches the string pointed to by s1 for the first character - that is not contained in the current separator string pointed to by s2. If no such character - is found, then there are no tokens in the string pointed to by s1 and the strtok function - returns a null pointer. If such a character is found, it is the start of the first token. -

- The strtok function then searches from there for a character that is contained in the - current separator string. If no such character is found, the current token extends to the - end of the string pointed to by s1, and subsequent searches for a token will return a null - pointer. If such a character is found, it is overwritten by a null character, which - terminates the current token. The strtok function saves a pointer to the following - character, from which the next search for a token will start. -

- Each subsequent call, with a null pointer as the value of the first argument, starts - searching from the saved pointer and behaves as described above. -

- The strtok function is not required to avoid data races. The implementation shall - behave as if no library function calls the strtok function. -

Returns -

- The strtok function returns a pointer to the first character of a token, or a null pointer - if there is no token. -

- EXAMPLE -

-        #include <string.h>
-        static char str[] = "?a???b,,,#c";
-        char *t;
-        t   =   strtok(str, "?");      //   t   points to the token "a"
-        t   =   strtok(NULL, ",");     //   t   points to the token "??b"
-        t   =   strtok(NULL, "#,");    //   t   points to the token "c"
-        t   =   strtok(NULL, "?");     //   t   is a null pointer
-
- - -

Contents -

7.23.6 Miscellaneous functions

- -

Contents -

7.23.6.1 The memset function
-

Synopsis -

-

-        #include <string.h>
-        void *memset(void *s, int c, size_t n);
-
-

Description -

- The memset function copies the value of c (converted to an unsigned char) into - each of the first n characters of the object pointed to by s. -

Returns -

- The memset function returns the value of s. - - -

Contents -

7.23.6.2 The strerror function
-

Synopsis -

-

-         #include <string.h>
-         char *strerror(int errnum);
-
-

Description -

- The strerror function maps the number in errnum to a message string. Typically, - the values for errnum come from errno, but strerror shall map any value of type - int to a message. -

- The strerror function is not required to avoid data races. The implementation shall - behave as if no library function calls the strerror function. -

Returns -

- The strerror function returns a pointer to the string, the contents of which are locale- - specific. The array pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the strerror function. - -

Contents -

7.23.6.3 The strlen function
-

Synopsis -

-

-         #include <string.h>
-         size_t strlen(const char *s);
-
-

Description -

- The strlen function computes the length of the string pointed to by s. -

Returns -

- The strlen function returns the number of characters that precede the terminating null - character. - - -

Contents -

7.24 Type-generic math <tgmath.h>

-

- The header <tgmath.h> includes the headers <math.h> and <complex.h> and - defines several type-generic macros. -

- Of the <math.h> and <complex.h> functions without an f (float) or l (long - double) suffix, several have one or more parameters whose corresponding real type is - double. For each such function, except modf, there is a corresponding type-generic - macro.304) The parameters whose corresponding real type is double in the function - synopsis are generic parameters. Use of the macro invokes a function whose - corresponding real type and type domain are determined by the arguments for the generic - parameters.305) -

- Use of the macro invokes a function whose generic parameters have the corresponding - real type determined as follows: -

-

- For each unsuffixed function in <math.h> for which there is a function in - <complex.h> with the same name except for a c prefix, the corresponding type- - generic macro (for both functions) has the same name as the function in <math.h>. The - corresponding type-generic macro for fabs and cabs is fabs. - - - - - -

-          <math.h>         <complex.h>              type-generic
-           function           function                 macro
-            acos              cacos                   acos
-            asin              casin                   asin
-            atan              catan                   atan
-            acosh             cacosh                  acosh
-            asinh             casinh                  asinh
-            atanh             catanh                  atanh
-            cos               ccos                    cos
-            sin               csin                    sin
-            tan               ctan                    tan
-            cosh              ccosh                   cosh
-            sinh              csinh                   sinh
-            tanh              ctanh                   tanh
-            exp               cexp                    exp
-            log               clog                    log
-            pow               cpow                    pow
-            sqrt              csqrt                   sqrt
-            fabs              cabs                    fabs
-
- If at least one argument for a generic parameter is complex, then use of the macro invokes - a complex function; otherwise, use of the macro invokes a real function. -

- For each unsuffixed function in <math.h> without a c-prefixed counterpart in - <complex.h> (except modf), the corresponding type-generic macro has the same - name as the function. These type-generic macros are: -

-         atan2              fma                  llround              remainder
-         cbrt               fmax                 log10                remquo
-         ceil               fmin                 log1p                rint
-         copysign           fmod                 log2                 round
-         erf                frexp                logb                 scalbn
-         erfc               hypot                lrint                scalbln
-         exp2               ilogb                lround               tgamma
-         expm1              ldexp                nearbyint            trunc
-         fdim               lgamma               nextafter
-         floor              llrint               nexttoward
-
- If all arguments for generic parameters are real, then use of the macro invokes a real - function; otherwise, use of the macro results in undefined behavior. - -

- For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a - function in <math.h>, the corresponding type-generic macro has the same name as the - function. These type-generic macros are: -

-        carg                     conj                     creal
-        cimag                    cproj
-
- Use of the macro with any real or complex argument invokes a complex function. -

- EXAMPLE With the declarations -

-         #include <tgmath.h>
-         int n;
-         float f;
-         double d;
-         long double ld;
-         float complex fc;
-         double complex dc;
-         long double complex ldc;
-
- functions invoked by use of type-generic macros are shown in the following table: - -
-                  macro use                                  invokes
-             exp(n)                              exp(n), the function
-             acosh(f)                            acoshf(f)
-             sin(d)                              sin(d), the function
-             atan(ld)                            atanl(ld)
-             log(fc)                             clogf(fc)
-             sqrt(dc)                            csqrt(dc)
-             pow(ldc, f)                         cpowl(ldc, f)
-             remainder(n, n)                     remainder(n, n), the function
-             nextafter(d, f)                     nextafter(d, f), the function
-             nexttoward(f, ld)                   nexttowardf(f, ld)
-             copysign(n, ld)                     copysignl(n, ld)
-             ceil(fc)                            undefined behavior
-             rint(dc)                            undefined behavior
-             fmax(ldc, ld)                       undefined behavior
-             carg(n)                             carg(n), the function
-             cproj(f)                            cprojf(f)
-             creal(d)                            creal(d), the function
-             cimag(ld)                           cimagl(ld)
-             fabs(fc)                            cabsf(fc)
-             carg(dc)                            carg(dc), the function
-             cproj(ldc)                          cprojl(ldc)
-
- -

Footnotes -

304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to - make available the corresponding ordinary function. - -

305) If the type of the argument is not compatible with the type of the parameter for the selected function, - the behavior is undefined. - - -

Contents -

7.25 Threads <threads.h>

- -

Contents -

7.25.1 Introduction

-

- The header <threads.h> defines macros, and declares types, enumeration constants, - and functions that support multiple threads of execution. -

- Implementations that define the macro __STDC_NO_THREADS__ need not provide - this header nor support any of its facilities. -

- The macros are -

-         ONCE_FLAG_INIT
-
- which expands to a value that can be used to initialize an object of type once_flag; - and -
-         TSS_DTOR_ITERATIONS
-
- which expands to an integer constant expression representing the maximum number of - times that destructors will be called when a thread terminates. -

- The types are -

-         cnd_t
-
- which is a complete object type that holds an identifier for a condition variable; -
-         thrd_t
-
- which is a complete object type that holds an identifier for a thread; -
-         tss_t
-
- which is a complete object type that holds an identifier for a thread-specific storage - pointer; -
-         mtx_t
-
- which is a complete object type that holds an identifier for a mutex; -
-         tss_dtor_t
-
- which is the function pointer type void (*)(void*), used for a destructor for a - thread-specific storage pointer; -
-         thrd_start_t
-
- which is the function pointer type int (*)(void*) that is passed to thrd_create - to create a new thread; -
-         once_flag
-
- which is a complete object type that holds a flag for use by call_once; and - -
-        xtime
-
- which is a structure type that holds a time specified in seconds and nanoseconds. The - structure shall contain at least the following members, in any order. -
-        time_t sec;
-        long nsec;
-
-

- The enumeration constants are -

-        mtx_plain
-
- which is passed to mtx_init to create a mutex object that supports neither timeout nor - test and return; -
-        mtx_recursive
-
- which is passed to mtx_init to create a mutex object that supports recursive locking; -
-        mtx_timed
-
- which is passed to mtx_init to create a mutex object that supports timeout; -
-        mtx_try
-
- which is passed to mtx_init to create a mutex object that supports test and return; -
-        thrd_timeout
-
- which is returned by a timed wait function to indicate that the time specified in the call - was reached without acquiring the requested resource; -
-        thrd_success
-
- which is returned by a function to indicate that the requested operation succeeded; -
-        thrd_busy
-
- which is returned by a function to indicate that the requested operation failed because a - resource requested by a test and return function is already in use; -
-        thrd_error
-
- which is returned by a function to indicate that the requested operation failed; and -
-        thrd_nomem
-
- which is returned by a function to indicate that the requested operation failed because it - was unable to allocate memory. - - -

Contents -

7.25.2 Initialization functions

- -

Contents -

7.25.2.1 The call_once function
-

Synopsis -

-

-         #include <threads.h>
-         void call_once(once_flag *flag, void (*func)(void));
-
-

Description -

- The call_once function uses the once_flag pointed to by flag to ensure that - func is called exactly once, the first time the call_once function is called with that - value of flag. Completion of an effective call to the call_once function synchronizes - with all subsequent calls to the call_once function with the same value of flag. -

Returns -

- The call_once function returns no value. - -

Contents -

7.25.3 Condition variable functions

- -

Contents -

7.25.3.1 The cnd_broadcast function
-

Synopsis -

-

-         #include <threads.h>
-         int cnd_broadcast(cnd_t *cond);
-
-

Description -

- The cnd_broadcast function unblocks all of the threads that are blocked on the - condition variable pointed to by cond at the time of the call. If no threads are blocked - on the condition variable pointed to by cond at the time of the call, the function does - nothing. -

Returns -

- The cnd_broadcast function returns thrd_success on success, or thrd_error - if the request could not be honored. - -

Contents -

7.25.3.2 The cnd_destroy function
-

Synopsis -

-

-         #include <threads.h>
-         void cnd_destroy(cnd_t *cond);
-
-

Description -

- The cnd_destroy function releases all resources used by the condition variable - pointed to by cond. The cnd_destroy function requires that no threads be blocked - waiting for the condition variable pointed to by cond. - -

Returns -

- The cnd_destroy function returns no value. - -

Contents -

7.25.3.3 The cnd_init function
-

Synopsis -

-

-        #include <threads.h>
-        int cnd_init(cnd_t *cond);
-
-

Description -

- The cnd_init function creates a condition variable. If it succeeds it sets the variable - pointed to by cond to a value that uniquely identifies the newly created condition - variable. A thread that calls cnd_wait on a newly created condition variable will - block. -

Returns -

- The cnd_init function returns thrd_success on success, or thrd_nomem if no - memory could be allocated for the newly created condition, or thrd_error if the - request could not be honored. - -

Contents -

7.25.3.4 The cnd_signal function
-

Synopsis -

-

-        #include <threads.h>
-        int cnd_signal(cnd_t *cond);
-
-

Description -

- The cnd_signal function unblocks one of the threads that are blocked on the - condition variable pointed to by cond at the time of the call. If no threads are blocked - on the condition variable at the time of the call, the function does nothing and return - success. -

Returns -

- The cnd_signal function returns thrd_success on success or thrd_error if - the request could not be honored. - -

Contents -

7.25.3.5 The cnd_timedwait function
-

Synopsis -

- -

-        #include <threads.h>
-        int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
-             const xtime *xt);
-
-

Description -

- The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and - endeavors to block until the condition variable pointed to by cond is signaled by a call to - cnd_signal or to cnd_broadcast, or until after the time specified by the xtime - object pointed to by xt. When the calling thread becomes unblocked it locks the variable - pointed to by mtx before it returns. The cnd_timedwait function requires that the - mutex pointed to by mtx be locked by the calling thread. -

Returns -

- The cnd_timedwait function returns thrd_success upon success, or - thrd_timeout if the time specified in the call was reached without acquiring the - requested resource, or thrd_error if the request could not be honored. - -

Contents -

7.25.3.6 The cnd_wait function
-

Synopsis -

-

-         #include <threads.h>
-         int cnd_wait(cnd_t *cond, mtx_t *mtx);
-
-

Description -

- The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors - to block until the condition variable pointed to by cond is signaled by a call to - cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it - locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is - not locked by the calling thread, the cnd_wait function will act as if the abort - function is called. -

Returns -

- The cnd_wait function returns thrd_success on success or thrd_error if the - request could not be honored. - -

Contents -

7.25.4 Mutex functions

- -

Contents -

7.25.4.1 The mtx_destroy function
-

Synopsis -

-

-         #include <threads.h>
-         void mtx_destroy(mtx_t *mtx);
-
-

Description -

- The mtx_destroy function releases any resources used by the mutex pointed to by - mtx. No threads can be blocked waiting for the mutex pointed to by mtx. - -

Returns -

- The mtx_destroy function returns no value. - -

Contents -

7.25.4.2 The mtx_init function
-

Synopsis -

-

-        #include <threads.h>
-        int mtx_init(mtx_t *mtx, int type);
-
-

Description -

- The mtx_init function creates a mutex object with properties indicated by type, - which must have one of the six values: - mtx_plain for a simple non-recursive mutex, - mtx_timed for a non-recursive mutex that supports timeout, - mtx_try for a non-recursive mutex that supports test and return, - mtx_plain | mtx_recursive for a simple recursive mutex, - mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or - mtx_try | mtx_recursive for a recursive mutex that supports test and return. -

- If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that - uniquely identifies the newly created mutex. -

Returns -

- The mtx_init function returns thrd_success on success, or thrd_error if the - request could not be honored. - -

Contents -

7.25.4.3 The mtx_lock function
-

Synopsis -

-

-        #include <threads.h>
-        int mtx_lock(mtx_t *mtx);
-
-

Description -

- The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex - is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock - on the same mutex shall synchronize with this operation. -

Returns -

- The mtx_lock function returns thrd_success on success, or thrd_busy if the - resource requested is already in use, or thrd_error if the request could not be - honored. - - -

Contents -

7.25.4.4 The mtx_timedlock function
-

Synopsis -

-

-         #include <threads.h>
-         int mtx_timedlock(mtx_t *mtx, const xtime *xt);
-
-

Description -

- The mtx_timedlock function endeavors to block until it locks the mutex pointed to by - mtx or until the time specified by the xtime object xt has passed. The specified mutex - shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same - mutex shall synchronize with this operation. -

Returns -

- The mtx_timedlock function returns thrd_success on success, or thrd_busy - if the resource requested is already in use, or thrd_timeout if the time specified was - reached without acquiring the requested resource, or thrd_error if the request could - not be honored. - -

Contents -

7.25.4.5 The mtx_trylock function
-

Synopsis -

-

-         #include <threads.h>
-         int mtx_trylock(mtx_t *mtx);
-
-

Description -

- The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The - specified mutex shall support either test and return or timeout. If the mutex is already - locked, the function returns without blocking. If the operation succeeds, prior calls to - mtx_unlock on the same mutex shall synchronize with this operation. -

Returns -

- The mtx_trylock function returns thrd_success on success, or thrd_busy if - the resource requested is already in use, or thrd_error if the request could not be - honored. - -

Contents -

7.25.4.6 The mtx_unlock function
-

Synopsis -

-

-         #include <threads.h>
-         int mtx_unlock(mtx_t *mtx);
-
-

Description -

- The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to - by mtx shall be locked by the calling thread. - -

Returns -

- The mtx_unlock function returns thrd_success on success or thrd_error if - the request could not be honored. - -

Contents -

7.25.5 Thread functions

- -

Contents -

7.25.5.1 The thrd_create function
-

Synopsis -

-

-        #include <threads.h>
-        int thrd_create(thrd_t *thr, thrd_start_t func,
-             void *arg);
-
-

Description -

- The thrd_create function creates a new thread executing func(arg). If the - thrd_create function succeeds, it sets the object pointed to by thr to the identifier of - the newly created thread. (A thread's identifier may be reused for a different thread once - the original thread has exited and either been detached or joined to another thread.) The - completion of the thrd_create function synchronizes with the beginning of the - execution of the new thread. -

Returns -

- The thrd_create function returns thrd_success on success, or thrd_nomem if - no memory could be allocated for the thread requested, or thrd_error if the request - could not be honored. - -

Contents -

7.25.5.2 The thrd_current function
-

Synopsis -

-

-        #include <threads.h>
-        thrd_t thrd_current(void);
-
-

Description -

- The thrd_current function identifies the thread that called it. -

Returns -

- The thrd_current function returns the identifier of the thread that called it. - -

Contents -

7.25.5.3 The thrd_detach function
-

Synopsis -

- -

-        #include <threads.h>
-        int thrd_detach(thrd_t thr);
-
-

Description -

- The thrd_detach function tells the operating system to dispose of any resources - allocated to the thread identified by thr when that thread terminates. The thread - identified by thr shall not have been previously detached or joined with another thread. -

Returns -

- The thrd_detach function returns thrd_success on success or thrd_error if - the request could not be honored. - -

Contents -

7.25.5.4 The thrd_equal function
-

Synopsis -

-

-         #include <threads.h>
-         int thrd_equal(thrd_t thr0, thrd_t thr1);
-
-

Description -

- The thrd_equal function will determine whether the thread identified by thr0 refers - to the thread identified by thr1. -

Returns -

- The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to - different threads. Otherwise the thrd_equal function returns a nonzero value. - -

Contents -

7.25.5.5 The thrd_exit function
-

Synopsis -

-

-         #include <threads.h>
-         void thrd_exit(int res);
-
-

Description -

- The thrd_exit function terminates execution of the calling thread and sets its result - code to res. -

Returns -

- The thrd_exit function returns no value. - -

Contents -

7.25.5.6 The thrd_join function
-

Synopsis -

-

-         #include <threads.h>
-         int thrd_join(thrd_t thr, int *res);
-
-

Description -

- The thrd_join function joins the thread identified by thr with the current thread by - blocking until the other thread has terminated. If the parameter res is not a null pointer, - - it stores the thread's result code in the integer pointed to by res. The termination of the - other thread synchronizes with the completion of the thrd_join function. The thread - identified by thr shall not have been previously detached or joined with another thread. -

Returns -

- The thrd_join function returns thrd_success on success or thrd_error if the - request could not be honored. - -

Contents -

7.25.5.7 The thrd_sleep function
-

Synopsis -

-

-        #include <threads.h>
-        void thrd_sleep(const xtime *xt);
-
-

Description -

- The thrd_sleep function suspends execution of the calling thread until after the time - specified by the xtime object pointed to by xt. -

Returns -

- The thrd_sleep function returns no value. - -

Contents -

7.25.5.8 The thrd_yield function
-

Synopsis -

-

-        #include <threads.h>
-        void thrd_yield(void);
-
-

Description -

- The thrd_yield function endeavors to permit other threads to run, even if the current - thread would ordinarily continue to run. -

Returns -

- The thrd_yield function returns no value. - -

Contents -

7.25.6 Thread-specific storage functions

- -

Contents -

7.25.6.1 The tss_create function
-

Synopsis -

-

-        #include <threads.h>
-        int tss_create(tss_t *key, tss_dtor_t dtor);
-
-

Description -

- The tss_create function creates a thread-specific storage pointer with destructor - dtor, which may be null. - -

Returns -

- If the tss_create function is successful, it sets the thread-specific storage pointed to - by key to a value that uniquely identifies the newly created pointer and returns - thrd_success; otherwise, thrd_error is returned and the thread-specific storage - pointed to by key is set to an undefined value. - -

Contents -

7.25.6.2 The tss_delete function
-

Synopsis -

-

-         #include <threads.h>
-         void tss_delete(tss_t key);
-
-

Description -

- The tss_delete function releases any resources used by the thread-specific storage - identified by key. -

Returns -

- The tss_delete function returns no value. - -

Contents -

7.25.6.3 The tss_get function
-

Synopsis -

-

-         #include <threads.h>
-         void *tss_get(tss_t key);
-
-

Description -

- The tss_get function returns the value for the current thread held in the thread-specific - storage identified by key. -

Returns -

- The tss_get function returns the value for the current thread if successful, or zero if - unsuccessful. - -

Contents -

7.25.6.4 The tss_set function
-

Synopsis -

-

-         #include <threads.h>
-         int tss_set(tss_t key, void *val);
-
-

Description -

- The tss_set function sets the value for the current thread held in the thread-specific - storage identified by key to val. - -

Returns -

- The tss_set function returns thrd_success on success or thrd_error if the - request could not be honored. - -

Contents -

7.25.7 Time functions

- -

Contents -

7.25.7.1 The xtime_get function
-

Synopsis -

-

-         #include <threads.h>
-         int xtime_get(xtime *xt, int base);
-
-

Description -

- The xtime_get function sets the xtime object pointed to by xt to hold the current - time based on the time base base. -

Returns -

- If the xtime_get function is successful it returns the nonzero value base, which must - be TIME_UTC; otherwise, it returns zero.306) - - - - - - -

Footnotes -

306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an - xtime object is system dependent. - - -

Contents -

7.26 Date and time <time.h>

- -

Contents -

7.26.1 Components of time

-

- The header <time.h> defines two macros, and declares several types and functions for - manipulating time. Many functions deal with a calendar time that represents the current - date (according to the Gregorian calendar) and time. Some functions deal with local - time, which is the calendar time expressed for some specific time zone, and with Daylight - Saving Time, which is a temporary change in the algorithm for determining local time. - The local time zone and Daylight Saving Time are implementation-defined. -

- The macros defined are NULL (described in 7.19); and -

-         CLOCKS_PER_SEC
-
- which expands to an expression with type clock_t (described below) that is the - number per second of the value returned by the clock function. -

- The types declared are size_t (described in 7.19); -

-         clock_t
-
- and -
-         time_t
-
- which are arithmetic types capable of representing times; and -
-         struct tm
-
- which holds the components of a calendar time, called the broken-down time. -

- The range and precision of times representable in clock_t and time_t are - implementation-defined. The tm structure shall contain at least the following members, - in any order. The semantics of the members and their normal ranges are expressed in the - comments.307) -

-         int    tm_sec;           //   seconds after the minute -- [0, 60]
-         int    tm_min;           //   minutes after the hour -- [0, 59]
-         int    tm_hour;          //   hours since midnight -- [0, 23]
-         int    tm_mday;          //   day of the month -- [1, 31]
-         int    tm_mon;           //   months since January -- [0, 11]
-         int    tm_year;          //   years since 1900
-         int    tm_wday;          //   days since Sunday -- [0, 6]
-         int    tm_yday;          //   days since January 1 -- [0, 365]
-         int    tm_isdst;         //   Daylight Saving Time flag
-
- - - - - The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight - Saving Time is not in effect, and negative if the information is not available. - -

Footnotes -

307) The range [0, 60] for tm_sec allows for a positive leap second. - - -

Contents -

7.26.2 Time manipulation functions

- -

Contents -

7.26.2.1 The clock function
-

Synopsis -

-

-         #include <time.h>
-         clock_t clock(void);
-
-

Description -

- The clock function determines the processor time used. -

Returns -

- The clock function returns the implementation's best approximation to the processor - time used by the program since the beginning of an implementation-defined era related - only to the program invocation. To determine the time in seconds, the value returned by - the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If - the processor time used is not available or its value cannot be represented, the function - returns the value (clock_t)(-1).308) - -

Footnotes -

308) In order to measure the time spent in a program, the clock function should be called at the start of - the program and its return value subtracted from the value returned by subsequent calls. - - -

Contents -

7.26.2.2 The difftime function
-

Synopsis -

-

-         #include <time.h>
-         double difftime(time_t time1, time_t time0);
-
-

Description -

- The difftime function computes the difference between two calendar times: time1 - - time0. -

Returns -

- The difftime function returns the difference expressed in seconds as a double. - - - - - - -

Contents -

7.26.2.3 The mktime function
-

Synopsis -

-

-         #include <time.h>
-         time_t mktime(struct tm *timeptr);
-
-

Description -

- The mktime function converts the broken-down time, expressed as local time, in the - structure pointed to by timeptr into a calendar time value with the same encoding as - that of the values returned by the time function. The original values of the tm_wday - and tm_yday components of the structure are ignored, and the original values of the - other components are not restricted to the ranges indicated above.309) On successful - completion, the values of the tm_wday and tm_yday components of the structure are - set appropriately, and the other components are set to represent the specified calendar - time, but with their values forced to the ranges indicated above; the final value of - tm_mday is not set until tm_mon and tm_year are determined. -

Returns -

- The mktime function returns the specified calendar time encoded as a value of type - time_t. If the calendar time cannot be represented, the function returns the value - (time_t)(-1). -

- EXAMPLE What day of the week is July 4, 2001? -

-         #include <stdio.h>
-         #include <time.h>
-         static const char *const wday[] = {
-                 "Sunday", "Monday", "Tuesday", "Wednesday",
-                 "Thursday", "Friday", "Saturday", "-unknown-"
-         };
-         struct tm time_str;
-         /* ... */
-
- - - - - -
-        time_str.tm_year   = 2001 - 1900;
-        time_str.tm_mon    = 7 - 1;
-        time_str.tm_mday   = 4;
-        time_str.tm_hour   = 0;
-        time_str.tm_min    = 0;
-        time_str.tm_sec    = 1;
-        time_str.tm_isdst = -1;
-        if (mktime(&time_str) == (time_t)(-1))
-              time_str.tm_wday = 7;
-        printf("%s\n", wday[time_str.tm_wday]);
-
- - -

Footnotes -

309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that - Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value - causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time. - - -

Contents -

7.26.2.4 The time function
-

Synopsis -

-

-        #include <time.h>
-        time_t time(time_t *timer);
-
-

Description -

- The time function determines the current calendar time. The encoding of the value is - unspecified. -

Returns -

- The time function returns the implementation's best approximation to the current - calendar time. The value (time_t)(-1) is returned if the calendar time is not - available. If timer is not a null pointer, the return value is also assigned to the object it - points to. - -

Contents -

7.26.3 Time conversion functions

-

- Except for the strftime function, these functions each return a pointer to one of two - types of static objects: a broken-down time structure or an array of char. Execution of - any of the functions that return a pointer to one of these object types may overwrite the - information in any object of the same type pointed to by the value returned from any - previous call to any of them and the functions are not required to avoid data races. The - implementation shall behave as if no other library functions call these functions. - -

Contents -

7.26.3.1 The asctime function
-

Synopsis -

-

-        #include <time.h>
-        char *asctime(const struct tm *timeptr);
-
-

Description -

- The asctime function converts the broken-down time in the structure pointed to by - timeptr into a string in the form - -

-        Sun Sep 16 01:03:52 1973\n\0
-
- using the equivalent of the following algorithm. - char *asctime(const struct tm *timeptr) - { -
-      static const char wday_name[7][3] = {
-           "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
-      };
-      static const char mon_name[12][3] = {
-           "Jan", "Feb", "Mar", "Apr", "May", "Jun",
-           "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
-      };
-      static char result[26];
-         sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
-              wday_name[timeptr->tm_wday],
-              mon_name[timeptr->tm_mon],
-              timeptr->tm_mday, timeptr->tm_hour,
-              timeptr->tm_min, timeptr->tm_sec,
-              1900 + timeptr->tm_year);
-         return result;
-
- } -

- If any of the fields of the broken-down time contain values that are outside their normal - ranges,310) the behavior of the asctime function is undefined. Likewise, if the - calculated year exceeds four digits or is less than the year 1000, the behavior is - undefined. -

Returns -

- The asctime function returns a pointer to the string. - -

Footnotes -

310) See 7.26.1. - - -

Contents -

7.26.3.2 The ctime function
-

Synopsis -

-

-         #include <time.h>
-         char *ctime(const time_t *timer);
-
-

Description -

- The ctime function converts the calendar time pointed to by timer to local time in the - form of a string. It is equivalent to -

-         asctime(localtime(timer))
-
- - - - -

Returns -

- The ctime function returns the pointer returned by the asctime function with that - broken-down time as argument. -

Forward references: the localtime function (7.26.3.4). - -

Contents -

7.26.3.3 The gmtime function
-

Synopsis -

-

-        #include <time.h>
-        struct tm *gmtime(const time_t *timer);
-
-

Description -

- The gmtime function converts the calendar time pointed to by timer into a broken- - down time, expressed as UTC. -

Returns -

- The gmtime function returns a pointer to the broken-down time, or a null pointer if the - specified time cannot be converted to UTC. - -

Contents -

7.26.3.4 The localtime function
-

Synopsis -

-

-        #include <time.h>
-        struct tm *localtime(const time_t *timer);
-
-

Description -

- The localtime function converts the calendar time pointed to by timer into a - broken-down time, expressed as local time. -

Returns -

- The localtime function returns a pointer to the broken-down time, or a null pointer if - the specified time cannot be converted to local time. - -

Contents -

7.26.3.5 The strftime function
-

Synopsis -

- -

-        #include <time.h>
-        size_t strftime(char * restrict s,
-             size_t maxsize,
-             const char * restrict format,
-             const struct tm * restrict timeptr);
-
-

Description -

- The strftime function places characters into the array pointed to by s as controlled by - the string pointed to by format. The format shall be a multibyte character sequence, - beginning and ending in its initial shift state. The format string consists of zero or - more conversion specifiers and ordinary multibyte characters. A conversion specifier - consists of a % character, possibly followed by an E or O modifier character (described - below), followed by a character that determines the behavior of the conversion specifier. - All ordinary multibyte characters (including the terminating null character) are copied - unchanged into the array. If copying takes place between objects that overlap, the - behavior is undefined. No more than maxsize characters are placed into the array. -

- Each conversion specifier is replaced by appropriate characters as described in the - following list. The appropriate characters are determined using the LC_TIME category - of the current locale and by the values of zero or more members of the broken-down time - structure pointed to by timeptr, as specified in brackets in the description. If any of - the specified values is outside the normal range, the characters stored are unspecified. - %a is replaced by the locale's abbreviated weekday name. [tm_wday] - %A is replaced by the locale's full weekday name. [tm_wday] - %b is replaced by the locale's abbreviated month name. [tm_mon] - %B is replaced by the locale's full month name. [tm_mon] - %c is replaced by the locale's appropriate date and time representation. [all specified -

-      in 7.26.1]
-
- %C is replaced by the year divided by 100 and truncated to an integer, as a decimal -
-      number (00-99). [tm_year]
-
- %d is replaced by the day of the month as a decimal number (01-31). [tm_mday] - %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year] - %e is replaced by the day of the month as a decimal number (1-31); a single digit is -
-      preceded by a space. [tm_mday]
-
- %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon, -
-      tm_mday]
-
- %g is replaced by the last 2 digits of the week-based year (see below) as a decimal -
-      number (00-99). [tm_year, tm_wday, tm_yday]
-
- %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997). -
-      [tm_year, tm_wday, tm_yday]
-
- %h is equivalent to ''%b''. [tm_mon] - %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour] - %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour] - %j is replaced by the day of the year as a decimal number (001-366). [tm_yday] - %m is replaced by the month as a decimal number (01-12). [tm_mon] - %M is replaced by the minute as a decimal number (00-59). [tm_min] - %n is replaced by a new-line character. - - %p is replaced by the locale's equivalent of the AM/PM designations associated with a -
-       12-hour clock. [tm_hour]
-
- %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec] - %R is equivalent to ''%H:%M''. [tm_hour, tm_min] - %S is replaced by the second as a decimal number (00-60). [tm_sec] - %t is replaced by a horizontal-tab character. - %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min, -
-       tm_sec]
-
- %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday -
-       is 1. [tm_wday]
-
- %U is replaced by the week number of the year (the first Sunday as the first day of week -
-       1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
-
- %V is replaced by the ISO 8601 week number (see below) as a decimal number -
-       (01-53). [tm_year, tm_wday, tm_yday]
-
- %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0. -
-       [tm_wday]
-
- %W is replaced by the week number of the year (the first Monday as the first day of -
-       week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
-
- %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1] - %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1] - %y is replaced by the last 2 digits of the year as a decimal number (00-99). -
-       [tm_year]
-
- %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year] - %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4 -
-       hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
-       zone is determinable. [tm_isdst]
-
- %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no -
-       time zone is determinable. [tm_isdst]
-
- %% is replaced by %. -

- Some conversion specifiers can be modified by the inclusion of an E or O modifier - character to indicate an alternative format or specification. If the alternative format or - specification does not exist for the current locale, the modifier is ignored. - %Ec is replaced by the locale's alternative date and time representation. - %EC is replaced by the name of the base year (period) in the locale's alternative -

-     representation.
-
- %Ex is replaced by the locale's alternative date representation. - %EX is replaced by the locale's alternative time representation. - %Ey is replaced by the offset from %EC (year only) in the locale's alternative -
-     representation.
-
- %EY is replaced by the locale's full alternative year representation. - - %Od is replaced by the day of the month, using the locale's alternative numeric symbols -
-     (filled as needed with leading zeros, or with leading spaces if there is no alternative
-     symbol for zero).
-
- %Oe is replaced by the day of the month, using the locale's alternative numeric symbols -
-     (filled as needed with leading spaces).
-
- %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric -
-     symbols.
-
- %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric -
-     symbols.
-
- %Om is replaced by the month, using the locale's alternative numeric symbols. - %OM is replaced by the minutes, using the locale's alternative numeric symbols. - %OS is replaced by the seconds, using the locale's alternative numeric symbols. - %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative -
-     representation, where Monday is 1.
-
- %OU is replaced by the week number, using the locale's alternative numeric symbols. - %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric -
-     symbols.
-
- %Ow is replaced by the weekday as a number, using the locale's alternative numeric -
-     symbols.
-
- %OW is replaced by the week number of the year, using the locale's alternative numeric -
-     symbols.
-
- %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric -
-     symbols.
-
-

- %g, %G, and %V give values according to the ISO 8601 week-based year. In this system, - weeks begin on a Monday and week 1 of the year is the week that includes January 4th, - which is also the week that includes the first Thursday of the year, and is also the first - week that contains at least four days in the year. If the first Monday of January is the - 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus, - for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If - December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of - the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and - %V is replaced by 01. -

- If a conversion specifier is not one of the above, the behavior is undefined. -

- In the "C" locale, the E and O modifiers are ignored and the replacement strings for the - following specifiers are: - %a the first three characters of %A. - %A one of ''Sunday'', ''Monday'', ... , ''Saturday''. - %b the first three characters of %B. - %B one of ''January'', ''February'', ... , ''December''. - %c equivalent to ''%a %b %e %T %Y''. - - %p one of ''AM'' or ''PM''. - %r equivalent to ''%I:%M:%S %p''. - %x equivalent to ''%m/%d/%y''. - %X equivalent to %T. - %Z implementation-defined. -

Returns -

- If the total number of resulting characters including the terminating null character is not - more than maxsize, the strftime function returns the number of characters placed - into the array pointed to by s not including the terminating null character. Otherwise, - zero is returned and the contents of the array are indeterminate. - - -

Contents -

7.27 Unicode utilities <uchar.h>

-

- The header <uchar.h> declares types and functions for manipulating Unicode - characters. -

- The types declared are mbstate_t (described in 7.29.1) and size_t (described in - 7.19); -

-         char16_t
-
- which is an unsigned integer type used for 16-bit characters and is the same type as - uint_least16_t (described in 7.20.1.2); and -
-         char32_t
-
- which is an unsigned integer type used for 32-bit characters and is the same type as - uint_least32_t (also described in 7.20.1.2). - -

Contents -

7.27.1 Restartable multibyte/wide character conversion functions

-

- These functions have a parameter, ps, of type pointer to mbstate_t that points to an - object that can completely describe the current conversion state of the associated - multibyte character sequence, which the functions alter as necessary. If ps is a null - pointer, each function uses its own internal mbstate_t object instead, which is - initialized at program startup to the initial conversion state; the functions are not required - to avoid data races in this case. The implementation behaves as if no library function - calls these functions with a null pointer for ps. - -

Contents -

7.27.1.1 The mbrtoc16 function
-

Synopsis -

-

-         #include <uchar.h>
-         size_t mbrtoc16(char16_t * restrict pc16,
-              const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the mbrtoc16 function is equivalent to the call: -

-                mbrtoc16(NULL, "", 1, ps)
-
- In this case, the values of the parameters pc16 and n are ignored. -

- If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the values of the - corresponding wide characters and then, if pc16 is not a null pointer, stores the value of - the first (or only) such character in the object pointed to by pc16. Subsequent calls will - - store successive wide characters without consuming any additional input until all the - characters have been stored. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. -

Returns -

- The mbrtoc16 function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that -

-                       corresponds to the null wide character (which is the value stored).
-
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte -
-                    character (which is the value stored); the value returned is the number
-                    of bytes that complete the multibyte character.
-
- (size_t)(-3) if the next character resulting from a previous call has been stored (no -
-              bytes from the input have been consumed by this call).
-
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) -
-              multibyte character, and all n bytes have been processed (no value is
-              stored).311)
-
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes -
-              do not contribute to a complete and valid multibyte character (no
-              value is stored); the value of the macro EILSEQ is stored in errno,
-              and the conversion state is unspecified.
-
- -

Footnotes -

311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - - -

Contents -

7.27.1.2 The c16rtomb function
-

Synopsis -

-

-         #include <uchar.h>
-         size_t c16rtomb(char * restrict s, char16_t c16,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the c16rtomb function is equivalent to the call -

-                 c16rtomb(buf, L'\0', ps)
-
- where buf is an internal buffer. -

- If s is not a null pointer, the c16rtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by c16 - (including any shift sequences), and stores the multibyte character representation in the - - - - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. -

Returns -

- The c16rtomb function returns the number of bytes stored in the array object (including - any shift sequences). When c16 is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - -

Contents -

7.27.1.3 The mbrtoc32 function
-

Synopsis -

-

-         #include <uchar.h>
-         size_t mbrtoc32(char32_t * restrict pc32,
-              const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the mbrtoc32 function is equivalent to the call: -

-                 mbrtoc32(NULL, "", 1, ps)
-
- In this case, the values of the parameters pc32 and n are ignored. -

- If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the values of the - corresponding wide characters and then, if pc32 is not a null pointer, stores the value of - the first (or only) such character in the object pointed to by pc32. Subsequent calls will - store successive wide characters without consuming any additional input until all the - characters have been stored. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. -

Returns -

- The mbrtoc32 function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that -

-                      corresponds to the null wide character (which is the value stored).
-
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte - -
-                    character (which is the value stored); the value returned is the number
-                    of bytes that complete the multibyte character.
-
- (size_t)(-3) if the next character resulting from a previous call has been stored (no -
-              bytes from the input have been consumed by this call).
-
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) -
-              multibyte character, and all n bytes have been processed (no value is
-              stored).312)
-
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes -
-              do not contribute to a complete and valid multibyte character (no
-              value is stored); the value of the macro EILSEQ is stored in errno,
-              and the conversion state is unspecified.
-
- -

Footnotes -

312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - - -

Contents -

7.27.1.4 The c32rtomb function
-

Synopsis -

-

-         #include <uchar.h>
-         size_t c32rtomb(char * restrict s, char32_t c32,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the c32rtomb function is equivalent to the call -

-                 c32rtomb(buf, L'\0', ps)
-
- where buf is an internal buffer. -

- If s is not a null pointer, the c32rtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by c32 - (including any shift sequences), and stores the multibyte character representation in the - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. -

Returns -

- The c32rtomb function returns the number of bytes stored in the array object (including - any shift sequences). When c32 is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - - - - - - -

Contents -

7.28 Extended multibyte and wide character utilities <wchar.h>

- -

Contents -

7.28.1 Introduction

-

- The header <wchar.h> defines four macros, and declares four data types, one tag, and - many functions.313) -

- The types declared are wchar_t and size_t (both described in 7.19); -

-           mbstate_t
-
- which is a complete object type other than an array type that can hold the conversion state - information necessary to convert between sequences of multibyte characters and wide - characters; -
-          wint_t
-
- which is an integer type unchanged by default argument promotions that can hold any - value corresponding to members of the extended character set, as well as at least one - value that does not correspond to any member of the extended character set (see WEOF - below);314) and -
-          struct tm
-
- which is declared as an incomplete structure type (the contents are described in 7.26.1). -

- The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX - (described in 7.20.3); and -

-          WEOF
-
- which expands to a constant expression of type wint_t whose value does not - correspond to any member of the extended character set.315) It is accepted (and returned) - by several functions in this subclause to indicate end-of-file, that is, no more input from a - stream. It is also used as a wide character value that does not correspond to any member - of the extended character set. -

- The functions declared are grouped as follows: -

-

- Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the behavior is - undefined. - -

Footnotes -

313) See ''future library directions'' (7.30.12). - -

314) wchar_t and wint_t can be the same integer type. - -

315) The value of the macro WEOF may differ from that of EOF and need not be negative. - - -

Contents -

7.28.2 Formatted wide character input/output functions

-

- The formatted wide character input/output functions shall behave as if there is a sequence - point after the actions associated with each specifier.316) - -

Footnotes -

316) The fwprintf functions perform writes to memory for the %n specifier. - - -

Contents -

7.28.2.1 The fwprintf function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         int fwprintf(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-
-

Description -

- The fwprintf function writes output to the stream pointed to by stream, under - control of the wide string pointed to by format that specifies how subsequent arguments - are converted for output. If there are insufficient arguments for the format, the behavior - is undefined. If the format is exhausted while arguments remain, the excess arguments - are evaluated (as always) but are otherwise ignored. The fwprintf function returns - when the end of the format string is encountered. -

- The format is composed of zero or more directives: ordinary wide characters (not %), - which are copied unchanged to the output stream; and conversion specifications, each of - which results in fetching zero or more subsequent arguments, converting them, if - applicable, according to the corresponding conversion specifier, and then writing the - result to the output stream. -

- Each conversion specification is introduced by the wide character %. After the %, the - following appear in sequence: -

-

- As noted above, a field width, or precision, or both, may be indicated by an asterisk. In - this case, an int argument supplies the field width or precision. The arguments - specifying field width, or precision, or both, shall appear (in that order) before the - argument (if any) to be converted. A negative field width argument is taken as a - flag - followed by a positive field width. A negative precision argument is taken as if the - precision were omitted. -

- The flag wide characters and their meanings are: - - The result of the conversion is left-justified within the field. (It is right-justified if -

-          this flag is not specified.)
-
- + The result of a signed conversion always begins with a plus or minus sign. (It -
-          begins with a sign only when a negative value is converted if this flag is not
-          specified.)318)
-
- space If the first wide character of a signed conversion is not a sign, or if a signed -
-       conversion results in no wide characters, a space is prefixed to the result. If the
-       space and + flags both appear, the space flag is ignored.
-
- # The result is converted to an ''alternative form''. For o conversion, it increases -
-          the precision, if and only if necessary, to force the first digit of the result to be a
-          zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
-          conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
-
- - - -
-           and G conversions, the result of converting a floating-point number always
-           contains a decimal-point wide character, even if no digits follow it. (Normally, a
-           decimal-point wide character appears in the result of these conversions only if a
-           digit follows it.) For g and G conversions, trailing zeros are not removed from the
-           result. For other conversions, the behavior is undefined.
-
- 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros -
-           (following any indication of sign or base) are used to pad to the field width rather
-           than performing space padding, except when converting an infinity or NaN. If the
-           0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
-           conversions, if a precision is specified, the 0 flag is ignored. For other
-           conversions, the behavior is undefined.
-
-

- The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -

-                signed char or unsigned char argument (the argument will have
-                been promoted according to the integer promotions, but its value shall be
-                converted to signed char or unsigned char before printing); or that
-                a following n conversion specifier applies to a pointer to a signed char
-                argument.
-
- h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-                short int or unsigned short int argument (the argument will
-                have been promoted according to the integer promotions, but its value shall
-                be converted to short int or unsigned short int before printing);
-                or that a following n conversion specifier applies to a pointer to a short
-                int argument.
-
- l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-                long int or unsigned long int argument; that a following n
-                conversion specifier applies to a pointer to a long int argument; that a
-                following c conversion specifier applies to a wint_t argument; that a
-                following s conversion specifier applies to a pointer to a wchar_t
-                argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
-                specifier.
-
- ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-              long long int or unsigned long long int argument; or that a
-              following n conversion specifier applies to a pointer to a long long int
-              argument.
-
- j Specifies that a following d, i, o, u, x, or X conversion specifier applies to - -
-                an intmax_t or uintmax_t argument; or that a following n conversion
-                specifier applies to a pointer to an intmax_t argument.
-
- z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-              size_t or the corresponding signed integer type argument; or that a
-              following n conversion specifier applies to a pointer to a signed integer type
-              corresponding to size_t argument.
-
- t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a -
-              ptrdiff_t or the corresponding unsigned integer type argument; or that a
-              following n conversion specifier applies to a pointer to a ptrdiff_t
-              argument.
-
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier -
-              applies to a long double argument.
-
- If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -

- The conversion specifiers and their meanings are: - d,i The int argument is converted to signed decimal in the style [-]dddd. The -

-             precision specifies the minimum number of digits to appear; if the value
-             being converted can be represented in fewer digits, it is expanded with
-             leading zeros. The default precision is 1. The result of converting a zero
-             value with a precision of zero is no wide characters.
-
- o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned -
-         decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
-         letters abcdef are used for x conversion and the letters ABCDEF for X
-         conversion. The precision specifies the minimum number of digits to appear;
-         if the value being converted can be represented in fewer digits, it is expanded
-         with leading zeros. The default precision is 1. The result of converting a
-         zero value with a precision of zero is no wide characters.
-
- f,F A double argument representing a floating-point number is converted to - -
-             decimal notation in the style [-]ddd.ddd, where the number of digits after
-             the decimal-point wide character is equal to the precision specification. If the
-             precision is missing, it is taken as 6; if the precision is zero and the # flag is
-             not specified, no decimal-point wide character appears. If a decimal-point
-             wide character appears, at least one digit appears before it. The value is
-             rounded to the appropriate number of digits.
-             A double argument representing an infinity is converted in one of the styles
-             [-]inf or [-]infinity -- which style is implementation-defined. A
-             double argument representing a NaN is converted in one of the styles
-             [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
-             any n-wchar-sequence, is implementation-defined. The F conversion
-             specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
-              nan, respectively.319)
-
- e,E A double argument representing a floating-point number is converted in the -
-              style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
-              argument is nonzero) before the decimal-point wide character and the number
-              of digits after it is equal to the precision; if the precision is missing, it is taken
-              as 6; if the precision is zero and the # flag is not specified, no decimal-point
-              wide character appears. The value is rounded to the appropriate number of
-              digits. The E conversion specifier produces a number with E instead of e
-              introducing the exponent. The exponent always contains at least two digits,
-              and only as many more digits as necessary to represent the exponent. If the
-              value is zero, the exponent is zero.
-              A double argument representing an infinity or NaN is converted in the style
-              of an f or F conversion specifier.
-
- g,G A double argument representing a floating-point number is converted in -
-              style f or e (or in style F or E in the case of a G conversion specifier),
-              depending on the value converted and the precision. Let P equal the
-              precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
-              Then, if a conversion with style E would have an exponent of X:
-              -- if P > X >= -4, the conversion is with style f (or F) and precision
-                P - (X + 1).
-              -- otherwise, the conversion is with style e (or E) and precision P - 1.
-              Finally, unless the # flag is used, any trailing zeros are removed from the
-              fractional portion of the result and the decimal-point wide character is
-              removed if there is no fractional portion remaining.
-              A double argument representing an infinity or NaN is converted in the style
-              of an f or F conversion specifier.
-
- a,A A double argument representing a floating-point number is converted in the -
-              style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
-              nonzero if the argument is a normalized floating-point number and is
-              otherwise unspecified) before the decimal-point wide character320) and the
-              number of hexadecimal digits after it is equal to the precision; if the precision
-              is missing and FLT_RADIX is a power of 2, then the precision is sufficient
-
- - - -
-              for an exact representation of the value; if the precision is missing and
-              FLT_RADIX is not a power of 2, then the precision is sufficient to
-              distinguish321) values of type double, except that trailing zeros may be
-              omitted; if the precision is zero and the # flag is not specified, no decimal-
-              point wide character appears. The letters abcdef are used for a conversion
-              and the letters ABCDEF for A conversion. The A conversion specifier
-              produces a number with X and P instead of x and p. The exponent always
-              contains at least one digit, and only as many more digits as necessary to
-              represent the decimal exponent of 2. If the value is zero, the exponent is
-              zero.
-              A double argument representing an infinity or NaN is converted in the style
-              of an f or F conversion specifier.
-
- c If no l length modifier is present, the int argument is converted to a wide -
-              character as if by calling btowc and the resulting wide character is written.
-              If an l length modifier is present, the wint_t argument is converted to
-              wchar_t and written.
-
- s If no l length modifier is present, the argument shall be a pointer to the initial -
-              element of a character array containing a multibyte character sequence
-              beginning in the initial shift state. Characters from the array are converted as
-              if by repeated calls to the mbrtowc function, with the conversion state
-              described by an mbstate_t object initialized to zero before the first
-              multibyte character is converted, and written up to (but not including) the
-              terminating null wide character. If the precision is specified, no more than
-              that many wide characters are written. If the precision is not specified or is
-              greater than the size of the converted array, the converted array shall contain a
-              null wide character.
-              If an l length modifier is present, the argument shall be a pointer to the initial
-              element of an array of wchar_t type. Wide characters from the array are
-              written up to (but not including) a terminating null wide character. If the
-              precision is specified, no more than that many wide characters are written. If
-              the precision is not specified or is greater than the size of the array, the array
-              shall contain a null wide character.
-
- p The argument shall be a pointer to void. The value of the pointer is -
-              converted to a sequence of printing wide characters, in an implementation-
-
- - -
-                defined manner.
-
- n The argument shall be a pointer to signed integer into which is written the -
-                number of wide characters written to the output stream so far by this call to
-                fwprintf. No argument is converted, but one is consumed. If the
-                conversion specification includes any flags, a field width, or a precision, the
-                behavior is undefined.
-
- % A % wide character is written. No argument is converted. The complete -
-                conversion specification shall be %%.
-
-

- If a conversion specification is invalid, the behavior is undefined.322) If any argument is - not the correct type for the corresponding conversion specification, the behavior is - undefined. -

- In no case does a nonexistent or small field width cause truncation of a field; if the result - of a conversion is wider than the field width, the field is expanded to contain the - conversion result. -

- For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded - to a hexadecimal floating number with the given precision. -

Recommended practice -

- For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly - representable in the given precision, the result should be one of the two adjacent numbers - in hexadecimal floating style with the given precision, with the extra stipulation that the - error should have a correct sign for the current rounding direction. -

- For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most - DECIMAL_DIG, then the result should be correctly rounded.323) If the number of - significant decimal digits is more than DECIMAL_DIG but the source value is exactly - representable with DECIMAL_DIG digits, then the result should be an exact - representation with trailing zeros. Otherwise, the source value is bounded by two - adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value - of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that - the error should have a correct sign for the current rounding direction. -

Returns -

- The fwprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - - -

Environmental limits -

- The number of wide characters that can be produced by any single conversion shall be at - least 4095. -

- EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal - places: -

-         #include <math.h>
-         #include <stdio.h>
-         #include <wchar.h>
-         /* ... */
-         wchar_t *weekday, *month; // pointers to wide strings
-         int day, hour, min;
-         fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
-                 weekday, month, day, hour, min);
-         fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
-
- -

Forward references: the btowc function (7.28.6.1.1), the mbrtowc function - (7.28.6.3.2). - -

Footnotes -

317) Note that 0 is taken as a flag, not as the beginning of a field width. - -

318) The results of all floating conversions of a negative zero, and of negative values that round to zero, - include a minus sign. - -

319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual - meaning; the # and 0 flag wide characters have no effect. - -

320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide - character so that subsequent digits align to nibble (4-bit) boundaries. - -

321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is - FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p - might suffice depending on the implementation's scheme for determining the digit to the left of the - decimal-point wide character. - -

322) See ''future library directions'' (7.30.12). - -

323) For binary-to-decimal conversion, the result format's values are the numbers representable with the - given format specifier. The number of significant digits is determined by the format specifier, and in - the case of fixed-point conversion by the source value as well. - - -

Contents -

7.28.2.2 The fwscanf function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         int fwscanf(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-
-

Description -

- The fwscanf function reads input from the stream pointed to by stream, under - control of the wide string pointed to by format that specifies the admissible input - sequences and how they are to be converted for assignment, using subsequent arguments - as pointers to the objects to receive the converted input. If there are insufficient - arguments for the format, the behavior is undefined. If the format is exhausted while - arguments remain, the excess arguments are evaluated (as always) but are otherwise - ignored. -

- The format is composed of zero or more directives: one or more white-space wide - characters, an ordinary wide character (neither % nor a white-space wide character), or a - conversion specification. Each conversion specification is introduced by the wide - character %. After the %, the following appear in sequence: -

-

- The fwscanf function executes each directive of the format in turn. When all directives - have been executed, or if a directive fails (as detailed below), the function returns. - Failures are described as input failures (due to the occurrence of an encoding error or the - unavailability of input characters), or matching failures (due to inappropriate input). -

- A directive composed of white-space wide character(s) is executed by reading input up to - the first non-white-space wide character (which remains unread), or until no more wide - characters can be read. -

- A directive that is an ordinary wide character is executed by reading the next wide - character of the stream. If that wide character differs from the directive, the directive - fails and the differing and subsequent wide characters remain unread. Similarly, if end- - of-file, an encoding error, or a read error prevents a wide character from being read, the - directive fails. -

- A directive that is a conversion specification defines a set of matching input sequences, as - described below for each specifier. A conversion specification is executed in the - following steps: -

- Input white-space wide characters (as specified by the iswspace function) are skipped, - unless the specification includes a [, c, or n specifier.324) -

- An input item is read from the stream, unless the specification includes an n specifier. An - input item is defined as the longest sequence of input wide characters which does not - exceed any specified field width and which is, or is a prefix of, a matching input - sequence.325) The first wide character, if any, after the input item remains unread. If the - length of the input item is zero, the execution of the directive fails; this condition is a - matching failure unless end-of-file, an encoding error, or a read error prevented input - from the stream, in which case it is an input failure. -

- Except in the case of a % specifier, the input item (or, in the case of a %n directive, the - count of input wide characters) is converted to a type appropriate to the conversion - specifier. If the input item is not a matching sequence, the execution of the directive fails: - this condition is a matching failure. Unless assignment suppression was indicated by a *, - the result of the conversion is placed in the object pointed to by the first argument - following the format argument that has not already received a conversion result. If this - - - - object does not have an appropriate type, or if the result of the conversion cannot be - represented in the object, the behavior is undefined. -

- The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -

-              to an argument with type pointer to signed char or unsigned char.
-
- h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to short int or unsigned short
-              int.
-
- l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to long int or unsigned long
-              int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
-              an argument with type pointer to double; or that a following c, s, or [
-              conversion specifier applies to an argument with type pointer to wchar_t.
-
- ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to long long int or unsigned
-              long long int.
-
- j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to intmax_t or uintmax_t.
-
- z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to size_t or the corresponding signed
-              integer type.
-
- t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies -
-              to an argument with type pointer to ptrdiff_t or the corresponding
-              unsigned integer type.
-
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier -
-              applies to an argument with type pointer to long double.
-
- If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -

- The conversion specifiers and their meanings are: - d Matches an optionally signed decimal integer, whose format is the same as -

-             expected for the subject sequence of the wcstol function with the value 10
-             for the base argument. The corresponding argument shall be a pointer to
-             signed integer.
-
- i Matches an optionally signed integer, whose format is the same as expected - -
-             for the subject sequence of the wcstol function with the value 0 for the
-             base argument. The corresponding argument shall be a pointer to signed
-           integer.
-
- o Matches an optionally signed octal integer, whose format is the same as -
-           expected for the subject sequence of the wcstoul function with the value 8
-           for the base argument. The corresponding argument shall be a pointer to
-           unsigned integer.
-
- u Matches an optionally signed decimal integer, whose format is the same as -
-           expected for the subject sequence of the wcstoul function with the value 10
-           for the base argument. The corresponding argument shall be a pointer to
-           unsigned integer.
-
- x Matches an optionally signed hexadecimal integer, whose format is the same -
-           as expected for the subject sequence of the wcstoul function with the value
-           16 for the base argument. The corresponding argument shall be a pointer to
-           unsigned integer.
-
- a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose -
-         format is the same as expected for the subject sequence of the wcstod
-         function. The corresponding argument shall be a pointer to floating.
-
- c Matches a sequence of wide characters of exactly the number specified by the -
-           field width (1 if no field width is present in the directive).
-           If no l length modifier is present, characters from the input field are
-           converted as if by repeated calls to the wcrtomb function, with the
-           conversion state described by an mbstate_t object initialized to zero
-           before the first wide character is converted. The corresponding argument
-           shall be a pointer to the initial element of a character array large enough to
-           accept the sequence. No null character is added.
-           If an l length modifier is present, the corresponding argument shall be a
-           pointer to the initial element of an array of wchar_t large enough to accept
-           the sequence. No null wide character is added.
-
- s Matches a sequence of non-white-space wide characters. - -
-           If no l length modifier is present, characters from the input field are
-           converted as if by repeated calls to the wcrtomb function, with the
-           conversion state described by an mbstate_t object initialized to zero
-           before the first wide character is converted. The corresponding argument
-           shall be a pointer to the initial element of a character array large enough to
-           accept the sequence and a terminating null character, which will be added
-           automatically.
-           If an l length modifier is present, the corresponding argument shall be a
-           pointer to the initial element of an array of wchar_t large enough to accept
-             the sequence and the terminating null wide character, which will be added
-             automatically.
-
- [ Matches a nonempty sequence of wide characters from a set of expected -
-             characters (the scanset).
-             If no l length modifier is present, characters from the input field are
-             converted as if by repeated calls to the wcrtomb function, with the
-             conversion state described by an mbstate_t object initialized to zero
-             before the first wide character is converted. The corresponding argument
-             shall be a pointer to the initial element of a character array large enough to
-             accept the sequence and a terminating null character, which will be added
-             automatically.
-             If an l length modifier is present, the corresponding argument shall be a
-             pointer to the initial element of an array of wchar_t large enough to accept
-             the sequence and the terminating null wide character, which will be added
-             automatically.
-             The conversion specifier includes all subsequent wide characters in the
-             format string, up to and including the matching right bracket (]). The wide
-             characters between the brackets (the scanlist) compose the scanset, unless the
-             wide character after the left bracket is a circumflex (^), in which case the
-             scanset contains all wide characters that do not appear in the scanlist between
-             the circumflex and the right bracket. If the conversion specifier begins with
-             [] or [^], the right bracket wide character is in the scanlist and the next
-             following right bracket wide character is the matching right bracket that ends
-             the specification; otherwise the first following right bracket wide character is
-             the one that ends the specification. If a - wide character is in the scanlist and
-             is not the first, nor the second where the first wide character is a ^, nor the
-             last character, the behavior is implementation-defined.
-
- p Matches an implementation-defined set of sequences, which should be the -
-             same as the set of sequences that may be produced by the %p conversion of
-             the fwprintf function. The corresponding argument shall be a pointer to a
-             pointer to void. The input item is converted to a pointer value in an
-             implementation-defined manner. If the input item is a value converted earlier
-             during the same program execution, the pointer that results shall compare
-             equal to that value; otherwise the behavior of the %p conversion is undefined.
-
- n No input is consumed. The corresponding argument shall be a pointer to - -
-             signed integer into which is to be written the number of wide characters read
-             from the input stream so far by this call to the fwscanf function. Execution
-             of a %n directive does not increment the assignment count returned at the
-             completion of execution of the fwscanf function. No argument is
-                converted, but one is consumed. If the conversion specification includes an
-                assignment-suppressing wide character or a field width, the behavior is
-                undefined.
-
- % Matches a single % wide character; no conversion or assignment occurs. The -
-                complete conversion specification shall be %%.
-
-

- If a conversion specification is invalid, the behavior is undefined.326) -

- The conversion specifiers A, E, F, G, and X are also valid and behave the same as, - respectively, a, e, f, g, and x. -

- Trailing white space (including new-line wide characters) is left unread unless matched - by a directive. The success of literal matches and suppressed assignments is not directly - determinable other than via the %n directive. -

Returns -

- The fwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. -

- EXAMPLE 1 The call: -

-          #include <stdio.h>
-          #include <wchar.h>
-          /* ... */
-          int n, i; float x; wchar_t name[50];
-          n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
-
- with the input line: -
-          25 54.32E-1 thompson
-
- will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -

- EXAMPLE 2 The call: -

-          #include <stdio.h>
-          #include <wchar.h>
-          /* ... */
-          int i; float x; double y;
-          fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
-
- with input: -
-          56789 0123 56a72
-
- will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value - 56.0. The next wide character read from the input stream will be a. - - - -

Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the - wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb - function (7.28.6.3.3). - -

Footnotes -

324) These white-space wide characters are not counted against a specified field width. - -

325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some - sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf. - -

326) See ''future library directions'' (7.30.12). - - -

Contents -

7.28.2.3 The swprintf function
-

Synopsis -

-

-         #include <wchar.h>
-         int swprintf(wchar_t * restrict s,
-              size_t n,
-              const wchar_t * restrict format, ...);
-
-

Description -

- The swprintf function is equivalent to fwprintf, except that the argument s - specifies an array of wide characters into which the generated output is to be written, - rather than written to a stream. No more than n wide characters are written, including a - terminating null wide character, which is always added (unless n is zero). -

Returns -

- The swprintf function returns the number of wide characters written in the array, not - counting the terminating null wide character, or a negative value if an encoding error - occurred or if n or more wide characters were requested to be written. - -

Contents -

7.28.2.4 The swscanf function
-

Synopsis -

-

-         #include <wchar.h>
-         int swscanf(const wchar_t * restrict s,
-              const wchar_t * restrict format, ...);
-
-

Description -

- The swscanf function is equivalent to fwscanf, except that the argument s specifies a - wide string from which the input is to be obtained, rather than from a stream. Reaching - the end of the wide string is equivalent to encountering end-of-file for the fwscanf - function. -

Returns -

- The swscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the swscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - - -

Contents -

7.28.2.5 The vfwprintf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <stdio.h>
-        #include <wchar.h>
-        int vfwprintf(FILE * restrict stream,
-             const wchar_t * restrict format,
-             va_list arg);
-
-

Description -

- The vfwprintf function is equivalent to fwprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwprintf function does not invoke the - va_end macro.327) -

Returns -

- The vfwprintf function returns the number of wide characters transmitted, or a - negative value if an output or encoding error occurred. -

- EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting - routine. -

-        #include <stdarg.h>
-        #include <stdio.h>
-        #include <wchar.h>
-        void error(char *function_name, wchar_t *format, ...)
-        {
-              va_list args;
-                 va_start(args, format);
-                 // print out name of function causing error
-                 fwprintf(stderr, L"ERROR in %s: ", function_name);
-                 // print out remainder of message
-                 vfwprintf(stderr, format, args);
-                 va_end(args);
-        }
-
- - - - - - -

Footnotes -

327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf - invoke the va_arg macro, the value of arg after the return is indeterminate. - - -

Contents -

7.28.2.6 The vfwscanf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <stdio.h>
-         #include <wchar.h>
-         int vfwscanf(FILE * restrict stream,
-              const wchar_t * restrict format,
-              va_list arg);
-
-

Description -

- The vfwscanf function is equivalent to fwscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwscanf function does not invoke the - va_end macro.327) -

Returns -

- The vfwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vfwscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.28.2.7 The vswprintf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <wchar.h>
-         int vswprintf(wchar_t * restrict s,
-              size_t n,
-              const wchar_t * restrict format,
-              va_list arg);
-
-

Description -

- The vswprintf function is equivalent to swprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswprintf function does not invoke the - va_end macro.327) -

Returns -

- The vswprintf function returns the number of wide characters written in the array, not - counting the terminating null wide character, or a negative value if an encoding error - occurred or if n or more wide characters were requested to be generated. - - -

Contents -

7.28.2.8 The vswscanf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <wchar.h>
-        int vswscanf(const wchar_t * restrict s,
-             const wchar_t * restrict format,
-             va_list arg);
-
-

Description -

- The vswscanf function is equivalent to swscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswscanf function does not invoke the - va_end macro.327) -

Returns -

- The vswscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vswscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.28.2.9 The vwprintf function
-

Synopsis -

-

-        #include <stdarg.h>
-        #include <wchar.h>
-        int vwprintf(const wchar_t * restrict format,
-             va_list arg);
-
-

Description -

- The vwprintf function is equivalent to wprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwprintf function does not invoke the - va_end macro.327) -

Returns -

- The vwprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - - -

Contents -

7.28.2.10 The vwscanf function
-

Synopsis -

-

-         #include <stdarg.h>
-         #include <wchar.h>
-         int vwscanf(const wchar_t * restrict format,
-              va_list arg);
-
-

Description -

- The vwscanf function is equivalent to wscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwscanf function does not invoke the - va_end macro.327) -

Returns -

- The vwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vwscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.28.2.11 The wprintf function
-

Synopsis -

-

-         #include <wchar.h>
-         int wprintf(const wchar_t * restrict format, ...);
-
-

Description -

- The wprintf function is equivalent to fwprintf with the argument stdout - interposed before the arguments to wprintf. -

Returns -

- The wprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - -

Contents -

7.28.2.12 The wscanf function
-

Synopsis -

-

-         #include <wchar.h>
-         int wscanf(const wchar_t * restrict format, ...);
-
-

Description -

- The wscanf function is equivalent to fwscanf with the argument stdin interposed - before the arguments to wscanf. - -

Returns -

- The wscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the wscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -

Contents -

7.28.3 Wide character input/output functions

- -

Contents -

7.28.3.1 The fgetwc function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wint_t fgetwc(FILE *stream);
-
-

Description -

- If the end-of-file indicator for the input stream pointed to by stream is not set and a - next wide character is present, the fgetwc function obtains that wide character as a - wchar_t converted to a wint_t and advances the associated file position indicator for - the stream (if defined). -

Returns -

- If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- - of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise, - the fgetwc function returns the next wide character from the input stream pointed to by - stream. If a read error occurs, the error indicator for the stream is set and the fgetwc - function returns WEOF. If an encoding error occurs (including too few bytes), the value of - the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328) - -

Footnotes -

328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. - Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs. - - -

Contents -

7.28.3.2 The fgetws function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wchar_t *fgetws(wchar_t * restrict s,
-              int n, FILE * restrict stream);
-
-

Description -

- The fgetws function reads at most one less than the number of wide characters - specified by n from the stream pointed to by stream into the array pointed to by s. No - - - - additional wide characters are read after a new-line wide character (which is retained) or - after end-of-file. A null wide character is written immediately after the last wide - character read into the array. -

Returns -

- The fgetws function returns s if successful. If end-of-file is encountered and no - characters have been read into the array, the contents of the array remain unchanged and a - null pointer is returned. If a read or encoding error occurs during the operation, the array - contents are indeterminate and a null pointer is returned. - -

Contents -

7.28.3.3 The fputwc function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wint_t fputwc(wchar_t c, FILE *stream);
-
-

Description -

- The fputwc function writes the wide character specified by c to the output stream - pointed to by stream, at the position indicated by the associated file position indicator - for the stream (if defined), and advances the indicator appropriately. If the file cannot - support positioning requests, or if the stream was opened with append mode, the - character is appended to the output stream. -

Returns -

- The fputwc function returns the wide character written. If a write error occurs, the - error indicator for the stream is set and fputwc returns WEOF. If an encoding error - occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF. - -

Contents -

7.28.3.4 The fputws function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         int fputws(const wchar_t * restrict s,
-              FILE * restrict stream);
-
-

Description -

- The fputws function writes the wide string pointed to by s to the stream pointed to by - stream. The terminating null wide character is not written. -

Returns -

- The fputws function returns EOF if a write or encoding error occurs; otherwise, it - returns a nonnegative value. - - -

Contents -

7.28.3.5 The fwide function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         int fwide(FILE *stream, int mode);
-
-

Description -

- The fwide function determines the orientation of the stream pointed to by stream. If - mode is greater than zero, the function first attempts to make the stream wide oriented. If - mode is less than zero, the function first attempts to make the stream byte oriented.329) - Otherwise, mode is zero and the function does not alter the orientation of the stream. -

Returns -

- The fwide function returns a value greater than zero if, after the call, the stream has - wide orientation, a value less than zero if the stream has byte orientation, or zero if the - stream has no orientation. - -

Footnotes -

329) If the orientation of the stream has already been determined, fwide does not change it. - - -

Contents -

7.28.3.6 The getwc function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wint_t getwc(FILE *stream);
-
-

Description -

- The getwc function is equivalent to fgetwc, except that if it is implemented as a - macro, it may evaluate stream more than once, so the argument should never be an - expression with side effects. -

Returns -

- The getwc function returns the next wide character from the input stream pointed to by - stream, or WEOF. - -

Contents -

7.28.3.7 The getwchar function
-

Synopsis -

-

-         #include <wchar.h>
-         wint_t getwchar(void);
-
- - - - - -

Description -

- The getwchar function is equivalent to getwc with the argument stdin. -

Returns -

- The getwchar function returns the next wide character from the input stream pointed to - by stdin, or WEOF. - -

Contents -

7.28.3.8 The putwc function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wint_t putwc(wchar_t c, FILE *stream);
-
-

Description -

- The putwc function is equivalent to fputwc, except that if it is implemented as a - macro, it may evaluate stream more than once, so that argument should never be an - expression with side effects. -

Returns -

- The putwc function returns the wide character written, or WEOF. - -

Contents -

7.28.3.9 The putwchar function
-

Synopsis -

-

-         #include <wchar.h>
-         wint_t putwchar(wchar_t c);
-
-

Description -

- The putwchar function is equivalent to putwc with the second argument stdout. -

Returns -

- The putwchar function returns the character written, or WEOF. - -

Contents -

7.28.3.10 The ungetwc function
-

Synopsis -

-

-         #include <stdio.h>
-         #include <wchar.h>
-         wint_t ungetwc(wint_t c, FILE *stream);
-
-

Description -

- The ungetwc function pushes the wide character specified by c back onto the input - stream pointed to by stream. Pushed-back wide characters will be returned by - subsequent reads on that stream in the reverse order of their pushing. A successful - - intervening call (with the stream pointed to by stream) to a file positioning function - (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the - stream. The external storage corresponding to the stream is unchanged. -

- One wide character of pushback is guaranteed, even if the call to the ungetwc function - follows just after a call to a formatted wide character input function fwscanf, - vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times - on the same stream without an intervening read or file positioning operation on that - stream, the operation may fail. -

- If the value of c equals that of the macro WEOF, the operation fails and the input stream is - unchanged. -

- A successful call to the ungetwc function clears the end-of-file indicator for the stream. - The value of the file position indicator for the stream after reading or discarding all - pushed-back wide characters is the same as it was before the wide characters were pushed - back. For a text or binary stream, the value of its file position indicator after a successful - call to the ungetwc function is unspecified until all pushed-back wide characters are - read or discarded. -

Returns -

- The ungetwc function returns the wide character pushed back, or WEOF if the operation - fails. - -

Contents -

7.28.4 General wide string utilities

-

- The header <wchar.h> declares a number of functions useful for wide string - manipulation. Various methods are used for determining the lengths of the arrays, but in - all cases a wchar_t * argument points to the initial (lowest addressed) element of the - array. If an array is accessed beyond the end of an object, the behavior is undefined. -

- Where an argument declared as size_t n determines the length of the array for a - function, n can have the value zero on a call to that function. Unless explicitly stated - otherwise in the description of a particular function in this subclause, pointer arguments - on such a call shall still have valid values, as described in 7.1.4. On such a call, a - function that locates a wide character finds no occurrence, a function that compares two - wide character sequences returns zero, and a function that copies wide characters copies - zero wide characters. - - -

Contents -

7.28.4.1 Wide string numeric conversion functions
- -

Contents -

7.28.4.1.1 The wcstod, wcstof, and wcstold functions
-

Synopsis -

-

-         #include <wchar.h>
-         double wcstod(const wchar_t * restrict nptr,
-              wchar_t ** restrict endptr);
-         float wcstof(const wchar_t * restrict nptr,
-              wchar_t ** restrict endptr);
-         long double wcstold(const wchar_t * restrict nptr,
-              wchar_t ** restrict endptr);
-
-

Description -

- The wcstod, wcstof, and wcstold functions convert the initial portion of the wide - string pointed to by nptr to double, float, and long double representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space wide characters (as specified by the iswspace - function), a subject sequence resembling a floating-point constant or representing an - infinity or NaN; and a final wide string of one or more unrecognized wide characters, - including the terminating null wide character of the input wide string. Then, they attempt - to convert the subject sequence to a floating-point number, and return the result. -

- The expected form of the subject sequence is an optional plus or minus sign, then one of - the following: -

- The subject sequence is defined as the longest initial subsequence of the input wide - string, starting with the first non-white-space wide character, that is of the expected form. - - The subject sequence contains no wide characters if the input wide string is not of the - expected form. -

- If the subject sequence has the expected form for a floating-point number, the sequence of - wide characters starting with the first digit or the decimal-point wide character - (whichever occurs first) is interpreted as a floating constant according to the rules of - 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that - if neither an exponent part nor a decimal-point wide character appears in a decimal - floating point number, or if a binary exponent part does not appear in a hexadecimal - floating point number, an exponent part of the appropriate type with value zero is - assumed to follow the last digit in the string. If the subject sequence begins with a minus - sign, the sequence is interpreted as negated.330) A wide character sequence INF or - INFINITY is interpreted as an infinity, if representable in the return type, else like a - floating constant that is too large for the range of the return type. A wide character - sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported - in the return type, else like a subject sequence part that does not have the expected form; - the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the - final wide string is stored in the object pointed to by endptr, provided that endptr is - not a null pointer. -

- If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the - value resulting from the conversion is correctly rounded. -

- In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -

- If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. -

Recommended practice -

- If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and - the result is not exactly representable, the result should be one of the two numbers in the - appropriate internal format that are adjacent to the hexadecimal floating source value, - with the extra stipulation that the error should have a correct sign for the current rounding - direction. - - - - -

- If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in - <float.h>) significant digits, the result should be correctly rounded. If the subject - sequence D has the decimal form and more than DECIMAL_DIG significant digits, - consider the two bounding, adjacent decimal strings L and U, both having - DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. - The result should be one of the (equal or adjacent) values that would be obtained by - correctly rounding L and U according to the current rounding direction, with the extra - stipulation that the error with respect to D should have a correct sign for the current - rounding direction.332) -

Returns -

- The functions return the converted value, if any. If no conversion could be performed, - zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), - plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the - return type and sign of the value), and the value of the macro ERANGE is stored in - errno. If the result underflows (7.12.1), the functions return a value whose magnitude is - no greater than the smallest normalized positive number in the return type; whether - errno acquires the value ERANGE is implementation-defined. - - - - - - -

Footnotes -

330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two - methods may yield different results if rounding is toward positive or negative infinity. In either case, - the functions honor the sign of zero if floating-point arithmetic supports signed zeros. - -

331) An implementation may use the n-wchar sequence to determine extra information to be represented in - the NaN's significand. - -

332) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round - to the same internal floating value, but if not will round to adjacent values. - - -

Contents -

7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
-

Synopsis -

-

-        #include <wchar.h>
-        long int wcstol(
-             const wchar_t * restrict nptr,
-             wchar_t ** restrict endptr,
-             int base);
-        long long int wcstoll(
-             const wchar_t * restrict nptr,
-             wchar_t ** restrict endptr,
-             int base);
-        unsigned long int wcstoul(
-             const wchar_t * restrict nptr,
-             wchar_t ** restrict endptr,
-             int base);
-        unsigned long long int wcstoull(
-             const wchar_t * restrict nptr,
-             wchar_t ** restrict endptr,
-             int base);
-
-

Description -

- The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial - portion of the wide string pointed to by nptr to long int, long long int, - unsigned long int, and unsigned long long int representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space wide characters (as specified by the iswspace - function), a subject sequence resembling an integer represented in some radix determined - by the value of base, and a final wide string of one or more unrecognized wide - characters, including the terminating null wide character of the input wide string. Then, - they attempt to convert the subject sequence to an integer, and return the result. -

- If the value of base is zero, the expected form of the subject sequence is that of an - integer constant as described for the corresponding single-byte characters in 6.4.4.1, - optionally preceded by a plus or minus sign, but not including an integer suffix. If the - value of base is between 2 and 36 (inclusive), the expected form of the subject sequence - is a sequence of letters and digits representing an integer with the radix specified by - base, optionally preceded by a plus or minus sign, but not including an integer suffix. - The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only - letters and digits whose ascribed values are less than that of base are permitted. If the - value of base is 16, the wide characters 0x or 0X may optionally precede the sequence - of letters and digits, following the sign if present. - -

- The subject sequence is defined as the longest initial subsequence of the input wide - string, starting with the first non-white-space wide character, that is of the expected form. - The subject sequence contains no wide characters if the input wide string is empty or - consists entirely of white space, or if the first non-white-space wide character is other - than a sign or a permissible letter or digit. -

- If the subject sequence has the expected form and the value of base is zero, the sequence - of wide characters starting with the first digit is interpreted as an integer constant - according to the rules of 6.4.4.1. If the subject sequence has the expected form and the - value of base is between 2 and 36, it is used as the base for conversion, ascribing to each - letter its value as given above. If the subject sequence begins with a minus sign, the value - resulting from the conversion is negated (in the return type). A pointer to the final wide - string is stored in the object pointed to by endptr, provided that endptr is not a null - pointer. -

- In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -

- If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. -

Returns -

- The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted - value, if any. If no conversion could be performed, zero is returned. If the correct value - is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, - LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type - sign of the value, if any), and the value of the macro ERANGE is stored in errno. - -

Contents -

7.28.4.2 Wide string copying functions
- -

Contents -

7.28.4.2.1 The wcscpy function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wcscpy(wchar_t * restrict s1,
-              const wchar_t * restrict s2);
-
-

Description -

- The wcscpy function copies the wide string pointed to by s2 (including the terminating - null wide character) into the array pointed to by s1. -

Returns -

- The wcscpy function returns the value of s1. - - -

Contents -

7.28.4.2.2 The wcsncpy function
-

Synopsis -

-

-          #include <wchar.h>
-          wchar_t *wcsncpy(wchar_t * restrict s1,
-               const wchar_t * restrict s2,
-               size_t n);
-
-

Description -

- The wcsncpy function copies not more than n wide characters (those that follow a null - wide character are not copied) from the array pointed to by s2 to the array pointed to by - s1.333) -

- If the array pointed to by s2 is a wide string that is shorter than n wide characters, null - wide characters are appended to the copy in the array pointed to by s1, until n wide - characters in all have been written. -

Returns -

- The wcsncpy function returns the value of s1. - -

Footnotes -

333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the - result will not be null-terminated. - - -

Contents -

7.28.4.2.3 The wmemcpy function
-

Synopsis -

-

-          #include <wchar.h>
-          wchar_t *wmemcpy(wchar_t * restrict s1,
-               const wchar_t * restrict s2,
-               size_t n);
-
-

Description -

- The wmemcpy function copies n wide characters from the object pointed to by s2 to the - object pointed to by s1. -

Returns -

- The wmemcpy function returns the value of s1. - - - - - - -

Contents -

7.28.4.2.4 The wmemmove function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
-              size_t n);
-
-

Description -

- The wmemmove function copies n wide characters from the object pointed to by s2 to - the object pointed to by s1. Copying takes place as if the n wide characters from the - object pointed to by s2 are first copied into a temporary array of n wide characters that - does not overlap the objects pointed to by s1 or s2, and then the n wide characters from - the temporary array are copied into the object pointed to by s1. -

Returns -

- The wmemmove function returns the value of s1. - -

Contents -

7.28.4.3 Wide string concatenation functions
- -

Contents -

7.28.4.3.1 The wcscat function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wcscat(wchar_t * restrict s1,
-              const wchar_t * restrict s2);
-
-

Description -

- The wcscat function appends a copy of the wide string pointed to by s2 (including the - terminating null wide character) to the end of the wide string pointed to by s1. The initial - wide character of s2 overwrites the null wide character at the end of s1. -

Returns -

- The wcscat function returns the value of s1. - -

Contents -

7.28.4.3.2 The wcsncat function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wcsncat(wchar_t * restrict s1,
-              const wchar_t * restrict s2,
-              size_t n);
-
-

Description -

- The wcsncat function appends not more than n wide characters (a null wide character - and those that follow it are not appended) from the array pointed to by s2 to the end of - - the wide string pointed to by s1. The initial wide character of s2 overwrites the null - wide character at the end of s1. A terminating null wide character is always appended to - the result.334) -

Returns -

- The wcsncat function returns the value of s1. - -

Footnotes -

334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is - wcslen(s1)+n+1. - - -

Contents -

7.28.4.4 Wide string comparison functions
-

- Unless explicitly stated otherwise, the functions described in this subclause order two - wide characters the same way as two integers of the underlying integer type designated - by wchar_t. - -

Contents -

7.28.4.4.1 The wcscmp function
-

Synopsis -

-

-         #include <wchar.h>
-         int wcscmp(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcscmp function compares the wide string pointed to by s1 to the wide string - pointed to by s2. -

Returns -

- The wcscmp function returns an integer greater than, equal to, or less than zero, - accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the - wide string pointed to by s2. - -

Contents -

7.28.4.4.2 The wcscoll function
-

Synopsis -

-

-         #include <wchar.h>
-         int wcscoll(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcscoll function compares the wide string pointed to by s1 to the wide string - pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the - current locale. -

Returns -

- The wcscoll function returns an integer greater than, equal to, or less than zero, - accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the - - - - wide string pointed to by s2 when both are interpreted as appropriate to the current - locale. - -

Contents -

7.28.4.4.3 The wcsncmp function
-

Synopsis -

-

-         #include <wchar.h>
-         int wcsncmp(const wchar_t *s1, const wchar_t *s2,
-              size_t n);
-
-

Description -

- The wcsncmp function compares not more than n wide characters (those that follow a - null wide character are not compared) from the array pointed to by s1 to the array - pointed to by s2. -

Returns -

- The wcsncmp function returns an integer greater than, equal to, or less than zero, - accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal - to, or less than the possibly null-terminated array pointed to by s2. - -

Contents -

7.28.4.4.4 The wcsxfrm function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t wcsxfrm(wchar_t * restrict s1,
-              const wchar_t * restrict s2,
-              size_t n);
-
-

Description -

- The wcsxfrm function transforms the wide string pointed to by s2 and places the - resulting wide string into the array pointed to by s1. The transformation is such that if - the wcscmp function is applied to two transformed wide strings, it returns a value greater - than, equal to, or less than zero, corresponding to the result of the wcscoll function - applied to the same two original wide strings. No more than n wide characters are placed - into the resulting array pointed to by s1, including the terminating null wide character. If - n is zero, s1 is permitted to be a null pointer. -

Returns -

- The wcsxfrm function returns the length of the transformed wide string (not including - the terminating null wide character). If the value returned is n or greater, the contents of - the array pointed to by s1 are indeterminate. -

- EXAMPLE The value of the following expression is the length of the array needed to hold the - transformation of the wide string pointed to by s: - -

-        1 + wcsxfrm(NULL, s, 0)
-
- - -

Contents -

7.28.4.4.5 The wmemcmp function
-

Synopsis -

-

-        #include <wchar.h>
-        int wmemcmp(const wchar_t *s1, const wchar_t *s2,
-             size_t n);
-
-

Description -

- The wmemcmp function compares the first n wide characters of the object pointed to by - s1 to the first n wide characters of the object pointed to by s2. -

Returns -

- The wmemcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the object pointed to by s1 is greater than, equal to, or less than the object - pointed to by s2. - -

Contents -

7.28.4.5 Wide string search functions
- -

Contents -

7.28.4.5.1 The wcschr function
-

Synopsis -

-

-        #include <wchar.h>
-        wchar_t *wcschr(const wchar_t *s, wchar_t c);
-
-

Description -

- The wcschr function locates the first occurrence of c in the wide string pointed to by s. - The terminating null wide character is considered to be part of the wide string. -

Returns -

- The wcschr function returns a pointer to the located wide character, or a null pointer if - the wide character does not occur in the wide string. - -

Contents -

7.28.4.5.2 The wcscspn function
-

Synopsis -

-

-        #include <wchar.h>
-        size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcscspn function computes the length of the maximum initial segment of the wide - string pointed to by s1 which consists entirely of wide characters not from the wide - string pointed to by s2. - -

Returns -

- The wcscspn function returns the length of the segment. - -

Contents -

7.28.4.5.3 The wcspbrk function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of - any wide character from the wide string pointed to by s2. -

Returns -

- The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if - no wide character from s2 occurs in s1. - -

Contents -

7.28.4.5.4 The wcsrchr function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
-
-

Description -

- The wcsrchr function locates the last occurrence of c in the wide string pointed to by - s. The terminating null wide character is considered to be part of the wide string. -

Returns -

- The wcsrchr function returns a pointer to the wide character, or a null pointer if c does - not occur in the wide string. - -

Contents -

7.28.4.5.5 The wcsspn function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcsspn function computes the length of the maximum initial segment of the wide - string pointed to by s1 which consists entirely of wide characters from the wide string - pointed to by s2. -

Returns -

- The wcsspn function returns the length of the segment. - - -

Contents -

7.28.4.5.6 The wcsstr function
-

Synopsis -

-

-        #include <wchar.h>
-        wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
-
-

Description -

- The wcsstr function locates the first occurrence in the wide string pointed to by s1 of - the sequence of wide characters (excluding the terminating null wide character) in the - wide string pointed to by s2. -

Returns -

- The wcsstr function returns a pointer to the located wide string, or a null pointer if the - wide string is not found. If s2 points to a wide string with zero length, the function - returns s1. - -

Contents -

7.28.4.5.7 The wcstok function
-

Synopsis -

-

-        #include <wchar.h>
-        wchar_t *wcstok(wchar_t * restrict s1,
-             const wchar_t * restrict s2,
-             wchar_t ** restrict ptr);
-
-

Description -

- A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into - a sequence of tokens, each of which is delimited by a wide character from the wide string - pointed to by s2. The third argument points to a caller-provided wchar_t pointer into - which the wcstok function stores information necessary for it to continue scanning the - same wide string. -

- The first call in a sequence has a non-null first argument and stores an initial value in the - object pointed to by ptr. Subsequent calls in the sequence have a null first argument and - the object pointed to by ptr is required to have the value stored by the previous call in - the sequence, which is then updated. The separator wide string pointed to by s2 may be - different from call to call. -

- The first call in the sequence searches the wide string pointed to by s1 for the first wide - character that is not contained in the current separator wide string pointed to by s2. If no - such wide character is found, then there are no tokens in the wide string pointed to by s1 - and the wcstok function returns a null pointer. If such a wide character is found, it is - the start of the first token. -

- The wcstok function then searches from there for a wide character that is contained in - the current separator wide string. If no such wide character is found, the current token - - extends to the end of the wide string pointed to by s1, and subsequent searches in the - same wide string for a token return a null pointer. If such a wide character is found, it is - overwritten by a null wide character, which terminates the current token. -

- In all cases, the wcstok function stores sufficient information in the pointer pointed to - by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null wide - character (if any). -

Returns -

- The wcstok function returns a pointer to the first wide character of a token, or a null - pointer if there is no token. -

- EXAMPLE -

-         #include <wchar.h>
-         static wchar_t str1[] = L"?a???b,,,#c";
-         static wchar_t str2[] = L"\t \t";
-         wchar_t *t, *ptr1, *ptr2;
-         t   =   wcstok(str1,   L"?", &ptr1);         //   t   points to the token L"a"
-         t   =   wcstok(NULL,   L",", &ptr1);         //   t   points to the token L"??b"
-         t   =   wcstok(str2,   L" \t", &ptr2);       //   t   is a null pointer
-         t   =   wcstok(NULL,   L"#,", &ptr1);        //   t   points to the token L"c"
-         t   =   wcstok(NULL,   L"?", &ptr1);         //   t   is a null pointer
-
- - -

Contents -

7.28.4.5.8 The wmemchr function
-

Synopsis -

-

-         #include <wchar.h>
-         wchar_t *wmemchr(const wchar_t *s, wchar_t c,
-              size_t n);
-
-

Description -

- The wmemchr function locates the first occurrence of c in the initial n wide characters of - the object pointed to by s. -

Returns -

- The wmemchr function returns a pointer to the located wide character, or a null pointer if - the wide character does not occur in the object. - - -

Contents -

7.28.4.6 Miscellaneous functions
- -

Contents -

7.28.4.6.1 The wcslen function
-

Synopsis -

-

-        #include <wchar.h>
-        size_t wcslen(const wchar_t *s);
-
-

Description -

- The wcslen function computes the length of the wide string pointed to by s. -

Returns -

- The wcslen function returns the number of wide characters that precede the terminating - null wide character. - -

Contents -

7.28.4.6.2 The wmemset function
-

Synopsis -

-

-        #include <wchar.h>
-        wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
-
-

Description -

- The wmemset function copies the value of c into each of the first n wide characters of - the object pointed to by s. -

Returns -

- The wmemset function returns the value of s. - -

Contents -

7.28.5 Wide character time conversion functions

- -

Contents -

7.28.5.1 The wcsftime function
-

Synopsis -

-

-        #include <time.h>
-        #include <wchar.h>
-        size_t wcsftime(wchar_t * restrict s,
-             size_t maxsize,
-             const wchar_t * restrict format,
-             const struct tm * restrict timeptr);
-
-

Description -

- The wcsftime function is equivalent to the strftime function, except that: -

-

Returns -

- If the total number of resulting wide characters including the terminating null wide - character is not more than maxsize, the wcsftime function returns the number of - wide characters placed into the array pointed to by s not including the terminating null - wide character. Otherwise, zero is returned and the contents of the array are - indeterminate. - -

Contents -

7.28.6 Extended multibyte/wide character conversion utilities

-

- The header <wchar.h> declares an extended set of functions useful for conversion - between multibyte characters and wide characters. -

- Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and - 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used - to describe the current conversion state from a particular multibyte character sequence to - a wide character sequence (or the reverse) under the rules of a particular setting for the - LC_CTYPE category of the current locale. -

- The initial conversion state corresponds, for a conversion in either direction, to the - beginning of a new multibyte character in the initial shift state. A zero-valued - mbstate_t object is (at least) one way to describe an initial conversion state. A zero- - valued mbstate_t object can be used to initiate conversion involving any multibyte - character sequence, in any LC_CTYPE category setting. If an mbstate_t object has - been altered by any of the functions described in this subclause, and is then used with a - different multibyte character sequence, or in the other conversion direction, or with a - different LC_CTYPE category setting than on earlier function calls, the behavior is - undefined.335) -

- On entry, each function takes the described conversion state (either internal or pointed to - by an argument) as current. The conversion state described by the referenced object is - altered as needed to track the shift state, and the position within a multibyte character, for - the associated multibyte character sequence. - - - - - - -

Footnotes -

335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and - mbsrtowcs functions as long as they are used to step sequentially through the same multibyte - character string. - - -

Contents -

7.28.6.1 Single-byte/wide character conversion functions
- -

Contents -

7.28.6.1.1 The btowc function
-

Synopsis -

-

-        #include <wchar.h>                                                                        *
-        wint_t btowc(int c);
-
-

Description -

- The btowc function determines whether c constitutes a valid single-byte character in the - initial shift state. -

Returns -

- The btowc function returns WEOF if c has the value EOF or if (unsigned char)c - does not constitute a valid single-byte character in the initial shift state. Otherwise, it - returns the wide character representation of that character. - -

Contents -

7.28.6.1.2 The wctob function
-

Synopsis -

-

-        #include <wchar.h>                                                                        *
-        int wctob(wint_t c);
-
-

Description -

- The wctob function determines whether c corresponds to a member of the extended - character set whose multibyte character representation is a single byte when in the initial - shift state. -

Returns -

- The wctob function returns EOF if c does not correspond to a multibyte character with - length one in the initial shift state. Otherwise, it returns the single-byte representation of - that character as an unsigned char converted to an int. - -

Contents -

7.28.6.2 Conversion state functions
- -

Contents -

7.28.6.2.1 The mbsinit function
-

Synopsis -

-

-        #include <wchar.h>
-        int mbsinit(const mbstate_t *ps);
-
-

Description -

- If ps is not a null pointer, the mbsinit function determines whether the referenced - mbstate_t object describes an initial conversion state. - -

Returns -

- The mbsinit function returns nonzero if ps is a null pointer or if the referenced object - describes an initial conversion state; otherwise, it returns zero. - -

Contents -

7.28.6.3 Restartable multibyte/wide character conversion functions
-

- These functions differ from the corresponding multibyte character functions of 7.22.7 - (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type - pointer to mbstate_t that points to an object that can completely describe the current - conversion state of the associated multibyte character sequence. If ps is a null pointer, - each function uses its own internal mbstate_t object instead, which is initialized at - program startup to the initial conversion state; the functions are not required to avoid data - races in this case. The implementation behaves as if no library function calls these - functions with a null pointer for ps. -

- Also unlike their corresponding functions, the return value does not represent whether the - encoding is state-dependent. - -

Contents -

7.28.6.3.1 The mbrlen function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t mbrlen(const char * restrict s,
-              size_t n,
-              mbstate_t * restrict ps);
-
-

Description -

- The mbrlen function is equivalent to the call: -

-         mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
-
- where internal is the mbstate_t object for the mbrlen function, except that the - expression designated by ps is evaluated only once. -

Returns -

- The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2), - or (size_t)(-1). -

Forward references: the mbrtowc function (7.28.6.3.2). - - -

Contents -

7.28.6.3.2 The mbrtowc function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t mbrtowc(wchar_t * restrict pwc,
-              const char * restrict s,
-              size_t n,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the mbrtowc function is equivalent to the call: -

-                 mbrtowc(NULL, "", 1, ps)
-
- In this case, the values of the parameters pwc and n are ignored. -

- If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the value of the - corresponding wide character and then, if pwc is not a null pointer, stores that value in - the object pointed to by pwc. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. -

Returns -

- The mbrtowc function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that -

-                       corresponds to the null wide character (which is the value stored).
-
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte -
-                    character (which is the value stored); the value returned is the number
-                    of bytes that complete the multibyte character.
-
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) -
-              multibyte character, and all n bytes have been processed (no value is
-              stored).336)
-
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes -
-              do not contribute to a complete and valid multibyte character (no
-              value is stored); the value of the macro EILSEQ is stored in errno,
-              and the conversion state is unspecified.
-
- - - -

Footnotes -

336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - - -

Contents -

7.28.6.3.3 The wcrtomb function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t wcrtomb(char * restrict s,
-              wchar_t wc,
-              mbstate_t * restrict ps);
-
-

Description -

- If s is a null pointer, the wcrtomb function is equivalent to the call -

-                 wcrtomb(buf, L'\0', ps)
-
- where buf is an internal buffer. -

- If s is not a null pointer, the wcrtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by wc - (including any shift sequences), and stores the multibyte character representation in the - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - wc is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. -

Returns -

- The wcrtomb function returns the number of bytes stored in the array object (including - any shift sequences). When wc is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - -

Contents -

7.28.6.4 Restartable multibyte/wide string conversion functions
-

- These functions differ from the corresponding multibyte string functions of 7.22.8 - (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to - mbstate_t that points to an object that can completely describe the current conversion - state of the associated multibyte character sequence. If ps is a null pointer, each function - uses its own internal mbstate_t object instead, which is initialized at program startup - to the initial conversion state; the functions are not required to avoid data races in this - case. The implementation behaves as if no library function calls these functions with a - null pointer for ps. -

- Also unlike their corresponding functions, the conversion source parameter, src, has a - pointer-to-pointer type. When the function is storing the results of conversions (that is, - when dst is not a null pointer), the pointer object pointed to by this parameter is updated - to reflect the amount of the source processed by that invocation. - - -

Contents -

7.28.6.4.1 The mbsrtowcs function
-

Synopsis -

-

-          #include <wchar.h>
-          size_t mbsrtowcs(wchar_t * restrict dst,
-               const char ** restrict src,
-               size_t len,
-               mbstate_t * restrict ps);
-
-

Description -

- The mbsrtowcs function converts a sequence of multibyte characters that begins in the - conversion state described by the object pointed to by ps, from the array indirectly - pointed to by src into a sequence of corresponding wide characters. If dst is not a null - pointer, the converted characters are stored into the array pointed to by dst. Conversion - continues up to and including a terminating null character, which is also stored. - Conversion stops earlier in two cases: when a sequence of bytes is encountered that does - not form a valid multibyte character, or (if dst is not a null pointer) when len wide - characters have been stored into the array pointed to by dst.337) Each conversion takes - place as if by a call to the mbrtowc function. -

- If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null character) or the address - just past the last multibyte character converted (if any). If conversion stopped due to - reaching a terminating null character and if dst is not a null pointer, the resulting state - described is the initial conversion state. -

Returns -

- If the input conversion encounters a sequence of bytes that do not form a valid multibyte - character, an encoding error occurs: the mbsrtowcs function stores the value of the - macro EILSEQ in errno and returns (size_t)(-1); the conversion state is - unspecified. Otherwise, it returns the number of multibyte characters successfully - converted, not including the terminating null character (if any). - - - - - - -

Footnotes -

337) Thus, the value of len is ignored if dst is a null pointer. - - -

Contents -

7.28.6.4.2 The wcsrtombs function
-

Synopsis -

-

-         #include <wchar.h>
-         size_t wcsrtombs(char * restrict dst,
-              const wchar_t ** restrict src,
-              size_t len,
-              mbstate_t * restrict ps);
-
-

Description -

- The wcsrtombs function converts a sequence of wide characters from the array - indirectly pointed to by src into a sequence of corresponding multibyte characters that - begins in the conversion state described by the object pointed to by ps. If dst is not a - null pointer, the converted characters are then stored into the array pointed to by dst. - Conversion continues up to and including a terminating null wide character, which is also - stored. Conversion stops earlier in two cases: when a wide character is reached that does - not correspond to a valid multibyte character, or (if dst is not a null pointer) when the - next multibyte character would exceed the limit of len total bytes to be stored into the - array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb - function.338) -

- If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null wide character) or the - address just past the last wide character converted (if any). If conversion stopped due to - reaching a terminating null wide character, the resulting state described is the initial - conversion state. -

Returns -

- If conversion stops because a wide character is reached that does not correspond to a - valid multibyte character, an encoding error occurs: the wcsrtombs function stores the - value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion - state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte - character sequence, not including the terminating null character (if any). - - - - - - -

Footnotes -

338) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. - - -

Contents -

7.29 Wide character classification and mapping utilities <wctype.h>

- -

Contents -

7.29.1 Introduction

-

- The header <wctype.h> defines one macro, and declares three data types and many - functions.339) -

- The types declared are -

-          wint_t
-
- described in 7.28.1; -
-          wctrans_t
-
- which is a scalar type that can hold values which represent locale-specific character - mappings; and -
-          wctype_t
-
- which is a scalar type that can hold values which represent locale-specific character - classifications. -

- The macro defined is WEOF (described in 7.28.1). -

- The functions declared are grouped as follows: -

-

- For all functions described in this subclause that accept an argument of type wint_t, the - value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If - this argument has any other value, the behavior is undefined. -

- The behavior of these functions is affected by the LC_CTYPE category of the current - locale. - - - - - - -

Footnotes -

339) See ''future library directions'' (7.30.13). - - -

Contents -

7.29.2 Wide character classification utilities

-

- The header <wctype.h> declares several functions useful for classifying wide - characters. -

- The term printing wide character refers to a member of a locale-specific set of wide - characters, each of which occupies at least one printing position on a display device. The - term control wide character refers to a member of a locale-specific set of wide characters - that are not printing wide characters. - -

Contents -

7.29.2.1 Wide character classification functions
-

- The functions in this subclause return nonzero (true) if and only if the value of the - argument wc conforms to that in the description of the function. -

- Each of the following functions returns true for each wide character that corresponds (as - if by a call to the wctob function) to a single-byte character for which the corresponding - character classification function from 7.4.1 returns true, except that the iswgraph and - iswpunct functions may differ with respect to wide characters other than L' ' that are - both printing and white-space wide characters.340) -

Forward references: the wctob function (7.28.6.1.2). - -

Footnotes -

340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call - iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true - (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc) - && iswspace(wc) is true, but not both. - - -

Contents -

7.29.2.1.1 The iswalnum function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswalnum(wint_t wc);
-
-

Description -

- The iswalnum function tests for any wide character for which iswalpha or - iswdigit is true. - -

Contents -

7.29.2.1.2 The iswalpha function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswalpha(wint_t wc);
-
-

Description -

- The iswalpha function tests for any wide character for which iswupper or - iswlower is true, or any wide character that is one of a locale-specific set of alphabetic - - - wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace - is true.341) - -

Footnotes -

341) The functions iswlower and iswupper test true or false separately for each of these additional - wide characters; all four combinations are possible. - - -

Contents -

7.29.2.1.3 The iswblank function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswblank(wint_t wc);
-
-

Description -

- The iswblank function tests for any wide character that is a standard blank wide - character or is one of a locale-specific set of wide characters for which iswspace is true - and that is used to separate words within a line of text. The standard blank wide - characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C" - locale, iswblank returns true only for the standard blank characters. - -

Contents -

7.29.2.1.4 The iswcntrl function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswcntrl(wint_t wc);
-
-

Description -

- The iswcntrl function tests for any control wide character. - -

Contents -

7.29.2.1.5 The iswdigit function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswdigit(wint_t wc);
-
-

Description -

- The iswdigit function tests for any wide character that corresponds to a decimal-digit - character (as defined in 5.2.1). - -

Contents -

7.29.2.1.6 The iswgraph function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswgraph(wint_t wc);
-
- - - - - -

Description -

- The iswgraph function tests for any wide character for which iswprint is true and - iswspace is false.342) - -

Footnotes -

342) Note that the behavior of the iswgraph and iswpunct functions may differ from their - corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution - characters other than ' '. - - -

Contents -

7.29.2.1.7 The iswlower function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswlower(wint_t wc);
-
-

Description -

- The iswlower function tests for any wide character that corresponds to a lowercase - letter or is one of a locale-specific set of wide characters for which none of iswcntrl, - iswdigit, iswpunct, or iswspace is true. - -

Contents -

7.29.2.1.8 The iswprint function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswprint(wint_t wc);
-
-

Description -

- The iswprint function tests for any printing wide character. - -

Contents -

7.29.2.1.9 The iswpunct function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswpunct(wint_t wc);
-
-

Description -

- The iswpunct function tests for any printing wide character that is one of a locale- - specific set of punctuation wide characters for which neither iswspace nor iswalnum - is true.342) - -

Contents -

7.29.2.1.10 The iswspace function
-

Synopsis -

-

-         #include <wctype.h>
-         int iswspace(wint_t wc);
-
- - - - -

Description -

- The iswspace function tests for any wide character that corresponds to a locale-specific - set of white-space wide characters for which none of iswalnum, iswgraph, or - iswpunct is true. - -

Contents -

7.29.2.1.11 The iswupper function
-

Synopsis -

-

-        #include <wctype.h>
-        int iswupper(wint_t wc);
-
-

Description -

- The iswupper function tests for any wide character that corresponds to an uppercase - letter or is one of a locale-specific set of wide characters for which none of iswcntrl, - iswdigit, iswpunct, or iswspace is true. - -

Contents -

7.29.2.1.12 The iswxdigit function
-

Synopsis -

-

-        #include <wctype.h>
-        int iswxdigit(wint_t wc);
-
-

Description -

- The iswxdigit function tests for any wide character that corresponds to a - hexadecimal-digit character (as defined in 6.4.4.1). - -

Contents -

7.29.2.2 Extensible wide character classification functions
-

- The functions wctype and iswctype provide extensible wide character classification - as well as testing equivalent to that performed by the functions described in the previous - subclause (7.29.2.1). - -

Contents -

7.29.2.2.1 The iswctype function
-

Synopsis -

-

-        #include <wctype.h>
-        int iswctype(wint_t wc, wctype_t desc);
-
-

Description -

- The iswctype function determines whether the wide character wc has the property - described by desc. The current setting of the LC_CTYPE category shall be the same as - during the call to wctype that returned the value desc. -

- Each of the following expressions has a truth-value equivalent to the call to the wide - character classification function (7.29.2.1) in the comment that follows the expression: - -

-         iswctype(wc,      wctype("alnum"))              //   iswalnum(wc)
-         iswctype(wc,      wctype("alpha"))              //   iswalpha(wc)
-         iswctype(wc,      wctype("blank"))              //   iswblank(wc)
-         iswctype(wc,      wctype("cntrl"))              //   iswcntrl(wc)
-         iswctype(wc,      wctype("digit"))              //   iswdigit(wc)
-         iswctype(wc,      wctype("graph"))              //   iswgraph(wc)
-         iswctype(wc,      wctype("lower"))              //   iswlower(wc)
-         iswctype(wc,      wctype("print"))              //   iswprint(wc)
-         iswctype(wc,      wctype("punct"))              //   iswpunct(wc)
-         iswctype(wc,      wctype("space"))              //   iswspace(wc)
-         iswctype(wc,      wctype("upper"))              //   iswupper(wc)
-         iswctype(wc,      wctype("xdigit"))             //   iswxdigit(wc)
-
-

Returns -

- The iswctype function returns nonzero (true) if and only if the value of the wide - character wc has the property described by desc. If desc is zero, the iswctype - function returns zero (false). -

Forward references: the wctype function (7.29.2.2.2). - -

Contents -

7.29.2.2.2 The wctype function
-

Synopsis -

-

-         #include <wctype.h>
-         wctype_t wctype(const char *property);
-
-

Description -

- The wctype function constructs a value with type wctype_t that describes a class of - wide characters identified by the string argument property. -

- The strings listed in the description of the iswctype function shall be valid in all - locales as property arguments to the wctype function. -

Returns -

- If property identifies a valid class of wide characters according to the LC_CTYPE - category of the current locale, the wctype function returns a nonzero value that is valid - as the second argument to the iswctype function; otherwise, it returns zero. - - -

Contents -

7.29.3 Wide character case mapping utilities

-

- The header <wctype.h> declares several functions useful for mapping wide characters. - -

Contents -

7.29.3.1 Wide character case mapping functions
- -

Contents -

7.29.3.1.1 The towlower function
-

Synopsis -

-

-        #include <wctype.h>
-        wint_t towlower(wint_t wc);
-
-

Description -

- The towlower function converts an uppercase letter to a corresponding lowercase letter. -

Returns -

- If the argument is a wide character for which iswupper is true and there are one or - more corresponding wide characters, as specified by the current locale, for which - iswlower is true, the towlower function returns one of the corresponding wide - characters (always the same one for any given locale); otherwise, the argument is - returned unchanged. - -

Contents -

7.29.3.1.2 The towupper function
-

Synopsis -

-

-        #include <wctype.h>
-        wint_t towupper(wint_t wc);
-
-

Description -

- The towupper function converts a lowercase letter to a corresponding uppercase letter. -

Returns -

- If the argument is a wide character for which iswlower is true and there are one or - more corresponding wide characters, as specified by the current locale, for which - iswupper is true, the towupper function returns one of the corresponding wide - characters (always the same one for any given locale); otherwise, the argument is - returned unchanged. - -

Contents -

7.29.3.2 Extensible wide character case mapping functions
-

- The functions wctrans and towctrans provide extensible wide character mapping as - well as case mapping equivalent to that performed by the functions described in the - previous subclause (7.29.3.1). - - -

Contents -

7.29.3.2.1 The towctrans function
-

Synopsis -

-

-         #include <wctype.h>
-         wint_t towctrans(wint_t wc, wctrans_t desc);
-
-

Description -

- The towctrans function maps the wide character wc using the mapping described by - desc. The current setting of the LC_CTYPE category shall be the same as during the call - to wctrans that returned the value desc. -

- Each of the following expressions behaves the same as the call to the wide character case - mapping function (7.29.3.1) in the comment that follows the expression: -

-         towctrans(wc, wctrans("tolower"))                     // towlower(wc)
-         towctrans(wc, wctrans("toupper"))                     // towupper(wc)
-
-

Returns -

- The towctrans function returns the mapped value of wc using the mapping described - by desc. If desc is zero, the towctrans function returns the value of wc. - -

Contents -

7.29.3.2.2 The wctrans function
-

Synopsis -

-

-         #include <wctype.h>
-         wctrans_t wctrans(const char *property);
-
-

Description -

- The wctrans function constructs a value with type wctrans_t that describes a - mapping between wide characters identified by the string argument property. -

- The strings listed in the description of the towctrans function shall be valid in all - locales as property arguments to the wctrans function. -

Returns -

- If property identifies a valid mapping of wide characters according to the LC_CTYPE - category of the current locale, the wctrans function returns a nonzero value that is valid - as the second argument to the towctrans function; otherwise, it returns zero. - - -

Contents -

7.30 Future library directions

-

- The following names are grouped under individual headers for convenience. All external - names described below are reserved no matter what headers are included by the program. - -

Contents -

7.30.1 Complex arithmetic <complex.h>

-

- The function names -

-       cerf               cexpm1              clog2
-       cerfc              clog10              clgamma
-       cexp2              clog1p              ctgamma
-
- and the same names suffixed with f or l may be added to the declarations in the - <complex.h> header. - -

Contents -

7.30.2 Character handling <ctype.h>

-

- Function names that begin with either is or to, and a lowercase letter may be added to - the declarations in the <ctype.h> header. - -

Contents -

7.30.3 Errors <errno.h>

-

- Macros that begin with E and a digit or E and an uppercase letter may be added to the - declarations in the <errno.h> header. - -

Contents -

7.30.4 Format conversion of integer types <inttypes.h>

-

- Macro names beginning with PRI or SCN followed by any lowercase letter or X may be - added to the macros defined in the <inttypes.h> header. - -

Contents -

7.30.5 Localization <locale.h>

-

- Macros that begin with LC_ and an uppercase letter may be added to the definitions in - the <locale.h> header. - -

Contents -

7.30.6 Signal handling <signal.h>

-

- Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase - letter may be added to the definitions in the <signal.h> header. - -

Contents -

7.30.7 Boolean type and values <stdbool.h>

-

- The ability to undefine and perhaps then redefine the macros bool, true, and false is - an obsolescent feature. - -

Contents -

7.30.8 Integer types <stdint.h>

-

- Typedef names beginning with int or uint and ending with _t may be added to the - types defined in the <stdint.h> header. Macro names beginning with INT or UINT - and ending with _MAX, _MIN, or _C may be added to the macros defined in the - <stdint.h> header. - - -

Contents -

7.30.9 Input/output <stdio.h>

-

- Lowercase letters may be added to the conversion specifiers and length modifiers in - fprintf and fscanf. Other characters may be used in extensions. -

- The use of ungetc on a binary stream where the file position indicator is zero prior to * - the call is an obsolescent feature. - -

Contents -

7.30.10 General utilities <stdlib.h>

-

- Function names that begin with str and a lowercase letter may be added to the - declarations in the <stdlib.h> header. - -

Contents -

7.30.11 String handling <string.h>

-

- Function names that begin with str, mem, or wcs and a lowercase letter may be added - to the declarations in the <string.h> header. - -

Contents -

7.30.12 Extended multibyte and wide character utilities <wchar.h>

-

- Function names that begin with wcs and a lowercase letter may be added to the - declarations in the <wchar.h> header. -

- Lowercase letters may be added to the conversion specifiers and length modifiers in - fwprintf and fwscanf. Other characters may be used in extensions. - -

Contents -

7.30.13 Wide character classification and mapping utilities

- <wctype.h> -

- Function names that begin with is or to and a lowercase letter may be added to the - declarations in the <wctype.h> header. - - -

Contents -

Annex A

-
-                                            (informative)
-                             Language syntax summary
-
-

- NOTE The notation is described in 6.1. - - -

Contents -

A.1 Lexical grammar

- -

Contents -

A.1.1 Lexical elements

- (6.4) token: -
-                keyword
-                identifier
-                constant
-                string-literal
-                punctuator
-
- (6.4) preprocessing-token: - -
-               header-name
-               identifier
-               pp-number
-               character-constant
-               string-literal
-               punctuator
-               each non-white-space character that cannot be one of the above
-
- -

Contents -

A.1.2 Keywords

- (6.4.1) keyword: one of -
-               alignof                     goto                  union
-               auto                        if                    unsigned
-               break                       inline                void
-               case                        int                   volatile
-               char                        long                  while
-               const                       register              _Alignas
-               continue                    restrict              _Atomic
-               default                     return                _Bool
-               do                          short                 _Complex
-               double                      signed                _Generic
-               else                        sizeof                _Imaginary
-               enum                        static                _Noreturn
-               extern                      struct                _Static_assert
-               float                       switch                _Thread_local
-               for                         typedef
-
- -

Contents -

A.1.3 Identifiers

- (6.4.2.1) identifier: -
-                identifier-nondigit
-                identifier identifier-nondigit
-                identifier digit
-
- (6.4.2.1) identifier-nondigit: -
-                nondigit
-                universal-character-name
-                other implementation-defined characters
-
- (6.4.2.1) nondigit: one of -
-               _ a b          c    d   e    f   g   h    i   j   k   l   m
-                    n o       p    q   r    s   t   u    v   w   x   y   z
-                    A B       C    D   E    F   G   H    I   J   K   L   M
-                    N O       P    Q   R    S   T   U    V   W   X   Y   Z
-
- (6.4.2.1) digit: one of - -
-                0 1 2         3    4   5    6   7   8    9
-
- -

Contents -

A.1.4 Universal character names

- (6.4.3) universal-character-name: -
-               \u hex-quad
-               \U hex-quad hex-quad
-
- (6.4.3) hex-quad: -
-               hexadecimal-digit hexadecimal-digit
-                            hexadecimal-digit hexadecimal-digit
-
- -

Contents -

A.1.5 Constants

- (6.4.4) constant: -
-               integer-constant
-               floating-constant
-               enumeration-constant
-               character-constant
-
- (6.4.4.1) integer-constant: -
-                decimal-constant integer-suffixopt
-                octal-constant integer-suffixopt
-                hexadecimal-constant integer-suffixopt
-
- (6.4.4.1) decimal-constant: -
-               nonzero-digit
-               decimal-constant digit
-
- (6.4.4.1) octal-constant: -
-                0
-                octal-constant octal-digit
-
- (6.4.4.1) hexadecimal-constant: -
-               hexadecimal-prefix hexadecimal-digit
-               hexadecimal-constant hexadecimal-digit
-
- (6.4.4.1) hexadecimal-prefix: one of -
-               0x 0X
-
- (6.4.4.1) nonzero-digit: one of -
-               1 2 3 4 5              6      7   8   9
-
- (6.4.4.1) octal-digit: one of - -
-                0 1 2 3           4   5      6   7
-
- (6.4.4.1) hexadecimal-digit: one of -
-               0 1 2 3 4 5                6    7    8   9
-               a b c d e f
-               A B C D E F
-
- (6.4.4.1) integer-suffix: -
-                unsigned-suffix long-suffixopt
-                unsigned-suffix long-long-suffix
-                long-suffix unsigned-suffixopt
-                long-long-suffix unsigned-suffixopt
-
- (6.4.4.1) unsigned-suffix: one of -
-                u U
-
- (6.4.4.1) long-suffix: one of -
-                l L
-
- (6.4.4.1) long-long-suffix: one of -
-                ll LL
-
- (6.4.4.2) floating-constant: -
-                decimal-floating-constant
-                hexadecimal-floating-constant
-
- (6.4.4.2) decimal-floating-constant: -
-               fractional-constant exponent-partopt floating-suffixopt
-               digit-sequence exponent-part floating-suffixopt
-
- (6.4.4.2) hexadecimal-floating-constant: -
-               hexadecimal-prefix hexadecimal-fractional-constant
-                             binary-exponent-part floating-suffixopt
-               hexadecimal-prefix hexadecimal-digit-sequence
-                             binary-exponent-part floating-suffixopt
-
- (6.4.4.2) fractional-constant: -
-                digit-sequenceopt . digit-sequence
-                digit-sequence .
-
- (6.4.4.2) exponent-part: -
-               e signopt digit-sequence
-               E signopt digit-sequence
-
- (6.4.4.2) sign: one of - -
-                + -
-
- (6.4.4.2) digit-sequence: -
-                digit
-                digit-sequence digit
-
- (6.4.4.2) hexadecimal-fractional-constant: -
-               hexadecimal-digit-sequenceopt .
-                              hexadecimal-digit-sequence
-               hexadecimal-digit-sequence .
-
- (6.4.4.2) binary-exponent-part: -
-                p signopt digit-sequence
-                P signopt digit-sequence
-
- (6.4.4.2) hexadecimal-digit-sequence: -
-               hexadecimal-digit
-               hexadecimal-digit-sequence hexadecimal-digit
-
- (6.4.4.2) floating-suffix: one of -
-                f l F L
-
- (6.4.4.3) enumeration-constant: -
-               identifier
-
- (6.4.4.4) character-constant: -
-               ' c-char-sequence '
-               L' c-char-sequence '
-               u' c-char-sequence '
-               U' c-char-sequence '
-
- (6.4.4.4) c-char-sequence: -
-                c-char
-                c-char-sequence c-char
-
- (6.4.4.4) c-char: -
-                any member of the source character set except
-                             the single-quote ', backslash \, or new-line character
-                escape-sequence
-
- (6.4.4.4) escape-sequence: - -
-               simple-escape-sequence
-               octal-escape-sequence
-               hexadecimal-escape-sequence
-               universal-character-name
-
- (6.4.4.4) simple-escape-sequence: one of -
-               \' \" \? \\
-               \a \b \f \n \r \t                   \v
-
- (6.4.4.4) octal-escape-sequence: -
-                \ octal-digit
-                \ octal-digit octal-digit
-                \ octal-digit octal-digit octal-digit
-
- (6.4.4.4) hexadecimal-escape-sequence: -
-               \x hexadecimal-digit
-               hexadecimal-escape-sequence hexadecimal-digit
-
- -

Contents -

A.1.6 String literals

- (6.4.5) string-literal: -
-                encoding-prefixopt " s-char-sequenceopt "
-
- (6.4.5) encoding-prefix: -
-               u8
-               u
-               U
-               L
-
- (6.4.5) s-char-sequence: -
-                s-char
-                s-char-sequence s-char
-
- (6.4.5) s-char: -
-                any member of the source character set except
-                             the double-quote ", backslash \, or new-line character
-                escape-sequence
-
- -

Contents -

A.1.7 Punctuators

- (6.4.6) punctuator: one of - -
-               [ ] ( ) { } . ->
-               ++ -- & * + - ~ !
-               / % << >> < > <= >=                      ==    !=    ^    |   &&   ||
-               ? : ; ...
-               = *= /= %= += -= <<=                     >>=    &=       ^=   |=
-               , # ##
-               <: :> <% %> %: %:%:
-
- -

Contents -

A.1.8 Header names

- (6.4.7) header-name: -
-               < h-char-sequence >
-               " q-char-sequence "
-
- (6.4.7) h-char-sequence: -
-               h-char
-               h-char-sequence h-char
-
- (6.4.7) h-char: -
-               any member of the source character set except
-                            the new-line character and >
-
- (6.4.7) q-char-sequence: -
-               q-char
-               q-char-sequence q-char
-
- (6.4.7) q-char: -
-               any member of the source character set except
-                            the new-line character and "
-
- -

Contents -

A.1.9 Preprocessing numbers

- (6.4.8) pp-number: - -
-               digit
-               . digit
-               pp-number   digit
-               pp-number   identifier-nondigit
-               pp-number   e sign
-               pp-number   E sign
-               pp-number   p sign
-               pp-number   P sign
-               pp-number   .
-
- -

Contents -

A.2 Phrase structure grammar

- -

Contents -

A.2.1 Expressions

- (6.5.1) primary-expression: -
-               identifier
-               constant
-               string-literal
-               ( expression )
-               generic-selection
-
- (6.5.1.1) generic-selection: -
-               _Generic ( assignment-expression , generic-assoc-list )
-
- (6.5.1.1) generic-assoc-list: -
-               generic-association
-               generic-assoc-list , generic-association
-
- (6.5.1.1) generic-association: -
-               type-name : assignment-expression
-               default : assignment-expression
-
- (6.5.2) postfix-expression: -
-               primary-expression
-               postfix-expression [ expression ]
-               postfix-expression ( argument-expression-listopt )
-               postfix-expression . identifier
-               postfix-expression -> identifier
-               postfix-expression ++
-               postfix-expression --
-               ( type-name ) { initializer-list }
-               ( type-name ) { initializer-list , }
-
- (6.5.2) argument-expression-list: -
-              assignment-expression
-              argument-expression-list , assignment-expression
-
- (6.5.3) unary-expression: - -
-               postfix-expression
-               ++ unary-expression
-               -- unary-expression
-               unary-operator cast-expression
-               sizeof unary-expression
-               sizeof ( type-name )
-               alignof ( type-name )
-
- (6.5.3) unary-operator: one of -
-               & * + - ~                !
-
- (6.5.4) cast-expression: -
-                unary-expression
-                ( type-name ) cast-expression
-
- (6.5.5) multiplicative-expression: -
-                cast-expression
-                multiplicative-expression * cast-expression
-                multiplicative-expression / cast-expression
-                multiplicative-expression % cast-expression
-
- (6.5.6) additive-expression: -
-                multiplicative-expression
-                additive-expression + multiplicative-expression
-                additive-expression - multiplicative-expression
-
- (6.5.7) shift-expression: -
-                 additive-expression
-                 shift-expression << additive-expression
-                 shift-expression >> additive-expression
-
- (6.5.8) relational-expression: -
-                shift-expression
-                relational-expression   <    shift-expression
-                relational-expression   >    shift-expression
-                relational-expression   <=   shift-expression
-                relational-expression   >=   shift-expression
-
- (6.5.9) equality-expression: -
-                relational-expression
-                equality-expression == relational-expression
-                equality-expression != relational-expression
-
- (6.5.10) AND-expression: -
-              equality-expression
-              AND-expression & equality-expression
-
- (6.5.11) exclusive-OR-expression: - -
-               AND-expression
-               exclusive-OR-expression ^ AND-expression
-
- (6.5.12) inclusive-OR-expression: -
-                exclusive-OR-expression
-                inclusive-OR-expression | exclusive-OR-expression
-
- (6.5.13) logical-AND-expression: -
-               inclusive-OR-expression
-               logical-AND-expression && inclusive-OR-expression
-
- (6.5.14) logical-OR-expression: -
-               logical-AND-expression
-               logical-OR-expression || logical-AND-expression
-
- (6.5.15) conditional-expression: -
-               logical-OR-expression
-               logical-OR-expression ? expression : conditional-expression
-
- (6.5.16) assignment-expression: -
-               conditional-expression
-               unary-expression assignment-operator assignment-expression
-
- (6.5.16) assignment-operator: one of -
-               = *= /= %= +=                -=    <<=    >>=      &=    ^=   |=
-
- (6.5.17) expression: -
-               assignment-expression
-               expression , assignment-expression
-
- (6.6) constant-expression: -
-               conditional-expression
-
- -

Contents -

A.2.2 Declarations

- (6.7) declaration: -
-                declaration-specifiers init-declarator-listopt ;
-                static_assert-declaration
-
- (6.7) declaration-specifiers: -
-                storage-class-specifier declaration-specifiersopt
-                type-specifier declaration-specifiersopt
-                type-qualifier declaration-specifiersopt
-                function-specifier declaration-specifiersopt
-                alignment-specifier declaration-specifiersopt
-
- (6.7) init-declarator-list: - -
-                init-declarator
-                init-declarator-list , init-declarator
-
- (6.7) init-declarator: -
-                declarator
-                declarator = initializer
-
- (6.7.1) storage-class-specifier: -
-               typedef
-               extern
-               static
-               _Thread_local
-               auto
-               register
-
- (6.7.2) type-specifier: -
-                void
-                char
-                short
-                int
-                long
-                float
-                double
-                signed
-                unsigned
-                _Bool
-                _Complex
-                atomic-type-specifier
-                struct-or-union-specifier
-                enum-specifier
-                typedef-name
-
- (6.7.2.1) struct-or-union-specifier: -
-                struct-or-union identifieropt { struct-declaration-list }
-                struct-or-union identifier
-
- (6.7.2.1) struct-or-union: -
-                struct
-                union
-
- (6.7.2.1) struct-declaration-list: -
-                struct-declaration
-                struct-declaration-list struct-declaration
-
- (6.7.2.1) struct-declaration: - -
-                specifier-qualifier-list struct-declarator-listopt ;
-                static_assert-declaration
-
- (6.7.2.1) specifier-qualifier-list: -
-                type-specifier specifier-qualifier-listopt
-                type-qualifier specifier-qualifier-listopt
-
- (6.7.2.1) struct-declarator-list: -
-                struct-declarator
-                struct-declarator-list , struct-declarator
-
- (6.7.2.1) struct-declarator: -
-                declarator
-                declaratoropt : constant-expression
-
- (6.7.2.2) enum-specifier: -
-               enum identifieropt { enumerator-list }
-               enum identifieropt { enumerator-list , }
-               enum identifier
-
- (6.7.2.2) enumerator-list: -
-               enumerator
-               enumerator-list , enumerator
-
- (6.7.2.2) enumerator: -
-               enumeration-constant
-               enumeration-constant = constant-expression
-
- (6.7.2.4) atomic-type-specifier: -
-               _Atomic ( type-name )
-
- (6.7.3) type-qualifier: -
-               const
-               restrict
-               volatile
-               _Atomic
-
- (6.7.4) function-specifier: -
-                inline
-                _Noreturn
-
- (6.7.5) alignment-specifier: -
-               _Alignas ( type-name )
-               _Alignas ( constant-expression )
-
- (6.7.6) declarator: - -
-               pointeropt direct-declarator
-
- (6.7.6) direct-declarator: -
-                identifier
-                ( declarator )
-                direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
-                direct-declarator [ static type-qualifier-listopt assignment-expression ]
-                direct-declarator [ type-qualifier-list static assignment-expression ]
-                direct-declarator [ type-qualifier-listopt * ]
-                direct-declarator ( parameter-type-list )
-                direct-declarator ( identifier-listopt )
-
- (6.7.6) pointer: -
-                * type-qualifier-listopt
-                * type-qualifier-listopt pointer
-
- (6.7.6) type-qualifier-list: -
-               type-qualifier
-               type-qualifier-list type-qualifier
-
- (6.7.6) parameter-type-list: -
-              parameter-list
-              parameter-list , ...
-
- (6.7.6) parameter-list: -
-              parameter-declaration
-              parameter-list , parameter-declaration
-
- (6.7.6) parameter-declaration: -
-              declaration-specifiers declarator
-              declaration-specifiers abstract-declaratoropt
-
- (6.7.6) identifier-list: -
-                identifier
-                identifier-list , identifier
-
- (6.7.7) type-name: -
-               specifier-qualifier-list abstract-declaratoropt
-
- (6.7.7) abstract-declarator: - -
-               pointer
-               pointeropt direct-abstract-declarator
-
- (6.7.7) direct-abstract-declarator: -
-                ( abstract-declarator )
-                direct-abstract-declaratoropt [ type-qualifier-listopt
-                               assignment-expressionopt ]
-                direct-abstract-declaratoropt [ static type-qualifier-listopt
-                               assignment-expression ]
-                direct-abstract-declaratoropt [ type-qualifier-list static
-                               assignment-expression ]
-                direct-abstract-declaratoropt [ * ]
-                direct-abstract-declaratoropt ( parameter-type-listopt )
-
- (6.7.8) typedef-name: -
-               identifier
-
- (6.7.9) initializer: -
-                 assignment-expression
-                 { initializer-list }
-                 { initializer-list , }
-
- (6.7.9) initializer-list: -
-                 designationopt initializer
-                 initializer-list , designationopt initializer
-
- (6.7.9) designation: -
-               designator-list =
-
- (6.7.9) designator-list: -
-               designator
-               designator-list designator
-
- (6.7.9) designator: -
-               [ constant-expression ]
-               . identifier
-
- (6.7.10) static_assert-declaration: - -
-                _Static_assert ( constant-expression , string-literal ) ;
-
- -

Contents -

A.2.3 Statements

- (6.8) statement: -
-               labeled-statement
-               compound-statement
-               expression-statement
-               selection-statement
-               iteration-statement
-               jump-statement
-
- (6.8.1) labeled-statement: -
-                identifier : statement
-                case constant-expression : statement
-                default : statement
-
- (6.8.2) compound-statement: -
-              { block-item-listopt }
-
- (6.8.2) block-item-list: -
-                block-item
-                block-item-list block-item
-
- (6.8.2) block-item: -
-                declaration
-                statement
-
- (6.8.3) expression-statement: -
-               expressionopt ;
-
- (6.8.4) selection-statement: -
-                if ( expression ) statement
-                if ( expression ) statement else statement
-                switch ( expression ) statement
-
- (6.8.5) iteration-statement: -
-                 while ( expression ) statement
-                 do statement while ( expression ) ;
-                 for ( expressionopt ; expressionopt ; expressionopt ) statement
-                 for ( declaration expressionopt ; expressionopt ) statement
-
- (6.8.6) jump-statement: - -
-               goto identifier ;
-               continue ;
-               break ;
-               return expressionopt ;
-
- -

Contents -

A.2.4 External definitions

- (6.9) translation-unit: -
-                external-declaration
-                translation-unit external-declaration
-
- (6.9) external-declaration: -
-                function-definition
-                declaration
-
- (6.9.1) function-definition: -
-                declaration-specifiers declarator declaration-listopt compound-statement
-
- (6.9.1) declaration-list: -
-               declaration
-               declaration-list declaration
-
- -

Contents -

A.3 Preprocessing directives

- (6.10) preprocessing-file: -
-               groupopt
-
- (6.10) group: -
-                 group-part
-                 group group-part
-
- (6.10) group-part: -
-               if-section
-               control-line
-               text-line
-               # non-directive
-
- (6.10) if-section: -
-                 if-group elif-groupsopt else-groupopt endif-line
-
- (6.10) if-group: -
-                # if     constant-expression new-line groupopt
-                # ifdef identifier new-line groupopt
-                # ifndef identifier new-line groupopt
-
- (6.10) elif-groups: -
-                elif-group
-                elif-groups elif-group
-
- (6.10) elif-group: - -
-                # elif       constant-expression new-line groupopt
-
- (6.10) else-group: -
-                # else        new-line groupopt
-
- (6.10) endif-line: -
-                # endif       new-line
-
- (6.10) control-line: -
-               # include pp-tokens new-line
-               # define identifier replacement-list new-line
-               # define identifier lparen identifier-listopt )
-                                               replacement-list new-line
-               # define identifier lparen ... ) replacement-list new-line
-               # define identifier lparen identifier-list , ... )
-                                               replacement-list new-line
-               # undef   identifier new-line
-               # line    pp-tokens new-line
-               # error   pp-tokensopt new-line
-               # pragma pp-tokensopt new-line
-               #         new-line
-
- (6.10) text-line: -
-                pp-tokensopt new-line
-
- (6.10) non-directive: -
-               pp-tokens new-line
-
- (6.10) lparen: -
-                  a ( character not immediately preceded by white-space
-
- (6.10) replacement-list: -
-               pp-tokensopt
-
- (6.10) pp-tokens: -
-               preprocessing-token
-               pp-tokens preprocessing-token
-
- (6.10) new-line: - -
-               the new-line character
-
- -

Contents -

Annex B

-
-                              (informative)
-                          Library summary
-
- -

Contents -

B.1 Diagnostics <assert.h>

-
-         NDEBUG
-         static_assert
-         void assert(scalar expression);
-
- -

Contents -

B.2 Complex <complex.h>

- - -
-         __STDC_NO_COMPLEX__           imaginary
-         complex                         _Imaginary_I
-         _Complex_I                      I
-         #pragma STDC CX_LIMITED_RANGE on-off-switch
-         double complex cacos(double complex z);
-         float complex cacosf(float complex z);
-         long double complex cacosl(long double complex z);
-         double complex casin(double complex z);
-         float complex casinf(float complex z);
-         long double complex casinl(long double complex z);
-         double complex catan(double complex z);
-         float complex catanf(float complex z);
-         long double complex catanl(long double complex z);
-         double complex ccos(double complex z);
-         float complex ccosf(float complex z);
-         long double complex ccosl(long double complex z);
-         double complex csin(double complex z);
-         float complex csinf(float complex z);
-         long double complex csinl(long double complex z);
-         double complex ctan(double complex z);
-         float complex ctanf(float complex z);
-         long double complex ctanl(long double complex z);
-         double complex cacosh(double complex z);
-         float complex cacoshf(float complex z);
-         long double complex cacoshl(long double complex z);
-         double complex casinh(double complex z);
-         float complex casinhf(float complex z);
-         long double complex casinhl(long double complex z);
-       double complex catanh(double complex z);
-       float complex catanhf(float complex z);
-       long double complex catanhl(long double complex z);
-       double complex ccosh(double complex z);
-       float complex ccoshf(float complex z);
-       long double complex ccoshl(long double complex z);
-       double complex csinh(double complex z);
-       float complex csinhf(float complex z);
-       long double complex csinhl(long double complex z);
-       double complex ctanh(double complex z);
-       float complex ctanhf(float complex z);
-       long double complex ctanhl(long double complex z);
-       double complex cexp(double complex z);
-       float complex cexpf(float complex z);
-       long double complex cexpl(long double complex z);
-       double complex clog(double complex z);
-       float complex clogf(float complex z);
-       long double complex clogl(long double complex z);
-       double cabs(double complex z);
-       float cabsf(float complex z);
-       long double cabsl(long double complex z);
-       double complex cpow(double complex x, double complex y);
-       float complex cpowf(float complex x, float complex y);
-       long double complex cpowl(long double complex x,
-            long double complex y);
-       double complex csqrt(double complex z);
-       float complex csqrtf(float complex z);
-       long double complex csqrtl(long double complex z);
-       double carg(double complex z);
-       float cargf(float complex z);
-       long double cargl(long double complex z);
-       double cimag(double complex z);
-       float cimagf(float complex z);
-       long double cimagl(long double complex z);
-       double complex CMPLX(double x, double y);
-       float complex CMPLXF(float x, float y);
-       long double complex CMPLXL(long double x, long double y);
-       double complex conj(double complex z);
-       float complex conjf(float complex z);
-       long double complex conjl(long double complex z);
-       double complex cproj(double complex z);
-         float complex cprojf(float complex z);
-         long double complex cprojl(long double complex z);
-         double creal(double complex z);
-         float crealf(float complex z);
-         long double creall(long double complex z);
-
- -

Contents -

B.3 Character handling <ctype.h>

-
-         int   isalnum(int c);
-         int   isalpha(int c);
-         int   isblank(int c);
-         int   iscntrl(int c);
-         int   isdigit(int c);
-         int   isgraph(int c);
-         int   islower(int c);
-         int   isprint(int c);
-         int   ispunct(int c);
-         int   isspace(int c);
-         int   isupper(int c);
-         int   isxdigit(int c);
-         int   tolower(int c);
-         int   toupper(int c);
-
- -

Contents -

B.4 Errors <errno.h>

-
-         EDOM           EILSEQ            ERANGE           errno
-         __STDC_WANT_LIB_EXT1__
-         errno_t
-
- -

Contents -

B.5 Floating-point environment <fenv.h>

- -
-         fenv_t               FE_OVERFLOW             FE_TOWARDZERO
-         fexcept_t            FE_UNDERFLOW            FE_UPWARD
-         FE_DIVBYZERO         FE_ALL_EXCEPT           FE_DFL_ENV
-         FE_INEXACT           FE_DOWNWARD
-         FE_INVALID           FE_TONEAREST
-         #pragma STDC FENV_ACCESS on-off-switch
-         int feclearexcept(int excepts);
-         int fegetexceptflag(fexcept_t *flagp, int excepts);
-         int feraiseexcept(int excepts);
-         int fesetexceptflag(const fexcept_t *flagp,
-              int excepts);
-         int fetestexcept(int excepts);
-       int   fegetround(void);
-       int   fesetround(int round);
-       int   fegetenv(fenv_t *envp);
-       int   feholdexcept(fenv_t *envp);
-       int   fesetenv(const fenv_t *envp);
-       int   feupdateenv(const fenv_t *envp);
-
- -

Contents -

B.6 Characteristics of floating types <float.h>

-
-       FLT_ROUNDS              DBL_DIG                 FLT_MAX
-       FLT_EVAL_METHOD         LDBL_DIG                DBL_MAX
-       FLT_HAS_SUBNORM         FLT_MIN_EXP             LDBL_MAX
-       DBL_HAS_SUBNORM         DBL_MIN_EXP             FLT_EPSILON
-       LDBL_HAS_SUBNORM        LDBL_MIN_EXP            DBL_EPSILON
-       FLT_RADIX               FLT_MIN_10_EXP          LDBL_EPSILON
-       FLT_MANT_DIG            DBL_MIN_10_EXP          FLT_MIN
-       DBL_MANT_DIG            LDBL_MIN_10_EXP         DBL_MIN
-       LDBL_MANT_DIG           FLT_MAX_EXP             LDBL_MIN
-       FLT_DECIMAL_DIG         DBL_MAX_EXP             FLT_TRUE_MIN
-       DBL_DECIMAL_DIG         LDBL_MAX_EXP            DBL_TRUE_MIN
-       LDBL_DECIMAL_DIG        FLT_MAX_10_EXP          LDBL_TRUE_MIN
-       DECIMAL_DIG             DBL_MAX_10_EXP
-       FLT_DIG                 LDBL_MAX_10_EXP
-
- -

Contents -

B.7 Format conversion of integer types <inttypes.h>

- -
-       imaxdiv_t
-       PRIdN         PRIdLEASTN       PRIdFASTN        PRIdMAX    PRIdPTR
-       PRIiN         PRIiLEASTN       PRIiFASTN        PRIiMAX    PRIiPTR
-       PRIoN         PRIoLEASTN       PRIoFASTN        PRIoMAX    PRIoPTR
-       PRIuN         PRIuLEASTN       PRIuFASTN        PRIuMAX    PRIuPTR
-       PRIxN         PRIxLEASTN       PRIxFASTN        PRIxMAX    PRIxPTR
-       PRIXN         PRIXLEASTN       PRIXFASTN        PRIXMAX    PRIXPTR
-       SCNdN         SCNdLEASTN       SCNdFASTN        SCNdMAX    SCNdPTR
-       SCNiN         SCNiLEASTN       SCNiFASTN        SCNiMAX    SCNiPTR
-       SCNoN         SCNoLEASTN       SCNoFASTN        SCNoMAX    SCNoPTR
-       SCNuN         SCNuLEASTN       SCNuFASTN        SCNuMAX    SCNuPTR
-       SCNxN         SCNxLEASTN       SCNxFASTN        SCNxMAX    SCNxPTR
-       intmax_t imaxabs(intmax_t j);
-       imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
-       intmax_t strtoimax(const char * restrict nptr,
-               char ** restrict endptr, int base);
-         uintmax_t strtoumax(const char * restrict nptr,
-                 char ** restrict endptr, int base);
-         intmax_t wcstoimax(const wchar_t * restrict nptr,
-                 wchar_t ** restrict endptr, int base);
-         uintmax_t wcstoumax(const wchar_t * restrict nptr,
-                 wchar_t ** restrict endptr, int base);
-
- -

Contents -

B.8 Alternative spellings <iso646.h>

-
-         and            bitor             not_eq           xor
-         and_eq         compl             or               xor_eq
-         bitand         not               or_eq
-
- -

Contents -

B.9 Sizes of integer types <limits.h>

-
-         CHAR_BIT       CHAR_MAX          INT_MIN          ULONG_MAX
-         SCHAR_MIN      MB_LEN_MAX        INT_MAX          LLONG_MIN
-         SCHAR_MAX      SHRT_MIN          UINT_MAX         LLONG_MAX
-         UCHAR_MAX      SHRT_MAX          LONG_MIN         ULLONG_MAX
-         CHAR_MIN       USHRT_MAX         LONG_MAX
-
- -

Contents -

B.10 Localization <locale.h>

-
-         struct lconv   LC_ALL            LC_CTYPE         LC_NUMERIC
-         NULL           LC_COLLATE        LC_MONETARY      LC_TIME
-         char *setlocale(int category, const char *locale);
-         struct lconv *localeconv(void);
-
- -

Contents -

B.11 Mathematics <math.h>

- - - - - -
-         float_t              FP_INFINITE             FP_FAST_FMAL
-         double_t             FP_NAN                  FP_ILOGB0
-         HUGE_VAL             FP_NORMAL               FP_ILOGBNAN
-         HUGE_VALF            FP_SUBNORMAL            MATH_ERRNO
-         HUGE_VALL            FP_ZERO                 MATH_ERREXCEPT
-         INFINITY             FP_FAST_FMA             math_errhandling
-         NAN                  FP_FAST_FMAF
-         #pragma STDC FP_CONTRACT on-off-switch
-         int fpclassify(real-floating x);
-         int isfinite(real-floating x);
-         int isinf(real-floating x);
-         int isnan(real-floating x);
-         int isnormal(real-floating x);
-         int signbit(real-floating x);
-       double acos(double x);
-       float acosf(float x);
-       long double acosl(long double x);
-       double asin(double x);
-       float asinf(float x);
-       long double asinl(long double x);
-       double atan(double x);
-       float atanf(float x);
-       long double atanl(long double x);
-       double atan2(double y, double x);
-       float atan2f(float y, float x);
-       long double atan2l(long double y, long double x);
-       double cos(double x);
-       float cosf(float x);
-       long double cosl(long double x);
-       double sin(double x);
-       float sinf(float x);
-       long double sinl(long double x);
-       double tan(double x);
-       float tanf(float x);
-       long double tanl(long double x);
-       double acosh(double x);
-       float acoshf(float x);
-       long double acoshl(long double x);
-       double asinh(double x);
-       float asinhf(float x);
-       long double asinhl(long double x);
-       double atanh(double x);
-       float atanhf(float x);
-       long double atanhl(long double x);
-       double cosh(double x);
-       float coshf(float x);
-       long double coshl(long double x);
-       double sinh(double x);
-       float sinhf(float x);
-       long double sinhl(long double x);
-       double tanh(double x);
-       float tanhf(float x);
-       long double tanhl(long double x);
-       double exp(double x);
-       float expf(float x);
-         long double expl(long double x);
-         double exp2(double x);
-         float exp2f(float x);
-         long double exp2l(long double x);
-         double expm1(double x);
-         float expm1f(float x);
-         long double expm1l(long double x);
-         double frexp(double value, int *exp);
-         float frexpf(float value, int *exp);
-         long double frexpl(long double value, int *exp);
-         int ilogb(double x);
-         int ilogbf(float x);
-         int ilogbl(long double x);
-         double ldexp(double x, int exp);
-         float ldexpf(float x, int exp);
-         long double ldexpl(long double x, int exp);
-         double log(double x);
-         float logf(float x);
-         long double logl(long double x);
-         double log10(double x);
-         float log10f(float x);
-         long double log10l(long double x);
-         double log1p(double x);
-         float log1pf(float x);
-         long double log1pl(long double x);
-         double log2(double x);
-         float log2f(float x);
-         long double log2l(long double x);
-         double logb(double x);
-         float logbf(float x);
-         long double logbl(long double x);
-         double modf(double value, double *iptr);
-         float modff(float value, float *iptr);
-         long double modfl(long double value, long double *iptr);
-         double scalbn(double x, int n);
-         float scalbnf(float x, int n);
-         long double scalbnl(long double x, int n);
-         double scalbln(double x, long int n);
-         float scalblnf(float x, long int n);
-         long double scalblnl(long double x, long int n);
-         double cbrt(double x);
-       float cbrtf(float x);
-       long double cbrtl(long double x);
-       double fabs(double x);
-       float fabsf(float x);
-       long double fabsl(long double x);
-       double hypot(double x, double y);
-       float hypotf(float x, float y);
-       long double hypotl(long double x, long double y);
-       double pow(double x, double y);
-       float powf(float x, float y);
-       long double powl(long double x, long double y);
-       double sqrt(double x);
-       float sqrtf(float x);
-       long double sqrtl(long double x);
-       double erf(double x);
-       float erff(float x);
-       long double erfl(long double x);
-       double erfc(double x);
-       float erfcf(float x);
-       long double erfcl(long double x);
-       double lgamma(double x);
-       float lgammaf(float x);
-       long double lgammal(long double x);
-       double tgamma(double x);
-       float tgammaf(float x);
-       long double tgammal(long double x);
-       double ceil(double x);
-       float ceilf(float x);
-       long double ceill(long double x);
-       double floor(double x);
-       float floorf(float x);
-       long double floorl(long double x);
-       double nearbyint(double x);
-       float nearbyintf(float x);
-       long double nearbyintl(long double x);
-       double rint(double x);
-       float rintf(float x);
-       long double rintl(long double x);
-       long int lrint(double x);
-       long int lrintf(float x);
-       long int lrintl(long double x);
-         long long int llrint(double x);
-         long long int llrintf(float x);
-         long long int llrintl(long double x);
-         double round(double x);
-         float roundf(float x);
-         long double roundl(long double x);
-         long int lround(double x);
-         long int lroundf(float x);
-         long int lroundl(long double x);
-         long long int llround(double x);
-         long long int llroundf(float x);
-         long long int llroundl(long double x);
-         double trunc(double x);
-         float truncf(float x);
-         long double truncl(long double x);
-         double fmod(double x, double y);
-         float fmodf(float x, float y);
-         long double fmodl(long double x, long double y);
-         double remainder(double x, double y);
-         float remainderf(float x, float y);
-         long double remainderl(long double x, long double y);
-         double remquo(double x, double y, int *quo);
-         float remquof(float x, float y, int *quo);
-         long double remquol(long double x, long double y,
-              int *quo);
-         double copysign(double x, double y);
-         float copysignf(float x, float y);
-         long double copysignl(long double x, long double y);
-         double nan(const char *tagp);
-         float nanf(const char *tagp);
-         long double nanl(const char *tagp);
-         double nextafter(double x, double y);
-         float nextafterf(float x, float y);
-         long double nextafterl(long double x, long double y);
-         double nexttoward(double x, long double y);
-         float nexttowardf(float x, long double y);
-         long double nexttowardl(long double x, long double y);
-         double fdim(double x, double y);
-         float fdimf(float x, float y);
-         long double fdiml(long double x, long double y);
-         double fmax(double x, double y);
-       float fmaxf(float x, float y);
-       long double fmaxl(long double x, long double y);
-       double fmin(double x, double y);
-       float fminf(float x, float y);
-       long double fminl(long double x, long double y);
-       double fma(double x, double y, double z);
-       float fmaf(float x, float y, float z);
-       long double fmal(long double x, long double y,
-            long double z);
-       int isgreater(real-floating x, real-floating y);
-       int isgreaterequal(real-floating x, real-floating y);
-       int isless(real-floating x, real-floating y);
-       int islessequal(real-floating x, real-floating y);
-       int islessgreater(real-floating x, real-floating y);
-       int isunordered(real-floating x, real-floating y);
-
- -

Contents -

B.12 Nonlocal jumps <setjmp.h>

-
-       jmp_buf
-       int setjmp(jmp_buf env);
-       _Noreturn void longjmp(jmp_buf env, int val);
-
- -

Contents -

B.13 Signal handling <signal.h>

- -
-       sig_atomic_t    SIG_IGN           SIGILL           SIGTERM
-       SIG_DFL         SIGABRT           SIGINT
-       SIG_ERR         SIGFPE            SIGSEGV
-       void (*signal(int sig, void (*func)(int)))(int);
-       int raise(int sig);
-
- -

Contents -

B.14 Alignment <stdalign.h>

-
-         alignas
-         __alignas_is_defined
-
- -

Contents -

B.15 Variable arguments <stdarg.h>

-
-         va_list
-         type va_arg(va_list ap, type);
-         void va_copy(va_list dest, va_list src);
-         void va_end(va_list ap);
-         void va_start(va_list ap, parmN);
-
- -

Contents -

B.16 Atomics <stdatomic.h>

- - -
-         ATOMIC_CHAR_LOCK_FREE           atomic_uint
-         ATOMIC_CHAR16_T_LOCK_FREE       atomic_long
-         ATOMIC_CHAR32_T_LOCK_FREE       atomic_ulong
-         ATOMIC_WCHAR_T_LOCK_FREE        atomic_llong
-         ATOMIC_SHORT_LOCK_FREE          atomic_ullong
-         ATOMIC_INT_LOCK_FREE            atomic_char16_t
-         ATOMIC_LONG_LOCK_FREE           atomic_char32_t
-         ATOMIC_LLONG_LOCK_FREE          atomic_wchar_t
-         ATOMIC_ADDRESS_LOCK_FREE        atomic_int_least8_t
-         ATOMIC_FLAG_INIT                atomic_uint_least8_t
-         memory_order                    atomic_int_least16_t
-         atomic_flag                     atomic_uint_least16_t
-         atomic_bool                     atomic_int_least32_t
-         atomic_address                  atomic_uint_least32_t
-         memory_order_relaxed            atomic_int_least64_t
-         memory_order_consume            atomic_uint_least64_t
-         memory_order_acquire            atomic_int_fast8_t
-         memory_order_release            atomic_uint_fast8_t
-         memory_order_acq_rel            atomic_int_fast16_t
-         memory_order_seq_cst            atomic_uint_fast16_t
-         atomic_char                     atomic_int_fast32_t
-         atomic_schar                    atomic_uint_fast32_t
-         atomic_uchar                    atomic_int_fast64_t
-         atomic_short                    atomic_uint_fast64_t
-         atomic_ushort                   atomic_intptr_t
-         atomic_int                      atomic_uintptr_t
-       atomic_size_t                     atomic_intmax_t
-       atomic_ptrdiff_t                  atomic_uintmax_t
-       #define ATOMIC_VAR_INIT(C value)
-       void atomic_init(volatile A *obj, C value);
-       type kill_dependency(type y);
-       void atomic_thread_fence(memory_order order);
-       void atomic_signal_fence(memory_order order);
-       _Bool atomic_is_lock_free(atomic_type const volatile *obj);
-       void atomic_store(volatile A *object, C desired);
-       void atomic_store_explicit(volatile A *object,
-             C desired, memory_order order);
-       C atomic_load(volatile A *object);
-       C atomic_load_explicit(volatile A *object,
-             memory_order order);
-       C atomic_exchange(volatile A *object, C desired);
-       C atomic_exchange_explicit(volatile A *object,
-             C desired, memory_order order);
-       _Bool atomic_compare_exchange_strong(volatile A *object,
-             C *expected, C desired);
-       _Bool atomic_compare_exchange_strong_explicit(
-             volatile A *object, C *expected, C desired,
-             memory_order success, memory_order failure);
-       _Bool atomic_compare_exchange_weak(volatile A *object,
-             C *expected, C desired);
-       _Bool atomic_compare_exchange_weak_explicit(
-             volatile A *object, C *expected, C desired,
-             memory_order success, memory_order failure);
-       C atomic_fetch_key(volatile A *object, M operand);
-       C atomic_fetch_key_explicit(volatile A *object,
-             M operand, memory_order order);
-       bool atomic_flag_test_and_set(
-             volatile atomic_flag *object);
-       bool atomic_flag_test_and_set_explicit(
-             volatile atomic_flag *object, memory_order order);
-       void atomic_flag_clear(volatile atomic_flag *object);
-       void atomic_flag_clear_explicit(
-             volatile atomic_flag *object, memory_order order);
-
- -

Contents -

B.17 Boolean type and values <stdbool.h>

-
-         bool
-         true
-         false
-         __bool_true_false_are_defined
-
- -

Contents -

B.18 Common definitions <stddef.h>

-
-         ptrdiff_t       max_align_t       NULL
-         size_t          wchar_t
-         offsetof(type, member-designator)
-         __STDC_WANT_LIB_EXT1__
-         rsize_t
-
- -

Contents -

B.19 Integer types <stdint.h>

- -
-         intN_t                INT_LEASTN_MIN          PTRDIFF_MAX
-         uintN_t               INT_LEASTN_MAX          SIG_ATOMIC_MIN
-         int_leastN_t          UINT_LEASTN_MAX         SIG_ATOMIC_MAX
-         uint_leastN_t         INT_FASTN_MIN           SIZE_MAX
-         int_fastN_t           INT_FASTN_MAX           WCHAR_MIN
-         uint_fastN_t          UINT_FASTN_MAX          WCHAR_MAX
-         intptr_t              INTPTR_MIN              WINT_MIN
-         uintptr_t             INTPTR_MAX              WINT_MAX
-         intmax_t              UINTPTR_MAX             INTN_C(value)
-         uintmax_t             INTMAX_MIN              UINTN_C(value)
-         INTN_MIN              INTMAX_MAX              INTMAX_C(value)
-         INTN_MAX              UINTMAX_MAX             UINTMAX_C(value)
-         UINTN_MAX             PTRDIFF_MIN
-         __STDC_WANT_LIB_EXT1__
-         RSIZE_MAX
-
- -

Contents -

B.20 Input/output <stdio.h>

- - - -
-       size_t          _IOLBF            FILENAME_MAX     TMP_MAX
-       FILE            _IONBF            L_tmpnam         stderr
-       fpos_t          BUFSIZ            SEEK_CUR         stdin
-       NULL            EOF               SEEK_END         stdout
-       _IOFBF          FOPEN_MAX         SEEK_SET
-       int remove(const char *filename);
-       int rename(const char *old, const char *new);
-       FILE *tmpfile(void);
-       char *tmpnam(char *s);
-       int fclose(FILE *stream);
-       int fflush(FILE *stream);
-       FILE *fopen(const char * restrict filename,
-            const char * restrict mode);
-       FILE *freopen(const char * restrict filename,
-            const char * restrict mode,
-            FILE * restrict stream);
-       void setbuf(FILE * restrict stream,
-            char * restrict buf);
-       int setvbuf(FILE * restrict stream,
-            char * restrict buf,
-            int mode, size_t size);
-       int fprintf(FILE * restrict stream,
-            const char * restrict format, ...);
-       int fscanf(FILE * restrict stream,
-            const char * restrict format, ...);
-       int printf(const char * restrict format, ...);
-       int scanf(const char * restrict format, ...);
-       int snprintf(char * restrict s, size_t n,
-            const char * restrict format, ...);
-       int sprintf(char * restrict s,
-            const char * restrict format, ...);
-       int sscanf(const char * restrict s,
-            const char * restrict format, ...);
-       int vfprintf(FILE * restrict stream,
-            const char * restrict format, va_list arg);
-       int vfscanf(FILE * restrict stream,
-            const char * restrict format, va_list arg);
-       int vprintf(const char * restrict format, va_list arg);
-       int vscanf(const char * restrict format, va_list arg);
-         int vsnprintf(char * restrict s, size_t n,
-              const char * restrict format, va_list arg);
-         int vsprintf(char * restrict s,
-              const char * restrict format, va_list arg);
-         int vsscanf(const char * restrict s,
-              const char * restrict format, va_list arg);
-         int fgetc(FILE *stream);
-         char *fgets(char * restrict s, int n,
-              FILE * restrict stream);
-         int fputc(int c, FILE *stream);
-         int fputs(const char * restrict s,
-              FILE * restrict stream);
-         int getc(FILE *stream);
-         int getchar(void);
-         int putc(int c, FILE *stream);                                       *
-         int putchar(int c);
-         int puts(const char *s);
-         int ungetc(int c, FILE *stream);
-         size_t fread(void * restrict ptr,
-              size_t size, size_t nmemb,
-              FILE * restrict stream);
-         size_t fwrite(const void * restrict ptr,
-              size_t size, size_t nmemb,
-              FILE * restrict stream);
-         int fgetpos(FILE * restrict stream,
-              fpos_t * restrict pos);
-         int fseek(FILE *stream, long int offset, int whence);
-         int fsetpos(FILE *stream, const fpos_t *pos);
-         long int ftell(FILE *stream);
-         void rewind(FILE *stream);
-         void clearerr(FILE *stream);
-         int feof(FILE *stream);
-         int ferror(FILE *stream);
-         void perror(const char *s);
-         __STDC_WANT_LIB_EXT1__
-         L_tmpnam_s    TMP_MAX_S         errno_t          rsize_t
-         errno_t tmpfile_s(FILE * restrict * restrict streamptr);
-         errno_t tmpnam_s(char *s, rsize_t maxsize);
-       errno_t fopen_s(FILE * restrict * restrict streamptr,
-            const char * restrict filename,
-            const char * restrict mode);
-       errno_t freopen_s(FILE * restrict * restrict newstreamptr,
-            const char * restrict filename,
-            const char * restrict mode,
-            FILE * restrict stream);
-       int fprintf_s(FILE * restrict stream,
-            const char * restrict format, ...);
-       int fscanf_s(FILE * restrict stream,
-            const char * restrict format, ...);
-       int printf_s(const char * restrict format, ...);
-       int scanf_s(const char * restrict format, ...);
-       int snprintf_s(char * restrict s, rsize_t n,
-            const char * restrict format, ...);
-       int sprintf_s(char * restrict s, rsize_t n,
-            const char * restrict format, ...);
-       int sscanf_s(const char * restrict s,
-            const char * restrict format, ...);
-       int vfprintf_s(FILE * restrict stream,
-            const char * restrict format,
-            va_list arg);
-       int vfscanf_s(FILE * restrict stream,
-            const char * restrict format,
-            va_list arg);
-       int vprintf_s(const char * restrict format,
-            va_list arg);
-       int vscanf_s(const char * restrict format,
-            va_list arg);
-       int vsnprintf_s(char * restrict s, rsize_t n,
-            const char * restrict format,
-            va_list arg);
-       int vsprintf_s(char * restrict s, rsize_t n,
-            const char * restrict format,
-            va_list arg);
-       int vsscanf_s(const char * restrict s,
-            const char * restrict format,
-            va_list arg);
-       char *gets_s(char *s, rsize_t n);
-
- -

Contents -

B.21 General utilities <stdlib.h>

- - -
-         size_t       ldiv_t            EXIT_FAILURE     MB_CUR_MAX
-         wchar_t      lldiv_t           EXIT_SUCCESS
-         div_t        NULL              RAND_MAX
-         double atof(const char *nptr);
-         int atoi(const char *nptr);
-         long int atol(const char *nptr);
-         long long int atoll(const char *nptr);
-         double strtod(const char * restrict nptr,
-              char ** restrict endptr);
-         float strtof(const char * restrict nptr,
-              char ** restrict endptr);
-         long double strtold(const char * restrict nptr,
-              char ** restrict endptr);
-         long int strtol(const char * restrict nptr,
-              char ** restrict endptr, int base);
-         long long int strtoll(const char * restrict nptr,
-              char ** restrict endptr, int base);
-         unsigned long int strtoul(
-              const char * restrict nptr,
-              char ** restrict endptr, int base);
-         unsigned long long int strtoull(
-              const char * restrict nptr,
-              char ** restrict endptr, int base);
-         int rand(void);
-         void srand(unsigned int seed);
-         void *aligned_alloc(size_t alignment, size_t size);
-         void *calloc(size_t nmemb, size_t size);
-         void free(void *ptr);
-         void *malloc(size_t size);
-         void *realloc(void *ptr, size_t size);
-         _Noreturn void abort(void);
-         int atexit(void (*func)(void));
-         int at_quick_exit(void (*func)(void));
-         _Noreturn void exit(int status);
-         _Noreturn void _Exit(int status);
-         char *getenv(const char *name);
-         _Noreturn void quick_exit(int status);
-         int system(const char *string);
-       void *bsearch(const void *key, const void *base,
-            size_t nmemb, size_t size,
-            int (*compar)(const void *, const void *));
-       void qsort(void *base, size_t nmemb, size_t size,
-            int (*compar)(const void *, const void *));
-       int abs(int j);
-       long int labs(long int j);
-       long long int llabs(long long int j);
-       div_t div(int numer, int denom);
-       ldiv_t ldiv(long int numer, long int denom);
-       lldiv_t lldiv(long long int numer,
-            long long int denom);
-       int mblen(const char *s, size_t n);
-       int mbtowc(wchar_t * restrict pwc,
-            const char * restrict s, size_t n);
-       int wctomb(char *s, wchar_t wchar);
-       size_t mbstowcs(wchar_t * restrict pwcs,
-            const char * restrict s, size_t n);
-       size_t wcstombs(char * restrict s,
-            const wchar_t * restrict pwcs, size_t n);
-       __STDC_WANT_LIB_EXT1__
-       errno_t
-       rsize_t
-       constraint_handler_t
-       constraint_handler_t set_constraint_handler_s(
-            constraint_handler_t handler);
-       void abort_handler_s(
-            const char * restrict msg,
-            void * restrict ptr,
-            errno_t error);
-       void ignore_handler_s(
-            const char * restrict msg,
-            void * restrict ptr,
-            errno_t error);
-       errno_t getenv_s(size_t * restrict len,
-                 char * restrict value, rsize_t maxsize,
-                 const char * restrict name);
-         void *bsearch_s(const void *key, const void *base,
-              rsize_t nmemb, rsize_t size,
-              int (*compar)(const void *k, const void *y,
-                              void *context),
-              void *context);
-         errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
-              int (*compar)(const void *x, const void *y,
-                              void *context),
-              void *context);
-         errno_t wctomb_s(int * restrict status,
-              char * restrict s,
-              rsize_t smax,
-              wchar_t wc);
-         errno_t mbstowcs_s(size_t * restrict retval,
-              wchar_t * restrict dst, rsize_t dstmax,
-              const char * restrict src, rsize_t len);
-         errno_t wcstombs_s(size_t * restrict retval,
-              char * restrict dst, rsize_t dstmax,
-              const wchar_t * restrict src, rsize_t len);
-
- -

Contents -

B.22 String handling <string.h>

- - -
-         size_t
-         NULL
-         void *memcpy(void * restrict s1,
-              const void * restrict s2, size_t n);
-         void *memmove(void *s1, const void *s2, size_t n);
-         char *strcpy(char * restrict s1,
-              const char * restrict s2);
-         char *strncpy(char * restrict s1,
-              const char * restrict s2, size_t n);
-         char *strcat(char * restrict s1,
-              const char * restrict s2);
-         char *strncat(char * restrict s1,
-              const char * restrict s2, size_t n);
-         int memcmp(const void *s1, const void *s2, size_t n);
-         int strcmp(const char *s1, const char *s2);
-         int strcoll(const char *s1, const char *s2);
-         int strncmp(const char *s1, const char *s2, size_t n);
-         size_t strxfrm(char * restrict s1,
-              const char * restrict s2, size_t n);
-         void *memchr(const void *s, int c, size_t n);
-       char *strchr(const char *s, int c);
-       size_t strcspn(const char *s1, const char *s2);
-       char *strpbrk(const char *s1, const char *s2);
-       char *strrchr(const char *s, int c);
-       size_t strspn(const char *s1, const char *s2);
-       char *strstr(const char *s1, const char *s2);
-       char *strtok(char * restrict s1,
-            const char * restrict s2);
-       void *memset(void *s, int c, size_t n);
-       char *strerror(int errnum);
-       size_t strlen(const char *s);
-       __STDC_WANT_LIB_EXT1__
-       errno_t
-       rsize_t
-       errno_t memcpy_s(void * restrict s1, rsize_t s1max,
-            const void * restrict s2, rsize_t n);
-       errno_t memmove_s(void *s1, rsize_t s1max,
-            const void *s2, rsize_t n);
-       errno_t strcpy_s(char * restrict s1,
-            rsize_t s1max,
-            const char * restrict s2);
-       errno_t strncpy_s(char * restrict s1,
-            rsize_t s1max,
-            const char * restrict s2,
-            rsize_t n);
-       errno_t strcat_s(char * restrict s1,
-            rsize_t s1max,
-            const char * restrict s2);
-       errno_t strncat_s(char * restrict s1,
-            rsize_t s1max,
-            const char * restrict s2,
-            rsize_t n);
-       char *strtok_s(char * restrict s1,
-            rsize_t * restrict s1max,
-            const char * restrict s2,
-            char ** restrict ptr);
-       errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
-       errno_t strerror_s(char *s, rsize_t maxsize,
-            errno_t errnum);
-       size_t strerrorlen_s(errno_t errnum);
-         size_t strnlen_s(const char *s, size_t maxsize);
-
- -

Contents -

B.23 Type-generic math <tgmath.h>

-
-         acos         sqrt              fmod             nextafter
-         asin         fabs              frexp            nexttoward
-         atan         atan2             hypot            remainder
-         acosh        cbrt              ilogb            remquo
-         asinh        ceil              ldexp            rint
-         atanh        copysign          lgamma           round
-         cos          erf               llrint           scalbn
-         sin          erfc              llround          scalbln
-         tan          exp2              log10            tgamma
-         cosh         expm1             log1p            trunc
-         sinh         fdim              log2             carg
-         tanh         floor             logb             cimag
-         exp          fma               lrint            conj
-         log          fmax              lround           cproj
-         pow          fmin              nearbyint        creal
-
- -

Contents -

B.24 Threads <threads.h>

- -
-         ONCE_FLAG_INIT                 mtx_plain
-         TSS_DTOR_ITERATIONS            mtx_recursive
-         cnd_t                          mtx_timed
-         thrd_t                         mtx_try
-         tss_t                          thrd_timeout
-         mtx_t                          thrd_success
-         tss_dtor_t                     thrd_busy
-         thrd_start_t                   thrd_error
-         once_flag                      thrd_nomem
-         xtime
-       void call_once(once_flag *flag, void (*func)(void));
-       int cnd_broadcast(cnd_t *cond);
-       void cnd_destroy(cnd_t *cond);
-       int cnd_init(cnd_t *cond);
-       int cnd_signal(cnd_t *cond);
-       int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
-            const xtime *xt);
-       int cnd_wait(cnd_t *cond, mtx_t *mtx);
-       void mtx_destroy(mtx_t *mtx);
-       int mtx_init(mtx_t *mtx, int type);
-       int mtx_lock(mtx_t *mtx);
-       int mtx_timedlock(mtx_t *mtx, const xtime *xt);
-       int mtx_trylock(mtx_t *mtx);
-       int mtx_unlock(mtx_t *mtx);
-       int thrd_create(thrd_t *thr, thrd_start_t func,
-            void *arg);
-       thrd_t thrd_current(void);
-       int thrd_detach(thrd_t thr);
-       int thrd_equal(thrd_t thr0, thrd_t thr1);
-       void thrd_exit(int res);
-       int thrd_join(thrd_t thr, int *res);
-       void thrd_sleep(const xtime *xt);
-       void thrd_yield(void);
-       int tss_create(tss_t *key, tss_dtor_t dtor);
-       void tss_delete(tss_t key);
-       void *tss_get(tss_t key);
-       int tss_set(tss_t key, void *val);
-       int xtime_get(xtime *xt, int base);
-
- -

Contents -

B.25 Date and time <time.h>

- -
-       NULL                  size_t                  time_t
-       CLOCKS_PER_SEC        clock_t                 struct tm
-       clock_t clock(void);
-       double difftime(time_t time1, time_t time0);
-       time_t mktime(struct tm *timeptr);
-       time_t time(time_t *timer);
-       char *asctime(const struct tm *timeptr);
-       char *ctime(const time_t *timer);
-       struct tm *gmtime(const time_t *timer);
-       struct tm *localtime(const time_t *timer);
-       size_t strftime(char * restrict s,
-            size_t maxsize,
-            const char * restrict format,
-            const struct tm * restrict timeptr);
-       __STDC_WANT_LIB_EXT1__
-       errno_t
-       rsize_t
-       errno_t asctime_s(char *s, rsize_t maxsize,
-            const struct tm *timeptr);
-         errno_t ctime_s(char *s, rsize_t maxsize,
-              const time_t *timer);
-         struct tm *gmtime_s(const time_t * restrict timer,
-              struct tm * restrict result);
-         struct tm *localtime_s(const time_t * restrict timer,
-              struct tm * restrict result);
-
- -

Contents -

B.26 Unicode utilities <uchar.h>

-
-         mbstate_t     size_t            char16_t         char32_t
-         size_t mbrtoc16(char16_t * restrict pc16,
-              const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-         size_t c16rtomb(char * restrict s, char16_t c16,
-              mbstate_t * restrict ps);
-         size_t mbrtoc32(char32_t * restrict pc32,
-              const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-         size_t c32rtomb(char * restrict s, char32_t c32,
-              mbstate_t * restrict ps);
-
- -

Contents -

B.27 Extended multibyte/wide character utilities <wchar.h>

- - - - - -
-         wchar_t             wint_t                  WCHAR_MAX
-         size_t              struct tm               WCHAR_MIN
-         mbstate_t           NULL                    WEOF
-         int fwprintf(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-         int fwscanf(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-         int swprintf(wchar_t * restrict s, size_t n,
-              const wchar_t * restrict format, ...);
-         int swscanf(const wchar_t * restrict s,
-              const wchar_t * restrict format, ...);
-         int vfwprintf(FILE * restrict stream,
-              const wchar_t * restrict format, va_list arg);
-         int vfwscanf(FILE * restrict stream,
-              const wchar_t * restrict format, va_list arg);
-         int vswprintf(wchar_t * restrict s, size_t n,
-              const wchar_t * restrict format, va_list arg);
-       int vswscanf(const wchar_t * restrict s,
-            const wchar_t * restrict format, va_list arg);
-       int vwprintf(const wchar_t * restrict format,
-            va_list arg);
-       int vwscanf(const wchar_t * restrict format,
-            va_list arg);
-       int wprintf(const wchar_t * restrict format, ...);
-       int wscanf(const wchar_t * restrict format, ...);
-       wint_t fgetwc(FILE *stream);
-       wchar_t *fgetws(wchar_t * restrict s, int n,
-            FILE * restrict stream);
-       wint_t fputwc(wchar_t c, FILE *stream);
-       int fputws(const wchar_t * restrict s,
-            FILE * restrict stream);
-       int fwide(FILE *stream, int mode);
-       wint_t getwc(FILE *stream);
-       wint_t getwchar(void);
-       wint_t putwc(wchar_t c, FILE *stream);
-       wint_t putwchar(wchar_t c);
-       wint_t ungetwc(wint_t c, FILE *stream);
-       double wcstod(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr);
-       float wcstof(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr);
-       long double wcstold(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr);
-       long int wcstol(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr, int base);
-       long long int wcstoll(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr, int base);
-       unsigned long int wcstoul(const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr, int base);
-       unsigned long long int wcstoull(
-            const wchar_t * restrict nptr,
-            wchar_t ** restrict endptr, int base);
-       wchar_t *wcscpy(wchar_t * restrict s1,
-            const wchar_t * restrict s2);
-       wchar_t *wcsncpy(wchar_t * restrict s1,
-            const wchar_t * restrict s2, size_t n);
-         wchar_t *wmemcpy(wchar_t * restrict s1,
-              const wchar_t * restrict s2, size_t n);
-         wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
-              size_t n);
-         wchar_t *wcscat(wchar_t * restrict s1,
-              const wchar_t * restrict s2);
-         wchar_t *wcsncat(wchar_t * restrict s1,
-              const wchar_t * restrict s2, size_t n);
-         int wcscmp(const wchar_t *s1, const wchar_t *s2);
-         int wcscoll(const wchar_t *s1, const wchar_t *s2);
-         int wcsncmp(const wchar_t *s1, const wchar_t *s2,
-              size_t n);
-         size_t wcsxfrm(wchar_t * restrict s1,
-              const wchar_t * restrict s2, size_t n);
-         int wmemcmp(const wchar_t *s1, const wchar_t *s2,
-              size_t n);
-         wchar_t *wcschr(const wchar_t *s, wchar_t c);
-         size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
-         wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
-         wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
-         size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
-         wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
-         wchar_t *wcstok(wchar_t * restrict s1,
-              const wchar_t * restrict s2,
-              wchar_t ** restrict ptr);
-         wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
-         size_t wcslen(const wchar_t *s);
-         wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
-         size_t wcsftime(wchar_t * restrict s, size_t maxsize,
-              const wchar_t * restrict format,
-              const struct tm * restrict timeptr);
-         wint_t btowc(int c);
-         int wctob(wint_t c);
-         int mbsinit(const mbstate_t *ps);
-         size_t mbrlen(const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-         size_t mbrtowc(wchar_t * restrict pwc,
-              const char * restrict s, size_t n,
-              mbstate_t * restrict ps);
-       size_t wcrtomb(char * restrict s, wchar_t wc,
-            mbstate_t * restrict ps);
-       size_t mbsrtowcs(wchar_t * restrict dst,
-            const char ** restrict src, size_t len,
-            mbstate_t * restrict ps);
-       size_t wcsrtombs(char * restrict dst,
-            const wchar_t ** restrict src, size_t len,
-            mbstate_t * restrict ps);
-       __STDC_WANT_LIB_EXT1__
-       errno_t
-       rsize_t
-       int fwprintf_s(FILE * restrict stream,
-            const wchar_t * restrict format, ...);
-       int fwscanf_s(FILE * restrict stream,
-            const wchar_t * restrict format, ...);
-       int snwprintf_s(wchar_t * restrict s,
-            rsize_t n,
-            const wchar_t * restrict format, ...);
-       int swprintf_s(wchar_t * restrict s, rsize_t n,
-            const wchar_t * restrict format, ...);
-       int swscanf_s(const wchar_t * restrict s,
-            const wchar_t * restrict format, ...);
-       int vfwprintf_s(FILE * restrict stream,
-            const wchar_t * restrict format,
-            va_list arg);
-       int vfwscanf_s(FILE * restrict stream,
-            const wchar_t * restrict format, va_list arg);
-       int vsnwprintf_s(wchar_t * restrict s,
-            rsize_t n,
-            const wchar_t * restrict format,
-            va_list arg);
-       int vswprintf_s(wchar_t * restrict s,
-            rsize_t n,
-            const wchar_t * restrict format,
-            va_list arg);
-       int vswscanf_s(const wchar_t * restrict s,
-            const wchar_t * restrict format,
-            va_list arg);
-         int vwprintf_s(const wchar_t * restrict format,
-              va_list arg);
-         int vwscanf_s(const wchar_t * restrict format,
-              va_list arg);
-         int wprintf_s(const wchar_t * restrict format, ...);
-         int wscanf_s(const wchar_t * restrict format, ...);
-         errno_t wcscpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2);
-         errno_t wcsncpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2,
-              rsize_t n);
-         errno_t wmemcpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2,
-              rsize_t n);
-         errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
-              const wchar_t *s2, rsize_t n);
-         errno_t wcscat_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2);
-         errno_t wcsncat_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2,
-              rsize_t n);
-         wchar_t *wcstok_s(wchar_t * restrict s1,
-              rsize_t * restrict s1max,
-              const wchar_t * restrict s2,
-              wchar_t ** restrict ptr);
-         size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
-         errno_t wcrtomb_s(size_t * restrict retval,
-              char * restrict s, rsize_t smax,
-              wchar_t wc, mbstate_t * restrict ps);
-         errno_t mbsrtowcs_s(size_t * restrict retval,
-              wchar_t * restrict dst, rsize_t dstmax,
-              const char ** restrict src, rsize_t len,
-              mbstate_t * restrict ps);
-       errno_t wcsrtombs_s(size_t * restrict retval,
-            char * restrict dst, rsize_t dstmax,
-            const wchar_t ** restrict src, rsize_t len,
-            mbstate_t * restrict ps);
-
- -

Contents -

B.28 Wide character classification and mapping utilities <wctype.h>

- -
-       wint_t          wctrans_t         wctype_t         WEOF
-       int iswalnum(wint_t wc);
-       int iswalpha(wint_t wc);
-       int iswblank(wint_t wc);
-       int iswcntrl(wint_t wc);
-       int iswdigit(wint_t wc);
-       int iswgraph(wint_t wc);
-       int iswlower(wint_t wc);
-       int iswprint(wint_t wc);
-       int iswpunct(wint_t wc);
-       int iswspace(wint_t wc);
-       int iswupper(wint_t wc);
-       int iswxdigit(wint_t wc);
-       int iswctype(wint_t wc, wctype_t desc);
-       wctype_t wctype(const char *property);
-       wint_t towlower(wint_t wc);
-       wint_t towupper(wint_t wc);
-       wint_t towctrans(wint_t wc, wctrans_t desc);
-       wctrans_t wctrans(const char *property);
-
- -

Contents -

Annex C

-
-                                     (informative)
-                                   Sequence points
-
-

- The following are the sequence points described in 5.1.2.3: -

- -

Contents -

Annex D

-
-                                     (normative)
-                Universal character names for identifiers
-
-

- This clause lists the hexadecimal code values that are valid in universal character names - in identifiers. - -

Contents -

D.1 Ranges of characters allowed

-

- 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, - 00D8-00F6, 00F8-00FF -

- 0100-167F, 1681-180D, 180F-1FFF -

- 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F -

- 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF -

- 3004-3007, 3021-302F, 3031-303F -

- 3040-D7FF -

- F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD -

- 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, - 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, - B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD - -

Contents -

D.2 Ranges of characters disallowed initially

-

- 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F - - -

Contents -

Annex E

-
-                                    (informative)
-                             Implementation limits
-
-

- The contents of the header <limits.h> are given below, in alphabetical order. The - minimum magnitudes shown shall be replaced by implementation-defined magnitudes - with the same sign. The values shall all be constant expressions suitable for use in #if - preprocessing directives. The components are described further in 5.2.4.2.1. -

-         #define    CHAR_BIT                               8
-         #define    CHAR_MAX          UCHAR_MAX or SCHAR_MAX
-         #define    CHAR_MIN                  0 or SCHAR_MIN
-         #define    INT_MAX                           +32767
-         #define    INT_MIN                           -32767
-         #define    LONG_MAX                     +2147483647
-         #define    LONG_MIN                     -2147483647
-         #define    LLONG_MAX           +9223372036854775807
-         #define    LLONG_MIN           -9223372036854775807
-         #define    MB_LEN_MAX                             1
-         #define    SCHAR_MAX                           +127
-         #define    SCHAR_MIN                           -127
-         #define    SHRT_MAX                          +32767
-         #define    SHRT_MIN                          -32767
-         #define    UCHAR_MAX                            255
-         #define    USHRT_MAX                          65535
-         #define    UINT_MAX                           65535
-         #define    ULONG_MAX                     4294967295
-         #define    ULLONG_MAX          18446744073709551615
-
-

- The contents of the header <float.h> are given below. All integer values, except - FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing - directives; all floating values shall be constant expressions. The components are - described further in 5.2.4.2.2. -

- The values given in the following list shall be replaced by implementation-defined - expressions: -

-         #define FLT_EVAL_METHOD
-         #define FLT_ROUNDS
-
-

- The values given in the following list shall be replaced by implementation-defined - constant expressions that are greater or equal in magnitude (absolute value) to those - shown, with the same sign: - -

-        #define    DLB_DECIMAL_DIG                                10
-        #define    DBL_DIG                                        10
-        #define    DBL_MANT_DIG
-        #define    DBL_MAX_10_EXP                               +37
-        #define    DBL_MAX_EXP
-        #define    DBL_MIN_10_EXP                               -37
-        #define    DBL_MIN_EXP
-        #define    DECIMAL_DIG                                    10
-        #define    FLT_DECIMAL_DIG                                 6
-        #define    FLT_DIG                                         6
-        #define    FLT_MANT_DIG
-        #define    FLT_MAX_10_EXP                               +37
-        #define    FLT_MAX_EXP
-        #define    FLT_MIN_10_EXP                               -37
-        #define    FLT_MIN_EXP
-        #define    FLT_RADIX                                       2
-        #define    LDLB_DECIMAL_DIG                               10
-        #define    LDBL_DIG                                       10
-        #define    LDBL_MANT_DIG
-        #define    LDBL_MAX_10_EXP                              +37
-        #define    LDBL_MAX_EXP
-        #define    LDBL_MIN_10_EXP                              -37
-        #define    LDBL_MIN_EXP
-
-

- The values given in the following list shall be replaced by implementation-defined - constant expressions with values that are greater than or equal to those shown: -

-        #define DBL_MAX                                      1E+37
-        #define FLT_MAX                                      1E+37
-        #define LDBL_MAX                                     1E+37
-
-

- The values given in the following list shall be replaced by implementation-defined - constant expressions with (positive) values that are less than or equal to those shown: - -

-        #define    DBL_EPSILON                                1E-9
-        #define    DBL_MIN                                   1E-37
-        #define    FLT_EPSILON                                1E-5
-        #define    FLT_MIN                                   1E-37
-        #define    LDBL_EPSILON                               1E-9
-        #define    LDBL_MIN                                  1E-37
-
- -

Contents -

Annex F

-
-                                           (normative)
-                       IEC 60559 floating-point arithmetic
-
- -

Contents -

F.1 Introduction

-

- This annex specifies C language support for the IEC 60559 floating-point standard. The - IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for - microprocessor systems, second edition (IEC 60559:1989), previously designated - IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic - (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point - Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove - dependencies on radix and word length. IEC 60559 generally refers to the floating-point - standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that - defines __STDC_IEC_559__ shall conform to the specifications in this annex.343) - Where a binding between the C language and IEC 60559 is indicated, the - IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since - negative and positive infinity are representable in IEC 60559 formats, all real numbers lie - within the range of representable values. - -

Footnotes -

343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these - specifications. - - -

Contents -

F.2 Types

-

- The C floating types match the IEC 60559 formats as follows: -

- Any non-IEC 60559 extended format used for the long double type shall have more - precision than IEC 60559 double and at least the range of IEC 60559 double.345) - - - - - -

Recommended practice -

- The long double type should match an IEC 60559 extended format. - -

Footnotes -

344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit - and quadruple 128-bit IEC 60559 formats. - -

345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include - all double values. - - -

Contents -

F.2.1 Infinities, signed zeros, and NaNs

-

- This specification does not define the behavior of signaling NaNs.346) It generally uses - the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan - functions in <math.h> provide designations for IEC 60559 NaNs and infinities. - -

Footnotes -

346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are - sufficient for closure of the arithmetic. - - -

Contents -

F.3 Operators and functions

-

- C operators and functions provide IEC 60559 required and recommended facilities as - listed below. -

- -

Contents -

F.4 Floating to integer conversion

-

- If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised - (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part - of the floating value exceeds the range of the integer type, then the ''invalid'' floating- - point exception is raised and the resulting value is unspecified. Otherwise, the resulting - value is determined by 6.3.1.4. Conversion of an integral floating value that does not - exceed the range of the integer type raises no floating-point exceptions; whether - conversion of a non-integral floating value raises the ''inexact'' floating-point exception is - unspecified.347) - -

Footnotes -

347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer - conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those - cases where it matters, library functions can be used to effect such conversions with or without raising - the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in - <math.h>. - - -

Contents -

F.5 Binary-decimal conversion

-

- Conversion from the widest supported IEC 60559 format to decimal with - DECIMAL_DIG digits and back is the identity function.348) -

- Conversions involving IEC 60559 formats follow all pertinent recommended practice. In - particular, conversion between any supported IEC 60559 format and decimal with - DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current - rounding mode), which assures that conversion from the widest supported IEC 60559 - format to decimal with DECIMAL_DIG digits and back is the identity function. - - - - -

- Functions such as strtod that convert character sequences to floating types honor the - rounding direction. Hence, if the rounding direction might be upward or downward, the - implementation cannot convert a minus-signed sequence by negating the converted - unsigned sequence. - -

Footnotes -

348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported, - DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest - IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and - DBL_DIG are 18 and 15, respectively, for these formats.) - - -

Contents -

F.6 The return statement

- If the return expression is evaluated in a floating-point format different from the return - type, the expression is converted as if by assignment349) to the return type of the function - and the resulting value is returned to the caller. - -

Footnotes -

349) Assignment removes any extra range and precision. - - -

Contents -

F.7 Contracted expressions

-

- A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed - zeros, subnormals, and the rounding directions in a manner consistent with the basic - arithmetic operations covered by IEC 60559. -

Recommended practice -

- A contracted expression should raise floating-point exceptions in a manner generally - consistent with the basic arithmetic operations. * - -

Contents -

F.8 Floating-point environment

-

- The floating-point environment defined in <fenv.h> includes the IEC 60559 floating- - point exception status flags and directed-rounding control modes. It includes also - IEC 60559 dynamic rounding precision and trap enablement modes, if the - implementation supports them.350) - -

Footnotes -

350) This specification does not require dynamic rounding precision nor trap enablement modes. - - -

Contents -

F.8.1 Environment management

-

- IEC 60559 requires that floating-point operations implicitly raise floating-point exception - status flags, and that rounding control modes can be set explicitly to affect result values of - floating-point operations. When the state for the FENV_ACCESS pragma (defined in - <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects - which respect sequence points.351) - - - - - - -

Footnotes -

351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating- - point control modes will be the default ones and the floating-point status flags will not be tested, - which allows certain optimizations (see F.9). - - -

Contents -

F.8.2 Translation

-

- During translation the IEC 60559 default modes are in effect: -

-

Recommended practice -

- The implementation should produce a diagnostic message for each translation-time - floating-point exception, other than ''inexact'';352) the implementation should then - proceed with the translation of the program. - -

Footnotes -

352) As floating constants are converted to appropriate internal representations at translation time, their - conversion is subject to default rounding modes and raises no execution-time floating-point exceptions - (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example - strtod, provide execution-time conversion of numeric strings. - - -

Contents -

F.8.3 Execution

-

- At program startup the floating-point environment is initialized as prescribed by - IEC 60559: -

- -

Contents -

F.8.4 Constant expressions

-

- An arithmetic constant expression of floating type, other than one in an initializer for an - object that has static or thread storage duration, is evaluated (as if) during execution; thus, - it is affected by any operative floating-point control modes and raises floating-point - exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma - is ''on'').353) -

- EXAMPLE - - - - -

-          #include <fenv.h>
-          #pragma STDC FENV_ACCESS ON
-          void f(void)
-          {
-                float w[] = { 0.0/0.0 };                  //   raises an exception
-                static float x = 0.0/0.0;                 //   does not raise an exception
-                float y = 0.0/0.0;                        //   raises an exception
-                double z = 0.0/0.0;                       //   raises an exception
-                /* ... */
-          }
-
-

- For the static initialization, the division is done at translation time, raising no (execution-time) floating- - point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at - execution time. - - -

Footnotes -

353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0 - are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and - 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the - efficiency of translation-time evaluation through static initialization, such as - -

-          const static double one_third = 1.0/3.0;
-
- - -

Contents -

F.8.5 Initialization

-

- All computation for automatic initialization is done (as if) at execution time; thus, it is - affected by any operative modes and raises floating-point exceptions as required by - IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation - for initialization of objects that have static or thread storage duration is done (as if) at - translation time. -

- EXAMPLE -

-          #include <fenv.h>
-          #pragma STDC FENV_ACCESS ON
-          void f(void)
-          {
-                float u[] = { 1.1e75 };                  //   raises exceptions
-                static float v = 1.1e75;                 //   does not raise exceptions
-                float w = 1.1e75;                        //   raises exceptions
-                double x = 1.1e75;                       //   may raise exceptions
-                float y = 1.1e75f;                       //   may raise exceptions
-                long double z = 1.1e75;                  //   does not raise exceptions
-                /* ... */
-          }
-
-

- The static initialization of v raises no (execution-time) floating-point exceptions because its computation is - done at translation time. The automatic initialization of u and w require an execution-time conversion to - float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations - of x and y entail execution-time conversion; however, in some expression evaluation methods, the - conversions is not to a narrower format, in which case no floating-point exception is raised.354) The - automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating- - point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to - - - - - their internal representations occur at translation time in all cases. - - -

Footnotes -

354) Use of float_t and double_t variables increases the likelihood of translation-time computation. - For example, the automatic initialization - -

-          double_t x = 1.1e75;
-
- could be done at translation time, regardless of the expression evaluation method. - - -

Contents -

F.8.6 Changing the environment

-

- Operations defined in 6.5 and functions and macros defined for the standard libraries - change floating-point status flags and control modes just as indicated by their - specifications (including conformance to IEC 60559). They do not change flags or modes - (so as to be detectable by the user) in any other cases. -

- If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559 - valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and - ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised - before ''inexact''. - -

Contents -

F.9 Optimization

-

- This section identifies code transformations that might subvert IEC 60559-specified - behavior, and others that do not. - -

Contents -

F.9.1 Global transformations

-

- Floating-point arithmetic operations and external function calls may entail side effects - which optimization shall honor, at least where the state of the FENV_ACCESS pragma is - ''on''. The flags and modes in the floating-point environment may be regarded as global - variables; floating-point operations (+, *, etc.) implicitly read the modes and write the - flags. -

- Concern about side effects may inhibit code motion and removal of seemingly useless - code. For example, in -

-          #include <fenv.h>
-          #pragma STDC FENV_ACCESS ON
-          void f(double x)
-          {
-               /* ... */
-               for (i = 0; i < n; i++) x + 1;
-               /* ... */
-          }
-
- x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop - body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of - course these optimizations are valid if the implementation can rule out the nettlesome - cases.) -

- This specification does not require support for trap handlers that maintain information - about the order or count of floating-point exceptions. Therefore, between function calls, - floating-point exceptions need not be precise: the actual order and number of occurrences - of floating-point exceptions (> 1) may vary from what the source code expresses. Thus, - - the preceding loop could be treated as -

-          if (0 < n) x + 1;
-
- -

Contents -

F.9.2 Expression transformations

-

- x/2 <-> x x 0.5 Although similar transformations involving inexact constants -

-                        generally do not yield numerically equivalent expressions, if the
-                        constants are exact then such transformations can be made on
-                        IEC 60559 machines and others that round perfectly.
-
- 1 x x and x/1 -> x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559 -
-                   machines, among others).355)
-
- x/x -> 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero, -
-                        infinite, or NaN.
-
- x - y <-> x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on -
-                        IEC 60559 machines, among others).
-
- x - y <-> -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1 -
-                        is +0 but -(1 - 1) is -0 (in the default rounding direction).356)
-
- x - x -> 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or -
-                        infinite.
-
- 0 x x -> 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN, -
-                        infinite, or -0.
-
- x+0-> x The expressions x + 0 and x are not equivalent if x is -0, because -
-                        (-0) + (+0) yields +0 (in the default rounding direction), not -0.
-
- x-0-> x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but -
-                        +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the
-                        FENV_ACCESS pragma is ''off'', promising default rounding, then
-                        the implementation can replace x - 0 by x, even if x might be zero.
-
- -x <-> 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because -
-                        -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is
-                        downward).
-
- - - -

Footnotes -

355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and - other transformations that remove arithmetic operators. - -

356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities. - Examples include: - -

-    1/(1/ (+-) (inf)) is (+-) (inf)
-
- and - -
-    conj(csqrt(z)) is csqrt(conj(z)),
-
- for complex z. - - -

Contents -

F.9.3 Relational operators

-

- x != x -> false The expression x != x is true if x is a NaN. - x = x -> true The expression x = x is false if x is a NaN. - x < y -> isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these -

-                expressions are not equivalent because of side effects when x or y is a
-                NaN and the state of the FENV_ACCESS pragma is ''on''. This
-                transformation, which would be desirable if extra code were required
-                to cause the ''invalid'' floating-point exception for unordered cases,
-                could be performed provided the state of the FENV_ACCESS pragma
-                is ''off''.
-
- The sense of relational operators shall be maintained. This includes handling unordered - cases as expressed by the source code. -

- EXAMPLE -

-          // calls g and raises ''invalid'' if a and b are unordered
-          if (a < b)
-                  f();
-          else
-                  g();
-
- is not equivalent to -
-          // calls f and raises ''invalid'' if a and b are unordered
-          if (a >= b)
-                  g();
-          else
-                  f();
-
- nor to -
-          // calls f without raising ''invalid'' if a and b are unordered
-          if (isgreaterequal(a,b))
-                  g();
-          else
-                  f();
-
- nor, unless the state of the FENV_ACCESS pragma is ''off'', to -
-          // calls g without raising ''invalid'' if a and b are unordered
-          if (isless(a,b))
-                  f();
-          else
-                  g();
-
- but is equivalent to - -
-         if (!(a < b))
-               g();
-         else
-               f();
-
- - -

Contents -

F.9.4 Constant arithmetic

-

- The implementation shall honor floating-point exceptions raised by execution-time - constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4 - and F.8.5.) An operation on constants that raises no floating-point exception can be - folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a - further check is required to assure that changing the rounding direction to downward does - not alter the sign of the result,357) and implementations that support dynamic rounding - precision modes shall assure further that the result of the operation raises no floating- - point exception when converted to the semantic type of the operation. - -

Footnotes -

357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward. - - -

Contents -

F.10 Mathematics <math.h>

-

- This subclause contains specifications of <math.h> facilities that are particularly suited - for IEC 60559 implementations. -

- The Standard C macro HUGE_VAL and its float and long double analogs, - HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive - infinities. -

- Special cases for functions in <math.h> are covered directly or indirectly by - IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The - other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and - (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags - in a manner consistent with the basic arithmetic operations covered by IEC 60559. -

- The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a - nonzero value. -

- The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in - subsequent subclauses of this annex. -

- The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of - rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value - whose magnitude is too large. -

- The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially - subnormal or zero) and suffers loss of accuracy.358) - - - -

- Whether or when library functions raise the ''inexact'' floating-point exception is - unspecified, unless explicitly specified otherwise. -

- Whether or when library functions raise an undeserved ''underflow'' floating-point - exception is unspecified.359) Otherwise, as implied by F.8.6, the <math.h> functions do - not raise spurious floating-point exceptions (detectable by the user), other than the - ''inexact'' floating-point exception. -

- Whether the functions honor the rounding direction mode is implementation-defined, - unless explicitly specified otherwise. -

- Functions with a NaN argument return a NaN result and raise no floating-point exception, - except where stated otherwise. -

- The specifications in the following subclauses append to the definitions in <math.h>. - For families of functions, the specifications apply to all of the functions even though only - the principal function is shown. Unless otherwise specified, where the symbol ''(+-)'' - occurs in both an argument and the result, the result has the same sign as the argument. -

Recommended practice -

- If a function with one or more NaN arguments returns a NaN result, the result should be - the same as one of the NaN arguments (after possible type conversion), except perhaps - for the sign. - -

Footnotes -

358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on - when the floating-point exception is raised. - -

359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if - avoiding them would be too costly. - - -

Contents -

F.10.1 Trigonometric functions

- -

Contents -

F.10.1.1 The acos functions
-

-

- -

Contents -

F.10.1.2 The asin functions
-

-

- -

Contents -

F.10.1.3 The atan functions
-

-

- -

Contents -

F.10.1.4 The atan2 functions
-

-

- -

Footnotes -

360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise - the ''divide-by-zero'' floating-point exception. - - -

Contents -

F.10.1.5 The cos functions
-

-

- -

Contents -

F.10.1.6 The sin functions
-

-

- -

Contents -

F.10.1.7 The tan functions
-

-

- -

Contents -

F.10.2 Hyperbolic functions

- -

Contents -

F.10.2.1 The acosh functions
-

-

- -

Contents -

F.10.2.2 The asinh functions
-

-

- -

Contents -

F.10.2.3 The atanh functions
-

-

- -

Contents -

F.10.2.4 The cosh functions
-

-

- -

Contents -

F.10.2.5 The sinh functions
-

-

- -

Contents -

F.10.2.6 The tanh functions
-

-

- -

Contents -

F.10.3 Exponential and logarithmic functions

- -

Contents -

F.10.3.1 The exp functions
-

-

- -

Contents -

F.10.3.2 The exp2 functions
-

-

- -

Contents -

F.10.3.3 The expm1 functions
-

-

- -

Contents -

F.10.3.4 The frexp functions
-

-

-

- frexp raises no floating-point exceptions. -

- When the radix of the argument is a power of 2, the returned value is exact and is - independent of the current rounding direction mode. -

- On a binary system, the body of the frexp function might be -

-         {
-                *exp = (value == 0) ? 0 : (int)(1 + logb(value));
-                return scalbn(value, -(*exp));
-         }
-
- -

Contents -

F.10.3.5 The ilogb functions
-

- When the correct result is representable in the range of the return type, the returned value - is exact and is independent of the current rounding direction mode. -

- If the correct result is outside the range of the return type, the numeric result is - unspecified and the ''invalid'' floating-point exception is raised. - - -

Contents -

F.10.3.6 The ldexp functions
-

- On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp). - -

Contents -

F.10.3.7 The log functions
-

-

- -

Contents -

F.10.3.8 The log10 functions
-

-

- -

Contents -

F.10.3.9 The log1p functions
-

-

- -

Contents -

F.10.3.10 The log2 functions
-

-

- -

Contents -

F.10.3.11 The logb functions
-

-

-

- The returned value is exact and is independent of the current rounding direction mode. - - -

Contents -

F.10.3.12 The modf functions
-

-

-

- The returned values are exact and are independent of the current rounding direction - mode. -

- modf behaves as though implemented by -

-         #include <math.h>
-         #include <fenv.h>
-         #pragma STDC FENV_ACCESS ON
-         double modf(double value, double *iptr)
-         {
-              int save_round = fegetround();
-              fesetround(FE_TOWARDZERO);
-              *iptr = nearbyint(value);
-              fesetround(save_round);
-              return copysign(
-                   isinf(value) ? 0.0 :
-                        value - (*iptr), value);
-         }
-
- -

Contents -

F.10.3.13 The scalbn and scalbln functions
-

-

-

- If the calculation does not overflow or underflow, the returned value is exact and - independent of the current rounding direction mode. - - -

Contents -

F.10.4 Power and absolute value functions

- -

Contents -

F.10.4.1 The cbrt functions
-

-

- -

Contents -

F.10.4.2 The fabs functions
-

-

-

- The returned value is exact and is independent of the current rounding direction mode. - -

Contents -

F.10.4.3 The hypot functions
-

-

- -

Contents -

F.10.4.4 The pow functions
-

-

- -

Contents -

F.10.4.5 The sqrt functions
-

- sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value - is dependent on the current rounding direction mode. - -

Contents -

F.10.5 Error and gamma functions

- -

Contents -

F.10.5.1 The erf functions
-

-

- -

Contents -

F.10.5.2 The erfc functions
-

-

- -

Contents -

F.10.5.3 The lgamma functions
-

-

- -

Contents -

F.10.5.4 The tgamma functions
-

-

- -

Contents -

F.10.6 Nearest integer functions

- -

Contents -

F.10.6.1 The ceil functions
-

-

-

- The returned value is independent of the current rounding direction mode. -

- The double version of ceil behaves as though implemented by -

-        #include <math.h>
-        #include <fenv.h>
-        #pragma STDC FENV_ACCESS ON
-        double ceil(double x)
-        {
-             double result;
-             int save_round = fegetround();
-             fesetround(FE_UPWARD);
-             result = rint(x); // or nearbyint instead of rint
-             fesetround(save_round);
-             return result;
-        }
-
-

- The ceil functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer arguments, as this implementation does. - -

Contents -

F.10.6.2 The floor functions
-

-

-

- The returned value and is independent of the current rounding direction mode. -

- See the sample implementation for ceil in F.10.6.1. The floor functions may, but are - not required to, raise the ''inexact'' floating-point exception for finite non-integer - arguments, as that implementation does. - -

Contents -

F.10.6.3 The nearbyint functions
-

- The nearbyint functions use IEC 60559 rounding according to the current rounding - direction. They do not raise the ''inexact'' floating-point exception if the result differs in - value from the argument. -

- -

Contents -

F.10.6.4 The rint functions
-

- The rint functions differ from the nearbyint functions only in that they do raise the - ''inexact'' floating-point exception if the result differs in value from the argument. - -

Contents -

F.10.6.5 The lrint and llrint functions
-

- The lrint and llrint functions provide floating-to-integer conversion as prescribed - by IEC 60559. They round according to the current rounding direction. If the rounded - value is outside the range of the return type, the numeric result is unspecified and the - ''invalid'' floating-point exception is raised. When they raise no other floating-point - exception and the result differs from the argument, they raise the ''inexact'' floating-point - exception. - -

Contents -

F.10.6.6 The round functions
-

-

-

- The returned value is independent of the current rounding direction mode. -

- The double version of round behaves as though implemented by -

-         #include <math.h>
-         #include <fenv.h>
-         #pragma STDC FENV_ACCESS ON
-         double round(double x)
-         {
-              double result;
-              fenv_t save_env;
-              feholdexcept(&save_env);
-              result = rint(x);
-              if (fetestexcept(FE_INEXACT)) {
-                   fesetround(FE_TOWARDZERO);
-                   result = rint(copysign(0.5 + fabs(x), x));
-              }
-              feupdateenv(&save_env);
-              return result;
-         }
-
- The round functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer numeric arguments, as this implementation does. - - -

Contents -

F.10.6.7 The lround and llround functions
-

- The lround and llround functions differ from the lrint and llrint functions - with the default rounding direction just in that the lround and llround functions - round halfway cases away from zero and need not raise the ''inexact'' floating-point - exception for non-integer arguments that round to within the range of the return type. - -

Contents -

F.10.6.8 The trunc functions
-

- The trunc functions use IEC 60559 rounding toward zero (regardless of the current - rounding direction). The returned value is exact. -

-

- The returned value is independent of the current rounding direction mode. The trunc - functions may, but are not required to, raise the ''inexact'' floating-point exception for - finite non-integer arguments. - -

Contents -

F.10.7 Remainder functions

- -

Contents -

F.10.7.1 The fmod functions
-

-

-

- When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. -

- The double version of fmod behaves as though implemented by - -

-        #include <math.h>
-        #include <fenv.h>
-        #pragma STDC FENV_ACCESS ON
-        double fmod(double x, double y)
-        {
-             double result;
-             result = remainder(fabs(x), (y = fabs(y)));
-             if (signbit(result)) result += y;
-             return copysign(result, x);
-        }
-
- -

Contents -

F.10.7.2 The remainder functions
-

- The remainder functions are fully specified as a basic arithmetic operation in - IEC 60559. -

- When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - -

Contents -

F.10.7.3 The remquo functions
-

- The remquo functions follow the specifications for the remainder functions. They - have no further specifications special to IEC 60559 implementations. -

- When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - -

Contents -

F.10.8 Manipulation functions

- -

Contents -

F.10.8.1 The copysign functions
-

- copysign is specified in the Appendix to IEC 60559. -

- The returned value is exact and is independent of the current rounding direction mode. - -

Contents -

F.10.8.2 The nan functions
-

- All IEC 60559 implementations support quiet NaNs, in all floating formats. -

- The returned value is exact and is independent of the current rounding direction mode. - -

Contents -

F.10.8.3 The nextafter functions
-

-

-

- Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - -

Contents -

F.10.8.4 The nexttoward functions
-

- No additional requirements beyond those on nextafter. -

- Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - - -

Contents -

F.10.9 Maximum, minimum, and positive difference functions

- -

Contents -

F.10.9.1 The fdim functions
-

- No additional requirements. - -

Contents -

F.10.9.2 The fmax functions
-

- If just one argument is a NaN, the fmax functions return the other argument (if both - arguments are NaNs, the functions return a NaN). -

- The returned value is exact and is independent of the current rounding direction mode. -

- The body of the fmax function might be361) -

-        { return (isgreaterequal(x, y) ||
-             isnan(y)) ? x : y; }
-
- -

Footnotes -

361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would - return +0; however, implementation in software might be impractical. - - -

Contents -

F.10.9.3 The fmin functions
-

- The fmin functions are analogous to the fmax functions (see F.10.9.2). -

- The returned value is exact and is independent of the current rounding direction mode. - -

Contents -

F.10.10 Floating multiply-add

- -

Contents -

F.10.10.1 The fma functions
-

-

- -

Contents -

F.10.11 Comparison macros

-

- Relational operators and their corresponding comparison macros (7.12.14) produce - equivalent result values, even if argument values are represented in wider formats. Thus, - comparison macro arguments represented in formats wider than their semantic types are - not converted to the semantic types, unless the wide evaluation method converts operands - of relational operators to their semantic types. The standard wide evaluation methods - characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert - operands of relational operators to their semantic types. - - -

Contents -

Annex G

-
-                                       (normative)
-                IEC 60559-compatible complex arithmetic
-
- -

Contents -

G.1 Introduction

-

- This annex supplements annex F to specify complex arithmetic for compatibility with - IEC 60559 real floating-point arithmetic. An implementation that defines * - __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362) - -

Footnotes -

362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform - to these specifications. - - -

Contents -

G.2 Types

-

- There is a new keyword _Imaginary, which is used to specify imaginary types. It is - used as a type specifier within declaration specifiers in the same way as _Complex is - (thus, _Imaginary float is a valid type name). -

- There are three imaginary types, designated as float _Imaginary, double - _Imaginary, and long double _Imaginary. The imaginary types (along with - the real floating and complex types) are floating types. -

- For imaginary types, the corresponding real type is given by deleting the keyword - _Imaginary from the type name. -

- Each imaginary type has the same representation and alignment requirements as the - corresponding real type. The value of an object of imaginary type is the value of the real - representation times the imaginary unit. -

- The imaginary type domain comprises the imaginary types. - -

Contents -

G.3 Conventions

-

- A complex or imaginary value with at least one infinite part is regarded as an infinity - (even if its other part is a NaN). A complex or imaginary value is a finite number if each - of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is - a zero if each of its parts is a zero. - - - - - - -

Contents -

G.4 Conversions

- -

Contents -

G.4.1 Imaginary types

-

- Conversions among imaginary types follow rules analogous to those for real floating - types. - -

Contents -

G.4.2 Real and imaginary

-

- When a value of imaginary type is converted to a real type other than _Bool,363) the - result is a positive zero. -

- When a value of real type is converted to an imaginary type, the result is a positive - imaginary zero. - -

Footnotes -

363) See 6.3.1.2. - - -

Contents -

G.4.3 Imaginary and complex

-

- When a value of imaginary type is converted to a complex type, the real part of the - complex result value is a positive zero and the imaginary part of the complex result value - is determined by the conversion rules for the corresponding real types. -

- When a value of complex type is converted to an imaginary type, the real part of the - complex value is discarded and the value of the imaginary part is converted according to - the conversion rules for the corresponding real types. - -

Contents -

G.5 Binary operators

-

- The following subclauses supplement 6.5 in order to specify the type of the result for an - operation with an imaginary operand. -

- For most operand types, the value of the result of a binary operator with an imaginary or - complex operand is completely determined, with reference to real arithmetic, by the usual - mathematical formula. For some operand types, the usual mathematical formula is - problematic because of its treatment of infinities and because of undue overflow or - underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is - not completely determined. - - - - - - -

Contents -

G.5.1 Multiplicative operators

-

Semantics -

- If one operand has real type and the other operand has imaginary type, then the result has - imaginary type. If both operands have imaginary type, then the result has real type. (If - either operand has complex type, then the result has complex type.) -

- If the operands are not both complex, then the result and floating-point exception - behavior of the * operator is defined by the usual mathematical formula: -

-        *                  u                   iv                 u + iv
-
- -
-        x                  xu                i(xv)            (xu) + i(xv)
-
- -
-        iy               i(yu)                -yv            (-yv) + i(yu)
-
- -
-        x + iy       (xu) + i(yu)        (-yv) + i(xv)
-
-

- If the second operand is not complex, then the result and floating-point exception - behavior of the / operator is defined by the usual mathematical formula: -

-        /                   u                       iv
-
- -
-        x                  x/u                 i(-x/v)
-
- -
-        iy               i(y/u)                     y/v
-
- -
-        x + iy       (x/u) + i(y/u)        (y/v) + i(-x/v)
-
-

- The * and / operators satisfy the following infinity properties for all real, imaginary, and - complex operands:364) -

-

- If both operands of the * operator are complex or if the second operand of the / operator - is complex, the operator raises floating-point exceptions if appropriate for the calculation - of the parts of the result, and may raise spurious floating-point exceptions. -

- EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note - that the imaginary unit I has imaginary type (see G.6). - -

-          #include <math.h>
-          #include <complex.h>
-          /* Multiply z * w ... */
-          double complex _Cmultd(double complex z, double complex w)
-          {
-                 #pragma STDC FP_CONTRACT OFF
-                 double a, b, c, d, ac, bd, ad, bc, x, y;
-                 a = creal(z); b = cimag(z);
-                 c = creal(w); d = cimag(w);
-                 ac = a * c;       bd = b * d;
-                 ad = a * d;       bc = b * c;
-                 x = ac - bd; y = ad + bc;
-                 if (isnan(x) && isnan(y)) {
-                         /* Recover infinities that computed as NaN+iNaN ... */
-                         int recalc = 0;
-                         if ( isinf(a) || isinf(b) ) { // z is infinite
-                                 /* "Box" the infinity and change NaNs in the other factor to 0 */
-                                 a = copysign(isinf(a) ? 1.0 : 0.0, a);
-                                 b = copysign(isinf(b) ? 1.0 : 0.0, b);
-                                 if (isnan(c)) c = copysign(0.0, c);
-                                 if (isnan(d)) d = copysign(0.0, d);
-                                 recalc = 1;
-                         }
-                         if ( isinf(c) || isinf(d) ) { // w is infinite
-                                 /* "Box" the infinity and change NaNs in the other factor to 0 */
-                                 c = copysign(isinf(c) ? 1.0 : 0.0, c);
-                                 d = copysign(isinf(d) ? 1.0 : 0.0, d);
-                                 if (isnan(a)) a = copysign(0.0, a);
-                                 if (isnan(b)) b = copysign(0.0, b);
-                                 recalc = 1;
-                         }
-                         if (!recalc && (isinf(ac) || isinf(bd) ||
-                                                isinf(ad) || isinf(bc))) {
-                                 /* Recover infinities from overflow by changing NaNs to 0 ... */
-                                 if (isnan(a)) a = copysign(0.0, a);
-                                 if (isnan(b)) b = copysign(0.0, b);
-                                 if (isnan(c)) c = copysign(0.0, c);
-                                 if (isnan(d)) d = copysign(0.0, d);
-                                 recalc = 1;
-                         }
-                         if (recalc) {
-                                   x = INFINITY * ( a * c - b * d );
-                                   y = INFINITY * ( a * d + b * c );
-                        }
-                  }
-                  return x + I * y;
-         }
-
-

- This implementation achieves the required treatment of infinities at the cost of only one isnan test in - ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur. - -

- EXAMPLE 2 Division of two double _Complex operands could be implemented as follows. - -

-         #include <math.h>
-         #include <complex.h>
-         /* Divide z / w ... */
-         double complex _Cdivd(double complex z, double complex w)
-         {
-                #pragma STDC FP_CONTRACT OFF
-                double a, b, c, d, logbw, denom, x, y;
-                int ilogbw = 0;
-                a = creal(z); b = cimag(z);
-                c = creal(w); d = cimag(w);
-                logbw = logb(fmax(fabs(c), fabs(d)));
-                if (logbw == INFINITY) {
-                       ilogbw = (int)logbw;
-                       c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);
-                }
-                denom = c * c + d * d;
-                x = scalbn((a * c + b * d) / denom, -ilogbw);
-                y = scalbn((b * c - a * d) / denom, -ilogbw);
-                  /* Recover infinities and zeros that computed as NaN+iNaN;                 */
-                  /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */
-                  if (isnan(x) && isnan(y)) {
-                        if ((denom == 0.0) &&
-                              (!isnan(a) || !isnan(b))) {
-                              x = copysign(INFINITY, c) * a;
-                              y = copysign(INFINITY, c) * b;
-                        }
-                        else if ((isinf(a) || isinf(b)) &&
-                              isfinite(c) && isfinite(d)) {
-                              a = copysign(isinf(a) ? 1.0 : 0.0,                        a);
-                              b = copysign(isinf(b) ? 1.0 : 0.0,                        b);
-                              x = INFINITY * ( a * c + b * d );
-                              y = INFINITY * ( b * c - a * d );
-                        }
-                        else if (isinf(logbw) &&
-                              isfinite(a) && isfinite(b)) {
-                              c = copysign(isinf(c) ? 1.0 : 0.0,                        c);
-                              d = copysign(isinf(d) ? 1.0 : 0.0,                        d);
-                              x = 0.0 * ( a * c + b * d );
-                              y = 0.0 * ( b * c - a * d );
-                        }
-                  }
-                  return x + I * y;
-         }
-
-

- Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than - for multiplication. In the spirit of the multiplication example above, this code does not defend against - overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of - with division, provides better roundoff characteristics. - - -

Footnotes -

364) These properties are already implied for those cases covered in the tables, but are required for all cases - (at least where the state for CX_LIMITED_RANGE is ''off''). - - -

Contents -

G.5.2 Additive operators

-

Semantics -

- If both operands have imaginary type, then the result has imaginary type. (If one operand - has real type and the other operand has imaginary type, or if either operand has complex - type, then the result has complex type.) -

- In all cases the result and floating-point exception behavior of a + or - operator is defined - by the usual mathematical formula: -

-        + or -              u                       iv                    u + iv
-
- -
-        x                 x(+-)u                     x (+-) iv              (x (+-) u) (+-) iv
-
- -
-        iy               (+-)u + iy                 i(y (+-) v)             (+-)u + i(y (+-) v)
-
- -
-        x + iy         (x (+-) u) + iy            x + i(y (+-) v)        (x (+-) u) + i(y (+-) v)
-
- -

Contents -

G.6 Complex arithmetic <complex.h>

-

- The macros -

-         imaginary
-
- and -
-         _Imaginary_I
-
- are defined, respectively, as _Imaginary and a constant expression of type const - float _Imaginary with the value of the imaginary unit. The macro -
-         I
-
- is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding - the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro - imaginary. -

- This subclause contains specifications for the <complex.h> functions that are - particularly suited to IEC 60559 implementations. For families of functions, the - specifications apply to all of the functions even though only the principal function is - - shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument - and the result, the result has the same sign as the argument. -

- The functions are continuous onto both sides of their branch cuts, taking into account the - sign of zero. For example, csqrt(-2 (+-) i0) = (+-)i(sqrt)2. - -

- Since complex and imaginary values are composed of real values, each function may be - regarded as computing real values from real values. Except as noted, the functions treat - real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a - manner consistent with the specifications for real functions in F.10.365) -

- The functions cimag, conj, cproj, and creal are fully specified for all - implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating- - point exceptions. -

- Each of the functions cabs and carg is specified by a formula in terms of a real - function (whose special cases are covered in annex F): -

-         cabs(x + iy) = hypot(x, y)
-         carg(x + iy) = atan2(y, x)
-
-

- Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by - a formula in terms of other complex functions (whose special cases are specified below): -

-         casin(z)        =   -i casinh(iz)
-         catan(z)        =   -i catanh(iz)
-         ccos(z)         =   ccosh(iz)
-         csin(z)         =   -i csinh(iz)
-         ctan(z)         =   -i ctanh(iz)
-
-

- For the other functions, the following subclauses specify behavior for special cases, - including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For - families of functions, the specifications apply to all of the functions even though only the - principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the - specifications for the upper half-plane imply the specifications for the lower half-plane; if - the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the - specifications for the first quadrant imply the specifications for the other three quadrants. -

- In the following subclauses, cis(y) is defined as cos(y) + i sin(y). - - - - - - -

Footnotes -

365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its - other part is a NaN. - - -

Contents -

G.6.1 Trigonometric functions

- -

Contents -

G.6.1.1 The cacos functions
-

-

- -

Contents -

G.6.2 Hyperbolic functions

- -

Contents -

G.6.2.1 The cacosh functions
-

-

- -

Contents -

G.6.2.2 The casinh functions
-

-

- -

Contents -

G.6.2.3 The catanh functions
-

-

- -

Contents -

G.6.2.4 The ccosh functions
-

-

- -

Contents -

G.6.2.5 The csinh functions
-

-

- -

Contents -

G.6.2.6 The ctanh functions
-

-

- -

Contents -

G.6.3 Exponential and logarithmic functions

- -

Contents -

G.6.3.1 The cexp functions
-

-

- -

Contents -

G.6.3.2 The clog functions
-

-

- -

Contents -

G.6.4 Power and absolute-value functions

- -

Contents -

G.6.4.1 The cpow functions
-

- The cpow functions raise floating-point exceptions if appropriate for the calculation of - the parts of the result, and may also raise spurious floating-point exceptions.366) - -

Footnotes -

366) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding - implementations that treat special cases more carefully. - - -

Contents -

G.6.4.2 The csqrt functions
-

-

- -

Contents -

G.7 Type-generic math <tgmath.h>

-

- Type-generic macros that accept complex arguments also accept imaginary arguments. If - an argument is imaginary, the macro expands to an expression whose type is real, - imaginary, or complex, as appropriate for the particular function: if the argument is - imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the - types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and - the types of the others are complex. -

- Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh, - sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real - functions: - -

-         cos(iy)     =   cosh(y)
-         sin(iy)     =   i sinh(y)
-         tan(iy)     =   i tanh(y)
-         cosh(iy)    =   cos(y)
-         sinh(iy)    =   i sin(y)
-         tanh(iy)    =   i tan(y)
-         asin(iy)    =   i asinh(y)
-         atan(iy)    =   i atanh(y)
-         asinh(iy)   =   i asin(y)
-         atanh(iy)   =   i atan(y)
-
- -

Contents -

Annex H

-
-                                     (informative)
-                     Language independent arithmetic
-
- -

Contents -

H.1 Introduction

-

- This annex documents the extent to which the C language supports the ISO/IEC 10967-1 - standard for language-independent arithmetic (LIA-1). LIA-1 is more general than - IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics. - -

Contents -

H.2 Types

-

- The relevant C arithmetic types meet the requirements of LIA-1 types if an - implementation adds notification of exceptional arithmetic operations and meets the 1 - unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8). - -

Contents -

H.2.1 Boolean type

-

- The LIA-1 data type Boolean is implemented by the C data type bool with values of - true and false, all from <stdbool.h>. - -

Contents -

H.2.2 Integer types

-

- The signed C integer types int, long int, long long int, and the corresponding - unsigned types are compatible with LIA-1. If an implementation adds support for the - LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are - LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense - in that overflows or out-of-bounds results silently wrap. An implementation that defines - signed integer types as also being modulo need not detect integer overflow, in which case, - only integer divide-by-zero need be detected. -

- The parameters for the integer data types can be accessed by the following: - maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX, -

-               ULLONG_MAX
-
- minint INT_MIN, LONG_MIN, LLONG_MIN -

- The parameter ''bounded'' is always true, and is not provided. The parameter ''minint'' - is always 0 for the unsigned types, and is not provided for those types. - - -

Contents -

H.2.2.1 Integer operations
-

- The integer operations on integer types are the following: - addI x + y - subI x - y - mulI x * y - divI, divtI x / y - remI, remtI x % y - negI -x - absI abs(x), labs(x), llabs(x) - eqI x == y - neqI x != y - lssI x < y - leqI x <= y - gtrI x > y - geqI x >= y - where x and y are expressions of the same integer type. - -

Contents -

H.2.3 Floating-point types

-

- The C floating-point types float, double, and long double are compatible with - LIA-1. If an implementation adds support for the LIA-1 exceptional values - ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant - with LIA-1. An implementation that uses IEC 60559 floating-point formats and - operations (see annex F) along with IEC 60559 status flags and traps has LIA-1 - conformant types. - -

Contents -

H.2.3.1 Floating-point parameters
-

- The parameters for a floating point data type can be accessed by the following: - r FLT_RADIX - p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG - emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP - emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP -

- The derived constants for the floating point types are accessed by the following: - - fmax FLT_MAX, DBL_MAX, LDBL_MAX - fminN FLT_MIN, DBL_MIN, LDBL_MIN - epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON - rnd_style FLT_ROUNDS - -

Contents -

H.2.3.2 Floating-point operations
-

- The floating-point operations on floating-point types are the following: - addF x + y - subF x - y - mulF x * y - divF x / y - negF -x - absF fabsf(x), fabs(x), fabsl(x) - exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x) - scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n), -

-               scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
-
- intpartF modff(x, &y), modf(x, &y), modfl(x, &y) - fractpartF modff(x, &y), modf(x, &y), modfl(x, &y) - eqF x == y - neqF x != y - lssF x < y - leqF x <= y - gtrF x > y - geqF x >= y - where x and y are expressions of the same floating point type, n is of type int, and li - is of type long int. - -

Contents -

H.2.3.3 Rounding styles
-

- The C Standard requires all floating types to use the same radix and rounding style, so - that only one identifier for each is provided to map to LIA-1. -

- The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles: - truncate FLT_ROUNDS == 0 - - nearest FLT_ROUNDS == 1 - other FLT_ROUNDS != 0 && FLT_ROUNDS != 1 - provided that an implementation extends FLT_ROUNDS to cover the rounding style used - in all relevant LIA-1 operations, not just addition as in C. - -

Contents -

H.2.4 Type conversions

-

- The LIA-1 type conversions are the following type casts: - cvtI' -> I (int)i, (long int)i, (long long int)i, -

-               (unsigned int)i, (unsigned long int)i,
-               (unsigned long long int)i
-
- cvtF -> I (int)x, (long int)x, (long long int)x, -
-               (unsigned int)x, (unsigned long int)x,
-               (unsigned long long int)x
-
- cvtI -> F (float)i, (double)i, (long double)i - cvtF' -> F (float)x, (double)x, (long double)x -

- In the above conversions from floating to integer, the use of (cast)x can be replaced with - (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x), - (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer - conversion functions, lrint(), llrint(), lround(), and llround(), can be - used. They all meet LIA-1's requirements on floating to integer rounding for in-range - values. For out-of-range values, the conversions shall silently wrap for the modulo types. -

- The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g., - fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x), - 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0 - to 65535.0 which can then be cast to unsigned short int. But, the - remainder() function is not useful for doing silent wrapping to signed integer types, - e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the - range -32767.0 to +32768.0 which is not, in general, in the range of signed short - int. -

- C's conversions (casts) from floating-point to floating-point can meet LIA-1 - requirements if an implementation uses round-to-nearest (IEC 60559 default). -

- C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an - implementation uses round-to-nearest. - - -

Contents -

H.3 Notification

-

- Notification is the process by which a user or program is informed that an exceptional - arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C - allows an implementation to cause a notification to occur when any arithmetic operation - returns an exceptional value as defined in LIA-1 clause 5. - -

Contents -

H.3.1 Notification alternatives

-

- LIA-1 requires at least the following two alternatives for handling of notifications: - setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and- - resume. -

- An implementation need only support a given notification alternative for the entire - program. An implementation may support the ability to switch between notification - alternatives during execution, but is not required to do so. An implementation can - provide separate selection for each kind of notification, but this is not required. -

- C allows an implementation to provide notification. C's SIGFPE (for traps) and - FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators) - can provide LIA-1 notification. -

- C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can - provide trap-and-terminate behavior, except for those LIA-1 operations implemented by - math library function calls. User-provided signal handlers for SIGFPE allow for trap- - and-resume behavior with the same constraint. - -

Contents -

H.3.1.1 Indicators
-

- C's <fenv.h> status flags are compatible with the LIA-1 indicators. -

- The following mapping is for floating-point types: - undefined FE_INVALID, FE_DIVBYZERO - floating_overflow FE_OVERFLOW - underflow FE_UNDERFLOW -

- The floating-point indicator interrogation and manipulation operations are: - set_indicators feraiseexcept(i) - clear_indicators feclearexcept(i) - test_indicators fetestexcept(i) - current_indicators fetestexcept(FE_ALL_EXCEPT) - where i is an expression of type int representing a subset of the LIA-1 indicators. -

- C allows an implementation to provide the following LIA-1 required behavior: at - program termination if any indicator is set the implementation shall send an unambiguous - - and ''hard to ignore'' message (see LIA-1 subclause 6.1.2) -

- LIA-1 does not make the distinction between floating-point and integer for ''undefined''. - This documentation makes that distinction because <fenv.h> covers only the floating- - point indicators. - -

Contents -

H.3.1.2 Traps
-

- C is compatible with LIA-1's trap requirements for arithmetic operations, but not for - math library functions (which are not permitted to invoke a user's signal handler for - SIGFPE). An implementation can provide an alternative of notification through - termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3). -

- LIA-1 does not require that traps be precise. -

- C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions, - if there is any signal raised for them. -

- C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic - exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism - allows trap-and-terminate (either default implementation behavior or user replacement for - it) or trap-and-resume, at the programmer's option. - - -

Contents -

Annex I

-
-                                     (informative)
-                                Common warnings
-
-

- An implementation may generate warnings in many situations, none of which are - specified as part of this International Standard. The following are a few of the more - common situations. -

-

- -

Contents -

Annex J

-
-                                      (informative)
-                                   Portability issues
-
-

- This annex collects some information about portability that appears in this International - Standard. - -

Contents -

J.1 Unspecified behavior

-

- The following are unspecified: -

- -

Contents -

J.2 Undefined behavior

-

- The behavior is undefined in the following circumstances: -

- -

Contents -

J.3 Implementation-defined behavior

-

- A conforming implementation is required to document its choice of behavior in each of - the areas listed in this subclause. The following are implementation-defined: - - -

Contents -

J.3.1 Translation

-

-

- -

Contents -

J.3.2 Environment

-

-

- -

Contents -

J.3.3 Identifiers

-

-

- -

Contents -

J.3.4 Characters

-

-

- -

Contents -

J.3.5 Integers

-

-

- -

Contents -

J.3.6 Floating point

-

-

- -

Contents -

J.3.7 Arrays and pointers

-

-

- -

Contents -

J.3.8 Hints

-

-

- -

Contents -

J.3.9 Structures, unions, enumerations, and bit-fields

-

-

- -

Contents -

J.3.10 Qualifiers

-

-

- -

Contents -

J.3.11 Preprocessing directives

-

-

- -

Contents -

J.3.12 Library functions

-

-

- -

Contents -

J.3.13 Architecture

-

-

- -

Contents -

J.4 Locale-specific behavior

-

- The following characteristics of a hosted environment are locale-specific and are required - to be documented by the implementation: -

- -

Contents -

J.5 Common extensions

-

- The following extensions are widely used in many systems, but are not portable to all - implementations. The inclusion of any extension that may cause a strictly conforming - program to become invalid renders an implementation nonconforming. Examples of such - extensions are new keywords, extra library functions declared in standard headers, or - predefined macros with names that do not begin with an underscore. - -

Contents -

J.5.1 Environment arguments

-

- In a hosted environment, the main function receives a third argument, char *envp[], - that points to a null-terminated array of pointers to char, each of which points to a string - that provides information about the environment for this execution of the program - (5.1.2.2.1). - -

Contents -

J.5.2 Specialized identifiers

-

- Characters other than the underscore _, letters, and digits, that are not part of the basic - source character set (such as the dollar sign $, or characters in national character sets) - may appear in an identifier (6.4.2). - -

Contents -

J.5.3 Lengths and cases of identifiers

-

- All characters in identifiers (with or without external linkage) are significant (6.4.2). - -

Contents -

J.5.4 Scopes of identifiers

-

- A function identifier, or the identifier of an object the declaration of which contains the - keyword extern, has file scope (6.2.1). - -

Contents -

J.5.5 Writable string literals

-

- String literals are modifiable (in which case, identical string literals should denote distinct - objects) (6.4.5). - - -

Contents -

J.5.6 Other arithmetic types

-

- Additional arithmetic types, such as __int128 or double double, and their - appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have - more range or precision than long double, may be used for evaluating expressions of - other floating types, and may be used to define float_t or double_t. - -

Contents -

J.5.7 Function pointer casts

-

- A pointer to an object or to void may be cast to a pointer to a function, allowing data to - be invoked as a function (6.5.4). -

- A pointer to a function may be cast to a pointer to an object or to void, allowing a - function to be inspected or modified (for example, by a debugger) (6.5.4). - -

Contents -

J.5.8 Extended bit-field types

-

- A bit-field may be declared with a type other than _Bool, unsigned int, or - signed int, with an appropriate maximum width (6.7.2.1). - -

Contents -

J.5.9 The fortran keyword

-

- The fortran function specifier may be used in a function declaration to indicate that - calls suitable for FORTRAN should be generated, or that a different representation for the - external name is to be generated (6.7.4). - -

Contents -

J.5.10 The asm keyword

-

- The asm keyword may be used to insert assembly language directly into the translator - output (6.8). The most common implementation is via a statement of the form: -

-        asm ( character-string-literal );
-
- -

Contents -

J.5.11 Multiple external definitions

-

- There may be more than one external definition for the identifier of an object, with or - without the explicit use of the keyword extern; if the definitions disagree, or more than - one is initialized, the behavior is undefined (6.9.2). - -

Contents -

J.5.12 Predefined macro names

-

- Macro names that do not begin with an underscore, describing the translation and - execution environments, are defined by the implementation before translation begins - (6.10.8). - - -

Contents -

J.5.13 Floating-point status flags

-

- If any floating-point status flags are set on normal termination after all calls to functions - registered by the atexit function have been made (see 7.22.4.4), the implementation - writes some diagnostics indicating the fact to the stderr stream, if it is still open, - -

Contents -

J.5.14 Extra arguments for signal handlers

-

- Handlers for specific signals are called with extra arguments in addition to the signal - number (7.14.1.1). - -

Contents -

J.5.15 Additional stream types and file-opening modes

-

- Additional mappings from files to streams are supported (7.21.2). -

- Additional file-opening modes may be specified by characters appended to the mode - argument of the fopen function (7.21.5.3). - -

Contents -

J.5.16 Defined file position indicator

-

- The file position indicator is decremented by each successful call to the ungetc or - ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10, - 7.28.3.10). - -

Contents -

J.5.17 Math error reporting

-

- Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors - instead of, or in addition to, setting errno or raising floating-point exceptions (7.3, - 7.12). - - -

Contents -

Annex K

-
-                                       (normative)
-                           Bounds-checking interfaces
-
- -

Contents -

K.1 Background

-

- Traditionally, the C Library has contained many functions that trust the programmer to - provide output character arrays big enough to hold the result being produced. Not only - do these functions not check that the arrays are big enough, they frequently lack the - information needed to perform such checks. While it is possible to write safe, robust, and - error-free code using the existing library, the library tends to promote programming styles - that lead to mysterious failures if a result is too big for the provided array. -

- A common programming style is to declare character arrays large enough to handle most - practical cases. However, if these arrays are not large enough to handle the resulting - strings, data can be written past the end of the array overwriting other data and program - structures. The program never gets any indication that a problem exists, and so never has - a chance to recover or to fail gracefully. -

- Worse, this style of programming has compromised the security of computers and - networks. Buffer overflows can often be exploited to run arbitrary code with the - permissions of the vulnerable (defective) program. -

- If the programmer writes runtime checks to verify lengths before calling library - functions, then those runtime checks frequently duplicate work done inside the library - functions, which discover string lengths as a side effect of doing their job. -

- This annex provides alternative library functions that promote safer, more secure - programming. The alternative functions verify that output buffers are large enough for - the intended result and return a failure indicator if they are not. Data is never written past - the end of an array. All string results are null terminated. -

- This annex also addresses another problem that complicates writing robust code: - functions that are not reentrant because they return pointers to static objects owned by the - function. Such functions can be troublesome since a previously returned result can - change if the function is called again, perhaps by another thread. - - -

Contents -

K.2 Scope

-

- This annex specifies a series of optional extensions that can be useful in the mitigation of - security vulnerabilities in programs, and comprise new functions, macros, and types - declared or defined in existing standard headers. -

- An implementation that defines __STDC_LIB_EXT1__ shall conform to the - specifications in this annex.367) -

- Subclause K.3 should be read as if it were merged into the parallel structure of named - subclauses of clause 7. - -

Footnotes -

367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these - specifications. - - -

Contents -

K.3 Library

- -

Contents -

K.3.1 Introduction

- -

Contents -

K.3.1.1 Standard headers
-

- The functions, macros, and types declared or defined in K.3 and its subclauses are not - declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 0 at the point in the source file - where the appropriate header is first included. -

- The functions, macros, and types declared or defined in K.3 and its subclauses are - declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 1 at the point in the source file - where the appropriate header is first included.368) -

- It is implementation-defined whether the functions, macros, and types declared or defined - in K.3 and its subclauses are declared or defined by their respective headers if - __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file - where the appropriate header is first included.369) -

- Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be - defined identically for all inclusions of any headers from subclause K.3. If - __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the - implementation shall issue a diagnostic as if a preprocessor error directive were used. - - - - -

Footnotes -

368) Future revisions of this International Standard may define meanings for other values of - __STDC_WANT_LIB_EXT1__. - -

369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in - headers. All other names are not reserved, and a conforming implementation is not permitted to use - them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an - unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the - implementation is not conforming. - - -

Contents -

K.3.1.2 Reserved identifiers
-

- Each macro name in any of the following subclauses is reserved for use as specified if it - is defined by any of its associated headers when included; unless explicitly stated - otherwise (see 7.1.4). -

- All identifiers with external linkage in any of the following subclauses are reserved for - use as identifiers with external linkage if any of them are used by the program. None of - them are reserved if none of them are used. -

- Each identifier with file scope listed in any of the following subclauses is reserved for use - as a macro name and as an identifier with file scope in the same name space if it is - defined by any of its associated headers when included. - -

Contents -

K.3.1.3 Use of errno
-

- An implementation may set errno for the functions defined in this annex, but is not - required to. - -

Contents -

K.3.1.4 Runtime-constraint violations
-

- Most functions in this annex include as part of their specification a list of runtime- - constraints. These runtime-constraints are requirements on the program using the - library.370) -

- Implementations shall verify that the runtime-constraints for a function are not violated - by the program. If a runtime-constraint is violated, the implementation shall call the - currently registered runtime-constraint handler (see set_constraint_handler_s - in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library - function result in only one call to the runtime-constraint handler. It is unspecified which - one of the multiple runtime-constraint violations cause the handler to be called. -

- If the runtime-constraints section for a function states an action to be performed when a - runtime-constraint violation occurs, the function shall perform the action before calling - the runtime-constraint handler. If the runtime-constraints section lists actions that are - prohibited when a runtime-constraint violation occurs, then such actions are prohibited to - the function both before calling the handler and after the handler returns. -

- The runtime-constraint handler might not return. If the handler does return, the library - function whose runtime-constraint was violated shall return some indication of failure as - given by the returns section in the function's specification. - - - - - -

Footnotes -

370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still - exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a - runtime-constraint violation by calling the runtime-constraint handler. This license comes directly - from the definition of undefined behavior. - - -

Contents -

K.3.2 Errors <errno.h>

-

- The header <errno.h> defines a type. -

- The type is -

-          errno_t
-
- which is type int.371) - -

Footnotes -

371) As a matter of programming style, errno_t may be used as the type of something that deals only - with the values that might be found in errno. For example, a function which returns the value of - errno might be declared as having the return type errno_t. - - -

Contents -

K.3.3 Common definitions <stddef.h>

-

- The header <stddef.h> defines a type. -

- The type is -

-          rsize_t
-
- which is the type size_t.372) - -

Footnotes -

372) See the description of the RSIZE_MAX macro in <stdint.h>. - - -

Contents -

K.3.4 Integer types <stdint.h>

-

- The header <stdint.h> defines a macro. -

- The macro is -

-          RSIZE_MAX
-
- which expands to a value373) of type size_t. Functions that have parameters of type - rsize_t consider it a runtime-constraint violation if the values of those parameters are - greater than RSIZE_MAX. -

Recommended practice -

- Extremely large object sizes are frequently a sign that an object's size was calculated - incorrectly. For example, negative numbers appear as very large positive numbers when - converted to an unsigned type like size_t. Also, some implementations do not support - objects as large as the maximum value that can be represented by type size_t. -

- For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect - programming errors. For implementations targeting machines with large address spaces, - it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest - object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of - some legitimate, but very large, objects. Implementations targeting machines with small - address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there - - - is no object size that is considered a runtime-constraint violation. - -

Footnotes -

373) The macro RSIZE_MAX need not expand to a constant expression. - - -

Contents -

K.3.5 Input/output <stdio.h>

-

- The header <stdio.h> defines several macros and two types. -

- The macros are -

-        L_tmpnam_s
-
- which expands to an integer constant expression that is the size needed for an array of - char large enough to hold a temporary file name string generated by the tmpnam_s - function; -
-        TMP_MAX_S
-
- which expands to an integer constant expression that is the maximum number of unique - file names that can be generated by the tmpnam_s function. -

- The types are -

-        errno_t
-
- which is type int; and -
-        rsize_t
-
- which is the type size_t. - -

Contents -

K.3.5.1 Operations on files
- -

Contents -

K.3.5.1.1 The tmpfile_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        errno_t tmpfile_s(FILE * restrict * restrict streamptr);
-
- Runtime-constraints -

- streamptr shall not be a null pointer. -

- If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file. -

Description -

- The tmpfile_s function creates a temporary binary file that is different from any other - existing file and that will automatically be removed when it is closed or at program - termination. If the program terminates abnormally, whether an open temporary file is - removed is implementation-defined. The file is opened for update with "wb+" mode - with the meaning that mode has in the fopen_s function (including the mode's effect - on exclusive access and file permissions). - -

- If the file was created successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - to FILE pointed to by streamptr will be set to a null pointer. -

Recommended practice - It should be possible to open at least TMP_MAX_S temporary files during the lifetime of - the program (this limit may be shared with tmpnam_s) and there should be no limit on - the number simultaneously open other than this limit and any limit on the number of open - files (FOPEN_MAX). -

Returns -

- The tmpfile_s function returns zero if it created the file. If it did not create the file or - there was a runtime-constraint violation, tmpfile_s returns a nonzero value. - -

Contents -

K.3.5.1.2 The tmpnam_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdio.h>
-         errno_t tmpnam_s(char *s, rsize_t maxsize);
-
- Runtime-constraints -

- s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX. - maxsize shall be greater than the length of the generated file name string. -

Description -

- The tmpnam_s function generates a string that is a valid file name and that is not the - same as the name of an existing file.374) The function is potentially capable of generating - TMP_MAX_S different strings, but any or all of them may already be in use by existing - files and thus not be suitable return values. The lengths of these strings shall be less than - the value of the L_tmpnam_s macro. -

- The tmpnam_s function generates a different string each time it is called. -

- It is assumed that s points to an array of at least maxsize characters. This array will be - set to generated string, as specified below. - - - - -

- The implementation shall behave as if no library function except tmpnam calls the - tmpnam_s function.375) -

Recommended practice -

- After a program obtains a file name using the tmpnam_s function and before the - program creates a file with that name, the possibility exists that someone else may create - a file with that same name. To avoid this race condition, the tmpfile_s function - should be used instead of tmpnam_s when possible. One situation that requires the use - of the tmpnam_s function is when the program needs to create a temporary directory - rather than a temporary file. -

Returns -

- If no suitable string can be generated, or if there is a runtime-constraint violation, the - tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize - is greater than zero) and returns a nonzero value. -

- Otherwise, the tmpnam_s function writes the string in the array pointed to by s and - returns zero. -

Environmental limits -

- The value of the macro TMP_MAX_S shall be at least 25. - -

Footnotes -

374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that - their names should not collide with those generated by conventional naming rules for the - implementation. It is still necessary to use the remove function to remove such files when their use - is ended, and before program termination. Implementations should take care in choosing the patterns - used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the - race condition and possible conflict when multiple programs run simultaneously by the same user - generate the same temporary file names. - -

375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming - convention for temporary files), but this is not required. - - -

Contents -

K.3.5.2 File access functions
- -

Contents -

K.3.5.2.1 The fopen_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        errno_t fopen_s(FILE * restrict * restrict streamptr,
-             const char * restrict filename,
-             const char * restrict mode);
-
- Runtime-constraints -

- None of streamptr, filename, or mode shall be a null pointer. -

- If there is a runtime-constraint violation, fopen_s does not attempt to open a file. - Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the - null pointer. - - - - - -

Description -

- The fopen_s function opens the file whose name is the string pointed to by - filename, and associates a stream with it. -

- The mode string shall be as described for fopen, with the addition that modes starting - with the character 'w' or 'a' may be preceded by the character 'u', see below: - uw truncate to zero length or create text file for writing, default -

-                permissions
-
- uwx create text file for writing, default permissions - ua append; open or create text file for writing at end-of-file, default -
-                permissions
-
- uwb truncate to zero length or create binary file for writing, default -
-                permissions
-
- uwbx create binary file for writing, default permissions - uab append; open or create binary file for writing at end-of-file, default -
-                permissions
-
- uw+ truncate to zero length or create text file for update, default -
-                permissions
-
- uw+x create text file for update, default permissions - ua+ append; open or create text file for update, writing at end-of-file, -
-                default permissions
-
- uw+b or uwb+ truncate to zero length or create binary file for update, default -
-                permissions
-
- uw+bx or uwb+x create binary file for update, default permissions - ua+b or uab+ append; open or create binary file for update, writing at end-of-file, -
-                default permissions
-
-

- Opening a file with exclusive mode ('x' as the last character in the mode argument) - fails if the file already exists or cannot be created. -

- To the extent that the underlying system supports the concepts, files opened for writing - shall be opened with exclusive (also known as non-shared) access. If the file is being - created, and the first character of the mode string is not 'u', to the extent that the - underlying system supports it, the file shall have a file permission that prevents other - users on the system from accessing the file. If the file is being created and first character - of the mode string is 'u', then by the time the file has been closed, it shall have the - system default file access permissions.376) -

- If the file was opened successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - - - - to FILE pointed to by streamptr will be set to a null pointer. -

Returns -

- The fopen_s function returns zero if it opened the file. If it did not open the file or if - there was a runtime-constraint violation, fopen_s returns a nonzero value. - -

Footnotes -

376) These are the same permissions that the file would have been created with by fopen. - - -

Contents -

K.3.5.2.2 The freopen_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        errno_t freopen_s(FILE * restrict * restrict newstreamptr,
-             const char * restrict filename,
-             const char * restrict mode,
-             FILE * restrict stream);
-
- Runtime-constraints -

- None of newstreamptr, mode, and stream shall be a null pointer. -

- If there is a runtime-constraint violation, freopen_s neither attempts to close any file - associated with stream nor attempts to open a file. Furthermore, if newstreamptr is - not a null pointer, fopen_s sets *newstreamptr to the null pointer. -

Description -

- The freopen_s function opens the file whose name is the string pointed to by - filename and associates the stream pointed to by stream with it. The mode - argument has the same meaning as in the fopen_s function (including the mode's effect - on exclusive access and file permissions). -

- If filename is a null pointer, the freopen_s function attempts to change the mode of - the stream to that specified by mode, as if the name of the file currently associated with - the stream had been used. It is implementation-defined which changes of mode are - permitted (if any), and under what circumstances. -

- The freopen_s function first attempts to close any file that is associated with stream. - Failure to close the file is ignored. The error and end-of-file indicators for the stream are - cleared. -

- If the file was opened successfully, then the pointer to FILE pointed to by - newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE - pointed to by newstreamptr will be set to a null pointer. -

Returns -

- The freopen_s function returns zero if it opened the file. If it did not open the file or - there was a runtime-constraint violation, freopen_s returns a nonzero value. - - -

Contents -

K.3.5.3 Formatted input/output functions
-

- Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - -

Contents -

K.3.5.3.1 The fprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdio.h>
-          int fprintf_s(FILE * restrict stream,
-               const char * restrict format, ...);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. The %n specifier377) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to fprintf_s corresponding to a %s specifier shall not be a - null pointer. -

- If there is a runtime-constraint violation,378) the fprintf_s function does not attempt - to produce further output, and it is unspecified to what extent fprintf_s produced - output before discovering the runtime-constraint violation. -

Description -

- The fprintf_s function is equivalent to the fprintf function except for the explicit - runtime-constraints listed above. -

Returns -

- The fprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - - -

Footnotes -

377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -

378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - - -

Contents -

K.3.5.3.2 The fscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdio.h>
-         int fscanf_s(FILE * restrict stream,
-              const char * restrict format, ...);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion - specifiers apply to a pair of arguments (unless assignment suppression is indicated by a - *). The first of these arguments is the same as for fscanf. That argument is - immediately followed in the argument list by the second argument, which has type - rsize_t and gives the number of elements in the array pointed to by the first argument - of the pair. If the first argument points to a scalar object, it is considered to be an array of - one element.380) -

- A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). -

Returns -

- The fscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - - - fscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. -

- EXAMPLE 1 The call: -

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdio.h>
-          /* ... */
-          int n, i; float x; char name[50];
-          n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
-
- with the input line: -
-          25 54.32E-1 thompson
-
- will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -

- EXAMPLE 2 The call: -

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdio.h>
-          /* ... */
-          int n; char s[5];
-          n = fscanf_s(stdin, "%s", s, sizeof s);
-
- with the input line: -
-          hello
-
- will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an - array of six characters to store it. - - -

Footnotes -

379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - -

380) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - - -

Contents -

K.3.5.3.3 The printf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdio.h>
-          int printf_s(const char * restrict format, ...);
-
- Runtime-constraints -

- format shall not be a null pointer. The %n specifier381) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to printf_s corresponding to a %s specifier shall not be a null pointer. -

- If there is a runtime-constraint violation, the printf_s function does not attempt to - produce further output, and it is unspecified to what extent printf_s produced output - before discovering the runtime-constraint violation. - - - -

Description -

- The printf_s function is equivalent to the printf function except for the explicit - runtime-constraints listed above. -

Returns -

- The printf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.4 The scanf_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        int scanf_s(const char * restrict format, ...);
-
- Runtime-constraints -

- format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the scanf_s function does not attempt to - perform further input, and it is unspecified to what extent scanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The scanf_s function is equivalent to fscanf_s with the argument stdin - interposed before the arguments to scanf_s. -

Returns -

- The scanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - scanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - -

Contents -

K.3.5.3.5 The snprintf_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        int snprintf_s(char * restrict s, rsize_t n,
-             const char * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to - - snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the - null character. -

Description -

- The snprintf_s function is equivalent to the snprintf function except for the - explicit runtime-constraints listed above. -

- The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the - array pointed to by s. -

Returns -

- The snprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - -

Footnotes -

382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.6 The sprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdio.h>
-          int sprintf_s(char * restrict s, rsize_t n,
-               const char * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier383) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to sprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. - - - - -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the - null character. -

Description -

- The sprintf_s function is equivalent to the sprintf function except for the - parameter n and the explicit runtime-constraints listed above. -

- The sprintf_s function, unlike snprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. -

Returns -

- If no runtime-constraint violation occurred, the sprintf_s function returns the number - of characters written in the array, not counting the terminating null character. If an - encoding error occurred, sprintf_s returns a negative value. If any other runtime- - constraint violation occurred, sprintf_s returns zero. - -

Footnotes -

383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.7 The sscanf_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        int sscanf_s(const char * restrict s,
-             const char * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the sscanf_s function does not attempt to - perform further input, and it is unspecified to what extent sscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The sscanf_s function is equivalent to fscanf_s, except that input is obtained from - a string (specified by the argument s) rather than from a stream. Reaching the end of the - string is equivalent to encountering end-of-file for the fscanf_s function. If copying - takes place between objects that overlap, the objects take on unspecified values. -

Returns -

- The sscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - sscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - -

Contents -

K.3.5.3.8 The vfprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdarg.h>
-          #include <stdio.h>
-          int vfprintf_s(FILE * restrict stream,
-               const char * restrict format,
-               va_list arg);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. The %n specifier384) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a - null pointer. -

- If there is a runtime-constraint violation, the vfprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vfprintf_s produced - output before discovering the runtime-constraint violation. -

Description -

- The vfprintf_s function is equivalent to the vfprintf function except for the - explicit runtime-constraints listed above. -

Returns -

- The vfprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.9 The vfscanf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdarg.h>
-          #include <stdio.h>
-          int vfscanf_s(FILE * restrict stream,
-               const char * restrict format,
-               va_list arg);
-
- - - - - - Runtime-constraints -

- Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vfscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vfscanf_s function is equivalent to fscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfscanf_s function does not invoke the - va_end macro.385) -

Returns -

- The vfscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - - -

Contents -

K.3.5.3.10 The vprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdarg.h>
-          #include <stdio.h>
-          int vprintf_s(const char * restrict format,
-               va_list arg);
-
- Runtime-constraints -

- format shall not be a null pointer. The %n specifier386) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to vprintf_s corresponding to a %s specifier shall not be a null pointer. -

- If there is a runtime-constraint violation, the vprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vprintf_s produced output - before discovering the runtime-constraint violation. - - -

Description -

- The vprintf_s function is equivalent to the vprintf function except for the explicit - runtime-constraints listed above. -

Returns -

- The vprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.11 The vscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <stdio.h>
-         int vscanf_s(const char * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vscanf_s function is equivalent to scanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vscanf_s function does not invoke the - va_end macro.387) -

Returns -

- The vscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - - - - - -

Footnotes -

387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - - -

Contents -

K.3.5.3.12 The vsnprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdarg.h>
-          #include <stdio.h>
-          int vsnprintf_s(char * restrict s, rsize_t n,
-               const char * restrict format,
-               va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to - vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the - null character. -

Description -

- The vsnprintf_s function is equivalent to the vsnprintf function except for the - explicit runtime-constraints listed above. -

- The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within - the array pointed to by s. -

Returns -

- The vsnprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - - - - - - -

Footnotes -

388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.13 The vsprintf_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdarg.h>
-          #include <stdio.h>
-          int vsprintf_s(char * restrict s, rsize_t n,
-               const char * restrict format,
-               va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier389) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to vsprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the - null character. -

Description -

- The vsprintf_s function is equivalent to the vsprintf function except for the - parameter n and the explicit runtime-constraints listed above. -

- The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. -

Returns -

- If no runtime-constraint violation occurred, the vsprintf_s function returns the - number of characters written in the array, not counting the terminating null character. If - an encoding error occurred, vsprintf_s returns a negative value. If any other - runtime-constraint violation occurred, vsprintf_s returns zero. - - - - - - -

Footnotes -

389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - - -

Contents -

K.3.5.3.14 The vsscanf_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdarg.h>
-        #include <stdio.h>
-        int vsscanf_s(const char * restrict s,
-             const char * restrict format,
-             va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vsscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vsscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vsscanf_s function is equivalent to sscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsscanf_s function does not invoke the - va_end macro.390) -

Returns -

- The vsscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - - -

Contents -

K.3.5.4 Character input/output functions
- -

Contents -

K.3.5.4.1 The gets_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <stdio.h>
-        char *gets_s(char *s, rsize_t n);
-
- - - - - - Runtime-constraints -

- s shall not be a null pointer. n shall neither be equal to zero nor be greater than - RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading - n-1 characters from stdin.391) -

- If there is a runtime-constraint violation, s[0] is set to the null character, and characters - are read and discarded from stdin until a new-line character is read, or end-of-file or a - read error occurs. -

Description -

- The gets_s function reads at most one less than the number of characters specified by n - from the stream pointed to by stdin, into the array pointed to by s. No additional - characters are read after a new-line character (which is discarded) or after end-of-file. - The discarded new-line character does not count towards number of characters read. A - null character is written immediately after the last character read into the array. -

- If end-of-file is encountered and no characters have been read into the array, or if a read - error occurs during the operation, then s[0] is set to the null character, and the other - elements of s take unspecified values. -

Recommended practice -

- The fgets function allows properly-written programs to safely process input lines too - long to store in the result array. In general this requires that callers of fgets pay - attention to the presence or absence of a new-line character in the result array. Consider - using fgets (along with any needed processing based on new-line characters) instead of - gets_s. -

Returns -

- The gets_s function returns s if successful. If there was a runtime-constraint violation, - or if end-of-file is encountered and no characters have been read into the array, or if a - read error occurs during the operation, then a null pointer is returned. - - - - - - -

Footnotes -

391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for - a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a - one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets - expect such a relationship. - - -

Contents -

K.3.6 General utilities <stdlib.h>

-

- The header <stdlib.h> defines three types. -

- The types are -

-         errno_t
-
- which is type int; and -
-         rsize_t
-
- which is the type size_t; and -
-         constraint_handler_t
-
- which has the following definition -
-         typedef void (*constraint_handler_t)(
-              const char * restrict msg,
-              void * restrict ptr,
-              errno_t error);
-
- -

Contents -

K.3.6.1 Runtime-constraint handling
- -

Contents -

K.3.6.1.1 The set_constraint_handler_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         constraint_handler_t set_constraint_handler_s(
-              constraint_handler_t handler);
-
-

Description -

- The set_constraint_handler_s function sets the runtime-constraint handler to - be handler. The runtime-constraint handler is the function to be called when a library - function detects a runtime-constraint violation. Only the most recent handler registered - with set_constraint_handler_s is called when a runtime-constraint violation - occurs. -

- When the handler is called, it is passed the following arguments in the following order: -

    -
  1. A pointer to a character string describing the runtime-constraint violation. -
  2. A null pointer or a pointer to an implementation defined object. -
  3. If the function calling the handler has a return type declared as errno_t, the - return value of the function is passed. Otherwise, a positive value of type - errno_t is passed. - -
-

- The implementation has a default constraint handler that is used if no calls to the - set_constraint_handler_s function have been made. The behavior of the - default handler is implementation-defined, and it may cause the program to exit or abort. -

- If the handler argument to set_constraint_handler_s is a null pointer, the - implementation default handler becomes the current constraint handler. -

Returns -

- The set_constraint_handler_s function returns a pointer to the previously - registered handler.392) - -

Footnotes -

392) If the previous handler was registered by calling set_constraint_handler_s with a null - pointer argument, a pointer to the implementation default handler is returned (not NULL). - - -

Contents -

K.3.6.1.2 The abort_handler_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         void abort_handler_s(
-              const char * restrict msg,
-              void * restrict ptr,
-              errno_t error);
-
-

Description -

- A pointer to the abort_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -

- The abort_handler_s function writes a message on the standard error stream in an - implementation-defined format. The message shall include the string pointed to by msg. - The abort_handler_s function then calls the abort function.393) -

Returns -

- The abort_handler_s function does not return to its caller. - - - - - - -

Footnotes -

393) Many implementations invoke a debugger when the abort function is called. - - -

Contents -

K.3.6.1.3 The ignore_handler_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         void ignore_handler_s(
-              const char * restrict msg,
-              void * restrict ptr,
-              errno_t error);
-
-

Description -

- A pointer to the ignore_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -

- The ignore_handler_s function simply returns to its caller.394) -

Returns -

- The ignore_handler_s function returns no value. - -

Footnotes -

394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in - which a runtime-constraint violation occurs will return to its caller. The caller can determine whether - a runtime-constraint violation occurred based on the library function's specification (usually, the - library function returns a nonzero errno_t). - - -

Contents -

K.3.6.2 Communication with the environment
- -

Contents -

K.3.6.2.1 The getenv_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         errno_t getenv_s(size_t * restrict len,
-                    char * restrict value, rsize_t maxsize,
-                    const char * restrict name);
-
- Runtime-constraints -

- name shall not be a null pointer. maxsize shall neither equal zero nor be greater than - RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer. -

- If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len - is not null), and the environment list is not searched. -

Description -

- The getenv_s function searches an environment list, provided by the host environment, - for a string that matches the string pointed to by name. - - - -

- If that name is found then getenv_s performs the following actions. If len is not a - null pointer, the length of the string associated with the matched list member is stored in - the integer pointed to by len. If the length of the associated string is less than maxsize, - then the associated string is copied to the array pointed to by value. -

- If that name is not found then getenv_s performs the following actions. If len is not - a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than - zero, then value[0] is set to the null character. -

- The set of environment names and the method for altering the environment list are - implementation-defined. -

Returns -

- The getenv_s function returns zero if the specified name is found and the associated - string was successfully stored in value. Otherwise, a nonzero value is returned. - -

Contents -

K.3.6.3 Searching and sorting utilities
-

- These utilities make use of a comparison function to search or sort arrays of unspecified - type. Where an argument declared as size_t nmemb specifies the length of the array - for a function, if nmemb has the value zero on a call to that function, then the comparison - function is not called, a search finds no matching element, sorting performs no - rearrangement, and the pointer to the array may be null. -

- The implementation shall ensure that the second argument of the comparison function - (when called from bsearch_s), or both arguments (when called from qsort_s), are - pointers to elements of the array.395) The first argument when called from bsearch_s - shall equal key. -

- The comparison function shall not alter the contents of either the array or search key. The - implementation may reorder elements of the array between calls to the comparison - function, but shall not otherwise alter the contents of any individual element. -

- When the same objects (consisting of size bytes, irrespective of their current positions - in the array) are passed more than once to the comparison function, the results shall be - consistent with one another. That is, for qsort_s they shall define a total ordering on - the array, and for bsearch_s the same object shall always compare the same way with - the key. - - - - - -

- A sequence point occurs immediately before and immediately after each call to the - comparison function, and also between any call to the comparison function and any - movement of the objects passed as arguments to that call. - -

Footnotes -

395) That is, if the value passed is p, then the following expressions are always valid and nonzero: - -

-          ((char *)p - (char *)base) % size == 0
-          (char *)p >= (char *)base
-          (char *)p < (char *)base + nmemb * size
-
- - -

Contents -

K.3.6.3.1 The bsearch_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <stdlib.h>
-          void *bsearch_s(const void *key, const void *base,
-               rsize_t nmemb, rsize_t size,
-               int (*compar)(const void *k, const void *y,
-                               void *context),
-               void *context);
-
- Runtime-constraints -

- Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then none of key, base, or compar shall be a null pointer. -

- If there is a runtime-constraint violation, the bsearch_s function does not search the - array. -

Description -

- The bsearch_s function searches an array of nmemb objects, the initial element of - which is pointed to by base, for an element that matches the object pointed to by key. - The size of each element of the array is specified by size. -

- The comparison function pointed to by compar is called with three arguments. The first - two point to the key object and to an array element, in that order. The function shall - return an integer less than, equal to, or greater than zero if the key object is considered, - respectively, to be less than, to match, or to be greater than the array element. The array - shall consist of: all the elements that compare less than, all the elements that compare - equal to, and all the elements that compare greater than the key object, in that order.396) - The third argument to the comparison function is the context argument passed to - bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison - function.397) - - - - - -

Returns -

- The bsearch_s function returns a pointer to a matching element of the array, or a null - pointer if no match is found or there is a runtime-constraint violation. If two elements - compare as equal, which element is matched is unspecified. - -

Footnotes -

396) In practice, this means that the entire array has been sorted according to the comparison function. - -

397) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - - -

Contents -

K.3.6.3.2 The qsort_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
-              int (*compar)(const void *x, const void *y,
-                              void *context),
-              void *context);
-
- Runtime-constraints -

- Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then neither base nor compar shall be a null pointer. -

- If there is a runtime-constraint violation, the qsort_s function does not sort the array. -

Description -

- The qsort_s function sorts an array of nmemb objects, the initial element of which is - pointed to by base. The size of each object is specified by size. -

- The contents of the array are sorted into ascending order according to a comparison - function pointed to by compar, which is called with three arguments. The first two - point to the objects being compared. The function shall return an integer less than, equal - to, or greater than zero if the first argument is considered to be respectively less than, - equal to, or greater than the second. The third argument to the comparison function is the - context argument passed to qsort_s. The sole use of context by qsort_s is to - pass it to the comparison function.398) -

- If two elements compare as equal, their relative order in the resulting sorted array is - unspecified. -

Returns -

- The qsort_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - - -

Footnotes -

398) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - - -

Contents -

K.3.6.4 Multibyte/wide character conversion functions
-

- The behavior of the multibyte character functions is affected by the LC_CTYPE category - of the current locale. For a state-dependent encoding, each function is placed into its - initial conversion state by a call for which its character pointer argument, s, is a null - pointer. Subsequent calls with s as other than a null pointer cause the internal conversion - state of the function to be altered as necessary. A call with s as a null pointer causes - these functions to set the int pointed to by their status argument to a nonzero value if - encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE - category causes the conversion state of these functions to be indeterminate. - -

Footnotes -

399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide - character codes, but are grouped with an adjacent multibyte character. - - -

Contents -

K.3.6.4.1 The wctomb_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdlib.h>
-         errno_t wctomb_s(int * restrict status,
-              char * restrict s,
-              rsize_t smax,
-              wchar_t wc);
-
- Runtime-constraints -

- Let n denote the number of bytes needed to represent the multibyte character - corresponding to the wide character given by wc (including any shift sequences). -

- If s is not a null pointer, then smax shall not be less than n, and smax shall not be - greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero. -

- If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to - by status, and if s is not a null pointer, no more than smax elements in the array - pointed to by s will be accessed. -

Description -

- The wctomb_s function determines n and stores the multibyte character representation - of wc in the array whose first element is pointed to by s (if s is not a null pointer). The - number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide - character, a null byte is stored, preceded by any shift sequence needed to restore the - initial shift state, and the function is left in the initial conversion state. -

- The implementation shall behave as if no library function calls the wctomb_s function. - - - - - -

- If s is a null pointer, the wctomb_s function stores into the int pointed to by status a - nonzero or zero value, if multibyte character encodings, respectively, do or do not have - state-dependent encodings. -

- If s is not a null pointer, the wctomb_s function stores into the int pointed to by - status either n or -1 if wc, respectively, does or does not correspond to a valid - multibyte character. -

- In no case will the int pointed to by status be set to a value greater than the - MB_CUR_MAX macro. -

Returns -

- The wctomb_s function returns zero if successful, and a nonzero value if there was a - runtime-constraint violation or wc did not correspond to a valid multibyte character. - -

Contents -

K.3.6.5 Multibyte/wide string conversion functions
-

- The behavior of the multibyte string functions is affected by the LC_CTYPE category of - the current locale. - -

Contents -

K.3.6.5.1 The mbstowcs_s function
-

Synopsis -

-

-         #include <stdlib.h>
-         errno_t mbstowcs_s(size_t * restrict retval,
-              wchar_t * restrict dst, rsize_t dstmax,
-              const char * restrict src, rsize_t len);
-
- Runtime-constraints -

- Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then a null character - shall occur within the first dstmax multibyte characters of the array pointed to by src. -

- If there is a runtime-constraint violation, then mbstowcs_s does the following. If - retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbstowcs_s sets dst[0] to the null wide character. -

Description -

- The mbstowcs_s function converts a sequence of multibyte characters that begins in - the initial shift state from the array pointed to by src into a sequence of corresponding - wide characters. If dst is not a null pointer, the converted characters are stored into the - array pointed to by dst. Conversion continues up to and including a terminating null - character, which is also stored. Conversion stops earlier in two cases: when a sequence of - - bytes is encountered that does not form a valid multibyte character, or (if dst is not a - null pointer) when len wide characters have been stored into the array pointed to by - dst.400) If dst is not a null pointer and no null wide character was stored into the array - pointed to by dst, then dst[len] is set to the null wide character. Each conversion - takes place as if by a call to the mbrtowc function. -

- Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbstowcs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the mbstowcs_s function stores into *retval the number of multibyte - characters successfully converted, not including the terminating null character (if any). -

- All elements following the terminating null wide character (if any) written by - mbstowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbstowcs_s returns.401) -

- If copying takes place between objects that overlap, the objects take on unspecified - values. -

Returns -

- The mbstowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - -

Footnotes -

400) Thus, the value of len is ignored if dst is a null pointer. - -

401) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - - -

Contents -

K.3.6.5.2 The wcstombs_s function
-

Synopsis -

-

-          #include <stdlib.h>
-          errno_t wcstombs_s(size_t * restrict retval,
-               char * restrict dst, rsize_t dstmax,
-               const wchar_t * restrict src, rsize_t len);
-
- Runtime-constraints -

- Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then the conversion - shall have been stopped (see below) because a terminating null wide character was - reached or because an encoding error occurred. - - - - - -

- If there is a runtime-constraint violation, then wcstombs_s does the following. If - retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcstombs_s sets dst[0] to the null character. -

Description -

- The wcstombs_s function converts a sequence of wide characters from the array - pointed to by src into a sequence of corresponding multibyte characters that begins in - the initial shift state. If dst is not a null pointer, the converted characters are then stored - into the array pointed to by dst. Conversion continues up to and including a terminating - null wide character, which is also stored. Conversion stops earlier in two cases: -

- If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.402) -

- Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the wcstombs_s function stores into *retval the number of bytes in the - resulting multibyte character sequence, not including the terminating null character (if - any). -

- All elements following the terminating null character (if any) written by wcstombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcstombs_s returns.403) -

- If copying takes place between objects that overlap, the objects take on unspecified - values. - - - -

Returns -

- The wcstombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - -

Footnotes -

402) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - -

403) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - - -

Contents -

K.3.7 String handling <string.h>

-

- The header <string.h> defines two types. -

- The types are -

-        errno_t
-
- which is type int; and -
-        rsize_t
-
- which is the type size_t. - -

Contents -

K.3.7.1 Copying functions
- -

Contents -

K.3.7.1.1 The memcpy_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <string.h>
-        errno_t memcpy_s(void * restrict s1, rsize_t s1max,
-             const void * restrict s2, rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -

- If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first - s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is - not greater than RSIZE_MAX. -

Description -

- The memcpy_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. -

Returns -

- The memcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - -

Contents -

K.3.7.1.2 The memmove_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t memmove_s(void *s1, rsize_t s1max,
-              const void *s2, rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -

- If there is a runtime-constraint violation, the memmove_s function stores zeros in the - first s1max characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. -

Description -

- The memmove_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. This copying takes place as if the n characters from the object - pointed to by s2 are first copied into a temporary array of n characters that does not - overlap the objects pointed to by s1 or s2, and then the n characters from the temporary - array are copied into the object pointed to by s1. -

Returns -

- The memmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Contents -

K.3.7.1.3 The strcpy_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t strcpy_s(char * restrict s1,
-              rsize_t s1max,
-              const char * restrict s2);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the - null character. - -

Description -

- The strcpy_s function copies the string pointed to by s2 (including the terminating - null character) into the array pointed to by s1. -

- All elements following the terminating null character (if any) written by strcpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcpy_s returns.404) -

Returns -

- The strcpy_s function returns zero405) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Footnotes -

404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - -

405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.7.1.4 The strncpy_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t strncpy_s(char * restrict s1,
-              rsize_t s1max,
-              const char * restrict s2,
-              rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than strnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the - null character. -

Description -

- The strncpy_s function copies not more than n successive characters (characters that - follow a null character are not copied) from the array pointed to by s2 to the array - pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null - character. - - - -

- All elements following the terminating null character (if any) written by strncpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncpy_s returns.406) -

Returns -

- The strncpy_s function returns zero407) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -

- EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. -

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         /* ... */
-         char src1[100] = "hello";
-         char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'};
-         char dst1[6], dst2[5], dst3[5];
-         int r1, r2, r3;
-         r1 = strncpy_s(dst1, 6, src1, 100);
-         r2 = strncpy_s(dst2, 5, src2, 7);
-         r3 = strncpy_s(dst3, 5, src2, 4);
-
- The first call will assign to r1 the value zero and to dst1 the sequence hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence \0. - The third call will assign to r3 the value zero and to dst3 the sequence good\0. - - -

Footnotes -

406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - -

407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.7.2 Concatenation functions
- -

Contents -

K.3.7.2.1 The strcat_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t strcat_s(char * restrict s1,
-              rsize_t s1max,
-              const char * restrict s2);
-
- Runtime-constraints -

- Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strcat_s. - - - - - -

- Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.408) m shall be greater than - strnlen_s(s2, m). Copying shall not take place between objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the - null character. -

Description -

- The strcat_s function appends a copy of the string pointed to by s2 (including the - terminating null character) to the end of the string pointed to by s1. The initial character - from s2 overwrites the null character at the end of s1. -

- All elements following the terminating null character (if any) written by strcat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcat_s returns.409) -

Returns -

- The strcat_s function returns zero410) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Footnotes -

408) Zero means that s1 was not null terminated upon entry to strcat_s. - -

409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - -

410) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.7.2.2 The strncat_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t strncat_s(char * restrict s1,
-              rsize_t s1max,
-              const char * restrict s2,
-              rsize_t n);
-
- Runtime-constraints -

- Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strncat_s. -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less - - - - than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take - place between objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the - null character. -

Description -

- The strncat_s function appends not more than n successive characters (characters - that follow a null character are not copied) from the array pointed to by s2 to the end of - the string pointed to by s1. The initial character from s2 overwrites the null character at - the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to - a null character. -

- All elements following the terminating null character (if any) written by strncat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncat_s returns.412) -

Returns -

- The strncat_s function returns zero413) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -

- EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. -

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         /* ... */
-         char s1[100] = "good";
-         char s2[6] = "hello";
-         char s3[6] = "hello";
-         char s4[7] = "abc";
-         char s5[1000] = "bye";
-         int r1, r2, r3, r4;
-         r1 = strncat_s(s1, 100, s5, 1000);
-         r2 = strncat_s(s2, 6, "", 1);
-         r3 = strncat_s(s3, 6, "X", 2);
-         r4 = strncat_s(s4, 7, "defghijklmn", 3);
-
- After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0. - - - - - After the second call r2 will have the value zero and s2 will contain the sequence hello\0. - After the third call r3 will have a nonzero value and s3 will contain the sequence \0. - After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0. - - -

Footnotes -

411) Zero means that s1 was not null terminated upon entry to strncat_s. - -

412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - -

413) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.7.3 Search functions
- -

Contents -

K.3.7.3.1 The strtok_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         char *strtok_s(char * restrict s1,
-              rsize_t * restrict s1max,
-              const char * restrict s2,
-              char ** restrict ptr);
-
- Runtime-constraints -

- None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max characters of s1 for the - first call, and shall occur within the first *s1max characters of where searching resumes - on subsequent calls. -

- If there is a runtime-constraint violation, the strtok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. -

Description -

- A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a - sequence of tokens, each of which is delimited by a character from the string pointed to - by s2. The fourth argument points to a caller-provided char pointer into which the - strtok_s function stores information necessary for it to continue scanning the same - string. -

- The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator string pointed to by - s2 may be different from call to call. -

- The first call in the sequence searches the string pointed to by s1 for the first character - that is not contained in the current separator string pointed to by s2. If no such character - is found, then there are no tokens in the string pointed to by s1 and the strtok_s - function returns a null pointer. If such a character is found, it is the start of the first token. - -

- The strtok_s function then searches from there for the first character in s1 that is - contained in the current separator string. If no such character is found, the current token - extends to the end of the string pointed to by s1, and subsequent searches in the same - string for a token return a null pointer. If such a character is found, it is overwritten by a - null character, which terminates the current token. -

- In all cases, the strtok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null character - (if any). -

Returns -

- The strtok_s function returns a pointer to the first character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -

- EXAMPLE -

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         static char str1[] = "?a???b,,,#c";
-         static char str2[] = "\t \t";
-         char *t, *ptr1, *ptr2;
-         rsize_t max1 = sizeof(str1);
-         rsize_t max2 = sizeof(str2);
-         t   =   strtok_s(str1,   &max1,   "?", &ptr1);        //   t   points to the token "a"
-         t   =   strtok_s(NULL,   &max1,   ",", &ptr1);        //   t   points to the token "??b"
-         t   =   strtok_s(str2,   &max2,   " \t", &ptr2);      //   t   is a null pointer
-         t   =   strtok_s(NULL,   &max1,   "#,", &ptr1);       //   t   points to the token "c"
-         t   =   strtok_s(NULL,   &max1,   "?", &ptr1);        //   t   is a null pointer
-
- - -

Contents -

K.3.7.4 Miscellaneous functions
- -

Contents -

K.3.7.4.1 The memset_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
-
- Runtime-constraints -

- s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n - shall not be greater than smax. -

- If there is a runtime-constraint violation, then if s is not a null pointer and smax is not - greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an - unsigned char) into each of the first smax characters of the object pointed to by s. - -

Description -

- The memset_s function copies the value of c (converted to an unsigned char) into - each of the first n characters of the object pointed to by s. Unlike memset, any call to - the memset_s function shall be evaluated strictly according to the rules of the abstract - machine as described in (5.1.2.3). That is, any call to the memset_s function shall - assume that the memory indicated by s and n may be accessible in the future and thus - must contain the values indicated by c. -

Returns -

- The memset_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Contents -

K.3.7.4.2 The strerror_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <string.h>
-        errno_t strerror_s(char *s, rsize_t maxsize,
-             errno_t errnum);
-
- Runtime-constraints -

- s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. - maxsize shall not equal zero. -

- If there is a runtime-constraint violation, then the array (if any) pointed to by s is not - modified. -

Description -

- The strerror_s function maps the number in errnum to a locale-specific message - string. Typically, the values for errnum come from errno, but strerror_s shall - map any value of type int to a message. -

- If the length of the desired string is less than maxsize, then the string is copied to the - array pointed to by s. -

- Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied - from the string to the array pointed to by s and then s[maxsize-1] is set to the null - character. Then, if maxsize is greater than 3, then s[maxsize-2], - s[maxsize-3], and s[maxsize-4] are set to the character period (.). -

Returns -

- The strerror_s function returns zero if the length of the desired string was less than - maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s - function returns a nonzero value. - - -

Contents -

K.3.7.4.3 The strerrorlen_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         size_t strerrorlen_s(errno_t errnum);
-
-

Description -

- The strerrorlen_s function calculates the length of the (untruncated) locale-specific - message string that the strerror_s function maps to errnum. -

Returns -

- The strerrorlen_s function returns the number of characters (not including the null - character) in the full message string. - -

Contents -

K.3.7.4.4 The strnlen_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <string.h>
-         size_t strnlen_s(const char *s, size_t maxsize);
-
-

Description -

- The strnlen_s function computes the length of the string pointed to by s. -

Returns -

- If s is a null pointer,414) then the strnlen_s function returns zero. -

- Otherwise, the strnlen_s function returns the number of characters that precede the - terminating null character. If there is no null character in the first maxsize characters of - s then strnlen_s returns maxsize. At most the first maxsize characters of s shall - be accessed by strnlen_s. - - - - - - -

Footnotes -

414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated string argument make - strnlen_s useful in algorithms that gracefully handle such exceptional data. - - -

Contents -

K.3.8 Date and time <time.h>

-

- The header <time.h> defines two types. -

- The types are -

-         errno_t
-
- which is type int; and -
-         rsize_t
-
- which is the type size_t. - -

Contents -

K.3.8.1 Components of time
-

- A broken-down time is normalized if the values of the members of the tm structure are in - their normal rages.415) - -

Footnotes -

415) The normal ranges are defined in 7.26.1. - - -

Contents -

K.3.8.2 Time conversion functions
-

- Like the strftime function, the asctime_s and ctime_s functions do not return a - pointer to a static object, and other library functions are permitted to call them. - -

Contents -

K.3.8.2.1 The asctime_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <time.h>
-         errno_t asctime_s(char *s, rsize_t maxsize,
-              const struct tm *timeptr);
-
- Runtime-constraints -

- Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr - shall be normalized. The calendar year represented by the broken-down time pointed to - by timeptr shall not be less than calendar year 0 and shall not be greater than calendar - year 9999. -

- If there is a runtime-constraint violation, there is no attempt to convert the time, and - s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is - not greater than RSIZE_MAX. -

Description -

- The asctime_s function converts the normalized broken-down time in the structure - pointed to by timeptr into a 26 character (including the null character) string in the - - - - form -

-         Sun Sep 16 01:03:52 1973\n\0
-
- The fields making up this string are (in order): -
    -
  1. The name of the day of the week represented by timeptr->tm_wday using the - following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat. -
  2. The character space. -
  3. The name of the month represented by timeptr->tm_mon using the following - three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, - Nov, and Dec. -
  4. The character space. -
  5. The value of timeptr->tm_mday as if printed using the fprintf format - "%2d". -
  6. The character space. -
  7. The value of timeptr->tm_hour as if printed using the fprintf format - "%.2d". -
  8. The character colon. -
  9. The value of timeptr->tm_min as if printed using the fprintf format - "%.2d". -
  10. The character colon. -
  11. The value of timeptr->tm_sec as if printed using the fprintf format - "%.2d". -
  12. The character space. -
  13. The value of timeptr->tm_year + 1900 as if printed using the fprintf - format "%4d". -
  14. The character new line. -
  15. The null character. -
-

Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - asctime_s function, consider using the strftime function instead. -

Returns -

- The asctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. - - -

Contents -

K.3.8.2.2 The ctime_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <time.h>
-        errno_t ctime_s(char *s, rsize_t maxsize,
-             const time_t *timer);
-
- Runtime-constraints -

- Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. -

- If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null - pointer and maxsize is not equal zero and is not greater than RSIZE_MAX. -

Description -

- The ctime_s function converts the calendar time pointed to by timer to local time in - the form of a string. It is equivalent to -

-        asctime_s(s, maxsize, localtime_s(timer))
-
-

Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - ctime_s function, consider using the strftime function instead. -

Returns -

- The ctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. - -

Contents -

K.3.8.2.3 The gmtime_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <time.h>
-        struct tm *gmtime_s(const time_t * restrict timer,
-             struct tm * restrict result);
-
- Runtime-constraints -

- Neither timer nor result shall be a null pointer. -

- If there is a runtime-constraint violation, there is no attempt to convert the time. -

Description -

- The gmtime_s function converts the calendar time pointed to by timer into a broken- - down time, expressed as UTC. The broken-down time is stored in the structure pointed - - to by result. -

Returns -

- The gmtime_s function returns result, or a null pointer if the specified time cannot - be converted to UTC or there is a runtime-constraint violation. - -

Contents -

K.3.8.2.4 The localtime_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <time.h>
-          struct tm *localtime_s(const time_t * restrict timer,
-               struct tm * restrict result);
-
- Runtime-constraints -

- Neither timer nor result shall be a null pointer. -

- If there is a runtime-constraint violation, there is no attempt to convert the time. -

Description -

- The localtime_s function converts the calendar time pointed to by timer into a - broken-down time, expressed as local time. The broken-down time is stored in the - structure pointed to by result. -

Returns -

- The localtime_s function returns result, or a null pointer if the specified time - cannot be converted to local time or there is a runtime-constraint violation. - -

Contents -

K.3.9 Extended multibyte and wide character utilities <wchar.h>

-

- The header <wchar.h> defines two types. -

- The types are -

-          errno_t
-
- which is type int; and -
-          rsize_t
-
- which is the type size_t. -

- Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - - -

Contents -

K.3.9.1 Formatted wide character input/output functions
- -

Contents -

K.3.9.1.1 The fwprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         int fwprintf_s(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. The %n specifier416) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a - null pointer. -

- If there is a runtime-constraint violation, the fwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent fwprintf_s produced - output before discovering the runtime-constraint violation. -

Description -

- The fwprintf_s function is equivalent to the fwprintf function except for the - explicit runtime-constraints listed above. -

Returns -

- The fwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.2 The fwscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdio.h>
-         #include <wchar.h>
-         int fwscanf_s(FILE * restrict stream,
-              const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. - - - -

- If there is a runtime-constraint violation, the fwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fwscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The fwscanf_s function is equivalent to fwscanf except that the c, s, and [ - conversion specifiers apply to a pair of arguments (unless assignment suppression is - indicated by a *). The first of these arguments is the same as for fwscanf. That - argument is immediately followed in the argument list by the second argument, which has - type size_t and gives the number of elements in the array pointed to by the first - argument of the pair. If the first argument points to a scalar object, it is considered to be - an array of one element.417) -

- A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). -

Returns -

- The fwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - fwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

417) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - - -

Contents -

K.3.9.1.3 The snwprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         int snwprintf_s(wchar_t * restrict s,
-              rsize_t n,
-              const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or - - - precision) shall not appear in the wide string pointed to by format. Any argument to - snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the - null wide character. -

Description -

- The snwprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -

- The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within - the array pointed to by s. -

Returns -

- The snwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating wide null - character, or a negative value if a runtime-constraint violation occurred. Thus, the null- - terminated output has been completely written if and only if the returned value is - nonnegative and less than n. - -

Footnotes -

418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.4 The swprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         int swprintf_s(wchar_t * restrict s, rsize_t n,
-              const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier419) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to swprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. - - - -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the - null wide character. -

Description -

- The swprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -

- The swprintf_s function, unlike snwprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. -

Returns -

- If no runtime-constraint violation occurred, the swprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, swprintf_s returns a negative value. If any other runtime-constraint - violation occurred, swprintf_s returns zero. - -

Footnotes -

419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.5 The swscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         int swscanf_s(const wchar_t * restrict s,
-              const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the swscanf_s function does not attempt to - perform further input, and it is unspecified to what extent swscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The swscanf_s function is equivalent to fwscanf_s, except that the argument s - specifies a wide string from which the input is to be obtained, rather than from a stream. - Reaching the end of the wide string is equivalent to encountering end-of-file for the - fwscanf_s function. -

Returns -

- The swscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - swscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - - -

Contents -

K.3.9.1.6 The vfwprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <stdio.h>
-         #include <wchar.h>
-         int vfwprintf_s(FILE * restrict stream,
-              const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- Neither stream nor format shall be a null pointer. The %n specifier420) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be - a null pointer. -

- If there is a runtime-constraint violation, the vfwprintf_s function does not attempt - to produce further output, and it is unspecified to what extent vfwprintf_s produced - output before discovering the runtime-constraint violation. -

Description -

- The vfwprintf_s function is equivalent to the vfwprintf function except for the - explicit runtime-constraints listed above. -

Returns -

- The vfwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.7 The vfwscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <stdio.h>
-         #include <wchar.h>
-         int vfwscanf_s(FILE * restrict stream,
-              const wchar_t * restrict format, va_list arg);
-
- - - - - Runtime-constraints -

- Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfwscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the - va_end macro.421) -

Returns -

- The vfwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - - -

Contents -

K.3.9.1.8 The vsnwprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <wchar.h>
-         int vsnwprintf_s(wchar_t * restrict s,
-              rsize_t n,
-              const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or - precision) shall not appear in the wide string pointed to by format. Any argument to - vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No - encoding error shall occur. - - -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to - the null wide character. -

Description -

- The vsnwprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -

- The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit - within the array pointed to by s. -

Returns -

- The vsnwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating null character, or - a negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - -

Footnotes -

422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.9 The vswprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <wchar.h>
-         int vswprintf_s(wchar_t * restrict s,
-              rsize_t n,
-              const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier423) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to vswprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. -

- If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the - null wide character. - - -

Description -

- The vswprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -

- The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the - array pointed to by s as a runtime-constraint violation. -

Returns -

- If no runtime-constraint violation occurred, the vswprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, vswprintf_s returns a negative value. If any other runtime-constraint - violation occurred, vswprintf_s returns zero. - -

Footnotes -

423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.10 The vswscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <wchar.h>
-         int vswscanf_s(const wchar_t * restrict s,
-              const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vswscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vswscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vswscanf_s function is equivalent to swscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswscanf_s function does not invoke the - va_end macro.424) - - - - - -

Returns -

- The vswscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vswscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - - -

Contents -

K.3.9.1.11 The vwprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <wchar.h>
-         int vwprintf_s(const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- format shall not be a null pointer. The %n specifier425) (modified or not by flags, field - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer. -

- If there is a runtime-constraint violation, the vwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vwprintf_s produced - output before discovering the runtime-constraint violation. -

Description -

- The vwprintf_s function is equivalent to the vwprintf function except for the - explicit runtime-constraints listed above. -

Returns -

- The vwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - - -

Footnotes -

425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.12 The vwscanf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <stdarg.h>
-         #include <wchar.h>
-         int vwscanf_s(const wchar_t * restrict format,
-              va_list arg);
-
- Runtime-constraints -

- format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the vwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vwscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The vwscanf_s function is equivalent to wscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwscanf_s function does not invoke the - va_end macro.426) -

Returns -

- The vwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -

Footnotes -

426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - - -

Contents -

K.3.9.1.13 The wprintf_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         int wprintf_s(const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- format shall not be a null pointer. The %n specifier427) (modified or not by flags, field - - - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to wprintf_s corresponding to a %s specifier shall not be a null pointer. -

- If there is a runtime-constraint violation, the wprintf_s function does not attempt to - produce further output, and it is unspecified to what extent wprintf_s produced output - before discovering the runtime-constraint violation. -

Description -

- The wprintf_s function is equivalent to the wprintf function except for the explicit - runtime-constraints listed above. -

Returns -

- The wprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - -

Footnotes -

427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - - -

Contents -

K.3.9.1.14 The wscanf_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <wchar.h>
-        int wscanf_s(const wchar_t * restrict format, ...);
-
- Runtime-constraints -

- format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -

- If there is a runtime-constraint violation, the wscanf_s function does not attempt to - perform further input, and it is unspecified to what extent wscanf_s performed input - before discovering the runtime-constraint violation. -

Description -

- The wscanf_s function is equivalent to fwscanf_s with the argument stdin - interposed before the arguments to wscanf_s. -

Returns -

- The wscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - wscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - -

Contents -

K.3.9.2 General wide string utilities
- -

Contents -

K.3.9.2.1 Wide string copying functions
- -

Contents -

K.3.9.2.1.1 The wcscpy_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         errno_t wcscpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the - null wide character. -

Description -

- The wcscpy_s function copies the wide string pointed to by s2 (including the - terminating null wide character) into the array pointed to by s1. -

- All elements following the terminating null wide character (if any) written by - wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscpy_s returns.428) -

Returns -

- The wcscpy_s function returns zero429) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - - -

Footnotes -

428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - -

429) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.9.2.1.2 The wcsncpy_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         errno_t wcsncpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2,
-              rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the - null wide character. -

Description -

- The wcsncpy_s function copies not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the array pointed to by s1. If no null wide character was copied from s2, then - s1[n] is set to a null wide character. -

- All elements following the terminating null wide character (if any) written by - wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncpy_s returns.430) -

Returns -

- The wcsncpy_s function returns zero431) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -

- EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. - - - - - -

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         /* ... */
-         wchar_t src1[100] = L"hello";
-         wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'};
-         wchar_t dst1[6], dst2[5], dst3[5];
-         int r1, r2, r3;
-         r1 = wcsncpy_s(dst1, 6, src1, 100);
-         r2 = wcsncpy_s(dst2, 5, src2, 7);
-         r3 = wcsncpy_s(dst3, 5, src2, 4);
-
- The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0. - The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0. - - -

Footnotes -

430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - -

431) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.9.2.1.3 The wmemcpy_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         errno_t wmemcpy_s(wchar_t * restrict s1,
-              rsize_t s1max,
-              const wchar_t * restrict s2,
-              rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -

- If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. -

Description -

- The wmemcpy_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. -

Returns -

- The wmemcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - -

Contents -

K.3.9.2.1.4 The wmemmove_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <wchar.h>
-        errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
-             const wchar_t *s2, rsize_t n);
-
- Runtime-constraints -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -

- If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. -

Description -

- The wmemmove_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. This copying takes place as if the n wide - characters from the object pointed to by s2 are first copied into a temporary array of n - wide characters that does not overlap the objects pointed to by s1 or s2, and then the n - wide characters from the temporary array are copied into the object pointed to by s1. -

Returns -

- The wmemmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Contents -

K.3.9.2.2 Wide string concatenation functions
- -

Contents -

K.3.9.2.2.1 The wcscat_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <wchar.h>
-        errno_t wcscat_s(wchar_t * restrict s1,
-             rsize_t s1max,
-             const wchar_t * restrict s2);
-
- Runtime-constraints -

- Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcscat_s. -

- Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.432) m shall be greater than - wcsnlen_s(s2, m). Copying shall not take place between objects that overlap. - -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the - null wide character. -

Description -

- The wcscat_s function appends a copy of the wide string pointed to by s2 (including - the terminating null wide character) to the end of the wide string pointed to by s1. The - initial wide character from s2 overwrites the null wide character at the end of s1. -

- All elements following the terminating null wide character (if any) written by - wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscat_s returns.433) -

Returns -

- The wcscat_s function returns zero434) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -

Footnotes -

432) Zero means that s1 was not null terminated upon entry to wcscat_s. - -

433) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - -

434) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.9.2.2.2 The wcsncat_s function
-

Synopsis -

-

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <wchar.h>
-          errno_t wcsncat_s(wchar_t * restrict s1,
-               rsize_t s1max,
-               const wchar_t * restrict s2,
-               rsize_t n);
-
- Runtime-constraints -

- Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcsncat_s. -

- Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less - than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take - place between objects that overlap. - - - -

- If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the - null wide character. -

Description -

- The wcsncat_s function appends not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the end of the wide string pointed to by s1. The initial wide character from s2 - overwrites the null wide character at the end of s1. If no null wide character was copied - from s2, then s1[s1max-m+n] is set to a null wide character. -

- All elements following the terminating null wide character (if any) written by - wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncat_s returns.436) -

Returns -

- The wcsncat_s function returns zero437) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -

- EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. -

-          #define __STDC_WANT_LIB_EXT1__ 1
-          #include <wchar.h>
-          /* ... */
-          wchar_t s1[100] = L"good";
-          wchar_t s2[6] = L"hello";
-          wchar_t s3[6] = L"hello";
-          wchar_t s4[7] = L"abc";
-          wchar_t s5[1000] = L"bye";
-          int r1, r2, r3, r4;
-          r1 = wcsncat_s(s1, 100, s5, 1000);
-          r2 = wcsncat_s(s2, 6, L"", 1);
-          r3 = wcsncat_s(s3, 6, L"X", 2);
-          r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
-
- After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0. - After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0. - After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0. - After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0. - - - - - - -

Footnotes -

435) Zero means that s1 was not null terminated upon entry to wcsncat_s. - -

436) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - -

437) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - - -

Contents -

K.3.9.2.3 Wide string search functions
- -

Contents -

K.3.9.2.3.1 The wcstok_s function
-

Synopsis -

-

-         #define __STDC_WANT_LIB_EXT1__ 1
-         #include <wchar.h>
-         wchar_t *wcstok_s(wchar_t * restrict s1,
-              rsize_t * restrict s1max,
-              const wchar_t * restrict s2,
-              wchar_t ** restrict ptr);
-
- Runtime-constraints -

- None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max wide characters of s1 for - the first call, and shall occur within the first *s1max wide characters of where searching - resumes on subsequent calls. -

- If there is a runtime-constraint violation, the wcstok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. -

Description -

- A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1 - into a sequence of tokens, each of which is delimited by a wide character from the wide - string pointed to by s2. The fourth argument points to a caller-provided wchar_t - pointer into which the wcstok_s function stores information necessary for it to - continue scanning the same wide string. -

- The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the wide character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator wide string pointed - to by s2 may be different from call to call. -

- The first call in the sequence searches the wide string pointed to by s1 for the first wide - character that is not contained in the current separator wide string pointed to by s2. If no - such wide character is found, then there are no tokens in the wide string pointed to by s1 - and the wcstok_s function returns a null pointer. If such a wide character is found, it is - the start of the first token. - -

- The wcstok_s function then searches from there for the first wide character in s1 that - is contained in the current separator wide string. If no such wide character is found, the - current token extends to the end of the wide string pointed to by s1, and subsequent - searches in the same wide string for a token return a null pointer. If such a wide character - is found, it is overwritten by a null wide character, which terminates the current token. -

- In all cases, the wcstok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null wide - character (if any). -

Returns -

- The wcstok_s function returns a pointer to the first wide character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -

- EXAMPLE -

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <wchar.h>
-        static wchar_t str1[] = L"?a???b,,,#c";
-        static wchar_t str2[] = L"\t \t";
-        wchar_t *t, *ptr1, *ptr2;
-        rsize_t max1 = wcslen(str1)+1;
-        rsize_t max2 = wcslen(str2)+1;
-        t   =   wcstok_s(str1,   &max1,   "?", &ptr1);        //   t   points to the token "a"
-        t   =   wcstok_s(NULL,   &max1,   ",", &ptr1);        //   t   points to the token "??b"
-        t   =   wcstok_s(str2,   &max2,   " \t", &ptr2);      //   t   is a null pointer
-        t   =   wcstok_s(NULL,   &max1,   "#,", &ptr1);       //   t   points to the token "c"
-        t   =   wcstok_s(NULL,   &max1,   "?", &ptr1);        //   t   is a null pointer
-
- - -

Contents -

K.3.9.2.4 Miscellaneous functions
- -

Contents -

K.3.9.2.4.1 The wcsnlen_s function
-

Synopsis -

-

-        #define __STDC_WANT_LIB_EXT1__ 1
-        #include <wchar.h>
-        size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
-
-

Description -

- The wcsnlen_s function computes the length of the wide string pointed to by s. -

Returns -

- If s is a null pointer,438) then the wcsnlen_s function returns zero. -

- Otherwise, the wcsnlen_s function returns the number of wide characters that precede - the terminating null wide character. If there is no null wide character in the first - maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first - - maxsize wide characters of s shall be accessed by wcsnlen_s. - -

Footnotes -

438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated wide string argument make - wcsnlen_s useful in algorithms that gracefully handle such exceptional data. - - -

Contents -

K.3.9.3 Extended multibyte/wide character conversion utilities
- -

Contents -

K.3.9.3.1 Restartable multibyte/wide character conversion functions
-

- Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the - conversion state) to be a null pointer. - -

Contents -

K.3.9.3.1.1 The wcrtomb_s function
-

Synopsis -

-

-         #include <wchar.h>
-         errno_t wcrtomb_s(size_t * restrict retval,
-              char * restrict s, rsize_t smax,
-              wchar_t wc, mbstate_t * restrict ps);
-
- Runtime-constraints -

- Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax - shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer, - then smax shall be not be less than the number of bytes to be stored in the array pointed - to by s. If s is a null pointer, then smax shall equal zero. -

- If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is - not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then - wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then - wcrtomb_s sets *retval to (size_t)(-1). -

Description -

- If s is a null pointer, the wcrtomb_s function is equivalent to the call -

-                 wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
-
- where retval and buf are internal variables of the appropriate types, and the size of - buf is greater than MB_CUR_MAX. -

- If s is not a null pointer, the wcrtomb_s function determines the number of bytes - needed to represent the multibyte character that corresponds to the wide character given - by wc (including any shift sequences), and stores the multibyte character representation - in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are - stored. If wc is a null wide character, a null byte is stored, preceded by any shift - sequence needed to restore the initial shift state; the resulting state described is the initial - conversion state. - - -

- If wc does not correspond to a valid multibyte character, an encoding error occurs: the - wcrtomb_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the wcrtomb_s function stores into - *retval the number of bytes (including any shift sequences) stored in the array pointed - to by s. -

Returns -

- The wcrtomb_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - -

Contents -

K.3.9.3.2 Restartable multibyte/wide string conversion functions
-

- Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not - permit the ps parameter (the pointer to the conversion state) to be a null pointer. - -

Contents -

K.3.9.3.2.1 The mbsrtowcs_s function
-

Synopsis -

-

-        #include <wchar.h>
-        errno_t mbsrtowcs_s(size_t * restrict retval,
-             wchar_t * restrict dst, rsize_t dstmax,
-             const char ** restrict src, rsize_t len,
-             mbstate_t * restrict ps);
-
- Runtime-constraints -

- None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null - character shall occur within the first dstmax multibyte characters of the array pointed to - by *src. -

- If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If - retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbsrtowcs_s sets dst[0] to the null wide character. -

Description -

- The mbsrtowcs_s function converts a sequence of multibyte characters that begins in - the conversion state described by the object pointed to by ps, from the array indirectly - pointed to by src into a sequence of corresponding wide characters. If dst is not a null - pointer, the converted characters are stored into the array pointed to by dst. Conversion - continues up to and including a terminating null character, which is also stored. - Conversion stops earlier in two cases: when a sequence of bytes is encountered that does - not form a valid multibyte character, or (if dst is not a null pointer) when len wide - - characters have been stored into the array pointed to by dst.439) If dst is not a null - pointer and no null wide character was stored into the array pointed to by dst, then - dst[len] is set to the null wide character. Each conversion takes place as if by a call - to the mbrtowc function. -

- If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null character) or the address - just past the last multibyte character converted (if any). If conversion stopped due to - reaching a terminating null character and if dst is not a null pointer, the resulting state - described is the initial conversion state. -

- Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into - *retval the number of multibyte characters successfully converted, not including the - terminating null character (if any). -

- All elements following the terminating null wide character (if any) written by - mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbsrtowcs_s returns.440) -

- If copying takes place between objects that overlap, the objects take on unspecified - values. -

Returns -

- The mbsrtowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - -

Footnotes -

439) Thus, the value of len is ignored if dst is a null pointer. - -

440) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - - -

Contents -

K.3.9.3.2.2 The wcsrtombs_s function
-

Synopsis -

-

-          #include <wchar.h>
-          errno_t wcsrtombs_s(size_t * restrict retval,
-               char * restrict dst, rsize_t dstmax,
-               const wchar_t ** restrict src, rsize_t len,
-               mbstate_t * restrict ps);
-
- - - - - - Runtime-constraints -

- None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then the - conversion shall have been stopped (see below) because a terminating null wide character - was reached or because an encoding error occurred. -

- If there is a runtime-constraint violation, then wcsrtombs_s does the following. If - retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcsrtombs_s sets dst[0] to the null character. -

Description -

- The wcsrtombs_s function converts a sequence of wide characters from the array - indirectly pointed to by src into a sequence of corresponding multibyte characters that - begins in the conversion state described by the object pointed to by ps. If dst is not a - null pointer, the converted characters are then stored into the array pointed to by dst. - Conversion continues up to and including a terminating null wide character, which is also - stored. Conversion stops earlier in two cases: -

- If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.441) -

- If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null wide character) or the - address just past the last wide character converted (if any). If conversion stopped due to - reaching a terminating null wide character, the resulting state described is the initial - conversion state. - - - -

- Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval - and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores - into *retval the number of bytes in the resulting multibyte character sequence, not - including the terminating null character (if any). -

- All elements following the terminating null character (if any) written by wcsrtombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcsrtombs_s returns.442) -

- If copying takes place between objects that overlap, the objects take on unspecified - values. -

Returns -

- The wcsrtombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - - - - - - -

Footnotes -

441) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - -

442) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - - -

Contents -

Annex L

-
-                                            (normative)
-                                         Analyzability
-
- -

Contents -

L.1 Scope

-

- This annex specifies optional behavior that can aid in the analyzability of C programs. -

- An implementation that defines __STDC_ANALYZABLE__ shall conform to the - specifications in this annex.443) - -

Footnotes -

443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these - specifications. - - -

Contents -

L.2 Definitions

- -

Contents -

L.2.1

-

- out-of-bounds store - an (attempted) access (3.1) that, at run time, for a given computational state, would - modify (or, for an object declared volatile, fetch) one or more bytes that lie outside - the bounds permitted by this Standard. - -

Contents -

L.2.2

-

- bounded undefined behavior - undefined behavior (3.4.3) that does not perform an out-of-bounds store. -

- NOTE 1 The behavior might perform a trap. - -

- NOTE 2 Any values produced or stored might be indeterminate values. - - -

Contents -

L.2.3

-

- critical undefined behavior - undefined behavior that is not bounded undefined behavior. -

- NOTE The behavior might perform an out-of-bounds store or perform a trap. - - - - - - -

Contents -

L.3 Requirements

-

- If the program performs a trap (3.19.5), the implementation is permitted to invoke a - runtime-constraint handler. Any such semantics are implementation-defined. -

- All undefined behavior shall be limited to bounded undefined behavior, except for the - following which are permitted to result in critical undefined behavior: -

- -

Contents -

Bibliography

-
    -
  1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was - published in The C Programming Language by Brian W. Kernighan and Dennis - M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T. -
  2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara, - California, USA, November 1984. -
  3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information - Processing Systems, Information Processing Systems Technical Report. -
  4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point - Arithmetic. -
  5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent - Floating-Point Arithmetic. -
  6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems, - second edition (previously designated IEC 559:1989). -
  7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and - symbols for use in the physical sciences and technology. -
  8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for - information interchange. -
  9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: - Fundamental terms. -
  10. ISO 4217:1995, Codes for the representation of currencies and funds. -
  11. ISO 8601:1988, Data elements and interchange formats -- Information - interchange -- Representation of dates and times. -
  12. ISO/IEC 9899:1990, Programming languages -- C. -
  13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1. -
  14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2. -
  15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity. -
  16. ISO/IEC 9899:1999, Programming languages -- C. -
  17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1. -
  18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2. -
  19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3. - -
  20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System - Interface (POSIX) -- Part 2: Shell and Utilities. -
  21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the - preparation of programming language standards. -
  22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet - Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. -
  23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to - ISO/IEC 10646-1:1993. -
  24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to - ISO/IEC 10646-1:1993. -
  25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993 - Transformation Format for 16 planes of group 00 (UTF-16). -
  26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS - Transformation Format 8 (UTF-8). -
  27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993. -
  28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993. -
  29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul - syllables. -
  30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993 - Tibetan. -
  31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33 - additional characters. -
  32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993. -
  33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993 - Identifiers for characters. -
  34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993 - Ethiopic. -
  35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993 - Unified Canadian Aboriginal Syllabics. -
  36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993 - Cherokee. -
  37. ISO/IEC 10967-1:1994, Information technology -- Language independent - arithmetic -- Part 1: Integer and floating point arithmetic. - -
  38. ISO/IEC TR 19769:2004, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions for the - programming language C to support new character data types. -
  39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions to the C library - -- Part 1: Bounds-checking interfaces. - -
- -

Contents -

Index

-
- [^ x ^], 3.20                                                    , (comma operator), 5.1.2.4, 6.5.17
-                                                                , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
- [_ x _], 3.21                                                         6.7.2.3, 6.7.9
- ! (logical negation operator), 6.5.3.3                         - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2
- != (inequality operator), 6.5.9                                - (unary minus operator), 6.5.3.3, F.3
- # operator, 6.10.3.2                                           -- (postfix decrement operator), 6.3.2.1, 6.5.2.4
- # preprocessing directive, 6.10.7                              -- (prefix decrement operator), 6.3.2.1, 6.5.3.1
- # punctuator, 6.10                                             -= (subtraction assignment operator), 6.5.16.2
- ## operator, 6.10.3.3                                          -> (structure/union pointer operator), 6.5.2.3
- #define preprocessing directive, 6.10.3                        . (structure/union member operator), 6.3.2.1,
- #elif preprocessing directive, 6.10.1                               6.5.2.3
- #else preprocessing directive, 6.10.1                          . punctuator, 6.7.9
- #endif preprocessing directive, 6.10.1                         ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3
- #error preprocessing directive, 4, 6.10.5                      / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1
- #if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,             /* */ (comment delimiters), 6.4.9
-      6.10.1, 7.1.4                                             // (comment delimiter), 6.4.9
- #ifdef preprocessing directive, 6.10.1                         /= (division assignment operator), 6.5.16.2
- #ifndef preprocessing directive, 6.10.1                        : (colon punctuator), 6.7.2.1
- #include preprocessing directive, 5.1.1.2,                     :> (alternative spelling of ]), 6.4.6
-      6.10.2                                                    ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3,
- #line preprocessing directive, 6.10.4                               6.8.5, 6.8.6
- #pragma preprocessing directive, 6.10.6                        < (less-than operator), 6.5.8
- #undef preprocessing directive, 6.10.3.5, 7.1.3,               <% (alternative spelling of {), 6.4.6
-      7.1.4                                                     <: (alternative spelling of [), 6.4.6
- % (remainder operator), 6.2.6.2, 6.5.5                         << (left-shift operator), 6.2.6.2, 6.5.7
- %: (alternative spelling of #), 6.4.6                          <<= (left-shift assignment operator), 6.5.16.2
- %:%: (alternative spelling of ##), 6.4.6                       <= (less-than-or-equal-to operator), 6.5.8
- %= (remainder assignment operator), 6.5.16.2                   <assert.h> header, 7.2
- %> (alternative spelling of }), 6.4.6                          <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2,
- & (address operator), 6.3.2.1, 6.5.3.2                              7.3, 7.24, 7.30.1, G.6, J.5.17
- & (bitwise AND operator), 6.2.6.2, 6.5.10                      <ctype.h> header, 7.4, 7.30.2
- && (logical AND operator), 5.1.2.4, 6.5.13                     <errno.h> header, 7.5, 7.30.3, K.3.2
- &= (bitwise AND assignment operator), 6.5.16.2                 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F,
- ' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,                H
-      7.4.1.10, 7.29.2.1.3                                      <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
- ( ) (cast operator), 6.5.4                                          7.28.4.1.1
- ( ) (function-call operator), 6.5.2.2                          <inttypes.h> header, 7.8, 7.30.4
- ( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5            <iso646.h> header, 4, 7.9
- ( ){ } (compound-literal operator), 6.5.2.5                    <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10
- * (asterisk punctuator), 6.7.6.1, 6.7.6.2                      <locale.h> header, 7.11, 7.30.5
- * (indirection operator), 6.5.2.1, 6.5.3.2                     <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,
- * (multiplication operator), 6.2.6.2, 6.5.5, F.3,                   F.10, J.5.17
-      G.5.1                                                     <setjmp.h> header, 7.13
- *= (multiplication assignment operator), 6.5.16.2              <signal.h> header, 7.14, 7.30.6
- + (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2,              <stdalign.h> header, 4, 7.15
-      6.5.6, F.3, G.5.2                                         <stdarg.h> header, 4, 6.7.6.3, 7.16
- + (unary plus operator), 6.5.3.3                               <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17
- ++ (postfix increment operator), 6.3.2.1, 6.5.2.4               <stdbool.h> header, 4, 7.18, 7.30.7, H
- ++ (prefix increment operator), 6.3.2.1, 6.5.3.1                <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
- += (addition assignment operator), 6.5.16.2
-
-      6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3                      \x hexadecimal digits (hexadecimal-character
- <stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8,                       escape sequence), 6.4.4.4
-      7.20, 7.30.8, K.3.3, K.3.4                              ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11
- <stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F,                ^= (bitwise exclusive OR assignment operator),
-      K.3.5                                                        6.5.16.2
- <stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F,              __alignas_is_defined macro, 7.15
-      K.3.1.4, K.3.6                                          __bool_true_false_are_defined
- <string.h> header, 7.23, 7.30.11, K.3.7                           macro, 7.18
- <tgmath.h> header, 7.24, G.7                                 __cplusplus macro, 6.10.8
- <threads.h> header, 6.10.8.3, 7.1.2, 7.25                    __DATE__ macro, 6.10.8.1
- <time.h> header, 7.26, K.3.8                                 __FILE__ macro, 6.10.8.1, 7.2.1.1
- <uchar.h> header, 6.4.4.4, 6.4.5, 7.27                       __func__ identifier, 6.4.2.2, 7.2.1.1
- <wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28,                   __LINE__ macro, 6.10.8.1, 7.2.1.1
-      7.30.12, F, K.3.9                                       __STDC_, 6.11.9
- <wctype.h> header, 7.29, 7.30.13                             __STDC__ macro, 6.10.8.1
- = (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9               __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1
- = (simple assignment operator), 6.5.16.1                     __STDC_HOSTED__ macro, 6.10.8.1
- == (equality operator), 6.5.9                                __STDC_IEC_559__ macro, 6.10.8.3, F.1
- > (greater-than operator), 6.5.8                             __STDC_IEC_559_COMPLEX__ macro,
- >= (greater-than-or-equal-to operator), 6.5.8                     6.10.8.3, G.1
- >> (right-shift operator), 6.2.6.2, 6.5.7                    __STDC_ISO_10646__ macro, 6.10.8.2
- >>= (right-shift assignment operator), 6.5.16.2              __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2
- ? : (conditional operator), 5.1.2.4, 6.5.15                  __STDC_MB_MIGHT_NEQ_WC__ macro,
- ?? (trigraph sequences), 5.2.1.1                                  6.10.8.2, 7.19
- [ ] (array subscript operator), 6.5.2.1, 6.5.3.2             __STDC_NO_COMPLEX__ macro, 6.10.8.3,
- [ ] (brackets punctuator), 6.7.6.2, 6.7.9                         7.3.1
- \ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4             __STDC_NO_THREADS__ macro, 6.10.8.3,
- \ (escape character), 6.4.4.4                                     7.17.1, 7.25.1
- \" (double-quote escape sequence), 6.4.4.4,                  __STDC_NO_VLA__ macro, 6.10.8.3
-      6.4.5, 6.10.9                                           __STDC_UTF_16__ macro, 6.10.8.2
- \\ (backslash escape sequence), 6.4.4.4, 6.10.9              __STDC_UTF_32__ macro, 6.10.8.2
- \' (single-quote escape sequence), 6.4.4.4, 6.4.5            __STDC_VERSION__ macro, 6.10.8.1
- \0 (null character), 5.2.1, 6.4.4.4, 6.4.5                   __STDC_WANT_LIB_EXT1__ macro, K.3.1.1
-   padding of binary stream, 7.21.2                           __TIME__ macro, 6.10.8.1
- \? (question-mark escape sequence), 6.4.4.4                  __VA_ARGS__ identifier, 6.10.3, 6.10.3.1
- \a (alert escape sequence), 5.2.2, 6.4.4.4                   _Alignas, 6.7.5
- \b (backspace escape sequence), 5.2.2, 6.4.4.4               _Atomic type qualifier, 6.7.3
- \f (form-feed escape sequence), 5.2.2, 6.4.4.4,              _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1,
-      7.4.1.10                                                     F.4
- \n (new-line escape sequence), 5.2.2, 6.4.4.4,               _Bool type conversions, 6.3.1.2
-      7.4.1.10                                                _Complex types, 6.2.5, 6.7.2, 7.3.1, G
- \octal digits (octal-character escape sequence),             _Complex_I macro, 7.3.1
-      6.4.4.4                                                 _Exit function, 7.22.4.5, 7.22.4.7
- \r (carriage-return escape sequence), 5.2.2,                 _Imaginary keyword, G.2
-      6.4.4.4, 7.4.1.10                                       _Imaginary types, 7.3.1, G
- \t (horizontal-tab escape sequence), 5.2.2,                  _Imaginary_I macro, 7.3.1, G.6
-      6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3                  _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
- \U (universal character names), 6.4.3                        _IOLBF macro, 7.21.1, 7.21.5.6
- \u (universal character names), 6.4.3                        _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
- \v (vertical-tab escape sequence), 5.2.2, 6.4.4.4,           _Noreturn, 6.7.4
-      7.4.1.10                                                _Pragma operator, 5.1.1.2, 6.10.9
-
- _Static_assert, 6.7.10, 7.2                                  allocated storage, order and contiguity, 7.22.3
- _Thread_local storage-class specifier, 6.2.4,                 and macro, 7.9
-      6.7.1                                                   AND operators
- { } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9,               bitwise (&), 6.2.6.2, 6.5.10
-      6.8.2                                                      bitwise assignment (&=), 6.5.16.2
- { } (compound-literal operator), 6.5.2.5                        logical (&&), 5.1.2.4, 6.5.13
- | (bitwise inclusive OR operator), 6.2.6.2, 6.5.12           and_eq macro, 7.9
- |= (bitwise inclusive OR assignment operator),               anonymous structure, 6.7.2.1
-      6.5.16.2                                                anonymous union, 6.7.2.1
- || (logical OR operator), 5.1.2.4, 6.5.14                    ANSI/IEEE 754, F.1
- ~ (bitwise complement operator), 6.2.6.2, 6.5.3.3            ANSI/IEEE 854, F.1
-                                                              argc (main function parameter), 5.1.2.2.1
- abort function, 7.2.1.1, 7.14.1.1, 7.21.3,                   argument, 3.3
-       7.22.4.1, 7.25.3.6, K.3.6.1.2                             array, 6.9.1
- abort_handler_s function, K.3.6.1.2                             default promotions, 6.5.2.2
- abs function, 7.22.6.1                                          function, 6.5.2.2, 6.9.1
- absolute-value functions                                        macro, substitution, 6.10.3.1
-    complex, 7.3.8, G.6.4                                     argument, complex, 7.3.9.1
-    integer, 7.8.2.1, 7.22.6.1                                argv (main function parameter), 5.1.2.2.1
-    real, 7.12.7, F.10.4                                      arithmetic constant expression, 6.6
- abstract declarator, 6.7.7                                   arithmetic conversions, usual, see usual arithmetic
- abstract machine, 5.1.2.3                                          conversions
- access, 3.1, 6.7.3, L.2.1                                    arithmetic operators
- accuracy, see floating-point accuracy                            additive, 6.2.6.2, 6.5.6, G.5.2
- acos functions, 7.12.4.1, F.10.1.1                              bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12
- acos type-generic macro, 7.24                                   increment and decrement, 6.5.2.4, 6.5.3.1
- acosh functions, 7.12.5.1, F.10.2.1                             multiplicative, 6.2.6.2, 6.5.5, G.5.1
- acosh type-generic macro, 7.24                                  shift, 6.2.6.2, 6.5.7
- acquire fence, 7.17.4                                           unary, 6.5.3.3
- acquire operation, 5.1.2.4                                   arithmetic types, 6.2.5
- active position, 5.2.2                                       arithmetic, pointer, 6.5.6
- actual argument, 3.3                                         array
- actual parameter (deprecated), 3.3                              argument, 6.9.1
- addition assignment operator (+=), 6.5.16.2                     declarator, 6.7.6.2
- addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2,               initialization, 6.7.9
-       6.5.6, F.3, G.5.2                                         multidimensional, 6.5.2.1
- additive expressions, 6.5.6, G.5.2                              parameter, 6.9.1
- address constant, 6.6                                           storage order, 6.5.2.1
- address operator (&), 6.3.2.1, 6.5.3.2                          subscript operator ([ ]), 6.5.2.1, 6.5.3.2
- address-free, 7.17.5                                            subscripting, 6.5.2.1
- aggregate initialization, 6.7.9                                 type, 6.2.5
- aggregate types, 6.2.5                                          type conversion, 6.3.2.1
- alert escape sequence (\a), 5.2.2, 6.4.4.4                      variable length, 6.7.6, 6.7.6.2, 6.10.8.3
- aliasing, 6.5                                                arrow operator (->), 6.5.2.3
- alignas macro, 7.15                                          as-if rule, 5.1.2.3
- aligned_alloc function, 7.22.3, 7.22.3.1                     ASCII code set, 5.2.1.1
- alignment, 3.2, 6.2.8, 7.22.3.1                              asctime function, 7.26.3.1
-    pointer, 6.2.5, 6.3.2.3                                   asctime_s function, K.3.8.2, K.3.8.2.1
-    structure/union member, 6.7.2.1                           asin functions, 7.12.4.2, F.10.1.2
- alignment specifier, 6.7.5                                    asin type-generic macro, 7.24, G.7
- alignof operator, 6.5.3, 6.5.3.4                             asinh functions, 7.12.5.2, F.10.2.2
-
- asinh type-generic macro, 7.24, G.7                           atomic_is_lock_free generic function,
- asm keyword, J.5.10                                               7.17.5.1
- assert macro, 7.2.1.1                                         ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
- assert.h header, 7.2                                          atomic_load generic functions, 7.17.7.2
- assignment                                                    ATOMIC_LONG_LOCK_FREE macro, 7.17.1
-    compound, 6.5.16.2                                         ATOMIC_SHORT_LOCK_FREE macro, 7.17.1
-    conversion, 6.5.16.1                                       atomic_signal_fence function, 7.17.4.2
-    expression, 6.5.16                                         atomic_store generic functions, 7.17.7.1
-    operators, 6.3.2.1, 6.5.16                                 atomic_thread_fence function, 7.17.4.1
-    simple, 6.5.16.1                                           ATOMIC_VAR_INIT macro, 7.17.2.1
- associativity of operators, 6.5                               ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1
- asterisk punctuator (*), 6.7.6.1, 6.7.6.2                     atomics header, 7.17
- at_quick_exit function, 7.22.4.2, 7.22.4.3,                   auto storage-class specifier, 6.7.1, 6.9
-      7.22.4.4, 7.22.4.5, 7.22.4.7                             automatic storage duration, 5.2.3, 6.2.4
- atan functions, 7.12.4.3, F.10.1.3
- atan type-generic macro, 7.24, G.7                            backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
- atan2 functions, 7.12.4.4, F.10.1.4                           backslash escape sequence (\\), 6.4.4.4, 6.10.9
- atan2 type-generic macro, 7.24                                backspace escape sequence (\b), 5.2.2, 6.4.4.4
- atanh functions, 7.12.5.3, F.10.2.3                           basic character set, 3.6, 3.7.2, 5.2.1
- atanh type-generic macro, 7.24, G.7                           basic types, 6.2.5
- atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4,                behavior, 3.4
-      7.22.4.5, 7.22.4.7, J.5.13                               binary streams, 7.21.2, 7.21.7.10, 7.21.9.2,
- atof function, 7.22.1, 7.22.1.1                                     7.21.9.4
- atoi function, 7.22.1, 7.22.1.2                               bit, 3.5
- atol function, 7.22.1, 7.22.1.2                                  high order, 3.6
- atoll function, 7.22.1, 7.22.1.2                                 low order, 3.6
- atomic lock-free macros, 7.17.1, 7.17.5                       bit-field, 6.7.2.1
- atomic operations, 5.1.2.4                                    bitand macro, 7.9
- atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1,               bitor macro, 7.9
-      6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3,           bitwise operators, 6.5
-      7.17.6                                                      AND, 6.2.6.2, 6.5.10
- atomic_address type, 7.17.1, 7.17.6                              AND assignment (&=), 6.5.16.2
- ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1                           complement (~), 6.2.6.2, 6.5.3.3
- atomic_bool type, 7.17.1, 7.17.6                                 exclusive OR, 6.2.6.2, 6.5.11
- ATOMIC_CHAR16_T_LOCK_FREE macro,                                 exclusive OR assignment (^=), 6.5.16.2
-      7.17.1                                                      inclusive OR, 6.2.6.2, 6.5.12
- ATOMIC_CHAR32_T_LOCK_FREE macro,                                 inclusive OR assignment (|=), 6.5.16.2
-      7.17.1                                                      shift, 6.2.6.2, 6.5.7
- ATOMIC_CHAR_LOCK_FREE macro, 7.17.1                           blank character, 7.4.1.3
- atomic_compare_exchange generic                               block, 6.8, 6.8.2, 6.8.4, 6.8.5
-      functions, 7.17.7.4                                      block scope, 6.2.1
- atomic_exchange generic functions, 7.17.7.3                   block structure, 6.2.1
- atomic_fetch and modify generic functions,                    bold type convention, 6.1
-      7.17.7.5                                                 bool macro, 7.18
- atomic_flag type, 7.17.1, 7.17.8                              boolean type, 6.3.1.2
- atomic_flag_clear functions, 7.17.8.2                         boolean type conversion, 6.3.1.1, 6.3.1.2
- ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8                        bounded undefined behavior, L.2.2
- atomic_flag_test_and_set functions,                           braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9,
-      7.17.8.1                                                       6.8.2
- atomic_init generic function, 7.17.2.2                        brackets operator ([ ]), 6.5.2.1, 6.5.3.2
- ATOMIC_INT_LOCK_FREE macro, 7.17.1                            brackets punctuator ([ ]), 6.7.6.2, 6.7.9
-
- branch cuts, 7.3.3                                                type-generic macro for, 7.24
- break statement, 6.8.6.3                                       ccosh functions, 7.3.6.4, G.6.2.4
- broken-down time, 7.26.1, 7.26.2.3, 7.26.3,                       type-generic macro for, 7.24
-      7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5,                   ceil functions, 7.12.9.1, F.10.6.1
-      K.3.8.2.1, K.3.8.2.3, K.3.8.2.4                           ceil type-generic macro, 7.24
- bsearch function, 7.22.5, 7.22.5.1                             cerf function, 7.30.1
- bsearch_s function, K.3.6.3, K.3.6.3.1                         cerfc function, 7.30.1
- btowc function, 7.28.6.1.1                                     cexp functions, 7.3.7.1, G.6.3.1
- BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5                            type-generic macro for, 7.24
- byte, 3.6, 6.5.3.4                                             cexp2 function, 7.30.1
- byte input/output functions, 7.21.1                            cexpm1 function, 7.30.1
- byte-oriented stream, 7.21.2                                   char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2,
-                                                                      K.3.9.1.2
- C program, 5.1.1.1                                             char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
- c16rtomb function, 7.27.1.2                                          6.3.1.8
- c32rtomb function, 7.27.1.4                                    char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
- cabs functions, 7.3.8.1, G.6                                   char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
-   type-generic macro for, 7.24                                 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1
- cacos functions, 7.3.5.1, G.6.1.1                              CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
-   type-generic macro for, 7.24                                 CHAR_MIN macro, 5.2.4.2.1
- cacosh functions, 7.3.6.1, G.6.2.1                             character, 3.7, 3.7.1
-   type-generic macro for, 7.24                                 character array initialization, 6.7.9
- calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4,           character case mapping functions, 7.4.2
-       7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2,                    wide character, 7.29.3.1
-       K.3.8.2.3, K.3.8.2.4                                           extensible, 7.29.3.2
- call by value, 6.5.2.2                                         character classification functions, 7.4.1
- call_once function, 7.25.1, 7.25.2.1                              wide character, 7.29.2.1
- calloc function, 7.22.3, 7.22.3.2                                    extensible, 7.29.2.2
- carg functions, 7.3.9.1, G.6                                   character constant, 5.1.1.2, 5.2.1, 6.4.4.4
- carg type-generic macro, 7.24, G.7                             character display semantics, 5.2.2
- carriage-return escape sequence (\r), 5.2.2,                   character handling header, 7.4, 7.11.1.1
-       6.4.4.4, 7.4.1.10                                        character input/output functions, 7.21.7, K.3.5.4
- carries a dependency, 5.1.2.4                                     wide character, 7.28.3
- case label, 6.8.1, 6.8.4.2                                     character sets, 5.2.1
- case mapping functions                                         character string literal, see string literal
-   character, 7.4.2                                             character type conversion, 6.3.1.1
-   wide character, 7.29.3.1                                     character types, 6.2.5, 6.7.9
-       extensible, 7.29.3.2                                     cimag functions, 7.3.9.2, 7.3.9.5, G.6
- casin functions, 7.3.5.2, G.6                                  cimag type-generic macro, 7.24, G.7
-   type-generic macro for, 7.24                                 cis function, G.6
- casinh functions, 7.3.6.2, G.6.2.2                             classification functions
-   type-generic macro for, 7.24                                    character, 7.4.1
- cast expression, 6.5.4                                            floating-point, 7.12.3
- cast operator (( )), 6.5.4                                        wide character, 7.29.2.1
- catan functions, 7.3.5.3, G.6                                        extensible, 7.29.2.2
-   type-generic macro for, 7.24                                 clearerr function, 7.21.10.1
- catanh functions, 7.3.6.3, G.6.2.3                             clgamma function, 7.30.1
-   type-generic macro for, 7.24                                 clock function, 7.26.2.1
- cbrt functions, 7.12.7.1, F.10.4.1                             clock_t type, 7.26.1, 7.26.2.1
- cbrt type-generic macro, 7.24                                  CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1
- ccos functions, 7.3.5.4, G.6                                   clog functions, 7.3.7.2, G.6.3.2
-
-   type-generic macro for, 7.24                                  string, 7.23.3, K.3.7.2
- clog10 function, 7.30.1                                         wide string, 7.28.4.3, K.3.9.2.2
- clog1p function, 7.30.1                                       concatenation, preprocessing, see preprocessing
- clog2 function, 7.30.1                                             concatenation
- CMPLX macros, 7.3.9.3                                         conceptual models, 5.1
- cnd_broadcast function, 7.25.3.1, 7.25.3.5,                   conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3,
-      7.25.3.6                                                      7.1.2, F.1, G.1, K.2, L.1
- cnd_destroy function, 7.25.3.2                                conditional inclusion, 6.10.1
- cnd_init function, 7.25.3.3                                   conditional operator (? :), 5.1.2.4, 6.5.15
- cnd_signal function, 7.25.3.4, 7.25.3.5,                      conflict, 5.1.2.4
-      7.25.3.6                                                 conformance, 4
- cnd_t type, 7.25.1                                            conj functions, 7.3.9.4, G.6
- cnd_timedwait function, 7.25.3.5                              conj type-generic macro, 7.24
- cnd_wait function, 7.25.3.3, 7.25.3.6                         const type qualifier, 6.7.3
- collating sequences, 5.2.1                                    const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
- colon punctuator (:), 6.7.2.1                                 constant expression, 6.6, F.8.4
- comma operator (,), 5.1.2.4, 6.5.17                           constants, 6.4.4
- comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,             as primary expression, 6.5.1
-      6.7.2.3, 6.7.9                                             character, 6.4.4.4
- command processor, 7.22.4.8                                     enumeration, 6.2.1, 6.4.4.3
- comment delimiters (/* */ and //), 6.4.9                        floating, 6.4.4.2
- comments, 5.1.1.2, 6.4, 6.4.9                                   hexadecimal, 6.4.4.1
- common extensions, J.5                                          integer, 6.4.4.1
- common initial sequence, 6.5.2.3                                octal, 6.4.4.1
- common real type, 6.3.1.8                                     constraint, 3.8, 4
- common warnings, I                                            constraint_handler_t type, K.3.6
- comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2,             consume operation, 5.1.2.4
-      K.3.6.3, K.3.6.3.1, K.3.6.3.2                            content of structure/union/enumeration, 6.7.2.3
-   string, 7.23.4                                              contiguity of allocated storage, 7.22.3
-   wide string, 7.28.4.4                                       continue statement, 6.8.6.2
- comparison macros, 7.12.14                                    contracted expression, 6.5, 7.12.2, F.7
- comparison, pointer, 6.5.8                                    control character, 5.2.1, 7.4
- compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6                   control wide character, 7.29.2
- compl macro, 7.9                                              conversion, 6.3
- complement operator (~), 6.2.6.2, 6.5.3.3                       arithmetic operands, 6.3.1
- complete type, 6.2.5                                            array argument, 6.9.1
- complex macro, 7.3.1                                            array parameter, 6.9.1
- complex numbers, 6.2.5, G                                       arrays, 6.3.2.1
- complex type conversion, 6.3.1.6, 6.3.1.7                       boolean, 6.3.1.2
- complex type domain, 6.2.5                                      boolean, characters, and integers, 6.3.1.1
- complex types, 6.2.5, 6.7.2, 6.10.8.3, G                        by assignment, 6.5.16.1
- complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2,                   by return statement, 6.8.6.4
-      7.3, 7.24, 7.30.1, G.6, J.5.17                             complex types, 6.3.1.6
- compliance, see conformance                                     explicit, 6.3
- components of time, 7.26.1, K.3.8.1                             function, 6.3.2.1
- composite type, 6.2.7                                           function argument, 6.5.2.2, 6.9.1
- compound assignment, 6.5.16.2                                   function designators, 6.3.2.1
- compound literals, 6.5.2.5                                      function parameter, 6.9.1
- compound statement, 6.8.2                                       imaginary, G.4.1
- compound-literal operator (( ){ }), 6.5.2.5                     imaginary and complex, G.4.3
- concatenation functions                                         implicit, 6.3
-
-    lvalues, 6.3.2.1                                             csinh functions, 7.3.6.5, G.6.2.5
-    pointer, 6.3.2.1, 6.3.2.3                                      type-generic macro for, 7.24
-    real and complex, 6.3.1.7                                    csqrt functions, 7.3.8.3, G.6.4.2
-    real and imaginary, G.4.2                                      type-generic macro for, 7.24
-    real floating and integer, 6.3.1.4, F.3, F.4                  ctan functions, 7.3.5.6, G.6
-    real floating types, 6.3.1.5, F.3                               type-generic macro for, 7.24
-    signed and unsigned integers, 6.3.1.3                        ctanh functions, 7.3.6.6, G.6.2.6
-    usual arithmetic, see usual arithmetic                         type-generic macro for, 7.24
-          conversions                                            ctgamma function, 7.30.1
-    void type, 6.3.2.2                                           ctime function, 7.26.3.2
- conversion functions                                            ctime_s function, K.3.8.2, K.3.8.2.2
-    multibyte/wide character, 7.22.7, K.3.6.4                    ctype.h header, 7.4, 7.30.2
-       extended, 7.28.6, K.3.9.3                                 current object, 6.7.9
-       restartable, 7.27.1, 7.28.6.3, K.3.9.3.1                  CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
-    multibyte/wide string, 7.22.8, K.3.6.5
-       restartable, 7.28.6.4, K.3.9.3.2                          data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6,
-    numeric, 7.8.2.3, 7.22.1                                          7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3,
-       wide string, 7.8.2.4, 7.28.4.1                                 7.28.6.4
-    single byte/wide character, 7.28.6.1                         data stream, see streams
-    time, 7.26.3, K.3.8.2                                        date and time header, 7.26, K.3.8
-       wide character, 7.28.5                                    Daylight Saving Time, 7.26.1
- conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,              DBL_DECIMAL_DIG macro, 5.2.4.2.2
-       7.28.2.2                                                  DBL_DIG macro, 5.2.4.2.2
- conversion state, 7.22.7, 7.27.1, 7.27.1.1,                     DBL_EPSILON macro, 5.2.4.2.2
-       7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6,                     DBL_HAS_SUBNORM macro, 5.2.4.2.2
-       7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3,             DBL_MANT_DIG macro, 5.2.4.2.2
-       7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4,                DBL_MAX macro, 5.2.4.2.2
-       K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1,           DBL_MAX_10_EXP macro, 5.2.4.2.2
-       K.3.9.3.2.2                                               DBL_MAX_EXP macro, 5.2.4.2.2
- conversion state functions, 7.28.6.2                            DBL_MIN macro, 5.2.4.2.2
- copying functions                                               DBL_MIN_10_EXP macro, 5.2.4.2.2
-    string, 7.23.2, K.3.7.1                                      DBL_MIN_EXP macro, 5.2.4.2.2
-    wide string, 7.28.4.2, K.3.9.2.1                             DBL_TRUE_MIN macro, 5.2.4.2.2
- copysign functions, 7.3.9.5, 7.12.11.1, F.3,                    decimal constant, 6.4.4.1
-       F.10.8.1                                                  decimal digit, 5.2.1
- copysign type-generic macro, 7.24                               decimal-point character, 7.1.1, 7.11.2.1
- correctly rounded result, 3.9                                   DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1,
- corresponding real type, 6.2.5                                       7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5
- cos functions, 7.12.4.5, F.10.1.5                               declaration specifiers, 6.7
- cos type-generic macro, 7.24, G.7                               declarations, 6.7
- cosh functions, 7.12.5.4, F.10.2.4                                function, 6.7.6.3
- cosh type-generic macro, 7.24, G.7                                pointer, 6.7.6.1
- cpow functions, 7.3.8.2, G.6.4.1                                  structure/union, 6.7.2.1
-    type-generic macro for, 7.24                                   typedef, 6.7.8
- cproj functions, 7.3.9.5, G.6                                   declarator, 6.7.6
- cproj type-generic macro, 7.24                                    abstract, 6.7.7
- creal functions, 7.3.9.6, G.6                                   declarator type derivation, 6.2.5, 6.7.6
- creal type-generic macro, 7.24, G.7                             decrement operators, see arithmetic operators,
- critical undefined behavior, L.2.3                                    increment and decrement
- csin functions, 7.3.5.5, G.6                                    default argument promotions, 6.5.2.2
-    type-generic macro for, 7.24                                 default initialization, 6.7.9
-
- default label, 6.8.1, 6.8.4.2                                  elif preprocessing directive, 6.10.1
- define preprocessing directive, 6.10.3                         ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3
- defined operator, 6.10.1, 6.10.8                               else preprocessing directive, 6.10.1
- definition, 6.7                                                 else statement, 6.8.4.1
-    function, 6.9.1                                             empty statement, 6.8.3
- dependency-ordered before, 5.1.2.4                             encoding error, 7.21.3, 7.27.1.1, 7.27.1.2,
- derived declarator types, 6.2.5                                      7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,
- derived types, 6.2.5                                                 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,
- designated initializer, 6.7.9                                        K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1,
- destringizing, 6.10.9                                                K.3.9.3.2.2
- device input/output, 5.1.2.3                                   end-of-file, 7.28.1
- diagnostic message, 3.10, 5.1.1.3                              end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1,
- diagnostics, 5.1.1.3                                                 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2,
- diagnostics header, 7.2                                              7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1,
- difftime function, 7.26.2.2                                          7.28.3.10
- digit, 5.2.1, 7.4                                              end-of-file macro, see EOF macro
- digraphs, 6.4.6                                                end-of-line indicator, 5.2.1
- direct input/output functions, 7.21.8                          endif preprocessing directive, 6.10.1
- display device, 5.2.2                                          enum type, 6.2.5, 6.7.2, 6.7.2.2
- div function, 7.22.6.2                                         enumerated type, 6.2.5
- div_t type, 7.22                                               enumeration, 6.2.5, 6.7.2.2
- division assignment operator (/=), 6.5.16.2                    enumeration constant, 6.2.1, 6.4.4.3
- division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1              enumeration content, 6.7.2.3
- do statement, 6.8.5.2                                          enumeration members, 6.7.2.2
- documentation of implementation, 4                             enumeration specifiers, 6.7.2.2
- domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4,            enumeration tag, 6.2.3, 6.7.2.3
-       7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7,                  enumerator, 6.7.2.2
-       7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11,                environment, 5
-       7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5,                  environment functions, 7.22.4, K.3.6.2
-       7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3                environment list, 7.22.4.6, K.3.6.2.1
- dot operator (.), 6.5.2.3                                      environmental considerations, 5.2
- double _Complex type, 6.2.5                                    environmental limits, 5.2.4, 7.13.1.1, 7.21.2,
- double _Complex type conversion, 6.3.1.6,                            7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2,
-       6.3.1.7, 6.3.1.8                                               7.22.4.3, 7.28.2.1, K.3.5.1.2
- double _Imaginary type, G.2                                    EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2,
- double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2,                        7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11,
-       7.28.2.2, F.2                                                  7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4,
- double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,                   7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9,
-       6.3.1.8                                                        7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4,
- double-precision arithmetic, 5.1.2.3                                 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12,
- double-quote escape sequence (\"), 6.4.4.4,                          7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7,
-       6.4.5, 6.10.9                                                  K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2,
- double_t type, 7.12, J.5.6                                           K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12,
-                                                                      K.3.9.1.14
- EDOM macro, 7.5, 7.12.1, see also domain error                 equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9
- effective type, 6.5                                            equal-to operator, see equality operator
- EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2,                 equality expressions, 6.5.9
-      7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,                   equality operator (==), 6.5.9
-      7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,           ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1,
-      see also encoding error                                         7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see
- element type, 6.2.5                                                  also range error, pole error
-
- erf functions, 7.12.8.1, F.10.5.1                               exp2 functions, 7.12.6.2, F.10.3.2
- erf type-generic macro, 7.24                                    exp2 type-generic macro, 7.24
- erfc functions, 7.12.8.2, F.10.5.2                              explicit conversion, 6.3
- erfc type-generic macro, 7.24                                   expm1 functions, 7.12.6.3, F.10.3.3
- errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4,               expm1 type-generic macro, 7.24
-       7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4,            exponent part, 6.4.4.2
-       7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1,           exponential functions
-       7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1,                     complex, 7.3.7, G.6.3
-       7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2,               real, 7.12.6, F.10.3
-       7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17,               expression, 6.5
-       K.3.1.3, K.3.7.4.2                                          assignment, 6.5.16
- errno.h header, 7.5, 7.30.3, K.3.2                                cast, 6.5.4
- errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1,                     constant, 6.6
-       K.3.7, K.3.8, K.3.9                                         evaluation, 5.1.2.3
- error                                                             full, 6.8
-    domain, see domain error                                       order of evaluation, see order of evaluation
-    encoding, see encoding error                                   parenthesized, 6.5.1
-    pole, see pole error                                           primary, 6.5.1
-    range, see range error                                         unary, 6.5.3
- error conditions, 7.12.1                                        expression statement, 6.8.3
- error functions, 7.12.8, F.10.5                                 extended alignment, 6.2.8
- error indicator, 7.21.1, 7.21.5.3, 7.21.7.1,                    extended character set, 3.7.2, 5.2.1, 5.2.1.2
-       7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7,                   extended characters, 5.2.1
-       7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3,                 extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
-       7.28.3.1, 7.28.3.3                                             7.20
- error preprocessing directive, 4, 6.10.5                        extended multibyte/wide character conversion
- error-handling functions, 7.21.10, 7.23.6.2,                         utilities, 7.28.6, K.3.9.3
-       K.3.7.4.2, K.3.7.4.3                                      extensible wide character case mapping functions,
- escape character (\), 6.4.4.4                                        7.29.3.2
- escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4                 extensible wide character classification functions,
- evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12                          7.29.2.2
- evaluation method, 5.2.4.2.2, 6.5, F.8.5                        extern storage-class specifier, 6.2.2, 6.7.1
- evaluation of expression, 5.1.2.3                               external definition, 6.9
- evaluation order, see order of evaluation                       external identifiers, underscore, 7.1.3
- exceptional condition, 6.5                                      external linkage, 6.2.2
- excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                   external name, 6.4.2.1
- excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                       external object definitions, 6.9.2
- exclusive OR operators
-    bitwise (^), 6.2.6.2, 6.5.11                                 fabs functions, 7.12.7.2, F.3, F.10.4.2
-    bitwise assignment (^=), 6.5.16.2                            fabs type-generic macro, 7.24, G.7
- executable program, 5.1.1.1                                     false macro, 7.18
- execution character set, 5.2.1                                  fclose function, 7.21.5.1
- execution environment, 5, 5.1.2, see also                       fdim functions, 7.12.12.1, F.10.9.1
-       environmental limits                                      fdim type-generic macro, 7.24
- execution sequence, 5.1.2.3, 6.8                                FE_ALL_EXCEPT macro, 7.6
- exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4,               FE_DFL_ENV macro, 7.6
-       7.22.4.5, 7.22.4.7                                        FE_DIVBYZERO macro, 7.6, 7.12, F.3
- EXIT_FAILURE macro, 7.22, 7.22.4.4                              FE_DOWNWARD macro, 7.6, F.3
- EXIT_SUCCESS macro, 7.22, 7.22.4.4                              FE_INEXACT macro, 7.6, F.3
- exp functions, 7.12.6.1, F.10.3.1                               FE_INVALID macro, 7.6, 7.12, F.3
- exp type-generic macro, 7.24                                    FE_OVERFLOW macro, 7.6, 7.12, F.3
-
- FE_TONEAREST macro, 7.6, F.3                                 float _Complex type conversion, 6.3.1.6,
- FE_TOWARDZERO macro, 7.6, F.3                                     6.3.1.7, 6.3.1.8
- FE_UNDERFLOW macro, 7.6, F.3                                 float _Imaginary type, G.2
- FE_UPWARD macro, 7.6, F.3                                    float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
- feclearexcept function, 7.6.2, 7.6.2.1, F.3                  float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
- fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3                 6.3.1.8
- fegetexceptflag function, 7.6.2, 7.6.2.2, F.3                float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
- fegetround function, 7.6, 7.6.3.1, F.3                            7.28.4.1.1
- feholdexcept function, 7.6.4.2, 7.6.4.3,                     float_t type, 7.12, J.5.6
-      7.6.4.4, F.3                                            floating constant, 6.4.4.2
- fence, 5.1.2.4                                               floating suffix, f or F, 6.4.4.2
- fences, 7.17.4                                               floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
- fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H                F.3, F.4
- FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9,                 floating types, 6.2.5, 6.11.1
-      F.10                                                    floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5,
- fenv_t type, 7.6                                                  7.22.1.3, F.5, see also contracted expression
- feof function, 7.21.10.2                                     floating-point arithmetic functions, 7.12, F.10
- feraiseexcept function, 7.6.2, 7.6.2.3, F.3                  floating-point classification functions, 7.12.3
- ferror function, 7.21.10.3                                   floating-point control mode, 7.6, F.8.6
- fesetenv function, 7.6.4.3, F.3                              floating-point environment, 7.6, F.8, F.8.6
- fesetexceptflag function, 7.6.2, 7.6.2.4, F.3                floating-point exception, 7.6, 7.6.2, F.10
- fesetround function, 7.6, 7.6.3.2, F.3                       floating-point number, 5.2.4.2.2, 6.2.5
- fetestexcept function, 7.6.2, 7.6.2.5, F.3                   floating-point rounding mode, 5.2.4.2.2
- feupdateenv function, 7.6.4.2, 7.6.4.4, F.3                  floating-point status flag, 7.6, F.8.6
- fexcept_t type, 7.6, F.3                                     floor functions, 7.12.9.2, F.10.6.2
- fflush function, 7.21.5.2, 7.21.5.3                          floor type-generic macro, 7.24
- fgetc function, 7.21.1, 7.21.3, 7.21.7.1,                    FLT_DECIMAL_DIG macro, 5.2.4.2.2
-      7.21.7.5, 7.21.8.1                                      FLT_DIG macro, 5.2.4.2.2
- fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3                 FLT_EPSILON macro, 5.2.4.2.2
- fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1                  FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12,
- fgetwc function, 7.21.1, 7.21.3, 7.28.3.1,                        F.10.11
-      7.28.3.6                                                FLT_HAS_SUBNORM macro, 5.2.4.2.2
- fgetws function, 7.21.1, 7.28.3.2                            FLT_MANT_DIG macro, 5.2.4.2.2
- field width, 7.21.6.1, 7.28.2.1                               FLT_MAX macro, 5.2.4.2.2
- file, 7.21.3                                                  FLT_MAX_10_EXP macro, 5.2.4.2.2
-   access functions, 7.21.5, K.3.5.2                          FLT_MAX_EXP macro, 5.2.4.2.2
-   name, 7.21.3                                               FLT_MIN macro, 5.2.4.2.2
-   operations, 7.21.4, K.3.5.1                                FLT_MIN_10_EXP macro, 5.2.4.2.2
-   position indicator, 7.21.1, 7.21.2, 7.21.3,                FLT_MIN_EXP macro, 5.2.4.2.2
-         7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10,             FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3,
-         7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2,                   7.28.2.1, 7.28.4.1.1
-         7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1,              FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3
-         7.28.3.3, 7.28.3.10                                  FLT_TRUE_MIN macro, 5.2.4.2.2
-   positioning functions, 7.21.9                              fma functions, 7.12, 7.12.13.1, F.10.10.1
- file scope, 6.2.1, 6.9                                        fma type-generic macro, 7.24
- FILE type, 7.21.1, 7.21.3                                    fmax functions, 7.12.12.2, F.10.9.2
- FILENAME_MAX macro, 7.21.1                                   fmax type-generic macro, 7.24
- flags, 7.21.6.1, 7.28.2.1, see also floating-point             fmin functions, 7.12.12.3, F.10.9.3
-      status flag                                              fmin type-generic macro, 7.24
- flexible array member, 6.7.2.1                                fmod functions, 7.12.10.1, F.10.7.1
- float _Complex type, 6.2.5                                   fmod type-generic macro, 7.24
-
- fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1                       K.3.5.3.7, K.3.5.3.9
- FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3,                    fseek function, 7.21.1, 7.21.5.3, 7.21.7.10,
-      K.3.5.1.1                                                      7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10
- fopen_s function, K.3.5.1.1, K.3.5.2.1,                       fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10,
-      K.3.5.2.2                                                      7.21.9.1, 7.21.9.3, 7.28.3.10
- for statement, 6.8.5, 6.8.5.3                                 ftell function, 7.21.9.2, 7.21.9.4
- form-feed character, 5.2.1, 6.4                               full declarator, 6.7.6
- form-feed escape sequence (\f), 5.2.2, 6.4.4.4,               full expression, 6.8
-      7.4.1.10                                                 fully buffered stream, 7.21.3
- formal argument (deprecated), 3.16                            function
- formal parameter, 3.16                                           argument, 6.5.2.2, 6.9.1
- formatted input/output functions, 7.11.1.1, 7.21.6,              body, 6.9.1
-      K.3.5.3                                                     call, 6.5.2.2
-    wide character, 7.28.2, K.3.9.1                                  library, 7.1.4
- fortran keyword, J.5.9                                           declarator, 6.7.6.3, 6.11.6
- forward reference, 3.11                                          definition, 6.7.6.3, 6.9.1, 6.11.7
- FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see                     designator, 6.3.2.1
-      also contracted expression                                  image, 5.2.3
- FP_FAST_FMA macro, 7.12                                          inline, 6.7.4
- FP_FAST_FMAF macro, 7.12                                         library, 5.1.1.1, 7.1.4
- FP_FAST_FMAL macro, 7.12                                         name length, 5.2.4.1, 6.4.2.1, 6.11.3
- FP_ILOGB0 macro, 7.12, 7.12.6.5                                  no-return, 6.7.4
- FP_ILOGBNAN macro, 7.12, 7.12.6.5                                parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1
- FP_INFINITE macro, 7.12, F.3                                     prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7,
- FP_NAN macro, 7.12, F.3                                                6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12
- FP_NORMAL macro, 7.12, F.3                                       prototype scope, 6.2.1, 6.7.6.2
- FP_SUBNORMAL macro, 7.12, F.3                                    recursive call, 6.5.2.2
- FP_ZERO macro, 7.12, F.3                                         return, 6.8.6.4, F.6
- fpclassify macro, 7.12.3.1, F.3                                  scope, 6.2.1
- fpos_t type, 7.21.1, 7.21.2                                      type, 6.2.5
- fprintf function, 7.8.1, 7.21.1, 7.21.6.1,                       type conversion, 6.3.2.1
-      7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6,                  function specifiers, 6.7.4
-      7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1                       function type, 6.2.5
- fprintf_s function, K.3.5.3.1                                 function-call operator (( )), 6.5.2.2
- fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3,              function-like macro, 6.10.3
-      7.21.7.7, 7.21.8.2                                       fundamental alignment, 6.2.8
- fputs function, 7.21.1, 7.21.7.4                              future directions
- fputwc function, 7.21.1, 7.21.3, 7.28.3.3,                       language, 6.11
-      7.28.3.8                                                    library, 7.30
- fputws function, 7.21.1, 7.28.3.4                             fwide function, 7.21.2, 7.28.3.5
- fread function, 7.21.1, 7.21.8.1                              fwprintf function, 7.8.1, 7.21.1, 7.21.6.2,
- free function, 7.22.3.3, 7.22.3.5                                   7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5,
- freestanding execution environment, 4, 5.1.2,                       7.28.2.11, K.3.9.1.1
-      5.1.2.1                                                  fwprintf_s function, K.3.9.1.1
- freopen function, 7.21.2, 7.21.5.4                            fwrite function, 7.21.1, 7.21.8.2
- freopen_s function, K.3.5.2.2                                 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2,
- frexp functions, 7.12.6.4, F.10.3.4                                 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10,
- frexp type-generic macro, 7.24                                      K.3.9.1.2
- fscanf function, 7.8.1, 7.21.1, 7.21.6.2,                     fwscanf_s function, K.3.9.1.2, K.3.9.1.5,
-      7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2                   K.3.9.1.7, K.3.9.1.14
- fscanf_s function, K.3.5.3.2, K.3.5.3.4,
-
- gamma functions, 7.12.8, F.10.5                               name spaces, 6.2.3
- general utilities, 7.22, K.3.6                                reserved, 6.4.1, 7.1.3, K.3.1.2
-   wide string, 7.28.4, K.3.9.2                                 scope, 6.2.1
- general wide string utilities, 7.28.4, K.3.9.2                 type, 6.2.5
- generic parameters, 7.24                                    identifier list, 6.7.6
- generic selection, 6.5.1.1                                  identifier nondigit, 6.4.2.1
- getc function, 7.21.1, 7.21.7.5, 7.21.7.6                   IEC 559, F.1
- getchar function, 7.21.1, 7.21.7.6                          IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3,
- getenv function, 7.22.4.6                                         7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G,
- getenv_s function, K.3.6.2.1                                      H.1
- gets function, K.3.5.4.1                                    IEEE 754, F.1
- gets_s function, K.3.5.4.1                                  IEEE 854, F.1
- getwc function, 7.21.1, 7.28.3.6, 7.28.3.7                  IEEE floating-point arithmetic standard, see
- getwchar function, 7.21.1, 7.28.3.7                               IEC 60559, ANSI/IEEE 754,
- gmtime function, 7.26.3.3                                         ANSI/IEEE 854
- gmtime_s function, K.3.8.2.3                                if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
- goto statement, 6.2.1, 6.8.1, 6.8.6.1                             6.10.1, 7.1.4
- graphic characters, 5.2.1                                   if statement, 6.8.4.1
- greater-than operator (>), 6.5.8                            ifdef preprocessing directive, 6.10.1
- greater-than-or-equal-to operator (>=), 6.5.8               ifndef preprocessing directive, 6.10.1
-                                                             ignore_handler_s function, K.3.6.1.3
- happens before, 5.1.2.4                                     ilogb functions, 7.12, 7.12.6.5, F.10.3.5
- header, 5.1.1.1, 7.1.2, see also standard headers           ilogb type-generic macro, 7.24
- header names, 6.4, 6.4.7, 6.10.2                            imaginary macro, 7.3.1, G.6
- hexadecimal constant, 6.4.4.1                               imaginary numbers, G
- hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4                imaginary type domain, G.2
- hexadecimal prefix, 6.4.4.1                                  imaginary types, G
- hexadecimal-character escape sequence                       imaxabs function, 7.8.2.1
-      (\x hexadecimal digits), 6.4.4.4                       imaxdiv function, 7.8, 7.8.2.2
- high-order bit, 3.6                                         imaxdiv_t type, 7.8
- horizontal-tab character, 5.2.1, 6.4                        implementation, 3.12
- horizontal-tab escape sequence (\r), 7.29.2.1.3             implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1,
- horizontal-tab escape sequence (\t), 5.2.2,                       6.7.6, 6.8.4.2, E, see also environmental
-      6.4.4.4, 7.4.1.3, 7.4.1.10                                   limits
- hosted execution environment, 4, 5.1.2, 5.1.2.2             implementation-defined behavior, 3.4.1, 4, J.3
- HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3,                     implementation-defined value, 3.19.1
-      7.28.4.1.1, F.10                                       implicit conversion, 6.3
- HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3,                    implicit initialization, 6.7.9
-      7.28.4.1.1, F.10                                       include preprocessing directive, 5.1.1.2, 6.10.2
- HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3,                    inclusive OR operators
-      7.28.4.1.1, F.10                                         bitwise (|), 6.2.6.2, 6.5.12
- hyperbolic functions                                           bitwise assignment (|=), 6.5.16.2
-   complex, 7.3.6, G.6.2                                     incomplete type, 6.2.5
-   real, 7.12.5, F.10.2                                      increment operators, see arithmetic operators,
- hypot functions, 7.12.7.3, F.10.4.3                               increment and decrement
- hypot type-generic macro, 7.24                              indeterminate value, 3.19.2
-                                                             indeterminately sequenced, 5.1.2.3, 6.5.2.2,
- I macro, 7.3.1, 7.3.9.5, G.6                                      6.5.2.4, 6.5.16.2, see also sequenced before,
- identifier, 6.4.2.1, 6.5.1                                         unsequenced
-    linkage, see linkage                                     indirection operator (*), 6.5.2.1, 6.5.3.2
-    maximum length, 6.4.2.1                                  inequality operator (!=), 6.5.9
-
- infinitary, 7.12.1                                                    extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20
- INFINITY macro, 7.3.9.5, 7.12, F.2.1                              inter-thread happens before, 5.1.2.4
- initial position, 5.2.2                                           interactive device, 5.1.2.3, 7.21.3, 7.21.5.3
- initial shift state, 5.2.1.2                                      internal linkage, 6.2.2
- initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9,            internal name, 6.4.2.1
-       F.8.5                                                       interrupt, 5.2.3
-    in blocks, 6.8                                                 INTMAX_C macro, 7.20.4.2
- initializer, 6.7.9                                                INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
-    permitted form, 6.6                                            INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
-    string literal, 6.3.2.1                                        intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
- inline, 6.7.4                                                           7.28.2.1, 7.28.2.2
- inner scope, 6.2.1                                                INTN_C macros, 7.20.4.1
- input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10,                     INTN_MAX macros, 7.20.2.1
-       K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9,                 INTN_MIN macros, 7.20.2.1
-       K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5,               intN_t types, 7.20.1.1
-       K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14               INTPTR_MAX macro, 7.20.2.4
- input/output functions                                            INTPTR_MIN macro, 7.20.2.4
-    character, 7.21.7, K.3.5.4                                     intptr_t type, 7.20.1.4
-    direct, 7.21.8                                                 inttypes.h header, 7.8, 7.30.4
-    formatted, 7.21.6, K.3.5.3                                     isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
-       wide character, 7.28.2, K.3.9.1                             isalpha function, 7.4.1.1, 7.4.1.2
-    wide character, 7.28.3                                         isblank function, 7.4.1.3
-       formatted, 7.28.2, K.3.9.1                                  iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7,
- input/output header, 7.21, K.3.5                                        7.4.1.11
- input/output, device, 5.1.2.3                                     isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5,
- int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2                       7.4.1.7, 7.4.1.11, 7.11.1.1
- int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,                   isfinite macro, 7.12.3.2, F.3
-       6.3.1.8                                                     isgraph function, 7.4.1.6
- INT_FASTN_MAX macros, 7.20.2.3                                    isgreater macro, 7.12.14.1, F.3
- INT_FASTN_MIN macros, 7.20.2.3                                    isgreaterequal macro, 7.12.14.2, F.3
- int_fastN_t types, 7.20.1.3                                       isinf macro, 7.12.3.3
- INT_LEASTN_MAX macros, 7.20.2.2                                   isless macro, 7.12.14.3, F.3
- INT_LEASTN_MIN macros, 7.20.2.2                                   islessequal macro, 7.12.14.4, F.3
- int_leastN_t types, 7.20.1.2                                      islessgreater macro, 7.12.14.5, F.3
- INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5                          islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
- INT_MIN macro, 5.2.4.2.1, 7.12                                          7.4.2.2
- integer arithmetic functions, 7.8.2.1, 7.8.2.2,                   isnan macro, 7.12.3.4, F.3
-       7.22.6                                                      isnormal macro, 7.12.3.5
- integer character constant, 6.4.4.4                               ISO 31-11, 2, 3
- integer constant, 6.4.4.1                                         ISO 4217, 2, 7.11.2.1
- integer constant expression, 6.3.2.3, 6.6, 6.7.2.1,               ISO 8601, 2, 7.26.3.5
-       6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1,           ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2
-       7.1.4                                                       ISO/IEC 10976-1, H.1
- integer conversion rank, 6.3.1.1                                  ISO/IEC 2382-1, 2, 3
- integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1,                  ISO/IEC 646, 2, 5.2.1.1
-       6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3,           ISO/IEC 9945-2, 7.11
-       7.21.6.1, 7.28.2.1                                          iso646.h header, 4, 7.9                          *
- integer suffix, 6.4.4.1                                            isprint function, 5.2.2, 7.4.1.8
- integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,               ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
-       F.3, F.4                                                          7.4.1.11
- integer types, 6.2.5, 7.20                                        isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
-
-       7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3,                   LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1
-       7.22.1.4, 7.28.2.2                                        LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3,
- isunordered macro, 7.12.14.6, F.3                                     7.28.4.4.2
- isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1,                   LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7,
-       7.4.2.2                                                         7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2,
- iswalnum function, 7.29.2.1.1, 7.29.2.1.9,                            7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5
-       7.29.2.1.10, 7.29.2.2.1                                   LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
- iswalpha function, 7.29.2.1.1, 7.29.2.1.2,                      LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
-       7.29.2.2.1                                                LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5
- iswblank function, 7.29.2.1.3, 7.29.2.2.1                       lconv structure type, 7.11
- iswcntrl function, 7.29.2.1.2, 7.29.2.1.4,                      LDBL_DECIMAL_DIG macro, 5.2.4.2.2
-       7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1                       LDBL_DIG macro, 5.2.4.2.2
- iswctype function, 7.29.2.2.1, 7.29.2.2.2                       LDBL_EPSILON macro, 5.2.4.2.2
- iswdigit function, 7.29.2.1.1, 7.29.2.1.2,                      LDBL_HAS_SUBNORM macro, 5.2.4.2.2
-       7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1           LDBL_MANT_DIG macro, 5.2.4.2.2
- iswgraph function, 7.29.2.1, 7.29.2.1.6,                        LDBL_MAX macro, 5.2.4.2.2
-       7.29.2.1.10, 7.29.2.2.1                                   LDBL_MAX_10_EXP macro, 5.2.4.2.2
- iswlower function, 7.29.2.1.2, 7.29.2.1.7,                      LDBL_MAX_EXP macro, 5.2.4.2.2
-       7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2                        LDBL_MIN macro, 5.2.4.2.2
- iswprint function, 7.29.2.1.6, 7.29.2.1.8,                      LDBL_MIN_10_EXP macro, 5.2.4.2.2
-       7.29.2.2.1                                                LDBL_MIN_EXP macro, 5.2.4.2.2
- iswpunct function, 7.29.2.1, 7.29.2.1.2,                        LDBL_TRUE_MIN macro, 5.2.4.2.2
-       7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10,                      ldexp functions, 7.12.6.6, F.10.3.6
-       7.29.2.1.11, 7.29.2.2.1                                   ldexp type-generic macro, 7.24
- iswspace function, 7.21.6.2, 7.28.2.2,                          ldiv function, 7.22.6.2
-       7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6,           ldiv_t type, 7.22
-       7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10,                      leading underscore in identifiers, 7.1.3
-       7.29.2.1.11, 7.29.2.2.1                                   left-shift assignment operator (<<=), 6.5.16.2
- iswupper function, 7.29.2.1.2, 7.29.2.1.11,                     left-shift operator (<<), 6.2.6.2, 6.5.7
-       7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2                        length
- iswxdigit function, 7.29.2.1.12, 7.29.2.2.1                        external name, 5.2.4.1, 6.4.2.1, 6.11.3
- isxdigit function, 7.4.1.12, 7.11.1.1                              function name, 5.2.4.1, 6.4.2.1, 6.11.3
- italic type convention, 3, 6.1                                     identifier, 6.4.2.1
- iteration statements, 6.8.5                                        internal name, 5.2.4.1, 6.4.2.1
-                                                                 length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1,
- jmp_buf type, 7.13                                                    7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1
- jump statements, 6.8.6                                          length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,
-                                                                       7.28.2.2
- keywords, 6.4.1, G.2, J.5.9, J.5.10                             less-than operator (<), 6.5.8
- kill_dependency macro, 5.1.2.4, 7.17.3.1                        less-than-or-equal-to operator (<=), 6.5.8
- known constant size, 6.2.5                                      letter, 5.2.1, 7.4
-                                                                 lexical elements, 5.1.1.2, 6.4
- L_tmpnam macro, 7.21.1, 7.21.4.4                                lgamma functions, 7.12.8.3, F.10.5.3
- L_tmpnam_s macro, K.3.5, K.3.5.1.2                              lgamma type-generic macro, 7.24
- label name, 6.2.1, 6.2.3                                        library, 5.1.1.1, 7, K.3
- labeled statement, 6.8.1                                           future directions, 7.30
- labs function, 7.22.6.1                                            summary, B
- language, 6                                                        terms, 7.1.1
-    future directions, 6.11                                         use of functions, 7.1.4
-    syntax summary, A                                            lifetime, 6.2.4
- Latin alphabet, 5.2.1, 6.4.2.1                                  limits
-
-    environmental, see environmental limits                      6.3.1.6, 6.3.1.7, 6.3.1.8
-    implementation, see implementation limits               long double _Imaginary type, G.2
-    numerical, see numerical limits                         long double suffix, l or L, 6.4.4.2
-    translation, see translation limits                     long double type, 6.2.5, 6.4.4.2, 6.7.2,
- limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10                      7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2
- line buffered stream, 7.21.3                               long double type conversion, 6.3.1.4, 6.3.1.5,
- line number, 6.10.4, 6.10.8.1                                   6.3.1.7, 6.3.1.8
- line preprocessing directive, 6.10.4                       long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,
- lines, 5.1.1.2, 7.21.2                                          7.21.6.2, 7.28.2.1, 7.28.2.2
-    preprocessing directive, 6.10                           long int type conversion, 6.3.1.1, 6.3.1.3,
- linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2,                6.3.1.4, 6.3.1.8
-       6.11.2                                               long integer suffix, l or L, 6.4.4.1
- llabs function, 7.22.6.1                                   long long int type, 6.2.5, 6.3.1.1, 6.7.2,
- lldiv function, 7.22.6.2                                        7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2
- lldiv_t type, 7.22                                         long long int type conversion, 6.3.1.1,
- LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                           6.3.1.3, 6.3.1.4, 6.3.1.8
-       7.28.4.1.2                                           long long integer suffix, ll or LL, 6.4.4.1
- LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4,                      LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
-       7.28.4.1.2                                           LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
- llrint functions, 7.12.9.5, F.3, F.10.6.5                  longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4,
- llrint type-generic macro, 7.24                                 7.22.4.7
- llround functions, 7.12.9.7, F.10.6.7                      loop body, 6.8.5
- llround type-generic macro, 7.24                           low-order bit, 3.6
- local time, 7.26.1                                         lowercase letter, 5.2.1
- locale, 3.4.2                                              lrint functions, 7.12.9.5, F.3, F.10.6.5
- locale-specific behavior, 3.4.2, J.4                        lrint type-generic macro, 7.24
- locale.h header, 7.11, 7.30.5                              lround functions, 7.12.9.7, F.10.6.7
- localeconv function, 7.11.1.1, 7.11.2.1                    lround type-generic macro, 7.24
- localization, 7.11                                         lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16,
- localtime function, 7.26.3.4                                    6.7.2.4
- localtime_s function, K.3.8.2.4                            lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1,
- log functions, 7.12.6.7, F.10.3.7                               6.5.16.2
- log type-generic macro, 7.24
- log10 functions, 7.12.6.8, F.10.3.8                        macro argument substitution, 6.10.3.1
- log10 type-generic macro, 7.24                             macro definition
- log1p functions, 7.12.6.9, F.10.3.9                          library function, 7.1.4
- log1p type-generic macro, 7.24                             macro invocation, 6.10.3
- log2 functions, 7.12.6.10, F.10.3.10                       macro name, 6.10.3
- log2 type-generic macro, 7.24                                length, 5.2.4.1
- logarithmic functions                                        predefined, 6.10.8, 6.11.9
-    complex, 7.3.7, G.6.3                                     redefinition, 6.10.3
-    real, 7.12.6, F.10.3                                      scope, 6.10.3.5
- logb functions, 7.12.6.11, F.3, F.10.3.11                  macro parameter, 6.10.3
- logb type-generic macro, 7.24                              macro preprocessor, 6.10
- logical operators                                          macro replacement, 6.10.3
-    AND (&&), 5.1.2.4, 6.5.13                               magnitude, complex, 7.3.8.1
-    negation (!), 6.5.3.3                                   main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4,
-    OR (||), 5.1.2.4, 6.5.14                                     7.21.3
- logical source lines, 5.1.1.2                              malloc function, 7.22.3, 7.22.3.4, 7.22.3.5
- long double _Complex type, 6.2.5                           manipulation functions
- long double _Complex type conversion,                        complex, 7.3.9
-
-   real, 7.12.11, F.10.8                                    modf functions, 7.12.6.12, F.10.3.12
- matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10,           modifiable lvalue, 6.3.2.1
-      K.3.9.1.7, K.3.9.1.10, K.3.9.1.12                     modification order, 5.1.2.4
- math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,              modulus functions, 7.12.6.12
-      F.10, J.5.17                                          modulus, complex, 7.3.8.1
- MATH_ERREXCEPT macro, 7.12, F.10                           mtx_destroy function, 7.25.4.1
- math_errhandling macro, 7.1.3, 7.12, F.10                  mtx_init function, 7.25.1, 7.25.4.2
- MATH_ERRNO macro, 7.12                                     mtx_lock function, 7.25.4.3
- max_align_t type, 7.19                                     mtx_t type, 7.25.1
- maximum functions, 7.12.12, F.10.9                         mtx_timedlock function, 7.25.4.4
- MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2,                   mtx_trylock function, 7.25.4.5
-      7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3,             mtx_unlock function, 7.25.4.3, 7.25.4.4,
-      K.3.6.4.1, K.3.9.3.1.1                                     7.25.4.5, 7.25.4.6
- MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22                   multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4
- mblen function, 7.22.7.1, 7.28.6.3                         multibyte conversion functions
- mbrlen function, 7.28.6.3.1                                  wide character, 7.22.7, K.3.6.4
- mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1                     extended, 7.28.6, K.3.9.3
- mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3                     restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
- mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2,                wide string, 7.22.8, K.3.6.5
-      7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2,                restartable, 7.28.6.4, K.3.9.3.2
-      7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1                    multibyte string, 7.1.1
- mbsinit function, 7.28.6.2.1                               multibyte/wide character conversion functions,
- mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2                       7.22.7, K.3.6.4
- mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1                 extended, 7.28.6, K.3.9.3
- mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1,                    restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
-      7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1,             multibyte/wide string conversion functions,
-      7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3,                    7.22.8, K.3.6.5
-      7.28.6.3.1, 7.28.6.4                                    restartable, 7.28.6.4, K.3.9.3.2
- mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4               multidimensional array, 6.5.2.1
- mbstowcs_s function, K.3.6.5.1                             multiplication assignment operator (*=), 6.5.16.2
- mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2,              multiplication operator (*), 6.2.6.2, 6.5.5, F.3,
-      7.22.8.1, 7.28.6.3                                         G.5.1
- member access operators (. and ->), 6.5.2.3                multiplicative expressions, 6.5.5, G.5.1
- member alignment, 6.7.2.1
- memchr function, 7.23.5.1                                  n-char sequence, 7.22.1.3
- memcmp function, 7.23.4, 7.23.4.1                          n-wchar sequence, 7.28.4.1.1
- memcpy function, 7.23.2.1                                  name
- memcpy_s function, K.3.7.1.1                                 external, 5.2.4.1, 6.4.2.1, 6.11.3
- memmove function, 7.23.2.2                                   file, 7.21.3
- memmove_s function, K.3.7.1.2                                internal, 5.2.4.1, 6.4.2.1
- memory location, 3.14                                        label, 6.2.3
- memory management functions, 7.22.3                          structure/union member, 6.2.3
- memory_order type, 7.17.1, 7.17.3                          name spaces, 6.2.3
- memset function, 7.23.6.1, K.3.7.4.1                       named label, 6.8.1
- memset_s function, K.3.7.4.1                               NaN, 5.2.4.2.2
- minimum functions, 7.12.12, F.10.9                         nan functions, 7.12.11.2, F.2.1, F.10.8.2
- minus operator, unary, 6.5.3.3                             NAN macro, 7.12, F.2.1
- miscellaneous functions                                    NDEBUG macro, 7.2
-   string, 7.23.6, K.3.7.4                                  nearbyint functions, 7.12.9.3, 7.12.9.4, F.3,
-   wide string, 7.28.4.6, K.3.9.2.4                              F.10.6.3
- mktime function, 7.26.2.3                                  nearbyint type-generic macro, 7.24
-
- nearest integer functions, 7.12.9, F.10.6                       operating system, 5.1.2.1, 7.22.4.8
- negation operator (!), 6.5.3.3                                  operations on files, 7.21.4, K.3.5.1
- negative zero, 6.2.6.2, 7.12.11.1                               operator, 6.4.6
- new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4           operators, 6.5
- new-line escape sequence (\n), 5.2.2, 6.4.4.4,                     additive, 6.2.6.2, 6.5.6
-      7.4.1.10                                                      alignof, 6.5.3.4
- nextafter functions, 7.12.11.3, 7.12.11.4, F.3,                    assignment, 6.5.16
-      F.10.8.3                                                      associativity, 6.5
- nextafter type-generic macro, 7.24                                 equality, 6.5.9
- nexttoward functions, 7.12.11.4, F.3, F.10.8.4                     multiplicative, 6.2.6.2, 6.5.5, G.5.1
- nexttoward type-generic macro, 7.24                                postfix, 6.5.2
- no linkage, 6.2.2                                                  precedence, 6.5
- no-return function, 6.7.4                                          preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
- non-stop floating-point control mode, 7.6.4.2                       relational, 6.5.8
- nongraphic characters, 5.2.2, 6.4.4.4                              shift, 6.5.7
- nonlocal jumps header, 7.13                                        sizeof, 6.5.3.4
- norm, complex, 7.3.8.1                                             unary, 6.5.3
- normalized broken-down time, K.3.8.1, K.3.8.2.1                    unary arithmetic, 6.5.3.3
- not macro, 7.9                                                  optional features, see conditional features
- not-equal-to operator, see inequality operator                  or macro, 7.9
- not_eq macro, 7.9                                               OR operators
- null character (\0), 5.2.1, 6.4.4.4, 6.4.5                         bitwise exclusive (^), 6.2.6.2, 6.5.11
-   padding of binary stream, 7.21.2                                 bitwise exclusive assignment (^=), 6.5.16.2
- NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1,                      bitwise inclusive (|), 6.2.6.2, 6.5.12
-      7.26.1, 7.28.1                                                bitwise inclusive assignment (|=), 6.5.16.2
- null pointer, 6.3.2.3                                              logical (||), 5.1.2.4, 6.5.14
- null pointer constant, 6.3.2.3                                  or_eq macro, 7.9
- null preprocessing directive, 6.10.7                            order of allocated storage, 7.22.3
- null statement, 6.8.3                                           order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3,
- null wide character, 7.1.1                                            see also sequence points
- number classification macros, 7.12, 7.12.3.1                     ordinary identifier name space, 6.2.3
- numeric conversion functions, 7.8.2.3, 7.22.1                   orientation of stream, 7.21.2, 7.28.3.5
-   wide string, 7.8.2.4, 7.28.4.1                                out-of-bounds store, L.2.1
- numerical limits, 5.2.4.2                                       outer scope, 6.2.1
-                                                                 over-aligned, 6.2.8
- object, 3.15
- object representation, 6.2.6.1                                  padding
- object type, 6.2.5                                                binary stream, 7.21.2
- object-like macro, 6.10.3                                         bits, 6.2.6.2, 7.20.1.1
- observable behavior, 5.1.2.3                                      structure/union, 6.2.6.1, 6.7.2.1
- obsolescence, 6.11, 7.30                                        parameter, 3.16
- octal constant, 6.4.4.1                                           array, 6.9.1
- octal digit, 6.4.4.1, 6.4.4.4                                     ellipsis, 6.7.6.3, 6.10.3
- octal-character escape sequence (\octal digits),                  function, 6.5.2.2, 6.7, 6.9.1
-      6.4.4.4                                                      macro, 6.10.3
- offsetof macro, 7.19                                              main function, 5.1.2.2.1
- on-off switch, 6.10.6                                             program, 5.1.2.2.1
- once_flag type, 7.25.1                                          parameter type list, 6.7.6.3
- ONCE_FLAG_INIT macro, 7.25.1                                    parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5
- ones' complement, 6.2.6.2                                       parenthesized expression, 6.5.1
- operand, 6.4.6, 6.5                                             parse state, 7.21.2
-
- perform a trap, 3.19.5                                        preprocessor, 6.10
- permitted form of initializer, 6.6                            PRIcFASTN macros, 7.8.1
- perror function, 7.21.10.4                                    PRIcLEASTN macros, 7.8.1
- phase angle, complex, 7.3.9.1                                 PRIcMAX macros, 7.8.1
- physical source lines, 5.1.1.2                                PRIcN macros, 7.8.1
- placemarker, 6.10.3.3                                         PRIcPTR macros, 7.8.1
- plus operator, unary, 6.5.3.3                                 primary expression, 6.5.1
- pointer arithmetic, 6.5.6                                     printf function, 7.21.1, 7.21.6.3, 7.21.6.10,
- pointer comparison, 6.5.8                                           K.3.5.3.3
- pointer declarator, 6.7.6.1                                   printf_s function, K.3.5.3.3
- pointer operator (->), 6.5.2.3                                printing character, 5.2.2, 7.4, 7.4.1.8
- pointer to function, 6.5.2.2                                  printing wide character, 7.29.2
- pointer type, 6.2.5                                           program diagnostics, 7.2.1
- pointer type conversion, 6.3.2.1, 6.3.2.3                     program execution, 5.1.2.2.2, 5.1.2.3
- pointer, null, 6.3.2.3                                        program file, 5.1.1.1
- pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8,             program image, 5.1.1.2
-      7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4,                program name (argv[0]), 5.1.2.2.1
-      7.12.8.3, 7.12.8.4                                       program parameters, 5.1.2.2.1
- portability, 4, J                                             program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
- position indicator, file, see file position indicator           program structure, 5.1.1.1
- positive difference, 7.12.12.1                                program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3,
- positive difference functions, 7.12.12, F.10.9                      5.1.2.3
- postfix decrement operator (--), 6.3.2.1, 6.5.2.4              program, conforming, 4
- postfix expressions, 6.5.2                                     program, strictly conforming, 4
- postfix increment operator (++), 6.3.2.1, 6.5.2.4              promotions
- pow functions, 7.12.7.4, F.10.4.4                                default argument, 6.5.2.2
- pow type-generic macro, 7.24                                     integer, 5.1.2.3, 6.3.1.1
- power functions                                               prototype, see function prototype
-   complex, 7.3.8, G.6.4                                       pseudo-random sequence functions, 7.22.2
-   real, 7.12.7, F.10.4                                        PTRDIFF_MAX macro, 7.20.3
- pp-number, 6.4.8                                              PTRDIFF_MIN macro, 7.20.3
- pragma operator, 6.10.9                                       ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1,
- pragma preprocessing directive, 6.10.6, 6.11.8                      7.21.6.2, 7.28.2.1, 7.28.2.2
- precedence of operators, 6.5                                  punctuators, 6.4.6
- precedence of syntax rules, 5.1.1.2                           putc function, 7.21.1, 7.21.7.7, 7.21.7.8
- precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1               putchar function, 7.21.1, 7.21.7.8
-   excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                         puts function, 7.21.1, 7.21.7.9
- predefined macro names, 6.10.8, 6.11.9                         putwc function, 7.21.1, 7.28.3.8, 7.28.3.9
- prefix decrement operator (--), 6.3.2.1, 6.5.3.1               putwchar function, 7.21.1, 7.28.3.9
- prefix increment operator (++), 6.3.2.1, 6.5.3.1
- preprocessing concatenation, 6.10.3.3                         qsort function, 7.22.5, 7.22.5.2
- preprocessing directives, 5.1.1.2, 6.10                       qsort_s function, K.3.6.3, K.3.6.3.2
- preprocessing file, 5.1.1.1, 6.10                              qualified types, 6.2.5
- preprocessing numbers, 6.4, 6.4.8                             qualified version of type, 6.2.5
- preprocessing operators                                       question-mark escape sequence (\?), 6.4.4.4
-   #, 6.10.3.2                                                 quick_exit function, 7.22.4.3, 7.22.4.4,
-   ##, 6.10.3.3                                                     7.22.4.7
-   _Pragma, 5.1.1.2, 6.10.9                                    quiet NaN, 5.2.4.2.2
-   defined, 6.10.1
- preprocessing tokens, 5.1.1.2, 6.4, 6.10                      raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1
- preprocessing translation unit, 5.1.1.1                       rand function, 7.22, 7.22.2.1, 7.22.2.2
-
- RAND_MAX macro, 7.22, 7.22.2.1                               restrict-qualified type, 6.2.5, 6.7.3
- range                                                        return statement, 6.8.6.4, F.6
-    excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                       rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5,
- range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1,                 7.28.3.10
-       7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6,                right-shift assignment operator (>>=), 6.5.16.2
-       7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2,               right-shift operator (>>), 6.2.6.2, 6.5.7
-       7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7,                rint functions, 7.12.9.4, F.3, F.10.6.4
-       7.12.11.3, 7.12.12.1, 7.12.13.1                        rint type-generic macro, 7.24
- rank, see integer conversion rank                            round functions, 7.12.9.6, F.10.6.6
- read-modify-write operations, 5.1.2.4                        round type-generic macro, 7.24
- real floating type conversion, 6.3.1.4, 6.3.1.5,              rounding mode, floating point, 5.2.4.2.2
-       6.3.1.7, F.3, F.4                                      RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2,
- real floating types, 6.2.5                                          K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13,
- real type domain, 6.2.5                                            K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2,
- real types, 6.2.5                                                  K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1,
- real-floating, 7.12.3                                               K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1,
- realloc function, 7.22.3, 7.22.3.5                                 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2,
- recommended practice, 3.17                                         K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4,
- recursion, 6.5.2.2                                                 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2,
- recursive function call, 6.5.2.2                                   K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1,
- redefinition of macro, 6.10.3                                       K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1,
- reentrancy, 5.1.2.3, 5.2.3                                         K.3.9.3.2.1, K.3.9.3.2.2
-    library functions, 7.1.4                                  rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2,
- referenced type, 6.2.5                                             K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
- register storage-class specifier, 6.7.1, 6.9                  runtime-constraint, 3.18
- relational expressions, 6.5.8                                Runtime-constraint handling functions, K.3.6.1
- relaxed atomic operations, 5.1.2.4                           rvalue, 6.3.2.1
- release fence, 7.17.4
- release operation, 5.1.2.4                                   same scope, 6.2.1
- release sequence, 5.1.2.4                                    save calling environment function, 7.13.1
- reliability of data, interrupted, 5.1.2.3                    scalar types, 6.2.5
- remainder assignment operator (%=), 6.5.16.2                 scalbln function, 7.12.6.13, F.3, F.10.3.13
- remainder functions, 7.12.10, F.10.7                         scalbln type-generic macro, 7.24
- remainder functions, 7.12.10.2, 7.12.10.3, F.3,              scalbn function, 7.12.6.13, F.3, F.10.3.13
-       F.10.7.2                                               scalbn type-generic macro, 7.24
- remainder operator (%), 6.2.6.2, 6.5.5                       scanf function, 7.21.1, 7.21.6.4, 7.21.6.11
- remainder type-generic macro, 7.24                           scanf_s function, K.3.5.3.4, K.3.5.3.11
- remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2               scanlist, 7.21.6.2, 7.28.2.2
- remquo functions, 7.12.10.3, F.3, F.10.7.3                   scanset, 7.21.6.2, 7.28.2.2
- remquo type-generic macro, 7.24                              SCHAR_MAX macro, 5.2.4.2.1
- rename function, 7.21.4.2                                    SCHAR_MIN macro, 5.2.4.2.1
- representations of types, 6.2.6                              SCNcFASTN macros, 7.8.1
-    pointer, 6.2.5                                            SCNcLEASTN macros, 7.8.1
- rescanning and replacement, 6.10.3.4                         SCNcMAX macros, 7.8.1
- reserved identifiers, 6.4.1, 7.1.3, K.3.1.2                   SCNcN macros, 7.8.1
- restartable multibyte/wide character conversion              SCNcPTR macros, 7.8.1
-       functions, 7.27.1, 7.28.6.3, K.3.9.3.1                 scope of identifier, 6.2.1, 6.9.2
- restartable multibyte/wide string conversion                 search functions
-       functions, 7.28.6.4, K.3.9.3.2                           string, 7.23.5, K.3.7.3
- restore calling environment function, 7.13.2                   utility, 7.22.5, K.3.6.3
- restrict type qualifier, 6.7.3, 6.7.3.1                         wide string, 7.28.4.5, K.3.9.2.3
-
- SEEK_CUR macro, 7.21.1, 7.21.9.2                                 sign and magnitude, 6.2.6.2
- SEEK_END macro, 7.21.1, 7.21.9.2                                 sign bit, 6.2.6.2
- SEEK_SET macro, 7.21.1, 7.21.9.2                                 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7
- selection statements, 6.8.4                                      signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
- self-referential structure, 6.7.2.3                              signal handling functions, 7.14.1
- semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3,                   signal.h header, 7.14, 7.30.6
-       6.8.5, 6.8.6                                               signaling NaN, 5.2.4.2.2, F.2.1
- separate compilation, 5.1.1.1                                    signals, 5.1.2.3, 5.2.3, 7.14.1
- separate translation, 5.1.1.1                                    signbit macro, 7.12.3.6, F.3
- sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14,               signed char type, 6.2.5, 7.21.6.1, 7.21.6.2,
-       6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8,                     7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2
-       7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3                  signed character, 6.3.1.1
- sequenced after, see sequenced before                            signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
- sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4,                signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
-       6.5.16, see also indeterminately sequenced,                     6.3.1.8
-       unsequenced                                                signed types, 6.2.5, 6.7.2
- sequencing of statements, 6.8                                    significand part, 6.4.4.2
- set_constraint_handler_s function,                               SIGSEGV macro, 7.14, 7.14.1.1
-       K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3                   SIGTERM macro, 7.14
- setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5                      simple assignment operator (=), 6.5.16.1
- setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1                          sin functions, 7.12.4.6, F.10.1.6
- setjmp.h header, 7.13                                            sin type-generic macro, 7.24, G.7
- setlocale function, 7.11.1.1, 7.11.2.1                           single-byte character, 3.7.1, 5.2.1.2
- setvbuf function, 7.21.1, 7.21.3, 7.21.5.1,                      single-byte/wide character conversion functions,
-       7.21.5.5, 7.21.5.6                                              7.28.6.1
- shall, 4                                                         single-precision arithmetic, 5.1.2.3
- shift expressions, 6.5.7                                         single-quote escape sequence (\'), 6.4.4.4, 6.4.5
- shift sequence, 7.1.1                                            singularity, 7.12.1
- shift states, 5.2.1.2                                            sinh functions, 7.12.5.5, F.10.2.5
- short identifier, character, 5.2.4.1, 6.4.3                       sinh type-generic macro, 7.24, G.7
- short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,                 SIZE_MAX macro, 7.20.3
-       7.21.6.2, 7.28.2.1, 7.28.2.2                               size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1,
- short int type conversion, 6.3.1.1, 6.3.1.3,                          7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27,
-       6.3.1.4, 6.3.1.8                                                7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4,
- SHRT_MAX macro, 5.2.4.2.1                                             K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
- SHRT_MIN macro, 5.2.4.2.1                                        sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
- side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4,           snprintf function, 7.21.6.5, 7.21.6.12,
-       6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5,                     K.3.5.3.5
-       7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1,                snprintf_s function, K.3.5.3.5, K.3.5.3.6
-       F.9.3                                                      snwprintf_s function, K.3.9.1.3, K.3.9.1.4
- SIG_ATOMIC_MAX macro, 7.20.3                                     sorting utility functions, 7.22.5, K.3.6.3
- SIG_ATOMIC_MIN macro, 7.20.3                                     source character set, 5.1.1.2, 5.2.1
- sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1,                      source file, 5.1.1.1
-       7.20.3                                                        name, 6.10.4, 6.10.8.1
- SIG_DFL macro, 7.14, 7.14.1.1                                    source file inclusion, 6.10.2
- SIG_ERR macro, 7.14, 7.14.1.1                                    source lines, 5.1.1.2
- SIG_IGN macro, 7.14, 7.14.1.1                                    source text, 5.1.1.2
- SIGABRT macro, 7.14, 7.22.4.1                                    space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
- SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17                          7.4.1.10, 7.29.2.1.3
- SIGILL macro, 7.14, 7.14.1.1                                     sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6
- SIGINT macro, 7.14                                               sprintf_s function, K.3.5.3.5, K.3.5.3.6
-
- sqrt functions, 7.12.7.5, F.3, F.10.4.5                         do, 6.8.5.2
- sqrt type-generic macro, 7.24                                   else, 6.8.4.1
- srand function, 7.22.2.2                                        expression, 6.8.3
- sscanf function, 7.21.6.7, 7.21.6.14                            for, 6.8.5.3
- sscanf_s function, K.3.5.3.7, K.3.5.3.14                        goto, 6.8.6.1
- standard error stream, 7.21.1, 7.21.3, 7.21.10.4                if, 6.8.4.1
- standard headers, 4, 7.1.2                                      iteration, 6.8.5
-    <assert.h>, 7.2                                              jump, 6.8.6
-    <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3,                labeled, 6.8.1
-         7.24, 7.30.1, G.6, J.5.17                               null, 6.8.3
-    <ctype.h>, 7.4, 7.30.2                                       return, 6.8.6.4, F.6
-    <errno.h>, 7.5, 7.30.3, K.3.2                                selection, 6.8.4
-    <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H                sequencing, 6.8
-    <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3,                      switch, 6.8.4.2
-         7.28.4.1.1                                              while, 6.8.5.1
-    <inttypes.h>, 7.8, 7.30.4                                 static assertions, 6.7.10
-    <iso646.h>, 4, 7.9                                        static storage duration, 6.2.4
-    <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10                     static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
-    <locale.h>, 7.11, 7.30.5                                  static, in array declarators, 6.7.6.2, 6.7.6.3
-    <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10,            static_assert declaration, 6.7.10
-         J.5.17                                               static_assert macro, 7.2
-    <setjmp.h>, 7.13                                          stdalign.h header, 4, 7.15
-    <signal.h>, 7.14, 7.30.6                                  stdarg.h header, 4, 6.7.6.3, 7.16
-    <stdalign.h>, 4, 7.15                                     stdatomic.h header, 6.10.8.3, 7.1.2, 7.17
-    <stdarg.h>, 4, 6.7.6.3, 7.16                              stdbool.h header, 4, 7.18, 7.30.7, H
-    <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17                      STDC, 6.10.6, 6.11.8
-    <stdbool.h>, 4, 7.18, 7.30.7, H                           stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
-    <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,                       6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3
-         6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3                   stderr macro, 7.21.1, 7.21.2, 7.21.3
-    <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,                stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4,
-         7.30.8, K.3.3, K.3.4                                       7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4,
-    <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5                    K.3.5.4.1, K.3.9.1.14
-    <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F,                  stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,
-         K.3.1.4, K.3.6                                             7.30.8, K.3.3, K.3.4
-    <string.h>, 7.23, 7.30.11, K.3.7                          stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5
-    <tgmath.h>, 7.24, G.7                                     stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F,
-    <threads.h>, 6.10.8.3, 7.1.2, 7.25                              K.3.1.4, K.3.6
-    <time.h>, 7.26, K.3.8                                     stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3,
-    <uchar.h>, 6.4.4.4, 6.4.5, 7.27                                 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9
-    <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,              storage duration, 6.2.4
-         F, K.3.9                                             storage order of array, 6.5.2.1
-    <wctype.h>, 7.29, 7.30.13                                 storage unit (bit-field), 6.2.6.1, 6.7.2.1
- standard input stream, 7.21.1, 7.21.3                        storage-class specifiers, 6.7.1, 6.11.5
- standard integer types, 6.2.5                                strcat function, 7.23.3.1
- standard output stream, 7.21.1, 7.21.3                       strcat_s function, K.3.7.2.1
- standard signed integer types, 6.2.5                         strchr function, 7.23.5.2
- state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4           strcmp function, 7.23.4, 7.23.4.2
- statements, 6.8                                              strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5
-    break, 6.8.6.3                                            strcpy function, 7.23.2.3
-    compound, 6.8.2                                           strcpy_s function, K.3.7.1.3
-    continue, 6.8.6.2                                         strcspn function, 7.23.5.3
-
- streams, 7.21.2, 7.22.4.4                                                7.22.1.4, 7.28.2.2
-    fully buffered, 7.21.3                                          strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4
-    line buffered, 7.21.3                                           strtoumax function, 7.8.2.3
-    orientation, 7.21.2                                             struct hack, see flexible array member
-    standard error, 7.21.1, 7.21.3                                  struct lconv, 7.11
-    standard input, 7.21.1, 7.21.3                                  struct tm, 7.26.1
-    standard output, 7.21.1, 7.21.3                                 structure
-    unbuffered, 7.21.3                                                 arrow operator (->), 6.5.2.3
- strerror function, 7.21.10.4, 7.23.6.2                                content, 6.7.2.3
- strerror_s function, K.3.7.4.2, K.3.7.4.3                             dot operator (.), 6.5.2.3
- strerrorlen_s function, K.3.7.4.3                                     initialization, 6.7.9
- strftime function, 7.11.1.1, 7.26.3, 7.26.3.5,                        member alignment, 6.7.2.1
-       7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2                         member name space, 6.2.3
- stricter, 6.2.8                                                       member operator (.), 6.3.2.1, 6.5.2.3
- strictly conforming program, 4                                        pointer operator (->), 6.5.2.3
- string, 7.1.1                                                         specifier, 6.7.2.1
-    comparison functions, 7.23.4                                       tag, 6.2.3, 6.7.2.3
-    concatenation functions, 7.23.3, K.3.7.2                           type, 6.2.5, 6.7.2.1
-    conversion functions, 7.11.1.1                                  strxfrm function, 7.11.1.1, 7.23.4.5
-    copying functions, 7.23.2, K.3.7.1                              subnormal floating-point numbers, 5.2.4.2.2
-    library function conventions, 7.23.1                            subscripting, 6.5.2.1
-    literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9           subtraction assignment operator (-=), 6.5.16.2
-    miscellaneous functions, 7.23.6, K.3.7.4                        subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2
-    numeric conversion functions, 7.8.2.3, 7.22.1                   suffix
-    search functions, 7.23.5, K.3.7.3                                  floating constant, 6.4.4.2
- string handling header, 7.23, K.3.7                                   integer constant, 6.4.4.1
- string.h header, 7.23, 7.30.11, K.3.7                              switch body, 6.8.4.2
- stringizing, 6.10.3.2, 6.10.9                                      switch case label, 6.8.1, 6.8.4.2
- strlen function, 7.23.6.3                                          switch default label, 6.8.1, 6.8.4.2
- strncat function, 7.23.3.2                                         switch statement, 6.8.1, 6.8.4.2
- strncat_s function, K.3.7.2.2                                      swprintf function, 7.28.2.3, 7.28.2.7,
- strncmp function, 7.23.4, 7.23.4.4                                       K.3.9.1.3, K.3.9.1.4
- strncpy function, 7.23.2.4                                         swprintf_s function, K.3.9.1.3, K.3.9.1.4
- strncpy_s function, K.3.7.1.4                                      swscanf function, 7.28.2.4, 7.28.2.8
- strnlen_s function, K.3.7.4.4                                      swscanf_s function, K.3.9.1.5, K.3.9.1.10
- stronger, 6.2.8                                                    symbols, 3
- strpbrk function, 7.23.5.4                                         synchronization operation, 5.1.2.4
- strrchr function, 7.23.5.5                                         synchronize with, 5.1.2.4
- strspn function, 7.23.5.6                                          syntactic categories, 6.1
- strstr function, 7.23.5.7                                          syntax notation, 6.1
- strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3,                    syntax rule precedence, 5.1.1.2
-       7.28.2.2, F.3                                                syntax summary, language, A
- strtof function, 7.12.11.2, 7.22.1.3, F.3                          system function, 7.22.4.8
- strtoimax function, 7.8.2.3
- strtok function, 7.23.5.8                                          tab characters, 5.2.1, 6.4
- strtok_s function, K.3.7.3.1                                       tag compatibility, 6.2.7
- strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2,                      tag name space, 6.2.3
-       7.22.1.4, 7.28.2.2                                           tags, 6.7.2.3
- strtold function, 7.12.11.2, 7.22.1.3, F.3                         tan functions, 7.12.4.7, F.10.1.7
- strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4                      tan type-generic macro, 7.24, G.7
- strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2,                     tanh functions, 7.12.5.6, F.10.2.6
-
- tanh type-generic macro, 7.24, G.7                            toupper function, 7.4.2.2
- temporary lifetime, 6.2.4                                     towctrans function, 7.29.3.2.1, 7.29.3.2.2
- tentative definition, 6.9.2                                    towlower function, 7.29.3.1.1, 7.29.3.2.1
- terms, 3                                                      towupper function, 7.29.3.1.2, 7.29.3.2.1
- text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4           translation environment, 5, 5.1.1
- tgamma functions, 7.12.8.4, F.10.5.4                          translation limits, 5.2.4.1
- tgamma type-generic macro, 7.24                               translation phases, 5.1.1.2
- tgmath.h header, 7.24, G.7                                    translation unit, 5.1.1.1, 6.9
- thrd_create function, 7.25.1, 7.25.5.1                        trap, see perform a trap
- thrd_current function, 7.25.5.2                               trap representation, 3.19.4, 6.2.6.1, 6.2.6.2,
- thrd_detach function, 7.25.5.3                                      6.3.2.3, 6.5.2.3
- thrd_equal function, 7.25.5.4                                 trigonometric functions
- thrd_exit function, 7.25.5.5                                     complex, 7.3.5, G.6.1
- thrd_join function, 7.25.5.6                                     real, 7.12.4, F.10.1
- thrd_sleep function, 7.25.5.7                                 trigraph sequences, 5.1.1.2, 5.2.1.1
- thrd_start_t type, 7.25.1                                     true macro, 7.18
- thrd_t type, 7.25.1                                           trunc functions, 7.12.9.8, F.10.6.8
- thrd_yield function, 7.25.5.8                                 trunc type-generic macro, 7.24
- thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6            truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3
- thread storage duration, 6.2.4, 7.6                           truncation toward zero, 6.5.5
- threads header, 7.25                                          tss_create function, 7.25.6.1
- threads.h header, 6.10.8.3, 7.1.2, 7.25                       tss_delete function, 7.25.6.2
- time                                                          TSS_DTOR_ITERATIONS macro, 7.25.1
-    broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1,           tss_dtor_t type, 7.25.1
-          7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1,             tss_get function, 7.25.6.3
-          K.3.8.2.3, K.3.8.2.4                                 tss_set function, 7.25.6.4
-    calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4,            tss_t type, 7.25.1
-          7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2,             two's complement, 6.2.6.2, 7.20.1.1
-          K.3.8.2.3, K.3.8.2.4                                 type category, 6.2.5
-    components, 7.26.1, K.3.8.1                                type conversion, 6.3
-    conversion functions, 7.26.3, K.3.8.2                      type definitions, 6.7.8
-       wide character, 7.28.5                                  type domain, 6.2.5, G.2
-    local, 7.26.1                                              type names, 6.7.7
-    manipulation functions, 7.26.2                             type punning, 6.5.2.3
-    normalized broken down, K.3.8.1, K.3.8.2.1                 type qualifiers, 6.7.3
- time function, 7.26.2.4                                       type specifiers, 6.7.2
- time.h header, 7.26, K.3.8                                    type-generic macro, 7.24, G.7
- time_t type, 7.26.1                                           typedef declaration, 6.7.8
- TIME_UTC macro, 7.25.7.1                                      typedef storage-class specifier, 6.7.1, 6.7.8
- tm structure type, 7.26.1, 7.28.1, K.3.8.1                    types, 6.2.5
- TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4                        atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3,
- TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2                           6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6
- tmpfile function, 7.21.4.3, 7.22.4.4                             character, 6.7.9
- tmpfile_s function, K.3.5.1.1, K.3.5.1.2                         compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6
- tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4,                     complex, 6.2.5, G
-       K.3.5.1.2                                                  composite, 6.2.7
- tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2                   const qualified, 6.7.3
- token, 5.1.1.2, 6.4, see also preprocessing tokens               conversions, 6.3
- token concatenation, 6.10.3.3                                    imaginary, G
- token pasting, 6.10.3.3                                          restrict qualified, 6.7.3
- tolower function, 7.4.2.1                                        volatile qualified, 6.7.3
-
- uchar.h header, 6.4.4.4, 6.4.5, 7.27                      universal character name, 6.4.3
- UCHAR_MAX macro, 5.2.4.2.1                                unnormalized floating-point numbers, 5.2.4.2.2
- UINT_FASTN_MAX macros, 7.20.2.3                           unqualified type, 6.2.5
- uint_fastN_t types, 7.20.1.3                              unqualified version of type, 6.2.5
- uint_least16_t type, 7.27                                 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also
- uint_least32_t type, 7.27                                       indeterminately sequenced, sequenced
- UINT_LEASTN_MAX macros, 7.20.2.2                                before
- uint_leastN_t types, 7.20.1.2                             unsigned char type, K.3.5.3.2, K.3.9.1.2
- UINT_MAX macro, 5.2.4.2.1                                 unsigned integer suffix, u or U, 6.4.4.1
- UINTMAX_C macro, 7.20.4.2                                 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1
- UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5             unsigned type conversion, 6.3.1.1, 6.3.1.3,
- uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,                   6.3.1.4, 6.3.1.8
-      7.28.2.1, 7.28.2.2                                   unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2,
- UINTN_C macros, 7.20.4.1                                        7.28.2.1, 7.28.2.2
- UINTN_MAX macros, 7.20.2.1                                unspecified behavior, 3.4.4, 4, J.1
- uintN_t types, 7.20.1.1                                   unspecified value, 3.19.3
- UINTPTR_MAX macro, 7.20.2.4                               uppercase letter, 5.2.1
- uintptr_t type, 7.20.1.4                                  use of library functions, 7.1.4
- ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                    USHRT_MAX macro, 5.2.4.2.1
-      7.28.4.1.2                                           usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6,
- ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                           6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
-      7.28.4.1.2                                           UTF-16, 6.10.8.2
- unary arithmetic operators, 6.5.3.3                       UTF-32, 6.10.8.2
- unary expression, 6.5.3                                   UTF-8 string literal, see string literal
- unary minus operator (-), 6.5.3.3, F.3                    utilities, general, 7.22, K.3.6
- unary operators, 6.5.3                                       wide string, 7.28.4, K.3.9.2
- unary plus operator (+), 6.5.3.3
- unbuffered stream, 7.21.3                                 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2,
- undef preprocessing directive, 6.10.3.5, 7.1.3,                7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
-      7.1.4                                                     7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
- undefined behavior, 3.4.3, 4, J.2                               7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
- underscore character, 6.4.2.1                                  7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
- underscore, leading, in identifier, 7.1.3                       K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
- ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2,             va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1,
-      7.21.9.3                                                  7.16.1.2, 7.16.1.3
- ungetwc function, 7.21.1, 7.28.3.10                       va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3,
- Unicode, 7.27, see also char16_t type,                         7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
-      char32_t type, wchar_t type                               7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
- Unicode required set, 6.10.8.2                                 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
- union                                                          7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
-   arrow operator (->), 6.5.2.3                                 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
-   content, 6.7.2.3                                        va_list type, 7.16, 7.16.1.3
-   dot operator (.), 6.5.2.3                               va_start macro, 7.16, 7.16.1, 7.16.1.1,
-   initialization, 6.7.9                                        7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8,
-   member alignment, 6.7.2.1                                    7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12,
-   member name space, 6.2.3                                     7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6,
-   member operator (.), 6.3.2.1, 6.5.2.3                        7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10,
-   pointer operator (->), 6.5.2.3                               K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7,
-   specifier, 6.7.2.1                                            K.3.9.1.10, K.3.9.1.12
-   tag, 6.2.3, 6.7.2.3                                     value, 3.19
-   type, 6.2.5, 6.7.2.1                                    value bits, 6.2.6.2
-
- variable arguments, 6.10.3, 7.16                             vswscanf function, 7.28.2.8
- variable arguments header, 7.16                              vswscanf_s function, K.3.9.1.10
- variable length array, 6.7.6, 6.7.6.2, 6.10.8.3              vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11
- variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3              vwprintf_s function, K.3.9.1.11
- vertical-tab character, 5.2.1, 6.4                           vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10
- vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4,           vwscanf_s function, K.3.9.1.12
-      7.4.1.10
- vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8               warnings, I
- vfprintf_s function, K.3.5.3.8, K.3.5.3.9,                   wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,
-      K.3.5.3.11, K.3.5.3.14                                      F, K.3.9
- vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9                 WCHAR_MAX macro, 7.20.3, 7.28.1
- vfscanf_s function, K.3.5.3.9, K.3.5.3.11,                   WCHAR_MIN macro, 7.20.3, 7.28.1
-      K.3.5.3.14                                              wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19,
- vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6                  7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1,
- vfwprintf_s function, K.3.9.1.6                                  7.28.2.1, 7.28.2.2
- vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10               wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2,
- vfwscanf_s function, K.3.9.1.7                                   7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1,
- visibility of identifier, 6.2.1                                   K.3.9.3.2.2
- visible sequence of side effects, 5.1.2.4                    wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1
- visible side effect, 5.1.2.4                                 wcscat function, 7.28.4.3.1
- VLA, see variable length array                               wcscat_s function, K.3.9.2.2.1
- void expression, 6.3.2.2                                     wcschr function, 7.28.4.5.1
- void function parameter, 6.7.6.3                             wcscmp function, 7.28.4.4.1, 7.28.4.4.4
- void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2,                 wcscoll function, 7.28.4.4.2, 7.28.4.4.4
-      K.3.9.1.2                                               wcscpy function, 7.28.4.2.1
- void type conversion, 6.3.2.2                                wcscpy_s function, K.3.9.2.1.1
- volatile storage, 5.1.2.3                                    wcscspn function, 7.28.4.5.2
- volatile type qualifier, 6.7.3                                wcsftime function, 7.11.1.1, 7.28.5.1
- volatile-qualified type, 6.2.5, 6.7.3                         wcslen function, 7.28.4.6.1
- vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10,               wcsncat function, 7.28.4.3.2
-      K.3.5.3.10                                              wcsncat_s function, K.3.9.2.2.2
- vprintf_s function, K.3.5.3.9, K.3.5.3.10,                   wcsncmp function, 7.28.4.4.3
-      K.3.5.3.11, K.3.5.3.14                                  wcsncpy function, 7.28.4.2.2
- vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11                 wcsncpy_s function, K.3.9.2.1.2
- vscanf_s function, K.3.5.3.9, K.3.5.3.11,                    wcsnlen_s function, K.3.9.2.4.1
-      K.3.5.3.14                                              wcspbrk function, 7.28.4.5.3
- vsnprintf function, 7.21.6.8, 7.21.6.12,                     wcsrchr function, 7.28.4.5.4
-      K.3.5.3.12                                              wcsrtombs function, 7.28.6.4.2, K.3.9.3.2
- vsnprintf_s function, K.3.5.3.9, K.3.5.3.11,                 wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2
-      K.3.5.3.12, K.3.5.3.13, K.3.5.3.14                      wcsspn function, 7.28.4.5.5
- vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9                  wcsstr function, 7.28.4.5.6
- vsprintf function, 7.21.6.8, 7.21.6.13,                      wcstod function, 7.21.6.2, 7.28.2.2
-      K.3.5.3.13                                              wcstod function, 7.28.4.1.1
- vsprintf_s function, K.3.5.3.9, K.3.5.3.11,                  wcstof function, 7.28.4.1.1
-      K.3.5.3.12, K.3.5.3.13, K.3.5.3.14                      wcstoimax function, 7.8.2.4
- vsscanf function, 7.21.6.8, 7.21.6.14                        wcstok function, 7.28.4.5.7
- vsscanf_s function, K.3.5.3.9, K.3.5.3.11,                   wcstok_s function, K.3.9.2.3.1
-      K.3.5.3.14                                              wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2,
- vswprintf function, 7.28.2.7, K.3.9.1.8,                         7.28.4.1.2
-      K.3.9.1.9                                               wcstold function, 7.28.4.1.1
- vswprintf_s function, K.3.9.1.8, K.3.9.1.9                   wcstoll function, 7.8.2.4, 7.28.4.1.2
-
- wcstombs function, 7.22.8.2, 7.28.6.4                           7.29.1
- wcstombs_s function, K.3.6.5.2                               wmemchr function, 7.28.4.5.8
- wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2,               wmemcmp function, 7.28.4.4.5
-      7.28.4.1.2                                              wmemcpy function, 7.28.4.2.3
- wcstoull function, 7.8.2.4, 7.28.4.1.2                       wmemcpy_s function, K.3.9.2.1.3
- wcstoumax function, 7.8.2.4                                  wmemmove function, 7.28.4.2.4
- wcsxfrm function, 7.28.4.4.4                                 wmemmove_s function, K.3.9.2.1.4
- wctob function, 7.28.6.1.2, 7.29.2.1                         wmemset function, 7.28.4.6.2
- wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3                wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11,
- wctomb_s function, K.3.6.4.1                                    K.3.9.1.13
- wctrans function, 7.29.3.2.1, 7.29.3.2.2                     wprintf_s function, K.3.9.1.13
- wctrans_t type, 7.29.1, 7.29.3.2.2                           wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12,
- wctype function, 7.29.2.2.1, 7.29.2.2.2                         7.28.3.10
- wctype.h header, 7.29, 7.30.13                               wscanf_s function, K.3.9.1.12, K.3.9.1.14
- wctype_t type, 7.29.1, 7.29.2.2.2
- weaker, 6.2.8                                                xor macro, 7.9
- WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6,            xor_eq macro, 7.9
-      7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10,                xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7,
-      7.28.6.1.1, 7.29.1                                          7.25.7.1
- while statement, 6.8.5.1                                     xtime_get function, 7.25.7.1
- white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
-      7.29.2.1.10
- white-space characters, 6.4
- wide character, 3.7.3
-   case mapping functions, 7.29.3.1
-      extensible, 7.29.3.2
-   classification functions, 7.29.2.1
-      extensible, 7.29.2.2
-   constant, 6.4.4.4
-   formatted input/output functions, 7.28.2,
-         K.3.9.1
-   input functions, 7.21.1
-   input/output functions, 7.21.1, 7.28.3
-   output functions, 7.21.1
-   single-byte conversion functions, 7.28.6.1
- wide string, 7.1.1
- wide string comparison functions, 7.28.4.4
- wide string concatenation functions, 7.28.4.3,
-      K.3.9.2.2
- wide string copying functions, 7.28.4.2, K.3.9.2.1
- wide string literal, see string literal
- wide string miscellaneous functions, 7.28.4.6,
-      K.3.9.2.4
- wide string numeric conversion functions, 7.8.2.4,
-      7.28.4.1
- wide string search functions, 7.28.4.5, K.3.9.2.3
- wide-oriented stream, 7.21.2
- width, 6.2.6.2
- WINT_MAX macro, 7.20.3
- WINT_MIN macro, 7.20.3
- wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1,
-
-

Contents - diff --git a/n1548.txt b/n1548.txt deleted file mode 100644 index 2afd8b7..0000000 --- a/n1548.txt +++ /dev/null @@ -1,26321 +0,0 @@ -N1548 Committee Draft -- December 2, 2010 ISO/IEC 9899:201x - - - - -INTERNATIONAL STANDARD (C)ISO/IEC ISO/IEC 9899:201x - - - - -Programming languages -- C - - - ABSTRACT - - - - (Cover sheet to be provided by ISO Secretariat.) - -This International Standard specifies the form and establishes the interpretation of -programs expressed in the programming language C. Its purpose is to promote -portability, reliability, maintainability, and efficient execution of C language programs on -a variety of computing systems. - -Clauses are included that detail the C language itself and the contents of the C language -execution library. Annexes summarize aspects of both of them, and enumerate factors -that influence the portability of C programs. - -Although this International Standard is intended to guide knowledgeable C language -programmers as well as implementors of C language translation systems, the document -itself is not designed to serve as a tutorial. - -Recipients of this draft are invited to submit, with their comments, notification of any -relevant patent rights of which they are aware and to provide supporting documentation. - -Changes from the previous draft (N1256) are indicated by ''diff marks'' in the right -margin: deleted text is marked with ''*'', new or changed text with '' ''. - -[page i] - - -[page ii] - -Contents -Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii -Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii -1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -2. Normative references . . . . . . . . . . . . . . . . . . . . . . . 2 -3. Terms, definitions, and symbols . . . . . . . . . . . . . . . . . . . 3 -4. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . 8 -5. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 5.1 Conceptual models . . . . . . . . . . . . . . . . . . . . . 10 - 5.1.1 Translation environment . . . . . . . . . . . . . . . . 10 - 5.1.2 Execution environments . . . . . . . . . . . . . . . . 12 - 5.2 Environmental considerations . . . . . . . . . . . . . . . . . 22 - 5.2.1 Character sets . . . . . . . . . . . . . . . . . . . . 22 - 5.2.2 Character display semantics . . . . . . . . . . . . . . 24 - 5.2.3 Signals and interrupts . . . . . . . . . . . . . . . . . 25 - 5.2.4 Environmental limits . . . . . . . . . . . . . . . . . 25 -6. Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.2.1 Scopes of identifiers . . . . . . . . . . . . . . . . . 35 - 6.2.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 36 - 6.2.3 Name spaces of identifiers . . . . . . . . . . . . . . . 37 - 6.2.4 Storage durations of objects . . . . . . . . . . . . . . 38 - 6.2.5 Types . . . . . . . . . . . . . . . . . . . . . . . 39 - 6.2.6 Representations of types . . . . . . . . . . . . . . . . 44 - 6.2.7 Compatible type and composite type . . . . . . . . . . . 47 - 6.2.8 Alignment of objects . . . . . . . . . . . . . . . . . 48 - 6.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 50 - 6.3.1 Arithmetic operands . . . . . . . . . . . . . . . . . 50 - 6.3.2 Other operands . . . . . . . . . . . . . . . . . . . 54 - 6.4 Lexical elements . . . . . . . . . . . . . . . . . . . . . . 57 - 6.4.1 Keywords . . . . . . . . . . . . . . . . . . . . . . 58 - 6.4.2 Identifiers . . . . . . . . . . . . . . . . . . . . . . 59 - 6.4.3 Universal character names . . . . . . . . . . . . . . . 61 - 6.4.4 Constants . . . . . . . . . . . . . . . . . . . . . . 62 - 6.4.5 String literals . . . . . . . . . . . . . . . . . . . . 70 - 6.4.6 Punctuators . . . . . . . . . . . . . . . . . . . . . 72 - 6.4.7 Header names . . . . . . . . . . . . . . . . . . . . 73 - 6.4.8 Preprocessing numbers . . . . . . . . . . . . . . . . 74 - 6.4.9 Comments . . . . . . . . . . . . . . . . . . . . . 75 - -[page iii] - - 6.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . 76 - 6.5.1 Primary expressions . . . . . . . . . . . . . . . . . 78 - 6.5.2 Postfix operators . . . . . . . . . . . . . . . . . . . 79 - 6.5.3 Unary operators . . . . . . . . . . . . . . . . . . . 88 - 6.5.4 Cast operators . . . . . . . . . . . . . . . . . . . . 91 - 6.5.5 Multiplicative operators . . . . . . . . . . . . . . . . 92 - 6.5.6 Additive operators . . . . . . . . . . . . . . . . . . 92 - 6.5.7 Bitwise shift operators . . . . . . . . . . . . . . . . . 94 - 6.5.8 Relational operators . . . . . . . . . . . . . . . . . . 95 - 6.5.9 Equality operators . . . . . . . . . . . . . . . . . . 96 - 6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . 97 - 6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . 98 - 6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . 98 - 6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . 99 - 6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . 99 - 6.5.15 Conditional operator . . . . . . . . . . . . . . . . . 100 - 6.5.16 Assignment operators . . . . . . . . . . . . . . . . . 101 - 6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . 104 - 6.6 Constant expressions . . . . . . . . . . . . . . . . . . . . . 105 - 6.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . 107 - 6.7.1 Storage-class specifiers . . . . . . . . . . . . . . . . 108 - 6.7.2 Type specifiers . . . . . . . . . . . . . . . . . . . . 109 - 6.7.3 Type qualifiers . . . . . . . . . . . . . . . . . . . . 120 - 6.7.4 Function specifiers . . . . . . . . . . . . . . . . . . 124 - 6.7.5 Alignment specifier . . . . . . . . . . . . . . . . . . 126 - 6.7.6 Declarators . . . . . . . . . . . . . . . . . . . . . 127 - 6.7.7 Type names . . . . . . . . . . . . . . . . . . . . . 135 - 6.7.8 Type definitions . . . . . . . . . . . . . . . . . . . 136 - 6.7.9 Initialization . . . . . . . . . . . . . . . . . . . . 138 - 6.7.10 Static assertions . . . . . . . . . . . . . . . . . . . 144 - 6.8 Statements and blocks . . . . . . . . . . . . . . . . . . . . 145 - 6.8.1 Labeled statements . . . . . . . . . . . . . . . . . . 145 - 6.8.2 Compound statement . . . . . . . . . . . . . . . . . 146 - 6.8.3 Expression and null statements . . . . . . . . . . . . . 146 - 6.8.4 Selection statements . . . . . . . . . . . . . . . . . 147 - 6.8.5 Iteration statements . . . . . . . . . . . . . . . . . . 149 - 6.8.6 Jump statements . . . . . . . . . . . . . . . . . . . 150 - 6.9 External definitions . . . . . . . . . . . . . . . . . . . . . 154 - 6.9.1 Function definitions . . . . . . . . . . . . . . . . . . 155 - 6.9.2 External object definitions . . . . . . . . . . . . . . . 157 - 6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . 159 - 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . 161 - 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . 163 - 6.10.3 Macro replacement . . . . . . . . . . . . . . . . . . 165 - -[page iv] - - 6.10.4 Line control . . . . . . . . . . . . . . . . . . . . . 172 - 6.10.5 Error directive . . . . . . . . . . . . . . . . . . . . 173 - 6.10.6 Pragma directive . . . . . . . . . . . . . . . . . . . 173 - 6.10.7 Null directive . . . . . . . . . . . . . . . . . . . . 174 - 6.10.8 Predefined macro names . . . . . . . . . . . . . . . . 174 - 6.10.9 Pragma operator . . . . . . . . . . . . . . . . . . . 176 - 6.11 Future language directions . . . . . . . . . . . . . . . . . . 178 - 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . 178 - 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 178 - 6.11.3 External names . . . . . . . . . . . . . . . . . . . 178 - 6.11.4 Character escape sequences . . . . . . . . . . . . . . 178 - 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . 178 - 6.11.6 Function declarators . . . . . . . . . . . . . . . . . 178 - 6.11.7 Function definitions . . . . . . . . . . . . . . . . . . 178 - 6.11.8 Pragma directives . . . . . . . . . . . . . . . . . . 178 - 6.11.9 Predefined macro names . . . . . . . . . . . . . . . . 178 -7. Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 - 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 179 - 7.1.1 Definitions of terms . . . . . . . . . . . . . . . . . . 179 - 7.1.2 Standard headers . . . . . . . . . . . . . . . . . . . 180 - 7.1.3 Reserved identifiers . . . . . . . . . . . . . . . . . . 181 - 7.1.4 Use of library functions . . . . . . . . . . . . . . . . 182 - 7.2 Diagnostics . . . . . . . . . . . . . . . . . . 185 - 7.2.1 Program diagnostics . . . . . . . . . . . . . . . . . 185 - 7.3 Complex arithmetic . . . . . . . . . . . . . . 187 - 7.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 187 - 7.3.2 Conventions . . . . . . . . . . . . . . . . . . . . . 188 - 7.3.3 Branch cuts . . . . . . . . . . . . . . . . . . . . . 188 - 7.3.4 The CX_LIMITED_RANGE pragma . . . . . . . . . . . 188 - 7.3.5 Trigonometric functions . . . . . . . . . . . . . . . . 189 - 7.3.6 Hyperbolic functions . . . . . . . . . . . . . . . . . 191 - 7.3.7 Exponential and logarithmic functions . . . . . . . . . . 193 - 7.3.8 Power and absolute-value functions . . . . . . . . . . . 194 - 7.3.9 Manipulation functions . . . . . . . . . . . . . . . . 195 - 7.4 Character handling . . . . . . . . . . . . . . . . 199 - 7.4.1 Character classification functions . . . . . . . . . . . . 199 - 7.4.2 Character case mapping functions . . . . . . . . . . . . 202 - 7.5 Errors . . . . . . . . . . . . . . . . . . . . . 204 - 7.6 Floating-point environment . . . . . . . . . . . . . 205 - 7.6.1 The FENV_ACCESS pragma . . . . . . . . . . . . . . 207 - 7.6.2 Floating-point exceptions . . . . . . . . . . . . . . . 208 - 7.6.3 Rounding . . . . . . . . . . . . . . . . . . . . . . 211 - 7.6.4 Environment . . . . . . . . . . . . . . . . . . . . 212 - 7.7 Characteristics of floating types . . . . . . . . . . . 215 - -[page v] - - 7.8 Format conversion of integer types . . . . . . . . 216 - 7.8.1 Macros for format specifiers . . . . . . . . . . . . . . 216 - 7.8.2 Functions for greatest-width integer types . . . . . . . . . 217 - 7.9 Alternative spellings . . . . . . . . . . . . . . . 220 - 7.10 Sizes of integer types . . . . . . . . . . . . . . 221 - 7.11 Localization . . . . . . . . . . . . . . . . . . 222 - 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . 223 - 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . 224 - 7.12 Mathematics . . . . . . . . . . . . . . . . . . . 230 - 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . 232 - 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . 234 - 7.12.3 Classification macros . . . . . . . . . . . . . . . . . 234 - 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . 237 - 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . 239 - 7.12.6 Exponential and logarithmic functions . . . . . . . . . . 241 - 7.12.7 Power and absolute-value functions . . . . . . . . . . . 246 - 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . 248 - 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . 250 - 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . 253 - 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . 254 - 7.12.12 Maximum, minimum, and positive difference functions . . . 256 - 7.12.13 Floating multiply-add . . . . . . . . . . . . . . . . . 257 - 7.12.14 Comparison macros . . . . . . . . . . . . . . . . . . 258 - 7.13 Nonlocal jumps . . . . . . . . . . . . . . . . 261 - 7.13.1 Save calling environment . . . . . . . . . . . . . . . 261 - 7.13.2 Restore calling environment . . . . . . . . . . . . . . 262 - 7.14 Signal handling . . . . . . . . . . . . . . . . . 264 - 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . 265 - 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . 266 - 7.15 Alignment . . . . . . . . . . . . . . . . . 267 - 7.16 Variable arguments . . . . . . . . . . . . . . . 268 - 7.16.1 Variable argument list access macros . . . . . . . . . . . 268 - 7.17 Atomics . . . . . . . . . . . . . . . . . . 272 - 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . 272 - 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . 273 - 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . 274 - 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . 277 - 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . 278 - 7.17.6 Atomic integer and address types . . . . . . . . . . . . 279 - 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . 281 - 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . 284 - 7.18 Boolean type and values . . . . . . . . . . . . 286 - 7.19 Common definitions . . . . . . . . . . . . . . . 287 - 7.20 Integer types . . . . . . . . . . . . . . . . . . 289 - -[page vi] - - 7.20.1 Integer types . . . . . . . . . . . . . . . . . . . . 289 - 7.20.2 Limits of specified-width integer types . . . . . . . . . . 291 - 7.20.3 Limits of other integer types . . . . . . . . . . . . . . 293 - 7.20.4 Macros for integer constants . . . . . . . . . . . . . . 294 - 7.21 Input/output . . . . . . . . . . . . . . . . . . 296 - 7.21.1 Introduction . . . . . . . . . . . . . . . . . . . . . 296 - 7.21.2 Streams . . . . . . . . . . . . . . . . . . . . . . 298 - 7.21.3 Files . . . . . . . . . . . . . . . . . . . . . . . . 300 - 7.21.4 Operations on files . . . . . . . . . . . . . . . . . . 302 - 7.21.5 File access functions . . . . . . . . . . . . . . . . . 304 - 7.21.6 Formatted input/output functions . . . . . . . . . . . . 309 - 7.21.7 Character input/output functions . . . . . . . . . . . . . 330 - 7.21.8 Direct input/output functions . . . . . . . . . . . . . . 334 - 7.21.9 File positioning functions . . . . . . . . . . . . . . . 335 - 7.21.10 Error-handling functions . . . . . . . . . . . . . . . . 338 - 7.22 General utilities . . . . . . . . . . . . . . . . 340 - 7.22.1 Numeric conversion functions . . . . . . . . . . . . . . 341 - 7.22.2 Pseudo-random sequence generation functions . . . . . . . 346 - 7.22.3 Memory management functions . . . . . . . . . . . . . 347 - 7.22.4 Communication with the environment . . . . . . . . . . 349 - 7.22.5 Searching and sorting utilities . . . . . . . . . . . . . . 353 - 7.22.6 Integer arithmetic functions . . . . . . . . . . . . . . 355 - 7.22.7 Multibyte/wide character conversion functions . . . . . . . 356 - 7.22.8 Multibyte/wide string conversion functions . . . . . . . . 358 - 7.23 String handling . . . . . . . . . . . . . . . . . 360 - 7.23.1 String function conventions . . . . . . . . . . . . . . . 360 - 7.23.2 Copying functions . . . . . . . . . . . . . . . . . . 360 - 7.23.3 Concatenation functions . . . . . . . . . . . . . . . . 362 - 7.23.4 Comparison functions . . . . . . . . . . . . . . . . . 363 - 7.23.5 Search functions . . . . . . . . . . . . . . . . . . . 365 - 7.23.6 Miscellaneous functions . . . . . . . . . . . . . . . . 368 - 7.24 Type-generic math . . . . . . . . . . . . . . . 370 - 7.25 Threads . . . . . . . . . . . . . . . . . . . 373 - 7.25.1 Introduction . . . . . . . . . . . . . . . . . . . . . 373 - 7.25.2 Initialization functions . . . . . . . . . . . . . . . . . 375 - 7.25.3 Condition variable functions . . . . . . . . . . . . . . 375 - 7.25.4 Mutex functions . . . . . . . . . . . . . . . . . . . 377 - 7.25.5 Thread functions . . . . . . . . . . . . . . . . . . . 380 - 7.25.6 Thread-specific storage functions . . . . . . . . . . . . 382 - 7.25.7 Time functions . . . . . . . . . . . . . . . . . . . . 384 - 7.26 Date and time . . . . . . . . . . . . . . . . . . 385 - 7.26.1 Components of time . . . . . . . . . . . . . . . . . 385 - 7.26.2 Time manipulation functions . . . . . . . . . . . . . . 386 - 7.26.3 Time conversion functions . . . . . . . . . . . . . . . 388 - -[page vii] - - 7.27 Unicode utilities . . . . . . . . . . . . . . . . . 395 - 7.27.1 Restartable multibyte/wide character conversion functions . . 395 - 7.28 Extended multibyte and wide character utilities . . . . . 399 - 7.28.1 Introduction . . . . . . . . . . . . . . . . . . . . . 399 - 7.28.2 Formatted wide character input/output functions . . . . . . 400 - 7.28.3 Wide character input/output functions . . . . . . . . . . 418 - 7.28.4 General wide string utilities . . . . . . . . . . . . . . 422 - 7.28.4.1 Wide string numeric conversion functions . . . . . 423 - 7.28.4.2 Wide string copying functions . . . . . . . . . . 427 - 7.28.4.3 Wide string concatenation functions . . . . . . . 429 - 7.28.4.4 Wide string comparison functions . . . . . . . . 430 - 7.28.4.5 Wide string search functions . . . . . . . . . . 432 - 7.28.4.6 Miscellaneous functions . . . . . . . . . . . . 436 - 7.28.5 Wide character time conversion functions . . . . . . . . . 436 - 7.28.6 Extended multibyte/wide character conversion utilities . . . . 437 - 7.28.6.1 Single-byte/wide character conversion functions . . . 438 - 7.28.6.2 Conversion state functions . . . . . . . . . . . 438 - 7.28.6.3 Restartable multibyte/wide character conversion - functions . . . . . . . . . . . . . . . . . . 439 - 7.28.6.4 Restartable multibyte/wide string conversion - functions . . . . . . . . . . . . . . . . . . 441 - 7.29 Wide character classification and mapping utilities . . . 444 - 7.29.1 Introduction . . . . . . . . . . . . . . . . . . . . . 444 - 7.29.2 Wide character classification utilities . . . . . . . . . . . 445 - 7.29.2.1 Wide character classification functions . . . . . . 445 - 7.29.2.2 Extensible wide character classification - functions . . . . . . . . . . . . . . . . . . 448 - 7.29.3 Wide character case mapping utilities . . . . . . . . . . . 450 - 7.29.3.1 Wide character case mapping functions . . . . . . 450 - 7.29.3.2 Extensible wide character case mapping - functions . . . . . . . . . . . . . . . . . . 450 - 7.30 Future library directions . . . . . . . . . . . . . . . . . . . 452 - 7.30.1 Complex arithmetic . . . . . . . . . . . 452 - 7.30.2 Character handling . . . . . . . . . . . . 452 - 7.30.3 Errors . . . . . . . . . . . . . . . . . 452 - 7.30.4 Format conversion of integer types . . . . 452 - 7.30.5 Localization . . . . . . . . . . . . . . 452 - 7.30.6 Signal handling . . . . . . . . . . . . . 452 - 7.30.7 Boolean type and values . . . . . . . . . 452 - 7.30.8 Integer types . . . . . . . . . . . . . . 452 - 7.30.9 Input/output . . . . . . . . . . . . . . . 453 - 7.30.10 General utilities . . . . . . . . . . . . . 453 - 7.30.11 String handling . . . . . . . . . . . . . 453 - -[page viii] - - 7.30.12 Extended multibyte and wide character utilities - . . . . . . . . . . . . . . . . . . . . 453 - 7.30.13 Wide character classification and mapping utilities - . . . . . . . . . . . . . . . . . . . . 453 -Annex A (informative) Language syntax summary . . . . . . . . . . . . 454 - A.1 Lexical grammar . . . . . . . . . . . . . . . . . . . . . . 454 - A.2 Phrase structure grammar . . . . . . . . . . . . . . . . . . . 461 - A.3 Preprocessing directives . . . . . . . . . . . . . . . . . . . 469 -Annex B (informative) Library summary . . . . . . . . . . . . . . . . 471 - B.1 Diagnostics . . . . . . . . . . . . . . . . . . 471 - B.2 Complex . . . . . . . . . . . . . . . . . . . 471 - B.3 Character handling . . . . . . . . . . . . . . . . 473 - B.4 Errors . . . . . . . . . . . . . . . . . . . . . 473 - B.5 Floating-point environment . . . . . . . . . . . . . 473 - B.6 Characteristics of floating types . . . . . . . . . . . 474 - B.7 Format conversion of integer types . . . . . . . . 474 - B.8 Alternative spellings . . . . . . . . . . . . . . . 475 - B.9 Sizes of integer types . . . . . . . . . . . . . . 475 - B.10 Localization . . . . . . . . . . . . . . . . . . 475 - B.11 Mathematics . . . . . . . . . . . . . . . . . . . 475 - B.12 Nonlocal jumps . . . . . . . . . . . . . . . . 480 - B.13 Signal handling . . . . . . . . . . . . . . . . . 480 - B.14 Alignment . . . . . . . . . . . . . . . . . 481 - B.15 Variable arguments . . . . . . . . . . . . . . . 481 - B.16 Atomics . . . . . . . . . . . . . . . . . . 481 - B.17 Boolean type and values . . . . . . . . . . . . 483 - B.18 Common definitions . . . . . . . . . . . . . . . 483 - B.19 Integer types . . . . . . . . . . . . . . . . . . 483 - B.20 Input/output . . . . . . . . . . . . . . . . . . 484 - B.21 General utilities . . . . . . . . . . . . . . . . 487 - B.22 String handling . . . . . . . . . . . . . . . . . 489 - B.23 Type-generic math . . . . . . . . . . . . . . . 491 - B.24 Threads . . . . . . . . . . . . . . . . . . . 491 - B.25 Date and time . . . . . . . . . . . . . . . . . . 492 - B.26 Unicode utilities . . . . . . . . . . . . . . . . . 493 - B.27 Extended multibyte/wide character utilities . . . . . . 493 - B.28 Wide character classification and mapping utilities . . . 498 -Annex C (informative) Sequence points . . . . . . . . . . . . . . . . . 499 -Annex D (normative) Universal character names for identifiers . . . . . . . 500 - D.1 Ranges of characters allowed . . . . . . . . . . . . . . . . . 500 - D.2 Ranges of characters disallowed initially . . . . . . . . . . . . . 500 -Annex E (informative) Implementation limits . . . . . . . . . . . . . . 501 - -[page ix] - -Annex F (normative) IEC 60559 floating-point arithmetic . . . . . . . . . . 503 - F.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 503 - F.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 503 - F.3 Operators and functions . . . . . . . . . . . . . . . . . . . 504 - F.4 Floating to integer conversion . . . . . . . . . . . . . . . . . 506 - F.5 Binary-decimal conversion . . . . . . . . . . . . . . . . . . 506 - F.6 The return statement . . . . . . . . . . . . . . . . . . . . 507 - F.7 Contracted expressions . . . . . . . . . . . . . . . . . . . . 507 - F.8 Floating-point environment . . . . . . . . . . . . . . . . . . 507 - F.9 Optimization . . . . . . . . . . . . . . . . . . . . . . . . 510 - F.10 Mathematics . . . . . . . . . . . . . . . . . . . 513 - F.10.1 Trigonometric functions . . . . . . . . . . . . . . . . 514 - F.10.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 516 - F.10.3 Exponential and logarithmic functions . . . . . . . . . . 516 - F.10.4 Power and absolute value functions . . . . . . . . . . . 520 - F.10.5 Error and gamma functions . . . . . . . . . . . . . . . 521 - F.10.6 Nearest integer functions . . . . . . . . . . . . . . . . 522 - F.10.7 Remainder functions . . . . . . . . . . . . . . . . . 524 - F.10.8 Manipulation functions . . . . . . . . . . . . . . . . 525 - F.10.9 Maximum, minimum, and positive difference functions . . . 526 - F.10.10 Floating multiply-add . . . . . . . . . . . . . . . . . 526 - F.10.11 Comparison macros . . . . . . . . . . . . . . . . . . 527 -Annex G (normative) IEC 60559-compatible complex arithmetic . . . . . . . 528 - G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.4 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 529 - G.4.1 Imaginary types . . . . . . . . . . . . . . . . . . . 529 - G.4.2 Real and imaginary . . . . . . . . . . . . . . . . . . 529 - G.4.3 Imaginary and complex . . . . . . . . . . . . . . . . 529 - G.5 Binary operators . . . . . . . . . . . . . . . . . . . . . . 529 - G.5.1 Multiplicative operators . . . . . . . . . . . . . . . . 530 - G.5.2 Additive operators . . . . . . . . . . . . . . . . . . 533 - G.6 Complex arithmetic . . . . . . . . . . . . . . 533 - G.6.1 Trigonometric functions . . . . . . . . . . . . . . . . 535 - G.6.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 535 - G.6.3 Exponential and logarithmic functions . . . . . . . . . . 539 - G.6.4 Power and absolute-value functions . . . . . . . . . . . 540 - G.7 Type-generic math . . . . . . . . . . . . . . . 541 -Annex H (informative) Language independent arithmetic . . . . . . . . . . 542 - H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 542 - H.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 - H.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 546 - -[page x] - -Annex I (informative) Common warnings . . . . . . . . . . . . . . . . 548 -Annex J (informative) Portability issues . . . . . . . . . . . . . . . . . 550 - J.1 Unspecified behavior . . . . . . . . . . . . . . . . . . . . . 550 - J.2 Undefined behavior . . . . . . . . . . . . . . . . . . . . . 553 - J.3 Implementation-defined behavior . . . . . . . . . . . . . . . . 566 - J.4 Locale-specific behavior . . . . . . . . . . . . . . . . . . . 574 - J.5 Common extensions . . . . . . . . . . . . . . . . . . . . . 575 -Annex K (normative) Bounds-checking interfaces . . . . . . . . . . . . . 578 - K.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 578 - K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 - K.3 Library . . . . . . . . . . . . . . . . . . . . . . . . . . 579 - K.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 579 - K.3.1.1 Standard headers . . . . . . . . . . . . . . . 579 - K.3.1.2 Reserved identifiers . . . . . . . . . . . . . . 580 - K.3.1.3 Use of errno . . . . . . . . . . . . . . . . . 580 - K.3.1.4 Runtime-constraint violations . . . . . . . . . . 580 - K.3.2 Errors . . . . . . . . . . . . . . . . . 581 - K.3.3 Common definitions . . . . . . . . . . . 581 - K.3.4 Integer types . . . . . . . . . . . . . . 581 - K.3.5 Input/output . . . . . . . . . . . . . . . 582 - K.3.5.1 Operations on files . . . . . . . . . . . . . . 582 - K.3.5.2 File access functions . . . . . . . . . . . . . . 584 - K.3.5.3 Formatted input/output functions . . . . . . . . . 587 - K.3.5.4 Character input/output functions . . . . . . . . . 598 - K.3.6 General utilities . . . . . . . . . . . . . 600 - K.3.6.1 Runtime-constraint handling . . . . . . . . . . 600 - K.3.6.2 Communication with the environment . . . . . . . 602 - K.3.6.3 Searching and sorting utilities . . . . . . . . . . 603 - K.3.6.4 Multibyte/wide character conversion functions . . . 606 - K.3.6.5 Multibyte/wide string conversion functions . . . . . 607 - K.3.7 String handling . . . . . . . . . . . . . 610 - K.3.7.1 Copying functions . . . . . . . . . . . . . . 610 - K.3.7.2 Concatenation functions . . . . . . . . . . . . 613 - K.3.7.3 Search functions . . . . . . . . . . . . . . . 616 - K.3.7.4 Miscellaneous functions . . . . . . . . . . . . 617 - K.3.8 Date and time . . . . . . . . . . . . . . . 620 - K.3.8.1 Components of time . . . . . . . . . . . . . . 620 - K.3.8.2 Time conversion functions . . . . . . . . . . . 620 - K.3.9 Extended multibyte and wide character utilities - . . . . . . . . . . . . . . . . . . . . 623 - K.3.9.1 Formatted wide character input/output functions . . . 624 - K.3.9.2 General wide string utilities . . . . . . . . . . . 635 - -[page xi] - - K.3.9.3 Extended multibyte/wide character conversion - utilities . . . . . . . . . . . . . . . . . . . 643 -Annex L (normative) Analyzability . . . . . . . . . . . . . . . . . . 648 - L.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 648 - L.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 648 - L.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 649 -Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 -Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653 - -[page xii] - - Foreword -1 ISO (the International Organization for Standardization) and IEC (the International - Electrotechnical Commission) form the specialized system for worldwide - standardization. National bodies that are member of ISO or IEC participate in the - development of International Standards through technical committees established by the - respective organization to deal with particular fields of technical activity. ISO and IEC - technical committees collaborate in fields of mutual interest. Other international - organizations, governmental and non-governmental, in liaison with ISO and IEC, also - take part in the work. -2 International Standards are drafted in accordance with the rules given in the ISO/IEC - Directives, Part 2. This International Standard was drafted in accordance with the fifth - edition (2004). -3 In the field of information technology, ISO and IEC have established a joint technical - committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical - committee are circulated to national bodies for voting. Publication as an International - Standard requires approval by at least 75% of the national bodies casting a vote. -4 Attention is drawn to the possibility that some of the elements of this document may be - the subject of patent rights. ISO and IEC shall not be held responsible for identifying any - or all such patent rights. -5 This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1, - Information technology, Subcommittee SC 22, Programming languages, their - environments and system software interfaces. The Working Group responsible for this - standard (WG 14) maintains a site on the World Wide Web at http://www.open- - std.org/JTC1/SC22/WG14/ containing additional information relevant to this - standard such as a Rationale for many of the decisions made during its preparation and a - log of Defect Reports and Responses. -6 This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as - corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and - ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include: - -- conditional (optional) features (including some that were previously mandatory) - -- support for multiple threads of execution including an improved memory sequencing - model, atomic objects, and thread-local storage ( and - ) - -- additional floating-point characteristic macros () - -- querying and specifying alignment of objects (, ) - -- Unicode characters and strings () (originally specified in - ISO/IEC TR 19769:2004) - -- type-generic expressions - -[page xiii] - - -- static assertions - -- anonymous structures and unions - -- no-return functions - -- macros to create complex numbers () - -- support for opening files for exclusive access - -- removed the gets function () - -- added the aligned_alloc, at_quick_exit, and quick_exit functions - () - -- (conditional) support for bounds-checking interfaces (originally specified in - ISO/IEC TR 24731-1:2007) - -- (conditional) support for analyzability -7 Major changes in the second edition included: - -- restricted character set support via digraphs and (originally specified - in AMD1) - -- wide character library support in and (originally - specified in AMD1) - -- more precise aliasing rules via effective type - -- restricted pointers - -- variable length arrays - -- flexible array members - -- static and type qualifiers in parameter array declarators - -- complex (and imaginary) support in - -- type-generic math macros in - -- the long long int type and library functions - -- increased minimum translation limits - -- additional floating-point characteristics in - -- remove implicit int - -- reliable integer division - -- universal character names (\u and \U) - -- extended identifiers - -- hexadecimal floating-point constants and %a and %A printf/scanf conversion - specifiers - -[page xiv] - --- compound literals --- designated initializers --- // comments --- extended integer types and library functions in and --- remove implicit function declaration --- preprocessor arithmetic done in intmax_t/uintmax_t --- mixed declarations and code --- new block scopes for selection and iteration statements --- integer constant type rules --- integer promotion rules --- macros with a variable number of arguments --- the vscanf family of functions in and --- additional math library functions in --- treatment of error conditions by math library functions (math_errhandling) --- floating-point environment access in --- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support --- trailing comma allowed in enum declaration --- %lf conversion specifier allowed in printf --- inline functions --- the snprintf family of functions in --- boolean type in --- idempotent type qualifiers --- empty macro arguments --- new structure type compatibility rules (tag compatibility) --- additional predefined macro names --- _Pragma preprocessing operator --- standard pragmas --- __func__ predefined identifier --- va_copy macro --- additional strftime conversion specifiers --- LIA compatibility annex - -[page xv] - - -- deprecate ungetc at the beginning of a binary file - -- remove deprecation of aliased array parameters - -- conversion of array to pointer not limited to lvalues - -- relaxed constraints on aggregate and union initialization - -- relaxed restrictions on portable header names - -- return without expression not permitted in function that returns a value (and vice - versa) -8 Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, * - I, J, the bibliography, and the index are for information only. In accordance with Part 2 of - the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples - are also for information only. - -[page xvi] - - Introduction -1 With the introduction of new devices and extended character sets, new features may be - added to this International Standard. Subclauses in the language and library clauses warn - implementors and programmers of usages which, though valid in themselves, may - conflict with future additions. -2 Certain features are obsolescent, which means that they may be considered for - withdrawal in future revisions of this International Standard. They are retained because - of their widespread use, but their use in new implementations (for implementation - features) or new programs (for language [6.11] or library features [7.30]) is discouraged. -3 This International Standard is divided into four major subdivisions: - -- preliminary elements (clauses 1-4); - -- the characteristics of environments that translate and execute C programs (clause 5); - -- the language syntax, constraints, and semantics (clause 6); - -- the library facilities (clause 7). -4 Examples are provided to illustrate possible forms of the constructions described. - Footnotes are provided to emphasize consequences of the rules described in that - subclause or elsewhere in this International Standard. References are used to refer to - other related subclauses. Recommendations are provided to give advice or guidance to - implementors. Annexes provide additional information and summarize the information - contained in this International Standard. A bibliography lists documents that were - referred to during the preparation of the standard. -5 The language clause (clause 6) is derived from ''The C Reference Manual''. -6 The library clause (clause 7) is based on the 1984 /usr/group Standard. - -[page xvii] - - -[page xviii] - - - - Programming languages -- C - - - - 1. Scope -1 This International Standard specifies the form and establishes the interpretation of - programs written in the C programming language.1) It specifies - -- the representation of C programs; - -- the syntax and constraints of the C language; - -- the semantic rules for interpreting C programs; - -- the representation of input data to be processed by C programs; - -- the representation of output data produced by C programs; - -- the restrictions and limits imposed by a conforming implementation of C. -2 This International Standard does not specify - -- the mechanism by which C programs are transformed for use by a data-processing - system; - -- the mechanism by which C programs are invoked for use by a data-processing - system; - -- the mechanism by which input data are transformed for use by a C program; - -- the mechanism by which output data are transformed after being produced by a C - program; - -- the size or complexity of a program and its data that will exceed the capacity of any - specific data-processing system or the capacity of a particular processor; - -- all minimal requirements of a data-processing system that is capable of supporting a - conforming implementation. - - - 1) This International Standard is designed to promote the portability of C programs among a variety of - data-processing systems. It is intended for use by implementors and programmers. - -[page 1] - - - 2. Normative references -1 The following referenced documents are indispensable for the application of this - document. For dated references, only the edition cited applies. For undated references, - the latest edition of the referenced document (including any amendments) applies. -2 ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for - use in the physical sciences and technology. -3 ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information - interchange. -4 ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental - terms. -5 ISO 4217, Codes for the representation of currencies and funds. -6 ISO 8601, Data elements and interchange formats -- Information interchange -- - Representation of dates and times. -7 ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded - Character Set (UCS). -8 IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously - designated IEC 559:1989). - -[page 2] - - - 3. Terms, definitions, and symbols -1 For the purposes of this International Standard, the following definitions apply. Other - terms are defined where they appear in italic type or on the left side of a syntax rule. - Terms explicitly defined in this International Standard are not to be presumed to refer - implicitly to similar terms defined elsewhere. Terms not defined in this International - Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not - defined in this International Standard are to be interpreted according to ISO 31-11. - 3.1 -1 access - to read or modify the value of an object -2 NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used. - -3 NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value. - -4 NOTE 3 Expressions that are not evaluated do not access objects. - - 3.2 -1 alignment - requirement that objects of a particular type be located on storage boundaries with - addresses that are particular multiples of a byte address - 3.3 -1 argument - actual argument - actual parameter (deprecated) - expression in the comma-separated list bounded by the parentheses in a function call - expression, or a sequence of preprocessing tokens in the comma-separated list bounded - by the parentheses in a function-like macro invocation - 3.4 -1 behavior - external appearance or action - 3.4.1 -1 implementation-defined behavior - unspecified behavior where each implementation documents how the choice is made -2 EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit - when a signed integer is shifted right. - - 3.4.2 -1 locale-specific behavior - behavior that depends on local conventions of nationality, culture, and language that each - implementation documents - -[page 3] - -2 EXAMPLE An example of locale-specific behavior is whether the islower function returns true for - characters other than the 26 lowercase Latin letters. - - 3.4.3 -1 undefined behavior - behavior, upon use of a nonportable or erroneous program construct or of erroneous data, - for which this International Standard imposes no requirements -2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable - results, to behaving during translation or program execution in a documented manner characteristic of the - environment (with or without the issuance of a diagnostic message), to terminating a translation or - execution (with the issuance of a diagnostic message). - -3 EXAMPLE An example of undefined behavior is the behavior on integer overflow. - - 3.4.4 -1 unspecified behavior - use of an unspecified value, or other behavior where this International Standard provides - two or more possibilities and imposes no further requirements on which is chosen in any - instance -2 EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are - evaluated. - - 3.5 -1 bit - unit of data storage in the execution environment large enough to hold an object that may - have one of two values -2 NOTE It need not be possible to express the address of each individual bit of an object. - - 3.6 -1 byte - addressable unit of data storage large enough to hold any member of the basic character - set of the execution environment -2 NOTE 1 It is possible to express the address of each individual byte of an object uniquely. - -3 NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation- - defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order - bit. - - 3.7 -1 character - member of a set of elements used for the organization, control, or - representation of data - 3.7.1 -1 character - single-byte character - bit representation that fits in a byte - -[page 4] - - 3.7.2 -1 multibyte character - sequence of one or more bytes representing a member of the extended character set of - either the source or the execution environment -2 NOTE The extended character set is a superset of the basic character set. - - 3.7.3 -1 wide character - bit representation that fits in an object of type wchar_t, capable of representing any - character in the current locale - 3.8 -1 constraint - restriction, either syntactic or semantic, by which the exposition of language elements is - to be interpreted - 3.9 -1 correctly rounded result - representation in the result format that is nearest in value, subject to the current rounding - mode, to what the result would be given unlimited range and precision - 3.10 -1 diagnostic message - message belonging to an implementation-defined subset of the implementation's message - output - 3.11 -1 forward reference - reference to a later subclause of this International Standard that contains additional - information relevant to this subclause - 3.12 -1 implementation - particular set of software, running in a particular translation environment under particular - control options, that performs translation of programs for, and supports execution of - functions in, a particular execution environment - 3.13 -1 implementation limit - restriction imposed upon programs by the implementation - 3.14 -1 memory location - either an object of scalar type, or a maximal sequence of adjacent bit-fields all having - nonzero width - -[page 5] - -2 NOTE 1 Two threads of execution can update and access separate memory locations without interfering - with each other. - -3 NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same - applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the - two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member - declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all - members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those - intervening bit-fields happen to be. - -4 EXAMPLE A structure declared as - struct { - char a; - int b:5, c:11, :0, d:8; - struct { int ee:8; } e; - } - contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate - memory locations, and can be modified concurrently without interfering with each other. The bit-fields b - and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently - modified, but b and a, for example, can be. - - 3.15 -1 object - region of data storage in the execution environment, the contents of which can represent - values -2 NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1. - - 3.16 -1 parameter - formal parameter - formal argument (deprecated) - object declared as part of a function declaration or definition that acquires a value on - entry to the function, or an identifier from the comma-separated list bounded by the - parentheses immediately following the macro name in a function-like macro definition - 3.17 -1 recommended practice - specification that is strongly recommended as being in keeping with the intent of the - standard, but that may be impractical for some implementations - 3.18 -1 runtime-constraint - requirement on a program when calling a library function -2 NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and - need not be diagnosed at translation time. - -3 NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime- - constraints for a library function are not violated by the program; see K.3.1.4. - -[page 6] - - 3.19 -1 value - precise meaning of the contents of an object when interpreted as having a specific type - 3.19.1 -1 implementation-defined value - unspecified value where each implementation documents how the choice is made - 3.19.2 -1 indeterminate value - either an unspecified value or a trap representation - 3.19.3 -1 unspecified value - valid value of the relevant type where this International Standard imposes no - requirements on which value is chosen in any instance -2 NOTE An unspecified value cannot be a trap representation. - - 3.19.4 -1 trap representation - an object representation that need not represent a value of the object type - 3.19.5 -1 perform a trap - interrupt execution of the program such that no further operations are performed -2 NOTE In this International Standard, when the word ''trap'' is not immediately followed by - ''representation'', this is the intended usage.2) - - 3.20 -1 [^ x^] - ceiling of x: the least integer greater than or equal to x -2 EXAMPLE [^2.4^] is 3, [^-2.4^] is -2. - - 3.21 -1 [_ x_] - floor of x: the greatest integer less than or equal to x -2 EXAMPLE [_2.4_] is 2, [_-2.4_] is -3. - - - - - 2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap - representation might perform a trap but is not required to (see 6.2.6.1). - -[page 7] - - - 4. Conformance -1 In this International Standard, ''shall'' is to be interpreted as a requirement on an - implementation or on a program; conversely, ''shall not'' is to be interpreted as a - prohibition. -2 If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime- - constraint is violated, the behavior is undefined. Undefined behavior is otherwise - indicated in this International Standard by the words ''undefined behavior'' or by the - omission of any explicit definition of behavior. There is no difference in emphasis among - these three; they all describe ''behavior that is undefined''. -3 A program that is correct in all other aspects, operating on correct data, containing - unspecified behavior shall be a correct program and act in accordance with 5.1.2.3. -4 The implementation shall not successfully translate a preprocessing translation unit - containing a #error preprocessing directive unless it is part of a group skipped by - conditional inclusion. -5 A strictly conforming program shall use only those features of the language and library - specified in this International Standard.3) It shall not produce output dependent on any - unspecified, undefined, or implementation-defined behavior, and shall not exceed any - minimum implementation limit. -6 The two forms of conforming implementation are hosted and freestanding. A conforming - hosted implementation shall accept any strictly conforming program. A conforming - freestanding implementation shall accept any strictly conforming program that does not - use complex types and in which the use of the features specified in the library clause - (clause 7) is confined to the contents of the standard headers , - , , , , , - , and . A conforming implementation may have extensions - (including additional library functions), provided they do not alter the behavior of any - strictly conforming program.4) - - - - 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded - by an appropriate conditional inclusion preprocessing directive using the related macro. For example: - #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */ - /* ... */ - fesetround(FE_UPWARD); - /* ... */ - #endif - - 4) This implies that a conforming implementation reserves no identifiers other than those explicitly - reserved in this International Standard. - -[page 8] - -7 A conforming program is one that is acceptable to a conforming implementation.5) -8 An implementation shall be accompanied by a document that defines all implementation- - defined and locale-specific characteristics and all extensions. - Forward references: conditional inclusion (6.10.1), error directive (6.10.5), - characteristics of floating types (7.7), alternative spellings - (7.9), sizes of integer types (7.10), alignment (7.15), - variable arguments (7.16), boolean type and values - (7.18), common definitions (7.19), integer types (7.20). - - - - - 5) Strictly conforming programs are intended to be maximally portable among conforming - implementations. Conforming programs may depend upon nonportable features of a conforming - implementation. - -[page 9] - - - 5. Environment -1 An implementation translates C source files and executes C programs in two data- - processing-system environments, which will be called the translation environment and - the execution environment in this International Standard. Their characteristics define and - constrain the results of executing conforming C programs constructed according to the - syntactic and semantic rules for conforming implementations. - Forward references: In this clause, only a few of many possible forward references - have been noted. - 5.1 Conceptual models - 5.1.1 Translation environment - 5.1.1.1 Program structure -1 A C program need not all be translated at the same time. The text of the program is kept - in units called source files, (or preprocessing files) in this International Standard. A - source file together with all the headers and source files included via the preprocessing - directive #include is known as a preprocessing translation unit. After preprocessing, a - preprocessing translation unit is called a translation unit. Previously translated translation - units may be preserved individually or in libraries. The separate translation units of a - program communicate by (for example) calls to functions whose identifiers have external - linkage, manipulation of objects whose identifiers have external linkage, or manipulation - of data files. Translation units may be separately translated and then later linked to - produce an executable program. - Forward references: linkages of identifiers (6.2.2), external definitions (6.9), - preprocessing directives (6.10). - 5.1.1.2 Translation phases -1 The precedence among the syntax rules of translation is specified by the following - phases.6) - 1. Physical source file multibyte characters are mapped, in an implementation- - defined manner, to the source character set (introducing new-line characters for - end-of-line indicators) if necessary. Trigraph sequences are replaced by - corresponding single-character internal representations. - - - - 6) Implementations shall behave as if these separate phases occur, even though many are typically folded - together in practice. Source files, translation units, and translated translation units need not - necessarily be stored as files, nor need there be any one-to-one correspondence between these entities - and any external representation. The description is conceptual only, and does not specify any - particular implementation. - -[page 10] - - 2. Each instance of a backslash character (\) immediately followed by a new-line - character is deleted, splicing physical source lines to form logical source lines. - Only the last backslash on any physical source line shall be eligible for being part - of such a splice. A source file that is not empty shall end in a new-line character, - which shall not be immediately preceded by a backslash character before any such - splicing takes place. - 3. The source file is decomposed into preprocessing tokens7) and sequences of - white-space characters (including comments). A source file shall not end in a - partial preprocessing token or in a partial comment. Each comment is replaced by - one space character. New-line characters are retained. Whether each nonempty - sequence of white-space characters other than new-line is retained or replaced by - one space character is implementation-defined. - 4. Preprocessing directives are executed, macro invocations are expanded, and - _Pragma unary operator expressions are executed. If a character sequence that - matches the syntax of a universal character name is produced by token - concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing - directive causes the named header or source file to be processed from phase 1 - through phase 4, recursively. All preprocessing directives are then deleted. - 5. Each source character set member and escape sequence in character constants and - string literals is converted to the corresponding member of the execution character - set; if there is no corresponding member, it is converted to an implementation- - defined member other than the null (wide) character.8) - 6. Adjacent string literal tokens are concatenated. - 7. White-space characters separating tokens are no longer significant. Each - preprocessing token is converted into a token. The resulting tokens are - syntactically and semantically analyzed and translated as a translation unit. - 8. All external object and function references are resolved. Library components are - linked to satisfy external references to functions and objects not defined in the - current translation. All such translator output is collected into a program image - which contains information needed for execution in its execution environment. -Forward references: universal character names (6.4.3), lexical elements (6.4), -preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9). - - - -7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is - context-dependent. For example, see the handling of < within a #include preprocessing directive. -8) An implementation need not convert all non-corresponding source characters to the same execution - character. - -[page 11] - - 5.1.1.3 Diagnostics -1 A conforming implementation shall produce at least one diagnostic message (identified in - an implementation-defined manner) if a preprocessing translation unit or translation unit - contains a violation of any syntax rule or constraint, even if the behavior is also explicitly - specified as undefined or implementation-defined. Diagnostic messages need not be - produced in other circumstances.9) -2 EXAMPLE An implementation shall issue a diagnostic for the translation unit: - char i; - int i; - because in those cases where wording in this International Standard describes the behavior for a construct - as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed. - - 5.1.2 Execution environments -1 Two execution environments are defined: freestanding and hosted. In both cases, - program startup occurs when a designated C function is called by the execution - environment. All objects with static storage duration shall be initialized (set to their - initial values) before program startup. The manner and timing of such initialization are - otherwise unspecified. Program termination returns control to the execution - environment. - Forward references: storage durations of objects (6.2.4), initialization (6.7.9). - 5.1.2.1 Freestanding environment -1 In a freestanding environment (in which C program execution may take place without any - benefit of an operating system), the name and type of the function called at program - startup are implementation-defined. Any library facilities available to a freestanding - program, other than the minimal set required by clause 4, are implementation-defined. -2 The effect of program termination in a freestanding environment is implementation- - defined. - 5.1.2.2 Hosted environment -1 A hosted environment need not be provided, but shall conform to the following - specifications if present. - - - - - 9) The intent is that an implementation should identify the nature of, and where possible localize, each - violation. Of course, an implementation is free to produce any number of diagnostics as long as a - valid program is still correctly translated. It may also successfully translate an invalid program. - -[page 12] - - 5.1.2.2.1 Program startup -1 The function called at program startup is named main. The implementation declares no - prototype for this function. It shall be defined with a return type of int and with no - parameters: - int main(void) { /* ... */ } - or with two parameters (referred to here as argc and argv, though any names may be - used, as they are local to the function in which they are declared): - int main(int argc, char *argv[]) { /* ... */ } - or equivalent;10) or in some other implementation-defined manner. -2 If they are declared, the parameters to the main function shall obey the following - constraints: - -- The value of argc shall be nonnegative. - -- argv[argc] shall be a null pointer. - -- If the value of argc is greater than zero, the array members argv[0] through - argv[argc-1] inclusive shall contain pointers to strings, which are given - implementation-defined values by the host environment prior to program startup. The - intent is to supply to the program information determined prior to program startup - from elsewhere in the hosted environment. If the host environment is not capable of - supplying strings with letters in both uppercase and lowercase, the implementation - shall ensure that the strings are received in lowercase. - -- If the value of argc is greater than zero, the string pointed to by argv[0] - represents the program name; argv[0][0] shall be the null character if the - program name is not available from the host environment. If the value of argc is - greater than one, the strings pointed to by argv[1] through argv[argc-1] - represent the program parameters. - -- The parameters argc and argv and the strings pointed to by the argv array shall - be modifiable by the program, and retain their last-stored values between program - startup and program termination. - 5.1.2.2.2 Program execution -1 In a hosted environment, a program may use all the functions, macros, type definitions, - and objects described in the library clause (clause 7). - - - - - 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as - char ** argv, and so on. - -[page 13] - - 5.1.2.2.3 Program termination -1 If the return type of the main function is a type compatible with int, a return from the - initial call to the main function is equivalent to calling the exit function with the value - returned by the main function as its argument;11) reaching the } that terminates the - main function returns a value of 0. If the return type is not compatible with int, the - termination status returned to the host environment is unspecified. - Forward references: definition of terms (7.1.1), the exit function (7.22.4.4). - 5.1.2.3 Program execution -1 The semantic descriptions in this International Standard describe the behavior of an - abstract machine in which issues of optimization are irrelevant. -2 Accessing a volatile object, modifying an object, modifying a file, or calling a function - that does any of those operations are all side effects,12) which are changes in the state of - the execution environment. Evaluation of an expression in general includes both value - computations and initiation of side effects. Value computation for an lvalue expression - includes determining the identity of the designated object. -3 Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations - executed by a single thread, which induces a partial order among those evaluations. - Given any two evaluations A and B, if A is sequenced before B, then the execution of A - shall precede the execution of B. (Conversely, if A is sequenced before B, then B is - sequenced after A.) If A is not sequenced before or after B, then A and B are - unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced - either before or after B, but it is unspecified which.13) The presence of a sequence point - between the evaluation of expressions A and B implies that every value computation and - side effect associated with A is sequenced before every value computation and side effect - associated with B. (A summary of the sequence points is given in annex C.) -4 In the abstract machine, all expressions are evaluated as specified by the semantics. An - actual implementation need not evaluate part of an expression if it can deduce that its - value is not used and that no needed side effects are produced (including any caused by - - 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main - will have ended in the former case, even where they would not have in the latter. - 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status - flags and control modes. Floating-point operations implicitly set the status flags; modes affect result - values of floating-point operations. Implementations that support such floating-point state are - required to regard changes to it as side effects -- see annex F for details. The floating-point - environment library provides a programming facility for indicating when these side - effects matter, freeing the implementations in other cases. - 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations - cannot interleave, but can be executed in any order. - -[page 14] - - calling a function or accessing a volatile object). -5 When the processing of the abstract machine is interrupted by receipt of a signal, the - values of objects that are neither lock-free atomic objects nor of type volatile - sig_atomic_t are unspecified, and the value of any object that is modified by the - handler that is neither a lock-free atomic object nor of type volatile - sig_atomic_t becomes undefined. -6 The least requirements on a conforming implementation are: - -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract - machine. - -- At program termination, all data written into files shall be identical to the result that - execution of the program according to the abstract semantics would have produced. - -- The input and output dynamics of interactive devices shall take place as specified in - 7.21.3. The intent of these requirements is that unbuffered or line-buffered output - appear as soon as possible, to ensure that prompting messages actually appear prior to - a program waiting for input. - This is the observable behavior of the program. -7 What constitutes an interactive device is implementation-defined. -8 More stringent correspondences between abstract and actual semantics may be defined by - each implementation. -9 EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual - semantics: at every sequence point, the values of the actual objects would agree with those specified by the - abstract semantics. The keyword volatile would then be redundant. -10 Alternatively, an implementation might perform various optimizations within each translation unit, such - that the actual semantics would agree with the abstract semantics only when making function calls across - translation unit boundaries. In such an implementation, at the time of each function entry and function - return where the calling function and the called function are in different translation units, the values of all - externally linked objects and of all objects accessible via pointers therein would agree with the abstract - semantics. Furthermore, at the time of each such function entry the values of the parameters of the called - function and of all objects accessible via pointers therein would agree with the abstract semantics. In this - type of implementation, objects referred to by interrupt service routines activated by the signal function - would require explicit specification of volatile storage, as well as other implementation-defined - restrictions. - -11 EXAMPLE 2 In executing the fragment - char c1, c2; - /* ... */ - c1 = c1 + c2; - the ''integer promotions'' require that the abstract machine promote the value of each variable to int size - and then add the two ints and truncate the sum. Provided the addition of two chars can be done without - overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only - produce the same result, possibly omitting the promotions. - -[page 15] - -12 EXAMPLE 3 Similarly, in the fragment - float f1, f2; - double d; - /* ... */ - f1 = f2 * d; - the multiplication may be executed using single-precision arithmetic if the implementation can ascertain - that the result would be the same as if it were executed using double-precision arithmetic (for example, if d - were replaced by the constant 2.0, which has type double). - -13 EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate - semantics. Values are independent of whether they are represented in a register or in memory. For - example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load - is required to round to the precision of the storage type. In particular, casts and assignments are required to - perform their specified conversion. For the fragment - double d1, d2; - float f; - d1 = f = expression; - d2 = (float) expression; - the values assigned to d1 and d2 are required to have been converted to float. - -14 EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in - precision as well as range. The implementation cannot generally apply the mathematical associative rules - for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of - overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to - rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real - numbers are often not valid (see F.9). - double x, y, z; - /* ... */ - x = (x * y) * z; // not equivalent to x *= y * z; - z = (x - y) + y ; // not equivalent to z = x; - z = x + x * y; // not equivalent to z = x * (1.0 + y); - y = x / 5.0; // not equivalent to y = x * 0.2; - -15 EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment - int a, b; - /* ... */ - a = a + 32760 + b + 5; - the expression statement behaves exactly the same as - a = (((a + 32760) + b) + 5); - due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is - next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in - which overflows produce an explicit trap and in which the range of values representable by an int is - [-32768, +32767], the implementation cannot rewrite this expression as - a = ((a + b) + 32765); - since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap - while the original expression would not; nor can the expression be rewritten either as - -[page 16] - - a = ((a + 32765) + b); - or - a = (a + (b + 32765)); - since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine - in which overflow silently generates some value and where positive and negative overflows cancel, the - above expression statement can be rewritten by the implementation in any of the above ways because the - same result will occur. - -16 EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the - following fragment - #include - int sum; - char *p; - /* ... */ - sum = sum * 10 - '0' + (*p++ = getchar()); - the expression statement is grouped as if it were written as - sum = (((sum * 10) - '0') + ((*(p++)) = (getchar()))); - but the actual increment of p can occur at any time between the previous sequence point and the next - sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned - value. - - Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the - signal function (7.14), files (7.21.3). - 5.1.2.4 Multi-threaded executions and data races -1 Under a hosted implementation, a program can have more than one thread of execution - (or thread) running concurrently. The execution of each thread proceeds as defined by - the remainder of this standard. The execution of the entire program consists of an - execution of all of its threads.14) Under a freestanding implementation, it is - implementation-defined whether a program can have more than one thread of execution. -2 The value of an object visible to a thread T at a particular point is the initial value of the - object, a value stored in the object by T , or a value stored in the object by another thread, - according to the rules below. -3 NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by - the desire to support atomic operations with explicit and detailed visibility constraints. However, it also - implicitly supports a simpler view for more restricted programs. - -4 Two expression evaluations conflict if one of them modifies a memory location and the - other one reads or modifies the same memory location. - - - - - 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of - atomic operations, for example, allow executions inconsistent with a simple interleaving as described - below. - -[page 17] - -5 The library defines a number of atomic operations (7.17) and operations on mutexes - (7.25.4) that are specially identified as synchronization operations. These operations play - a special role in making assignments in one thread visible to another. A synchronization - operation on one or more memory locations is either an acquire operation, a release - operation, both an acquire and release operation, or a consume operation. A - synchronization operation without an associated memory location is a fence and can be - either an acquire fence, a release fence, or both an acquire and release fence. In addition, - there are relaxed atomic operations, which are not synchronization operations, and - atomic read-modify-write operations, which have special characteristics. -6 NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations - composing the mutex. Correspondingly, a call that releases the same mutex will perform a release - operation on those same locations. Informally, performing a release operation on A forces prior side effects - on other memory locations to become visible to other threads that later perform an acquire or consume - operation on A. We do not include relaxed atomic operations as synchronization operations although, like - synchronization operations, they cannot contribute to data races. - -7 All modifications to a particular atomic object M occur in some particular total order, - called the modification order of M. If A and B are modifications of an atomic object M, - and A happens before B, then A shall precede B in the modification order of M, which is - defined below. -8 NOTE 3 This states that the modification orders must respect the ''happens before'' relation. - -9 NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be - combined into a single total order for all objects. In general this will be impossible since different threads - may observe modifications to different variables in inconsistent orders. - -10 A release sequence on an atomic object M is a maximal contiguous sub-sequence of side - effects in the modification order of M, where the first operation is a release and every - subsequent operation either is performed by the same thread that performed the release or - is an atomic read-modify-write operation. -11 Certain library calls synchronize with other library calls performed by another thread. In - particular, an atomic operation A that performs a release operation on an object M - synchronizes with an atomic operation B that performs an acquire operation on M and - reads a value written by any side effect in the release sequence headed by A. -12 NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as - described below. Such a requirement would sometimes interfere with efficient implementation. - -13 NOTE 6 The specifications of the synchronization operations define when one reads the value written by - another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total - order. Each mutex acquisition ''reads the value written'' by the last mutex release. - -14 An evaluation A carries a dependency 15) to an evaluation B if: - - - 15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly - strictly intra-thread. - -[page 18] - - -- the value of A is used as an operand of B, unless: - o B is an invocation of the kill_dependency macro, - - o A is the left operand of a && or || operator, - - o A is the left operand of a ? : operator, or - - o A is the left operand of a , operator; - or - -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A - is sequenced before B, or - -- for some evaluation X, A carries a dependency to X and X carries a dependency to B. -15 An evaluation A is dependency-ordered before16) an evaluation B if: - -- A performs a release operation on an atomic object M, and B performs a consume - operation on M and reads a value written by any side effect in the release sequence - headed by A, or - -- for some evaluation X, A is dependency-ordered before X and X carries a - dependency to B. -16 An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A - is dependency-ordered before B, or, for some evaluation X: - -- A synchronizes with X and X is sequenced before B, - -- A is sequenced before X and X inter-thread happens before B, or - -- A inter-thread happens before X and X inter-thread happens before B. -17 NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced - before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The - first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed - by ''sequenced before''. The reason for this limitation is that a consume operation participating in a - ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this - consume operation actually carries a dependency. The reason that this limitation applies only to the end of - such a concatenation is that any subsequent release operation will provide the required ordering for a prior - consume operation. The second exception is that a concatenation is not permitted to consist entirely of - ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be - transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships - consisting entirely of ''sequenced before''. - -18 An evaluation A happens before an evaluation B if A is sequenced before B or A inter- - thread happens before B. - - - - 16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses - release/consume in place of release/acquire. - -[page 19] - -19 A visible side effect A on an object M with respect to a value computation B of M - satisfies the conditions: - -- A happens before B, and - -- there is no other side effect X to M such that A happens before X and X happens - before B. - The value of a non-atomic scalar object M, as determined by evaluation B, shall be the - value stored by the visible side effect A. -20 NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data - race and the behavior is undefined. - -21 NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually - detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable - restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent) - execution. - -22 The visible sequence of side effects on an atomic object M, with respect to a value - computation B of M, is a maximal contiguous sub-sequence of side effects in the - modification order of M, where the first side effect is visible with respect to B, and for - every subsequent side effect, it is not the case that B happens before it. The value of an - atomic object M, as determined by evaluation B, shall be the value stored by some - operation in the visible sequence of M with respect to B. Furthermore, if a value - computation A of an atomic object M happens before a value computation B of M, and - the value computed by A corresponds to the value stored by side effect X, then the value - computed by B shall either equal the value computed by A, or be the value stored by side - effect Y , where Y follows X in the modification order of M. -23 NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if - both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee - provided by most hardware available to C atomic operations. - -24 NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the - values observed by loads of atomics, which we are restricting here. The intended reading is that there must - exist an association of atomic loads with modifications they observe that, together with suitably chosen - modification orders and the ''happens before'' relation derived as described above, satisfy the resulting - constraints as imposed here. - -25 The execution of a program contains a data race if it contains two conflicting actions in - different threads, at least one of which is not atomic, and neither happens before the - other. Any such data race results in undefined behavior. -26 NOTE 12 It can be shown that programs that correctly use simple mutexes and - memory_order_seq_cst operations to prevent all data races, and use no other synchronization - operations, behave as though the operations executed by their constituent threads were simply interleaved, - with each value computation of an object being the last value stored in that interleaving. This is normally - referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data- - race-free programs cannot observe most program transformations that do not change single-threaded - program semantics. In fact, most single-threaded program transformations continue to be allowed, since - any program that behaves differently as a result must contain undefined behavior. - -[page 20] - -27 NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location - that would not be modified by the abstract machine are generally precluded by this standard, since such an - assignment might overwrite another assignment by a different thread in cases in which an abstract machine - execution would not have encountered a data race. This includes implementations of data member - assignment that overwrite adjacent members in separate memory locations. We also generally preclude - reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the - "visible sequence" rules. - -28 NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may - not preserve the semantics of the program as defined in this standard, since they potentially introduce a data - race. However, they are typically valid in the context of an optimizing compiler that targets a specific - machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that - is not tolerant of races or provides hardware race detection. - -[page 21] - - 5.2 Environmental considerations - 5.2.1 Character sets -1 Two sets of characters and their associated collating sequences shall be defined: the set in - which source files are written (the source character set), and the set interpreted in the - execution environment (the execution character set). Each set is further divided into a - basic character set, whose contents are given by this subclause, and a set of zero or more - locale-specific members (which are not members of the basic character set) called - extended characters. The combined set is also called the extended character set. The - values of the members of the execution character set are implementation-defined. -2 In a character constant or string literal, members of the execution character set shall be - represented by corresponding members of the source character set or by escape - sequences consisting of the backslash \ followed by one or more characters. A byte with - all bits set to 0, called the null character, shall exist in the basic execution character set; it - is used to terminate a character string. -3 Both the basic source and basic execution character sets shall have the following - members: the 26 uppercase letters of the Latin alphabet - A B C D E F G H I J K L M - N O P Q R S T U V W X Y Z - the 26 lowercase letters of the Latin alphabet - a b c d e f g h i j k l m - n o p q r s t u v w x y z - the 10 decimal digits - 0 1 2 3 4 5 6 7 8 9 - the following 29 graphic characters - ! " # % & ' ( ) * + , - . / : - ; < = > ? [ \ ] ^ _ { | } ~ - the space character, and control characters representing horizontal tab, vertical tab, and - form feed. The representation of each member of the source and execution basic - character sets shall fit in a byte. In both the source and execution basic character sets, the - value of each character after 0 in the above list of decimal digits shall be one greater than - the value of the previous. In source files, there shall be some way of indicating the end of - each line of text; this International Standard treats such an end-of-line indicator as if it - were a single new-line character. In the basic execution character set, there shall be - control characters representing alert, backspace, carriage return, and new line. If any - other characters are encountered in a source file (except in an identifier, a character - constant, a string literal, a header name, a comment, or a preprocessing token that is never - -[page 22] - - converted to a token), the behavior is undefined. -4 A letter is an uppercase letter or a lowercase letter as defined above; in this International - Standard the term does not include other characters that are letters in other alphabets. -5 The universal character name construct provides a way to name other characters. - Forward references: universal character names (6.4.3), character constants (6.4.4.4), - preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1). - 5.2.1.1 Trigraph sequences -1 Before any other processing takes place, each occurrence of one of the following - sequences of three characters (called trigraph sequences17)) is replaced with the - corresponding single character. - ??= # ??) ] ??! | - ??( [ ??' ^ ??> } - ??/ \ ??< { ??- ~ - No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed - above is not changed. -2 EXAMPLE 1 - ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??) - becomes - #define arraycheck(a, b) a[b] || b[a] - -3 EXAMPLE 2 The following source line - printf("Eh???/n"); - becomes (after replacement of the trigraph sequence ??/) - printf("Eh?\n"); - - 5.2.1.2 Multibyte characters -1 The source character set may contain multibyte characters, used to represent members of - the extended character set. The execution character set may also contain multibyte - characters, which need not have the same encoding as for the source character set. For - both character sets, the following shall hold: - -- The basic character set shall be present and each character shall be encoded as a - single byte. - -- The presence, meaning, and representation of any additional members is locale- - specific. - - 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as - described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set. - -[page 23] - - -- A multibyte character set may have a state-dependent encoding, wherein each - sequence of multibyte characters begins in an initial shift state and enters other - locale-specific shift states when specific multibyte characters are encountered in the - sequence. While in the initial shift state, all single-byte characters retain their usual - interpretation and do not alter the shift state. The interpretation for subsequent bytes - in the sequence is a function of the current shift state. - -- A byte with all bits zero shall be interpreted as a null character independent of shift - state. Such a byte shall not occur as part of any other multibyte character. -2 For source files, the following shall hold: - -- An identifier, comment, string literal, character constant, or header name shall begin - and end in the initial shift state. - -- An identifier, comment, string literal, character constant, or header name shall consist - of a sequence of valid multibyte characters. - 5.2.2 Character display semantics -1 The active position is that location on a display device where the next character output by - the fputc function would appear. The intent of writing a printing character (as defined - by the isprint function) to a display device is to display a graphic representation of - that character at the active position and then advance the active position to the next - position on the current line. The direction of writing is locale-specific. If the active - position is at the final position of a line (if there is one), the behavior of the display device - is unspecified. -2 Alphabetic escape sequences representing nongraphic characters in the execution - character set are intended to produce actions on display devices as follows: - \a (alert) Produces an audible or visible alert without changing the active position. - \b (backspace) Moves the active position to the previous position on the current line. If - the active position is at the initial position of a line, the behavior of the display - device is unspecified. - \f ( form feed) Moves the active position to the initial position at the start of the next - logical page. - \n (new line) Moves the active position to the initial position of the next line. - \r (carriage return) Moves the active position to the initial position of the current line. - \t (horizontal tab) Moves the active position to the next horizontal tabulation position - on the current line. If the active position is at or past the last defined horizontal - tabulation position, the behavior of the display device is unspecified. - \v (vertical tab) Moves the active position to the initial position of the next vertical - tabulation position. If the active position is at or past the last defined vertical - -[page 24] - - tabulation position, the behavior of the display device is unspecified. -3 Each of these escape sequences shall produce a unique implementation-defined value - which can be stored in a single char object. The external representations in a text file - need not be identical to the internal representations, and are outside the scope of this - International Standard. - Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3). - 5.2.3 Signals and interrupts -1 Functions shall be implemented such that they may be interrupted at any time by a signal, - or may be called by a signal handler, or both, with no alteration to earlier, but still active, - invocations' control flow (after the interruption), function return values, or objects with - automatic storage duration. All such objects shall be maintained outside the function - image (the instructions that compose the executable representation of a function) on a - per-invocation basis. - 5.2.4 Environmental limits -1 Both the translation and execution environments constrain the implementation of - language translators and libraries. The following summarizes the language-related - environmental limits on a conforming implementation; the library-related limits are - discussed in clause 7. - 5.2.4.1 Translation limits -1 The implementation shall be able to translate and execute at least one program that - contains at least one instance of every one of the following limits:18) - -- 127 nesting levels of blocks - -- 63 nesting levels of conditional inclusion - -- 12 pointer, array, and function declarators (in any combinations) modifying an - arithmetic, structure, union, or void type in a declaration - -- 63 nesting levels of parenthesized declarators within a full declarator - -- 63 nesting levels of parenthesized expressions within a full expression - -- 63 significant initial characters in an internal identifier or a macro name (each - universal character name or extended source character is considered a single - character) - -- 31 significant initial characters in an external identifier (each universal character name - specifying a short identifier of 0000FFFF or less is considered 6 characters, each - - - 18) Implementations should avoid imposing fixed translation limits whenever possible. - -[page 25] - - universal character name specifying a short identifier of 00010000 or more is - considered 10 characters, and each extended source character is considered the same - number of characters as the corresponding universal character name, if any)19) - -- 4095 external identifiers in one translation unit - -- 511 identifiers with block scope declared in one block - -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit - -- 127 parameters in one function definition - -- 127 arguments in one function call - -- 127 parameters in one macro definition - -- 127 arguments in one macro invocation - -- 4095 characters in a logical source line - -- 4095 characters in a string literal (after concatenation) - -- 65535 bytes in an object (in a hosted environment only) - -- 15 nesting levels for #included files - -- 1023 case labels for a switch statement (excluding those for any nested switch - statements) - -- 1023 members in a single structure or union - -- 1023 enumeration constants in a single enumeration - -- 63 levels of nested structure or union definitions in a single struct-declaration-list - 5.2.4.2 Numerical limits -1 An implementation is required to document all the limits specified in this subclause, - which are specified in the headers and . Additional limits are - specified in . - Forward references: integer types (7.20). - 5.2.4.2.1 Sizes of integer types -1 The values given below shall be replaced by constant expressions suitable for use in #if - preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the - following shall be replaced by expressions that have the same type as would an - expression that is an object of the corresponding type converted according to the integer - promotions. Their implementation-defined values shall be equal or greater in magnitude - - - 19) See ''future language directions'' (6.11.3). - -[page 26] - -(absolute value) to those shown, with the same sign. --- number of bits for smallest object that is not a bit-field (byte) - CHAR_BIT 8 --- minimum value for an object of type signed char - SCHAR_MIN -127 // -(27 - 1) --- maximum value for an object of type signed char - SCHAR_MAX +127 // 27 - 1 --- maximum value for an object of type unsigned char - UCHAR_MAX 255 // 28 - 1 --- minimum value for an object of type char - CHAR_MIN see below --- maximum value for an object of type char - CHAR_MAX see below --- maximum number of bytes in a multibyte character, for any supported locale - MB_LEN_MAX 1 --- minimum value for an object of type short int - SHRT_MIN -32767 // -(215 - 1) --- maximum value for an object of type short int - SHRT_MAX +32767 // 215 - 1 --- maximum value for an object of type unsigned short int - USHRT_MAX 65535 // 216 - 1 --- minimum value for an object of type int - INT_MIN -32767 // -(215 - 1) --- maximum value for an object of type int - INT_MAX +32767 // 215 - 1 --- maximum value for an object of type unsigned int - UINT_MAX 65535 // 216 - 1 --- minimum value for an object of type long int - LONG_MIN -2147483647 // -(231 - 1) --- maximum value for an object of type long int - LONG_MAX +2147483647 // 231 - 1 --- maximum value for an object of type unsigned long int - ULONG_MAX 4294967295 // 232 - 1 - -[page 27] - - -- minimum value for an object of type long long int - LLONG_MIN -9223372036854775807 // -(263 - 1) - -- maximum value for an object of type long long int - LLONG_MAX +9223372036854775807 // 263 - 1 - -- maximum value for an object of type unsigned long long int - ULLONG_MAX 18446744073709551615 // 264 - 1 -2 If the value of an object of type char is treated as a signed integer when used in an - expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the - value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of - CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of - UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1. - Forward references: representations of types (6.2.6), conditional inclusion (6.10.1). - 5.2.4.2.2 Characteristics of floating types -1 The characteristics of floating types are defined in terms of a model that describes a - representation of floating-point numbers and values that provide information about an - implementation's floating-point arithmetic.21) The following parameters are used to - define the model for each floating-point type: - s sign ((+-)1) - b base or radix of exponent representation (an integer > 1) - e exponent (an integer between a minimum emin and a maximum emax ) - p precision (the number of base-b digits in the significand) - fk nonnegative integers less than b (the significand digits) -2 A floating-point number (x) is defined by the following model: - p - x = sb e (Sum) f k b-k , - k=1 - emin <= e <= emax - -3 In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be - able to contain other kinds of floating-point numbers, such as subnormal floating-point - numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0, - e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and - NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates - through almost every arithmetic operation without raising a floating-point exception; a - signaling NaN generally raises a floating-point exception when occurring as an - - - 20) See 6.2.5. - 21) The floating-point model is intended to clarify the description of each floating-point characteristic and - does not require the floating-point arithmetic of the implementation to be identical. - -[page 28] - - arithmetic operand.22) -4 An implementation may give zero and values that are not floating-point numbers (such as - infinities and NaNs) a sign or may leave them unsigned. Wherever such values are - unsigned, any requirement in this International Standard to retrieve the sign shall produce - an unspecified sign, and any requirement to set the sign shall be ignored. -5 The minimum range of representable values for a floating type is the most negative finite - floating-point number representable in that type through the most positive finite floating- - point number representable in that type. In addition, if negative infinity is representable - in a type, the range of that type is extended to all negative real numbers; likewise, if - positive infinity is representable in a type, the range of that type is extended to all positive - real numbers. -6 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in - and that return floating-point results is implementation- - defined, as is the accuracy of the conversion between floating-point internal - representations and string representations performed by the library functions in - , , and . The implementation may state that the - accuracy is unknown. -7 All integer values in the header, except FLT_ROUNDS, shall be constant - expressions suitable for use in #if preprocessing directives; all floating values shall be - constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, - and FLT_ROUNDS have separate names for all three floating-point types. The floating- - point model representation is provided for all values except FLT_EVAL_METHOD and - FLT_ROUNDS. -8 The rounding mode for floating-point addition is characterized by the implementation- - defined value of FLT_ROUNDS:23) - -1 indeterminable - 0 toward zero - 1 to nearest - 2 toward positive infinity - 3 toward negative infinity - All other values for FLT_ROUNDS characterize implementation-defined rounding - behavior. - - - 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support - IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with - similar behavior. - 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through - the function fesetround in . - -[page 29] - -9 Except for assignment and cast (which remove all extra range and precision), the values - yielded by operators with floating operands and values subject to the usual arithmetic - conversions and of floating constants are evaluated to a format whose range and precision - may be greater than required by the type. The use of evaluation formats is characterized - by the implementation-defined value of FLT_EVAL_METHOD:24) - -1 indeterminable; - 0 evaluate all operations and constants just to the range and precision of the - type; - 1 evaluate operations and constants of type float and double to the - range and precision of the double type, evaluate long double - operations and constants to the range and precision of the long double - type; - 2 evaluate all operations and constants to the range and precision of the - long double type. - All other negative values for FLT_EVAL_METHOD characterize implementation-defined - behavior. -10 The presence or absence of subnormal numbers is characterized by the implementation- - defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and - LDBL_HAS_SUBNORM: - -1 indeterminable25) - 0 absent26) (type does not support subnormal numbers) - 1 present (type does support subnormal numbers) -11 The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater or equal in magnitude (absolute value) to - those shown, with the same sign: - -- radix of exponent representation, b - FLT_RADIX 2 - - - - - 24) The evaluation method determines evaluation formats of expressions involving all floating types, not - just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float - _Complex operands is represented in the double _Complex format, and its parts are evaluated to - double. - 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret - subnormal representations as zero, nor as nonzero. - 26) Characterization as absent is intended if no floating-point operations produce subnormal results from - non-subnormal inputs, even if the type format includes representations of subnormal numbers. - -[page 30] - --- number of base-FLT_RADIX digits in the floating-point significand, p - FLT_MANT_DIG - DBL_MANT_DIG - LDBL_MANT_DIG --- number of decimal digits, n, such that any floating-point number with p radix b digits - can be rounded to a floating-point number with n decimal digits and back again - without change to the value, - { p log10 b if b is a power of 10 - { - { [^1 + p log10 b^] otherwise - FLT_DECIMAL_DIG 6 - DBL_DECIMAL_DIG 10 - LDBL_DECIMAL_DIG 10 --- number of decimal digits, n, such that any floating-point number in the widest - supported floating type with pmax radix b digits can be rounded to a floating-point - number with n decimal digits and back again without change to the value, - { pmax log10 b if b is a power of 10 - { - { [^1 + pmax log10 b^] otherwise - DECIMAL_DIG 10 --- number of decimal digits, q, such that any floating-point number with q decimal digits - can be rounded into a floating-point number with p radix b digits and back again - without change to the q decimal digits, - { p log10 b if b is a power of 10 - { - { [_( p - 1) log10 b_] otherwise - FLT_DIG 6 - DBL_DIG 10 - LDBL_DIG 10 --- minimum negative integer such that FLT_RADIX raised to one less than that power is - a normalized floating-point number, emin - FLT_MIN_EXP - DBL_MIN_EXP - LDBL_MIN_EXP - -[page 31] - - -- minimum negative integer such that 10 raised to that power is in the range of - normalized floating-point numbers, [^log10 b emin -1 ^] - [ ] - FLT_MIN_10_EXP -37 - DBL_MIN_10_EXP -37 - LDBL_MIN_10_EXP -37 - -- maximum integer such that FLT_RADIX raised to one less than that power is a - representable finite floating-point number, emax - FLT_MAX_EXP - DBL_MAX_EXP - LDBL_MAX_EXP - -- maximum integer such that 10 raised to that power is in the range of representable - finite floating-point numbers, [_log10 ((1 - b- p )b emax )_] - FLT_MAX_10_EXP +37 - DBL_MAX_10_EXP +37 - LDBL_MAX_10_EXP +37 -12 The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater than or equal to those shown: - -- maximum representable finite floating-point number, (1 - b- p )b emax - FLT_MAX 1E+37 - DBL_MAX 1E+37 - LDBL_MAX 1E+37 -13 The values given in the following list shall be replaced by constant expressions with - implementation-defined (positive) values that are less than or equal to those shown: - -- the difference between 1 and the least value greater than 1 that is representable in the - given floating point type, b1- p - FLT_EPSILON 1E-5 - DBL_EPSILON 1E-9 - LDBL_EPSILON 1E-9 - -- minimum normalized positive floating-point number, b emin -1 - FLT_MIN 1E-37 - DBL_MIN 1E-37 - LDBL_MIN 1E-37 - -[page 32] - - -- minimum positive floating-point number27) - FLT_TRUE_MIN 1E-37 - DBL_TRUE_MIN 1E-37 - LDBL_TRUE_MIN 1E-37 - Recommended practice -14 Conversion from (at least) double to decimal with DECIMAL_DIG digits and back - should be the identity function. -15 EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum - requirements of this International Standard, and the appropriate values in a header for type - float: - 6 - x = s16e (Sum) f k 16-k , - k=1 - -31 <= e <= +32 - - FLT_RADIX 16 - FLT_MANT_DIG 6 - FLT_EPSILON 9.53674316E-07F - FLT_DECIMAL_DIG 9 - FLT_DIG 6 - FLT_MIN_EXP -31 - FLT_MIN 2.93873588E-39F - FLT_MIN_10_EXP -38 - FLT_MAX_EXP +32 - FLT_MAX 3.40282347E+38F - FLT_MAX_10_EXP +38 - -16 EXAMPLE 2 The following describes floating-point representations that also meet the requirements for - single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a - header for types float and double: - 24 - x f = s2e (Sum) f k 2-k , - k=1 - -125 <= e <= +128 - - 53 - x d = s2e (Sum) f k 2-k , - k=1 - -1021 <= e <= +1024 - - FLT_RADIX 2 - DECIMAL_DIG 17 - FLT_MANT_DIG 24 - FLT_EPSILON 1.19209290E-07F // decimal constant - FLT_EPSILON 0X1P-23F // hex constant - FLT_DECIMAL_DIG 9 - - - 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a - positive number no greater than the minimum normalized positive number for the type. - 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent - limits are one less than shown here. - -[page 33] - - FLT_DIG 6 - FLT_MIN_EXP -125 - FLT_MIN 1.17549435E-38F // decimal constant - FLT_MIN 0X1P-126F // hex constant - FLT_TRUE_MIN 1.40129846E-45F // decimal constant - FLT_TRUE_MIN 0X1P-149F // hex constant - FLT_HAS_SUBNORM 1 - FLT_MIN_10_EXP -37 - FLT_MAX_EXP +128 - FLT_MAX 3.40282347E+38F // decimal constant - FLT_MAX 0X1.fffffeP127F // hex constant - FLT_MAX_10_EXP +38 - DBL_MANT_DIG 53 - DBL_EPSILON 2.2204460492503131E-16 // decimal constant - DBL_EPSILON 0X1P-52 // hex constant - DBL_DECIMAL_DIG 17 - DBL_DIG 15 - DBL_MIN_EXP -1021 - DBL_MIN 2.2250738585072014E-308 // decimal constant - DBL_MIN 0X1P-1022 // hex constant - DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant - DBL_TRUE_MIN 0X1P-1074 // hex constant - DBL_HAS_SUBNORM 1 - DBL_MIN_10_EXP -307 - DBL_MAX_EXP +1024 - DBL_MAX 1.7976931348623157E+308 // decimal constant - DBL_MAX 0X1.fffffffffffffP1023 // hex constant - DBL_MAX_10_EXP +308 -If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For -example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of -precision), then DECIMAL_DIG would be 21. - -Forward references: conditional inclusion (6.10.1), complex arithmetic - (7.3), extended multibyte and wide character utilities -(7.28), floating-point environment (7.6), general utilities -(7.22), input/output (7.21), mathematics (7.12). - -[page 34] - - - 6. Language - 6.1 Notation -1 In the syntax notation used in this clause, syntactic categories (nonterminals) are - indicated by italic type, and literal words and character set members (terminals) by bold - type. A colon (:) following a nonterminal introduces its definition. Alternative - definitions are listed on separate lines, except when prefaced by the words ''one of''. An - optional symbol is indicated by the subscript ''opt'', so that - { expressionopt } - indicates an optional expression enclosed in braces. -2 When syntactic categories are referred to in the main text, they are not italicized and - words are separated by spaces instead of hyphens. -3 A summary of the language syntax is given in annex A. - 6.2 Concepts - 6.2.1 Scopes of identifiers -1 An identifier can denote an object; a function; a tag or a member of a structure, union, or - enumeration; a typedef name; a label name; a macro name; or a macro parameter. The - same identifier can denote different entities at different points in the program. A member - of an enumeration is called an enumeration constant. Macro names and macro - parameters are not considered further here, because prior to the semantic phase of - program translation any occurrences of macro names in the source file are replaced by the - preprocessing token sequences that constitute their macro definitions. -2 For each different entity that an identifier designates, the identifier is visible (i.e., can be - used) only within a region of program text called its scope. Different entities designated - by the same identifier either have different scopes, or are in different name spaces. There - are four kinds of scopes: function, file, block, and function prototype. (A function - prototype is a declaration of a function that declares the types of its parameters.) -3 A label name is the only kind of identifier that has function scope. It can be used (in a - goto statement) anywhere in the function in which it appears, and is declared implicitly - by its syntactic appearance (followed by a : and a statement). -4 Every other identifier has scope determined by the placement of its declaration (in a - declarator or type specifier). If the declarator or type specifier that declares the identifier - appears outside of any block or list of parameters, the identifier has file scope, which - terminates at the end of the translation unit. If the declarator or type specifier that - declares the identifier appears inside a block or within the list of parameter declarations in - a function definition, the identifier has block scope, which terminates at the end of the - associated block. If the declarator or type specifier that declares the identifier appears - -[page 35] - - within the list of parameter declarations in a function prototype (not part of a function - definition), the identifier has function prototype scope, which terminates at the end of the - function declarator. If an identifier designates two different entities in the same name - space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end - strictly before the scope of the other entity (the outer scope). Within the inner scope, the - identifier designates the entity declared in the inner scope; the entity declared in the outer - scope is hidden (and not visible) within the inner scope. -5 Unless explicitly stated otherwise, where this International Standard uses the term - ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the - entity in the relevant name space whose declaration is visible at the point the identifier - occurs. -6 Two identifiers have the same scope if and only if their scopes terminate at the same - point. -7 Structure, union, and enumeration tags have scope that begins just after the appearance of - the tag in a type specifier that declares the tag. Each enumeration constant has scope that - begins just after the appearance of its defining enumerator in an enumerator list. Any - other identifier has scope that begins just after the completion of its declarator. -8 As a special case, a type name (which is not a declaration of an identifier) is considered to - have a scope that begins just after the place within the type name where the omitted - identifier would appear were it not omitted. - Forward references: declarations (6.7), function calls (6.5.2.2), function definitions - (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3), - source file inclusion (6.10.2), statements (6.8). - 6.2.2 Linkages of identifiers -1 An identifier declared in different scopes or in the same scope more than once can be - made to refer to the same object or function by a process called linkage.29) There are - three kinds of linkage: external, internal, and none. -2 In the set of translation units and libraries that constitutes an entire program, each - declaration of a particular identifier with external linkage denotes the same object or - function. Within one translation unit, each declaration of an identifier with internal - linkage denotes the same object or function. Each declaration of an identifier with no - linkage denotes a unique entity. -3 If the declaration of a file scope identifier for an object or a function contains the storage- - class specifier static, the identifier has internal linkage.30) - - - - 29) There is no linkage between different identifiers. - -[page 36] - -4 For an identifier declared with the storage-class specifier extern in a scope in which a - prior declaration of that identifier is visible,31) if the prior declaration specifies internal or - external linkage, the linkage of the identifier at the later declaration is the same as the - linkage specified at the prior declaration. If no prior declaration is visible, or if the prior - declaration specifies no linkage, then the identifier has external linkage. -5 If the declaration of an identifier for a function has no storage-class specifier, its linkage - is determined exactly as if it were declared with the storage-class specifier extern. If - the declaration of an identifier for an object has file scope and no storage-class specifier, - its linkage is external. -6 The following identifiers have no linkage: an identifier declared to be anything other than - an object or a function; an identifier declared to be a function parameter; a block scope - identifier for an object declared without the storage-class specifier extern. -7 If, within a translation unit, the same identifier appears with both internal and external - linkage, the behavior is undefined. - Forward references: declarations (6.7), expressions (6.5), external definitions (6.9), - statements (6.8). - 6.2.3 Name spaces of identifiers -1 If more than one declaration of a particular identifier is visible at any point in a - translation unit, the syntactic context disambiguates uses that refer to different entities. - Thus, there are separate name spaces for various categories of identifiers, as follows: - -- label names (disambiguated by the syntax of the label declaration and use); - -- the tags of structures, unions, and enumerations (disambiguated by following any32) - of the keywords struct, union, or enum); - -- the members of structures or unions; each structure or union has a separate name - space for its members (disambiguated by the type of the expression used to access the - member via the . or -> operator); - -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as - enumeration constants). - Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), - structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags - (6.7.2.3), the goto statement (6.8.6.1). - - 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see - 6.7.1. - 31) As specified in 6.2.1, the later declaration might hide the prior declaration. - 32) There is only one name space for tags even though three are possible. - -[page 37] - - 6.2.4 Storage durations of objects -1 An object has a storage duration that determines its lifetime. There are four storage - durations: static, thread, automatic, and allocated. Allocated storage is described in - 7.22.3. -2 The lifetime of an object is the portion of program execution during which storage is - guaranteed to be reserved for it. An object exists, has a constant address,33) and retains - its last-stored value throughout its lifetime.34) If an object is referred to outside of its - lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when - the object it points to (or just past) reaches the end of its lifetime. -3 An object whose identifier is declared without the storage-class specifier - _Thread_local, and either with external or internal linkage or with the storage-class - specifier static, has static storage duration. Its lifetime is the entire execution of the - program and its stored value is initialized only once, prior to program startup. -4 An object whose identifier is declared with the storage-class specifier _Thread_local - has thread storage duration. Its lifetime is the entire execution of the thread for which it - is created, and its stored value is initialized when the thread is started. There is a distinct - object per thread, and use of the declared name in an expression refers to the object - associated with the thread evaluating the expression. The result of attempting to - indirectly access an object with thread storage duration from a thread other than the one - with which the object is associated is implementation-defined. -5 An object whose identifier is declared with no linkage and without the storage-class - specifier static has automatic storage duration, as do some compound literals. The - result of attempting to indirectly access an object with automatic storage duration from a - thread other than the one with which the object is associated is implementation-defined. -6 For such an object that does not have a variable length array type, its lifetime extends - from entry into the block with which it is associated until execution of that block ends in - any way. (Entering an enclosed block or calling a function suspends, but does not end, - execution of the current block.) If the block is entered recursively, a new instance of the - object is created each time. The initial value of the object is indeterminate. If an - initialization is specified for the object, it is performed each time the declaration or - compound literal is reached in the execution of the block; otherwise, the value becomes - indeterminate each time the declaration is reached. - - - - 33) The term ''constant address'' means that two pointers to the object constructed at possibly different - times will compare equal. The address may be different during two different executions of the same - program. - 34) In the case of a volatile object, the last store need not be explicit in the program. - -[page 38] - -7 For such an object that does have a variable length array type, its lifetime extends from - the declaration of the object until execution of the program leaves the scope of the - declaration.35) If the scope is entered recursively, a new instance of the object is created - each time. The initial value of the object is indeterminate. -8 A non-lvalue expression with structure or union type, where the structure or union - contains a member with array type (including, recursively, members of all contained - structures and unions) refers to an object with automatic storage duration and temporary - lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the - value of the expression. Its lifetime ends when the evaluation of the containing full - expression or full declarator ends. Any attempt to modify an object with temporary - lifetime results in undefined behavior. - Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators - (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8). - 6.2.5 Types -1 The meaning of a value stored in an object or returned by a function is determined by the - type of the expression used to access it. (An identifier declared to be an object is the - simplest such expression; the type is specified in the declaration of the identifier.) Types - are partitioned into object types (types that describe objects) and function types (types - that describe functions). At various points within a translation unit an object type may be - incomplete (lacking sufficient information to determine the size of objects of that type) or - complete (having sufficient information).37) -2 An object declared as type _Bool is large enough to store the values 0 and 1. -3 An object declared as type char is large enough to store any member of the basic - execution character set. If a member of the basic execution character set is stored in a - char object, its value is guaranteed to be nonnegative. If any other character is stored in - a char object, the resulting value is implementation-defined but shall be within the range - of values that can be represented in that type. -4 There are five standard signed integer types, designated as signed char, short - int, int, long int, and long long int. (These and other types may be - designated in several additional ways, as described in 6.7.2.) There may also be - implementation-defined extended signed integer types.38) The standard and extended - signed integer types are collectively called signed integer types.39) - - 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an - embedded block prior to the declaration, leaves the scope of the declaration. - 36) The address of such an object is taken implicitly when an array member is accessed. - 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at - different points within a translation unit. - -[page 39] - -5 An object declared as type signed char occupies the same amount of storage as a - ''plain'' char object. A ''plain'' int object has the natural size suggested by the - architecture of the execution environment (large enough to contain any value in the range - INT_MIN to INT_MAX as defined in the header ). -6 For each of the signed integer types, there is a corresponding (but different) unsigned - integer type (designated with the keyword unsigned) that uses the same amount of - storage (including sign information) and has the same alignment requirements. The type - _Bool and the unsigned integer types that correspond to the standard signed integer - types are the standard unsigned integer types. The unsigned integer types that - correspond to the extended signed integer types are the extended unsigned integer types. - The standard and extended unsigned integer types are collectively called unsigned integer - types.40) -7 The standard signed integer types and standard unsigned integer types are collectively - called the standard integer types, the extended signed integer types and extended - unsigned integer types are collectively called the extended integer types. -8 For any two integer types with the same signedness and different integer conversion rank - (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a - subrange of the values of the other type. -9 The range of nonnegative values of a signed integer type is a subrange of the - corresponding unsigned integer type, and the representation of the same value in each - type is the same.41) A computation involving unsigned operands can never overflow, - because a result that cannot be represented by the resulting unsigned integer type is - reduced modulo the number that is one greater than the largest value that can be - represented by the resulting type. -10 There are three real floating types, designated as float, double, and long - double.42) The set of values of the type float is a subset of the set of values of the - type double; the set of values of the type double is a subset of the set of values of the - type long double. - - - 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - 39) Therefore, any statement in this Standard about signed integer types also applies to the extended - signed integer types. - 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended - unsigned integer types. - 41) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - 42) See ''future language directions'' (6.11.1). - -[page 40] - -11 There are three complex types, designated as float _Complex, double - _Complex, and long double _Complex.43) (Complex types are a conditional - feature that implementations need not support; see 6.10.8.3.) The real floating and - complex types are collectively called the floating types. -12 For each floating type there is a corresponding real type, which is always a real floating - type. For real floating types, it is the same type. For complex types, it is the type given - by deleting the keyword _Complex from the type name. -13 Each complex type has the same representation and alignment requirements as an array - type containing exactly two elements of the corresponding real type; the first element is - equal to the real part, and the second element to the imaginary part, of the complex - number. -14 The type char, the signed and unsigned integer types, and the floating types are - collectively called the basic types. The basic types are complete object types. Even if the - implementation defines two or more basic types to have the same representation, they are - nevertheless different types.44) -15 The three types char, signed char, and unsigned char are collectively called - the character types. The implementation shall define char to have the same range, - representation, and behavior as either signed char or unsigned char.45) -16 An enumeration comprises a set of named integer constant values. Each distinct - enumeration constitutes a different enumerated type. -17 The type char, the signed and unsigned integer types, and the enumerated types are - collectively called integer types. The integer and real floating types are collectively called - real types. -18 Integer and floating types are collectively called arithmetic types. Each arithmetic type - belongs to one type domain: the real type domain comprises the real types, the complex - type domain comprises the complex types. -19 The void type comprises an empty set of values; it is an incomplete object type that - cannot be completed. - - - - 43) A specification for imaginary types is in annex G. - 44) An implementation may define new keywords that provide alternative ways to designate a basic (or - any other) type; this does not violate the requirement that all basic types be different. - Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - 45) CHAR_MIN, defined in , will have one of the values 0 or SCHAR_MIN, and this can be - used to distinguish the two options. Irrespective of the choice made, char is a separate type from the - other two and is not compatible with either. - -[page 41] - -20 Any number of derived types can be constructed from the object and function types, as - follows: - -- An array type describes a contiguously allocated nonempty set of objects with a - particular member object type, called the element type. The element type shall be - complete whenever the array type is specified. Array types are characterized by their - element type and by the number of elements in the array. An array type is said to be - derived from its element type, and if its element type is T , the array type is sometimes - called ''array of T ''. The construction of an array type from an element type is called - ''array type derivation''. - -- A structure type describes a sequentially allocated nonempty set of member objects - (and, in certain circumstances, an incomplete array), each of which has an optionally - specified name and possibly distinct type. - -- A union type describes an overlapping nonempty set of member objects, each of - which has an optionally specified name and possibly distinct type. - -- A function type describes a function with specified return type. A function type is - characterized by its return type and the number and types of its parameters. A - function type is said to be derived from its return type, and if its return type is T , the - function type is sometimes called ''function returning T ''. The construction of a - function type from a return type is called ''function type derivation''. - -- A pointer type may be derived from a function type or an object type, called the - referenced type. A pointer type describes an object whose value provides a reference - to an entity of the referenced type. A pointer type derived from the referenced type T - is sometimes called ''pointer to T ''. The construction of a pointer type from a - referenced type is called ''pointer type derivation''. A pointer type is a complete - object type. - -- An atomic type describes the type designated by the construct _Atomic ( type- - name ). (Atomic types are a conditional feature that implementations need not - support; see 6.10.8.3.) - These methods of constructing derived types can be applied recursively. -21 Arithmetic types and pointer types are collectively called scalar types. Array and - structure types are collectively called aggregate types.46) -22 An array type of unknown size is an incomplete type. It is completed, for an identifier of - that type, by specifying the size in a later declaration (with internal or external linkage). - A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete - - - 46) Note that aggregate type does not include union type because an object with union type can only - contain one member at a time. - -[page 42] - - type. It is completed, for all declarations of that type, by declaring the same structure or - union tag with its defining content later in the same scope. -23 A type has known constant size if the type is not incomplete and is not a variable length - array type. -24 Array, function, and pointer types are collectively called derived declarator types. A - declarator type derivation from a type T is the construction of a derived declarator type - from T by the application of an array-type, a function-type, or a pointer-type derivation to - T. -25 A type is characterized by its type category, which is either the outermost derivation of a - derived type (as noted above in the construction of derived types), or the type itself if the - type consists of no derived types. -26 Any type so far mentioned is an unqualified type. Each unqualified type has several - qualified versions of its type,47) corresponding to the combinations of one, two, or all - three of the const, volatile, and restrict qualifiers. The qualified or unqualified - versions of a type are distinct types that belong to the same type category and have the - same representation and alignment requirements.48) A derived type is not qualified by the - qualifiers (if any) of the type from which it is derived. -27 Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier - designates an atomic type. The size, representation, and alignment of an atomic type - need not be the same as those of the corresponding unqualified type. Therefore, this - Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the - atomic version of a type is permitted along with the other qualified versions of a type. - The phrase ''qualified or unqualified type'', without specific mention of atomic, does not - include the atomic types. -28 A pointer to void shall have the same representation and alignment requirements as a - pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of - compatible types shall have the same representation and alignment requirements. All - pointers to structure types shall have the same representation and alignment requirements - as each other. All pointers to union types shall have the same representation and - alignment requirements as each other. Pointers to other types need not have the same - representation or alignment requirements. -29 EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is - pointer, not a floating type. The const-qualified version of this type is designated as ''float * const'' - whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const- - - - 47) See 6.7.3 regarding qualified array and function types. - 48) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - -[page 43] - - qualified float'' and is a pointer to a qualified type. - -30 EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to - function returning struct tag''. The array has length five and the function has a single parameter of type - float. Its type category is array. - - Forward references: compatible type and composite type (6.2.7), declarations (6.7). - 6.2.6 Representations of types - 6.2.6.1 General -1 The representations of all types are unspecified except as stated in this subclause. -2 Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, - the number, order, and encoding of which are either explicitly specified or - implementation-defined. -3 Values stored in unsigned bit-fields and objects of type unsigned char shall be - represented using a pure binary notation.49) -4 Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT - bits, where n is the size of an object of that type, in bytes. The value may be copied into - an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is - called the object representation of the value. Values stored in bit-fields consist of m bits, - where m is the size specified for the bit-field. The object representation is the set of m - bits the bit-field comprises in the addressable storage unit holding it. Two values (other - than NaNs) with the same object representation compare equal, but values that compare - equal may have different object representations. -5 Certain object representations need not represent a value of the object type. If the stored - value of an object has such a representation and is read by an lvalue expression that does - not have character type, the behavior is undefined. If such a representation is produced - by a side effect that modifies all or any part of the object by an lvalue expression that - does not have character type, the behavior is undefined.50) Such a representation is called - a trap representation. -6 When a value is stored in an object of structure or union type, including in a member - object, the bytes of the object representation that correspond to any padding bytes take - unspecified values.51) The value of a structure or union object is never a trap - - - 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values - represented by successive bits are additive, begin with 1, and are multiplied by successive integral - powers of 2, except perhaps the bit with the highest position. (Adapted from the American National - Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of - type unsigned char range from 0 to 2 - CHAR_BIT - - 1. - 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined - behavior, but the value of the variable cannot be used until a proper value is stored in it. - -[page 44] - - representation, even though the value of a member of the structure or union object may be - a trap representation. -7 When a value is stored in a member of an object of union type, the bytes of the object - representation that do not correspond to that member but do correspond to other members - take unspecified values. -8 Where an operator is applied to a value that has more than one object representation, - which object representation is used shall not affect the value of the result.52) Where a - value is stored in an object using a type that has more than one object representation for - that value, it is unspecified which representation is used, but a trap representation shall - not be generated. -9 Loads and stores of objects with atomic types are done with - memory_order_seq_cst semantics. - Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function - designators (6.3.2.1), order and consistency (7.17.3). - 6.2.6.2 Integer types -1 For unsigned integer types other than unsigned char, the bits of the object - representation shall be divided into two groups: value bits and padding bits (there need - not be any of the latter). If there are N value bits, each bit shall represent a different - power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of - representing values from 0 to 2 N - 1 using a pure binary representation; this shall be - known as the value representation. The values of any padding bits are unspecified.53) -2 For signed integer types, the bits of the object representation shall be divided into three - groups: value bits, padding bits, and the sign bit. There need not be any padding bits; - signed char shall not have any padding bits. There shall be exactly one sign bit. - Each bit that is a value bit shall have the same value as the same bit in the object - representation of the corresponding unsigned type (if there are M value bits in the signed - type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect - - 51) Thus, for example, structure assignment need not copy any padding bits. - 52) It is possible for objects x and y with the same effective type T to have the same value when they are - accessed as objects of type T, but to have different values in other contexts. In particular, if == is - defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0. - Furthermore, x == y does not necessarily imply that x and y have the same value; other operations - on values of type T may distinguish between them. - 53) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow, and this cannot occur - with unsigned types. All other combinations of padding bits are alternative object representations of - the value specified by the value bits. - -[page 45] - - the resulting value. If the sign bit is one, the value shall be modified in one of the - following ways: - -- the corresponding value with sign bit 0 is negated (sign and magnitude); - -- the sign bit has the value -(2 M ) (two's complement); - -- the sign bit has the value -(2 M - 1) (ones' complement). - Which of these applies is implementation-defined, as is whether the value with sign bit 1 - and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones' - complement), is a trap representation or a normal value. In the case of sign and - magnitude and ones' complement, if this representation is a normal value it is called a - negative zero. -3 If the implementation supports negative zeros, they shall be generated only by: - -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value; - -- the +, -, *, /, and % operators where one operand is a negative zero and the result is - zero; - -- compound assignment operators based on the above cases. - It is unspecified whether these cases actually generate a negative zero or a normal zero, - and whether a negative zero becomes a normal zero when stored in an object. -4 If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<, - and >> operators with operands that would produce such a value is undefined. -5 The values of any padding bits are unspecified.54) A valid (non-trap) object representation - of a signed integer type where the sign bit is zero is a valid object representation of the - corresponding unsigned type, and shall represent the same value. For any integer type, - the object representation where all the bits are zero shall be a representation of the value - zero in that type. -6 The precision of an integer type is the number of bits it uses to represent values, - excluding any sign and padding bits. The width of an integer type is the same but - including any sign bit; thus for unsigned integer types the two values are the same, while - for signed integer types the width is one greater than the precision. - - - - - 54) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow. All other - combinations of padding bits are alternative object representations of the value specified by the value - bits. - -[page 46] - - 6.2.7 Compatible type and composite type -1 Two types have compatible type if their types are the same. Additional rules for - determining whether two types are compatible are described in 6.7.2 for type specifiers, - in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure, - union, or enumerated types declared in separate translation units are compatible if their - tags and members satisfy the following requirements: If one is declared with a tag, the - other shall be declared with the same tag. If both are completed anywhere within their - respective translation units, then the following additional requirements apply: there shall - be a one-to-one correspondence between their members such that each pair of - corresponding members are declared with compatible types; if one member of the pair is - declared with an alignment specifier, the other is declared with an equivalent alignment - specifier; and if one member of the pair is declared with a name, the other is declared - with the same name. For two structures, corresponding members shall be declared in the - same order. For two structures or unions, corresponding bit-fields shall have the same - widths. For two enumerations, corresponding members shall have the same values. -2 All declarations that refer to the same object or function shall have compatible type; - otherwise, the behavior is undefined. -3 A composite type can be constructed from two types that are compatible; it is a type that - is compatible with both of the two types and satisfies the following conditions: - -- If both types are array types, the following rules are applied: - o If one type is an array of known constant size, the composite type is an array of - that size. - o Otherwise, if one type is a variable length array whose size is specified by an - expression that is not evaluated, the behavior is undefined. - o Otherwise, if one type is a variable length array whose size is specified, the - composite type is a variable length array of that size. - o Otherwise, if one type is a variable length array of unspecified size, the composite - type is a variable length array of unspecified size. - o Otherwise, both types are arrays of unknown size and the composite type is an - array of unknown size. - The element type of the composite type is the composite type of the two element - types. - -- If only one type is a function type with a parameter type list (a function prototype), - the composite type is a function prototype with the parameter type list. - - - 55) Two types need not be identical to be compatible. - -[page 47] - - -- If both types are function types with parameter type lists, the type of each parameter - in the composite parameter type list is the composite type of the corresponding - parameters. - These rules apply recursively to the types from which the two types are derived. -4 For an identifier with internal or external linkage declared in a scope in which a prior - declaration of that identifier is visible,56) if the prior declaration specifies internal or - external linkage, the type of the identifier at the later declaration becomes the composite - type. - Forward references: array declarators (6.7.6.2). -5 EXAMPLE Given the following two file scope declarations: - int f(int (*)(), double (*)[3]); - int f(int (*)(char *), double (*)[]); - The resulting composite type for the function is: - int f(int (*)(char *), double (*)[3]); - - 6.2.8 Alignment of objects -1 Complete object types have alignment requirements which place restrictions on the - addresses at which objects of that type may be allocated. An alignment is an - implementation-defined integer value representing the number of bytes between - successive addresses at which a given object can be allocated. An object type imposes an - alignment requirement on every object of that type: stricter alignment can be requested - using the _Alignas keyword. -2 A fundamental alignment is represented by an alignment less than or equal to the greatest - alignment supported by the implementation in all contexts, which is equal to - alignof(max_align_t). -3 An extended alignment is represented by an alignment greater than - alignof(max_align_t). It is implementation-defined whether any extended - alignments are supported and the contexts in which they are supported. A type having an - extended alignment requirement is an over-aligned type.57) -4 Alignments are represented as values of the type size_t. Valid alignments include only - those values returned by an alignof expression for fundamental types, plus an - additional implementation-defined set of values, which may be empty. Every valid - alignment value shall be a nonnegative integral power of two. - - - 56) As specified in 6.2.1, the later declaration might hide the prior declaration. - 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended - alignment has been applied. - -[page 48] - -5 Alignments have an order from weaker to stronger or stricter alignments. Stricter - alignments have larger alignment values. An address that satisfies an alignment - requirement also satisfies any weaker valid alignment requirement. -6 The alignment requirement of a complete type can be queried using an alignof - expression. The types char, signed char, and unsigned char shall have the - weakest alignment requirement. -7 Comparing alignments is meaningful and provides the obvious results: - -- Two alignments are equal when their numeric values are equal. - -- Two alignments are different when their numeric values are not equal. - -- When an alignment is larger than another it represents a stricter alignment. - -[page 49] - - 6.3 Conversions -1 Several operators convert operand values from one type to another automatically. This - subclause specifies the result required from such an implicit conversion, as well as those - that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes - the conversions performed by most ordinary operators; it is supplemented as required by - the discussion of each operator in 6.5. -2 Conversion of an operand value to a compatible type causes no change to the value or the - representation. - Forward references: cast operators (6.5.4). - 6.3.1 Arithmetic operands - 6.3.1.1 Boolean, characters, and integers -1 Every integer type has an integer conversion rank defined as follows: - -- No two signed integer types shall have the same rank, even if they have the same - representation. - -- The rank of a signed integer type shall be greater than the rank of any signed integer - type with less precision. - -- The rank of long long int shall be greater than the rank of long int, which - shall be greater than the rank of int, which shall be greater than the rank of short - int, which shall be greater than the rank of signed char. - -- The rank of any unsigned integer type shall equal the rank of the corresponding - signed integer type, if any. - -- The rank of any standard integer type shall be greater than the rank of any extended - integer type with the same width. - -- The rank of char shall equal the rank of signed char and unsigned char. - -- The rank of _Bool shall be less than the rank of all other standard integer types. - -- The rank of any enumerated type shall equal the rank of the compatible integer type - (see 6.7.2.2). - -- The rank of any extended signed integer type relative to another extended signed - integer type with the same precision is implementation-defined, but still subject to the - other rules for determining the integer conversion rank. - -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has - greater rank than T3, then T1 has greater rank than T3. -2 The following may be used in an expression wherever an int or unsigned int may - be used: - -[page 50] - - -- An object or expression with an integer type (other than int or unsigned int) - whose integer conversion rank is less than or equal to the rank of int and - unsigned int. - -- A bit-field of type _Bool, int, signed int, or unsigned int. - If an int can represent all values of the original type (as restricted by the width, for a - bit-field), the value is converted to an int; otherwise, it is converted to an unsigned - int. These are called the integer promotions.58) All other types are unchanged by the - integer promotions. -3 The integer promotions preserve value including sign. As discussed earlier, whether a - ''plain'' char is treated as signed is implementation-defined. - Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers - (6.7.2.1). - 6.3.1.2 Boolean type -1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal - to 0; otherwise, the result is 1.59) - 6.3.1.3 Signed and unsigned integers -1 When a value with integer type is converted to another integer type other than _Bool, if - the value can be represented by the new type, it is unchanged. -2 Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or - subtracting one more than the maximum value that can be represented in the new type - until the value is in the range of the new type.60) -3 Otherwise, the new type is signed and the value cannot be represented in it; either the - result is implementation-defined or an implementation-defined signal is raised. - 6.3.1.4 Real floating and integer -1 When a finite value of real floating type is converted to an integer type other than _Bool, - the fractional part is discarded (i.e., the value is truncated toward zero). If the value of - the integral part cannot be represented by the integer type, the behavior is undefined.61) - - - 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain - argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the - shift operators, as specified by their respective subclauses. - 59) NaNs do not compare equal to 0 and thus convert to 1. - 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression. - 61) The remaindering operation performed when a value of integer type is converted to unsigned type - need not be performed when a value of real floating type is converted to unsigned type. Thus, the - range of portable real floating values is (-1, Utype_MAX+1). - -[page 51] - -2 When a value of integer type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - 6.3.1.5 Real floating types -1 When a value of real floating type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - 6.3.1.6 Complex types -1 When a value of complex type is converted to another complex type, both the real and - imaginary parts follow the conversion rules for the corresponding real types. - 6.3.1.7 Real and complex -1 When a value of real type is converted to a complex type, the real part of the complex - result value is determined by the rules of conversion to the corresponding real type and - the imaginary part of the complex result value is a positive zero or an unsigned zero. -2 When a value of complex type is converted to a real type, the imaginary part of the - complex value is discarded and the value of the real part is converted according to the - conversion rules for the corresponding real type. - 6.3.1.8 Usual arithmetic conversions -1 Many operators that expect operands of arithmetic type cause conversions and yield result - types in a similar way. The purpose is to determine a common real type for the operands - and result. For the specified operands, each operand is converted, without change of type - domain, to a type whose corresponding real type is the common real type. Unless - explicitly stated otherwise, the common real type is also the corresponding real type of - the result, whose type domain is the type domain of the operands if they are the same, - and complex otherwise. This pattern is called the usual arithmetic conversions: - First, if the corresponding real type of either operand is long double, the other - operand is converted, without change of type domain, to a type whose - -[page 52] - - corresponding real type is long double. - Otherwise, if the corresponding real type of either operand is double, the other - operand is converted, without change of type domain, to a type whose - corresponding real type is double. - Otherwise, if the corresponding real type of either operand is float, the other - operand is converted, without change of type domain, to a type whose - corresponding real type is float.62) - Otherwise, the integer promotions are performed on both operands. Then the - following rules are applied to the promoted operands: - If both operands have the same type, then no further conversion is needed. - Otherwise, if both operands have signed integer types or both have unsigned - integer types, the operand with the type of lesser integer conversion rank is - converted to the type of the operand with greater rank. - Otherwise, if the operand that has unsigned integer type has rank greater or - equal to the rank of the type of the other operand, then the operand with - signed integer type is converted to the type of the operand with unsigned - integer type. - Otherwise, if the type of the operand with signed integer type can represent - all of the values of the type of the operand with unsigned integer type, then - the operand with unsigned integer type is converted to the type of the - operand with signed integer type. - Otherwise, both operands are converted to the unsigned integer type - corresponding to the type of the operand with signed integer type. -2 The values of floating operands and of the results of floating expressions may be - represented in greater precision and range than that required by the type; the types are not - changed thereby.63) - - - - - 62) For example, addition of a double _Complex and a float entails just the conversion of the - float operand to double (and yields a double _Complex result). - 63) The cast and assignment operators are still required to remove extra range and precision. - -[page 53] - - 6.3.2 Other operands - 6.3.2.1 Lvalues, arrays, and function designators -1 An lvalue is an expression (with an object type other than void) that potentially - designates an object;64) if an lvalue does not designate an object when it is evaluated, the - behavior is undefined. When an object is said to have a particular type, the type is - specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that - does not have array type, does not have an incomplete type, does not have a const- - qualified type, and if it is a structure or union, does not have any member (including, - recursively, any member or element of all contained aggregates or unions) with a const- - qualified type. -2 Except when it is the operand of the sizeof operator, the unary & operator, the ++ - operator, the -- operator, or the left operand of the . operator or an assignment operator, - an lvalue that does not have array type is converted to the value stored in the designated - object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has - qualified type, the value has the unqualified version of the type of the lvalue; additionally, - if the lvalue has atomic type, the value has the non-atomic version of the type of the - lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete - type and does not have array type, the behavior is undefined. If the lvalue designates an - object of automatic storage duration that could have been declared with the register - storage class (never had its address taken), and that object is uninitialized (not declared - with an initializer and no assignment to it has been performed prior to use), the behavior - is undefined. -3 Except when it is the operand of the sizeof operator or the unary & operator, or is a - string literal used to initialize an array, an expression that has type ''array of type'' is - converted to an expression with type ''pointer to type'' that points to the initial element of - the array object and is not an lvalue. If the array object has register storage class, the - behavior is undefined. -4 A function designator is an expression that has function type. Except when it is the - operand of the sizeof operator65) or the unary & operator, a function designator with - type ''function returning type'' is converted to an expression that has type ''pointer to - - - 64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left - operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an - object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described - as the ''value of an expression''. - An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary - expression that is a pointer to an object, *E is an lvalue that designates the object to which E points. - 65) Because this conversion does not occur, the operand of the sizeof operator remains a function - designator and violates the constraint in 6.5.3.4. - -[page 54] - - function returning type''. - Forward references: address and indirection operators (6.5.3.2), assignment operators - (6.5.16), common definitions (7.19), initialization (6.7.9), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3). - 6.3.2.2 void -1 The (nonexistent) value of a void expression (an expression that has type void) shall not - be used in any way, and implicit or explicit conversions (except to void) shall not be - applied to such an expression. If an expression of any other type is evaluated as a void - expression, its value or designator is discarded. (A void expression is evaluated for its - side effects.) - 6.3.2.3 Pointers -1 A pointer to void may be converted to or from a pointer to any object type. A pointer to - any object type may be converted to a pointer to void and back again; the result shall - compare equal to the original pointer. -2 For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to - the q-qualified version of the type; the values stored in the original and converted pointers - shall compare equal. -3 An integer constant expression with the value 0, or such an expression cast to type - void *, is called a null pointer constant.66) If a null pointer constant is converted to a - pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal - to a pointer to any object or function. -4 Conversion of a null pointer to another pointer type yields a null pointer of that type. - Any two null pointers shall compare equal. -5 An integer may be converted to any pointer type. Except as previously specified, the - result is implementation-defined, might not be correctly aligned, might not point to an - entity of the referenced type, and might be a trap representation.67) -6 Any pointer type may be converted to an integer type. Except as previously specified, the - result is implementation-defined. If the result cannot be represented in the integer type, - the behavior is undefined. The result need not be in the range of values of any integer - type. - - - - - 66) The macro NULL is defined in (and other headers) as a null pointer constant; see 7.19. - 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to - be consistent with the addressing structure of the execution environment. - -[page 55] - -7 A pointer to an object type may be converted to a pointer to a different object type. If the - resulting pointer is not correctly aligned68) for the referenced type, the behavior is - undefined. Otherwise, when converted back again, the result shall compare equal to the - original pointer. When a pointer to an object is converted to a pointer to a character type, - the result points to the lowest addressed byte of the object. Successive increments of the - result, up to the size of the object, yield pointers to the remaining bytes of the object. -8 A pointer to a function of one type may be converted to a pointer to a function of another - type and back again; the result shall compare equal to the original pointer. If a converted - pointer is used to call a function whose type is not compatible with the referenced type, - the behavior is undefined. - Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types - capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1). - - - - - 68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a - pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is - correctly aligned for a pointer to type C. - -[page 56] - - 6.4 Lexical elements - Syntax -1 token: - keyword - identifier - constant - string-literal - punctuator - preprocessing-token: - header-name - identifier - pp-number - character-constant - string-literal - punctuator - each non-white-space character that cannot be one of the above - Constraints -2 Each preprocessing token that is converted to a token shall have the lexical form of a - keyword, an identifier, a constant, a string literal, or a punctuator. - Semantics -3 A token is the minimal lexical element of the language in translation phases 7 and 8. The - categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. - A preprocessing token is the minimal lexical element of the language in translation - phases 3 through 6. The categories of preprocessing tokens are: header names, - identifiers, preprocessing numbers, character constants, string literals, punctuators, and - single non-white-space characters that do not lexically match the other preprocessing - token categories.69) If a ' or a " character matches the last category, the behavior is - undefined. Preprocessing tokens can be separated by white space; this consists of - comments (described later), or white-space characters (space, horizontal tab, new-line, - vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances - during translation phase 4, white space (or the absence thereof) serves as more than - preprocessing token separation. White space may appear within a preprocessing token - only as part of a header name or between the quotation characters in a character constant - or string literal. - - - - 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot - occur in source files. - -[page 57] - -4 If the input stream has been parsed into preprocessing tokens up to a given character, the - next preprocessing token is the longest sequence of characters that could constitute a - preprocessing token. There is one exception to this rule: header name preprocessing - tokens are recognized only within #include preprocessing directives and in - implementation-defined locations within #pragma directives. In such contexts, a - sequence of characters that could be either a header name or a string literal is recognized - as the former. -5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a - valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex - might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program - fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or - not E is a macro name. - -6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on - increment operators, even though the parse x ++ + ++ y might yield a correct expression. - - Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5), - floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals - (6.4.5). - 6.4.1 Keywords - Syntax -1 keyword: one of - alignof goto union - auto if unsigned - break inline void - case int volatile - char long while - const register _Alignas - continue restrict _Atomic - default return _Bool - do short _Complex - double signed _Generic - else sizeof _Imaginary - enum static _Noreturn - extern struct _Static_assert - float switch _Thread_local - for typedef - Semantics -2 The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as - keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for - -[page 58] - - specifying imaginary types.70) - 6.4.2 Identifiers - 6.4.2.1 General - Syntax -1 identifier: - identifier-nondigit - identifier identifier-nondigit - identifier digit - identifier-nondigit: - nondigit - universal-character-name - other implementation-defined characters - nondigit: one of - _ a b c d e f g h i j k l m - n o p q r s t u v w x y z - A B C D E F G H I J K L M - N O P Q R S T U V W X Y Z - digit: one of - 0 1 2 3 4 5 6 7 8 9 - Semantics -2 An identifier is a sequence of nondigit characters (including the underscore _, the - lowercase and uppercase Latin letters, and other characters) and digits, which designates - one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. - There is no specific limit on the maximum length of an identifier. -3 Each universal character name in an identifier shall designate a character whose encoding - in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character - shall not be a universal character name designating a character whose encoding falls into - one of the ranges specified in D.2. An implementation may allow multibyte characters - that are not part of the basic source character set to appear in identifiers; which characters - and their correspondence to universal character names is implementation-defined. - - - - 70) One possible specification for imaginary types appears in annex G. - 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character - name may be used in forming valid external identifiers. For example, some otherwise unused - character or sequence of characters may be used to encode the \u in a universal character name. - Extended characters may produce a long external identifier. - -[page 59] - -4 When preprocessing tokens are converted to tokens during translation phase 7, if a - preprocessing token could be converted to either a keyword or an identifier, it is converted - to a keyword. - Implementation limits -5 As discussed in 5.2.4.1, an implementation may limit the number of significant initial - characters in an identifier; the limit for an external name (an identifier that has external - linkage) may be more restrictive than that for an internal name (a macro name or an - identifier that does not have external linkage). The number of significant characters in an - identifier is implementation-defined. -6 Any identifiers that differ in a significant character are different identifiers. If two - identifiers differ only in nonsignificant characters, the behavior is undefined. - Forward references: universal character names (6.4.3), macro replacement (6.10.3). - 6.4.2.2 Predefined identifiers - Semantics -1 The identifier __func__ shall be implicitly declared by the translator as if, - immediately following the opening brace of each function definition, the declaration - static const char __func__[] = "function-name"; - appeared, where function-name is the name of the lexically-enclosing function.72) -2 This name is encoded as if the implicit declaration had been written in the source - character set and then translated into the execution character set as indicated in translation - phase 5. -3 EXAMPLE Consider the code fragment: - #include - void myfunc(void) - { - printf("%s\n", __func__); - /* ... */ - } - Each time the function is called, it will print to the standard output stream: - myfunc - - Forward references: function definitions (6.9.1). - - - - - 72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other - identifier is explicitly declared using the name __func__, the behavior is undefined. - -[page 60] - - 6.4.3 Universal character names - Syntax -1 universal-character-name: - \u hex-quad - \U hex-quad hex-quad - hex-quad: - hexadecimal-digit hexadecimal-digit - hexadecimal-digit hexadecimal-digit - Constraints -2 A universal character name shall not specify a character whose short identifier is less than - 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through - DFFF inclusive.73) - Description -3 Universal character names may be used in identifiers, character constants, and string - literals to designate characters that are not in the basic character set. - Semantics -4 The universal character name \Unnnnnnnn designates the character whose eight-digit - short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal - character name \unnnn designates the character whose four-digit short identifier is nnnn - (and whose eight-digit short identifier is 0000nnnn). - - - - - 73) The disallowed characters are the characters in the basic character set and the code positions reserved - by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by - UTF-16). - - 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997. - -[page 61] - - 6.4.4 Constants - Syntax -1 constant: - integer-constant - floating-constant - enumeration-constant - character-constant - Constraints -2 Each constant shall have a type and the value of a constant shall be in the range of - representable values for its type. - Semantics -3 Each constant has a type, determined by its form and value, as detailed later. - 6.4.4.1 Integer constants - Syntax -1 integer-constant: - decimal-constant integer-suffixopt - octal-constant integer-suffixopt - hexadecimal-constant integer-suffixopt - decimal-constant: - nonzero-digit - decimal-constant digit - octal-constant: - 0 - octal-constant octal-digit - hexadecimal-constant: - hexadecimal-prefix hexadecimal-digit - hexadecimal-constant hexadecimal-digit - hexadecimal-prefix: one of - 0x 0X - nonzero-digit: one of - 1 2 3 4 5 6 7 8 9 - octal-digit: one of - 0 1 2 3 4 5 6 7 - -[page 62] - - hexadecimal-digit: one of - 0 1 2 3 4 5 6 7 8 9 - a b c d e f - A B C D E F - integer-suffix: - unsigned-suffix long-suffixopt - unsigned-suffix long-long-suffix - long-suffix unsigned-suffixopt - long-long-suffix unsigned-suffixopt - unsigned-suffix: one of - u U - long-suffix: one of - l L - long-long-suffix: one of - ll LL - Description -2 An integer constant begins with a digit, but has no period or exponent part. It may have a - prefix that specifies its base and a suffix that specifies its type. -3 A decimal constant begins with a nonzero digit and consists of a sequence of decimal - digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the - digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed - by a sequence of the decimal digits and the letters a (or A) through f (or F) with values - 10 through 15 respectively. - Semantics -4 The value of a decimal constant is computed base 10; that of an octal constant, base 8; - that of a hexadecimal constant, base 16. The lexically first digit is the most significant. -5 The type of an integer constant is the first of the corresponding list in which its value can - be represented. - -[page 63] - - Octal or Hexadecimal - Suffix Decimal Constant Constant - - none int int - long int unsigned int - long long int long int - unsigned long int - long long int - unsigned long long int - - u or U unsigned int unsigned int - unsigned long int unsigned long int - unsigned long long int unsigned long long int - - l or L long int long int - long long int unsigned long int - long long int - unsigned long long int - - Both u or U unsigned long int unsigned long int - and l or L unsigned long long int unsigned long long int - - ll or LL long long int long long int - unsigned long long int - - Both u or U unsigned long long int unsigned long long int - and ll or LL -6 If an integer constant cannot be represented by any type in its list, it may have an - extended integer type, if the extended integer type can represent its value. If all of the - types in the list for the constant are signed, the extended integer type shall be signed. If - all of the types in the list for the constant are unsigned, the extended integer type shall be - unsigned. If the list contains both signed and unsigned types, the extended integer type - may be signed or unsigned. If an integer constant cannot be represented by any type in - its list and has no extended integer type, then the integer constant has no type. - -[page 64] - - 6.4.4.2 Floating constants - Syntax -1 floating-constant: - decimal-floating-constant - hexadecimal-floating-constant - decimal-floating-constant: - fractional-constant exponent-partopt floating-suffixopt - digit-sequence exponent-part floating-suffixopt - hexadecimal-floating-constant: - hexadecimal-prefix hexadecimal-fractional-constant - binary-exponent-part floating-suffixopt - hexadecimal-prefix hexadecimal-digit-sequence - binary-exponent-part floating-suffixopt - fractional-constant: - digit-sequenceopt . digit-sequence - digit-sequence . - exponent-part: - e signopt digit-sequence - E signopt digit-sequence - sign: one of - + - - digit-sequence: - digit - digit-sequence digit - hexadecimal-fractional-constant: - hexadecimal-digit-sequenceopt . - hexadecimal-digit-sequence - hexadecimal-digit-sequence . - binary-exponent-part: - p signopt digit-sequence - P signopt digit-sequence - hexadecimal-digit-sequence: - hexadecimal-digit - hexadecimal-digit-sequence hexadecimal-digit - floating-suffix: one of - f l F L - -[page 65] - - Description -2 A floating constant has a significand part that may be followed by an exponent part and a - suffix that specifies its type. The components of the significand part may include a digit - sequence representing the whole-number part, followed by a period (.), followed by a - digit sequence representing the fraction part. The components of the exponent part are an - e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. - Either the whole-number part or the fraction part has to be present; for decimal floating - constants, either the period or the exponent part has to be present. - Semantics -3 The significand part is interpreted as a (decimal or hexadecimal) rational number; the - digit sequence in the exponent part is interpreted as a decimal integer. For decimal - floating constants, the exponent indicates the power of 10 by which the significand part is - to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 - by which the significand part is to be scaled. For decimal floating constants, and also for - hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either - the nearest representable value, or the larger or smaller representable value immediately - adjacent to the nearest representable value, chosen in an implementation-defined manner. - For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is - correctly rounded. -4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has - type float. If suffixed by the letter l or L, it has type long double. -5 Floating constants are converted to internal format as if at translation-time. The - conversion of a floating constant shall not raise an exceptional condition or a floating- - point exception at execution time. All floating constants of the same source form75) shall - convert to the same internal format with the same value. - Recommended practice -6 The implementation should produce a diagnostic message if a hexadecimal constant - cannot be represented exactly in its evaluation format; the implementation should then - proceed with the translation of the program. -7 The translation-time conversion of floating constants should match the execution-time - conversion of character strings by library functions, such as strtod, given matching - inputs suitable for both conversions, the same result format, and default execution-time - rounding.76) - - 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not - convert to the same internal format and value. - 76) The specification for the library functions recommends more accurate conversion than required for - floating constants (see 7.22.1.3). - -[page 66] - - 6.4.4.3 Enumeration constants - Syntax -1 enumeration-constant: - identifier - Semantics -2 An identifier declared as an enumeration constant has type int. - Forward references: enumeration specifiers (6.7.2.2). - 6.4.4.4 Character constants - Syntax -1 character-constant: - ' c-char-sequence ' - L' c-char-sequence ' - u' c-char-sequence ' - U' c-char-sequence ' - c-char-sequence: - c-char - c-char-sequence c-char - c-char: - any member of the source character set except - the single-quote ', backslash \, or new-line character - escape-sequence - escape-sequence: - simple-escape-sequence - octal-escape-sequence - hexadecimal-escape-sequence - universal-character-name - simple-escape-sequence: one of - \' \" \? \\ - \a \b \f \n \r \t \v - octal-escape-sequence: - \ octal-digit - \ octal-digit octal-digit - \ octal-digit octal-digit octal-digit - -[page 67] - - hexadecimal-escape-sequence: - \x hexadecimal-digit - hexadecimal-escape-sequence hexadecimal-digit - Description -2 An integer character constant is a sequence of one or more multibyte characters enclosed - in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the - letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are - any members of the source character set; they are mapped in an implementation-defined - manner to members of the execution character set. -3 The single-quote ', the double-quote ", the question-mark ?, the backslash \, and - arbitrary integer values are representable according to the following table of escape - sequences: - single quote ' \' - double quote " \" - question mark ? \? - backslash \ \\ - octal character \octal digits - hexadecimal character \x hexadecimal digits -4 The double-quote " and question-mark ? are representable either by themselves or by the - escape sequences \" and \?, respectively, but the single-quote ' and the backslash \ - shall be represented, respectively, by the escape sequences \' and \\. -5 The octal digits that follow the backslash in an octal escape sequence are taken to be part - of the construction of a single character for an integer character constant or of a single - wide character for a wide character constant. The numerical value of the octal integer so - formed specifies the value of the desired character or wide character. -6 The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape - sequence are taken to be part of the construction of a single character for an integer - character constant or of a single wide character for a wide character constant. The - numerical value of the hexadecimal integer so formed specifies the value of the desired - character or wide character. -7 Each octal or hexadecimal escape sequence is the longest sequence of characters that can - constitute the escape sequence. -8 In addition, characters not in the basic character set are representable by universal - character names and certain nongraphic characters are representable by escape sequences - consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, - and \v.77) - -[page 68] - - Constraints -9 The value of an octal or hexadecimal escape sequence shall be in the range of - representable values for the corresponding type: - Prefix Corresponding Type - none unsigned char - L the unsigned type corresponding to wchar_t - u char16_t - U char32_t - Semantics -10 An integer character constant has type int. The value of an integer character constant - containing a single character that maps to a single-byte execution character is the - numerical value of the representation of the mapped character interpreted as an integer. - The value of an integer character constant containing more than one character (e.g., - 'ab'), or containing a character or escape sequence that does not map to a single-byte - execution character, is implementation-defined. If an integer character constant contains - a single character or escape sequence, its value is the one that results when an object with - type char whose value is that of the single character or escape sequence is converted to - type int. -11 A wide character constant prefixed by the letter L has type wchar_t, an integer type - defined in the header; a wide character constant prefixed by the letter u or - U has type char16_t or char32_t, respectively, unsigned integer types defined in the - header. The value of a wide character constant containing a single - multibyte character that maps to a single member of the extended execution character set - is the wide character corresponding to that multibyte character, as defined by the - mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an - implementation-defined current locale. The value of a wide character constant containing - more than one multibyte character or a single multibyte character that maps to multiple - members of the extended execution character set, or containing a multibyte character or - escape sequence not represented in the extended execution character set, is - implementation-defined. -12 EXAMPLE 1 The construction '\0' is commonly used to represent the null character. - -13 EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight - bits for objects that have type char. In an implementation in which type char has the same range of - values as signed char, the integer character constant '\xFF' has the value -1; if type char has the - same range of values as unsigned char, the character constant '\xFF' has the value +255. - - - - - 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, - the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4). - -[page 69] - -14 EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123' - specifies an integer character constant containing only one character, since a hexadecimal escape sequence - is terminated only by a non-hexadecimal character. To specify an integer character constant containing the - two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal - escape sequence is terminated after three octal digits. (The value of this two-character integer character - constant is implementation-defined.) - -15 EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction - L'\1234' specifies the implementation-defined value that results from the combination of the values - 0123 and '4'. - - Forward references: common definitions (7.19), the mbtowc function - (7.22.7.2), Unicode utilities (7.27). - 6.4.5 String literals - Syntax -1 string-literal: - encoding-prefixopt " s-char-sequenceopt " - encoding-prefix: - u8 - u - U - L - s-char-sequence: - s-char - s-char-sequence s-char - s-char: - any member of the source character set except - the double-quote ", backslash \, or new-line character - escape-sequence - Constraints -2 A sequence of adjacent string literal tokens shall not include both a wide string literal and - a UTF-8 string literal. - Description -3 A character string literal is a sequence of zero or more multibyte characters enclosed in - double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8. - A wide string literal is the same, except prefixed by the letter L, u, or U. -4 The same considerations apply to each element of the sequence in a string literal as if it - were in an integer character constant (for a character or UTF-8 string literal) or a wide - character constant (for a wide string literal), except that the single-quote ' is - representable either by itself or by the escape sequence \', but the double-quote " shall - -[page 70] - - be represented by the escape sequence \". - Semantics -5 In translation phase 6, the multibyte character sequences specified by any sequence of - adjacent character and identically-prefixed string literal tokens are concatenated into a - single multibyte character sequence. If any of the tokens has an encoding prefix, the - resulting multibyte character sequence is treated as having the same prefix; otherwise, it - is treated as a character string literal. Whether differently-prefixed wide string literal - tokens can be concatenated and, if so, the treatment of the resulting multibyte character - sequence are implementation-defined. -6 In translation phase 7, a byte or code of value zero is appended to each multibyte - character sequence that results from a string literal or literals.78) The multibyte character - sequence is then used to initialize an array of static storage duration and length just - sufficient to contain the sequence. For character string literals, the array elements have - type char, and are initialized with the individual bytes of the multibyte character - sequence. For UTF-8 string literals, the array elements have type char, and are - initialized with the characters of the multibyte character sequence, as encoded in UTF-8. - For wide string literals prefixed by the letter L, the array elements have type wchar_t - and are initialized with the sequence of wide characters corresponding to the multibyte - character sequence, as defined by the mbstowcs function with an implementation- - defined current locale. For wide string literals prefixed by the letter u or U, the array - elements have type char16_t or char32_t, respectively, and are initialized with the - sequence of wide characters corresponding to the multibyte character sequence, as - defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for - its type, with an implementation-defined current locale. The value of a string literal - containing a multibyte character or escape sequence not represented in the execution - character set is implementation-defined. -7 It is unspecified whether these arrays are distinct provided their elements have the - appropriate values. If the program attempts to modify such an array, the behavior is - undefined. -8 EXAMPLE 1 This pair of adjacent character string literals - "\x12" "3" - produces a single character string literal containing the two characters whose values are '\x12' and '3', - because escape sequences are converted into single members of the execution character set just prior to - adjacent string literal concatenation. - -9 EXAMPLE 2 Each of the sequences of adjacent string literal tokens - - - - 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a - \0 escape sequence. - -[page 71] - - "a" "b" L"c" - "a" L"b" "c" - L"a" "b" L"c" - L"a" L"b" L"c" - is equivalent to the string literal - L"abc" - Likewise, each of the sequences - "a" "b" u"c" - "a" u"b" "c" - u"a" "b" u"c" - u"a" u"b" u"c" - is equivalent to - u"abc" - - Forward references: common definitions (7.19), the mbstowcs - function (7.22.8.1), Unicode utilities (7.27). - 6.4.6 Punctuators - Syntax -1 punctuator: one of - [ ] ( ) { } . -> - ++ -- & * + - ~ ! - / % << >> < > <= >= == != ^ | && || - ? : ; ... - = *= /= %= += -= <<= >>= &= ^= |= - , # ## - <: :> <% %> %: %:%: - Semantics -2 A punctuator is a symbol that has independent syntactic and semantic significance. - Depending on context, it may specify an operation to be performed (which in turn may - yield a value or a function designator, produce a side effect, or some combination thereof) - in which case it is known as an operator (other forms of operator also exist in some - contexts). An operand is an entity on which an operator acts. - -[page 72] - -3 In all aspects of the language, the six tokens79) - <: :> <% %> %: %:%: - behave, respectively, the same as the six tokens - [ ] { } # ## - except for their spelling.80) - Forward references: expressions (6.5), declarations (6.7), preprocessing directives - (6.10), statements (6.8). - 6.4.7 Header names - Syntax -1 header-name: - < h-char-sequence > - " q-char-sequence " - h-char-sequence: - h-char - h-char-sequence h-char - h-char: - any member of the source character set except - the new-line character and > - q-char-sequence: - q-char - q-char-sequence q-char - q-char: - any member of the source character set except - the new-line character and " - Semantics -2 The sequences in both forms of header names are mapped in an implementation-defined - manner to headers or external source file names as specified in 6.10.2. -3 If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters, - the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the - - - - - 79) These tokens are sometimes called ''digraphs''. - 80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely - interchanged. - -[page 73] - - sequence between the " delimiters, the behavior is undefined.81) Header name - preprocessing tokens are recognized only within #include preprocessing directives and - in implementation-defined locations within #pragma directives.82) -4 EXAMPLE The following sequence of characters: - 0x3<1/a.h>1e2 - #include <1/a.h> - #define const.member@$ - forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited - by a { on the left and a } on the right). - {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2} - {#}{include} {<1/a.h>} - {#}{define} {const}{.}{member}{@}{$} - - Forward references: source file inclusion (6.10.2). - 6.4.8 Preprocessing numbers - Syntax -1 pp-number: - digit - . digit - pp-number digit - pp-number identifier-nondigit - pp-number e sign - pp-number E sign - pp-number p sign - pp-number P sign - pp-number . - Description -2 A preprocessing number begins with a digit optionally preceded by a period (.) and may - be followed by valid identifier characters and the character sequences e+, e-, E+, E-, - p+, p-, P+, or P-. -3 Preprocessing number tokens lexically include all floating and integer constant tokens. - Semantics -4 A preprocessing number does not have type or a value; it acquires both after a successful - conversion (as part of translation phase 7) to a floating constant token or an integer - constant token. - - - 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior. - 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9. - -[page 74] - - 6.4.9 Comments -1 Except within a character constant, a string literal, or a comment, the characters /* - introduce a comment. The contents of such a comment are examined only to identify - multibyte characters and to find the characters */ that terminate it.83) -2 Except within a character constant, a string literal, or a comment, the characters // - introduce a comment that includes all multibyte characters up to, but not including, the - next new-line character. The contents of such a comment are examined only to identify - multibyte characters and to find the terminating new-line character. -3 EXAMPLE - "a//b" // four-character string literal - #include "//e" // undefined behavior - // */ // comment, not syntax error - f = g/**//h; // equivalent to f = g / h; - //\ - i(); // part of a two-line comment - /\ - / j(); // part of a two-line comment - #define glue(x,y) x##y - glue(/,/) k(); // syntax error, not comment - /*//*/ l(); // equivalent to l(); - m = n//**/o - + p; // equivalent to m = n + p; - - - - - 83) Thus, /* ... */ comments do not nest. - -[page 75] - - 6.5 Expressions -1 An expression is a sequence of operators and operands that specifies computation of a - value, or that designates an object or a function, or that generates side effects, or that - performs a combination thereof. The value computations of the operands of an operator - are sequenced before the value computation of the result of the operator. -2 If a side effect on a scalar object is unsequenced relative to either a different side effect - on the same scalar object or a value computation using the value of the same scalar - object, the behavior is undefined. If there are multiple allowable orderings of the - subexpressions of an expression, the behavior is undefined if such an unsequenced side - effect occurs in any of the orderings.84) -3 The grouping of operators and operands is indicated by the syntax.85) Except as specified - later, side effects and value computations of subexpressions are unsequenced.86) * -4 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, - collectively described as bitwise operators) are required to have operands that have - integer type. These operators yield values that depend on the internal representations of - integers, and have implementation-defined and undefined aspects for signed types. -5 If an exceptional condition occurs during the evaluation of an expression (that is, if the - result is not mathematically defined or not in the range of representable values for its - type), the behavior is undefined. - - - - 84) This paragraph renders undefined statement expressions such as - i = ++i + 1; - a[i++] = i; - while allowing - i = i + 1; - a[i] = i; - - 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same - as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the - expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in - 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators - (6.5.3), and an operand contained between any of the following pairs of operators: grouping - parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and - the conditional operator ? : (6.5.15). - Within each major subclause, the operators have the same precedence. Left- or right-associativity is - indicated in each subclause by the syntax for the expressions discussed therein. - 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and - indeterminately sequenced evaluations of its subexpressions need not be performed consistently in - different evaluations. - -[page 76] - -6 The effective type of an object for an access to its stored value is the declared type of the - object, if any.87) If a value is stored into an object having no declared type through an - lvalue having a type that is not a character type, then the type of the lvalue becomes the - effective type of the object for that access and for subsequent accesses that do not modify - the stored value. If a value is copied into an object having no declared type using - memcpy or memmove, or is copied as an array of character type, then the effective type - of the modified object for that access and for subsequent accesses that do not modify the - value is the effective type of the object from which the value is copied, if it has one. For - all other accesses to an object having no declared type, the effective type of the object is - simply the type of the lvalue used for the access. -7 An object shall have its stored value accessed only by an lvalue expression that has one of - the following types:88) - -- a type compatible with the effective type of the object, - -- a qualified version of a type compatible with the effective type of the object, - -- a type that is the signed or unsigned type corresponding to the effective type of the - object, - -- a type that is the signed or unsigned type corresponding to a qualified version of the - effective type of the object, - -- an aggregate or union type that includes one of the aforementioned types among its - members (including, recursively, a member of a subaggregate or contained union), or - -- a character type. -8 A floating expression may be contracted, that is, evaluated as though it were a single - operation, thereby omitting rounding errors implied by the source code and the - expression evaluation method.89) The FP_CONTRACT pragma in provides a - way to disallow contracted expressions. Otherwise, whether and how expressions are - contracted is implementation-defined.90) - Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2). - - - 87) Allocated objects have no declared type. - 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased. - 89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and - range, while the final operation is rounded to the format determined by the expression evaluation - method. A contracted expression might also omit the raising of floating-point exceptions. - 90) This license is specifically intended to allow implementations to exploit fast machine instructions that - combine multiple C operators. As contractions potentially undermine predictability, and can even - decrease accuracy for containing expressions, their use needs to be well-defined and clearly - documented. - -[page 77] - - 6.5.1 Primary expressions - Syntax -1 primary-expression: - identifier - constant - string-literal - ( expression ) - generic-selection - Semantics -2 An identifier is a primary expression, provided it has been declared as designating an - object (in which case it is an lvalue) or a function (in which case it is a function - designator).91) -3 A constant is a primary expression. Its type depends on its form and value, as detailed in - 6.4.4. -4 A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5. -5 A parenthesized expression is a primary expression. Its type and value are identical to - those of the unparenthesized expression. It is an lvalue, a function designator, or a void - expression if the unparenthesized expression is, respectively, an lvalue, a function - designator, or a void expression. - Forward references: declarations (6.7). - 6.5.1.1 Generic selection - Syntax -1 generic-selection: - _Generic ( assignment-expression , generic-assoc-list ) - generic-assoc-list: - generic-association - generic-assoc-list , generic-association - generic-association: - type-name : assignment-expression - default : assignment-expression - Constraints -2 A generic selection shall have no more than one default generic association. The type - name in a generic association shall specify a complete object type other than a variably - - 91) Thus, an undeclared identifier is a violation of the syntax. - -[page 78] - - modified type. No two generic associations in the same generic selection shall specify - compatible types. The controlling expression of a generic selection shall have type - compatible with at most one of the types named in its generic association list. If a - generic selection has no default generic association, its controlling expression shall - have type compatible with exactly one of the types named in its generic association list. - Semantics -3 The controlling expression of a generic selection is not evaluated. If a generic selection - has a generic association with a type name that is compatible with the type of the - controlling expression, then the result expression of the generic selection is the - expression in that generic association. Otherwise, the result expression of the generic - selection is the expression in the default generic association. None of the expressions - from any other generic association of the generic selection is evaluated. -4 The type and value of a generic selection are identical to those of its result expression. It - is an lvalue, a function designator, or a void expression if its result expression is, - respectively, an lvalue, a function designator, or a void expression. -5 EXAMPLE The cbrt type-generic macro could be implemented as follows: - #define cbrt(X) _Generic((X), \ - long double: cbrtl, \ - default: cbrt, \ - float: cbrtf \ - )(X) - - 6.5.2 Postfix operators - Syntax -1 postfix-expression: - primary-expression - postfix-expression [ expression ] - postfix-expression ( argument-expression-listopt ) - postfix-expression . identifier - postfix-expression -> identifier - postfix-expression ++ - postfix-expression -- - ( type-name ) { initializer-list } - ( type-name ) { initializer-list , } - argument-expression-list: - assignment-expression - argument-expression-list , assignment-expression - -[page 79] - - 6.5.2.1 Array subscripting - Constraints -1 One of the expressions shall have type ''pointer to complete object type'', the other - expression shall have integer type, and the result has type ''type''. - Semantics -2 A postfix expression followed by an expression in square brackets [] is a subscripted - designation of an element of an array object. The definition of the subscript operator [] - is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that - apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the - initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th - element of E1 (counting from zero). -3 Successive subscript operators designate an element of a multidimensional array object. - If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as - other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with - dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or - implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional - array, which itself is converted into a pointer if used as other than an lvalue. It follows - from this that arrays are stored in row-major order (last subscript varies fastest). -4 EXAMPLE Consider the array object defined by the declaration - int x[3][5]; - Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an - array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to - a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually - entails multiplying i by the size of the object to which the pointer points, namely an array of five int - objects. The results are added and indirection is applied to yield an array of five ints. When used in the - expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j] - yields an int. - - Forward references: additive operators (6.5.6), address and indirection operators - (6.5.3.2), array declarators (6.7.6.2). - 6.5.2.2 Function calls - Constraints -1 The expression that denotes the called function92) shall have type pointer to function - returning void or returning a complete object type other than an array type. -2 If the expression that denotes the called function has a type that includes a prototype, the - number of arguments shall agree with the number of parameters. Each argument shall - - - 92) Most often, this is the result of converting an identifier that is a function designator. - -[page 80] - - have a type such that its value may be assigned to an object with the unqualified version - of the type of its corresponding parameter. - Semantics -3 A postfix expression followed by parentheses () containing a possibly empty, comma- - separated list of expressions is a function call. The postfix expression denotes the called - function. The list of expressions specifies the arguments to the function. -4 An argument may be an expression of any complete object type. In preparing for the call - to a function, the arguments are evaluated, and each parameter is assigned the value of the - corresponding argument.93) -5 If the expression that denotes the called function has type pointer to function returning an - object type, the function call expression has the same type as that object type, and has the - value determined as specified in 6.8.6.4. Otherwise, the function call has type void. * -6 If the expression that denotes the called function has a type that does not include a - prototype, the integer promotions are performed on each argument, and arguments that - have type float are promoted to double. These are called the default argument - promotions. If the number of arguments does not equal the number of parameters, the - behavior is undefined. If the function is defined with a type that includes a prototype, and - either the prototype ends with an ellipsis (, ...) or the types of the arguments after - promotion are not compatible with the types of the parameters, the behavior is undefined. - If the function is defined with a type that does not include a prototype, and the types of - the arguments after promotion are not compatible with those of the parameters after - promotion, the behavior is undefined, except for the following cases: - -- one promoted type is a signed integer type, the other promoted type is the - corresponding unsigned integer type, and the value is representable in both types; - -- both types are pointers to qualified or unqualified versions of a character type or - void. -7 If the expression that denotes the called function has a type that does include a prototype, - the arguments are implicitly converted, as if by assignment, to the types of the - corresponding parameters, taking the type of each parameter to be the unqualified version - of its declared type. The ellipsis notation in a function prototype declarator causes - argument type conversion to stop after the last declared parameter. The default argument - promotions are performed on trailing arguments. - - - - 93) A function may change the values of its parameters, but these changes cannot affect the values of the - arguments. On the other hand, it is possible to pass a pointer to an object, and the function may - change the value of the object pointed to. A parameter declared to have array or function type is - adjusted to have a pointer type as described in 6.9.1. - -[page 81] - -8 No other conversions are performed implicitly; in particular, the number and types of - arguments are not compared with those of the parameters in a function definition that - does not include a function prototype declarator. -9 If the function is defined with a type that is not compatible with the type (of the - expression) pointed to by the expression that denotes the called function, the behavior is - undefined. -10 There is a sequence point after the evaluations of the function designator and the actual - arguments but before the actual call. Every evaluation in the calling function (including - other function calls) that is not otherwise specifically sequenced before or after the - execution of the body of the called function is indeterminately sequenced with respect to - the execution of the called function.94) -11 Recursive function calls shall be permitted, both directly and indirectly through any chain - of other functions. -12 EXAMPLE In the function call - (*pf[f1()]) (f2(), f3() + f4()) - the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before - the function pointed to by pf[f1()] is called. - - Forward references: function declarators (including prototypes) (6.7.6.3), function - definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1). - 6.5.2.3 Structure and union members - Constraints -1 The first operand of the . operator shall have an atomic, qualified, or unqualified - structure or union type, and the second operand shall name a member of that type. -2 The first operand of the -> operator shall have type ''pointer to atomic, qualified, or - unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the - second operand shall name a member of the type pointed to. - Semantics -3 A postfix expression followed by the . operator and an identifier designates a member of - a structure or union object. The value is that of the named member,95) and is an lvalue if - the first expression is an lvalue. If the first expression has qualified type, the result has - the so-qualified version of the type of the designated member. - - 94) In other words, function executions do not ''interleave'' with each other. - 95) If the member used to read the contents of a union object is not the same as the member last used to - store a value in the object, the appropriate part of the object representation of the value is reinterpreted - as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type - punning''). This might be a trap representation. - -[page 82] - -4 A postfix expression followed by the -> operator and an identifier designates a member - of a structure or union object. The value is that of the named member of the object to - which the first expression points, and is an lvalue.96) If the first expression is a pointer to - a qualified type, the result has the so-qualified version of the type of the designated - member. -5 Accessing a member of an atomic structure or union object results in undefined - behavior.97) -6 One special guarantee is made in order to simplify the use of unions: if a union contains - several structures that share a common initial sequence (see below), and if the union - object currently contains one of these structures, it is permitted to inspect the common - initial part of any of them anywhere that a declaration of the completed type of the union - is visible. Two structures share a common initial sequence if corresponding members - have compatible types (and, for bit-fields, the same widths) for a sequence of one or more - initial members. -7 EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or - union, f().x is a valid postfix expression but is not an lvalue. - -8 EXAMPLE 2 In: - struct s { int i; const int ci; }; - struct s s; - const struct s cs; - volatile struct s vs; - the various members have the types: - s.i int - s.ci const int - cs.i const int - cs.ci const int - vs.i volatile int - vs.ci volatile const int - - - - - 96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to - its operand), the expression (&E)->MOS is the same as E.MOS. - 97) For example, a data race would occur if access to the entire structure or union in one thread conflicts - with access to a member from another thread, where at least one access is a modification. Members - can be safely accessed using a non-atomic object which is assigned to or from the atomic object. - -[page 83] - -9 EXAMPLE 3 The following is a valid fragment: - union { - struct { - int alltypes; - } n; - struct { - int type; - int intnode; - } ni; - struct { - int type; - double doublenode; - } nf; - } u; - u.nf.type = 1; - u.nf.doublenode = 3.14; - /* ... */ - if (u.n.alltypes == 1) - if (sin(u.nf.doublenode) == 0.0) - /* ... */ - The following is not a valid fragment (because the union type is not visible within function f): - struct t1 { int m; }; - struct t2 { int m; }; - int f(struct t1 *p1, struct t2 *p2) - { - if (p1->m < 0) - p2->m = -p2->m; - return p1->m; - } - int g() - { - union { - struct t1 s1; - struct t2 s2; - } u; - /* ... */ - return f(&u.s1, &u.s2); - } - - Forward references: address and indirection operators (6.5.3.2), structure and union - specifiers (6.7.2.1). - -[page 84] - - 6.5.2.4 Postfix increment and decrement operators - Constraints -1 The operand of the postfix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. - Semantics -2 The result of the postfix ++ operator is the value of the operand. As a side effect, the - value of the operand object is incremented (that is, the value 1 of the appropriate type is - added to it). See the discussions of additive operators and compound assignment for - information on constraints, types, and conversions and the effects of operations on - pointers. The value computation of the result is sequenced before the side effect of - updating the stored value of the operand. With respect to an indeterminately-sequenced - function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object - with atomic type is a read-modify-write operation with memory_order_seq_cst - memory order semantics.98) -3 The postfix -- operator is analogous to the postfix ++ operator, except that the value of - the operand is decremented (that is, the value 1 of the appropriate type is subtracted from - it). - Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - 6.5.2.5 Compound literals - Constraints -1 The type name shall specify a complete object type or an array of unknown size, but not a - variable length array type. -2 All the constraints for initializer lists in 6.7.9 also apply to compound literals. - Semantics -3 A postfix expression that consists of a parenthesized type name followed by a brace- - enclosed list of initializers is a compound literal. It provides an unnamed object whose - value is given by the initializer list.99) - - - 98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence - where T is the type of E: - T tmp; - T result = E; - do { - tmp = result + 1; - } while (!atomic_compare_exchange_strong(&E, &result, tmp)); - with result being the result of the operation. - -[page 85] - -4 If the type name specifies an array of unknown size, the size is determined by the - initializer list as specified in 6.7.9, and the type of the compound literal is that of the - completed array type. Otherwise (when the type name specifies an object type), the type - of the compound literal is that specified by the type name. In either case, the result is an - lvalue. -5 The value of the compound literal is that of an unnamed object initialized by the - initializer list. If the compound literal occurs outside the body of a function, the object - has static storage duration; otherwise, it has automatic storage duration associated with - the enclosing block. -6 All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100) -7 String literals, and compound literals with const-qualified types, need not designate - distinct objects.101) -8 EXAMPLE 1 The file scope definition - int *p = (int []){2, 4}; - initializes p to point to the first element of an array of two ints, the first having the value two and the - second, four. The expressions in this compound literal are required to be constant. The unnamed object - has static storage duration. - -9 EXAMPLE 2 In contrast, in - void f(void) - { - int *p; - /*...*/ - p = (int [2]){*p}; - /*...*/ - } - p is assigned the address of the first element of an array of two ints, the first having the value previously - pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The - unnamed object has automatic storage duration. - -10 EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects - created using compound literals can be passed to functions without depending on member order: - drawline((struct point){.x=1, .y=1}, - (struct point){.x=3, .y=4}); - Or, if drawline instead expected pointers to struct point: - - - - 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types - or void only, and the result of a cast expression is not an lvalue. - 100) For example, subobjects without explicit initializers are initialized to zero. - 101) This allows implementations to share storage for string literals and constant compound literals with - the same or overlapping representations. - -[page 86] - - drawline(&(struct point){.x=1, .y=1}, - &(struct point){.x=3, .y=4}); - -11 EXAMPLE 4 A read-only compound literal can be specified through constructions like: - (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6} - -12 EXAMPLE 5 The following three expressions have different meanings: - "/tmp/fileXXXXXX" - (char []){"/tmp/fileXXXXXX"} - (const char []){"/tmp/fileXXXXXX"} - The first always has static storage duration and has type array of char, but need not be modifiable; the last - two have automatic storage duration when they occur within the body of a function, and the first of these - two is modifiable. - -13 EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory - and can even be shared. For example, - (const char []){"abc"} == "abc" - might yield 1 if the literals' storage is shared. - -14 EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly - linked object. For example, there is no way to write a self-referential compound literal that could be used - as the function argument in place of the named object endless_zeros below: - struct int_list { int car; struct int_list *cdr; }; - struct int_list endless_zeros = {0, &endless_zeros}; - eval(endless_zeros); - -15 EXAMPLE 8 Each compound literal creates only a single object in a given scope: - struct s { int i; }; - int f (void) - { - struct s *p = 0, *q; - int j = 0; - again: - q = p, p = &((struct s){ j++ }); - if (j < 2) goto again; - return p == q && q->i == 1; - } - The function f() always returns the value 1. -16 Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the - lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would - have an indeterminate value, which would result in undefined behavior. - - Forward references: type names (6.7.7), initialization (6.7.9). - -[page 87] - - 6.5.3 Unary operators - Syntax -1 unary-expression: - postfix-expression - ++ unary-expression - -- unary-expression - unary-operator cast-expression - sizeof unary-expression - sizeof ( type-name ) - alignof ( type-name ) - unary-operator: one of - & * + - ~ ! - 6.5.3.1 Prefix increment and decrement operators - Constraints -1 The operand of the prefix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. - Semantics -2 The value of the operand of the prefix ++ operator is incremented. The result is the new - value of the operand after incrementation. The expression ++E is equivalent to (E+=1). - See the discussions of additive operators and compound assignment for information on - constraints, types, side effects, and conversions and the effects of operations on pointers. -3 The prefix -- operator is analogous to the prefix ++ operator, except that the value of the - operand is decremented. - Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - 6.5.3.2 Address and indirection operators - Constraints -1 The operand of the unary & operator shall be either a function designator, the result of a - [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is - not declared with the register storage-class specifier. -2 The operand of the unary * operator shall have pointer type. - Semantics -3 The unary & operator yields the address of its operand. If the operand has type ''type'', - the result has type ''pointer to type''. If the operand is the result of a unary * operator, - neither that operator nor the & operator is evaluated and the result is as if both were - omitted, except that the constraints on the operators still apply and the result is not an - -[page 88] - - lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor - the unary * that is implied by the [] is evaluated and the result is as if the & operator - were removed and the [] operator were changed to a + operator. Otherwise, the result is - a pointer to the object or function designated by its operand. -4 The unary * operator denotes indirection. If the operand points to a function, the result is - a function designator; if it points to an object, the result is an lvalue designating the - object. If the operand has type ''pointer to type'', the result has type ''type''. If an - invalid value has been assigned to the pointer, the behavior of the unary * operator is - undefined.102) - Forward references: storage-class specifiers (6.7.1), structure and union specifiers - (6.7.2.1). - 6.5.3.3 Unary arithmetic operators - Constraints -1 The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, - integer type; of the ! operator, scalar type. - Semantics -2 The result of the unary + operator is the value of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -3 The result of the unary - operator is the negative of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -4 The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, - each bit in the result is set if and only if the corresponding bit in the converted operand is - not set). The integer promotions are performed on the operand, and the result has the - promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent - to the maximum value representable in that type minus E. -5 The result of the logical negation operator ! is 0 if the value of its operand compares - unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. - The expression !E is equivalent to (0==E). - - - - 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is - always true that if E is a function designator or an lvalue that is a valid operand of the unary & - operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of - an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. - Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an - address inappropriately aligned for the type of object pointed to, and the address of an object after the - end of its lifetime. - -[page 89] - - 6.5.3.4 The sizeof and alignof operators - Constraints -1 The sizeof operator shall not be applied to an expression that has function type or an - incomplete type, to the parenthesized name of such a type, or to an expression that - designates a bit-field member. The alignof operator shall not be applied to a function - type or an incomplete type. - Semantics -2 The sizeof operator yields the size (in bytes) of its operand, which may be an - expression or the parenthesized name of a type. The size is determined from the type of - the operand. The result is an integer. If the type of the operand is a variable length array - type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an - integer constant. -3 The alignof operator yields the alignment requirement of its operand type. The result - is an integer constant. When applied to an array type, the result is the alignment - requirement of the element type. -4 When sizeof is applied to an operand that has type char, unsigned char, or - signed char, (or a qualified version thereof) the result is 1. When applied to an - operand that has array type, the result is the total number of bytes in the array.103) When - applied to an operand that has structure or union type, the result is the total number of - bytes in such an object, including internal and trailing padding. -5 The value of the result of both operators is implementation-defined, and its type (an - unsigned integer type) is size_t, defined in (and other headers). -6 EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage - allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to - allocate and return a pointer to void. For example: - extern void *alloc(size_t); - double *dp = alloc(sizeof *dp); - The implementation of the alloc function should ensure that its return value is aligned suitably for - conversion to a pointer to double. - -7 EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array: - sizeof array / sizeof array[0] - -8 EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a - function: - #include - - - - 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the - size of the adjusted (pointer) type (see 6.9.1). - -[page 90] - - size_t fsize3(int n) - { - char b[n+3]; // variable length array - return sizeof b; // execution time sizeof - } - int main() - { - size_t size; - size = fsize3(10); // fsize3 returns 13 - return 0; - } - - Forward references: common definitions (7.19), declarations (6.7), - structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2). - 6.5.4 Cast operators - Syntax -1 cast-expression: - unary-expression - ( type-name ) cast-expression - Constraints -2 Unless the type name specifies a void type, the type name shall specify atomic, qualified, - or unqualified scalar type, and the operand shall have scalar type. -3 Conversions that involve pointers, other than where permitted by the constraints of - 6.5.16.1, shall be specified by means of an explicit cast. -4 A pointer type shall not be converted to any floating type. A floating type shall not be - converted to any pointer type. - Semantics -5 Preceding an expression by a parenthesized type name converts the value of the - expression to the named type. This construction is called a cast.104) A cast that specifies - no conversion has no effect on the type or value of an expression. -6 If the value of the expression is represented with greater precision or range than required - by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the - type of the expression is the same as the named type and removes any extra range and - precision. - Forward references: equality operators (6.5.9), function declarators (including - prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7). - - 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the - unqualified version of the type. - -[page 91] - - 6.5.5 Multiplicative operators - Syntax -1 multiplicative-expression: - cast-expression - multiplicative-expression * cast-expression - multiplicative-expression / cast-expression - multiplicative-expression % cast-expression - Constraints -2 Each of the operands shall have arithmetic type. The operands of the % operator shall - have integer type. - Semantics -3 The usual arithmetic conversions are performed on the operands. -4 The result of the binary * operator is the product of the operands. -5 The result of the / operator is the quotient from the division of the first operand by the - second; the result of the % operator is the remainder. In both operations, if the value of - the second operand is zero, the behavior is undefined. -6 When integers are divided, the result of the / operator is the algebraic quotient with any - fractional part discarded.105) If the quotient a/b is representable, the expression - (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is - undefined. - 6.5.6 Additive operators - Syntax -1 additive-expression: - multiplicative-expression - additive-expression + multiplicative-expression - additive-expression - multiplicative-expression - Constraints -2 For addition, either both operands shall have arithmetic type, or one operand shall be a - pointer to a complete object type and the other shall have integer type. (Incrementing is - equivalent to adding 1.) -3 For subtraction, one of the following shall hold: - - - - - 105) This is often called ''truncation toward zero''. - -[page 92] - - -- both operands have arithmetic type; - -- both operands are pointers to qualified or unqualified versions of compatible complete - object types; or - -- the left operand is a pointer to a complete object type and the right operand has - integer type. - (Decrementing is equivalent to subtracting 1.) - Semantics -4 If both operands have arithmetic type, the usual arithmetic conversions are performed on - them. -5 The result of the binary + operator is the sum of the operands. -6 The result of the binary - operator is the difference resulting from the subtraction of the - second operand from the first. -7 For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -8 When an expression that has integer type is added to or subtracted from a pointer, the - result has the type of the pointer operand. If the pointer operand points to an element of - an array object, and the array is large enough, the result points to an element offset from - the original element such that the difference of the subscripts of the resulting and original - array elements equals the integer expression. In other words, if the expression P points to - the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and - (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of - the array object, provided they exist. Moreover, if the expression P points to the last - element of an array object, the expression (P)+1 points one past the last element of the - array object, and if the expression Q points one past the last element of an array object, - the expression (Q)-1 points to the last element of the array object. If both the pointer - operand and the result point to elements of the same array object, or one past the last - element of the array object, the evaluation shall not produce an overflow; otherwise, the - behavior is undefined. If the result points one past the last element of the array object, it - shall not be used as the operand of a unary * operator that is evaluated. -9 When two pointers are subtracted, both shall point to elements of the same array object, - or one past the last element of the array object; the result is the difference of the - subscripts of the two array elements. The size of the result is implementation-defined, - and its type (a signed integer type) is ptrdiff_t defined in the header. - If the result is not representable in an object of that type, the behavior is undefined. In - other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of - an array object, the expression (P)-(Q) has the value i-j provided the value fits in an - -[page 93] - - object of type ptrdiff_t. Moreover, if the expression P points either to an element of - an array object or one past the last element of an array object, and the expression Q points - to the last element of the same array object, the expression ((Q)+1)-(P) has the same - value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the - expression P points one past the last element of the array object, even though the - expression (Q)+1 does not point to an element of the array object.106) -10 EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types. - { - int n = 4, m = 3; - int a[n][m]; - int (*p)[m] = a; // p == &a[0] - p += 1; // p == &a[1] - (*p)[2] = 99; // a[1][2] == 99 - n = p - a; // n == 1 - } -11 If array a in the above example were declared to be an array of known constant size, and pointer p were - declared to be a pointer to an array of the same known constant size (pointing to a), the results would be - the same. - - Forward references: array declarators (6.7.6.2), common definitions - (7.19). - 6.5.7 Bitwise shift operators - Syntax -1 shift-expression: - additive-expression - shift-expression << additive-expression - shift-expression >> additive-expression - Constraints -2 Each of the operands shall have integer type. - Semantics -3 The integer promotions are performed on each of the operands. The type of the result is - that of the promoted left operand. If the value of the right operand is negative or is - - 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In - this scheme the integer expression added to or subtracted from the converted pointer is first multiplied - by the size of the object originally pointed to, and the resulting pointer is converted back to the - original type. For pointer subtraction, the result of the difference between the character pointers is - similarly divided by the size of the object originally pointed to. - When viewed in this way, an implementation need only provide one extra byte (which may overlap - another object in the program) just after the end of the object in order to satisfy the ''one past the last - element'' requirements. - -[page 94] - - greater than or equal to the width of the promoted left operand, the behavior is undefined. -4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with - zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo - one more than the maximum value representable in the result type. If E1 has a signed - type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is - the resulting value; otherwise, the behavior is undefined. -5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type - or if E1 has a signed type and a nonnegative value, the value of the result is the integral - part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the - resulting value is implementation-defined. - 6.5.8 Relational operators - Syntax -1 relational-expression: - shift-expression - relational-expression < shift-expression - relational-expression > shift-expression - relational-expression <= shift-expression - relational-expression >= shift-expression - Constraints -2 One of the following shall hold: - -- both operands have real type; or * - -- both operands are pointers to qualified or unqualified versions of compatible object - types. - Semantics -3 If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. -4 For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -5 When two pointers are compared, the result depends on the relative locations in the - address space of the objects pointed to. If two pointers to object types both point to the - same object, or both point one past the last element of the same array object, they - compare equal. If the objects pointed to are members of the same aggregate object, - pointers to structure members declared later compare greater than pointers to members - declared earlier in the structure, and pointers to array elements with larger subscript - values compare greater than pointers to elements of the same array with lower subscript - -[page 95] - - values. All pointers to members of the same union object compare equal. If the - expression P points to an element of an array object and the expression Q points to the - last element of the same array object, the pointer expression Q+1 compares greater than - P. In all other cases, the behavior is undefined. -6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= - (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is - false.107) The result has type int. - 6.5.9 Equality operators - Syntax -1 equality-expression: - relational-expression - equality-expression == relational-expression - equality-expression != relational-expression - Constraints -2 One of the following shall hold: - -- both operands have arithmetic type; - -- both operands are pointers to qualified or unqualified versions of compatible types; - -- one operand is a pointer to an object type and the other is a pointer to a qualified or - unqualified version of void; or - -- one operand is a pointer and the other is a null pointer constant. - Semantics -3 The == (equal to) and != (not equal to) operators are analogous to the relational - operators except for their lower precedence.108) Each of the operators yields 1 if the - specified relation is true and 0 if it is false. The result has type int. For any pair of - operands, exactly one of the relations is true. -4 If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. Values of complex types are equal if and only if both their real parts are equal - and also their imaginary parts are equal. Any two values of arithmetic types from - different type domains are equal if and only if the results of their conversions to the - (complex) result type determined by the usual arithmetic conversions are equal. - - - - 107) The expression a>= &= ^= |= - Constraints -2 An assignment operator shall have a modifiable lvalue as its left operand. - Semantics -3 An assignment operator stores a value in the object designated by the left operand. An - assignment expression has the value of the left operand after the assignment,111) but is not - an lvalue. The type of an assignment expression is the type the left operand would have - after lvalue conversion. The side effect of updating the stored value of the left operand is - sequenced after the value computations of the left and right operands. The evaluations of - the operands are unsequenced. - - - - - 111) The implementation is permitted to read the object to determine the value but is not required to, even - when the object has volatile-qualified type. - -[page 101] - - 6.5.16.1 Simple assignment - Constraints -1 One of the following shall hold:112) - -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has - arithmetic type; - -- the left operand has an atomic, qualified, or unqualified version of a structure or union - type compatible with the type of the right; - -- the left operand has atomic, qualified, or unqualified pointer type, and (considering - the type the left operand would have after lvalue conversion) both operands are - pointers to qualified or unqualified versions of compatible types, and the type pointed - to by the left has all the qualifiers of the type pointed to by the right; - -- the left operand has atomic, qualified, or unqualified pointer type, and (considering - the type the left operand would have after lvalue conversion) one operand is a pointer - to an object type, and the other is a pointer to a qualified or unqualified version of - void, and the type pointed to by the left has all the qualifiers of the type pointed to - by the right; - -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null - pointer constant; or - -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a - pointer. - Semantics -2 In simple assignment (=), the value of the right operand is converted to the type of the - assignment expression and replaces the value stored in the object designated by the left - operand. -3 If the value being stored in an object is read from another object that overlaps in any way - the storage of the first object, then the overlap shall be exact and the two objects shall - have qualified or unqualified versions of a compatible type; otherwise, the behavior is - undefined. -4 EXAMPLE 1 In the program fragment - - - - - 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion - (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type - qualifiers that were applied to the type category of the expression (for example, it removes const but - not volatile from the type int volatile * const). - -[page 102] - - int f(void); - char c; - /* ... */ - if ((c = f()) == -1) - /* ... */ - the int value returned by the function may be truncated when stored in the char, and then converted back - to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of - values as unsigned char (and char is narrower than int), the result of the conversion cannot be - negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the - variable c should be declared as int. - -5 EXAMPLE 2 In the fragment: - char c; - int i; - long l; - l = (c = i); - the value of i is converted to the type of the assignment expression c = i, that is, char type. The value - of the expression enclosed in parentheses is then converted to the type of the outer assignment expression, - that is, long int type. - -6 EXAMPLE 3 Consider the fragment: - const char **cpp; - char *p; - const char c = 'A'; - cpp = &p; // constraint violation - *cpp = &c; // valid - *p = 0; // valid - The first assignment is unsafe because it would allow the following valid code to attempt to change the - value of the const object c. - - 6.5.16.2 Compound assignment - Constraints -1 For the operators += and -= only, either the left operand shall be an atomic, qualified, or - unqualified pointer to a complete object type, and the right shall have integer type; or the - left operand shall have atomic, qualified, or unqualified arithmetic type, and the right - shall have arithmetic type. -2 For the other operators, the left operand shall have atomic, qualified, or unqualified - arithmetic type, and (considering the type the left operand would have after lvalue - conversion) each operand shall have arithmetic type consistent with those allowed by the - corresponding binary operator. - Semantics -3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment - expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with - respect to an indeterminately-sequenced function call, the operation of a compound - -[page 103] - - assignment is a single evaluation. If E1 has an atomic type, compound assignment is a - read-modify-write operation with memory_order_seq_cst memory order - semantics.113) - 6.5.17 Comma operator - Syntax -1 expression: - assignment-expression - expression , assignment-expression - Semantics -2 The left operand of a comma operator is evaluated as a void expression; there is a - sequence point between its evaluation and that of the right operand. Then the right - operand is evaluated; the result has its type and value.114) * -3 EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot - appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists - of initializers). On the other hand, it can be used within a parenthesized expression or within the second - expression of a conditional operator in such contexts. In the function call - f(a, (t=3, t+2), c) - the function has three arguments, the second of which has the value 5. - - Forward references: initialization (6.7.9). - - - - - 113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence - where T is the type of E1: - T tmp = E1; - T result; - do { - result = tmp op (E2); - } while (!atomic_compare_exchange_strong(&E1, &tmp, result)); - with result being the result of the operation. - 114) A comma operator does not yield an lvalue. - -[page 104] - - 6.6 Constant expressions - Syntax -1 constant-expression: - conditional-expression - Description -2 A constant expression can be evaluated during translation rather than runtime, and - accordingly may be used in any place that a constant may be. - Constraints -3 Constant expressions shall not contain assignment, increment, decrement, function-call, - or comma operators, except when they are contained within a subexpression that is not - evaluated.115) -4 Each constant expression shall evaluate to a constant that is in the range of representable - values for its type. - Semantics -5 An expression that evaluates to a constant is required in several contexts. If a floating - expression is evaluated in the translation environment, the arithmetic precision and range - shall be at least as great as if the expression were being evaluated in the execution - environment.116) -6 An integer constant expression117) shall have integer type and shall only have operands - that are integer constants, enumeration constants, character constants, sizeof - expressions whose results are integer constants, and floating constants that are the - immediate operands of casts. Cast operators in an integer constant expression shall only - convert arithmetic types to integer types, except as part of an operand to the sizeof - operator. -7 More latitude is permitted for constant expressions in initializers. Such a constant - expression shall be, or evaluate to, one of the following: - -- an arithmetic constant expression, - - - - 115) The operand of a sizeof operator is usually not evaluated (6.5.3.4). - 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in - the translation environment. - 117) An integer constant expression is required in a number of contexts such as the size of a bit-field - member of a structure, the value of an enumeration constant, and the size of a non-variable length - array. Further constraints that apply to the integer constant expressions used in conditional-inclusion - preprocessing directives are discussed in 6.10.1. - -[page 105] - - -- a null pointer constant, - -- an address constant, or - -- an address constant for a complete object type plus or minus an integer constant - expression. -8 An arithmetic constant expression shall have arithmetic type and shall only have - operands that are integer constants, floating constants, enumeration constants, character - constants, and sizeof expressions. Cast operators in an arithmetic constant expression - shall only convert arithmetic types to arithmetic types, except as part of an operand to a - sizeof operator whose result is an integer constant. -9 An address constant is a null pointer, a pointer to an lvalue designating an object of static - storage duration, or a pointer to a function designator; it shall be created explicitly using - the unary & operator or an integer constant cast to pointer type, or implicitly by the use of - an expression of array or function type. The array-subscript [] and member-access . - and -> operators, the address & and indirection * unary operators, and pointer casts may - be used in the creation of an address constant, but the value of an object shall not be - accessed by use of these operators. -10 An implementation may accept other forms of constant expressions. -11 The semantic rules for the evaluation of a constant expression are the same as for - nonconstant expressions.118) - Forward references: array declarators (6.7.6.2), initialization (6.7.9). - - - - - 118) Thus, in the following initialization, - static int i = 2 || 1 / 0; - the expression is a valid integer constant expression with value one. - -[page 106] - - 6.7 Declarations - Syntax -1 declaration: - declaration-specifiers init-declarator-listopt ; - static_assert-declaration - declaration-specifiers: - storage-class-specifier declaration-specifiersopt - type-specifier declaration-specifiersopt - type-qualifier declaration-specifiersopt - function-specifier declaration-specifiersopt - alignment-specifier declaration-specifiersopt - init-declarator-list: - init-declarator - init-declarator-list , init-declarator - init-declarator: - declarator - declarator = initializer - Constraints -2 A declaration other than a static_assert declaration shall declare at least a declarator - (other than the parameters of a function or the members of a structure or union), a tag, or - the members of an enumeration. -3 If an identifier has no linkage, there shall be no more than one declaration of the identifier - (in a declarator or type specifier) with the same scope and in the same name space, except - that a typedef name can be redefined to denote the same type as it currently does and tags - may be redeclared as specified in 6.7.2.3. -4 All declarations in the same scope that refer to the same object or function shall specify - compatible types. - Semantics -5 A declaration specifies the interpretation and attributes of a set of identifiers. A definition - of an identifier is a declaration for that identifier that: - -- for an object, causes storage to be reserved for that object; - -- for a function, includes the function body;119) - - - - 119) Function definitions have a different syntax, described in 6.9.1. - -[page 107] - - -- for an enumeration constant or typedef name, is the (only) declaration of the - identifier. -6 The declaration specifiers consist of a sequence of specifiers that indicate the linkage, - storage duration, and part of the type of the entities that the declarators denote. The init- - declarator-list is a comma-separated sequence of declarators, each of which may have - additional type information, or an initializer, or both. The declarators contain the - identifiers (if any) being declared. -7 If an identifier for an object is declared with no linkage, the type for the object shall be - complete by the end of its declarator, or by the end of its init-declarator if it has an - initializer; in the case of function parameters (including in prototypes), it is the adjusted - type (see 6.7.6.3) that is required to be complete. - Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization - (6.7.9), type names (6.7.7), type qualifiers (6.7.3). - 6.7.1 Storage-class specifiers - Syntax -1 storage-class-specifier: - typedef - extern - static - _Thread_local - auto - register - Constraints -2 At most, one storage-class specifier may be given in the declaration specifiers in a - declaration, except that _Thread_local may appear with static or extern.120) -3 In the declaration of an object with block scope, if the declaration specifiers include - _Thread_local, they shall also include either static or extern. If - _Thread_local appears in any declaration of an object, it shall be present in every - declaration of that object. - Semantics -4 The typedef specifier is called a ''storage-class specifier'' for syntactic convenience - only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations - were discussed in 6.2.2 and 6.2.4. - - - - 120) See ''future language directions'' (6.11.5). - -[page 108] - -5 A declaration of an identifier for an object with storage-class specifier register - suggests that access to the object be as fast as possible. The extent to which such - suggestions are effective is implementation-defined.121) -6 The declaration of an identifier for a function that has block scope shall have no explicit - storage-class specifier other than extern. -7 If an aggregate or union object is declared with a storage-class specifier other than - typedef, the properties resulting from the storage-class specifier, except with respect to - linkage, also apply to the members of the object, and so on recursively for any aggregate - or union member objects. - Forward references: type definitions (6.7.8). - 6.7.2 Type specifiers - Syntax -1 type-specifier: - void - char - short - int - long - float - double - signed - unsigned - _Bool - _Complex - atomic-type-specifier - struct-or-union-specifier - enum-specifier - typedef-name - Constraints -2 At least one type specifier shall be given in the declaration specifiers in each declaration, - and in the specifier-qualifier list in each struct declaration and type name. Each list of - - - 121) The implementation may treat any register declaration simply as an auto declaration. However, - whether or not addressable storage is actually used, the address of any part of an object declared with - storage-class specifier register cannot be computed, either explicitly (by use of the unary & - operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in - 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier - register is sizeof. - -[page 109] - - type specifiers shall be one of the following multisets (delimited by commas, when there - is more than one multiset per item); the type specifiers may occur in any order, possibly - intermixed with the other declaration specifiers. - -- void - -- char - -- signed char - -- unsigned char - -- short, signed short, short int, or signed short int - -- unsigned short, or unsigned short int - -- int, signed, or signed int - -- unsigned, or unsigned int - -- long, signed long, long int, or signed long int - -- unsigned long, or unsigned long int - -- long long, signed long long, long long int, or - signed long long int - -- unsigned long long, or unsigned long long int - -- float - -- double - -- long double - -- _Bool - -- float _Complex - -- double _Complex - -- long double _Complex - -- atomic type specifier - -- struct or union specifier - -- enum specifier - -- typedef name -3 The type specifier _Complex shall not be used if the implementation does not support - complex types (see 6.10.8.3). - -[page 110] - - Semantics -4 Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1 - through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The - characteristics of the other types are discussed in 6.2.5. -5 Each of the comma-separated multisets designates the same type, except that for bit- - fields, it is implementation-defined whether the specifier int designates the same type as - signed int or the same type as unsigned int. - Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2), - structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8). - 6.7.2.1 Structure and union specifiers - Syntax -1 struct-or-union-specifier: - struct-or-union identifieropt { struct-declaration-list } - struct-or-union identifier - struct-or-union: - struct - union - struct-declaration-list: - struct-declaration - struct-declaration-list struct-declaration - struct-declaration: - specifier-qualifier-list struct-declarator-listopt ; - static_assert-declaration - specifier-qualifier-list: - type-specifier specifier-qualifier-listopt - type-qualifier specifier-qualifier-listopt - struct-declarator-list: - struct-declarator - struct-declarator-list , struct-declarator - struct-declarator: - declarator - declaratoropt : constant-expression - Constraints -2 A struct-declaration that does not declare an anonymous structure or anonymous union - shall contain a struct-declarator-list. - -[page 111] - -3 A structure or union shall not contain a member with incomplete or function type (hence, - a structure shall not contain an instance of itself, but may contain a pointer to an instance - of itself), except that the last member of a structure with more than one named member - may have incomplete array type; such a structure (and any union containing, possibly - recursively, a member that is such a structure) shall not be a member of a structure or an - element of an array. -4 The expression that specifies the width of a bit-field shall be an integer constant - expression with a nonnegative value that does not exceed the width of an object of the - type that would be specified were the colon and expression omitted.122) If the value is - zero, the declaration shall have no declarator. -5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed - int, unsigned int, or some other implementation-defined type. It is - implementation-defined whether atomic types are permitted. - Semantics -6 As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose - storage is allocated in an ordered sequence, and a union is a type consisting of a sequence - of members whose storage overlap. -7 Structure and union specifiers have the same form. The keywords struct and union - indicate that the type being specified is, respectively, a structure type or a union type. -8 The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type, - within a translation unit. The struct-declaration-list is a sequence of declarations for the - members of the structure or union. If the struct-declaration-list contains no named - members, no anonymous structures, and no anonymous unions, the behavior is undefined. - The type is incomplete until immediately after the } that terminates the list, and complete - thereafter. -9 A member of a structure or union may have any complete object type other than a - variably modified type.123) In addition, a member may be declared to consist of a - specified number of bits (including a sign bit, if any). Such a member is called a - bit-field;124) its width is preceded by a colon. -10 A bit-field is interpreted as having a signed or unsigned integer type consisting of the - specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of - - 122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and - value bits) of a _Bool may be just 1 bit. - 123) A structure or union cannot contain a member with a variably modified type because member names - are not ordinary identifiers as defined in 6.2.3. - 124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to - or arrays of bit-field objects. - -[page 112] - - type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool - bit-field has the semantics of a _Bool. -11 An implementation may allocate any addressable storage unit large enough to hold a bit- - field. If enough space remains, a bit-field that immediately follows another bit-field in a - structure shall be packed into adjacent bits of the same unit. If insufficient space remains, - whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is - implementation-defined. The order of allocation of bit-fields within a unit (high-order to - low-order or low-order to high-order) is implementation-defined. The alignment of the - addressable storage unit is unspecified. -12 A bit-field declaration with no declarator, but only a colon and a width, indicates an - unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0 - indicates that no further bit-field is to be packed into the unit in which the previous bit- - field, if any, was placed. -13 An unnamed member of structure type with no tag is called an anonymous structure; an - unnamed member of union type with no tag is called an anonymous union. The members - of an anonymous structure or union are considered to be members of the containing - structure or union. This applies recursively if the containing structure or union is also - anonymous. -14 Each non-bit-field member of a structure or union object is aligned in an implementation- - defined manner appropriate to its type. -15 Within a structure object, the non-bit-field members and the units in which bit-fields - reside have addresses that increase in the order in which they are declared. A pointer to a - structure object, suitably converted, points to its initial member (or if that member is a - bit-field, then to the unit in which it resides), and vice versa. There may be unnamed - padding within a structure object, but not at its beginning. -16 The size of a union is sufficient to contain the largest of its members. The value of at - most one of the members can be stored in a union object at any time. A pointer to a - union object, suitably converted, points to each of its members (or if a member is a bit- - field, then to the unit in which it resides), and vice versa. -17 There may be unnamed padding at the end of a structure or union. -18 As a special case, the last element of a structure with more than one named member may - have an incomplete array type; this is called a flexible array member. In most situations, - - - 125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int, - then it is implementation-defined whether the bit-field is signed or unsigned. - 126) An unnamed bit-field structure member is useful for padding to conform to externally imposed - layouts. - -[page 113] - - the flexible array member is ignored. In particular, the size of the structure is as if the - flexible array member were omitted except that it may have more trailing padding than - the omission would imply. However, when a . (or ->) operator has a left operand that is - (a pointer to) a structure with a flexible array member and the right operand names that - member, it behaves as if that member were replaced with the longest array (with the same - element type) that would not make the structure larger than the object being accessed; the - offset of the array shall remain that of the flexible array member, even if this would differ - from that of the replacement array. If this array would have no elements, it behaves as if - it had one element but the behavior is undefined if any attempt is made to access that - element or to generate a pointer one past it. -19 EXAMPLE 1 The following illustrates anonymous structures and unions: - struct v { - union { // anonymous union - struct { int i, j; }; // anonymous structure - struct { long k, l; } w; - }; - int m; - } v1; - v1.i = 2; // valid - v1.k = 3; // invalid: inner structure is not anonymous - v1.w.k = 5; // valid - -20 EXAMPLE 2 After the declaration: - struct s { int n; double d[]; }; - the structure struct s has a flexible array member d. A typical way to use this is: - int m = /* some value */; - struct s *p = malloc(sizeof (struct s) + sizeof (double [m])); - and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if - p had been declared as: - struct { int n; double d[m]; } *p; - (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might - not be the same). -21 Following the above declaration: - struct s t1 = { 0 }; // valid - struct s t2 = { 1, { 4.2 }}; // invalid - t1.n = 4; // valid - t1.d[0] = 4.2; // might be undefined behavior - The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not - contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that - sizeof (struct s) >= offsetof(struct s, d) + sizeof (double) - in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming - code. - -[page 114] - -22 After the further declaration: - struct ss { int n; }; - the expressions: - sizeof (struct s) >= sizeof (struct ss) - sizeof (struct s) >= offsetof(struct s, d) - are always equal to 1. -23 If sizeof (double) is 8, then after the following code is executed: - struct s *s1; - struct s *s2; - s1 = malloc(sizeof (struct s) + 64); - s2 = malloc(sizeof (struct s) + 46); - and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most - purposes, as if the identifiers had been declared as: - struct { int n; double d[8]; } *s1; - struct { int n; double d[5]; } *s2; -24 Following the further successful assignments: - s1 = malloc(sizeof (struct s) + 10); - s2 = malloc(sizeof (struct s) + 6); - they then behave as if the declarations were: - struct { int n; double d[1]; } *s1, *s2; - and: - double *dp; - dp = &(s1->d[0]); // valid - *dp = 42; // valid - dp = &(s2->d[0]); // valid - *dp = 42; // undefined behavior -25 The assignment: - *s1 = *s2; - only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes - of the structure, they might be copied or simply overwritten with indeterminate values. - - Forward references: declarators (6.7.6), tags (6.7.2.3). - -[page 115] - - 6.7.2.2 Enumeration specifiers - Syntax -1 enum-specifier: - enum identifieropt { enumerator-list } - enum identifieropt { enumerator-list , } - enum identifier - enumerator-list: - enumerator - enumerator-list , enumerator - enumerator: - enumeration-constant - enumeration-constant = constant-expression - Constraints -2 The expression that defines the value of an enumeration constant shall be an integer - constant expression that has a value representable as an int. - Semantics -3 The identifiers in an enumerator list are declared as constants that have type int and - may appear wherever such are permitted.127) An enumerator with = defines its - enumeration constant as the value of the constant expression. If the first enumerator has - no =, the value of its enumeration constant is 0. Each subsequent enumerator with no = - defines its enumeration constant as the value of the constant expression obtained by - adding 1 to the value of the previous enumeration constant. (The use of enumerators with - = may produce enumeration constants with values that duplicate other values in the same - enumeration.) The enumerators of an enumeration are also known as its members. -4 Each enumerated type shall be compatible with char, a signed integer type, or an - unsigned integer type. The choice of type is implementation-defined,128) but shall be - capable of representing the values of all the members of the enumeration. The - enumerated type is incomplete until immediately after the } that terminates the list of - enumerator declarations, and complete thereafter. - - - - - 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from - each other and from other identifiers declared in ordinary declarators. - 128) An implementation may delay the choice of which integer type until all enumeration constants have - been seen. - -[page 116] - -5 EXAMPLE The following fragment: - enum hue { chartreuse, burgundy, claret=20, winedark }; - enum hue col, *cp; - col = claret; - cp = &col; - if (*cp != burgundy) - /* ... */ - makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a - pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }. - - Forward references: tags (6.7.2.3). - 6.7.2.3 Tags - Constraints -1 A specific type shall have its content defined at most once. -2 Where two declarations that use the same tag declare the same type, they shall both use - the same choice of struct, union, or enum. -3 A type specifier of the form - enum identifier - without an enumerator list shall only appear after the type it specifies is complete. - Semantics -4 All declarations of structure, union, or enumerated types that have the same scope and - use the same tag declare the same type. Irrespective of whether there is a tag or what - other declarations of the type are in the same translation unit, the type is incomplete129) - until immediately after the closing brace of the list defining the content, and complete - thereafter. -5 Two declarations of structure, union, or enumerated types which are in different scopes or - use different tags declare distinct types. Each declaration of a structure, union, or - enumerated type which does not include a tag declares a distinct type. -6 A type specifier of the form - - - - - 129) An incomplete type may only by used when the size of an object of that type is not needed. It is not - needed, for example, when a typedef name is declared to be a specifier for a structure or union, or - when a pointer to or a function returning a structure or union is being declared. (See incomplete types - in 6.2.5.) The specification has to be complete before such a function is called or defined. - -[page 117] - - struct-or-union identifieropt { struct-declaration-list } - or - enum identifieropt { enumerator-list } - or - enum identifieropt { enumerator-list , } - declares a structure, union, or enumerated type. The list defines the structure content, - union content, or enumeration content. If an identifier is provided,130) the type specifier - also declares the identifier to be the tag of that type. -7 A declaration of the form - struct-or-union identifier ; - specifies a structure or union type and declares the identifier as a tag of that type.131) -8 If a type specifier of the form - struct-or-union identifier - occurs other than as part of one of the above forms, and no other declaration of the - identifier as a tag is visible, then it declares an incomplete structure or union type, and - declares the identifier as the tag of that type.131) -9 If a type specifier of the form - struct-or-union identifier - or - enum identifier - occurs other than as part of one of the above forms, and a declaration of the identifier as a - tag is visible, then it specifies the same type as that other declaration, and does not - redeclare the tag. -10 EXAMPLE 1 This mechanism allows declaration of a self-referential structure. - struct tnode { - int count; - struct tnode *left, *right; - }; - specifies a structure that contains an integer and two pointers to objects of the same type. Once this - declaration has been given, the declaration - - - - - 130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration - of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations - can make use of that typedef name to declare objects having the specified structure, union, or - enumerated type. - 131) A similar construction with enum does not exist. - -[page 118] - - struct tnode s, *sp; - declares s to be an object of the given type and sp to be a pointer to an object of the given type. With - these declarations, the expression sp->left refers to the left struct tnode pointer of the object to - which sp points; the expression s.right->count designates the count member of the right struct - tnode pointed to from s. -11 The following alternative formulation uses the typedef mechanism: - typedef struct tnode TNODE; - struct tnode { - int count; - TNODE *left, *right; - }; - TNODE s, *sp; - -12 EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential - structures, the declarations - struct s1 { struct s2 *s2p; /* ... */ }; // D1 - struct s2 { struct s1 *s1p; /* ... */ }; // D2 - specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already - declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in - D2. To eliminate this context sensitivity, the declaration - struct s2; - may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then - completes the specification of the new type. - - Forward references: declarators (6.7.6), type definitions (6.7.8). - 6.7.2.4 Atomic type specifiers - Syntax -1 atomic-type-specifier: - _Atomic ( type-name ) - Constraints -2 Atomic type specifiers shall not be used if the implementation does not support atomic - types (see 6.10.8.3). -3 The type name in an atomic type specifier shall not refer to an array type, a function type, - an atomic type, or a qualified type. - Semantics -4 The properties associated with atomic types are meaningful only for expressions that are - lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is - interpreted as a type specifier (with a type name), not as a type qualifier. - -[page 119] - - 6.7.3 Type qualifiers - Syntax -1 type-qualifier: - const - restrict - volatile - _Atomic - Constraints -2 Types other than pointer types whose referenced type is an object type shall not be - restrict-qualified. -3 The type modified by the _Atomic qualifier shall not be an array type or a function - type. - Semantics -4 The properties associated with qualified types are meaningful only for expressions that - are lvalues.132) -5 If the same qualifier appears more than once in the same specifier-qualifier-list, either - directly or via one or more typedefs, the behavior is the same as if it appeared only - once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier- - list, the resulting type is the so-qualified atomic type. -6 If an attempt is made to modify an object defined with a const-qualified type through use - of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is - made to refer to an object defined with a volatile-qualified type through use of an lvalue - with non-volatile-qualified type, the behavior is undefined.133) -7 An object that has volatile-qualified type may be modified in ways unknown to the - implementation or have other unknown side effects. Therefore any expression referring - to such an object shall be evaluated strictly according to the rules of the abstract machine, - as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the - object shall agree with that prescribed by the abstract machine, except as modified by the - - - - - 132) The implementation may place a const object that is not volatile in a read-only region of - storage. Moreover, the implementation need not allocate storage for such an object if its address is - never used. - 133) This applies to those objects that behave as if they were defined with qualified types, even if they are - never actually defined as objects in the program (such as an object at a memory-mapped input/output - address). - -[page 120] - - unknown factors mentioned previously.134) What constitutes an access to an object that - has volatile-qualified type is implementation-defined. -8 An object that is accessed through a restrict-qualified pointer has a special association - with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to - that object use, directly or indirectly, the value of that particular pointer.135) The intended - use of the restrict qualifier (like the register storage class) is to promote - optimization, and deleting all instances of the qualifier from all preprocessing translation - units composing a conforming program does not change its meaning (i.e., observable - behavior). -9 If the specification of an array type includes any type qualifiers, the element type is so- - qualified, not the array type. If the specification of a function type includes any type - qualifiers, the behavior is undefined.136) -10 For two qualified types to be compatible, both shall have the identically qualified version - of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers - does not affect the specified type. -11 EXAMPLE 1 An object declared - extern const volatile int real_time_clock; - may be modifiable by hardware, but cannot be assigned to, incremented, or decremented. - -12 EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers - modify an aggregate type: - const struct s { int mem; } cs = { 1 }; - struct s ncs; // the object ncs is modifiable - typedef int A[2][3]; - const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int - int *pi; - const int *pci; - ncs = cs; // valid - cs = ncs; // violates modifiable lvalue constraint for = - pi = &ncs.mem; // valid - pi = &cs.mem; // violates type constraints for = - pci = &cs.mem; // valid - pi = a[0]; // invalid: a[0] has type ''const int *'' - - - - 134) A volatile declaration may be used to describe an object corresponding to a memory-mapped - input/output port or an object accessed by an asynchronously interrupting function. Actions on - objects so declared shall not be ''optimized out'' by an implementation or reordered except as - permitted by the rules for evaluating expressions. - 135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this - association between the allocated object and the pointer. - 136) Both of these can occur through the use of typedefs. - -[page 121] - -13 EXAMPLE 3 The declaration - _Atomic volatile int *p; - specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type. - - 6.7.3.1 Formal definition of restrict -1 Let D be a declaration of an ordinary identifier that provides a means of designating an - object P as a restrict-qualified pointer to type T. -2 If D appears inside a block and does not have storage class extern, let B denote the - block. If D appears in the list of parameter declarations of a function definition, let B - denote the associated block. Otherwise, let B denote the block of main (or the block of - whatever function is called at program startup in a freestanding environment). -3 In what follows, a pointer expression E is said to be based on object P if (at some - sequence point in the execution of B prior to the evaluation of E) modifying P to point to - a copy of the array object into which it formerly pointed would change the value of E.137) - Note that ''based'' is defined only for expressions with pointer types. -4 During each execution of B, let L be any lvalue that has &L based on P. If L is used to - access the value of the object X that it designates, and X is also modified (by any means), - then the following requirements apply: T shall not be const-qualified. Every other lvalue - used to access the value of X shall also have its address based on P. Every access that - modifies X shall be considered also to modify P, for the purposes of this subclause. If P - is assigned the value of a pointer expression E that is based on another restricted pointer - object P2, associated with block B2, then either the execution of B2 shall begin before - the execution of B, or the execution of B2 shall end prior to the assignment. If these - requirements are not met, then the behavior is undefined. -5 Here an execution of B means that portion of the execution of the program that would - correspond to the lifetime of an object with scalar type and automatic storage duration - associated with B. -6 A translator is free to ignore any or all aliasing implications of uses of restrict. -7 EXAMPLE 1 The file scope declarations - int * restrict a; - int * restrict b; - extern int c[]; - assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the - program, then it is never accessed using either of the other two. - - - 137) In other words, E depends on the value of P itself rather than on the value of an object referenced - indirectly through P. For example, if identifier p has type (int **restrict), then the pointer - expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer - expressions *p and p[1] are not. - -[page 122] - -8 EXAMPLE 2 The function parameter declarations in the following example - void f(int n, int * restrict p, int * restrict q) - { - while (n-- > 0) - *p++ = *q++; - } - assert that, during each execution of the function, if an object is accessed through one of the pointer - parameters, then it is not also accessed through the other. -9 The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence - analysis of function f without examining any of the calls of f in the program. The cost is that the - programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the - second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through - both p and q. - void g(void) - { - extern int d[100]; - f(50, d + 50, d); // valid - f(50, d + 1, d); // undefined behavior - } - -10 EXAMPLE 3 The function parameter declarations - void h(int n, int * restrict p, int * restrict q, int * restrict r) - { - int i; - for (i = 0; i < n; i++) - p[i] = q[i] + r[i]; - } - illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b - are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not - modified within function h. - -11 EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a - function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments - between restricted pointers declared in nested blocks have defined behavior. - { - int * restrict p1; - int * restrict q1; - p1 = q1; // undefined behavior - { - int * restrict p2 = p1; // valid - int * restrict q2 = q1; // valid - p1 = q2; // undefined behavior - p2 = q2; // undefined behavior - } - } - -[page 123] - -12 The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more - precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For - example, this permits new_vector to return a vector. - typedef struct { int n; float * restrict v; } vector; - vector new_vector(int n) - { - vector t; - t.n = n; - t.v = malloc(n * sizeof (float)); - return t; - } - - 6.7.4 Function specifiers - Syntax -1 function-specifier: - inline - _Noreturn - Constraints -2 Function specifiers shall be used only in the declaration of an identifier for a function. -3 An inline definition of a function with external linkage shall not contain a definition of a - modifiable object with static or thread storage duration, and shall not contain a reference - to an identifier with internal linkage. -4 In a hosted environment, no function specifier(s) shall appear in a declaration of main. - Semantics -5 A function specifier may appear more than once; the behavior is the same as if it - appeared only once. -6 A function declared with an inline function specifier is an inline function. Making a * - function an inline function suggests that calls to the function be as fast as possible.138) - The extent to which such suggestions are effective is implementation-defined.139) - - - - - 138) By using, for example, an alternative to the usual function call mechanism, such as ''inline - substitution''. Inline substitution is not textual substitution, nor does it create a new function. - Therefore, for example, the expansion of a macro used within the body of the function uses the - definition it had at the point the function body appears, and not where the function is called; and - identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a - single address, regardless of the number of inline definitions that occur in addition to the external - definition. - 139) For example, an implementation might never perform inline substitution, or might only perform inline - substitutions to calls in the scope of an inline declaration. - -[page 124] - -7 Any function with internal linkage can be an inline function. For a function with external - linkage, the following restrictions apply: If a function is declared with an inline - function specifier, then it shall also be defined in the same translation unit. If all of the - file scope declarations for a function in a translation unit include the inline function - specifier without extern, then the definition in that translation unit is an inline - definition. An inline definition does not provide an external definition for the function, - and does not forbid an external definition in another translation unit. An inline definition - provides an alternative to an external definition, which a translator may use to implement - any call to the function in the same translation unit. It is unspecified whether a call to the - function uses the inline definition or the external definition.140) -8 A function declared with a _Noreturn function specifier shall not return to its caller. - Recommended practice -9 The implementation should produce a diagnostic message for a function declared with a - _Noreturn function specifier that appears to be capable of returning to its caller. -10 EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external - definition, or a definition available for use only within the translation unit. A file scope declaration with - extern creates an external definition. The following example shows an entire translation unit. - inline double fahr(double t) - { - return (9.0 * t) / 5.0 + 32.0; - } - inline double cels(double t) - { - return (5.0 * (t - 32.0)) / 9.0; - } - extern double fahr(double); // creates an external definition - double convert(int is_fahr, double temp) - { - /* A translator may perform inline substitutions */ - return is_fahr ? cels(temp) : fahr(temp); - } -11 Note that the definition of fahr is an external definition because fahr is also declared with extern, but - the definition of cels is an inline definition. Because cels has external linkage and is referenced, an - external definition has to appear in another translation unit (see 6.9); the inline definition and the external - definition are distinct and either may be used for the call. - -12 EXAMPLE 2 - - - - - 140) Since an inline definition is distinct from the corresponding external definition and from any other - corresponding inline definitions in other translation units, all corresponding objects with static storage - duration are also distinct in each of the definitions. - -[page 125] - - _Noreturn void f () { - abort(); // ok - } - _Noreturn void g (int i) { // causes undefined behavior if i <= 0 - if (i > 0) abort(); - } - - Forward references: function definitions (6.9.1). - 6.7.5 Alignment specifier - Syntax -1 alignment-specifier: - _Alignas ( type-name ) - _Alignas ( constant-expression ) - Constraints -2 An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or - a function, or a parameter, or an object declared with the register storage-class - specifier. -3 The constant expression shall be an integer constant expression. It shall evaluate to a - valid fundamental alignment, or to a valid extended alignment supported by the - implementation in the context in which it appears, or to zero. -4 The combined effect of all alignment attributes in a declaration shall not specify an - alignment that is less strict than the alignment that would otherwise be required for the - type of the object or member being declared. - Semantics -5 The first form is equivalent to _Alignas(alignof(type-name)). -6 The alignment requirement of the declared object or member is taken to be the specified - alignment. An alignment specification of zero has no effect.141) When multiple - alignment specifiers occur in a declaration, the effective alignment requirement is the - strictest specified alignment. -7 If the definition of an object has an alignment specifier, any other declaration of that - object shall either specify equivalent alignment or have no alignment specifier. If the - definition of an object does not have an alignment specifier, any other declaration of that - object shall also have no alignment specifier. If declarations of an object in different - translation units have different alignment specifiers, the behavior is undefined. - - - - 141) An alignment specification of zero also does not affect other alignment specifications in the same - declaration. - -[page 126] - - 6.7.6 Declarators - Syntax -1 declarator: - pointeropt direct-declarator - direct-declarator: - identifier - ( declarator ) - direct-declarator [ type-qualifier-listopt assignment-expressionopt ] - direct-declarator [ static type-qualifier-listopt assignment-expression ] - direct-declarator [ type-qualifier-list static assignment-expression ] - direct-declarator [ type-qualifier-listopt * ] - direct-declarator ( parameter-type-list ) - direct-declarator ( identifier-listopt ) - pointer: - * type-qualifier-listopt - * type-qualifier-listopt pointer - type-qualifier-list: - type-qualifier - type-qualifier-list type-qualifier - parameter-type-list: - parameter-list - parameter-list , ... - parameter-list: - parameter-declaration - parameter-list , parameter-declaration - parameter-declaration: - declaration-specifiers declarator - declaration-specifiers abstract-declaratoropt - identifier-list: - identifier - identifier-list , identifier - Semantics -2 Each declarator declares one identifier, and asserts that when an operand of the same - form as the declarator appears in an expression, it designates a function or object with the - scope, storage duration, and type indicated by the declaration specifiers. -3 A full declarator is a declarator that is not part of another declarator. The end of a full - declarator is a sequence point. If, in the nested sequence of declarators in a full - -[page 127] - - declarator, there is a declarator specifying a variable length array type, the type specified - by the full declarator is said to be variably modified. Furthermore, any type derived by - declarator type derivation from a variably modified type is itself variably modified. -4 In the following subclauses, consider a declaration - T D1 - where T contains the declaration specifiers that specify a type T (such as int) and D1 is - a declarator that contains an identifier ident. The type specified for the identifier ident in - the various forms of declarator is described inductively using this notation. -5 If, in the declaration ''T D1'', D1 has the form - identifier - then the type specified for ident is T . -6 If, in the declaration ''T D1'', D1 has the form - ( D ) - then ident has the type specified by the declaration ''T D''. Thus, a declarator in - parentheses is identical to the unparenthesized declarator, but the binding of complicated - declarators may be altered by parentheses. - Implementation limits -7 As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and - function declarators that modify an arithmetic, structure, union, or void type, either - directly or via one or more typedefs. - Forward references: array declarators (6.7.6.2), type definitions (6.7.8). - 6.7.6.1 Pointer declarators - Semantics -1 If, in the declaration ''T D1'', D1 has the form - * type-qualifier-listopt D - and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list - pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer. -2 For two pointer types to be compatible, both shall be identically qualified and both shall - be pointers to compatible types. -3 EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer - to a constant value'' and a ''constant pointer to a variable value''. - -[page 128] - - const int *ptr_to_constant; - int *const constant_ptr; - The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer, - but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the - int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the - same location. -4 The declaration of the constant pointer constant_ptr may be clarified by including a definition for the - type ''pointer to int''. - typedef int *int_ptr; - const int_ptr constant_ptr; - declares constant_ptr as an object that has type ''const-qualified pointer to int''. - - 6.7.6.2 Array declarators - Constraints -1 In addition to optional type qualifiers and the keyword static, the [ and ] may delimit - an expression or *. If they delimit an expression (which specifies the size of an array), the - expression shall have an integer type. If the expression is a constant expression, it shall - have a value greater than zero. The element type shall not be an incomplete or function - type. The optional type qualifiers and the keyword static shall appear only in a - declaration of a function parameter with an array type, and then only in the outermost - array type derivation. -2 If an identifier is declared as having a variably modified type, it shall be an ordinary - identifier (as defined in 6.2.3), have no linkage, and have either block scope or function - prototype scope. If an identifier is declared to be an object with static or thread storage - duration, it shall not have a variable length array type. - Semantics -3 If, in the declaration ''T D1'', D1 has one of the forms: - D[ type-qualifier-listopt assignment-expressionopt ] - D[ static type-qualifier-listopt assignment-expression ] - D[ type-qualifier-list static assignment-expression ] - D[ type-qualifier-listopt * ] - and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142) - (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.) -4 If the size is not present, the array type is an incomplete type. If the size is * instead of - being an expression, the array type is a variable length array type of unspecified size, - which can only be used in declarations or type names with function prototype scope;143) - - 142) When several ''array of'' specifications are adjacent, a multidimensional array is declared. - -[page 129] - - such arrays are nonetheless complete types. If the size is an integer constant expression - and the element type has a known constant size, the array type is not a variable length - array type; otherwise, the array type is a variable length array type. (Variable length - arrays are a conditional feature that implementations need not support; see 6.10.8.3.) -5 If the size is an expression that is not an integer constant expression: if it occurs in a - declaration at function prototype scope, it is treated as if it were replaced by *; otherwise, - each time it is evaluated it shall have a value greater than zero. The size of each instance - of a variable length array type does not change during its lifetime. Where a size - expression is part of the operand of a sizeof operator and changing the value of the - size expression would not affect the result of the operator, it is unspecified whether or not - the size expression is evaluated. -6 For two array types to be compatible, both shall have compatible element types, and if - both size specifiers are present, and are integer constant expressions, then both size - specifiers shall have the same constant value. If the two array types are used in a context - which requires them to be compatible, it is undefined behavior if the two size specifiers - evaluate to unequal values. -7 EXAMPLE 1 - float fa[11], *afp[17]; - declares an array of float numbers and an array of pointers to float numbers. - -8 EXAMPLE 2 Note the distinction between the declarations - extern int *x; - extern int y[]; - The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size - (an incomplete type), the storage for which is defined elsewhere. - -9 EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types. - extern int n; - extern int m; - void fcompat(void) - { - int a[n][6][m]; - int (*p)[4][n+1]; - int c[n][n][6][m]; - int (*r)[n][n][n+1]; - p = a; // invalid: not compatible because 4 != 6 - r = c; // compatible, but defined behavior only if - // n == 6 and m == n+1 - } - - - - - 143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3). - -[page 130] - -10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or - function prototype scope. Array objects declared with the _Thread_local, static, or extern - storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with - the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all - identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of - structures or unions. - extern int n; - int A[n]; // invalid: file scope VLA - extern int (*p2)[n]; // invalid: file scope VM - int B[100]; // valid: file scope but not VM - void fvla(int m, int C[m][m]); // valid: VLA with prototype scope - void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA - { - typedef int VLA[m][m]; // valid: block scope typedef VLA - struct tag { - int (*y)[n]; // invalid: y not ordinary identifier - int z[n]; // invalid: z not ordinary identifier - }; - int D[m]; // valid: auto VLA - static int E[m]; // invalid: static block scope VLA - extern int F[m]; // invalid: F has linkage and is VLA - int (*s)[m]; // valid: auto pointer to VLA - extern int (*r)[m]; // invalid: r has linkage and points to VLA - static int (*q)[m] = &B; // valid: q is a static block pointer to VLA - } - - Forward references: function declarators (6.7.6.3), function definitions (6.9.1), - initialization (6.7.9). - 6.7.6.3 Function declarators (including prototypes) - Constraints -1 A function declarator shall not specify a return type that is a function type or an array - type. -2 The only storage-class specifier that shall occur in a parameter declaration is register. -3 An identifier list in a function declarator that is not part of a definition of that function - shall be empty. -4 After adjustment, the parameters in a parameter type list in a function declarator that is - part of a definition of that function shall not have incomplete type. - Semantics -5 If, in the declaration ''T D1'', D1 has the form - -[page 131] - - D( parameter-type-list ) - or - D( identifier-listopt ) - and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list - T '', then the type specified for ident is ''derived-declarator-type-list function returning - T ''. -6 A parameter type list specifies the types of, and may declare identifiers for, the - parameters of the function. -7 A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to - type'', where the type qualifiers (if any) are those specified within the [ and ] of the - array type derivation. If the keyword static also appears within the [ and ] of the - array type derivation, then for each call to the function, the value of the corresponding - actual argument shall provide access to the first element of an array with at least as many - elements as specified by the size expression. -8 A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to - function returning type'', as in 6.3.2.1. -9 If the list terminates with an ellipsis (, ...), no information about the number or types - of the parameters after the comma is supplied.144) -10 The special case of an unnamed parameter of type void as the only item in the list - specifies that the function has no parameters. -11 If, in a parameter declaration, an identifier can be treated either as a typedef name or as a - parameter name, it shall be taken as a typedef name. -12 If the function declarator is not part of a definition of that function, parameters may have - incomplete type and may use the [*] notation in their sequences of declarator specifiers - to specify variable length array types. -13 The storage-class specifier in the declaration specifiers for a parameter declaration, if - present, is ignored unless the declared parameter is one of the members of the parameter - type list for a function definition. -14 An identifier list declares only the identifiers of the parameters of the function. An empty - list in a function declarator that is part of a definition of that function specifies that the - function has no parameters. The empty list in a function declarator that is not part of a - definition of that function specifies that no information about the number or types of the - parameters is supplied.145) - - - - 144) The macros defined in the header (7.16) may be used to access arguments that - correspond to the ellipsis. - -[page 132] - -15 For two function types to be compatible, both shall specify compatible return types.146) - Moreover, the parameter type lists, if both are present, shall agree in the number of - parameters and in use of the ellipsis terminator; corresponding parameters shall have - compatible types. If one type has a parameter type list and the other type is specified by a - function declarator that is not part of a function definition and that contains an empty - identifier list, the parameter list shall not have an ellipsis terminator and the type of each - parameter shall be compatible with the type that results from the application of the - default argument promotions. If one type has a parameter type list and the other type is - specified by a function definition that contains a (possibly empty) identifier list, both shall - agree in the number of parameters, and the type of each prototype parameter shall be - compatible with the type that results from the application of the default argument - promotions to the type of the corresponding identifier. (In the determination of type - compatibility and of a composite type, each parameter declared with function or array - type is taken as having the adjusted type and each parameter declared with qualified type - is taken as having the unqualified version of its declared type.) -16 EXAMPLE 1 The declaration - int f(void), *fip(), (*pfi)(); - declares a function f with no parameters returning an int, a function fip with no parameter specification - returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an - int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the - declaration suggests, and the same construction in an expression requires, the calling of a function fip, - and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the - extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function - designator, which is then used to call the function; it returns an int. -17 If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the - declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either - internal or external linkage (depending on what file scope declarations for these identifiers are visible), and - the identifier of the pointer pfi has block scope and no linkage. - -18 EXAMPLE 2 The declaration - int (*apfi[3])(int *x, int *y); - declares an array apfi of three pointers to functions returning int. Each of these functions has two - parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and - go out of scope at the end of the declaration of apfi. - -19 EXAMPLE 3 The declaration - int (*fpfi(int (*)(long), int))(int, ...); - declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two - parameters: a pointer to a function returning an int (with one parameter of type long int), and an int. - The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more - - - 145) See ''future language directions'' (6.11.6). - 146) If both function types are ''old style'', parameter types are not compared. - -[page 133] - - additional arguments of any type. - -20 EXAMPLE 4 The following prototype has a variably modified parameter. - void addscalar(int n, int m, - double a[n][n*m+300], double x); - int main() - { - double b[4][308]; - addscalar(4, 2, b, 2.17); - return 0; - } - void addscalar(int n, int m, - double a[n][n*m+300], double x) - { - for (int i = 0; i < n; i++) - for (int j = 0, k = n*m+300; j < k; j++) - // a is a pointer to a VLA with n*m+300 elements - a[i][j] += x; - } - -21 EXAMPLE 5 The following are all compatible function prototype declarators. - double maximum(int n, int m, double a[n][m]); - double maximum(int n, int m, double a[*][*]); - double maximum(int n, int m, double a[ ][*]); - double maximum(int n, int m, double a[ ][m]); - as are: - void f(double (* restrict a)[5]); - void f(double a[restrict][5]); - void f(double a[restrict 3][5]); - void f(double a[restrict static 3][5]); - (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a - non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.) - - Forward references: function definitions (6.9.1), type names (6.7.7). - -[page 134] - - 6.7.7 Type names - Syntax -1 type-name: - specifier-qualifier-list abstract-declaratoropt - abstract-declarator: - pointer - pointeropt direct-abstract-declarator - direct-abstract-declarator: - ( abstract-declarator ) - direct-abstract-declaratoropt [ type-qualifier-listopt - assignment-expressionopt ] - direct-abstract-declaratoropt [ static type-qualifier-listopt - assignment-expression ] - direct-abstract-declaratoropt [ type-qualifier-list static - assignment-expression ] - direct-abstract-declaratoropt [ * ] - direct-abstract-declaratoropt ( parameter-type-listopt ) - Semantics -2 In several contexts, it is necessary to specify a type. This is accomplished using a type - name, which is syntactically a declaration for a function or an object of that type that - omits the identifier.147) -3 EXAMPLE The constructions - (a) int - (b) int * - (c) int *[3] - (d) int (*)[3] - (e) int (*)[*] - (f) int *() - (g) int (*)(void) - (h) int (*const [])(unsigned int, ...) - name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an - array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function - with no parameter specification returning a pointer to int, (g) pointer to function with no parameters - returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one - parameter that has type unsigned int and an unspecified number of other parameters, returning an - int. - - - - - 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no - parameter specification'', rather than redundant parentheses around the omitted identifier. - -[page 135] - - 6.7.8 Type definitions - Syntax -1 typedef-name: - identifier - Constraints -2 If a typedef name specifies a variably modified type then it shall have block scope. - Semantics -3 In a declaration whose storage-class specifier is typedef, each declarator defines an - identifier to be a typedef name that denotes the type specified for the identifier in the way - described in 6.7.6. Any array size expressions associated with variable length array - declarators are evaluated each time the declaration of the typedef name is reached in the - order of execution. A typedef declaration does not introduce a new type, only a - synonym for the type so specified. That is, in the following declarations: - typedef T type_ident; - type_ident D; - type_ident is defined as a typedef name with the type specified by the declaration - specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator- - type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A - typedef name shares the same name space as other identifiers declared in ordinary - declarators. -4 EXAMPLE 1 After - typedef int MILES, KLICKSP(); - typedef struct { double hi, lo; } range; - the constructions - MILES distance; - extern KLICKSP *metricp; - range x; - range z, *zp; - are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no - parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to - such a structure. The object distance has a type compatible with any other int object. - -5 EXAMPLE 2 After the declarations - typedef struct s1 { int x; } t1, *tp1; - typedef struct s2 { int x; } t2, *tp2; - type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct - s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int. - -[page 136] - -6 EXAMPLE 3 The following obscure constructions - typedef signed int t; - typedef int plain; - struct tag { - unsigned t:4; - const t:5; - plain r:5; - }; - declare a typedef name t with type signed int, a typedef name plain with type int, and a structure - with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const- - qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or - [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15]. - (The choice of range is implementation-defined.) The first two bit-field declarations differ in that - unsigned is a type specifier (which forces t to be the name of a structure member), while const is a - type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed - in an inner scope by - t f(t (t)); - long t; - then a function f is declared with type ''function returning signed int with one unnamed parameter - with type pointer to function returning signed int with one unnamed parameter with type signed - int'', and an identifier t with type long int. - -7 EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the - following declarations of the signal function specify exactly the same type, the first without making use - of any typedef names. - typedef void fv(int), (*pfv)(int); - void (*signal(int, void (*)(int)))(int); - fv *signal(int, fv *); - pfv signal(int, pfv); - -8 EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the - time the typedef name is defined, not each time it is used: - void copyt(int n) - { - typedef int B[n]; // B is n ints, n evaluated now - n += 1; - B a; // a is n ints, n without += 1 - int b[n]; // a and b are different sizes - for (int i = 1; i < n; i++) - a[i-1] = b[i]; - } - -[page 137] - - 6.7.9 Initialization - Syntax -1 initializer: - assignment-expression - { initializer-list } - { initializer-list , } - initializer-list: - designationopt initializer - initializer-list , designationopt initializer - designation: - designator-list = - designator-list: - designator - designator-list designator - designator: - [ constant-expression ] - . identifier - Constraints -2 No initializer shall attempt to provide a value for an object not contained within the entity - being initialized. -3 The type of the entity to be initialized shall be an array of unknown size or a complete - object type that is not a variable length array type. -4 All the expressions in an initializer for an object that has static or thread storage duration - shall be constant expressions or string literals. -5 If the declaration of an identifier has block scope, and the identifier has external or - internal linkage, the declaration shall have no initializer for the identifier. -6 If a designator has the form - [ constant-expression ] - then the current object (defined below) shall have array type and the expression shall be - an integer constant expression. If the array is of unknown size, any nonnegative value is - valid. -7 If a designator has the form - . identifier - then the current object (defined below) shall have structure or union type and the - identifier shall be the name of a member of that type. - -[page 138] - - Semantics -8 An initializer specifies the initial value stored in an object. -9 Except where explicitly stated otherwise, for the purposes of this subclause unnamed - members of objects of structure and union type do not participate in initialization. - Unnamed members of structure objects have indeterminate value even after initialization. -10 If an object that has automatic storage duration is not initialized explicitly, its value is - indeterminate. If an object that has static or thread storage duration is not initialized - explicitly, then: - -- if it has pointer type, it is initialized to a null pointer; - -- if it has arithmetic type, it is initialized to (positive or unsigned) zero; - -- if it is an aggregate, every member is initialized (recursively) according to these rules, - and any padding is initialized to zero bits; - -- if it is a union, the first named member is initialized (recursively) according to these - rules, and any padding is initialized to zero bits; -11 The initializer for a scalar shall be a single expression, optionally enclosed in braces. The - initial value of the object is that of the expression (after conversion); the same type - constraints and conversions as for simple assignment apply, taking the type of the scalar - to be the unqualified version of its declared type. -12 The rest of this subclause deals with initializers for objects that have aggregate or union - type. -13 The initializer for a structure or union object that has automatic storage duration shall be - either an initializer list as described below, or a single expression that has compatible - structure or union type. In the latter case, the initial value of the object, including - unnamed members, is that of the expression. -14 An array of character type may be initialized by a character string literal or UTF-8 string - literal, optionally enclosed in braces. Successive bytes of the string literal (including the - terminating null character if there is room or if the array is of unknown size) initialize the - elements of the array. -15 An array with element type compatible with a qualified or unqualified version of - wchar_t may be initialized by a wide string literal, optionally enclosed in braces. - Successive wide characters of the wide string literal (including the terminating null wide - character if there is room or if the array is of unknown size) initialize the elements of the - array. -16 Otherwise, the initializer for an object that has aggregate or union type shall be a brace- - enclosed list of initializers for the elements or named members. - -[page 139] - -17 Each brace-enclosed initializer list has an associated current object. When no - designations are present, subobjects of the current object are initialized in order according - to the type of the current object: array elements in increasing subscript order, structure - members in declaration order, and the first named member of a union.148) In contrast, a - designation causes the following initializer to begin initialization of the subobject - described by the designator. Initialization then continues forward in order, beginning - with the next subobject after that described by the designator.149) -18 Each designator list begins its description with the current object associated with the - closest surrounding brace pair. Each item in the designator list (in order) specifies a - particular member of its current object and changes the current object for the next - designator (if any) to be that member.150) The current object that results at the end of the - designator list is the subobject to be initialized by the following initializer. -19 The initialization shall occur in initializer list order, each initializer provided for a - particular subobject overriding any previously listed initializer for the same subobject;151) - all subobjects that are not initialized explicitly shall be initialized implicitly the same as - objects that have static storage duration. -20 If the aggregate or union contains elements or members that are aggregates or unions, - these rules apply recursively to the subaggregates or contained unions. If the initializer of - a subaggregate or contained union begins with a left brace, the initializers enclosed by - that brace and its matching right brace initialize the elements or members of the - subaggregate or the contained union. Otherwise, only enough initializers from the list are - taken to account for the elements or members of the subaggregate or the first member of - the contained union; any remaining initializers are left to initialize the next element or - member of the aggregate of which the current subaggregate or contained union is a part. -21 If there are fewer initializers in a brace-enclosed list than there are elements or members - of an aggregate, or fewer characters in a string literal used to initialize an array of known - size than there are elements in the array, the remainder of the aggregate shall be - initialized implicitly the same as objects that have static storage duration. - - - - 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its - subobjects are initialized as usual, but the subaggregate or contained union does not become the - current object: current objects are associated only with brace-enclosed initializer lists. - 149) After a union member is initialized, the next object is not the next member of the union; instead, it is - the next subobject of an object containing the union. - 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with - the surrounding brace pair. Note, too, that each separate designator list is independent. - 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might - not be evaluated at all. - -[page 140] - -22 If an array of unknown size is initialized, its size is determined by the largest indexed - element with an explicit initializer. The array type is completed at the end of its - initializer list. -23 The evaluations of the initialization list expressions are indeterminately sequenced with - respect to one another and thus the order in which any side effects occur is - unspecified.152) -24 EXAMPLE 1 Provided that has been #included, the declarations - int i = 3.5; - double complex c = 5 + 3 * I; - define and initialize i with the value 3 and c with the value 5.0 + i3.0. - -25 EXAMPLE 2 The declaration - int x[] = { 1, 3, 5 }; - defines and initializes x as a one-dimensional array object that has three elements, as no size was specified - and there are three initializers. - -26 EXAMPLE 3 The declaration - int y[4][3] = { - { 1, 3, 5 }, - { 2, 4, 6 }, - { 3, 5, 7 }, - }; - is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object - y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and - y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have - been achieved by - int y[4][3] = { - 1, 3, 5, 2, 4, 6, 3, 5, 7 - }; - The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the - next three are taken successively for y[1] and y[2]. - -27 EXAMPLE 4 The declaration - int z[4][3] = { - { 1 }, { 2 }, { 3 }, { 4 } - }; - initializes the first column of z as specified and initializes the rest with zeros. - -28 EXAMPLE 5 The declaration - struct { int a[3], b; } w[] = { { 1 }, 2 }; - is a definition with an inconsistently bracketed initialization. It defines an array with two element - - - - 152) In particular, the evaluation order need not be the same as the order of subobject initialization. - -[page 141] - - structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero. - -29 EXAMPLE 6 The declaration - short q[4][3][2] = { - { 1 }, - { 2, 3 }, - { 4, 5, 6 } - }; - contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array - object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize - q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for - q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is - only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers - for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their - respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a - diagnostic message would have been issued. The same initialization result could have been achieved by: - short q[4][3][2] = { - 1, 0, 0, 0, 0, 0, - 2, 3, 0, 0, 0, 0, - 4, 5, 6 - }; - or by: - short q[4][3][2] = { - { - { 1 }, - }, - { - { 2, 3 }, - }, - { - { 4, 5 }, - { 6 }, - } - }; - in a fully bracketed form. -30 Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to - cause confusion. - -31 EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the - declaration - typedef int A[]; // OK - declared with block scope - the declaration - A a = { 1, 2 }, b = { 3, 4, 5 }; - is identical to - int a[] = { 1, 2 }, b[] = { 3, 4, 5 }; - due to the rules for incomplete types. - -[page 142] - -32 EXAMPLE 8 The declaration - char s[] = "abc", t[3] = "abc"; - defines ''plain'' char array objects s and t whose elements are initialized with character string literals. - This declaration is identical to - char s[] = { 'a', 'b', 'c', '\0' }, - t[] = { 'a', 'b', 'c' }; - The contents of the arrays are modifiable. On the other hand, the declaration - char *p = "abc"; - defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char'' - with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to - modify the contents of the array, the behavior is undefined. - -33 EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using - designators: - enum { member_one, member_two }; - const char *nm[] = { - [member_two] = "member two", - [member_one] = "member one", - }; - -34 EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order: - div_t answer = { .quot = 2, .rem = -1 }; - -35 EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists - might be misunderstood: - struct { int a[3], b; } w[] = - { [0].a = {1}, [1].a[0] = 2 }; - -36 EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator: - int a[MAX] = { - 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0 - }; -37 In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less - than ten, some of the values provided by the first five initializers will be overridden by the second five. - -38 EXAMPLE 13 Any member of a union can be initialized: - union { /* ... */ } u = { .any_member = 42 }; - - Forward references: common definitions (7.19). - -[page 143] - - 6.7.10 Static assertions - Syntax -1 static_assert-declaration: - _Static_assert ( constant-expression , string-literal ) ; - Constraints -2 The constant expression shall compare unequal to 0. - Semantics -3 The constant expression shall be an integer constant expression. If the value of the - constant expression compares unequal to 0, the declaration has no effect. Otherwise, the - constraint is violated and the implementation shall produce a diagnostic message that - includes the text of the string literal, except that characters not in the basic source - character set are not required to appear in the message. - Forward references: diagnostics (7.2). - -[page 144] - - 6.8 Statements and blocks - Syntax -1 statement: - labeled-statement - compound-statement - expression-statement - selection-statement - iteration-statement - jump-statement - Semantics -2 A statement specifies an action to be performed. Except as indicated, statements are - executed in sequence. -3 A block allows a set of declarations and statements to be grouped into one syntactic unit. - The initializers of objects that have automatic storage duration, and the variable length - array declarators of ordinary identifiers with block scope, are evaluated and the values are - stored in the objects (including storing an indeterminate value in objects without an - initializer) each time the declaration is reached in the order of execution, as if it were a - statement, and within each declaration in the order that declarators appear. -4 A full expression is an expression that is not part of another expression or of a declarator. - Each of the following is a full expression: an initializer that is not part of a compound - literal; the expression in an expression statement; the controlling expression of a selection - statement (if or switch); the controlling expression of a while or do statement; each - of the (optional) expressions of a for statement; the (optional) expression in a return - statement. There is a sequence point between the evaluation of a full expression and the - evaluation of the next full expression to be evaluated. - Forward references: expression and null statements (6.8.3), selection statements - (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4). - 6.8.1 Labeled statements - Syntax -1 labeled-statement: - identifier : statement - case constant-expression : statement - default : statement - Constraints -2 A case or default label shall appear only in a switch statement. Further - constraints on such labels are discussed under the switch statement. - -[page 145] - -3 Label names shall be unique within a function. - Semantics -4 Any statement may be preceded by a prefix that declares an identifier as a label name. - Labels in themselves do not alter the flow of control, which continues unimpeded across - them. - Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2). - 6.8.2 Compound statement - Syntax -1 compound-statement: - { block-item-listopt } - block-item-list: - block-item - block-item-list block-item - block-item: - declaration - statement - Semantics -2 A compound statement is a block. - 6.8.3 Expression and null statements - Syntax -1 expression-statement: - expressionopt ; - Semantics -2 The expression in an expression statement is evaluated as a void expression for its side - effects.153) -3 A null statement (consisting of just a semicolon) performs no operations. -4 EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the - discarding of its value may be made explicit by converting the expression to a void expression by means of - a cast: - int p(int); - /* ... */ - (void)p(0); - - - - 153) Such as assignments, and function calls which have side effects. - -[page 146] - -5 EXAMPLE 2 In the program fragment - char *s; - /* ... */ - while (*s++ != '\0') - ; - a null statement is used to supply an empty loop body to the iteration statement. - -6 EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound - statement. - while (loop1) { - /* ... */ - while (loop2) { - /* ... */ - if (want_out) - goto end_loop1; - /* ... */ - } - /* ... */ - end_loop1: ; - } - - Forward references: iteration statements (6.8.5). - 6.8.4 Selection statements - Syntax -1 selection-statement: - if ( expression ) statement - if ( expression ) statement else statement - switch ( expression ) statement - Semantics -2 A selection statement selects among a set of statements depending on the value of a - controlling expression. -3 A selection statement is a block whose scope is a strict subset of the scope of its - enclosing block. Each associated substatement is also a block whose scope is a strict - subset of the scope of the selection statement. - 6.8.4.1 The if statement - Constraints -1 The controlling expression of an if statement shall have scalar type. - Semantics -2 In both forms, the first substatement is executed if the expression compares unequal to 0. - In the else form, the second substatement is executed if the expression compares equal - -[page 147] - - to 0. If the first substatement is reached via a label, the second substatement is not - executed. -3 An else is associated with the lexically nearest preceding if that is allowed by the - syntax. - 6.8.4.2 The switch statement - Constraints -1 The controlling expression of a switch statement shall have integer type. -2 If a switch statement has an associated case or default label within the scope of an - identifier with a variably modified type, the entire switch statement shall be within the - scope of that identifier.154) -3 The expression of each case label shall be an integer constant expression and no two of - the case constant expressions in the same switch statement shall have the same value - after conversion. There may be at most one default label in a switch statement. - (Any enclosed switch statement may have a default label or case constant - expressions with values that duplicate case constant expressions in the enclosing - switch statement.) - Semantics -4 A switch statement causes control to jump to, into, or past the statement that is the - switch body, depending on the value of a controlling expression, and on the presence of a - default label and the values of any case labels on or in the switch body. A case or - default label is accessible only within the closest enclosing switch statement. -5 The integer promotions are performed on the controlling expression. The constant - expression in each case label is converted to the promoted type of the controlling - expression. If a converted value matches that of the promoted controlling expression, - control jumps to the statement following the matched case label. Otherwise, if there is - a default label, control jumps to the labeled statement. If no converted case constant - expression matches and there is no default label, no part of the switch body is - executed. - Implementation limits -6 As discussed in 5.2.4.1, the implementation may limit the number of case values in a - switch statement. - - - - - 154) That is, the declaration either precedes the switch statement, or it follows the last case or - default label associated with the switch that is in the block containing the declaration. - -[page 148] - -7 EXAMPLE In the artificial program fragment - switch (expr) - { - int i = 4; - f(i); - case 0: - i = 17; - /* falls through into default code */ - default: - printf("%d\n", i); - } - the object whose identifier is i exists with automatic storage duration (within the block) but is never - initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will - access an indeterminate value. Similarly, the call to the function f cannot be reached. - - 6.8.5 Iteration statements - Syntax -1 iteration-statement: - while ( expression ) statement - do statement while ( expression ) ; - for ( expressionopt ; expressionopt ; expressionopt ) statement - for ( declaration expressionopt ; expressionopt ) statement - Constraints -2 The controlling expression of an iteration statement shall have scalar type. -3 The declaration part of a for statement shall only declare identifiers for objects having - storage class auto or register. - Semantics -4 An iteration statement causes a statement called the loop body to be executed repeatedly - until the controlling expression compares equal to 0. The repetition occurs regardless of - whether the loop body is entered from the iteration statement or by a jump.155) -5 An iteration statement is a block whose scope is a strict subset of the scope of its - enclosing block. The loop body is also a block whose scope is a strict subset of the scope - of the iteration statement. -6 An iteration statement whose controlling expression is not a constant expression,156) that - performs no input/output operations, does not access volatile objects, and performs no - synchronization or atomic operations in its body, controlling expression, or (in the case of - - 155) Code jumped over is not executed. In particular, the controlling expression of a for or while - statement is not evaluated before entering the loop body, nor is clause-1 of a for statement. - 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression. - -[page 149] - - a for statement) its expression-3, may be assumed by the implementation to - terminate.157) - 6.8.5.1 The while statement -1 The evaluation of the controlling expression takes place before each execution of the loop - body. - 6.8.5.2 The do statement -1 The evaluation of the controlling expression takes place after each execution of the loop - body. - 6.8.5.3 The for statement -1 The statement - for ( clause-1 ; expression-2 ; expression-3 ) statement - behaves as follows: The expression expression-2 is the controlling expression that is - evaluated before each execution of the loop body. The expression expression-3 is - evaluated as a void expression after each execution of the loop body. If clause-1 is a - declaration, the scope of any identifiers it declares is the remainder of the declaration and - the entire loop, including the other two expressions; it is reached in the order of execution - before the first evaluation of the controlling expression. If clause-1 is an expression, it is - evaluated as a void expression before the first evaluation of the controlling expression.158) -2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a - nonzero constant. - 6.8.6 Jump statements - Syntax -1 jump-statement: - goto identifier ; - continue ; - break ; - return expressionopt ; - - - - - 157) This is intended to allow compiler transformations such as removal of empty loops even when - termination cannot be proven. - 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in - the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration, - such that execution of the loop continues until the expression compares equal to 0; and expression-3 - specifies an operation (such as incrementing) that is performed after each iteration. - -[page 150] - - Semantics -2 A jump statement causes an unconditional jump to another place. - 6.8.6.1 The goto statement - Constraints -1 The identifier in a goto statement shall name a label located somewhere in the enclosing - function. A goto statement shall not jump from outside the scope of an identifier having - a variably modified type to inside the scope of that identifier. - Semantics -2 A goto statement causes an unconditional jump to the statement prefixed by the named - label in the enclosing function. -3 EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The - following outline presents one possible approach to a problem based on these three assumptions: - 1. The general initialization code accesses objects only visible to the current function. - 2. The general initialization code is too large to warrant duplication. - 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by - continue statements, for example.) - /* ... */ - goto first_time; - for (;;) { - // determine next operation - /* ... */ - if (need to reinitialize) { - // reinitialize-only code - /* ... */ - first_time: - // general initialization code - /* ... */ - continue; - } - // handle other operations - /* ... */ - } - -[page 151] - -4 EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably - modified types. A jump within the scope, however, is permitted. - goto lab3; // invalid: going INTO scope of VLA. - { - double a[n]; - a[j] = 4.4; - lab3: - a[j] = 3.3; - goto lab4; // valid: going WITHIN scope of VLA. - a[j] = 5.5; - lab4: - a[j] = 6.6; - } - goto lab4; // invalid: going INTO scope of VLA. - - 6.8.6.2 The continue statement - Constraints -1 A continue statement shall appear only in or as a loop body. - Semantics -2 A continue statement causes a jump to the loop-continuation portion of the smallest - enclosing iteration statement; that is, to the end of the loop body. More precisely, in each - of the statements - while (/* ... */) { do { for (/* ... */) { - /* ... */ /* ... */ /* ... */ - continue; continue; continue; - /* ... */ /* ... */ /* ... */ - contin: ; contin: ; contin: ; - } } while (/* ... */); } - unless the continue statement shown is in an enclosed iteration statement (in which - case it is interpreted within that statement), it is equivalent to goto contin;.159) - 6.8.6.3 The break statement - Constraints -1 A break statement shall appear only in or as a switch body or loop body. - Semantics -2 A break statement terminates execution of the smallest enclosing switch or iteration - statement. - - - - 159) Following the contin: label is a null statement. - -[page 152] - - 6.8.6.4 The return statement - Constraints -1 A return statement with an expression shall not appear in a function whose return type - is void. A return statement without an expression shall only appear in a function - whose return type is void. - Semantics -2 A return statement terminates execution of the current function and returns control to - its caller. A function may have any number of return statements. -3 If a return statement with an expression is executed, the value of the expression is - returned to the caller as the value of the function call expression. If the expression has a - type different from the return type of the function in which it appears, the value is - converted as if by assignment to an object having the return type of the function.160) -4 EXAMPLE In: - struct s { double i; } f(void); - union { - struct { - int f1; - struct s f2; - } u1; - struct { - struct s f3; - int f4; - } u2; - } g; - struct s f(void) - { - return g.u1.f2; - } - /* ... */ - g.u2.f3 = f(); - there is no undefined behavior, although there would be if the assignment were done directly (without using - a function call to fetch the value). - - - - - 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not - apply to the case of function return. The representation of floating-point values may have wider range - or precision than implied by the type; a cast may be used to remove this extra range and precision. - -[page 153] - - 6.9 External definitions - Syntax -1 translation-unit: - external-declaration - translation-unit external-declaration - external-declaration: - function-definition - declaration - Constraints -2 The storage-class specifiers auto and register shall not appear in the declaration - specifiers in an external declaration. -3 There shall be no more than one external definition for each identifier declared with - internal linkage in a translation unit. Moreover, if an identifier declared with internal - linkage is used in an expression (other than as a part of the operand of a sizeof - operator whose result is an integer constant), there shall be exactly one external definition - for the identifier in the translation unit. - Semantics -4 As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit, - which consists of a sequence of external declarations. These are described as ''external'' - because they appear outside any function (and hence have file scope). As discussed in - 6.7, a declaration that also causes storage to be reserved for an object or a function named - by the identifier is a definition. -5 An external definition is an external declaration that is also a definition of a function - (other than an inline definition) or an object. If an identifier declared with external - linkage is used in an expression (other than as part of the operand of a sizeof operator - whose result is an integer constant), somewhere in the entire program there shall be - exactly one external definition for the identifier; otherwise, there shall be no more than - one.161) - - - - - 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no - external definition for it. - -[page 154] - - 6.9.1 Function definitions - Syntax -1 function-definition: - declaration-specifiers declarator declaration-listopt compound-statement - declaration-list: - declaration - declaration-list declaration - Constraints -2 The identifier declared in a function definition (which is the name of the function) shall - have a function type, as specified by the declarator portion of the function definition.162) -3 The return type of a function shall be void or a complete object type other than array - type. -4 The storage-class specifier, if any, in the declaration specifiers shall be either extern or - static. -5 If the declarator includes a parameter type list, the declaration of each parameter shall - include an identifier, except for the special case of a parameter list consisting of a single - parameter of type void, in which case there shall not be an identifier. No declaration list - shall follow. -6 If the declarator includes an identifier list, each declaration in the declaration list shall - have at least one declarator, those declarators shall declare only identifiers from the - identifier list, and every identifier in the identifier list shall be declared. An identifier - declared as a typedef name shall not be redeclared as a parameter. The declarations in the - declaration list shall contain no storage-class specifier other than register and no - initializations. - - - - 162) The intent is that the type category in a function definition cannot be inherited from a typedef: - typedef int F(void); // type F is ''function with no parameters - // returning int'' - F f, g; // f and g both have type compatible with F - F f { /* ... */ } // WRONG: syntax/constraint error - F g() { /* ... */ } // WRONG: declares that g returns a function - int f(void) { /* ... */ } // RIGHT: f has type compatible with F - int g() { /* ... */ } // RIGHT: g has type compatible with F - F *e(void) { /* ... */ } // e returns a pointer to a function - F *((e))(void) { /* ... */ } // same: parentheses irrelevant - int (*fp)(void); // fp points to a function that has type F - F *Fp; // Fp points to a function that has type F - -[page 155] - - Semantics -7 The declarator in a function definition specifies the name of the function being defined - and the identifiers of its parameters. If the declarator includes a parameter type list, the - list also specifies the types of all the parameters; such a declarator also serves as a - function prototype for later calls to the same function in the same translation unit. If the - declarator includes an identifier list,163) the types of the parameters shall be declared in a - following declaration list. In either case, the type of each parameter is adjusted as - described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object - type. -8 If a function that accepts a variable number of arguments is defined without a parameter - type list that ends with the ellipsis notation, the behavior is undefined. -9 Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout - of the storage for parameters is unspecified. -10 On entry to the function, the size expressions of each variably modified parameter are - evaluated and the value of each argument expression is converted to the type of the - corresponding parameter as if by assignment. (Array expressions and function - designators as arguments were converted to pointers before the call.) -11 After all parameters have been assigned, the compound statement that constitutes the - body of the function definition is executed. -12 If the } that terminates a function is reached, and the value of the function call is used by - the caller, the behavior is undefined. -13 EXAMPLE 1 In the following: - extern int max(int a, int b) - { - return a > b ? a : b; - } - extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the - function declarator; and - { return a > b ? a : b; } - is the function body. The following similar definition uses the identifier-list form for the parameter - declarations: - - - - - 163) See ''future language directions'' (6.11.7). - 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block. - -[page 156] - - extern int max(a, b) - int a, b; - { - return a > b ? a : b; - } - Here int a, b; is the declaration list for the parameters. The difference between these two definitions is - that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls - to the function, whereas the second form does not. - -14 EXAMPLE 2 To pass one function to another, one might say - int f(void); - /* ... */ - g(f); - Then the definition of g might read - void g(int (*funcp)(void)) - { - /* ... */ - (*funcp)(); /* or funcp(); ... */ - } - or, equivalently, - void g(int func(void)) - { - /* ... */ - func(); /* or (*func)(); ... */ - } - - 6.9.2 External object definitions - Semantics -1 If the declaration of an identifier for an object has file scope and an initializer, the - declaration is an external definition for the identifier. -2 A declaration of an identifier for an object that has file scope without an initializer, and - without a storage-class specifier or with the storage-class specifier static, constitutes a - tentative definition. If a translation unit contains one or more tentative definitions for an - identifier, and the translation unit contains no external definition for that identifier, then - the behavior is exactly as if the translation unit contains a file scope declaration of that - identifier, with the composite type as of the end of the translation unit, with an initializer - equal to 0. -3 If the declaration of an identifier for an object is a tentative definition and has internal - linkage, the declared type shall not be an incomplete type. - -[page 157] - -4 EXAMPLE 1 - int i1 = 1; // definition, external linkage - static int i2 = 2; // definition, internal linkage - extern int i3 = 3; // definition, external linkage - int i4; // tentative definition, external linkage - static int i5; // tentative definition, internal linkage - int i1; // valid tentative definition, refers to previous - int i2; // 6.2.2 renders undefined, linkage disagreement - int i3; // valid tentative definition, refers to previous - int i4; // valid tentative definition, refers to previous - int i5; // 6.2.2 renders undefined, linkage disagreement - extern int i1; // refers to previous, whose linkage is external - extern int i2; // refers to previous, whose linkage is internal - extern int i3; // refers to previous, whose linkage is external - extern int i4; // refers to previous, whose linkage is external - extern int i5; // refers to previous, whose linkage is internal - -5 EXAMPLE 2 If at the end of the translation unit containing - int i[]; - the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to - zero on program startup. - -[page 158] - - 6.10 Preprocessing directives - Syntax -1 preprocessing-file: - groupopt - group: - group-part - group group-part - group-part: - if-section - control-line - text-line - # non-directive - if-section: - if-group elif-groupsopt else-groupopt endif-line - if-group: - # if constant-expression new-line groupopt - # ifdef identifier new-line groupopt - # ifndef identifier new-line groupopt - elif-groups: - elif-group - elif-groups elif-group - elif-group: - # elif constant-expression new-line groupopt - else-group: - # else new-line groupopt - endif-line: - # endif new-line - -[page 159] - - control-line: - # include pp-tokens new-line - # define identifier replacement-list new-line - # define identifier lparen identifier-listopt ) - replacement-list new-line - # define identifier lparen ... ) replacement-list new-line - # define identifier lparen identifier-list , ... ) - replacement-list new-line - # undef identifier new-line - # line pp-tokens new-line - # error pp-tokensopt new-line - # pragma pp-tokensopt new-line - # new-line - text-line: - pp-tokensopt new-line - non-directive: - pp-tokens new-line - lparen: - a ( character not immediately preceded by white-space - replacement-list: - pp-tokensopt - pp-tokens: - preprocessing-token - pp-tokens preprocessing-token - new-line: - the new-line character - Description -2 A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the - following constraints: The first token in the sequence is a # preprocessing token that (at - the start of translation phase 4) is either the first character in the source file (optionally - after white space containing no new-line characters) or that follows white space - containing at least one new-line character. The last token in the sequence is the first new- - line character that follows the first token in the sequence.165) A new-line character ends - the preprocessing directive even if it occurs within what would otherwise be an - - 165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic - significance, as all white space is equivalent except in certain situations during preprocessing (see the - # character string literal creation operator in 6.10.3.2, for example). - -[page 160] - - invocation of a function-like macro. -3 A text line shall not begin with a # preprocessing token. A non-directive shall not begin - with any of the directive names appearing in the syntax. -4 When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any - sequence of preprocessing tokens to occur between the directive name and the following - new-line character. - Constraints -5 The only white-space characters that shall appear between preprocessing tokens within a - preprocessing directive (from just after the introducing # preprocessing token through - just before the terminating new-line character) are space and horizontal-tab (including - spaces that have replaced comments or possibly other white-space characters in - translation phase 3). - Semantics -6 The implementation can process and skip sections of source files conditionally, include - other source files, and replace macros. These capabilities are called preprocessing, - because conceptually they occur before translation of the resulting translation unit. -7 The preprocessing tokens within a preprocessing directive are not subject to macro - expansion unless otherwise stated. -8 EXAMPLE In: - #define EMPTY - EMPTY # include - the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not - begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been - replaced. - - 6.10.1 Conditional inclusion - Constraints -1 The expression that controls conditional inclusion shall be an integer constant expression - except that: identifiers (including those lexically identical to keywords) are interpreted as * - described below;166) and it may contain unary operator expressions of the form - defined identifier - or - defined ( identifier ) - which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is - - - 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers - either are or are not macro names -- there simply are no keywords, enumeration constants, etc. - -[page 161] - - predefined or if it has been the subject of a #define preprocessing directive without an - intervening #undef directive with the same subject identifier), 0 if it is not. -2 Each preprocessing token that remains (in the list of preprocessing tokens that will - become the controlling expression) after all macro replacements have occurred shall be in - the lexical form of a token (6.4). - Semantics -3 Preprocessing directives of the forms - # if constant-expression new-line groupopt - # elif constant-expression new-line groupopt - check whether the controlling constant expression evaluates to nonzero. -4 Prior to evaluation, macro invocations in the list of preprocessing tokens that will become - the controlling constant expression are replaced (except for those macro names modified - by the defined unary operator), just as in normal text. If the token defined is - generated as a result of this replacement process or use of the defined unary operator - does not match one of the two specified forms prior to macro replacement, the behavior is - undefined. After all replacements due to macro expansion and the defined unary - operator have been performed, all remaining identifiers (including those lexically - identical to keywords) are replaced with the pp-number 0, and then each preprocessing - token is converted into a token. The resulting tokens compose the controlling constant - expression which is evaluated according to the rules of 6.6. For the purposes of this - token conversion and evaluation, all signed integer types and all unsigned integer types - act as if they have the same representation as, respectively, the types intmax_t and - uintmax_t defined in the header .167) This includes interpreting - character constants, which may involve converting escape sequences into execution - character set members. Whether the numeric value for these character constants matches - the value obtained when an identical character constant occurs in an expression (other - than within a #if or #elif directive) is implementation-defined.168) Also, whether a - single-character character constant may have a negative value is implementation-defined. - - - - - 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant - 0x8000 is signed and positive within a #if expression even though it would be unsigned in - translation phase 7. - 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to - evaluate to the same value in these two contexts. - #if 'z' - 'a' == 25 - if ('z' - 'a' == 25) - -[page 162] - -5 Preprocessing directives of the forms - # ifdef identifier new-line groupopt - # ifndef identifier new-line groupopt - check whether the identifier is or is not currently defined as a macro name. Their - conditions are equivalent to #if defined identifier and #if !defined identifier - respectively. -6 Each directive's condition is checked in order. If it evaluates to false (zero), the group - that it controls is skipped: directives are processed only through the name that determines - the directive in order to keep track of the level of nested conditionals; the rest of the - directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the - group. Only the first group whose control condition evaluates to true (nonzero) is - processed. If none of the conditions evaluates to true, and there is a #else directive, the - group controlled by the #else is processed; lacking a #else directive, all the groups - until the #endif are skipped.169) - Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest - integer types (7.20.1.5). - 6.10.2 Source file inclusion - Constraints -1 A #include directive shall identify a header or source file that can be processed by the - implementation. - Semantics -2 A preprocessing directive of the form - # include new-line - searches a sequence of implementation-defined places for a header identified uniquely by - the specified sequence between the < and > delimiters, and causes the replacement of that - directive by the entire contents of the header. How the places are specified or the header - identified is implementation-defined. -3 A preprocessing directive of the form - # include "q-char-sequence" new-line - causes the replacement of that directive by the entire contents of the source file identified - by the specified sequence between the " delimiters. The named source file is searched - - - 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive - before the terminating new-line character. However, comments may appear anywhere in a source file, - including within a preprocessing directive. - -[page 163] - - for in an implementation-defined manner. If this search is not supported, or if the search - fails, the directive is reprocessed as if it read - # include new-line - with the identical contained sequence (including > characters, if any) from the original - directive. -4 A preprocessing directive of the form - # include pp-tokens new-line - (that does not match one of the two previous forms) is permitted. The preprocessing - tokens after include in the directive are processed just as in normal text. (Each - identifier currently defined as a macro name is replaced by its replacement list of - preprocessing tokens.) The directive resulting after all replacements shall match one of - the two previous forms.170) The method by which a sequence of preprocessing tokens - between a < and a > preprocessing token pair or a pair of " characters is combined into a - single header name preprocessing token is implementation-defined. -5 The implementation shall provide unique mappings for sequences consisting of one or - more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The - first character shall not be a digit. The implementation may ignore distinctions of - alphabetical case and restrict the mapping to eight significant characters before the - period. -6 A #include preprocessing directive may appear in a source file that has been read - because of a #include directive in another file, up to an implementation-defined - nesting limit (see 5.2.4.1). -7 EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following: - #include - #include "myprog.h" - - - - - 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation - phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive. - -[page 164] - -8 EXAMPLE 2 This illustrates macro-replaced #include directives: - #if VERSION == 1 - #define INCFILE "vers1.h" - #elif VERSION == 2 - #define INCFILE "vers2.h" // and so on - #else - #define INCFILE "versN.h" - #endif - #include INCFILE - - Forward references: macro replacement (6.10.3). - 6.10.3 Macro replacement - Constraints -1 Two replacement lists are identical if and only if the preprocessing tokens in both have - the same number, ordering, spelling, and white-space separation, where all white-space - separations are considered identical. -2 An identifier currently defined as an object-like macro shall not be redefined by another - #define preprocessing directive unless the second definition is an object-like macro - definition and the two replacement lists are identical. Likewise, an identifier currently - defined as a function-like macro shall not be redefined by another #define - preprocessing directive unless the second definition is a function-like macro definition - that has the same number and spelling of parameters, and the two replacement lists are - identical. -3 There shall be white-space between the identifier and the replacement list in the definition - of an object-like macro. -4 If the identifier-list in the macro definition does not end with an ellipsis, the number of - arguments (including those arguments consisting of no preprocessing tokens) in an - invocation of a function-like macro shall equal the number of parameters in the macro - definition. Otherwise, there shall be more arguments in the invocation than there are - parameters in the macro definition (excluding the ...). There shall exist a ) - preprocessing token that terminates the invocation. -5 The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like - macro that uses the ellipsis notation in the parameters. -6 A parameter identifier in a function-like macro shall be uniquely declared within its - scope. - Semantics -7 The identifier immediately following the define is called the macro name. There is one - name space for macro names. Any white-space characters preceding or following the - replacement list of preprocessing tokens are not considered part of the replacement list - -[page 165] - - for either form of macro. -8 If a # preprocessing token, followed by an identifier, occurs lexically at the point at which - a preprocessing directive could begin, the identifier is not subject to macro replacement. -9 A preprocessing directive of the form - # define identifier replacement-list new-line - defines an object-like macro that causes each subsequent instance of the macro name171) - to be replaced by the replacement list of preprocessing tokens that constitute the - remainder of the directive. The replacement list is then rescanned for more macro names - as specified below. -10 A preprocessing directive of the form - # define identifier lparen identifier-listopt ) replacement-list new-line - # define identifier lparen ... ) replacement-list new-line - # define identifier lparen identifier-list , ... ) replacement-list new-line - defines a function-like macro with parameters, whose use is similar syntactically to a - function call. The parameters are specified by the optional list of identifiers, whose scope - extends from their declaration in the identifier list until the new-line character that - terminates the #define preprocessing directive. Each subsequent instance of the - function-like macro name followed by a ( as the next preprocessing token introduces the - sequence of preprocessing tokens that is replaced by the replacement list in the definition - (an invocation of the macro). The replaced sequence of preprocessing tokens is - terminated by the matching ) preprocessing token, skipping intervening matched pairs of - left and right parenthesis preprocessing tokens. Within the sequence of preprocessing - tokens making up an invocation of a function-like macro, new-line is considered a normal - white-space character. -11 The sequence of preprocessing tokens bounded by the outside-most matching parentheses - forms the list of arguments for the function-like macro. The individual arguments within - the list are separated by comma preprocessing tokens, but comma preprocessing tokens - between matching inner parentheses do not separate arguments. If there are sequences of - preprocessing tokens within the list of arguments that would otherwise act as - preprocessing directives,172) the behavior is undefined. -12 If there is a ... in the identifier-list in the macro definition, then the trailing arguments, - including any separating comma preprocessing tokens, are merged to form a single item: - - - 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens, - not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they - are never scanned for macro names or parameters. - 172) Despite the name, a non-directive is a preprocessing directive. - -[page 166] - - the variable arguments. The number of arguments so combined is such that, following - merger, the number of arguments is one more than the number of parameters in the macro - definition (excluding the ...). - 6.10.3.1 Argument substitution -1 After the arguments for the invocation of a function-like macro have been identified, - argument substitution takes place. A parameter in the replacement list, unless preceded - by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is - replaced by the corresponding argument after all macros contained therein have been - expanded. Before being substituted, each argument's preprocessing tokens are - completely macro replaced as if they formed the rest of the preprocessing file; no other - preprocessing tokens are available. -2 An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it - were a parameter, and the variable arguments shall form the preprocessing tokens used to - replace it. - 6.10.3.2 The # operator - Constraints -1 Each # preprocessing token in the replacement list for a function-like macro shall be - followed by a parameter as the next preprocessing token in the replacement list. - Semantics -2 If, in the replacement list, a parameter is immediately preceded by a # preprocessing - token, both are replaced by a single character string literal preprocessing token that - contains the spelling of the preprocessing token sequence for the corresponding - argument. Each occurrence of white space between the argument's preprocessing tokens - becomes a single space character in the character string literal. White space before the - first preprocessing token and after the last preprocessing token composing the argument - is deleted. Otherwise, the original spelling of each preprocessing token in the argument - is retained in the character string literal, except for special handling for producing the - spelling of string literals and character constants: a \ character is inserted before each " - and \ character of a character constant or string literal (including the delimiting " - characters), except that it is implementation-defined whether a \ character is inserted - before the \ character beginning a universal character name. If the replacement that - results is not a valid character string literal, the behavior is undefined. The character - string literal corresponding to an empty argument is "". The order of evaluation of # and - ## operators is unspecified. - -[page 167] - - 6.10.3.3 The ## operator - Constraints -1 A ## preprocessing token shall not occur at the beginning or at the end of a replacement - list for either form of macro definition. - Semantics -2 If, in the replacement list of a function-like macro, a parameter is immediately preceded - or followed by a ## preprocessing token, the parameter is replaced by the corresponding - argument's preprocessing token sequence; however, if an argument consists of no - preprocessing tokens, the parameter is replaced by a placemarker preprocessing token - instead.173) -3 For both object-like and function-like macro invocations, before the replacement list is - reexamined for more macro names to replace, each instance of a ## preprocessing token - in the replacement list (not from an argument) is deleted and the preceding preprocessing - token is concatenated with the following preprocessing token. Placemarker - preprocessing tokens are handled specially: concatenation of two placemarkers results in - a single placemarker preprocessing token, and concatenation of a placemarker with a - non-placemarker preprocessing token results in the non-placemarker preprocessing token. - If the result is not a valid preprocessing token, the behavior is undefined. The resulting - token is available for further macro replacement. The order of evaluation of ## operators - is unspecified. -4 EXAMPLE In the following fragment: - #define hash_hash # ## # - #define mkstr(a) # a - #define in_between(a) mkstr(a) - #define join(c, d) in_between(c hash_hash d) - char p[] = join(x, y); // equivalent to - // char p[] = "x ## y"; - The expansion produces, at various stages: - join(x, y) - in_between(x hash_hash y) - in_between(x ## y) - mkstr(x ## y) - "x ## y" - In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but - this new token is not the ## operator. - - - 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that - exist only within translation phase 4. - -[page 168] - - 6.10.3.4 Rescanning and further replacement -1 After all parameters in the replacement list have been substituted and # and ## - processing has taken place, all placemarker preprocessing tokens are removed. The - resulting preprocessing token sequence is then rescanned, along with all subsequent - preprocessing tokens of the source file, for more macro names to replace. -2 If the name of the macro being replaced is found during this scan of the replacement list - (not including the rest of the source file's preprocessing tokens), it is not replaced. - Furthermore, if any nested replacements encounter the name of the macro being replaced, - it is not replaced. These nonreplaced macro name preprocessing tokens are no longer - available for further replacement even if they are later (re)examined in contexts in which - that macro name preprocessing token would otherwise have been replaced. -3 The resulting completely macro-replaced preprocessing token sequence is not processed - as a preprocessing directive even if it resembles one, but all pragma unary operator - expressions within it are then processed as specified in 6.10.9 below. - 6.10.3.5 Scope of macro definitions -1 A macro definition lasts (independent of block structure) until a corresponding #undef - directive is encountered or (if none is encountered) until the end of the preprocessing - translation unit. Macro definitions have no significance after translation phase 4. -2 A preprocessing directive of the form - # undef identifier new-line - causes the specified identifier no longer to be defined as a macro name. It is ignored if - the specified identifier is not currently defined as a macro name. -3 EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in - #define TABSIZE 100 - int table[TABSIZE]; - -4 EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments. - It has the advantages of working for any compatible types of the arguments and of generating in-line code - without the overhead of function calling. It has the disadvantages of evaluating one or the other of its - arguments a second time (including side effects) and generating more code than a function if invoked - several times. It also cannot have its address taken, as it has none. - #define max(a, b) ((a) > (b) ? (a) : (b)) - The parentheses ensure that the arguments and the resulting expression are bound properly. - -[page 169] - -5 EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence - #define x 3 - #define f(a) f(x * (a)) - #undef x - #define x 2 - #define g f - #define z z[0] - #define h g(~ - #define m(a) a(w) - #define w 0,1 - #define t(a) a - #define p() int - #define q(x) x - #define r(x,y) x ## y - #define str(x) # x - f(y+1) + f(f(z)) % t(t(g)(0) + t)(1); - g(x+(3,4)-w) | h 5) & m - (f)^m(m); - p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) }; - char c[2][6] = { str(hello), str() }; - results in - f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1); - f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1); - int i[] = { 1, 23, 4, 5, }; - char c[2][6] = { "hello", "" }; - -6 EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the - sequence - #define str(s) # s - #define xstr(s) str(s) - #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \ - x ## s, x ## t) - #define INCFILE(n) vers ## n - #define glue(a, b) a ## b - #define xglue(a, b) glue(a, b) - #define HIGHLOW "hello" - #define LOW LOW ", world" - debug(1, 2); - fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away - == 0) str(: @\n), s); - #include xstr(INCFILE(2).h) - glue(HIGH, LOW); - xglue(HIGH, LOW) - results in - -[page 170] - - printf("x" "1" "= %d, x" "2" "= %s", x1, x2); - fputs( - "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n", - s); - #include "vers2.h" (after macro replacement, before file access) - "hello"; - "hello" ", world" - or, after concatenation of the character string literals, - printf("x1= %d, x2= %s", x1, x2); - fputs( - "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n", - s); - #include "vers2.h" (after macro replacement, before file access) - "hello"; - "hello, world" - Space around the # and ## tokens in the macro definition is optional. - -7 EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence - #define t(x,y,z) x ## y ## z - int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,), - t(10,,), t(,11,), t(,,12), t(,,) }; - results in - int j[] = { 123, 45, 67, 89, - 10, 11, 12, }; - -8 EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid. - #define OBJ_LIKE (1-1) - #define OBJ_LIKE /* white space */ (1-1) /* other */ - #define FUNC_LIKE(a) ( a ) - #define FUNC_LIKE( a )( /* note the white space */ \ - a /* other stuff on this line - */ ) - But the following redefinitions are invalid: - #define OBJ_LIKE (0) // different token sequence - #define OBJ_LIKE (1 - 1) // different white space - #define FUNC_LIKE(b) ( a ) // different parameter usage - #define FUNC_LIKE(b) ( b ) // different parameter spelling - -9 EXAMPLE 7 Finally, to show the variable argument list macro facilities: - #define debug(...) fprintf(stderr, __VA_ARGS__) - #define showlist(...) puts(#__VA_ARGS__) - #define report(test, ...) ((test)?puts(#test):\ - printf(__VA_ARGS__)) - debug("Flag"); - debug("X = %d\n", x); - showlist(The first, second, and third items.); - report(x>y, "x is %d but y is %d", x, y); - -[page 171] - - results in - fprintf(stderr, "Flag" ); - fprintf(stderr, "X = %d\n", x ); - puts( "The first, second, and third items." ); - ((x>y)?puts("x>y"): - printf("x is %d but y is %d", x, y)); - - 6.10.4 Line control - Constraints -1 The string literal of a #line directive, if present, shall be a character string literal. - Semantics -2 The line number of the current source line is one greater than the number of new-line - characters read or introduced in translation phase 1 (5.1.1.2) while processing the source - file to the current token. -3 A preprocessing directive of the form - # line digit-sequence new-line - causes the implementation to behave as if the following sequence of source lines begins - with a source line that has a line number as specified by the digit sequence (interpreted as - a decimal integer). The digit sequence shall not specify zero, nor a number greater than - 2147483647. -4 A preprocessing directive of the form - # line digit-sequence "s-char-sequenceopt" new-line - sets the presumed line number similarly and changes the presumed name of the source - file to be the contents of the character string literal. -5 A preprocessing directive of the form - # line pp-tokens new-line - (that does not match one of the two previous forms) is permitted. The preprocessing - tokens after line on the directive are processed just as in normal text (each identifier - currently defined as a macro name is replaced by its replacement list of preprocessing - tokens). The directive resulting after all replacements shall match one of the two - previous forms and is then processed as appropriate. - -[page 172] - - 6.10.5 Error directive - Semantics -1 A preprocessing directive of the form - # error pp-tokensopt new-line - causes the implementation to produce a diagnostic message that includes the specified - sequence of preprocessing tokens. - 6.10.6 Pragma directive - Semantics -1 A preprocessing directive of the form - # pragma pp-tokensopt new-line - where the preprocessing token STDC does not immediately follow pragma in the - directive (prior to any macro replacement)174) causes the implementation to behave in an - implementation-defined manner. The behavior might cause translation to fail or cause the - translator or the resulting program to behave in a non-conforming manner. Any such - pragma that is not recognized by the implementation is ignored. -2 If the preprocessing token STDC does immediately follow pragma in the directive (prior - to any macro replacement), then no macro replacement is performed on the directive, and - the directive shall have one of the following forms175) whose meanings are described - elsewhere: - #pragma STDC FP_CONTRACT on-off-switch - #pragma STDC FENV_ACCESS on-off-switch - #pragma STDC CX_LIMITED_RANGE on-off-switch - on-off-switch: one of - ON OFF DEFAULT - Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma - (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4). - - - - - 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted - except for in standard pragmas (where STDC immediately follows pragma). If the result of macro - replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still - implementation-defined; an implementation is permitted to behave as if it were the standard pragma, - but is not required to. - 175) See ''future language directions'' (6.11.8). - -[page 173] - - 6.10.7 Null directive - Semantics -1 A preprocessing directive of the form - # new-line - has no effect. - 6.10.8 Predefined macro names -1 The values of the predefined macros listed in the following subclauses176) (except for - __FILE__ and __LINE__) remain constant throughout the translation unit. -2 None of these macro names, nor the identifier defined, shall be the subject of a - #define or a #undef preprocessing directive. Any other predefined macro names - shall begin with a leading underscore followed by an uppercase letter or a second - underscore. -3 The implementation shall not predefine the macro __cplusplus, nor shall it define it - in any standard header. - Forward references: standard headers (7.1.2). - 6.10.8.1 Mandatory macros -1 The following macro names shall be defined by the implementation: - __DATE__ The date of translation of the preprocessing translation unit: a character - string literal of the form "Mmm dd yyyy", where the names of the - months are the same as those generated by the asctime function, and the - first character of dd is a space character if the value is less than 10. If the - date of translation is not available, an implementation-defined valid date - shall be supplied. - __FILE__ The presumed name of the current source file (a character string literal).177) - __LINE__ The presumed line number (within the current source file) of the current - source line (an integer constant).177) - __STDC__ The integer constant 1, intended to indicate a conforming implementation. - __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted - implementation or the integer constant 0 if it is not. - - - - - 176) See ''future language directions'' (6.11.9). - 177) The presumed source file name and line number can be changed by the #line directive. - -[page 174] - - __STDC_VERSION__ The integer constant 201ymmL.178) - __TIME__ The time of translation of the preprocessing translation unit: a character - string literal of the form "hh:mm:ss" as in the time generated by the - asctime function. If the time of translation is not available, an - implementation-defined valid time shall be supplied. - Forward references: the asctime function (7.26.3.1). - 6.10.8.2 Environment macros -1 The following macro names are conditionally defined by the implementation: - __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example, - 199712L). If this symbol is defined, then every character in the Unicode - required set, when stored in an object of type wchar_t, has the same - value as the short identifier of that character. The Unicode required set - consists of all the characters that are defined by ISO/IEC 10646, along with - all amendments and technical corrigenda, as of the specified year and - month. If some other encoding is used, the macro shall not be defined and - the actual encoding used is implementation-defined. - __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in - the encoding for wchar_t, a member of the basic character set need not - have a code value equal to its value when used as the lone character in an - integer character constant. - __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type - char16_t are UTF-16 encoded. If some other encoding is used, the - macro shall not be defined and the actual encoding used is implementation- - defined. - __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type - char32_t are UTF-32 encoded. If some other encoding is used, the - macro shall not be defined and the actual encoding used is implementation- - defined. - Forward references: common definitions (7.19), unicode utilities (7.27). - - - - - 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in - ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will - remain an integer constant of type long int that is increased with each revision of this International - Standard. - -[page 175] - - 6.10.8.3 Conditional feature macros -1 The following macro names are conditionally defined by the implementation: - __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to - the specifications in annex L (Analyzability). - __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the - specifications in annex F (IEC 60559 floating-point arithmetic). - __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate - adherence to the specifications in annex G (IEC 60559 compatible complex - arithmetic). - __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support - for the extensions defined in annex K (Bounds-checking interfaces).179) - __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the - implementation does not support complex types or the - header. - __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the - implementation does not support atomic types (including the _Atomic - type qualifier and the header) or the - header. - __STDC_NO_VLA__ The integer constant 1, intended to indicate that the - implementation does not support variable length arrays or variably - modified types. -2 An implementation that defines __STDC_NO_COMPLEX__ shall not define - __STDC_IEC_559_COMPLEX__. - 6.10.9 Pragma operator - Semantics -1 A unary operator expression of the form: - _Pragma ( string-literal ) - is processed as follows: The string literal is destringized by deleting the L prefix, if - present, deleting the leading and trailing double-quotes, replacing each escape sequence - \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The - resulting sequence of characters is processed through translation phase 3 to produce - preprocessing tokens that are executed as if they were the pp-tokens in a pragma - - - 179) The intention is that this will remain an integer constant of type long int that is increased with - each revision of this International Standard. - -[page 176] - - directive. The original four preprocessing tokens in the unary operator expression are - removed. -2 EXAMPLE A directive of the form: - #pragma listing on "..\listing.dir" - can also be expressed as: - _Pragma ( "listing on \"..\\listing.dir\"" ) - The latter form is processed in the same way whether it appears literally as shown, or results from macro - replacement, as in: - #define LISTING(x) PRAGMA(listing on #x) - #define PRAGMA(x) _Pragma(#x) - LISTING ( ..\listing.dir ) - -[page 177] - - 6.11 Future language directions - 6.11.1 Floating types -1 Future standardization may include additional floating-point types, including those with - greater range, precision, or both than long double. - 6.11.2 Linkages of identifiers -1 Declaring an identifier with internal linkage at file scope without the static storage- - class specifier is an obsolescent feature. - 6.11.3 External names -1 Restriction of the significance of an external name to fewer than 255 characters - (considering each universal character name or extended source character as a single - character) is an obsolescent feature that is a concession to existing implementations. - 6.11.4 Character escape sequences -1 Lowercase letters as escape sequences are reserved for future standardization. Other - characters may be used in extensions. - 6.11.5 Storage-class specifiers -1 The placement of a storage-class specifier other than at the beginning of the declaration - specifiers in a declaration is an obsolescent feature. - 6.11.6 Function declarators -1 The use of function declarators with empty parentheses (not prototype-format parameter - type declarators) is an obsolescent feature. - 6.11.7 Function definitions -1 The use of function definitions with separate parameter identifier and declaration lists - (not prototype-format parameter type and identifier declarators) is an obsolescent feature. - 6.11.8 Pragma directives -1 Pragmas whose first preprocessing token is STDC are reserved for future standardization. - 6.11.9 Predefined macro names -1 Macro names beginning with __STDC_ are reserved for future standardization. - -[page 178] - - - 7. Library - 7.1 Introduction - 7.1.1 Definitions of terms -1 A string is a contiguous sequence of characters terminated by and including the first null - character. The term multibyte string is sometimes used instead to emphasize special - processing given to multibyte characters contained in the string or to avoid confusion - with a wide string. A pointer to a string is a pointer to its initial (lowest addressed) - character. The length of a string is the number of bytes preceding the null character and - the value of a string is the sequence of the values of the contained characters, in order. -2 The decimal-point character is the character used by functions that convert floating-point - numbers to or from character sequences to denote the beginning of the fractional part of - such character sequences.180) It is represented in the text and examples by a period, but - may be changed by the setlocale function. -3 A null wide character is a wide character with code value zero. -4 A wide string is a contiguous sequence of wide characters terminated by and including - the first null wide character. A pointer to a wide string is a pointer to its initial (lowest - addressed) wide character. The length of a wide string is the number of wide characters - preceding the null wide character and the value of a wide string is the sequence of code - values of the contained wide characters, in order. -5 A shift sequence is a contiguous sequence of bytes within a multibyte string that - (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a - corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte - character.181) - Forward references: character handling (7.4), the setlocale function (7.11.1.1). - - - - - 180) The functions that make use of the decimal-point character are the numeric conversion functions - (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2). - 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large - enough to count all the bytes in any complete multibyte character plus at least one adjacent shift - sequence of maximum length. Whether these counts provide for more than one shift sequence is the - implementation's choice. - -[page 179] - - 7.1.2 Standard headers -1 Each library function is declared, with a type that includes a prototype, in a header,182) - whose contents are made available by the #include preprocessing directive. The - header declares a set of related functions, plus any necessary types and additional macros - needed to facilitate their use. Declarations of types described in this clause shall not - include type qualifiers, unless explicitly stated otherwise. -2 The standard headers are183) - - - - - - - -3 If a file with the same name as one of the above < and > delimited sequences, not - provided as part of the implementation, is placed in any of the standard places that are - searched for included source files, the behavior is undefined. -4 Standard headers may be included in any order; each may be included more than once in - a given scope, with no effect different from being included only once, except that the - effect of including depends on the definition of NDEBUG (see 7.2). If - used, a header shall be included outside of any external declaration or definition, and it - shall first be included before the first reference to any of the functions or objects it - declares, or to any of the types or macros it defines. However, if an identifier is declared - or defined in more than one header, the second and subsequent associated headers may be - included after the initial reference to the identifier. The program shall not have any - macros with names lexically identical to keywords currently defined prior to the - inclusion. -5 Any definition of an object-like macro described in this clause shall expand to code that is - fully protected by parentheses where necessary, so that it groups in an arbitrary - expression as if it were a single identifier. -6 Any declaration of a library function shall have external linkage. - - - - - 182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names - necessarily valid source file names. - 183) The headers , , and are conditional features that - implementations need not support; see 6.10.8.3. - -[page 180] - -7 A summary of the contents of the standard headers is given in annex B. - Forward references: diagnostics (7.2). - 7.1.3 Reserved identifiers -1 Each header declares or defines all identifiers listed in its associated subclause, and - optionally declares or defines identifiers listed in its associated future library directions - subclause and identifiers which are always reserved either for any use or for use as file - scope identifiers. - -- All identifiers that begin with an underscore and either an uppercase letter or another - underscore are always reserved for any use. - -- All identifiers that begin with an underscore are always reserved for use as identifiers - with file scope in both the ordinary and tag name spaces. - -- Each macro name in any of the following subclauses (including the future library - directions) is reserved for use as specified if any of its associated headers is included; - unless explicitly stated otherwise (see 7.1.4). - -- All identifiers with external linkage in any of the following subclauses (including the - future library directions) and errno are always reserved for use as identifiers with - external linkage.184) - -- Each identifier with file scope listed in any of the following subclauses (including the - future library directions) is reserved for use as a macro name and as an identifier with - file scope in the same name space if any of its associated headers is included. -2 No other identifiers are reserved. If the program declares or defines an identifier in a - context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved - identifier as a macro name, the behavior is undefined. -3 If the program removes (with #undef) any macro definition of an identifier in the first - group listed above, the behavior is undefined. - - - - - 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp, - va_copy, and va_end. - -[page 181] - - 7.1.4 Use of library functions -1 Each of the following statements applies unless explicitly stated otherwise in the detailed - descriptions that follow: If an argument to a function has an invalid value (such as a value - outside the domain of the function, or a pointer outside the address space of the program, - or a null pointer, or a pointer to non-modifiable storage when the corresponding - parameter is not const-qualified) or a type (after promotion) not expected by a function - with variable number of arguments, the behavior is undefined. If a function argument is - described as being an array, the pointer actually passed to the function shall have a value - such that all address computations and accesses to objects (that would be valid if the - pointer did point to the first element of such an array) are in fact valid. Any function - declared in a header may be additionally implemented as a function-like macro defined in - the header, so if a library function is declared explicitly when its header is included, one - of the techniques shown below can be used to ensure the declaration is not affected by - such a macro. Any macro definition of a function can be suppressed locally by enclosing - the name of the function in parentheses, because the name is then not followed by the left - parenthesis that indicates expansion of a macro function name. For the same syntactic - reason, it is permitted to take the address of a library function even if it is also defined as - a macro.185) The use of #undef to remove any macro definition will also ensure that an - actual function is referred to. Any invocation of a library function that is implemented as - a macro shall expand to code that evaluates each of its arguments exactly once, fully - protected by parentheses where necessary, so it is generally safe to use arbitrary - expressions as arguments.186) Likewise, those function-like macros described in the - following subclauses may be invoked in an expression anywhere a function with a - compatible return type could be called.187) All object-like macros listed as expanding to - - - 185) This means that an implementation shall provide an actual function for each library function, even if it - also provides a macro for that function. - 186) Such macros might not contain the sequence points that the corresponding function calls do. - 187) Because external identifiers and some macro names beginning with an underscore are reserved, - implementations may provide special semantics for such names. For example, the identifier - _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the - appropriate header could specify - #define abs(x) _BUILTIN_abs(x) - for a compiler whose code generator will accept it. - In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine - function may write - #undef abs - whether the implementation's header provides a macro implementation of abs or a built-in - implementation. The prototype for the function, which precedes and is hidden by any macro - definition, is thereby revealed also. - -[page 182] - - integer constant expressions shall additionally be suitable for use in #if preprocessing - directives. -2 Provided that a library function can be declared without reference to any type defined in a - header, it is also permissible to declare the function and use it without including its - associated header. -3 There is a sequence point immediately before a library function returns. -4 The functions in the standard library are not guaranteed to be reentrant and may modify - objects with static or thread storage duration.188) -5 Unless explicitly stated otherwise in the detailed descriptions that follow, library - functions shall prevent data races as follows: A library function shall not directly or - indirectly access objects accessible by threads other than the current thread unless the - objects are accessed directly or indirectly via the function's arguments. A library - function shall not directly or indirectly modify objects accessible by threads other than - the current thread unless the objects are accessed directly or indirectly via the function's - non-const arguments.189) Implementations may share their own internal objects between - threads if the objects are not visible to users and are protected against data races. -6 Unless otherwise specified, library functions shall perform all operations solely within the - current thread if those operations have effects that are visible to users.190) -7 EXAMPLE The function atoi may be used in any of several ways: - -- by use of its associated header (possibly generating a macro expansion) - #include - const char *str; - /* ... */ - i = atoi(str); - -- by use of its associated header (assuredly generating a true function reference) - - - - - 188) Thus, a signal handler cannot, in general, call standard library functions. - 189) This means, for example, that an implementation is not permitted to use a static object for internal - purposes without synchronization because it could cause a data race even in programs that do not - explicitly share objects between threads. - 190) This allows implementations to parallelize operations if there are no visible side effects. - -[page 183] - - #include - #undef atoi - const char *str; - /* ... */ - i = atoi(str); - or - #include - const char *str; - /* ... */ - i = (atoi)(str); --- by explicit declaration - extern int atoi(const char *); - const char *str; - /* ... */ - i = atoi(str); - -[page 184] - - 7.2 Diagnostics -1 The header defines the assert and static_assert macros and - refers to another macro, - NDEBUG - which is not defined by . If NDEBUG is defined as a macro name at the - point in the source file where is included, the assert macro is defined - simply as - #define assert(ignore) ((void)0) - The assert macro is redefined according to the current state of NDEBUG each time that - is included. -2 The assert macro shall be implemented as a macro, not as an actual function. If the - macro definition is suppressed in order to access an actual function, the behavior is - undefined. -3 The macro - static_assert - expands to _Static_assert. - 7.2.1 Program diagnostics - 7.2.1.1 The assert macro - Synopsis -1 #include - void assert(scalar expression); - Description -2 The assert macro puts diagnostic tests into programs; it expands to a void expression. - When it is executed, if expression (which shall have a scalar type) is false (that is, - compares equal to 0), the assert macro writes information about the particular call that - failed (including the text of the argument, the name of the source file, the source line - number, and the name of the enclosing function -- the latter are respectively the values of - the preprocessing macros __FILE__ and __LINE__ and of the identifier - __func__) on the standard error stream in an implementation-defined format.191) It - then calls the abort function. - - - - 191) The message written might be of the form: - Assertion failed: expression, function abc, file xyz, line nnn. - -[page 185] - - Returns -3 The assert macro returns no value. - Forward references: the abort function (7.22.4.1). - -[page 186] - - 7.3 Complex arithmetic - 7.3.1 Introduction -1 The header defines macros and declares functions that support complex - arithmetic.192) -2 Implementations that define the macro __STDC_NO_COMPLEX__ need not provide - this header nor support any of its facilities. -3 Each synopsis specifies a family of functions consisting of a principal function with one - or more double complex parameters and a double complex or double return - value; and other functions with the same name but with f and l suffixes which are - corresponding functions with float and long double parameters and return values. -4 The macro - complex - expands to _Complex; the macro - _Complex_I - expands to a constant expression of type const float _Complex, with the value of - the imaginary unit.193) -5 The macros - imaginary - and - _Imaginary_I - are defined if and only if the implementation supports imaginary types;194) if defined, - they expand to _Imaginary and a constant expression of type const float - _Imaginary with the value of the imaginary unit. -6 The macro - I - expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not - defined, I shall expand to _Complex_I. -7 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then - redefine the macros complex, imaginary, and I. - - 192) See ''future library directions'' (7.30.1). - 193) The imaginary unit is a number i such that i 2 = -1. - 194) A specification for imaginary types is in informative annex G. - -[page 187] - - Forward references: IEC 60559-compatible complex arithmetic (annex G). - 7.3.2 Conventions -1 Values are interpreted as radians, not degrees. An implementation may set errno but is - not required to. - 7.3.3 Branch cuts -1 Some of the functions below have branch cuts, across which the function is - discontinuous. For implementations with a signed zero (including all IEC 60559 - implementations) that follow the specifications of annex G, the sign of zero distinguishes - one side of a cut from another so the function is continuous (except for format - limitations) as the cut is approached from either side. For example, for the square root - function, which has a branch cut along the negative real axis, the top of the cut, with - imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with - imaginary part -0, maps to the negative imaginary axis. -2 Implementations that do not support a signed zero (see annex F) cannot distinguish the - sides of branch cuts. These implementations shall map a cut so the function is continuous - as the cut is approached coming around the finite endpoint of the cut in a counter - clockwise direction. (Branch cuts for the functions specified here have just one finite - endpoint.) For example, for the square root function, coming counter clockwise around - the finite endpoint of the cut along the negative real axis approaches the cut from above, - so the cut maps to the positive imaginary axis. - 7.3.4 The CX_LIMITED_RANGE pragma - Synopsis -1 #include - #pragma STDC CX_LIMITED_RANGE on-off-switch - Description -2 The usual mathematical formulas for complex multiply, divide, and absolute value are - problematic because of their treatment of infinities and because of undue overflow and - underflow. The CX_LIMITED_RANGE pragma can be used to inform the - implementation that (where the state is ''on'') the usual mathematical formulas are - acceptable.195) The pragma can occur either outside external declarations or preceding all - explicit declarations and statements inside a compound statement. When outside external - declarations, the pragma takes effect from its occurrence until another - CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit. - When inside a compound statement, the pragma takes effect from its occurrence until - another CX_LIMITED_RANGE pragma is encountered (including within a nested - compound statement), or until the end of the compound statement; at the end of a - compound statement the state for the pragma is restored to its condition just before the - -[page 188] - - compound statement. If this pragma is used in any other context, the behavior is - undefined. The default state for the pragma is ''off''. - 7.3.5 Trigonometric functions - 7.3.5.1 The cacos functions - Synopsis -1 #include - double complex cacos(double complex z); - float complex cacosf(float complex z); - long double complex cacosl(long double complex z); - Description -2 The cacos functions compute the complex arc cosine of z, with branch cuts outside the - interval [-1, +1] along the real axis. - Returns -3 The cacos functions return the complex arc cosine value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the - real axis. - 7.3.5.2 The casin functions - Synopsis -1 #include - double complex casin(double complex z); - float complex casinf(float complex z); - long double complex casinl(long double complex z); - Description -2 The casin functions compute the complex arc sine of z, with branch cuts outside the - interval [-1, +1] along the real axis. - Returns -3 The casin functions return the complex arc sine value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] - - 195) The purpose of the pragma is to allow the implementation to use the formulas: - (x + iy) x (u + iv) = (xu - yv) + i(yu + xv) - (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 ) - | x + iy | = (sqrt) x 2 + y 2 - ----- - where the programmer can determine they are safe. - -[page 189] - - along the real axis. - 7.3.5.3 The catan functions - Synopsis -1 #include - double complex catan(double complex z); - float complex catanf(float complex z); - long double complex catanl(long double complex z); - Description -2 The catan functions compute the complex arc tangent of z, with branch cuts outside the - interval [-i, +i] along the imaginary axis. - Returns -3 The catan functions return the complex arc tangent value, in the range of a strip - mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] - along the real axis. - 7.3.5.4 The ccos functions - Synopsis -1 #include - double complex ccos(double complex z); - float complex ccosf(float complex z); - long double complex ccosl(long double complex z); - Description -2 The ccos functions compute the complex cosine of z. - Returns -3 The ccos functions return the complex cosine value. - 7.3.5.5 The csin functions - Synopsis -1 #include - double complex csin(double complex z); - float complex csinf(float complex z); - long double complex csinl(long double complex z); - Description -2 The csin functions compute the complex sine of z. - -[page 190] - - Returns -3 The csin functions return the complex sine value. - 7.3.5.6 The ctan functions - Synopsis -1 #include - double complex ctan(double complex z); - float complex ctanf(float complex z); - long double complex ctanl(long double complex z); - Description -2 The ctan functions compute the complex tangent of z. - Returns -3 The ctan functions return the complex tangent value. - 7.3.6 Hyperbolic functions - 7.3.6.1 The cacosh functions - Synopsis -1 #include - double complex cacosh(double complex z); - float complex cacoshf(float complex z); - long double complex cacoshl(long double complex z); - Description -2 The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch - cut at values less than 1 along the real axis. - Returns -3 The cacosh functions return the complex arc hyperbolic cosine value, in the range of a - half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the - imaginary axis. - 7.3.6.2 The casinh functions - Synopsis -1 #include - double complex casinh(double complex z); - float complex casinhf(float complex z); - long double complex casinhl(long double complex z); - -[page 191] - - Description -2 The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts - outside the interval [-i, +i] along the imaginary axis. - Returns -3 The casinh functions return the complex arc hyperbolic sine value, in the range of a - strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] - along the imaginary axis. - 7.3.6.3 The catanh functions - Synopsis -1 #include - double complex catanh(double complex z); - float complex catanhf(float complex z); - long double complex catanhl(long double complex z); - Description -2 The catanh functions compute the complex arc hyperbolic tangent of z, with branch - cuts outside the interval [-1, +1] along the real axis. - Returns -3 The catanh functions return the complex arc hyperbolic tangent value, in the range of a - strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] - along the imaginary axis. - 7.3.6.4 The ccosh functions - Synopsis -1 #include - double complex ccosh(double complex z); - float complex ccoshf(float complex z); - long double complex ccoshl(long double complex z); - Description -2 The ccosh functions compute the complex hyperbolic cosine of z. - Returns -3 The ccosh functions return the complex hyperbolic cosine value. - -[page 192] - - 7.3.6.5 The csinh functions - Synopsis -1 #include - double complex csinh(double complex z); - float complex csinhf(float complex z); - long double complex csinhl(long double complex z); - Description -2 The csinh functions compute the complex hyperbolic sine of z. - Returns -3 The csinh functions return the complex hyperbolic sine value. - 7.3.6.6 The ctanh functions - Synopsis -1 #include - double complex ctanh(double complex z); - float complex ctanhf(float complex z); - long double complex ctanhl(long double complex z); - Description -2 The ctanh functions compute the complex hyperbolic tangent of z. - Returns -3 The ctanh functions return the complex hyperbolic tangent value. - 7.3.7 Exponential and logarithmic functions - 7.3.7.1 The cexp functions - Synopsis -1 #include - double complex cexp(double complex z); - float complex cexpf(float complex z); - long double complex cexpl(long double complex z); - Description -2 The cexp functions compute the complex base-e exponential of z. - Returns -3 The cexp functions return the complex base-e exponential value. - -[page 193] - - 7.3.7.2 The clog functions - Synopsis -1 #include - double complex clog(double complex z); - float complex clogf(float complex z); - long double complex clogl(long double complex z); - Description -2 The clog functions compute the complex natural (base-e) logarithm of z, with a branch - cut along the negative real axis. - Returns -3 The clog functions return the complex natural logarithm value, in the range of a strip - mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the - imaginary axis. - 7.3.8 Power and absolute-value functions - 7.3.8.1 The cabs functions - Synopsis -1 #include - double cabs(double complex z); - float cabsf(float complex z); - long double cabsl(long double complex z); - Description -2 The cabs functions compute the complex absolute value (also called norm, modulus, or - magnitude) of z. - Returns -3 The cabs functions return the complex absolute value. - 7.3.8.2 The cpow functions - Synopsis -1 #include - double complex cpow(double complex x, double complex y); - float complex cpowf(float complex x, float complex y); - long double complex cpowl(long double complex x, - long double complex y); - -[page 194] - - Description -2 The cpow functions compute the complex power function xy , with a branch cut for the - first parameter along the negative real axis. - Returns -3 The cpow functions return the complex power function value. - 7.3.8.3 The csqrt functions - Synopsis -1 #include - double complex csqrt(double complex z); - float complex csqrtf(float complex z); - long double complex csqrtl(long double complex z); - Description -2 The csqrt functions compute the complex square root of z, with a branch cut along the - negative real axis. - Returns -3 The csqrt functions return the complex square root value, in the range of the right half- - plane (including the imaginary axis). - 7.3.9 Manipulation functions - 7.3.9.1 The carg functions - Synopsis -1 #include - double carg(double complex z); - float cargf(float complex z); - long double cargl(long double complex z); - Description -2 The carg functions compute the argument (also called phase angle) of z, with a branch - cut along the negative real axis. - Returns -3 The carg functions return the value of the argument in the interval [-pi , +pi ]. - -[page 195] - - 7.3.9.2 The cimag functions - Synopsis -1 #include - double cimag(double complex z); - float cimagf(float complex z); - long double cimagl(long double complex z); - Description -2 The cimag functions compute the imaginary part of z.196) - Returns -3 The cimag functions return the imaginary part value (as a real). - 7.3.9.3 The CMPLX macros - Synopsis -1 #include - double complex CMPLX(double x, double y); - float complex CMPLXF(float x, float y); - long double complex CMPLXL(long double x, long double y); - Description -2 The CMPLX macros expand to an expression of the specified complex type, with the real - part having the (converted) value of x and the imaginary part having the (converted) - value of y. - Recommended practice -3 The resulting expression should be suitable for use as an initializer for an object with - static or thread storage duration, provided both arguments are likewise suitable. - Returns -4 The CMPLX macros return the complex value x + i y. -5 NOTE These macros act as if the implementation supported imaginary types and the definitions were: - #define CMPLX(x, y) ((double complex)((double)(x) + \ - _Imaginary_I * (double)(y))) - #define CMPLXF(x, y) ((float complex)((float)(x) + \ - _Imaginary_I * (float)(y))) - #define CMPLXL(x, y) ((long double complex)((long double)(x) + \ - _Imaginary_I * (long double)(y))) - - - - - 196) For a variable z of complex type, z == creal(z) + cimag(z)*I. - -[page 196] - - 7.3.9.4 The conj functions - Synopsis -1 #include - double complex conj(double complex z); - float complex conjf(float complex z); - long double complex conjl(long double complex z); - Description -2 The conj functions compute the complex conjugate of z, by reversing the sign of its - imaginary part. - Returns -3 The conj functions return the complex conjugate value. - 7.3.9.5 The cproj functions - Synopsis -1 #include - double complex cproj(double complex z); - float complex cprojf(float complex z); - long double complex cprojl(long double complex z); - Description -2 The cproj functions compute a projection of z onto the Riemann sphere: z projects to - z except that all complex infinities (even those with one infinite part and one NaN part) - project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is - equivalent to - INFINITY + I * copysign(0.0, cimag(z)) - Returns -3 The cproj functions return the value of the projection onto the Riemann sphere. - 7.3.9.6 The creal functions - Synopsis -1 #include - double creal(double complex z); - float crealf(float complex z); - long double creall(long double complex z); - Description -2 The creal functions compute the real part of z.197) - -[page 197] - - Returns -3 The creal functions return the real part value. - - - - - 197) For a variable z of complex type, z == creal(z) + cimag(z)*I. - -[page 198] - - 7.4 Character handling -1 The header declares several functions useful for classifying and mapping - characters.198) In all cases the argument is an int, the value of which shall be - representable as an unsigned char or shall equal the value of the macro EOF. If the - argument has any other value, the behavior is undefined. -2 The behavior of these functions is affected by the current locale. Those functions that - have locale-specific aspects only when not in the "C" locale are noted below. -3 The term printing character refers to a member of a locale-specific set of characters, each - of which occupies one printing position on a display device; the term control character - refers to a member of a locale-specific set of characters that are not printing - characters.199) All letters and digits are printing characters. - Forward references: EOF (7.21.1), localization (7.11). - 7.4.1 Character classification functions -1 The functions in this subclause return nonzero (true) if and only if the value of the - argument c conforms to that in the description of the function. - 7.4.1.1 The isalnum function - Synopsis -1 #include - int isalnum(int c); - Description -2 The isalnum function tests for any character for which isalpha or isdigit is true. - 7.4.1.2 The isalpha function - Synopsis -1 #include - int isalpha(int c); - Description -2 The isalpha function tests for any character for which isupper or islower is true, - or any character that is one of a locale-specific set of alphabetic characters for which - - - - 198) See ''future library directions'' (7.30.2). - 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those - whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose - values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL). - -[page 199] - - none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale, - isalpha returns true only for the characters for which isupper or islower is true. - 7.4.1.3 The isblank function - Synopsis -1 #include - int isblank(int c); - Description -2 The isblank function tests for any character that is a standard blank character or is one - of a locale-specific set of characters for which isspace is true and that is used to - separate words within a line of text. The standard blank characters are the following: - space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only - for the standard blank characters. - 7.4.1.4 The iscntrl function - Synopsis -1 #include - int iscntrl(int c); - Description -2 The iscntrl function tests for any control character. - 7.4.1.5 The isdigit function - Synopsis -1 #include - int isdigit(int c); - Description -2 The isdigit function tests for any decimal-digit character (as defined in 5.2.1). - 7.4.1.6 The isgraph function - Synopsis -1 #include - int isgraph(int c); - - - - - 200) The functions islower and isupper test true or false separately for each of these additional - characters; all four combinations are possible. - -[page 200] - - Description -2 The isgraph function tests for any printing character except space (' '). - 7.4.1.7 The islower function - Synopsis -1 #include - int islower(int c); - Description -2 The islower function tests for any character that is a lowercase letter or is one of a - locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or - isspace is true. In the "C" locale, islower returns true only for the lowercase - letters (as defined in 5.2.1). - 7.4.1.8 The isprint function - Synopsis -1 #include - int isprint(int c); - Description -2 The isprint function tests for any printing character including space (' '). - 7.4.1.9 The ispunct function - Synopsis -1 #include - int ispunct(int c); - Description -2 The ispunct function tests for any printing character that is one of a locale-specific set - of punctuation characters for which neither isspace nor isalnum is true. In the "C" - locale, ispunct returns true for every printing character for which neither isspace - nor isalnum is true. - 7.4.1.10 The isspace function - Synopsis -1 #include - int isspace(int c); - Description -2 The isspace function tests for any character that is a standard white-space character or - is one of a locale-specific set of characters for which isalnum is false. The standard - -[page 201] - - white-space characters are the following: space (' '), form feed ('\f'), new-line - ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the - "C" locale, isspace returns true only for the standard white-space characters. - 7.4.1.11 The isupper function - Synopsis -1 #include - int isupper(int c); - Description -2 The isupper function tests for any character that is an uppercase letter or is one of a - locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or - isspace is true. In the "C" locale, isupper returns true only for the uppercase - letters (as defined in 5.2.1). - 7.4.1.12 The isxdigit function - Synopsis -1 #include - int isxdigit(int c); - Description -2 The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1). - 7.4.2 Character case mapping functions - 7.4.2.1 The tolower function - Synopsis -1 #include - int tolower(int c); - Description -2 The tolower function converts an uppercase letter to a corresponding lowercase letter. - Returns -3 If the argument is a character for which isupper is true and there are one or more - corresponding characters, as specified by the current locale, for which islower is true, - the tolower function returns one of the corresponding characters (always the same one - for any given locale); otherwise, the argument is returned unchanged. - -[page 202] - - 7.4.2.2 The toupper function - Synopsis -1 #include - int toupper(int c); - Description -2 The toupper function converts a lowercase letter to a corresponding uppercase letter. - Returns -3 If the argument is a character for which islower is true and there are one or more - corresponding characters, as specified by the current locale, for which isupper is true, - the toupper function returns one of the corresponding characters (always the same one - for any given locale); otherwise, the argument is returned unchanged. - -[page 203] - - 7.5 Errors -1 The header defines several macros, all relating to the reporting of error - conditions. -2 The macros are - EDOM - EILSEQ - ERANGE - which expand to integer constant expressions with type int, distinct positive values, and - which are suitable for use in #if preprocessing directives; and - errno - which expands to a modifiable lvalue201) that has type int and thread local storage - duration, the value of which is set to a positive error number by several library functions. - If a macro definition is suppressed in order to access an actual object, or a program - defines an identifier with the name errno, the behavior is undefined. -3 The value of errno in the initial thread is zero at program startup (the initial value of - errno in other threads is an indeterminate value), but is never set to zero by any library - function.202) The value of errno may be set to nonzero by a library function call - whether or not there is an error, provided the use of errno is not documented in the - description of the function in this International Standard. -4 Additional macro definitions, beginning with E and a digit or E and an uppercase - letter,203) may also be specified by the implementation. - - - - - 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue - resulting from a function call (for example, *errno()). - 202) Thus, a program that uses errno for error checking should set it to zero before a library function call, - then inspect it before a subsequent library function call. Of course, a library function can save the - value of errno on entry and then set it to zero, as long as the original value is restored if errno's - value is still zero just before the return. - 203) See ''future library directions'' (7.30.3). - -[page 204] - - 7.6 Floating-point environment -1 The header defines several macros, and declares types and functions that - provide access to the floating-point environment. The floating-point environment refers - collectively to any floating-point status flags and control modes supported by the - implementation.204) A floating-point status flag is a system variable whose value is set - (but never cleared) when a floating-point exception is raised, which occurs as a side effect - of exceptional floating-point arithmetic to provide auxiliary information.205) A floating- - point control mode is a system variable whose value may be set by the user to affect the - subsequent behavior of floating-point arithmetic. -2 The floating-point environment has thread storage duration. The initial state for a - thread's floating-point environment is the current state of the floating-point environment - of the thread that creates it at the time of creation. -3 Certain programming conventions support the intended model of use for the floating- - point environment:206) - -- a function call does not alter its caller's floating-point control modes, clear its caller's - floating-point status flags, nor depend on the state of its caller's floating-point status - flags unless the function is so documented; - -- a function call is assumed to require default floating-point control modes, unless its - documentation promises otherwise; - -- a function call is assumed to have the potential for raising floating-point exceptions, - unless its documentation promises otherwise. -4 The type - fenv_t - represents the entire floating-point environment. -5 The type - fexcept_t - represents the floating-point status flags collectively, including any status the - implementation associates with the flags. - - - 204) This header is designed to support the floating-point exception status flags and directed-rounding - control modes required by IEC 60559, and other similar floating-point state information. It is also - designed to facilitate code portability among all systems. - 205) A floating-point status flag is not an object and can be set more than once within an expression. - 206) With these conventions, a programmer can safely assume default floating-point control modes (or be - unaware of them). The responsibilities associated with accessing the floating-point environment fall - on the programmer or program that does so explicitly. - -[page 205] - -6 Each of the macros - FE_DIVBYZERO - FE_INEXACT - FE_INVALID - FE_OVERFLOW - FE_UNDERFLOW - is defined if and only if the implementation supports the floating-point exception by - means of the functions in 7.6.2.207) Additional implementation-defined floating-point - exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also - be specified by the implementation. The defined macros expand to integer constant - expressions with values such that bitwise ORs of all combinations of the macros result in - distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in - zero.208) -7 The macro - FE_ALL_EXCEPT - is simply the bitwise OR of all floating-point exception macros defined by the - implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0. -8 Each of the macros - FE_DOWNWARD - FE_TONEAREST - FE_TOWARDZERO - FE_UPWARD - is defined if and only if the implementation supports getting and setting the represented - rounding direction by means of the fegetround and fesetround functions. - Additional implementation-defined rounding directions, with macro definitions beginning - with FE_ and an uppercase letter, may also be specified by the implementation. The - defined macros expand to integer constant expressions whose values are distinct - nonnegative values.209) -9 The macro - - - - 207) The implementation supports a floating-point exception if there are circumstances where a call to at - least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not - necessary for all the functions to succeed all the time. - 208) The macros should be distinct powers of two. - 209) Even though the rounding direction macros may expand to constants corresponding to the values of - FLT_ROUNDS, they are not required to do so. - -[page 206] - - FE_DFL_ENV - represents the default floating-point environment -- the one installed at program startup - -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to - functions that manage the floating-point environment. -10 Additional implementation-defined environments, with macro definitions beginning with - FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may - also be specified by the implementation. - 7.6.1 The FENV_ACCESS pragma - Synopsis -1 #include - #pragma STDC FENV_ACCESS on-off-switch - Description -2 The FENV_ACCESS pragma provides a means to inform the implementation when a - program might access the floating-point environment to test floating-point status flags or - run under non-default floating-point control modes.210) The pragma shall occur either - outside external declarations or preceding all explicit declarations and statements inside a - compound statement. When outside external declarations, the pragma takes effect from - its occurrence until another FENV_ACCESS pragma is encountered, or until the end of - the translation unit. When inside a compound statement, the pragma takes effect from its - occurrence until another FENV_ACCESS pragma is encountered (including within a - nested compound statement), or until the end of the compound statement; at the end of a - compound statement the state for the pragma is restored to its condition just before the - compound statement. If this pragma is used in any other context, the behavior is - undefined. If part of a program tests floating-point status flags, sets floating-point control - modes, or runs under non-default mode settings, but was translated with the state for the - FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or - ''off'') for the pragma is implementation-defined. (When execution passes from a part of - the program translated with FENV_ACCESS ''off'' to a part translated with - FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the - floating-point control modes have their default settings.) - - - - - 210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag - tests and mode changes (e.g., global common subexpression elimination, code motion, and constant - folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default - modes are in effect and the flags are not tested. - -[page 207] - -3 EXAMPLE - #include - void f(double x) - { - #pragma STDC FENV_ACCESS ON - void g(double); - void h(double); - /* ... */ - g(x + 1); - h(x + 1); - /* ... */ - } -4 If the function g might depend on status flags set as a side effect of the first x + 1, or if the second - x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall - contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211) - - 7.6.2 Floating-point exceptions -1 The following functions provide access to the floating-point status flags.212) The int - input argument for the functions represents a subset of floating-point exceptions, and can - be zero or the bitwise OR of one or more floating-point exception macros, for example - FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these - functions is undefined. - 7.6.2.1 The feclearexcept function - Synopsis -1 #include - int feclearexcept(int excepts); - Description -2 The feclearexcept function attempts to clear the supported floating-point exceptions - represented by its argument. - Returns -3 The feclearexcept function returns zero if the excepts argument is zero or if all - the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value. - - - 211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other - hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is - ''off'', just one evaluation of x + 1 would suffice. - 212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic - abstraction of flags that are either set or clear. An implementation may endow floating-point status - flags with more information -- for example, the address of the code which first raised the floating- - point exception; the functions fegetexceptflag and fesetexceptflag deal with the full - content of flags. - -[page 208] - - 7.6.2.2 The fegetexceptflag function - Synopsis -1 #include - int fegetexceptflag(fexcept_t *flagp, - int excepts); - Description -2 The fegetexceptflag function attempts to store an implementation-defined - representation of the states of the floating-point status flags indicated by the argument - excepts in the object pointed to by the argument flagp. - Returns -3 The fegetexceptflag function returns zero if the representation was successfully - stored. Otherwise, it returns a nonzero value. - 7.6.2.3 The feraiseexcept function - Synopsis -1 #include - int feraiseexcept(int excepts); - Description -2 The feraiseexcept function attempts to raise the supported floating-point exceptions - represented by its argument.213) The order in which these floating-point exceptions are - raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function - additionally raises the ''inexact'' floating-point exception whenever it raises the - ''overflow'' or ''underflow'' floating-point exception is implementation-defined. - Returns -3 The feraiseexcept function returns zero if the excepts argument is zero or if all - the specified exceptions were successfully raised. Otherwise, it returns a nonzero value. - - - - - 213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations. - Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification - in F.8.6 is in the same spirit. - -[page 209] - - 7.6.2.4 The fesetexceptflag function - Synopsis -1 #include - int fesetexceptflag(const fexcept_t *flagp, - int excepts); - Description -2 The fesetexceptflag function attempts to set the floating-point status flags - indicated by the argument excepts to the states stored in the object pointed to by - flagp. The value of *flagp shall have been set by a previous call to - fegetexceptflag whose second argument represented at least those floating-point - exceptions represented by the argument excepts. This function does not raise floating- - point exceptions, but only sets the state of the flags. - Returns -3 The fesetexceptflag function returns zero if the excepts argument is zero or if - all the specified flags were successfully set to the appropriate state. Otherwise, it returns - a nonzero value. - 7.6.2.5 The fetestexcept function - Synopsis -1 #include - int fetestexcept(int excepts); - Description -2 The fetestexcept function determines which of a specified subset of the floating- - point exception flags are currently set. The excepts argument specifies the floating- - point status flags to be queried.214) - Returns -3 The fetestexcept function returns the value of the bitwise OR of the floating-point - exception macros corresponding to the currently set floating-point exceptions included in - excepts. -4 EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set: - - - - - 214) This mechanism allows testing several floating-point exceptions with just one function call. - -[page 210] - - #include - /* ... */ - { - #pragma STDC FENV_ACCESS ON - int set_excepts; - feclearexcept(FE_INVALID | FE_OVERFLOW); - // maybe raise exceptions - set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW); - if (set_excepts & FE_INVALID) f(); - if (set_excepts & FE_OVERFLOW) g(); - /* ... */ - } - - 7.6.3 Rounding -1 The fegetround and fesetround functions provide control of rounding direction - modes. - 7.6.3.1 The fegetround function - Synopsis -1 #include - int fegetround(void); - Description -2 The fegetround function gets the current rounding direction. - Returns -3 The fegetround function returns the value of the rounding direction macro - representing the current rounding direction or a negative value if there is no such - rounding direction macro or the current rounding direction is not determinable. - 7.6.3.2 The fesetround function - Synopsis -1 #include - int fesetround(int round); - Description -2 The fesetround function establishes the rounding direction represented by its - argument round. If the argument is not equal to the value of a rounding direction macro, - the rounding direction is not changed. - Returns -3 The fesetround function returns zero if and only if the requested rounding direction - was established. - -[page 211] - -4 EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the - rounding direction fails. - #include - #include - void f(int round_dir) - { - #pragma STDC FENV_ACCESS ON - int save_round; - int setround_ok; - save_round = fegetround(); - setround_ok = fesetround(round_dir); - assert(setround_ok == 0); - /* ... */ - fesetround(save_round); - /* ... */ - } - - 7.6.4 Environment -1 The functions in this section manage the floating-point environment -- status flags and - control modes -- as one entity. - 7.6.4.1 The fegetenv function - Synopsis -1 #include - int fegetenv(fenv_t *envp); - Description -2 The fegetenv function attempts to store the current floating-point environment in the - object pointed to by envp. - Returns -3 The fegetenv function returns zero if the environment was successfully stored. - Otherwise, it returns a nonzero value. - 7.6.4.2 The feholdexcept function - Synopsis -1 #include - int feholdexcept(fenv_t *envp); - Description -2 The feholdexcept function saves the current floating-point environment in the object - pointed to by envp, clears the floating-point status flags, and then installs a non-stop - (continue on floating-point exceptions) mode, if available, for all floating-point - exceptions.215) - -[page 212] - - Returns -3 The feholdexcept function returns zero if and only if non-stop floating-point - exception handling was successfully installed. - 7.6.4.3 The fesetenv function - Synopsis -1 #include - int fesetenv(const fenv_t *envp); - Description -2 The fesetenv function attempts to establish the floating-point environment represented - by the object pointed to by envp. The argument envp shall point to an object set by a - call to fegetenv or feholdexcept, or equal a floating-point environment macro. - Note that fesetenv merely installs the state of the floating-point status flags - represented through its argument, and does not raise these floating-point exceptions. - Returns -3 The fesetenv function returns zero if the environment was successfully established. - Otherwise, it returns a nonzero value. - 7.6.4.4 The feupdateenv function - Synopsis -1 #include - int feupdateenv(const fenv_t *envp); - Description -2 The feupdateenv function attempts to save the currently raised floating-point - exceptions in its automatic storage, install the floating-point environment represented by - the object pointed to by envp, and then raise the saved floating-point exceptions. The - argument envp shall point to an object set by a call to feholdexcept or fegetenv, - or equal a floating-point environment macro. - Returns -3 The feupdateenv function returns zero if all the actions were successfully carried out. - Otherwise, it returns a nonzero value. - - - - - 215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap - handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For - such systems, the feholdexcept function can be used in conjunction with the feupdateenv - function to write routines that hide spurious floating-point exceptions from their callers. - -[page 213] - -4 EXAMPLE Hide spurious underflow floating-point exceptions: - #include - double f(double x) - { - #pragma STDC FENV_ACCESS ON - double result; - fenv_t save_env; - if (feholdexcept(&save_env)) - return /* indication of an environmental problem */; - // compute result - if (/* test spurious underflow */) - if (feclearexcept(FE_UNDERFLOW)) - return /* indication of an environmental problem */; - if (feupdateenv(&save_env)) - return /* indication of an environmental problem */; - return result; - } - -[page 214] - - 7.7 Characteristics of floating types -1 The header defines several macros that expand to various limits and - parameters of the standard floating-point types. -2 The macros, their meanings, and the constraints (or restrictions) on their values are listed - in 5.2.4.2.2. - -[page 215] - - 7.8 Format conversion of integer types -1 The header includes the header and extends it with - additional facilities provided by hosted implementations. -2 It declares functions for manipulating greatest-width integers and converting numeric - character strings to greatest-width integers, and it declares the type - imaxdiv_t - which is a structure type that is the type of the value returned by the imaxdiv function. - For each type declared in , it defines corresponding macros for conversion - specifiers for use with the formatted input/output functions.216) - Forward references: integer types (7.20), formatted input/output - functions (7.21.6), formatted wide character input/output functions (7.28.2). - 7.8.1 Macros for format specifiers -1 Each of the following object-like macros expands to a character string literal containing a * - conversion specifier, possibly modified by a length modifier, suitable for use within the - format argument of a formatted input/output function when converting the corresponding - integer type. These macro names have the general form of PRI (character string literals - for the fprintf and fwprintf family) or SCN (character string literals for the - fscanf and fwscanf family),217) followed by the conversion specifier, followed by a - name corresponding to a similar type name in 7.20.1. In these names, N represents the - width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a - format string to print the value of an integer of type int_fast32_t. -2 The fprintf macros for signed integers are: - PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR - PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR -3 The fprintf macros for unsigned integers are: - PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR - PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR - PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR - PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR -4 The fscanf macros for signed integers are: - - - - 216) See ''future library directions'' (7.30.4). - 217) Separate macros are given for use with fprintf and fscanf functions because, in the general case, - different format specifiers may be required for fprintf and fscanf, even when the type is the - same. - -[page 216] - - SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR - SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR -5 The fscanf macros for unsigned integers are: - SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR - SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR - SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR -6 For each type that the implementation provides in , the corresponding - fprintf macros shall be defined and the corresponding fscanf macros shall be - defined unless the implementation does not have a suitable fscanf length modifier for - the type. -7 EXAMPLE - #include - #include - int main(void) - { - uintmax_t i = UINTMAX_MAX; // this type always exists - wprintf(L"The largest integer value is %020" - PRIxMAX "\n", i); - return 0; - } - - 7.8.2 Functions for greatest-width integer types - 7.8.2.1 The imaxabs function - Synopsis -1 #include - intmax_t imaxabs(intmax_t j); - Description -2 The imaxabs function computes the absolute value of an integer j. If the result cannot - be represented, the behavior is undefined.218) - Returns -3 The imaxabs function returns the absolute value. - - - - - 218) The absolute value of the most negative number cannot be represented in two's complement. - -[page 217] - - 7.8.2.2 The imaxdiv function - Synopsis -1 #include - imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); - Description -2 The imaxdiv function computes numer / denom and numer % denom in a single - operation. - Returns -3 The imaxdiv function returns a structure of type imaxdiv_t comprising both the - quotient and the remainder. The structure shall contain (in either order) the members - quot (the quotient) and rem (the remainder), each of which has type intmax_t. If - either part of the result cannot be represented, the behavior is undefined. - 7.8.2.3 The strtoimax and strtoumax functions - Synopsis -1 #include - intmax_t strtoimax(const char * restrict nptr, - char ** restrict endptr, int base); - uintmax_t strtoumax(const char * restrict nptr, - char ** restrict endptr, int base); - Description -2 The strtoimax and strtoumax functions are equivalent to the strtol, strtoll, - strtoul, and strtoull functions, except that the initial portion of the string is - converted to intmax_t and uintmax_t representation, respectively. - Returns -3 The strtoimax and strtoumax functions return the converted value, if any. If no - conversion could be performed, zero is returned. If the correct value is outside the range - of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned - (according to the return type and sign of the value, if any), and the value of the macro - ERANGE is stored in errno. - Forward references: the strtol, strtoll, strtoul, and strtoull functions - (7.22.1.4). - -[page 218] - - 7.8.2.4 The wcstoimax and wcstoumax functions - Synopsis -1 #include // for wchar_t - #include - intmax_t wcstoimax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - uintmax_t wcstoumax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - Description -2 The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll, - wcstoul, and wcstoull functions except that the initial portion of the wide string is - converted to intmax_t and uintmax_t representation, respectively. - Returns -3 The wcstoimax function returns the converted value, if any. If no conversion could be - performed, zero is returned. If the correct value is outside the range of representable - values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the - return type and sign of the value, if any), and the value of the macro ERANGE is stored in - errno. - Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions - (7.28.4.1.2). - -[page 219] - - 7.9 Alternative spellings -1 The header defines the following eleven macros (on the left) that expand - to the corresponding tokens (on the right): - and && - and_eq &= - bitand & - bitor | - compl ~ - not ! - not_eq != - or || - or_eq |= - xor ^ - xor_eq ^= - -[page 220] - - 7.10 Sizes of integer types -1 The header defines several macros that expand to various limits and - parameters of the standard integer types. -2 The macros, their meanings, and the constraints (or restrictions) on their values are listed - in 5.2.4.2.1. - -[page 221] - - 7.11 Localization -1 The header declares two functions, one type, and defines several macros. -2 The type is - struct lconv - which contains members related to the formatting of numeric values. The structure shall - contain at least the following members, in any order. The semantics of the members and - their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have - the values specified in the comments. - char *decimal_point; // "." - char *thousands_sep; // "" - char *grouping; // "" - char *mon_decimal_point; // "" - char *mon_thousands_sep; // "" - char *mon_grouping; // "" - char *positive_sign; // "" - char *negative_sign; // "" - char *currency_symbol; // "" - char frac_digits; // CHAR_MAX - char p_cs_precedes; // CHAR_MAX - char n_cs_precedes; // CHAR_MAX - char p_sep_by_space; // CHAR_MAX - char n_sep_by_space; // CHAR_MAX - char p_sign_posn; // CHAR_MAX - char n_sign_posn; // CHAR_MAX - char *int_curr_symbol; // "" - char int_frac_digits; // CHAR_MAX - char int_p_cs_precedes; // CHAR_MAX - char int_n_cs_precedes; // CHAR_MAX - char int_p_sep_by_space; // CHAR_MAX - char int_n_sep_by_space; // CHAR_MAX - char int_p_sign_posn; // CHAR_MAX - char int_n_sign_posn; // CHAR_MAX - -[page 222] - -3 The macros defined are NULL (described in 7.19); and - LC_ALL - LC_COLLATE - LC_CTYPE - LC_MONETARY - LC_NUMERIC - LC_TIME - which expand to integer constant expressions with distinct values, suitable for use as the - first argument to the setlocale function.219) Additional macro definitions, beginning - with the characters LC_ and an uppercase letter,220) may also be specified by the - implementation. - 7.11.1 Locale control - 7.11.1.1 The setlocale function - Synopsis -1 #include - char *setlocale(int category, const char *locale); - Description -2 The setlocale function selects the appropriate portion of the program's locale as - specified by the category and locale arguments. The setlocale function may be - used to change or query the program's entire current locale or portions thereof. The value - LC_ALL for category names the program's entire locale; the other values for - category name only a portion of the program's locale. LC_COLLATE affects the - behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of - the character handling functions221) and the multibyte and wide character functions. - LC_MONETARY affects the monetary formatting information returned by the - localeconv function. LC_NUMERIC affects the decimal-point character for the - formatted input/output functions and the string conversion functions, as well as the - nonmonetary formatting information returned by the localeconv function. LC_TIME - affects the behavior of the strftime and wcsftime functions. -3 A value of "C" for locale specifies the minimal environment for C translation; a value - of "" for locale specifies the locale-specific native environment. Other - implementation-defined strings may be passed as the second argument to setlocale. - - 219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C. - 220) See ''future library directions'' (7.30.5). - 221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and - isxdigit. - -[page 223] - -4 At program startup, the equivalent of - setlocale(LC_ALL, "C"); - is executed. -5 A call to the setlocale function may introduce a data race with other calls to the - setlocale function or with calls to functions that are affected by the current locale. - The implementation shall behave as if no library function calls the setlocale function. - Returns -6 If a pointer to a string is given for locale and the selection can be honored, the - setlocale function returns a pointer to the string associated with the specified - category for the new locale. If the selection cannot be honored, the setlocale - function returns a null pointer and the program's locale is not changed. -7 A null pointer for locale causes the setlocale function to return a pointer to the - string associated with the category for the program's current locale; the program's - locale is not changed.222) -8 The pointer to string returned by the setlocale function is such that a subsequent call - with that string value and its associated category will restore that part of the program's - locale. The string pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the setlocale function. - Forward references: formatted input/output functions (7.21.6), multibyte/wide - character conversion functions (7.22.7), multibyte/wide string conversion functions - (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the - strftime function (7.26.3.5), the strxfrm function (7.23.4.5). - 7.11.2 Numeric formatting convention inquiry - 7.11.2.1 The localeconv function - Synopsis -1 #include - struct lconv *localeconv(void); - Description -2 The localeconv function sets the components of an object with type struct lconv - with values appropriate for the formatting of numeric quantities (monetary and otherwise) - according to the rules of the current locale. - - - - 222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous - locale when category has the value LC_ALL. - -[page 224] - -3 The members of the structure with type char * are pointers to strings, any of which - (except decimal_point) can point to "", to indicate that the value is not available in - the current locale or is of zero length. Apart from grouping and mon_grouping, the - strings shall start and end in the initial shift state. The members with type char are - nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not - available in the current locale. The members include the following: - char *decimal_point - The decimal-point character used to format nonmonetary quantities. - char *thousands_sep - The character used to separate groups of digits before the decimal-point - character in formatted nonmonetary quantities. - char *grouping - A string whose elements indicate the size of each group of digits in - formatted nonmonetary quantities. - char *mon_decimal_point - The decimal-point used to format monetary quantities. - char *mon_thousands_sep - The separator for groups of digits before the decimal-point in formatted - monetary quantities. - char *mon_grouping - A string whose elements indicate the size of each group of digits in - formatted monetary quantities. - char *positive_sign - The string used to indicate a nonnegative-valued formatted monetary - quantity. - char *negative_sign - The string used to indicate a negative-valued formatted monetary quantity. - char *currency_symbol - The local currency symbol applicable to the current locale. - char frac_digits - The number of fractional digits (those after the decimal-point) to be - displayed in a locally formatted monetary quantity. - char p_cs_precedes - Set to 1 or 0 if the currency_symbol respectively precedes or - succeeds the value for a nonnegative locally formatted monetary quantity. - -[page 225] - -char n_cs_precedes - Set to 1 or 0 if the currency_symbol respectively precedes or - succeeds the value for a negative locally formatted monetary quantity. -char p_sep_by_space - Set to a value indicating the separation of the currency_symbol, the - sign string, and the value for a nonnegative locally formatted monetary - quantity. -char n_sep_by_space - Set to a value indicating the separation of the currency_symbol, the - sign string, and the value for a negative locally formatted monetary - quantity. -char p_sign_posn - Set to a value indicating the positioning of the positive_sign for a - nonnegative locally formatted monetary quantity. -char n_sign_posn - Set to a value indicating the positioning of the negative_sign for a - negative locally formatted monetary quantity. -char *int_curr_symbol - The international currency symbol applicable to the current locale. The - first three characters contain the alphabetic international currency symbol - in accordance with those specified in ISO 4217. The fourth character - (immediately preceding the null character) is the character used to separate - the international currency symbol from the monetary quantity. -char int_frac_digits - The number of fractional digits (those after the decimal-point) to be - displayed in an internationally formatted monetary quantity. -char int_p_cs_precedes - Set to 1 or 0 if the int_curr_symbol respectively precedes or - succeeds the value for a nonnegative internationally formatted monetary - quantity. -char int_n_cs_precedes - Set to 1 or 0 if the int_curr_symbol respectively precedes or - succeeds the value for a negative internationally formatted monetary - quantity. -char int_p_sep_by_space - Set to a value indicating the separation of the int_curr_symbol, the - sign string, and the value for a nonnegative internationally formatted - monetary quantity. - -[page 226] - - char int_n_sep_by_space - Set to a value indicating the separation of the int_curr_symbol, the - sign string, and the value for a negative internationally formatted monetary - quantity. - char int_p_sign_posn - Set to a value indicating the positioning of the positive_sign for a - nonnegative internationally formatted monetary quantity. - char int_n_sign_posn - Set to a value indicating the positioning of the negative_sign for a - negative internationally formatted monetary quantity. -4 The elements of grouping and mon_grouping are interpreted according to the - following: - CHAR_MAX No further grouping is to be performed. - 0 The previous element is to be repeatedly used for the remainder of the - digits. - other The integer value is the number of digits that compose the current group. - The next element is examined to determine the size of the next group of - digits before the current group. -5 The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space, - and int_n_sep_by_space are interpreted according to the following: - 0 No space separates the currency symbol and value. - 1 If the currency symbol and sign string are adjacent, a space separates them from the - value; otherwise, a space separates the currency symbol from the value. - 2 If the currency symbol and sign string are adjacent, a space separates them; - otherwise, a space separates the sign string from the value. - For int_p_sep_by_space and int_n_sep_by_space, the fourth character of - int_curr_symbol is used instead of a space. -6 The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and - int_n_sign_posn are interpreted according to the following: - 0 Parentheses surround the quantity and currency symbol. - 1 The sign string precedes the quantity and currency symbol. - 2 The sign string succeeds the quantity and currency symbol. - 3 The sign string immediately precedes the currency symbol. - 4 The sign string immediately succeeds the currency symbol. - -[page 227] - -7 The implementation shall behave as if no library function calls the localeconv - function. - Returns -8 The localeconv function returns a pointer to the filled-in object. The structure - pointed to by the return value shall not be modified by the program, but may be - overwritten by a subsequent call to the localeconv function. In addition, calls to the - setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may - overwrite the contents of the structure. -9 EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format - monetary quantities. - Local format International format - - Country Positive Negative Positive Negative - - Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56 - Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234 - Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56 - Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C -10 For these four countries, the respective values for the monetary members of the structure returned by - localeconv could be: - Country1 Country2 Country3 Country4 - - mon_decimal_point "," "" "," "." - mon_thousands_sep "." "." "." "," - mon_grouping "\3" "\3" "\3" "\3" - positive_sign "" "" "" "" - negative_sign "-" "-" "-" "C" - currency_symbol "mk" "L." "\u0192" "SFrs." - frac_digits 2 0 2 2 - p_cs_precedes 0 1 1 1 - n_cs_precedes 0 1 1 1 - p_sep_by_space 1 0 1 0 - n_sep_by_space 1 0 2 0 - p_sign_posn 1 1 1 1 - n_sign_posn 1 1 4 2 - int_curr_symbol "FIM " "ITL " "NLG " "CHF " - int_frac_digits 2 0 2 2 - int_p_cs_precedes 1 1 1 1 - int_n_cs_precedes 1 1 1 1 - int_p_sep_by_space 1 1 1 1 - int_n_sep_by_space 2 1 2 1 - int_p_sign_posn 1 1 1 1 - int_n_sign_posn 4 1 4 2 - -[page 228] - -11 EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members - affect the formatted value. - p_sep_by_space - - p_cs_precedes p_sign_posn 0 1 2 - - 0 0 (1.25$) (1.25 $) (1.25$) - 1 +1.25$ +1.25 $ + 1.25$ - 2 1.25$+ 1.25 $+ 1.25$ + - 3 1.25+$ 1.25 +$ 1.25+ $ - 4 1.25$+ 1.25 $+ 1.25$ + - - 1 0 ($1.25) ($ 1.25) ($1.25) - 1 +$1.25 +$ 1.25 + $1.25 - 2 $1.25+ $ 1.25+ $1.25 + - 3 +$1.25 +$ 1.25 + $1.25 - 4 $+1.25 $+ 1.25 $ +1.25 - -[page 229] - - 7.12 Mathematics -1 The header declares two types and many mathematical functions and defines - several macros. Most synopses specify a family of functions consisting of a principal - function with one or more double parameters, a double return value, or both; and - other functions with the same name but with f and l suffixes, which are corresponding - functions with float and long double parameters, return values, or both.223) - Integer arithmetic functions and conversion functions are discussed later. -2 The types - float_t - double_t - are floating types at least as wide as float and double, respectively, and such that - double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0, - float_t and double_t are float and double, respectively; if - FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals - 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are - otherwise implementation-defined.224) -3 The macro - HUGE_VAL - expands to a positive double constant expression, not necessarily representable as a - float. The macros - HUGE_VALF - HUGE_VALL - are respectively float and long double analogs of HUGE_VAL.225) -4 The macro - INFINITY - expands to a constant expression of type float representing positive or unsigned - infinity, if available; else to a positive constant of type float that overflows at - - - - 223) Particularly on systems with wide expression evaluation, a function might pass arguments - and return values in wider format than the synopsis prototype indicates. - 224) The types float_t and double_t are intended to be the implementation's most efficient types at - least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the - type float_t is the narrowest type used by the implementation to evaluate floating expressions. - 225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that - supports infinities. - -[page 230] - - translation time.226) -5 The macro - NAN - is defined if and only if the implementation supports quiet NaNs for the float type. It - expands to a constant expression of type float representing a quiet NaN. -6 The number classification macros - FP_INFINITE - FP_NAN - FP_NORMAL - FP_SUBNORMAL - FP_ZERO - represent the mutually exclusive kinds of floating-point values. They expand to integer - constant expressions with distinct values. Additional implementation-defined floating- - point classifications, with macro definitions beginning with FP_ and an uppercase letter, - may also be specified by the implementation. -7 The macro - FP_FAST_FMA - is optionally defined. If defined, it indicates that the fma function generally executes - about as fast as, or faster than, a multiply and an add of double operands.227) The - macros - FP_FAST_FMAF - FP_FAST_FMAL - are, respectively, float and long double analogs of FP_FAST_FMA. If defined, - these macros expand to the integer constant 1. -8 The macros - FP_ILOGB0 - FP_ILOGBNAN - expand to integer constant expressions whose values are returned by ilogb(x) if x is - zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or - -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN. - - - 226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic. - 227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented - directly with a hardware multiply-add instruction. Software implementations are expected to be - substantially slower. - -[page 231] - -9 The macros - MATH_ERRNO - MATH_ERREXCEPT - expand to the integer constants 1 and 2, respectively; the macro - math_errhandling - expands to an expression that has type int and the value MATH_ERRNO, - MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is - constant for the duration of the program. It is unspecified whether - math_errhandling is a macro or an identifier with external linkage. If a macro - definition is suppressed or a program defines an identifier with the name - math_errhandling, the behavior is undefined. If the expression - math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation - shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in - . - 7.12.1 Treatment of error conditions -1 The behavior of each of the functions in is specified for all representable - values of its input arguments, except where stated otherwise. Each function shall execute - as if it were a single operation without raising SIGFPE and without generating any of the - floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect - the result of the function. -2 For all functions, a domain error occurs if an input argument is outside the domain over - which the mathematical function is defined. The description of each function lists any - required domain errors; an implementation may define additional domain errors, provided - that such errors are consistent with the mathematical definition of the function.228) On a - domain error, the function returns an implementation-defined value; if the integer - expression math_errhandling & MATH_ERRNO is nonzero, the integer expression - errno acquires the value EDOM; if the integer expression math_errhandling & - MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised. -3 Similarly, a pole error (also known as a singularity or infinitary) occurs if the - mathematical function has an exact infinite result as the finite input argument(s) are - approached in the limit (for example, log(0.0)). The description of each function lists - any required pole errors; an implementation may define additional pole errors, provided - that such errors are consistent with the mathematical definition of the function. On a pole - error, the function returns an implementation-defined value; if the integer expression - - - 228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain - error if the mathematical domain of the function does not include the infinity. - -[page 232] - - math_errhandling & MATH_ERRNO is nonzero, the integer expression errno - acquires the value ERANGE; if the integer expression math_errhandling & - MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised. -4 Likewise, a range error occurs if the mathematical result of the function cannot be - represented in an object of the specified type, due to extreme magnitude. -5 A floating result overflows if the magnitude of the mathematical result is finite but so - large that the mathematical result cannot be represented without extraordinary roundoff - error in an object of the specified type. If a floating result overflows and default rounding - is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or * - HUGE_VALL according to the return type, with the same sign as the correct value of the - function; if the integer expression math_errhandling & MATH_ERRNO is nonzero, - the integer expression errno acquires the value ERANGE; if the integer expression - math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating- - point exception is raised. -6 The result underflows if the magnitude of the mathematical result is so small that the - mathematical result cannot be represented, without extraordinary roundoff error, in an - object of the specified type.229) If the result underflows, the function returns an - implementation-defined value whose magnitude is no greater than the smallest - normalized positive number in the specified type; if the integer expression - math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the - value ERANGE is implementation-defined; if the integer expression - math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow'' - floating-point exception is raised is implementation-defined. -7 If a domain, pole, or range error occurs and the integer expression - math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to - the value corresponding to the error or left unmodified. If no such error occurs, errno - shall be left unmodified regardless of the setting of math_errhandling. - - - - - 229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and - also ''flush-to-zero'' underflow. - 230) Math errors are being indicated by the floating-point exception flags rather than by errno. - -[page 233] - - 7.12.2 The FP_CONTRACT pragma - Synopsis -1 #include - #pragma STDC FP_CONTRACT on-off-switch - Description -2 The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the - state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur - either outside external declarations or preceding all explicit declarations and statements - inside a compound statement. When outside external declarations, the pragma takes - effect from its occurrence until another FP_CONTRACT pragma is encountered, or until - the end of the translation unit. When inside a compound statement, the pragma takes - effect from its occurrence until another FP_CONTRACT pragma is encountered - (including within a nested compound statement), or until the end of the compound - statement; at the end of a compound statement the state for the pragma is restored to its - condition just before the compound statement. If this pragma is used in any other - context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is - implementation-defined. - 7.12.3 Classification macros -1 In the synopses in this subclause, real-floating indicates that the argument shall be an - expression of real floating type. - 7.12.3.1 The fpclassify macro - Synopsis -1 #include - int fpclassify(real-floating x); - Description -2 The fpclassify macro classifies its argument value as NaN, infinite, normal, - subnormal, zero, or into another implementation-defined category. First, an argument - represented in a format wider than its semantic type is converted to its semantic type. - Then classification is based on the type of the argument.231) - Returns -3 The fpclassify macro returns the value of the number classification macro - appropriate to the value of its argument. * - - - 231) Since an expression can be evaluated with more range and precision than its type has, it is important to - know the type that classification is based on. For example, a normal long double value might - become subnormal when converted to double, and zero when converted to float. - -[page 234] - - 7.12.3.2 The isfinite macro - Synopsis -1 #include - int isfinite(real-floating x); - Description -2 The isfinite macro determines whether its argument has a finite value (zero, - subnormal, or normal, and not infinite or NaN). First, an argument represented in a - format wider than its semantic type is converted to its semantic type. Then determination - is based on the type of the argument. - Returns -3 The isfinite macro returns a nonzero value if and only if its argument has a finite - value. - 7.12.3.3 The isinf macro - Synopsis -1 #include - int isinf(real-floating x); - Description -2 The isinf macro determines whether its argument value is an infinity (positive or - negative). First, an argument represented in a format wider than its semantic type is - converted to its semantic type. Then determination is based on the type of the argument. - Returns -3 The isinf macro returns a nonzero value if and only if its argument has an infinite - value. - 7.12.3.4 The isnan macro - Synopsis -1 #include - int isnan(real-floating x); - Description -2 The isnan macro determines whether its argument value is a NaN. First, an argument - represented in a format wider than its semantic type is converted to its semantic type. - Then determination is based on the type of the argument.232) - - - 232) For the isnan macro, the type for determination does not matter unless the implementation supports - NaNs in the evaluation type but not in the semantic type. - -[page 235] - - Returns -3 The isnan macro returns a nonzero value if and only if its argument has a NaN value. - 7.12.3.5 The isnormal macro - Synopsis -1 #include - int isnormal(real-floating x); - Description -2 The isnormal macro determines whether its argument value is normal (neither zero, - subnormal, infinite, nor NaN). First, an argument represented in a format wider than its - semantic type is converted to its semantic type. Then determination is based on the type - of the argument. - Returns -3 The isnormal macro returns a nonzero value if and only if its argument has a normal - value. - 7.12.3.6 The signbit macro - Synopsis -1 #include - int signbit(real-floating x); - Description -2 The signbit macro determines whether the sign of its argument value is negative.233) - Returns -3 The signbit macro returns a nonzero value if and only if the sign of its argument value - is negative. - - - - - 233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is - unsigned, it is treated as positive. - -[page 236] - - 7.12.4 Trigonometric functions - 7.12.4.1 The acos functions - Synopsis -1 #include - double acos(double x); - float acosf(float x); - long double acosl(long double x); - Description -2 The acos functions compute the principal value of the arc cosine of x. A domain error - occurs for arguments not in the interval [-1, +1]. - Returns -3 The acos functions return arccos x in the interval [0, pi ] radians. - 7.12.4.2 The asin functions - Synopsis -1 #include - double asin(double x); - float asinf(float x); - long double asinl(long double x); - Description -2 The asin functions compute the principal value of the arc sine of x. A domain error - occurs for arguments not in the interval [-1, +1]. - Returns -3 The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians. - 7.12.4.3 The atan functions - Synopsis -1 #include - double atan(double x); - float atanf(float x); - long double atanl(long double x); - Description -2 The atan functions compute the principal value of the arc tangent of x. - -[page 237] - - Returns -3 The atan functions return arctan x in the interval [-pi /2, +pi /2] radians. - 7.12.4.4 The atan2 functions - Synopsis -1 #include - double atan2(double y, double x); - float atan2f(float y, float x); - long double atan2l(long double y, long double x); - Description -2 The atan2 functions compute the value of the arc tangent of y/x, using the signs of both - arguments to determine the quadrant of the return value. A domain error may occur if - both arguments are zero. - Returns -3 The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians. - 7.12.4.5 The cos functions - Synopsis -1 #include - double cos(double x); - float cosf(float x); - long double cosl(long double x); - Description -2 The cos functions compute the cosine of x (measured in radians). - Returns -3 The cos functions return cos x. - 7.12.4.6 The sin functions - Synopsis -1 #include - double sin(double x); - float sinf(float x); - long double sinl(long double x); - Description -2 The sin functions compute the sine of x (measured in radians). - -[page 238] - - Returns -3 The sin functions return sin x. - 7.12.4.7 The tan functions - Synopsis -1 #include - double tan(double x); - float tanf(float x); - long double tanl(long double x); - Description -2 The tan functions return the tangent of x (measured in radians). - Returns -3 The tan functions return tan x. - 7.12.5 Hyperbolic functions - 7.12.5.1 The acosh functions - Synopsis -1 #include - double acosh(double x); - float acoshf(float x); - long double acoshl(long double x); - Description -2 The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain - error occurs for arguments less than 1. - Returns -3 The acosh functions return arcosh x in the interval [0, +(inf)]. - 7.12.5.2 The asinh functions - Synopsis -1 #include - double asinh(double x); - float asinhf(float x); - long double asinhl(long double x); - Description -2 The asinh functions compute the arc hyperbolic sine of x. - -[page 239] - - Returns -3 The asinh functions return arsinh x. - 7.12.5.3 The atanh functions - Synopsis -1 #include - double atanh(double x); - float atanhf(float x); - long double atanhl(long double x); - Description -2 The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs - for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals - -1 or +1. - Returns -3 The atanh functions return artanh x. - 7.12.5.4 The cosh functions - Synopsis -1 #include - double cosh(double x); - float coshf(float x); - long double coshl(long double x); - Description -2 The cosh functions compute the hyperbolic cosine of x. A range error occurs if the - magnitude of x is too large. - Returns -3 The cosh functions return cosh x. - 7.12.5.5 The sinh functions - Synopsis -1 #include - double sinh(double x); - float sinhf(float x); - long double sinhl(long double x); - Description -2 The sinh functions compute the hyperbolic sine of x. A range error occurs if the - magnitude of x is too large. - -[page 240] - - Returns -3 The sinh functions return sinh x. - 7.12.5.6 The tanh functions - Synopsis -1 #include - double tanh(double x); - float tanhf(float x); - long double tanhl(long double x); - Description -2 The tanh functions compute the hyperbolic tangent of x. - Returns -3 The tanh functions return tanh x. - 7.12.6 Exponential and logarithmic functions - 7.12.6.1 The exp functions - Synopsis -1 #include - double exp(double x); - float expf(float x); - long double expl(long double x); - Description -2 The exp functions compute the base-e exponential of x. A range error occurs if the - magnitude of x is too large. - Returns -3 The exp functions return ex . - 7.12.6.2 The exp2 functions - Synopsis -1 #include - double exp2(double x); - float exp2f(float x); - long double exp2l(long double x); - Description -2 The exp2 functions compute the base-2 exponential of x. A range error occurs if the - magnitude of x is too large. - -[page 241] - - Returns -3 The exp2 functions return 2x . - 7.12.6.3 The expm1 functions - Synopsis -1 #include - double expm1(double x); - float expm1f(float x); - long double expm1l(long double x); - Description -2 The expm1 functions compute the base-e exponential of the argument, minus 1. A range - error occurs if x is too large.234) - Returns -3 The expm1 functions return ex - 1. - 7.12.6.4 The frexp functions - Synopsis -1 #include - double frexp(double value, int *exp); - float frexpf(float value, int *exp); - long double frexpl(long double value, int *exp); - Description -2 The frexp functions break a floating-point number into a normalized fraction and an - integral power of 2. They store the integer in the int object pointed to by exp. - Returns -3 If value is not a floating-point number or if the integral power of 2 is outside the range - of int, the results are unspecified. Otherwise, the frexp functions return the value x, - such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp . - If value is zero, both parts of the result are zero. - - - - - 234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1. - -[page 242] - - 7.12.6.5 The ilogb functions - Synopsis -1 #include - int ilogb(double x); - int ilogbf(float x); - int ilogbl(long double x); - Description -2 The ilogb functions extract the exponent of x as a signed int value. If x is zero they - compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is - a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling - the corresponding logb function and casting the returned value to type int. A domain - error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside - the range of the return type, the numeric result is unspecified. - Returns -3 The ilogb functions return the exponent of x as a signed int value. - Forward references: the logb functions (7.12.6.11). - 7.12.6.6 The ldexp functions - Synopsis -1 #include - double ldexp(double x, int exp); - float ldexpf(float x, int exp); - long double ldexpl(long double x, int exp); - Description -2 The ldexp functions multiply a floating-point number by an integral power of 2. A - range error may occur. - Returns -3 The ldexp functions return x x 2exp . - 7.12.6.7 The log functions - Synopsis -1 #include - double log(double x); - float logf(float x); - long double logl(long double x); - -[page 243] - - Description -2 The log functions compute the base-e (natural) logarithm of x. A domain error occurs if - the argument is negative. A pole error may occur if the argument is zero. - Returns -3 The log functions return loge x. - 7.12.6.8 The log10 functions - Synopsis -1 #include - double log10(double x); - float log10f(float x); - long double log10l(long double x); - Description -2 The log10 functions compute the base-10 (common) logarithm of x. A domain error - occurs if the argument is negative. A pole error may occur if the argument is zero. - Returns -3 The log10 functions return log10 x. - 7.12.6.9 The log1p functions - Synopsis -1 #include - double log1p(double x); - float log1pf(float x); - long double log1pl(long double x); - Description -2 The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235) - A domain error occurs if the argument is less than -1. A pole error may occur if the - argument equals -1. - Returns -3 The log1p functions return loge (1 + x). - - - - - 235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x). - -[page 244] - - 7.12.6.10 The log2 functions - Synopsis -1 #include - double log2(double x); - float log2f(float x); - long double log2l(long double x); - Description -2 The log2 functions compute the base-2 logarithm of x. A domain error occurs if the - argument is less than zero. A pole error may occur if the argument is zero. - Returns -3 The log2 functions return log2 x. - 7.12.6.11 The logb functions - Synopsis -1 #include - double logb(double x); - float logbf(float x); - long double logbl(long double x); - Description -2 The logb functions extract the exponent of x, as a signed integer value in floating-point - format. If x is subnormal it is treated as though it were normalized; thus, for positive - finite x, - 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX - A domain error or pole error may occur if the argument is zero. - Returns -3 The logb functions return the signed exponent of x. - 7.12.6.12 The modf functions - Synopsis -1 #include - double modf(double value, double *iptr); - float modff(float value, float *iptr); - long double modfl(long double value, long double *iptr); - Description -2 The modf functions break the argument value into integral and fractional parts, each of - which has the same type and sign as the argument. They store the integral part (in - -[page 245] - - floating-point format) in the object pointed to by iptr. - Returns -3 The modf functions return the signed fractional part of value. - 7.12.6.13 The scalbn and scalbln functions - Synopsis -1 #include - double scalbn(double x, int n); - float scalbnf(float x, int n); - long double scalbnl(long double x, int n); - double scalbln(double x, long int n); - float scalblnf(float x, long int n); - long double scalblnl(long double x, long int n); - Description -2 The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not - normally by computing FLT_RADIXn explicitly. A range error may occur. - Returns -3 The scalbn and scalbln functions return x x FLT_RADIXn . - 7.12.7 Power and absolute-value functions - 7.12.7.1 The cbrt functions - Synopsis -1 #include - double cbrt(double x); - float cbrtf(float x); - long double cbrtl(long double x); - Description -2 The cbrt functions compute the real cube root of x. - Returns -3 The cbrt functions return x1/3 . - -[page 246] - - 7.12.7.2 The fabs functions - Synopsis -1 #include - double fabs(double x); - float fabsf(float x); - long double fabsl(long double x); - Description -2 The fabs functions compute the absolute value of a floating-point number x. - Returns -3 The fabs functions return | x |. - 7.12.7.3 The hypot functions - Synopsis -1 #include - double hypot(double x, double y); - float hypotf(float x, float y); - long double hypotl(long double x, long double y); - Description -2 The hypot functions compute the square root of the sum of the squares of x and y, - without undue overflow or underflow. A range error may occur. -3 Returns -4 The hypot functions return (sqrt)x2 + y2 . - - - ----- - 7.12.7.4 The pow functions - Synopsis -1 #include - double pow(double x, double y); - float powf(float x, float y); - long double powl(long double x, long double y); - Description -2 The pow functions compute x raised to the power y. A domain error occurs if x is finite - and negative and y is finite and not an integer value. A range error may occur. A domain - error may occur if x is zero and y is zero. A domain error or pole error may occur if x is - zero and y is less than zero. - -[page 247] - - Returns -3 The pow functions return xy . - 7.12.7.5 The sqrt functions - Synopsis -1 #include - double sqrt(double x); - float sqrtf(float x); - long double sqrtl(long double x); - Description -2 The sqrt functions compute the nonnegative square root of x. A domain error occurs if - the argument is less than zero. - Returns -3 The sqrt functions return (sqrt)x. - - - - - 7.12.8 Error and gamma functions - 7.12.8.1 The erf functions - Synopsis -1 #include - double erf(double x); - float erff(float x); - long double erfl(long double x); - Description -2 The erf functions compute the error function of x. - Returns -3 2 x - (integral) e-t dt. - 2 - The erf functions return erf x = - (sqrt)pi - - - - 0 - - 7.12.8.2 The erfc functions - Synopsis -1 #include - double erfc(double x); - float erfcf(float x); - long double erfcl(long double x); - Description -2 The erfc functions compute the complementary error function of x. A range error - occurs if x is too large. - -[page 248] - - Returns -3 2 (inf) - (integral) e-t dt. - 2 - The erfc functions return erfc x = 1 - erf x = - (sqrt)pi - - - - x - - 7.12.8.3 The lgamma functions - Synopsis -1 #include - double lgamma(double x); - float lgammaf(float x); - long double lgammal(long double x); - Description -2 The lgamma functions compute the natural logarithm of the absolute value of gamma of - x. A range error occurs if x is too large. A pole error may occur if x is a negative integer - or zero. - Returns -3 The lgamma functions return loge | (Gamma)(x) |. - 7.12.8.4 The tgamma functions - Synopsis -1 #include - double tgamma(double x); - float tgammaf(float x); - long double tgammal(long double x); - Description -2 The tgamma functions compute the gamma function of x. A domain error or pole error - may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is - too large and may occur if the magnitude of x is too small. - Returns -3 The tgamma functions return (Gamma)(x). - -[page 249] - - 7.12.9 Nearest integer functions - 7.12.9.1 The ceil functions - Synopsis -1 #include - double ceil(double x); - float ceilf(float x); - long double ceill(long double x); - Description -2 The ceil functions compute the smallest integer value not less than x. - Returns -3 The ceil functions return [^x^], expressed as a floating-point number. - 7.12.9.2 The floor functions - Synopsis -1 #include - double floor(double x); - float floorf(float x); - long double floorl(long double x); - Description -2 The floor functions compute the largest integer value not greater than x. - Returns -3 The floor functions return [_x_], expressed as a floating-point number. - 7.12.9.3 The nearbyint functions - Synopsis -1 #include - double nearbyint(double x); - float nearbyintf(float x); - long double nearbyintl(long double x); - Description -2 The nearbyint functions round their argument to an integer value in floating-point - format, using the current rounding direction and without raising the ''inexact'' floating- - point exception. - -[page 250] - - Returns -3 The nearbyint functions return the rounded integer value. - 7.12.9.4 The rint functions - Synopsis -1 #include - double rint(double x); - float rintf(float x); - long double rintl(long double x); - Description -2 The rint functions differ from the nearbyint functions (7.12.9.3) only in that the - rint functions may raise the ''inexact'' floating-point exception if the result differs in - value from the argument. - Returns -3 The rint functions return the rounded integer value. - 7.12.9.5 The lrint and llrint functions - Synopsis -1 #include - long int lrint(double x); - long int lrintf(float x); - long int lrintl(long double x); - long long int llrint(double x); - long long int llrintf(float x); - long long int llrintl(long double x); - Description -2 The lrint and llrint functions round their argument to the nearest integer value, - rounding according to the current rounding direction. If the rounded value is outside the - range of the return type, the numeric result is unspecified and a domain error or range - error may occur. - Returns -3 The lrint and llrint functions return the rounded integer value. - -[page 251] - - 7.12.9.6 The round functions - Synopsis -1 #include - double round(double x); - float roundf(float x); - long double roundl(long double x); - Description -2 The round functions round their argument to the nearest integer value in floating-point - format, rounding halfway cases away from zero, regardless of the current rounding - direction. - Returns -3 The round functions return the rounded integer value. - 7.12.9.7 The lround and llround functions - Synopsis -1 #include - long int lround(double x); - long int lroundf(float x); - long int lroundl(long double x); - long long int llround(double x); - long long int llroundf(float x); - long long int llroundl(long double x); - Description -2 The lround and llround functions round their argument to the nearest integer value, - rounding halfway cases away from zero, regardless of the current rounding direction. If - the rounded value is outside the range of the return type, the numeric result is unspecified - and a domain error or range error may occur. - Returns -3 The lround and llround functions return the rounded integer value. - 7.12.9.8 The trunc functions - Synopsis -1 #include - double trunc(double x); - float truncf(float x); - long double truncl(long double x); - -[page 252] - - Description -2 The trunc functions round their argument to the integer value, in floating format, - nearest to but no larger in magnitude than the argument. - Returns -3 The trunc functions return the truncated integer value. - 7.12.10 Remainder functions - 7.12.10.1 The fmod functions - Synopsis -1 #include - double fmod(double x, double y); - float fmodf(float x, float y); - long double fmodl(long double x, long double y); - Description -2 The fmod functions compute the floating-point remainder of x/y. - Returns -3 The fmod functions return the value x - ny, for some integer n such that, if y is nonzero, - the result has the same sign as x and magnitude less than the magnitude of y. If y is zero, - whether a domain error occurs or the fmod functions return zero is implementation- - defined. - 7.12.10.2 The remainder functions - Synopsis -1 #include - double remainder(double x, double y); - float remainderf(float x, float y); - long double remainderl(long double x, long double y); - Description -2 The remainder functions compute the remainder x REM y required by IEC 60559.236) - - - - - 236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the - mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever - | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for * - all implementations. - -[page 253] - - Returns -3 The remainder functions return x REM y. If y is zero, whether a domain error occurs - or the functions return zero is implementation defined. - 7.12.10.3 The remquo functions - Synopsis -1 #include - double remquo(double x, double y, int *quo); - float remquof(float x, float y, int *quo); - long double remquol(long double x, long double y, - int *quo); - Description -2 The remquo functions compute the same remainder as the remainder functions. In - the object pointed to by quo they store a value whose sign is the sign of x/y and whose - magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where - n is an implementation-defined integer greater than or equal to 3. - Returns -3 The remquo functions return x REM y. If y is zero, the value stored in the object - pointed to by quo is unspecified and whether a domain error occurs or the functions - return zero is implementation defined. - 7.12.11 Manipulation functions - 7.12.11.1 The copysign functions - Synopsis -1 #include - double copysign(double x, double y); - float copysignf(float x, float y); - long double copysignl(long double x, long double y); - Description -2 The copysign functions produce a value with the magnitude of x and the sign of y. - They produce a NaN (with the sign of y) if x is a NaN. On implementations that - represent a signed zero but do not treat negative zero consistently in arithmetic - operations, the copysign functions regard the sign of zero as positive. - Returns -3 The copysign functions return a value with the magnitude of x and the sign of y. - -[page 254] - - 7.12.11.2 The nan functions - Synopsis -1 #include - double nan(const char *tagp); - float nanf(const char *tagp); - long double nanl(const char *tagp); - Description -2 The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char- - sequence)", (char**) NULL); the call nan("") is equivalent to - strtod("NAN()", (char**) NULL). If tagp does not point to an n-char - sequence or an empty string, the call is equivalent to strtod("NAN", (char**) - NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof - and strtold. - Returns -3 The nan functions return a quiet NaN, if available, with content indicated through tagp. - If the implementation does not support quiet NaNs, the functions return zero. - Forward references: the strtod, strtof, and strtold functions (7.22.1.3). - 7.12.11.3 The nextafter functions - Synopsis -1 #include - double nextafter(double x, double y); - float nextafterf(float x, float y); - long double nextafterl(long double x, long double y); - Description -2 The nextafter functions determine the next representable value, in the type of the - function, after x in the direction of y, where x and y are first converted to the type of the - function.237) The nextafter functions return y if x equals y. A range error may occur - if the magnitude of x is the largest finite value representable in the type and the result is - infinite or not representable in the type. - Returns -3 The nextafter functions return the next representable value in the specified format - after x in the direction of y. - - - 237) The argument values are converted to the type of the function, even by a macro implementation of the - function. - -[page 255] - - 7.12.11.4 The nexttoward functions - Synopsis -1 #include - double nexttoward(double x, long double y); - float nexttowardf(float x, long double y); - long double nexttowardl(long double x, long double y); - Description -2 The nexttoward functions are equivalent to the nextafter functions except that the - second parameter has type long double and the functions return y converted to the - type of the function if x equals y.238) - 7.12.12 Maximum, minimum, and positive difference functions - 7.12.12.1 The fdim functions - Synopsis -1 #include - double fdim(double x, double y); - float fdimf(float x, float y); - long double fdiml(long double x, long double y); - Description -2 The fdim functions determine the positive difference between their arguments: - {x - y if x > y - { - {+0 if x <= y - A range error may occur. - Returns -3 The fdim functions return the positive difference value. - 7.12.12.2 The fmax functions - Synopsis -1 #include - double fmax(double x, double y); - float fmaxf(float x, float y); - long double fmaxl(long double x, long double y); - - - - 238) The result of the nexttoward functions is determined in the type of the function, without loss of - range or precision in a floating second argument. - -[page 256] - - Description -2 The fmax functions determine the maximum numeric value of their arguments.239) - Returns -3 The fmax functions return the maximum numeric value of their arguments. - 7.12.12.3 The fmin functions - Synopsis -1 #include - double fmin(double x, double y); - float fminf(float x, float y); - long double fminl(long double x, long double y); - Description -2 The fmin functions determine the minimum numeric value of their arguments.240) - Returns -3 The fmin functions return the minimum numeric value of their arguments. - 7.12.13 Floating multiply-add - 7.12.13.1 The fma functions - Synopsis -1 #include - double fma(double x, double y, double z); - float fmaf(float x, float y, float z); - long double fmal(long double x, long double y, - long double z); - Description -2 The fma functions compute (x x y) + z, rounded as one ternary operation: they compute - the value (as if) to infinite precision and round once to the result format, according to the - current rounding mode. A range error may occur. - Returns -3 The fma functions return (x x y) + z, rounded as one ternary operation. - - - - - 239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the - fmax functions choose the numeric value. See F.10.9.2. - 240) The fmin functions are analogous to the fmax functions in their treatment of NaNs. - -[page 257] - - 7.12.14 Comparison macros -1 The relational and equality operators support the usual mathematical relationships - between numeric values. For any ordered pair of numeric values exactly one of the - relationships -- less, greater, and equal -- is true. Relational operators may raise the - ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a - numeric value, or for two NaNs, just the unordered relationship is true.241) The following - subclauses provide macros that are quiet (non floating-point exception raising) versions - of the relational operators, and other comparison macros that facilitate writing efficient - code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In - the synopses in this subclause, real-floating indicates that the argument shall be an - expression of real floating type242) (both arguments need not have the same type).243) - 7.12.14.1 The isgreater macro - Synopsis -1 #include - int isgreater(real-floating x, real-floating y); - Description -2 The isgreater macro determines whether its first argument is greater than its second - argument. The value of isgreater(x, y) is always equal to (x) > (y); however, - unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point - exception when x and y are unordered. - Returns -3 The isgreater macro returns the value of (x) > (y). - 7.12.14.2 The isgreaterequal macro - Synopsis -1 #include - int isgreaterequal(real-floating x, real-floating y); - - - - - 241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if - the operands compare unordered, as an error indicator for programs written without consideration of - NaNs; the result in these cases is false. - 242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is - undefined. - 243) Whether an argument represented in a format wider than its semantic type is converted to the semantic - type is unspecified. - -[page 258] - - Description -2 The isgreaterequal macro determines whether its first argument is greater than or - equal to its second argument. The value of isgreaterequal(x, y) is always equal - to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does - not raise the ''invalid'' floating-point exception when x and y are unordered. - Returns -3 The isgreaterequal macro returns the value of (x) >= (y). - 7.12.14.3 The isless macro - Synopsis -1 #include - int isless(real-floating x, real-floating y); - Description -2 The isless macro determines whether its first argument is less than its second - argument. The value of isless(x, y) is always equal to (x) < (y); however, - unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point - exception when x and y are unordered. - Returns -3 The isless macro returns the value of (x) < (y). - 7.12.14.4 The islessequal macro - Synopsis -1 #include - int islessequal(real-floating x, real-floating y); - Description -2 The islessequal macro determines whether its first argument is less than or equal to - its second argument. The value of islessequal(x, y) is always equal to - (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise - the ''invalid'' floating-point exception when x and y are unordered. - Returns -3 The islessequal macro returns the value of (x) <= (y). - -[page 259] - - 7.12.14.5 The islessgreater macro - Synopsis -1 #include - int islessgreater(real-floating x, real-floating y); - Description -2 The islessgreater macro determines whether its first argument is less than or - greater than its second argument. The islessgreater(x, y) macro is similar to - (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise - the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x - and y twice). - Returns -3 The islessgreater macro returns the value of (x) < (y) || (x) > (y). - 7.12.14.6 The isunordered macro - Synopsis -1 #include - int isunordered(real-floating x, real-floating y); - Description -2 The isunordered macro determines whether its arguments are unordered. - Returns -3 The isunordered macro returns 1 if its arguments are unordered and 0 otherwise. - -[page 260] - - 7.13 Nonlocal jumps -1 The header defines the macro setjmp, and declares one function and - one type, for bypassing the normal function call and return discipline.244) -2 The type declared is - jmp_buf - which is an array type suitable for holding the information needed to restore a calling - environment. The environment of a call to the setjmp macro consists of information - sufficient for a call to the longjmp function to return execution to the correct block and - invocation of that block, were it called recursively. It does not include the state of the - floating-point status flags, of open files, or of any other component of the abstract - machine. -3 It is unspecified whether setjmp is a macro or an identifier declared with external - linkage. If a macro definition is suppressed in order to access an actual function, or a - program defines an external identifier with the name setjmp, the behavior is undefined. - 7.13.1 Save calling environment - 7.13.1.1 The setjmp macro - Synopsis -1 #include - int setjmp(jmp_buf env); - Description -2 The setjmp macro saves its calling environment in its jmp_buf argument for later use - by the longjmp function. - Returns -3 If the return is from a direct invocation, the setjmp macro returns the value zero. If the - return is from a call to the longjmp function, the setjmp macro returns a nonzero - value. - Environmental limits -4 An invocation of the setjmp macro shall appear only in one of the following contexts: - -- the entire controlling expression of a selection or iteration statement; - -- one operand of a relational or equality operator with the other operand an integer - constant expression, with the resulting expression being the entire controlling - - - 244) These functions are useful for dealing with unusual conditions encountered in a low-level function of - a program. - -[page 261] - - expression of a selection or iteration statement; - -- the operand of a unary ! operator with the resulting expression being the entire - controlling expression of a selection or iteration statement; or - -- the entire expression of an expression statement (possibly cast to void). -5 If the invocation appears in any other context, the behavior is undefined. - 7.13.2 Restore calling environment - 7.13.2.1 The longjmp function - Synopsis -1 #include - _Noreturn void longjmp(jmp_buf env, int val); - Description -2 The longjmp function restores the environment saved by the most recent invocation of - the setjmp macro in the same invocation of the program with the corresponding - jmp_buf argument. If there has been no such invocation, or if the function containing - the invocation of the setjmp macro has terminated execution245) in the interim, or if the - invocation of the setjmp macro was within the scope of an identifier with variably - modified type and execution has left that scope in the interim, the behavior is undefined. -3 All accessible objects have values, and all other components of the abstract machine246) - have state, as of the time the longjmp function was called, except that the values of - objects of automatic storage duration that are local to the function containing the - invocation of the corresponding setjmp macro that do not have volatile-qualified type - and have been changed between the setjmp invocation and longjmp call are - indeterminate. - Returns -4 After longjmp is completed, program execution continues as if the corresponding - invocation of the setjmp macro had just returned the value specified by val. The - longjmp function cannot cause the setjmp macro to return the value 0; if val is 0, - the setjmp macro returns the value 1. -5 EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation - might cause memory associated with a variable length array object to be squandered. - - - - - 245) For example, by executing a return statement or because another longjmp call has caused a - transfer to a setjmp invocation in a function earlier in the set of nested calls. - 246) This includes, but is not limited to, the floating-point status flags and the state of open files. - -[page 262] - - #include - jmp_buf buf; - void g(int n); - void h(int n); - int n = 6; - void f(void) - { - int x[n]; // valid: f is not terminated - setjmp(buf); - g(n); - } - void g(int n) - { - int a[n]; // a may remain allocated - h(n); - } - void h(int n) - { - int b[n]; // b may remain allocated - longjmp(buf, 2); // might cause memory loss - } - -[page 263] - - 7.14 Signal handling -1 The header declares a type and two functions and defines several macros, - for handling various signals (conditions that may be reported during program execution). -2 The type defined is - sig_atomic_t - which is the (possibly volatile-qualified) integer type of an object that can be accessed as - an atomic entity, even in the presence of asynchronous interrupts. -3 The macros defined are - SIG_DFL - SIG_ERR - SIG_IGN - which expand to constant expressions with distinct values that have type compatible with - the second argument to, and the return value of, the signal function, and whose values - compare unequal to the address of any declarable function; and the following, which - expand to positive integer constant expressions with type int and distinct values that are - the signal numbers, each corresponding to the specified condition: - SIGABRT abnormal termination, such as is initiated by the abort function - SIGFPE an erroneous arithmetic operation, such as zero divide or an operation - resulting in overflow - SIGILL detection of an invalid function image, such as an invalid instruction - SIGINT receipt of an interactive attention signal - SIGSEGV an invalid access to storage - SIGTERM a termination request sent to the program -4 An implementation need not generate any of these signals, except as a result of explicit - calls to the raise function. Additional signals and pointers to undeclarable functions, - with macro definitions beginning, respectively, with the letters SIG and an uppercase - letter or with SIG_ and an uppercase letter,247) may also be specified by the - implementation. The complete set of signals, their semantics, and their default handling - is implementation-defined; all signal numbers shall be positive. - - - - - 247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms - (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation, - and termination. - -[page 264] - - 7.14.1 Specify signal handling - 7.14.1.1 The signal function - Synopsis -1 #include - void (*signal(int sig, void (*func)(int)))(int); - Description -2 The signal function chooses one of three ways in which receipt of the signal number - sig is to be subsequently handled. If the value of func is SIG_DFL, default handling - for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored. - Otherwise, func shall point to a function to be called when that signal occurs. An - invocation of such a function because of a signal, or (recursively) of any further functions - called by that invocation (other than functions in the standard library),248) is called a - signal handler. -3 When a signal occurs and func points to a function, it is implementation-defined - whether the equivalent of signal(sig, SIG_DFL); is executed or the - implementation prevents some implementation-defined set of signals (at least including - sig) from occurring until the current signal handling has completed; in the case of - SIGILL, the implementation may alternatively define that no action is taken. Then the - equivalent of (*func)(sig); is executed. If and when the function returns, if the - value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined - value corresponding to a computational exception, the behavior is undefined; otherwise - the program will resume execution at the point it was interrupted. -4 If the signal occurs as the result of calling the abort or raise function, the signal - handler shall not call the raise function. -5 If the signal occurs other than as the result of calling the abort or raise function, the - behavior is undefined if the signal handler refers to any object with static or thread - storage duration that is not a lock-free atomic object other than by assigning a value to an - object declared as volatile sig_atomic_t, or the signal handler calls any function - in the standard library other than the abort function, the _Exit function, the - quick_exit function, or the signal function with the first argument equal to the - signal number corresponding to the signal that caused the invocation of the handler. - Furthermore, if such a call to the signal function results in a SIG_ERR return, the - value of errno is indeterminate.249) - - - 248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler - called via the abort function). - 249) If any signal is generated by an asynchronous signal handler, the behavior is undefined. - -[page 265] - -6 At program startup, the equivalent of - signal(sig, SIG_IGN); - may be executed for some signals selected in an implementation-defined manner; the - equivalent of - signal(sig, SIG_DFL); - is executed for all other signals defined by the implementation. -7 The implementation shall behave as if no library function calls the signal function. - Returns -8 If the request can be honored, the signal function returns the value of func for the - most recent successful call to signal for the specified signal sig. Otherwise, a value of - SIG_ERR is returned and a positive value is stored in errno. - Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the - _Exit function (7.22.4.5), the quick_exit function (7.22.4.7). - 7.14.2 Send signal - 7.14.2.1 The raise function - Synopsis -1 #include - int raise(int sig); - Description -2 The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a - signal handler is called, the raise function shall not return until after the signal handler - does. - Returns -3 The raise function returns zero if successful, nonzero if unsuccessful. - -[page 266] - - 7.15 Alignment -1 The header defines two macros. -2 The macro - alignas - expands to _Alignas. -3 The remaining macro is suitable for use in #if preprocessing directives. It is - __alignas_is_defined - which expands to the integer constant 1. - -[page 267] - - 7.16 Variable arguments -1 The header declares a type and defines four macros, for advancing - through a list of arguments whose number and types are not known to the called function - when it is translated. -2 A function may be called with a variable number of arguments of varying types. As - described in 6.9.1, its parameter list contains one or more parameters. The rightmost - parameter plays a special role in the access mechanism, and will be designated parmN in - this description. -3 The type declared is - va_list - which is a complete object type suitable for holding information needed by the macros - va_start, va_arg, va_end, and va_copy. If access to the varying arguments is - desired, the called function shall declare an object (generally referred to as ap in this - subclause) having type va_list. The object ap may be passed as an argument to - another function; if that function invokes the va_arg macro with parameter ap, the - value of ap in the calling function is indeterminate and shall be passed to the va_end - macro prior to any further reference to ap.250) - 7.16.1 Variable argument list access macros -1 The va_start and va_arg macros described in this subclause shall be implemented - as macros, not functions. It is unspecified whether va_copy and va_end are macros or - identifiers declared with external linkage. If a macro definition is suppressed in order to - access an actual function, or a program defines an external identifier with the same name, - the behavior is undefined. Each invocation of the va_start and va_copy macros - shall be matched by a corresponding invocation of the va_end macro in the same - function. - 7.16.1.1 The va_arg macro - Synopsis -1 #include - type va_arg(va_list ap, type); - Description -2 The va_arg macro expands to an expression that has the specified type and the value of - the next argument in the call. The parameter ap shall have been initialized by the - va_start or va_copy macro (without an intervening invocation of the va_end - - 250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which - case the original function may make further use of the original list after the other function returns. - -[page 268] - - macro for the same ap). Each invocation of the va_arg macro modifies ap so that the - values of successive arguments are returned in turn. The parameter type shall be a type - name specified such that the type of a pointer to an object that has the specified type can - be obtained simply by postfixing a * to type. If there is no actual next argument, or if - type is not compatible with the type of the actual next argument (as promoted according - to the default argument promotions), the behavior is undefined, except for the following - cases: - -- one type is a signed integer type, the other type is the corresponding unsigned integer - type, and the value is representable in both types; - -- one type is pointer to void and the other is a pointer to a character type. - Returns -3 The first invocation of the va_arg macro after that of the va_start macro returns the - value of the argument after that specified by parmN . Successive invocations return the - values of the remaining arguments in succession. - 7.16.1.2 The va_copy macro - Synopsis -1 #include - void va_copy(va_list dest, va_list src); - Description -2 The va_copy macro initializes dest as a copy of src, as if the va_start macro had - been applied to dest followed by the same sequence of uses of the va_arg macro as - had previously been used to reach the present state of src. Neither the va_copy nor - va_start macro shall be invoked to reinitialize dest without an intervening - invocation of the va_end macro for the same dest. - Returns -3 The va_copy macro returns no value. - 7.16.1.3 The va_end macro - Synopsis -1 #include - void va_end(va_list ap); - Description -2 The va_end macro facilitates a normal return from the function whose variable - argument list was referred to by the expansion of the va_start macro, or the function - containing the expansion of the va_copy macro, that initialized the va_list ap. The - va_end macro may modify ap so that it is no longer usable (without being reinitialized - -[page 269] - - by the va_start or va_copy macro). If there is no corresponding invocation of the - va_start or va_copy macro, or if the va_end macro is not invoked before the - return, the behavior is undefined. - Returns -3 The va_end macro returns no value. - 7.16.1.4 The va_start macro - Synopsis -1 #include - void va_start(va_list ap, parmN); - Description -2 The va_start macro shall be invoked before any access to the unnamed arguments. -3 The va_start macro initializes ap for subsequent use by the va_arg and va_end - macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap - without an intervening invocation of the va_end macro for the same ap. -4 The parameter parmN is the identifier of the rightmost parameter in the variable - parameter list in the function definition (the one just before the , ...). If the parameter - parmN is declared with the register storage class, with a function or array type, or - with a type that is not compatible with the type that results after application of the default - argument promotions, the behavior is undefined. - Returns -5 The va_start macro returns no value. -6 EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not - more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of - pointers is specified by the first argument to f1. - #include - #define MAXARGS 31 - void f1(int n_ptrs, ...) - { - va_list ap; - char *array[MAXARGS]; - int ptr_no = 0; - -[page 270] - - if (n_ptrs > MAXARGS) - n_ptrs = MAXARGS; - va_start(ap, n_ptrs); - while (ptr_no < n_ptrs) - array[ptr_no++] = va_arg(ap, char *); - va_end(ap); - f2(n_ptrs, array); - } - Each call to f1 is required to have visible the definition of the function or a declaration such as - void f1(int, ...); - -7 EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the - indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list - is gathered again and passed to function f4. - #include - #define MAXARGS 31 - void f3(int n_ptrs, int f4_after, ...) - { - va_list ap, ap_save; - char *array[MAXARGS]; - int ptr_no = 0; - if (n_ptrs > MAXARGS) - n_ptrs = MAXARGS; - va_start(ap, f4_after); - while (ptr_no < n_ptrs) { - array[ptr_no++] = va_arg(ap, char *); - if (ptr_no == f4_after) - va_copy(ap_save, ap); - } - va_end(ap); - f2(n_ptrs, array); - // Now process the saved copy. - n_ptrs -= f4_after; - ptr_no = 0; - while (ptr_no < n_ptrs) - array[ptr_no++] = va_arg(ap_save, char *); - va_end(ap_save); - f4(n_ptrs, array); - } - -[page 271] - - 7.17 Atomics - 7.17.1 Introduction -1 The header defines several macros and declares several types and - functions for performing atomic operations on data shared between threads. -2 Implementations that define the macro __STDC_NO_THREADS__ need not provide - this header nor support any of its facilities. -3 The macros defined are the atomic lock-free macros - ATOMIC_CHAR_LOCK_FREE - ATOMIC_CHAR16_T_LOCK_FREE - ATOMIC_CHAR32_T_LOCK_FREE - ATOMIC_WCHAR_T_LOCK_FREE - ATOMIC_SHORT_LOCK_FREE - ATOMIC_INT_LOCK_FREE - ATOMIC_LONG_LOCK_FREE - ATOMIC_LLONG_LOCK_FREE - ATOMIC_ADDRESS_LOCK_FREE - which indicate the lock-free property of the corresponding atomic types (both signed and - unsigned); and - ATOMIC_FLAG_INIT - which expands to an initializer for an object of type atomic_flag. -4 The types include - memory_order - which is an enumerated type whose enumerators identify memory ordering constraints; - atomic_flag - which is a structure type representing a lock-free, primitive atomic flag; - atomic_bool - which is a structure type representing the atomic analog of the type _Bool; - atomic_address - which is a structure type representing the atomic analog of a pointer type; and several - atomic analogs of integer types. -5 In the following operation definitions: - -- An A refers to one of the atomic types. - -[page 272] - - -- A C refers to its corresponding non-atomic type. The atomic_address atomic - type corresponds to the void * non-atomic type. - -- An M refers to the type of the other argument for arithmetic operations. For atomic - integer types, M is C. For atomic address types, M is ptrdiff_t. - -- The functions not ending in _explicit have the same semantics as the - corresponding _explicit function with memory_order_seq_cst for the - memory_order argument. -6 NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not - changed in the standard. This qualification means that volatility is preserved when applying these - operations to volatile objects. - - 7.17.2 Initialization - 7.17.2.1 The ATOMIC_VAR_INIT macro - Synopsis -1 #include - #define ATOMIC_VAR_INIT(C value) - Description -2 The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an - atomic object of a type that is initialization-compatible with value. An atomic object - with automatic storage duration that is not explicitly initialized using - ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero) - initialization for objects with static or thread-local storage duration is guaranteed to - produce a valid state. -3 Concurrent access to the variable being initialized, even via an atomic operation, - constitutes a data race. -4 EXAMPLE - atomic_int guide = ATOMIC_VAR_INIT(42); - - 7.17.2.2 The atomic_init generic function - Synopsis -1 #include - void atomic_init(volatile A *obj, C value); - Description -2 The atomic_init generic function initializes the atomic object pointed to by obj to - the value value, while also initializing any additional state that the implementation - might need to carry for the atomic object. - -[page 273] - -3 Although this function initializes an atomic object, it does not avoid data races; - concurrent access to the variable being initialized, even via an atomic operation, - constitutes a data race. - Returns -4 The atomic_init generic function returns no value. -5 EXAMPLE - atomic_int guide; - atomic_init(&guide, 42); - - 7.17.3 Order and consistency -1 The enumerated type memory_order specifies the detailed regular (non-atomic) - memory synchronization operations as defined in 5.1.2.4 and may provide for operation - ordering. Its enumeration constants are as follows: - memory_order_relaxed - memory_order_consume - memory_order_acquire - memory_order_release - memory_order_acq_rel - memory_order_seq_cst -2 For memory_order_relaxed, no operation orders memory. -3 For memory_order_release, memory_order_acq_rel, and - memory_order_seq_cst, a store operation performs a release operation on the - affected memory location. -4 For memory_order_acquire, memory_order_acq_rel, and - memory_order_seq_cst, a load operation performs an acquire operation on the - affected memory location. -5 For memory_order_consume, a load operation performs a consume operation on the - affected memory location. -6 For memory_order_seq_cst, there shall be a single total order S on all operations, - consistent with the ''happens before'' order and modification orders for all affected - locations, such that each memory_order_seq_cst operation that loads a value - observes either the last preceding modification according to this order S, or the result of - an operation that is not memory_order_seq_cst. -7 NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to - an order that does include lock and unlock operations, since the ordering between those is already included - in the ''happens before'' ordering. - -8 NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to - memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic - -[page 274] - - object be indivisible with respect to all other atomic accesses to that object. - -9 For an atomic operation B that reads the value of an atomic object M, if there is a - memory_order_seq_cst fence X sequenced before B, then B observes either the - last memory_order_seq_cst modification of M preceding X in the total order S or - a later modification of M in its modification order. -10 For atomic operations A and B on an atomic object M, where A modifies M and B takes - its value, if there is a memory_order_seq_cst fence X such that A is sequenced - before X and B follows X in S, then B observes either the effects of A or a later - modification of M in its modification order. -11 For atomic operations A and B on an atomic object M, where A modifies M and B takes - its value, if there are memory_order_seq_cst fences X and Y such that A is - sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes - either the effects of A or a later modification of M in its modification order. -12 Atomic read-modify-write operations shall always read the last value (in the modification - order) stored before the write associated with the read-modify-write operation. -13 An atomic store shall only store a value that has been computed from constants and - program input values by a finite sequence of program evaluations, such that each - evaluation observes the values of variables as computed by the last prior assignment in - the sequence.251) The ordering of evaluations in this sequence shall be such that - -- If an evaluation B observes a value computed by A in a different thread, then B does - not happen before A. - -- If an evaluation A is included in the sequence, then all evaluations that assign to the - same variable and happen before A are also included. -14 NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when - relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this - sequence out of thread order. For example, with x and y initially zero, - // Thread 1: - r1 = atomic_load_explicit(&y, memory_order_relaxed); - atomic_store_explicit(&x, r1, memory_order_relaxed); - - // Thread 2: - r2 = atomic_load_explicit(&x, memory_order_relaxed); - atomic_store_explicit(&y, 42, memory_order_relaxed); - is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of: - - - - - 251) Among other implications, atomic variables shall not decay. - -[page 275] - - atomic_store_explicit(&y, 42, memory_order_relaxed); - r1 = atomic_load_explicit(&y, memory_order_relaxed); - atomic_store_explicit(&x, r1, memory_order_relaxed); - r2 = atomic_load_explicit(&x, memory_order_relaxed); - On the other hand, - // Thread 1: - r1 = atomic_load_explicit(&y, memory_order_relaxed); - atomic_store_explicit(&x, r1, memory_order_relaxed); - - // Thread 2: - r2 = atomic_load_explicit(&x, memory_order_relaxed); - atomic_store_explicit(&y, r2, memory_order_relaxed); - is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results - in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with - weaker than memory_order_acq_rel ordering, the second requirement has no impact. - - Recommended practice -15 The requirements do not forbid r1 == 42 && r2 == 42 in the following example, - with x and y initially zero: - // Thread 1: - r1 = atomic_load_explicit(&x, memory_order_relaxed); - if (r1 == 42) - atomic_store_explicit(&y, r1, memory_order_relaxed); - - // Thread 2: - r2 = atomic_load_explicit(&y, memory_order_relaxed); - if (r2 == 42) - atomic_store_explicit(&x, 42, memory_order_relaxed); - However, this is not useful behavior, and implementations should not allow it. -16 Implementations should make atomic stores visible to atomic loads within a reasonable - amount of time. - 7.17.3.1 The kill_dependency macro - Synopsis -1 #include - type kill_dependency(type y); - Description -2 The kill_dependency macro terminates a dependency chain; the argument does not - carry a dependency to the return value. - -[page 276] - - Returns -3 The kill_dependency macro returns the value of y. - 7.17.4 Fences -1 This subclause introduces synchronization primitives called fences. Fences can have - acquire semantics, release semantics, or both. A fence with acquire semantics is called - an acquire fence; a fence with release semantics is called a release fence. -2 A release fence A synchronizes with an acquire fence B if there exist atomic operations - X and Y , both operating on some atomic object M, such that A is sequenced before X, X - modifies M, Y is sequenced before B, and Y reads the value written by X or a value - written by any side effect in the hypothetical release sequence X would head if it were a - release operation. -3 A release fence A synchronizes with an atomic operation B that performs an acquire - operation on an atomic object M if there exists an atomic operation X such that A is - sequenced before X, X modifies M, and B reads the value written by X or a value written - by any side effect in the hypothetical release sequence X would head if it were a release - operation. -4 An atomic operation A that is a release operation on an atomic object M synchronizes - with an acquire fence B if there exists some atomic operation X on M such that X is - sequenced before B and reads the value written by A or a value written by any side effect - in the release sequence headed by A. - 7.17.4.1 The atomic_thread_fence function - Synopsis -1 #include - void atomic_thread_fence(memory_order order); - Description -2 Depending on the value of order, this operation: - -- has no effects, if order == memory_order_relaxed; - -- is an acquire fence, if order == memory_order_acquire or order == - memory_order_consume; - -- is a release fence, if order == memory_order_release; - -- is both an acquire fence and a release fence, if order == - memory_order_acq_rel; - -- is a sequentially consistent acquire and release fence, if order == - memory_order_seq_cst. - -[page 277] - - Returns -3 The atomic_thread_fence function returns no value. - 7.17.4.2 The atomic_signal_fence function - Synopsis -1 #include - void atomic_signal_fence(memory_order order); - Description -2 Equivalent to atomic_thread_fence(order), except that ''synchronizes with'' - relationships are established only between a thread and a signal handler executed in the - same thread. -3 NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions - performed by the thread become visible to the signal handler. - -4 NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with - atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would - have inserted are not emitted. - - Returns -5 The atomic_signal_fence function returns no value. - 7.17.5 Lock-free property -1 The atomic lock-free macros indicate the lock-free property of integer and address atomic - types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that - the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free. -2 NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same - memory location via two different addresses will communicate atomically. The implementation should not - depend on any per-process state. This restriction enables communication via memory mapped into a - process more than once and memory shared between two processes. - - 7.17.5.1 The atomic_is_lock_free generic function - Synopsis -1 #include - _Bool atomic_is_lock_free(atomic_type const volatile *obj); - Description -2 The atomic_is_lock_free generic function indicates whether or not the object - pointed to by obj is lock-free. atomic_type can be any atomic type. - Returns -3 The atomic_is_lock_free generic function returns nonzero (true) if and only if the - object's operations are lock-free. The result of a lock-free query on one object cannot be - -[page 278] - - inferred from the result of a lock-free query on another object. - 7.17.6 Atomic integer and address types -1 For each line in the following table, the atomic type name is declared as the - corresponding direct type. - -[page 279] - - Atomic type name Direct type - atomic_char _Atomic char - atomic_schar _Atomic signed char - atomic_uchar _Atomic unsigned char - atomic_short _Atomic short - atomic_ushort _Atomic unsigned short - atomic_int _Atomic int - atomic_uint _Atomic unsigned int - atomic_long _Atomic long - atomic_ulong _Atomic unsigned long - atomic_llong _Atomic long long - atomic_ullong _Atomic unsigned long long - atomic_char16_t _Atomic char16_t - atomic_char32_t _Atomic char32_t - atomic_wchar_t _Atomic wchar_t - atomic_int_least8_t _Atomic int_least8_t - atomic_uint_least8_t _Atomic uint_least8_t - atomic_int_least16_t _Atomic int_least16_t - atomic_uint_least16_t _Atomic uint_least16_t - atomic_int_least32_t _Atomic int_least32_t - atomic_uint_least32_t _Atomic uint_least32_t - atomic_int_least64_t _Atomic int_least64_t - atomic_uint_least64_t _Atomic uint_least64_t - atomic_int_fast8_t _Atomic int_fast8_t - atomic_uint_fast8_t _Atomic uint_fast8_t - atomic_int_fast16_t _Atomic int_fast16_t - atomic_uint_fast16_t _Atomic uint_fast16_t - atomic_int_fast32_t _Atomic int_fast32_t - atomic_uint_fast32_t _Atomic uint_fast32_t - atomic_int_fast64_t _Atomic int_fast64_t - atomic_uint_fast64_t _Atomic uint_fast64_t - atomic_intptr_t _Atomic intptr_t - atomic_uintptr_t _Atomic uintptr_t - atomic_size_t _Atomic size_t - atomic_ptrdiff_t _Atomic ptrdiff_t - atomic_intmax_t _Atomic intmax_t - atomic_uintmax_t _Atomic uintmax_t -2 The semantics of the operations on these types are defined in 7.17.7. -3 The atomic_bool type provides an atomic boolean. - -[page 280] - -4 The atomic_address type provides atomic void * operations. The unit of - addition/subtraction shall be one byte. -5 NOTE The representation of atomic integer and address types need not have the same size as their - corresponding regular types. They should have the same size whenever possible, as it eases effort required - to port existing code. - - 7.17.7 Operations on atomic types -1 There are only a few kinds of operations on atomic types, though there are many - instances of those kinds. This subclause specifies each general kind. - 7.17.7.1 The atomic_store generic functions - Synopsis -1 #include - void atomic_store(volatile A *object, C desired); - void atomic_store_explicit(volatile A *object, - C desired, memory_order order); - Description -2 The order argument shall not be memory_order_acquire, - memory_order_consume, nor memory_order_acq_rel. Atomically replace the - value pointed to by object with the value of desired. Memory is affected according - to the value of order. - Returns -3 The atomic_store generic functions return no value. - 7.17.7.2 The atomic_load generic functions - Synopsis -1 #include - C atomic_load(volatile A *object); - C atomic_load_explicit(volatile A *object, - memory_order order); - Description -2 The order argument shall not be memory_order_release nor - memory_order_acq_rel. Memory is affected according to the value of order. - Returns - Atomically returns the value pointed to by object. - -[page 281] - - 7.17.7.3 The atomic_exchange generic functions - Synopsis -1 #include - C atomic_exchange(volatile A *object, C desired); - C atomic_exchange_explicit(volatile A *object, - C desired, memory_order order); - Description -2 Atomically replace the value pointed to by object with desired. Memory is affected - according to the value of order. These operations are read-modify-write operations - (5.1.2.4). - Returns -3 Atomically returns the value pointed to by object immediately before the effects. - 7.17.7.4 The atomic_compare_exchange generic functions - Synopsis -1 #include - _Bool atomic_compare_exchange_strong(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_strong_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - _Bool atomic_compare_exchange_weak(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_weak_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - Description -2 The failure argument shall not be memory_order_release nor - memory_order_acq_rel. The failure argument shall be no stronger than the - success argument. Atomically, compares the value pointed to by object for equality - with that in expected, and if true, replaces the value pointed to by object with - desired, and if false, updates the value in expected with the value pointed to by - object. Further, if the comparison is true, memory is affected according to the value of - success, and if the comparison is false, memory is affected according to the value of - failure. These operations are atomic read-modify-write operations (5.1.2.4). -3 NOTE 1 The effect of the compare-and-exchange operations is - -[page 282] - - if (*object == *expected) - *object = desired; - else - *expected = *object; - -4 The weak compare-and-exchange operations may fail spuriously, that is, return zero - while leaving the value pointed to by expected unchanged. -5 NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of - machines, e.g. load-locked store-conditional machines. - -6 EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will - be in a loop. - exp = atomic_load(&cur); - do { - des = function(exp); - } while (!atomic_compare_exchange_weak(&cur, &exp, des)); - When a compare-and-exchange is in a loop, the weak version will yield better performance on some - platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the - strong one is preferable. - - Returns -7 The result of the comparison. - 7.17.7.5 The atomic_fetch and modify generic functions -1 The following operations perform arithmetic and bitwise computations. All of these - operations are applicable to an object of any atomic integer type. Only addition and - subtraction are applicable to atomic_address. None of these operations is applicable - to atomic_bool. The key, operator, and computation correspondence is: - key op computation - add + addition - sub - subtraction - or | bitwise inclusive or - xor ^ bitwise exclusive or - and & bitwise and - Synopsis -2 #include - C atomic_fetch_key(volatile A *object, M operand); - C atomic_fetch_key_explicit(volatile A *object, - M operand, memory_order order); - Description -3 Atomically replaces the value pointed to by object with the result of the computation - applied to the value pointed to by object and the given operand. Memory is affected - according to the value of order. These operations are atomic read-modify-write - -[page 283] - - operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's - complement representation with silent wrap-around on overflow; there are no undefined - results. For address types, the result may be an undefined address, but the operations - otherwise have no undefined behavior. - Returns -4 Atomically, the value pointed to by object immediately before the effects. -5 NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the - operation of the corresponding op= compound assignment operators. The only differences are that the - compound assignment operators are not guaranteed to operate atomically, and the value yielded by a - compound assignment operator is the updated value of the object, whereas the value returned by the - atomic_fetch and modify generic functions is the previous value of the atomic object. - - 7.17.8 Atomic flag type and operations -1 The atomic_flag type provides the classic test-and-set functionality. It has two - states, set and clear. -2 Operations on an object of type atomic_flag shall be lock free. -3 NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so - the atomic_flag type is the minimum hardware-implemented type needed to conform to this - International standard. The remaining types can be emulated with atomic_flag, though with less than - ideal properties. - -4 The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the - clear state. An atomic_flag that is not explicitly initialized with - ATOMIC_FLAG_INIT is initially in an indeterminate state. -5 EXAMPLE - atomic_flag guard = ATOMIC_FLAG_INIT; - - 7.17.8.1 The atomic_flag_test_and_set functions - Synopsis -1 #include - bool atomic_flag_test_and_set( - volatile atomic_flag *object); - bool atomic_flag_test_and_set_explicit( - volatile atomic_flag *object, memory_order order); - Description -2 Atomically sets the value pointed to by object to true. Memory is affected according - to the value of order. These operations are atomic read-modify-write operations - (5.1.2.4). - -[page 284] - - Returns -3 Atomically, the value of the object immediately before the effects. - 7.17.8.2 The atomic_flag_clear functions - Synopsis -1 #include - void atomic_flag_clear(volatile atomic_flag *object); - void atomic_flag_clear_explicit( - volatile atomic_flag *object, memory_order order); - Description -2 The order argument shall not be memory_order_acquire nor - memory_order_acq_rel. Atomically sets the value pointed to by object to false. - Memory is affected according to the value of order. - Returns -3 The atomic_flag_clear functions return no value. - -[page 285] - - 7.18 Boolean type and values -1 The header defines four macros. -2 The macro - bool - expands to _Bool. -3 The remaining three macros are suitable for use in #if preprocessing directives. They - are - true - which expands to the integer constant 1, - false - which expands to the integer constant 0, and - __bool_true_false_are_defined - which expands to the integer constant 1. -4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then - redefine the macros bool, true, and false.252) - - - - - 252) See ''future library directions'' (7.30.7). - -[page 286] - - 7.19 Common definitions -1 The header defines the following macros and declares the following types. - Some are also defined in other headers, as noted in their respective subclauses. -2 The types are - ptrdiff_t - which is the signed integer type of the result of subtracting two pointers; - size_t - which is the unsigned integer type of the result of the sizeof operator; - max_align_t - which is an object type whose alignment is as great as is supported by the implementation - in all contexts; and - wchar_t - which is an integer type whose range of values can represent distinct codes for all - members of the largest extended character set specified among the supported locales; the - null character shall have the code value zero. Each member of the basic character set - shall have a code value equal to its value when used as the lone character in an integer - character constant if an implementation does not define - __STDC_MB_MIGHT_NEQ_WC__. -3 The macros are - NULL - which expands to an implementation-defined null pointer constant; and - offsetof(type, member-designator) - which expands to an integer constant expression that has type size_t, the value of - which is the offset in bytes, to the structure member (designated by member-designator), - from the beginning of its structure (designated by type). The type and member designator - shall be such that given - static type t; - then the expression &(t.member-designator) evaluates to an address constant. (If the - specified member is a bit-field, the behavior is undefined.) - Recommended practice -4 The types used for size_t and ptrdiff_t should not have an integer conversion rank - greater than that of signed long int unless the implementation supports objects - large enough to make this necessary. - -[page 287] - -Forward references: localization (7.11). - -[page 288] - - 7.20 Integer types -1 The header declares sets of integer types having specified widths, and - defines corresponding sets of macros.253) It also defines macros that specify limits of - integer types corresponding to types defined in other standard headers. -2 Types are defined in the following categories: - -- integer types having certain exact widths; - -- integer types having at least certain specified widths; - -- fastest integer types having at least certain specified widths; - -- integer types wide enough to hold pointers to objects; - -- integer types having greatest width. - (Some of these types may denote the same type.) -3 Corresponding macros specify limits of the declared types and construct suitable - constants. -4 For each type described herein that the implementation provides,254) shall - declare that typedef name and define the associated macros. Conversely, for each type - described herein that the implementation does not provide, shall not - declare that typedef name nor shall it define the associated macros. An implementation - shall provide those types described as ''required'', but need not provide any of the others - (described as ''optional''). - 7.20.1 Integer types -1 When typedef names differing only in the absence or presence of the initial u are defined, - they shall denote corresponding signed and unsigned types as described in 6.2.5; an - implementation providing one of these corresponding types shall also provide the other. -2 In the following descriptions, the symbol N represents an unsigned decimal integer with - no leading zeros (e.g., 8 or 24, but not 04 or 048). - - - - - 253) See ''future library directions'' (7.30.8). - 254) Some of these types may denote implementation-defined extended integer types. - -[page 289] - - 7.20.1.1 Exact-width integer types -1 The typedef name intN_t designates a signed integer type with width N , no padding - bits, and a two's complement representation. Thus, int8_t denotes such a signed - integer type with a width of exactly 8 bits. -2 The typedef name uintN_t designates an unsigned integer type with width N and no - padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of - exactly 24 bits. -3 These types are optional. However, if an implementation provides integer types with - widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a - two's complement representation, it shall define the corresponding typedef names. - 7.20.1.2 Minimum-width integer types -1 The typedef name int_leastN_t designates a signed integer type with a width of at - least N , such that no signed integer type with lesser size has at least the specified width. - Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits. -2 The typedef name uint_leastN_t designates an unsigned integer type with a width - of at least N , such that no unsigned integer type with lesser size has at least the specified - width. Thus, uint_least16_t denotes an unsigned integer type with a width of at - least 16 bits. -3 The following types are required: - int_least8_t uint_least8_t - int_least16_t uint_least16_t - int_least32_t uint_least32_t - int_least64_t uint_least64_t - All other types of this form are optional. - 7.20.1.3 Fastest minimum-width integer types -1 Each of the following types designates an integer type that is usually fastest255) to operate - with among all integer types that have at least the specified width. -2 The typedef name int_fastN_t designates the fastest signed integer type with a width - of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer - type with a width of at least N . - - - - - 255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear - grounds for choosing one type over another, it will simply pick some integer type satisfying the - signedness and width requirements. - -[page 290] - -3 The following types are required: - int_fast8_t uint_fast8_t - int_fast16_t uint_fast16_t - int_fast32_t uint_fast32_t - int_fast64_t uint_fast64_t - All other types of this form are optional. - 7.20.1.4 Integer types capable of holding object pointers -1 The following type designates a signed integer type with the property that any valid - pointer to void can be converted to this type, then converted back to pointer to void, - and the result will compare equal to the original pointer: - intptr_t - The following type designates an unsigned integer type with the property that any valid - pointer to void can be converted to this type, then converted back to pointer to void, - and the result will compare equal to the original pointer: - uintptr_t - These types are optional. - 7.20.1.5 Greatest-width integer types -1 The following type designates a signed integer type capable of representing any value of - any signed integer type: - intmax_t - The following type designates an unsigned integer type capable of representing any value - of any unsigned integer type: - uintmax_t - These types are required. - 7.20.2 Limits of specified-width integer types -1 The following object-like macros specify the minimum and maximum limits of the types * - declared in . Each macro name corresponds to a similar type name in - 7.20.1. -2 Each instance of any defined macro shall be replaced by a constant expression suitable - for use in #if preprocessing directives, and this expression shall have the same type as - would an expression that is an object of the corresponding type converted according to - the integer promotions. Its implementation-defined value shall be equal to or greater in - magnitude (absolute value) than the corresponding value given below, with the same sign, - except where stated to be exactly the given value. - -[page 291] - - 7.20.2.1 Limits of exact-width integer types -1 -- minimum values of exact-width signed integer types - INTN_MIN exactly -(2 N -1 ) - -- maximum values of exact-width signed integer types - INTN_MAX exactly 2 N -1 - 1 - -- maximum values of exact-width unsigned integer types - UINTN_MAX exactly 2 N - 1 - 7.20.2.2 Limits of minimum-width integer types -1 -- minimum values of minimum-width signed integer types - INT_LEASTN_MIN -(2 N -1 - 1) - -- maximum values of minimum-width signed integer types - INT_LEASTN_MAX 2 N -1 - 1 - -- maximum values of minimum-width unsigned integer types - UINT_LEASTN_MAX 2N - 1 - 7.20.2.3 Limits of fastest minimum-width integer types -1 -- minimum values of fastest minimum-width signed integer types - INT_FASTN_MIN -(2 N -1 - 1) - -- maximum values of fastest minimum-width signed integer types - INT_FASTN_MAX 2 N -1 - 1 - -- maximum values of fastest minimum-width unsigned integer types - UINT_FASTN_MAX 2N - 1 - 7.20.2.4 Limits of integer types capable of holding object pointers -1 -- minimum value of pointer-holding signed integer type - INTPTR_MIN -(215 - 1) - -- maximum value of pointer-holding signed integer type - INTPTR_MAX 215 - 1 - -- maximum value of pointer-holding unsigned integer type - UINTPTR_MAX 216 - 1 - -[page 292] - - 7.20.2.5 Limits of greatest-width integer types -1 -- minimum value of greatest-width signed integer type - INTMAX_MIN -(263 - 1) - -- maximum value of greatest-width signed integer type - INTMAX_MAX 263 - 1 - -- maximum value of greatest-width unsigned integer type - UINTMAX_MAX 264 - 1 - 7.20.3 Limits of other integer types -1 The following object-like macros specify the minimum and maximum limits of integer * - types corresponding to types defined in other standard headers. -2 Each instance of these macros shall be replaced by a constant expression suitable for use - in #if preprocessing directives, and this expression shall have the same type as would an - expression that is an object of the corresponding type converted according to the integer - promotions. Its implementation-defined value shall be equal to or greater in magnitude - (absolute value) than the corresponding value given below, with the same sign. An - implementation shall define only the macros corresponding to those typedef names it - actually provides.256) - -- limits of ptrdiff_t - PTRDIFF_MIN -65535 - PTRDIFF_MAX +65535 - -- limits of sig_atomic_t - SIG_ATOMIC_MIN see below - SIG_ATOMIC_MAX see below - -- limit of size_t - SIZE_MAX 65535 - -- limits of wchar_t - WCHAR_MIN see below - WCHAR_MAX see below - -- limits of wint_t - - - - - 256) A freestanding implementation need not provide all of these types. - -[page 293] - - WINT_MIN see below - WINT_MAX see below -3 If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of - SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX - shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer - type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of - SIG_ATOMIC_MAX shall be no less than 255. -4 If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN - shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127; - otherwise, wchar_t is defined as an unsigned integer type, and the value of - WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257) -5 If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall - be no greater than -32767 and the value of WINT_MAX shall be no less than 32767; - otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN - shall be 0 and the value of WINT_MAX shall be no less than 65535. - 7.20.4 Macros for integer constants -1 The following function-like macros expand to integer constants suitable for initializing * - objects that have integer types corresponding to types defined in . Each - macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5. -2 The argument in any instance of these macros shall be an unsuffixed integer constant (as - defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type. -3 Each invocation of one of these macros shall expand to an integer constant expression - suitable for use in #if preprocessing directives. The type of the expression shall have - the same type as would an expression of the corresponding type converted according to - the integer promotions. The value of the expression shall be that of the argument. - 7.20.4.1 Macros for minimum-width integer constants -1 The macro INTN_C(value) shall expand to an integer constant expression - corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand - to an integer constant expression corresponding to the type uint_leastN_t. For - example, if uint_least64_t is a name for the type unsigned long long int, - then UINT64_C(0x123) might expand to the integer constant 0x123ULL. - - - - - 257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended - character set. - -[page 294] - - 7.20.4.2 Macros for greatest-width integer constants -1 The following macro expands to an integer constant expression having the value specified - by its argument and the type intmax_t: - INTMAX_C(value) - The following macro expands to an integer constant expression having the value specified - by its argument and the type uintmax_t: - UINTMAX_C(value) - -[page 295] - - 7.21 Input/output - 7.21.1 Introduction -1 The header defines several macros, and declares three types and many - functions for performing input and output. -2 The types declared are size_t (described in 7.19); - FILE - which is an object type capable of recording all the information needed to control a - stream, including its file position indicator, a pointer to its associated buffer (if any), an - error indicator that records whether a read/write error has occurred, and an end-of-file - indicator that records whether the end of the file has been reached; and - fpos_t - which is a complete object type other than an array type capable of recording all the - information needed to specify uniquely every position within a file. -3 The macros are NULL (described in 7.19); - _IOFBF - _IOLBF - _IONBF - which expand to integer constant expressions with distinct values, suitable for use as the - third argument to the setvbuf function; - BUFSIZ - which expands to an integer constant expression that is the size of the buffer used by the - setbuf function; - EOF - which expands to an integer constant expression, with type int and a negative value, that - is returned by several functions to indicate end-of-file, that is, no more input from a - stream; - FOPEN_MAX - which expands to an integer constant expression that is the minimum number of files that - the implementation guarantees can be open simultaneously; - FILENAME_MAX - which expands to an integer constant expression that is the size needed for an array of - char large enough to hold the longest file name string that the implementation - -[page 296] - - guarantees can be opened;258) - L_tmpnam - which expands to an integer constant expression that is the size needed for an array of - char large enough to hold a temporary file name string generated by the tmpnam - function; - SEEK_CUR - SEEK_END - SEEK_SET - which expand to integer constant expressions with distinct values, suitable for use as the - third argument to the fseek function; - TMP_MAX - which expands to an integer constant expression that is the minimum number of unique - file names that can be generated by the tmpnam function; - stderr - stdin - stdout - which are expressions of type ''pointer to FILE'' that point to the FILE objects - associated, respectively, with the standard error, input, and output streams. -4 The header declares a number of functions useful for wide character input - and output. The wide character input/output functions described in that subclause - provide operations analogous to most of those described here, except that the - fundamental units internal to the program are wide characters. The external - representation (in the file) is a sequence of ''generalized'' multibyte characters, as - described further in 7.21.3. -5 The input/output functions are given the following collective terms: - -- The wide character input functions -- those functions described in 7.28 that perform - input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar, - fwscanf, wscanf, vfwscanf, and vwscanf. - -- The wide character output functions -- those functions described in 7.28 that perform - output from wide characters and wide strings: fputwc, fputws, putwc, - putwchar, fwprintf, wprintf, vfwprintf, and vwprintf. - - - 258) If the implementation imposes no practical limit on the length of file name strings, the value of - FILENAME_MAX should instead be the recommended size of an array intended to hold a file name - string. Of course, file name string contents are subject to other system-specific constraints; therefore - all possible strings of length FILENAME_MAX cannot be expected to be opened successfully. - -[page 297] - - -- The wide character input/output functions -- the union of the ungetwc function, the - wide character input functions, and the wide character output functions. - -- The byte input/output functions -- those functions described in this subclause that - perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread, - fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf, * - ungetc, vfprintf, vfscanf, vprintf, and vscanf. - Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the - tmpnam function (7.21.4.4), (7.28). - 7.21.2 Streams -1 Input and output, whether to or from physical devices such as terminals and tape drives, - or whether to or from files supported on structured storage devices, are mapped into - logical data streams, whose properties are more uniform than their various inputs and - outputs. Two forms of mapping are supported, for text streams and for binary - streams.259) -2 A text stream is an ordered sequence of characters composed into lines, each line - consisting of zero or more characters plus a terminating new-line character. Whether the - last line requires a terminating new-line character is implementation-defined. Characters - may have to be added, altered, or deleted on input and output to conform to differing - conventions for representing text in the host environment. Thus, there need not be a one- - to-one correspondence between the characters in a stream and those in the external - representation. Data read in from a text stream will necessarily compare equal to the data - that were earlier written out to that stream only if: the data consist only of printing - characters and the control characters horizontal tab and new-line; no new-line character is - immediately preceded by space characters; and the last character is a new-line character. - Whether space characters that are written out immediately before a new-line character - appear when read in is implementation-defined. -3 A binary stream is an ordered sequence of characters that can transparently record - internal data. Data read in from a binary stream shall compare equal to the data that were - earlier written out to that stream, under the same implementation. Such a stream may, - however, have an implementation-defined number of null characters appended to the end - of the stream. -4 Each stream has an orientation. After a stream is associated with an external file, but - before any operations are performed on it, the stream is without orientation. Once a wide - character input/output function has been applied to a stream without orientation, the - - - 259) An implementation need not distinguish between text streams and binary streams. In such an - implementation, there need be no new-line characters in a text stream nor any limit to the length of a - line. - -[page 298] - - stream becomes a wide-oriented stream. Similarly, once a byte input/output function has - been applied to a stream without orientation, the stream becomes a byte-oriented stream. - Only a call to the freopen function or the fwide function can otherwise alter the - orientation of a stream. (A successful call to freopen removes any orientation.)260) -5 Byte input/output functions shall not be applied to a wide-oriented stream and wide - character input/output functions shall not be applied to a byte-oriented stream. The - remaining stream operations do not affect, and are not affected by, a stream's orientation, - except for the following additional restrictions: - -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both - text and binary streams. - -- For wide-oriented streams, after a successful call to a file-positioning function that - leaves the file position indicator prior to the end-of-file, a wide character output - function can overwrite a partial multibyte character; any file contents beyond the - byte(s) written are henceforth indeterminate. -6 Each wide-oriented stream has an associated mbstate_t object that stores the current - parse state of the stream. A successful call to fgetpos stores a representation of the - value of this mbstate_t object as part of the value of the fpos_t object. A later - successful call to fsetpos using the same stored fpos_t value restores the value of - the associated mbstate_t object as well as the position within the controlled stream. - Environmental limits -7 An implementation shall support text files with lines containing at least 254 characters, - including the terminating new-line character. The value of the macro BUFSIZ shall be at - least 256. - Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5), - mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function - (7.21.9.3). - - - - - 260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup. - -[page 299] - - 7.21.3 Files -1 A stream is associated with an external file (which may be a physical device) by opening - a file, which may involve creating a new file. Creating an existing file causes its former - contents to be discarded, if necessary. If a file can support positioning requests (such as a - disk file, as opposed to a terminal), then a file position indicator associated with the - stream is positioned at the start (character number zero) of the file, unless the file is - opened with append mode in which case it is implementation-defined whether the file - position indicator is initially positioned at the beginning or the end of the file. The file - position indicator is maintained by subsequent reads, writes, and positioning requests, to - facilitate an orderly progression through the file. -2 Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text - stream causes the associated file to be truncated beyond that point is implementation- - defined. -3 When a stream is unbuffered, characters are intended to appear from the source or at the - destination as soon as possible. Otherwise characters may be accumulated and - transmitted to or from the host environment as a block. When a stream is fully buffered, - characters are intended to be transmitted to or from the host environment as a block when - a buffer is filled. When a stream is line buffered, characters are intended to be - transmitted to or from the host environment as a block when a new-line character is - encountered. Furthermore, characters are intended to be transmitted as a block to the host - environment when a buffer is filled, when input is requested on an unbuffered stream, or - when input is requested on a line buffered stream that requires the transmission of - characters from the host environment. Support for these characteristics is - implementation-defined, and may be affected via the setbuf and setvbuf functions. -4 A file may be disassociated from a controlling stream by closing the file. Output streams - are flushed (any unwritten buffer contents are transmitted to the host environment) before - the stream is disassociated from the file. The value of a pointer to a FILE object is - indeterminate after the associated file is closed (including the standard text streams). - Whether a file of zero length (on which no characters have been written by an output - stream) actually exists is implementation-defined. -5 The file may be subsequently reopened, by the same or another program execution, and - its contents reclaimed or modified (if it can be repositioned at its start). If the main - function returns to its original caller, or if the exit function is called, all open files are - closed (hence all output streams are flushed) before program termination. Other paths to - program termination, such as calling the abort function, need not close all files - properly. -6 The address of the FILE object used to control a stream may be significant; a copy of a - FILE object need not serve in place of the original. - -[page 300] - -7 At program startup, three text streams are predefined and need not be opened explicitly - -- standard input (for reading conventional input), standard output (for writing - conventional output), and standard error (for writing diagnostic output). As initially - opened, the standard error stream is not fully buffered; the standard input and standard - output streams are fully buffered if and only if the stream can be determined not to refer - to an interactive device. -8 Functions that open additional (nontemporary) files require a file name, which is a string. - The rules for composing valid file names are implementation-defined. Whether the same - file can be simultaneously open multiple times is also implementation-defined. -9 Although both text and binary wide-oriented streams are conceptually sequences of wide - characters, the external file associated with a wide-oriented stream is a sequence of - multibyte characters, generalized as follows: - -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte - encodings valid for use internal to the program). - -- A file need not begin nor end in the initial shift state.261) -10 Moreover, the encodings used for multibyte characters may differ among files. Both the - nature and choice of such encodings are implementation-defined. -11 The wide character input functions read multibyte characters from the stream and convert - them to wide characters as if they were read by successive calls to the fgetwc function. - Each conversion occurs as if by a call to the mbrtowc function, with the conversion state - described by the stream's own mbstate_t object. The byte input functions read - characters from the stream as if by successive calls to the fgetc function. -12 The wide character output functions convert wide characters to multibyte characters and - write them to the stream as if they were written by successive calls to the fputwc - function. Each conversion occurs as if by a call to the wcrtomb function, with the - conversion state described by the stream's own mbstate_t object. The byte output - functions write characters to the stream as if by successive calls to the fputc function. -13 In some cases, some of the byte input/output functions also perform conversions between - multibyte characters and wide characters. These conversions also occur as if by calls to - the mbrtowc and wcrtomb functions. -14 An encoding error occurs if the character sequence presented to the underlying - mbrtowc function does not form a valid (generalized) multibyte character, or if the code - value passed to the underlying wcrtomb does not correspond to a valid (generalized) - - - 261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has - undefined behavior for a binary stream (because of possible trailing null characters) or for any stream - with state-dependent encoding that does not assuredly end in the initial shift state. - -[page 301] - - multibyte character. The wide character input/output functions and the byte input/output - functions store the value of the macro EILSEQ in errno if and only if an encoding error - occurs. - Environmental limits -15 The value of FOPEN_MAX shall be at least eight, including the three standard text - streams. - Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the - fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function - (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the - fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function - (7.28.6.3.2), the wcrtomb function (7.28.6.3.3). - 7.21.4 Operations on files - 7.21.4.1 The remove function - Synopsis -1 #include - int remove(const char *filename); - Description -2 The remove function causes the file whose name is the string pointed to by filename - to be no longer accessible by that name. A subsequent attempt to open that file using that - name will fail, unless it is created anew. If the file is open, the behavior of the remove - function is implementation-defined. - Returns -3 The remove function returns zero if the operation succeeds, nonzero if it fails. - 7.21.4.2 The rename function - Synopsis -1 #include - int rename(const char *old, const char *new); - Description -2 The rename function causes the file whose name is the string pointed to by old to be - henceforth known by the name given by the string pointed to by new. The file named - old is no longer accessible by that name. If a file named by the string pointed to by new - exists prior to the call to the rename function, the behavior is implementation-defined. - -[page 302] - - Returns -3 The rename function returns zero if the operation succeeds, nonzero if it fails,262) in - which case if the file existed previously it is still known by its original name. - 7.21.4.3 The tmpfile function - Synopsis -1 #include - FILE *tmpfile(void); - Description -2 The tmpfile function creates a temporary binary file that is different from any other - existing file and that will automatically be removed when it is closed or at program - termination. If the program terminates abnormally, whether an open temporary file is - removed is implementation-defined. The file is opened for update with "wb+" mode. - Recommended practice -3 It should be possible to open at least TMP_MAX temporary files during the lifetime of the - program (this limit may be shared with tmpnam) and there should be no limit on the - number simultaneously open other than this limit and any limit on the number of open - files (FOPEN_MAX). - Returns -4 The tmpfile function returns a pointer to the stream of the file that it created. If the file - cannot be created, the tmpfile function returns a null pointer. - Forward references: the fopen function (7.21.5.3). - 7.21.4.4 The tmpnam function - Synopsis -1 #include - char *tmpnam(char *s); - Description -2 The tmpnam function generates a string that is a valid file name and that is not the same - as the name of an existing file.263) The function is potentially capable of generating at - - - 262) Among the reasons the implementation may cause the rename function to fail are that the file is open - or that it is necessary to copy its contents to effectuate its renaming. - 263) Files created using strings generated by the tmpnam function are temporary only in the sense that - their names should not collide with those generated by conventional naming rules for the - implementation. It is still necessary to use the remove function to remove such files when their use - is ended, and before program termination. - -[page 303] - - least TMP_MAX different strings, but any or all of them may already be in use by existing - files and thus not be suitable return values. -3 The tmpnam function generates a different string each time it is called. -4 Calls to the tmpnam function with a null pointer argument may introduce data races with - each other. The implementation shall behave as if no library function calls the tmpnam - function. - Returns -5 If no suitable string can be generated, the tmpnam function returns a null pointer. - Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an - internal static object and returns a pointer to that object (subsequent calls to the tmpnam - function may modify the same object). If the argument is not a null pointer, it is assumed - to point to an array of at least L_tmpnam chars; the tmpnam function writes its result - in that array and returns the argument as its value. - Environmental limits -6 The value of the macro TMP_MAX shall be at least 25. - 7.21.5 File access functions - 7.21.5.1 The fclose function - Synopsis -1 #include - int fclose(FILE *stream); - Description -2 A successful call to the fclose function causes the stream pointed to by stream to be - flushed and the associated file to be closed. Any unwritten buffered data for the stream - are delivered to the host environment to be written to the file; any unread buffered data - are discarded. Whether or not the call succeeds, the stream is disassociated from the file - and any buffer set by the setbuf or setvbuf function is disassociated from the stream - (and deallocated if it was automatically allocated). - Returns -3 The fclose function returns zero if the stream was successfully closed, or EOF if any - errors were detected. - -[page 304] - - 7.21.5.2 The fflush function - Synopsis -1 #include - int fflush(FILE *stream); - Description -2 If stream points to an output stream or an update stream in which the most recent - operation was not input, the fflush function causes any unwritten data for that stream - to be delivered to the host environment to be written to the file; otherwise, the behavior is - undefined. -3 If stream is a null pointer, the fflush function performs this flushing action on all - streams for which the behavior is defined above. - Returns -4 The fflush function sets the error indicator for the stream and returns EOF if a write - error occurs, otherwise it returns zero. - Forward references: the fopen function (7.21.5.3). - 7.21.5.3 The fopen function - Synopsis -1 #include - FILE *fopen(const char * restrict filename, - const char * restrict mode); - Description -2 The fopen function opens the file whose name is the string pointed to by filename, - and associates a stream with it. -3 The argument mode points to a string. If the string is one of the following, the file is - open in the indicated mode. Otherwise, the behavior is undefined.264) - r open text file for reading - w truncate to zero length or create text file for writing - wx create text file for writing - a append; open or create text file for writing at end-of-file - rb open binary file for reading - wb truncate to zero length or create binary file for writing - - - 264) If the string begins with one of the above sequences, the implementation might choose to ignore the - remaining characters, or it might use them to select different kinds of a file (some of which might not - conform to the properties in 7.21.2). - -[page 305] - - wbx create binary file for writing - ab append; open or create binary file for writing at end-of-file - r+ open text file for update (reading and writing) - w+ truncate to zero length or create text file for update - w+x create text file for update - a+ append; open or create text file for update, writing at end-of-file - r+b or rb+ open binary file for update (reading and writing) - w+b or wb+ truncate to zero length or create binary file for update - w+bx or wb+x create binary file for update - a+b or ab+ append; open or create binary file for update, writing at end-of-file -4 Opening a file with read mode ('r' as the first character in the mode argument) fails if - the file does not exist or cannot be read. -5 Opening a file with exclusive mode ('x' as the last character in the mode argument) - fails if the file already exists or cannot be created. Otherwise, the file is created with - exclusive (also known as non-shared) access to the extent that the underlying system - supports exclusive access. -6 Opening a file with append mode ('a' as the first character in the mode argument) - causes all subsequent writes to the file to be forced to the then current end-of-file, - regardless of intervening calls to the fseek function. In some implementations, opening - a binary file with append mode ('b' as the second or third character in the above list of - mode argument values) may initially position the file position indicator for the stream - beyond the last data written, because of null character padding. -7 When a file is opened with update mode ('+' as the second or third character in the - above list of mode argument values), both input and output may be performed on the - associated stream. However, output shall not be directly followed by input without an - intervening call to the fflush function or to a file positioning function (fseek, - fsetpos, or rewind), and input shall not be directly followed by output without an - intervening call to a file positioning function, unless the input operation encounters end- - of-file. Opening (or creating) a text file with update mode may instead open (or create) a - binary stream in some implementations. -8 When opened, a stream is fully buffered if and only if it can be determined not to refer to - an interactive device. The error and end-of-file indicators for the stream are cleared. - Returns -9 The fopen function returns a pointer to the object controlling the stream. If the open - operation fails, fopen returns a null pointer. - Forward references: file positioning functions (7.21.9). - -[page 306] - - 7.21.5.4 The freopen function - Synopsis -1 #include - FILE *freopen(const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - Description -2 The freopen function opens the file whose name is the string pointed to by filename - and associates the stream pointed to by stream with it. The mode argument is used just - as in the fopen function.265) -3 If filename is a null pointer, the freopen function attempts to change the mode of - the stream to that specified by mode, as if the name of the file currently associated with - the stream had been used. It is implementation-defined which changes of mode are - permitted (if any), and under what circumstances. -4 The freopen function first attempts to close any file that is associated with the specified - stream. Failure to close the file is ignored. The error and end-of-file indicators for the - stream are cleared. - Returns -5 The freopen function returns a null pointer if the open operation fails. Otherwise, - freopen returns the value of stream. - 7.21.5.5 The setbuf function - Synopsis -1 #include - void setbuf(FILE * restrict stream, - char * restrict buf); - Description -2 Except that it returns no value, the setbuf function is equivalent to the setvbuf - function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf - is a null pointer), with the value _IONBF for mode. - - - - - 265) The primary use of the freopen function is to change the file associated with a standard text stream - (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value - returned by the fopen function may be assigned. - -[page 307] - - Returns -3 The setbuf function returns no value. - Forward references: the setvbuf function (7.21.5.6). - 7.21.5.6 The setvbuf function - Synopsis -1 #include - int setvbuf(FILE * restrict stream, - char * restrict buf, - int mode, size_t size); - Description -2 The setvbuf function may be used only after the stream pointed to by stream has - been associated with an open file and before any other operation (other than an - unsuccessful call to setvbuf) is performed on the stream. The argument mode - determines how stream will be buffered, as follows: _IOFBF causes input/output to be - fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes - input/output to be unbuffered. If buf is not a null pointer, the array it points to may be - used instead of a buffer allocated by the setvbuf function266) and the argument size - specifies the size of the array; otherwise, size may determine the size of a buffer - allocated by the setvbuf function. The contents of the array at any time are - indeterminate. - Returns -3 The setvbuf function returns zero on success, or nonzero if an invalid value is given - for mode or if the request cannot be honored. - - - - - 266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed - before a buffer that has automatic storage duration is deallocated upon block exit. - -[page 308] - - 7.21.6 Formatted input/output functions -1 The formatted input/output functions shall behave as if there is a sequence point after the - actions associated with each specifier.267) - 7.21.6.1 The fprintf function - Synopsis -1 #include - int fprintf(FILE * restrict stream, - const char * restrict format, ...); - Description -2 The fprintf function writes output to the stream pointed to by stream, under control - of the string pointed to by format that specifies how subsequent arguments are - converted for output. If there are insufficient arguments for the format, the behavior is - undefined. If the format is exhausted while arguments remain, the excess arguments are - evaluated (as always) but are otherwise ignored. The fprintf function returns when - the end of the format string is encountered. -3 The format shall be a multibyte character sequence, beginning and ending in its initial - shift state. The format is composed of zero or more directives: ordinary multibyte - characters (not %), which are copied unchanged to the output stream; and conversion - specifications, each of which results in fetching zero or more subsequent arguments, - converting them, if applicable, according to the corresponding conversion specifier, and - then writing the result to the output stream. -4 Each conversion specification is introduced by the character %. After the %, the following - appear in sequence: - -- Zero or more flags (in any order) that modify the meaning of the conversion - specification. - -- An optional minimum field width. If the converted value has fewer characters than the - field width, it is padded with spaces (by default) on the left (or right, if the left - adjustment flag, described later, has been given) to the field width. The field width - takes the form of an asterisk * (described later) or a nonnegative decimal integer.268) - -- An optional precision that gives the minimum number of digits to appear for the d, i, - o, u, x, and X conversions, the number of digits to appear after the decimal-point - character for a, A, e, E, f, and F conversions, the maximum number of significant - digits for the g and G conversions, or the maximum number of bytes to be written for - - - 267) The fprintf functions perform writes to memory for the %n specifier. - 268) Note that 0 is taken as a flag, not as the beginning of a field width. - -[page 309] - - s conversions. The precision takes the form of a period (.) followed either by an - asterisk * (described later) or by an optional decimal integer; if only the period is - specified, the precision is taken as zero. If a precision appears with any other - conversion specifier, the behavior is undefined. - -- An optional length modifier that specifies the size of the argument. - -- A conversion specifier character that specifies the type of conversion to be applied. -5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In - this case, an int argument supplies the field width or precision. The arguments - specifying field width, or precision, or both, shall appear (in that order) before the - argument (if any) to be converted. A negative field width argument is taken as a - flag - followed by a positive field width. A negative precision argument is taken as if the - precision were omitted. -6 The flag characters and their meanings are: - - The result of the conversion is left-justified within the field. (It is right-justified if - this flag is not specified.) - + The result of a signed conversion always begins with a plus or minus sign. (It - begins with a sign only when a negative value is converted if this flag is not - specified.)269) - space If the first character of a signed conversion is not a sign, or if a signed conversion - results in no characters, a space is prefixed to the result. If the space and + flags - both appear, the space flag is ignored. - # The result is converted to an ''alternative form''. For o conversion, it increases - the precision, if and only if necessary, to force the first digit of the result to be a - zero (if the value and precision are both 0, a single 0 is printed). For x (or X) - conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, - and G conversions, the result of converting a floating-point number always - contains a decimal-point character, even if no digits follow it. (Normally, a - decimal-point character appears in the result of these conversions only if a digit - follows it.) For g and G conversions, trailing zeros are not removed from the - result. For other conversions, the behavior is undefined. - 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros - (following any indication of sign or base) are used to pad to the field width rather - than performing space padding, except when converting an infinity or NaN. If the - 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X - - - 269) The results of all floating conversions of a negative zero, and of negative values that round to zero, - include a minus sign. - -[page 310] - - conversions, if a precision is specified, the 0 flag is ignored. For other - conversions, the behavior is undefined. -7 The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - signed char or unsigned char argument (the argument will have - been promoted according to the integer promotions, but its value shall be - converted to signed char or unsigned char before printing); or that - a following n conversion specifier applies to a pointer to a signed char - argument. - h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - short int or unsigned short int argument (the argument will - have been promoted according to the integer promotions, but its value shall - be converted to short int or unsigned short int before printing); - or that a following n conversion specifier applies to a pointer to a short - int argument. - l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - long int or unsigned long int argument; that a following n - conversion specifier applies to a pointer to a long int argument; that a - following c conversion specifier applies to a wint_t argument; that a - following s conversion specifier applies to a pointer to a wchar_t - argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion - specifier. - ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - long long int or unsigned long long int argument; or that a - following n conversion specifier applies to a pointer to a long long int - argument. - j Specifies that a following d, i, o, u, x, or X conversion specifier applies to - an intmax_t or uintmax_t argument; or that a following n conversion - specifier applies to a pointer to an intmax_t argument. - z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - size_t or the corresponding signed integer type argument; or that a - following n conversion specifier applies to a pointer to a signed integer type - corresponding to size_t argument. - t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - ptrdiff_t or the corresponding unsigned integer type argument; or that a - following n conversion specifier applies to a pointer to a ptrdiff_t - argument. - -[page 311] - - L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier - applies to a long double argument. - If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -8 The conversion specifiers and their meanings are: - d,i The int argument is converted to signed decimal in the style [-]dddd. The - precision specifies the minimum number of digits to appear; if the value - being converted can be represented in fewer digits, it is expanded with - leading zeros. The default precision is 1. The result of converting a zero - value with a precision of zero is no characters. - o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned - decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the - letters abcdef are used for x conversion and the letters ABCDEF for X - conversion. The precision specifies the minimum number of digits to appear; - if the value being converted can be represented in fewer digits, it is expanded - with leading zeros. The default precision is 1. The result of converting a - zero value with a precision of zero is no characters. - f,F A double argument representing a floating-point number is converted to - decimal notation in the style [-]ddd.ddd, where the number of digits after - the decimal-point character is equal to the precision specification. If the - precision is missing, it is taken as 6; if the precision is zero and the # flag is - not specified, no decimal-point character appears. If a decimal-point - character appears, at least one digit appears before it. The value is rounded to - the appropriate number of digits. - A double argument representing an infinity is converted in one of the styles - [-]inf or [-]infinity -- which style is implementation-defined. A - double argument representing a NaN is converted in one of the styles - [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of - any n-char-sequence, is implementation-defined. The F conversion specifier - produces INF, INFINITY, or NAN instead of inf, infinity, or nan, - respectively.270) - e,E A double argument representing a floating-point number is converted in the - style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the - argument is nonzero) before the decimal-point character and the number of - digits after it is equal to the precision; if the precision is missing, it is taken as - - - 270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning; - the # and 0 flag characters have no effect. - -[page 312] - - 6; if the precision is zero and the # flag is not specified, no decimal-point - character appears. The value is rounded to the appropriate number of digits. - The E conversion specifier produces a number with E instead of e - introducing the exponent. The exponent always contains at least two digits, - and only as many more digits as necessary to represent the exponent. If the - value is zero, the exponent is zero. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -g,G A double argument representing a floating-point number is converted in - style f or e (or in style F or E in the case of a G conversion specifier), - depending on the value converted and the precision. Let P equal the - precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. - Then, if a conversion with style E would have an exponent of X: - -- if P > X >= -4, the conversion is with style f (or F) and precision - P - (X + 1). - -- otherwise, the conversion is with style e (or E) and precision P - 1. - Finally, unless the # flag is used, any trailing zeros are removed from the - fractional portion of the result and the decimal-point character is removed if - there is no fractional portion remaining. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -a,A A double argument representing a floating-point number is converted in the - style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is - nonzero if the argument is a normalized floating-point number and is - otherwise unspecified) before the decimal-point character271) and the number - of hexadecimal digits after it is equal to the precision; if the precision is - missing and FLT_RADIX is a power of 2, then the precision is sufficient for - an exact representation of the value; if the precision is missing and - FLT_RADIX is not a power of 2, then the precision is sufficient to - - - - -271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so - that subsequent digits align to nibble (4-bit) boundaries. - -[page 313] - - distinguish272) values of type double, except that trailing zeros may be - omitted; if the precision is zero and the # flag is not specified, no decimal- - point character appears. The letters abcdef are used for a conversion and - the letters ABCDEF for A conversion. The A conversion specifier produces a - number with X and P instead of x and p. The exponent always contains at - least one digit, and only as many more digits as necessary to represent the - decimal exponent of 2. If the value is zero, the exponent is zero. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -c If no l length modifier is present, the int argument is converted to an - unsigned char, and the resulting character is written. - If an l length modifier is present, the wint_t argument is converted as if by - an ls conversion specification with no precision and an argument that points - to the initial element of a two-element array of wchar_t, the first element - containing the wint_t argument to the lc conversion specification and the - second a null wide character. -s If no l length modifier is present, the argument shall be a pointer to the initial - element of an array of character type.273) Characters from the array are - written up to (but not including) the terminating null character. If the - precision is specified, no more than that many bytes are written. If the - precision is not specified or is greater than the size of the array, the array shall - contain a null character. - If an l length modifier is present, the argument shall be a pointer to the initial - element of an array of wchar_t type. Wide characters from the array are - converted to multibyte characters (each as if by a call to the wcrtomb - function, with the conversion state described by an mbstate_t object - initialized to zero before the first wide character is converted) up to and - including a terminating null wide character. The resulting multibyte - characters are written up to (but not including) the terminating null character - (byte). If no precision is specified, the array shall contain a null wide - character. If a precision is specified, no more than that many bytes are - written (including shift sequences, if any), and the array shall contain a null - wide character if, to equal the multibyte character sequence length given by - -272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is - FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p - might suffice depending on the implementation's scheme for determining the digit to the left of the - decimal-point character. -273) No special provisions are made for multibyte characters. - -[page 314] - - the precision, the function would need to access a wide character one past the - end of the array. In no case is a partial multibyte character written.274) - p The argument shall be a pointer to void. The value of the pointer is - converted to a sequence of printing characters, in an implementation-defined - manner. - n The argument shall be a pointer to signed integer into which is written the - number of characters written to the output stream so far by this call to - fprintf. No argument is converted, but one is consumed. If the conversion - specification includes any flags, a field width, or a precision, the behavior is - undefined. - % A % character is written. No argument is converted. The complete - conversion specification shall be %%. -9 If a conversion specification is invalid, the behavior is undefined.275) If any argument is - not the correct type for the corresponding conversion specification, the behavior is - undefined. -10 In no case does a nonexistent or small field width cause truncation of a field; if the result - of a conversion is wider than the field width, the field is expanded to contain the - conversion result. -11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded - to a hexadecimal floating number with the given precision. - Recommended practice -12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly - representable in the given precision, the result should be one of the two adjacent numbers - in hexadecimal floating style with the given precision, with the extra stipulation that the - error should have a correct sign for the current rounding direction. -13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most - DECIMAL_DIG, then the result should be correctly rounded.276) If the number of - significant decimal digits is more than DECIMAL_DIG but the source value is exactly - representable with DECIMAL_DIG digits, then the result should be an exact - representation with trailing zeros. Otherwise, the source value is bounded by two - adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value - - - 274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding. - 275) See ''future library directions'' (7.30.9). - 276) For binary-to-decimal conversion, the result format's values are the numbers representable with the - given format specifier. The number of significant digits is determined by the format specifier, and in - the case of fixed-point conversion by the source value as well. - -[page 315] - - of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that - the error should have a correct sign for the current rounding direction. - Returns -14 The fprintf function returns the number of characters transmitted, or a negative value - if an output or encoding error occurred. - Environmental limits -15 The number of characters that can be produced by any single conversion shall be at least - 4095. -16 EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal - places: - #include - #include - /* ... */ - char *weekday, *month; // pointers to strings - int day, hour, min; - fprintf(stdout, "%s, %s %d, %.2d:%.2d\n", - weekday, month, day, hour, min); - fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0)); - -17 EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the - members of the extended character set that consist of more than one byte each consist of exactly two bytes, - the first of which is denoted here by a and the second by an uppercase letter. -18 Given the following wide string with length seven, - static wchar_t wstr[] = L" X Yabc Z W"; - the seven calls - fprintf(stdout, "|1234567890123|\n"); - fprintf(stdout, "|%13ls|\n", wstr); - fprintf(stdout, "|%-13.9ls|\n", wstr); - fprintf(stdout, "|%13.10ls|\n", wstr); - fprintf(stdout, "|%13.11ls|\n", wstr); - fprintf(stdout, "|%13.15ls|\n", &wstr[2]); - fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]); - will print the following seven lines: - |1234567890123| - | X Yabc Z W| - | X Yabc Z | - | X Yabc Z| - | X Yabc Z W| - | abc Z W| - | Z| - - Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3). - -[page 316] - - 7.21.6.2 The fscanf function - Synopsis -1 #include - int fscanf(FILE * restrict stream, - const char * restrict format, ...); - Description -2 The fscanf function reads input from the stream pointed to by stream, under control - of the string pointed to by format that specifies the admissible input sequences and how - they are to be converted for assignment, using subsequent arguments as pointers to the - objects to receive the converted input. If there are insufficient arguments for the format, - the behavior is undefined. If the format is exhausted while arguments remain, the excess - arguments are evaluated (as always) but are otherwise ignored. -3 The format shall be a multibyte character sequence, beginning and ending in its initial - shift state. The format is composed of zero or more directives: one or more white-space - characters, an ordinary multibyte character (neither % nor a white-space character), or a - conversion specification. Each conversion specification is introduced by the character %. - After the %, the following appear in sequence: - -- An optional assignment-suppressing character *. - -- An optional decimal integer greater than zero that specifies the maximum field width - (in characters). - -- An optional length modifier that specifies the size of the receiving object. - -- A conversion specifier character that specifies the type of conversion to be applied. -4 The fscanf function executes each directive of the format in turn. When all directives - have been executed, or if a directive fails (as detailed below), the function returns. - Failures are described as input failures (due to the occurrence of an encoding error or the - unavailability of input characters), or matching failures (due to inappropriate input). -5 A directive composed of white-space character(s) is executed by reading input up to the - first non-white-space character (which remains unread), or until no more characters can - be read. -6 A directive that is an ordinary multibyte character is executed by reading the next - characters of the stream. If any of those characters differ from the ones composing the - directive, the directive fails and the differing and subsequent characters remain unread. - Similarly, if end-of-file, an encoding error, or a read error prevents a character from being - read, the directive fails. -7 A directive that is a conversion specification defines a set of matching input sequences, as - described below for each specifier. A conversion specification is executed in the - -[page 317] - - following steps: -8 Input white-space characters (as specified by the isspace function) are skipped, unless - the specification includes a [, c, or n specifier.277) -9 An input item is read from the stream, unless the specification includes an n specifier. An - input item is defined as the longest sequence of input characters which does not exceed - any specified field width and which is, or is a prefix of, a matching input sequence.278) - The first character, if any, after the input item remains unread. If the length of the input - item is zero, the execution of the directive fails; this condition is a matching failure unless - end-of-file, an encoding error, or a read error prevented input from the stream, in which - case it is an input failure. -10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the - count of input characters) is converted to a type appropriate to the conversion specifier. If - the input item is not a matching sequence, the execution of the directive fails: this - condition is a matching failure. Unless assignment suppression was indicated by a *, the - result of the conversion is placed in the object pointed to by the first argument following - the format argument that has not already received a conversion result. If this object - does not have an appropriate type, or if the result of the conversion cannot be represented - in the object, the behavior is undefined. -11 The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to signed char or unsigned char. - h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to short int or unsigned short - int. - l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to long int or unsigned long - int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to - an argument with type pointer to double; or that a following c, s, or [ - conversion specifier applies to an argument with type pointer to wchar_t. - ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to long long int or unsigned - long long int. - - - - 277) These white-space characters are not counted against a specified field width. - 278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences - that are acceptable to strtod, strtol, etc., are unacceptable to fscanf. - -[page 318] - - j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to intmax_t or uintmax_t. - z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to size_t or the corresponding signed - integer type. - t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to ptrdiff_t or the corresponding - unsigned integer type. - L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier - applies to an argument with type pointer to long double. - If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -12 The conversion specifiers and their meanings are: - d Matches an optionally signed decimal integer, whose format is the same as - expected for the subject sequence of the strtol function with the value 10 - for the base argument. The corresponding argument shall be a pointer to - signed integer. - i Matches an optionally signed integer, whose format is the same as expected - for the subject sequence of the strtol function with the value 0 for the - base argument. The corresponding argument shall be a pointer to signed - integer. - o Matches an optionally signed octal integer, whose format is the same as - expected for the subject sequence of the strtoul function with the value 8 - for the base argument. The corresponding argument shall be a pointer to - unsigned integer. - u Matches an optionally signed decimal integer, whose format is the same as - expected for the subject sequence of the strtoul function with the value 10 - for the base argument. The corresponding argument shall be a pointer to - unsigned integer. - x Matches an optionally signed hexadecimal integer, whose format is the same - as expected for the subject sequence of the strtoul function with the value - 16 for the base argument. The corresponding argument shall be a pointer to - unsigned integer. - a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose - format is the same as expected for the subject sequence of the strtod - function. The corresponding argument shall be a pointer to floating. - -[page 319] - -c Matches a sequence of characters of exactly the number specified by the field - width (1 if no field width is present in the directive).279) - If no l length modifier is present, the corresponding argument shall be a - pointer to the initial element of a character array large enough to accept the - sequence. No null character is added. - If an l length modifier is present, the input shall be a sequence of multibyte - characters that begins in the initial shift state. Each multibyte character in the - sequence is converted to a wide character as if by a call to the mbrtowc - function, with the conversion state described by an mbstate_t object - initialized to zero before the first multibyte character is converted. The - corresponding argument shall be a pointer to the initial element of an array of - wchar_t large enough to accept the resulting sequence of wide characters. - No null wide character is added. -s Matches a sequence of non-white-space characters.279) - If no l length modifier is present, the corresponding argument shall be a - pointer to the initial element of a character array large enough to accept the - sequence and a terminating null character, which will be added automatically. - If an l length modifier is present, the input shall be a sequence of multibyte - characters that begins in the initial shift state. Each multibyte character is - converted to a wide character as if by a call to the mbrtowc function, with - the conversion state described by an mbstate_t object initialized to zero - before the first multibyte character is converted. The corresponding argument - shall be a pointer to the initial element of an array of wchar_t large enough - to accept the sequence and the terminating null wide character, which will be - added automatically. -[ Matches a nonempty sequence of characters from a set of expected characters - (the scanset).279) - If no l length modifier is present, the corresponding argument shall be a - pointer to the initial element of a character array large enough to accept the - sequence and a terminating null character, which will be added automatically. - If an l length modifier is present, the input shall be a sequence of multibyte - characters that begins in the initial shift state. Each multibyte character is - converted to a wide character as if by a call to the mbrtowc function, with - the conversion state described by an mbstate_t object initialized to zero - -279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [ - conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The - resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state. - -[page 320] - - before the first multibyte character is converted. The corresponding argument - shall be a pointer to the initial element of an array of wchar_t large enough - to accept the sequence and the terminating null wide character, which will be - added automatically. - The conversion specifier includes all subsequent characters in the format - string, up to and including the matching right bracket (]). The characters - between the brackets (the scanlist) compose the scanset, unless the character - after the left bracket is a circumflex (^), in which case the scanset contains all - characters that do not appear in the scanlist between the circumflex and the - right bracket. If the conversion specifier begins with [] or [^], the right - bracket character is in the scanlist and the next following right bracket - character is the matching right bracket that ends the specification; otherwise - the first following right bracket character is the one that ends the - specification. If a - character is in the scanlist and is not the first, nor the - second where the first character is a ^, nor the last character, the behavior is - implementation-defined. - p Matches an implementation-defined set of sequences, which should be the - same as the set of sequences that may be produced by the %p conversion of - the fprintf function. The corresponding argument shall be a pointer to a - pointer to void. The input item is converted to a pointer value in an - implementation-defined manner. If the input item is a value converted earlier - during the same program execution, the pointer that results shall compare - equal to that value; otherwise the behavior of the %p conversion is undefined. - n No input is consumed. The corresponding argument shall be a pointer to - signed integer into which is to be written the number of characters read from - the input stream so far by this call to the fscanf function. Execution of a - %n directive does not increment the assignment count returned at the - completion of execution of the fscanf function. No argument is converted, - but one is consumed. If the conversion specification includes an assignment- - suppressing character or a field width, the behavior is undefined. - % Matches a single % character; no conversion or assignment occurs. The - complete conversion specification shall be %%. -13 If a conversion specification is invalid, the behavior is undefined.280) -14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as, - respectively, a, e, f, g, and x. - - - - 280) See ''future library directions'' (7.30.9). - -[page 321] - -15 Trailing white space (including new-line characters) is left unread unless matched by a - directive. The success of literal matches and suppressed assignments is not directly - determinable other than via the %n directive. - Returns -16 The fscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. -17 EXAMPLE 1 The call: - #include - /* ... */ - int n, i; float x; char name[50]; - n = fscanf(stdin, "%d%f%s", &i, &x, name); - with the input line: - 25 54.32E-1 thompson - will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -18 EXAMPLE 2 The call: - #include - /* ... */ - int i; float x; char name[50]; - fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name); - with input: - 56789 0123 56a72 - will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the - sequence 56\0. The next character read from the input stream will be a. - -19 EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name: - #include - /* ... */ - int count; float quant; char units[21], item[21]; - do { - count = fscanf(stdin, "%f%20s of %20s", &quant, units, item); - fscanf(stdin,"%*[^\n]"); - } while (!feof(stdin) && !ferror(stdin)); -20 If the stdin stream contains the following lines: - 2 quarts of oil - -12.8degrees Celsius - lots of luck - 10.0LBS of - dirt - 100ergs of energy - -[page 322] - - the execution of the above example will be analogous to the following assignments: - quant = 2; strcpy(units, "quarts"); strcpy(item, "oil"); - count = 3; - quant = -12.8; strcpy(units, "degrees"); - count = 2; // "C" fails to match "o" - count = 0; // "l" fails to match "%f" - quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt"); - count = 3; - count = 0; // "100e" fails to match "%f" - count = EOF; - -21 EXAMPLE 4 In: - #include - /* ... */ - int d1, d2, n1, n2, i; - i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2); - the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value - of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i. - -22 EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the - members of the extended character set that consist of more than one byte each consist of exactly two bytes, - the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as - such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes - entry into the alternate shift state. -23 After the call: - #include - /* ... */ - char str[50]; - fscanf(stdin, "a%s", str); - with the input line: - a(uparrow) X Y(downarrow) bc - str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte - characters, in the more general case) appears to be a single-byte white-space character. -24 In contrast, after the call: - #include - #include - /* ... */ - wchar_t wstr[50]; - fscanf(stdin, "a%ls", wstr); - with the same input line, wstr will contain the two wide characters that correspond to X and Y and a - terminating null wide character. -25 However, the call: - -[page 323] - - #include - #include - /* ... */ - wchar_t wstr[50]; - fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr); - with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format - string. -26 Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte - character Y, after the call: - #include - #include - /* ... */ - wchar_t wstr[50]; - fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr); - with the same input line, zero will again be returned, but stdin will be left with a partially consumed - multibyte character. - - Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the - strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state - (7.28.6), the wcrtomb function (7.28.6.3.3). - 7.21.6.3 The printf function - Synopsis -1 #include - int printf(const char * restrict format, ...); - Description -2 The printf function is equivalent to fprintf with the argument stdout interposed - before the arguments to printf. - Returns -3 The printf function returns the number of characters transmitted, or a negative value if - an output or encoding error occurred. - 7.21.6.4 The scanf function - Synopsis -1 #include - int scanf(const char * restrict format, ...); - Description -2 The scanf function is equivalent to fscanf with the argument stdin interposed - before the arguments to scanf. - -[page 324] - - Returns -3 The scanf function returns the value of the macro EOF if an input failure occurs before - the first conversion (if any) has completed. Otherwise, the scanf function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. - 7.21.6.5 The snprintf function - Synopsis -1 #include - int snprintf(char * restrict s, size_t n, - const char * restrict format, ...); - Description -2 The snprintf function is equivalent to fprintf, except that the output is written into - an array (specified by argument s) rather than to a stream. If n is zero, nothing is written, - and s may be a null pointer. Otherwise, output characters beyond the n-1st are - discarded rather than being written to the array, and a null character is written at the end - of the characters actually written into the array. If copying takes place between objects - that overlap, the behavior is undefined. - Returns -3 The snprintf function returns the number of characters that would have been written - had n been sufficiently large, not counting the terminating null character, or a negative - value if an encoding error occurred. Thus, the null-terminated output has been - completely written if and only if the returned value is nonnegative and less than n. - 7.21.6.6 The sprintf function - Synopsis -1 #include - int sprintf(char * restrict s, - const char * restrict format, ...); - Description -2 The sprintf function is equivalent to fprintf, except that the output is written into - an array (specified by the argument s) rather than to a stream. A null character is written - at the end of the characters written; it is not counted as part of the returned value. If - copying takes place between objects that overlap, the behavior is undefined. - Returns -3 The sprintf function returns the number of characters written in the array, not - counting the terminating null character, or a negative value if an encoding error occurred. - -[page 325] - - 7.21.6.7 The sscanf function - Synopsis -1 #include - int sscanf(const char * restrict s, - const char * restrict format, ...); - Description -2 The sscanf function is equivalent to fscanf, except that input is obtained from a - string (specified by the argument s) rather than from a stream. Reaching the end of the - string is equivalent to encountering end-of-file for the fscanf function. If copying - takes place between objects that overlap, the behavior is undefined. - Returns -3 The sscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the sscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.21.6.8 The vfprintf function - Synopsis -1 #include - #include - int vfprintf(FILE * restrict stream, - const char * restrict format, - va_list arg); - Description -2 The vfprintf function is equivalent to fprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfprintf function does not invoke the - va_end macro.281) - Returns -3 The vfprintf function returns the number of characters transmitted, or a negative - value if an output or encoding error occurred. -4 EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine. - - - - - 281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and - vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate. - -[page 326] - - #include - #include - void error(char *function_name, char *format, ...) - { - va_list args; - va_start(args, format); - // print out name of function causing error - fprintf(stderr, "ERROR in %s: ", function_name); - // print out remainder of message - vfprintf(stderr, format, args); - va_end(args); - } - - 7.21.6.9 The vfscanf function - Synopsis -1 #include - #include - int vfscanf(FILE * restrict stream, - const char * restrict format, - va_list arg); - Description -2 The vfscanf function is equivalent to fscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfscanf function does not invoke the - va_end macro.281) - Returns -3 The vfscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vfscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.21.6.10 The vprintf function - Synopsis -1 #include - #include - int vprintf(const char * restrict format, - va_list arg); - Description -2 The vprintf function is equivalent to printf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - -[page 327] - - possibly subsequent va_arg calls). The vprintf function does not invoke the - va_end macro.281) - Returns -3 The vprintf function returns the number of characters transmitted, or a negative value - if an output or encoding error occurred. - 7.21.6.11 The vscanf function - Synopsis -1 #include - #include - int vscanf(const char * restrict format, - va_list arg); - Description -2 The vscanf function is equivalent to scanf, with the variable argument list replaced - by arg, which shall have been initialized by the va_start macro (and possibly - subsequent va_arg calls). The vscanf function does not invoke the va_end - macro.281) - Returns -3 The vscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.21.6.12 The vsnprintf function - Synopsis -1 #include - #include - int vsnprintf(char * restrict s, size_t n, - const char * restrict format, - va_list arg); - Description -2 The vsnprintf function is equivalent to snprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsnprintf function does not invoke the - va_end macro.281) If copying takes place between objects that overlap, the behavior is - undefined. - -[page 328] - - Returns -3 The vsnprintf function returns the number of characters that would have been written - had n been sufficiently large, not counting the terminating null character, or a negative - value if an encoding error occurred. Thus, the null-terminated output has been - completely written if and only if the returned value is nonnegative and less than n. - 7.21.6.13 The vsprintf function - Synopsis -1 #include - #include - int vsprintf(char * restrict s, - const char * restrict format, - va_list arg); - Description -2 The vsprintf function is equivalent to sprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsprintf function does not invoke the - va_end macro.281) If copying takes place between objects that overlap, the behavior is - undefined. - Returns -3 The vsprintf function returns the number of characters written in the array, not - counting the terminating null character, or a negative value if an encoding error occurred. - 7.21.6.14 The vsscanf function - Synopsis -1 #include - #include - int vsscanf(const char * restrict s, - const char * restrict format, - va_list arg); - Description -2 The vsscanf function is equivalent to sscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsscanf function does not invoke the - va_end macro.281) - Returns -3 The vsscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vsscanf function - -[page 329] - - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.21.7 Character input/output functions - 7.21.7.1 The fgetc function - Synopsis -1 #include - int fgetc(FILE *stream); - Description -2 If the end-of-file indicator for the input stream pointed to by stream is not set and a - next character is present, the fgetc function obtains that character as an unsigned - char converted to an int and advances the associated file position indicator for the - stream (if defined). - Returns -3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- - of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the - fgetc function returns the next character from the input stream pointed to by stream. - If a read error occurs, the error indicator for the stream is set and the fgetc function - returns EOF.282) - 7.21.7.2 The fgets function - Synopsis -1 #include - char *fgets(char * restrict s, int n, - FILE * restrict stream); - Description -2 The fgets function reads at most one less than the number of characters specified by n - from the stream pointed to by stream into the array pointed to by s. No additional - characters are read after a new-line character (which is retained) or after end-of-file. A - null character is written immediately after the last character read into the array. - Returns -3 The fgets function returns s if successful. If end-of-file is encountered and no - characters have been read into the array, the contents of the array remain unchanged and a - null pointer is returned. If a read error occurs during the operation, the array contents are - indeterminate and a null pointer is returned. - - 282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. - -[page 330] - - 7.21.7.3 The fputc function - Synopsis -1 #include - int fputc(int c, FILE *stream); - Description -2 The fputc function writes the character specified by c (converted to an unsigned - char) to the output stream pointed to by stream, at the position indicated by the - associated file position indicator for the stream (if defined), and advances the indicator - appropriately. If the file cannot support positioning requests, or if the stream was opened - with append mode, the character is appended to the output stream. - Returns -3 The fputc function returns the character written. If a write error occurs, the error - indicator for the stream is set and fputc returns EOF. - 7.21.7.4 The fputs function - Synopsis -1 #include - int fputs(const char * restrict s, - FILE * restrict stream); - Description -2 The fputs function writes the string pointed to by s to the stream pointed to by - stream. The terminating null character is not written. - Returns -3 The fputs function returns EOF if a write error occurs; otherwise it returns a - nonnegative value. - 7.21.7.5 The getc function - Synopsis -1 #include - int getc(FILE *stream); - Description -2 The getc function is equivalent to fgetc, except that if it is implemented as a macro, it - may evaluate stream more than once, so the argument should never be an expression - with side effects. - -[page 331] - - Returns -3 The getc function returns the next character from the input stream pointed to by - stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and - getc returns EOF. If a read error occurs, the error indicator for the stream is set and - getc returns EOF. - 7.21.7.6 The getchar function - Synopsis -1 #include - int getchar(void); - Description -2 The getchar function is equivalent to getc with the argument stdin. - Returns -3 The getchar function returns the next character from the input stream pointed to by - stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and - getchar returns EOF. If a read error occurs, the error indicator for the stream is set and - getchar returns EOF. * - 7.21.7.7 The putc function - Synopsis -1 #include - int putc(int c, FILE *stream); - Description -2 The putc function is equivalent to fputc, except that if it is implemented as a macro, it - may evaluate stream more than once, so that argument should never be an expression - with side effects. - Returns -3 The putc function returns the character written. If a write error occurs, the error - indicator for the stream is set and putc returns EOF. - 7.21.7.8 The putchar function - Synopsis -1 #include - int putchar(int c); - Description -2 The putchar function is equivalent to putc with the second argument stdout. - -[page 332] - - Returns -3 The putchar function returns the character written. If a write error occurs, the error - indicator for the stream is set and putchar returns EOF. - 7.21.7.9 The puts function - Synopsis -1 #include - int puts(const char *s); - Description -2 The puts function writes the string pointed to by s to the stream pointed to by stdout, - and appends a new-line character to the output. The terminating null character is not - written. - Returns -3 The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative - value. - 7.21.7.10 The ungetc function - Synopsis -1 #include - int ungetc(int c, FILE *stream); - Description -2 The ungetc function pushes the character specified by c (converted to an unsigned - char) back onto the input stream pointed to by stream. Pushed-back characters will be - returned by subsequent reads on that stream in the reverse order of their pushing. A - successful intervening call (with the stream pointed to by stream) to a file positioning - function (fseek, fsetpos, or rewind) discards any pushed-back characters for the - stream. The external storage corresponding to the stream is unchanged. -3 One character of pushback is guaranteed. If the ungetc function is called too many - times on the same stream without an intervening read or file positioning operation on that - stream, the operation may fail. -4 If the value of c equals that of the macro EOF, the operation fails and the input stream is - unchanged. -5 A successful call to the ungetc function clears the end-of-file indicator for the stream. - The value of the file position indicator for the stream after reading or discarding all - pushed-back characters shall be the same as it was before the characters were pushed - back. For a text stream, the value of its file position indicator after a successful call to the - ungetc function is unspecified until all pushed-back characters are read or discarded. - -[page 333] - - For a binary stream, its file position indicator is decremented by each successful call to - the ungetc function; if its value was zero before a call, it is indeterminate after the - call.283) - Returns -6 The ungetc function returns the character pushed back after conversion, or EOF if the - operation fails. - Forward references: file positioning functions (7.21.9). - 7.21.8 Direct input/output functions - 7.21.8.1 The fread function - Synopsis -1 #include - size_t fread(void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - Description -2 The fread function reads, into the array pointed to by ptr, up to nmemb elements - whose size is specified by size, from the stream pointed to by stream. For each - object, size calls are made to the fgetc function and the results stored, in the order - read, in an array of unsigned char exactly overlaying the object. The file position - indicator for the stream (if defined) is advanced by the number of characters successfully - read. If an error occurs, the resulting value of the file position indicator for the stream is - indeterminate. If a partial element is read, its value is indeterminate. - Returns -3 The fread function returns the number of elements successfully read, which may be - less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, - fread returns zero and the contents of the array and the state of the stream remain - unchanged. - - - - - 283) See ''future library directions'' (7.30.9). - -[page 334] - - 7.21.8.2 The fwrite function - Synopsis -1 #include - size_t fwrite(const void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - Description -2 The fwrite function writes, from the array pointed to by ptr, up to nmemb elements - whose size is specified by size, to the stream pointed to by stream. For each object, - size calls are made to the fputc function, taking the values (in order) from an array of - unsigned char exactly overlaying the object. The file position indicator for the - stream (if defined) is advanced by the number of characters successfully written. If an - error occurs, the resulting value of the file position indicator for the stream is - indeterminate. - Returns -3 The fwrite function returns the number of elements successfully written, which will be - less than nmemb only if a write error is encountered. If size or nmemb is zero, - fwrite returns zero and the state of the stream remains unchanged. - 7.21.9 File positioning functions - 7.21.9.1 The fgetpos function - Synopsis -1 #include - int fgetpos(FILE * restrict stream, - fpos_t * restrict pos); - Description -2 The fgetpos function stores the current values of the parse state (if any) and file - position indicator for the stream pointed to by stream in the object pointed to by pos. - The values stored contain unspecified information usable by the fsetpos function for - repositioning the stream to its position at the time of the call to the fgetpos function. - Returns -3 If successful, the fgetpos function returns zero; on failure, the fgetpos function - returns nonzero and stores an implementation-defined positive value in errno. - Forward references: the fsetpos function (7.21.9.3). - -[page 335] - - 7.21.9.2 The fseek function - Synopsis -1 #include - int fseek(FILE *stream, long int offset, int whence); - Description -2 The fseek function sets the file position indicator for the stream pointed to by stream. - If a read or write error occurs, the error indicator for the stream is set and fseek fails. -3 For a binary stream, the new position, measured in characters from the beginning of the - file, is obtained by adding offset to the position specified by whence. The specified - position is the beginning of the file if whence is SEEK_SET, the current value of the file - position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not - meaningfully support fseek calls with a whence value of SEEK_END. -4 For a text stream, either offset shall be zero, or offset shall be a value returned by - an earlier successful call to the ftell function on a stream associated with the same file - and whence shall be SEEK_SET. -5 After determining the new position, a successful call to the fseek function undoes any - effects of the ungetc function on the stream, clears the end-of-file indicator for the - stream, and then establishes the new position. After a successful fseek call, the next - operation on an update stream may be either input or output. - Returns -6 The fseek function returns nonzero only for a request that cannot be satisfied. - Forward references: the ftell function (7.21.9.4). - 7.21.9.3 The fsetpos function - Synopsis -1 #include - int fsetpos(FILE *stream, const fpos_t *pos); - Description -2 The fsetpos function sets the mbstate_t object (if any) and file position indicator - for the stream pointed to by stream according to the value of the object pointed to by - pos, which shall be a value obtained from an earlier successful call to the fgetpos - function on a stream associated with the same file. If a read or write error occurs, the - error indicator for the stream is set and fsetpos fails. -3 A successful call to the fsetpos function undoes any effects of the ungetc function - on the stream, clears the end-of-file indicator for the stream, and then establishes the new - parse state and position. After a successful fsetpos call, the next operation on an - -[page 336] - - update stream may be either input or output. - Returns -4 If successful, the fsetpos function returns zero; on failure, the fsetpos function - returns nonzero and stores an implementation-defined positive value in errno. - 7.21.9.4 The ftell function - Synopsis -1 #include - long int ftell(FILE *stream); - Description -2 The ftell function obtains the current value of the file position indicator for the stream - pointed to by stream. For a binary stream, the value is the number of characters from - the beginning of the file. For a text stream, its file position indicator contains unspecified - information, usable by the fseek function for returning the file position indicator for the - stream to its position at the time of the ftell call; the difference between two such - return values is not necessarily a meaningful measure of the number of characters written - or read. - Returns -3 If successful, the ftell function returns the current value of the file position indicator - for the stream. On failure, the ftell function returns -1L and stores an - implementation-defined positive value in errno. - 7.21.9.5 The rewind function - Synopsis -1 #include - void rewind(FILE *stream); - Description -2 The rewind function sets the file position indicator for the stream pointed to by - stream to the beginning of the file. It is equivalent to - (void)fseek(stream, 0L, SEEK_SET) - except that the error indicator for the stream is also cleared. - Returns -3 The rewind function returns no value. - -[page 337] - - 7.21.10 Error-handling functions - 7.21.10.1 The clearerr function - Synopsis -1 #include - void clearerr(FILE *stream); - Description -2 The clearerr function clears the end-of-file and error indicators for the stream pointed - to by stream. - Returns -3 The clearerr function returns no value. - 7.21.10.2 The feof function - Synopsis -1 #include - int feof(FILE *stream); - Description -2 The feof function tests the end-of-file indicator for the stream pointed to by stream. - Returns -3 The feof function returns nonzero if and only if the end-of-file indicator is set for - stream. - 7.21.10.3 The ferror function - Synopsis -1 #include - int ferror(FILE *stream); - Description -2 The ferror function tests the error indicator for the stream pointed to by stream. - Returns -3 The ferror function returns nonzero if and only if the error indicator is set for - stream. - -[page 338] - - 7.21.10.4 The perror function - Synopsis -1 #include - void perror(const char *s); - Description -2 The perror function maps the error number in the integer expression errno to an - error message. It writes a sequence of characters to the standard error stream thus: first - (if s is not a null pointer and the character pointed to by s is not the null character), the - string pointed to by s followed by a colon (:) and a space; then an appropriate error - message string followed by a new-line character. The contents of the error message - strings are the same as those returned by the strerror function with argument errno. - Returns -3 The perror function returns no value. - Forward references: the strerror function (7.23.6.2). - -[page 339] - - 7.22 General utilities -1 The header declares five types and several functions of general utility, and - defines several macros.284) -2 The types declared are size_t and wchar_t (both described in 7.19), - div_t - which is a structure type that is the type of the value returned by the div function, - ldiv_t - which is a structure type that is the type of the value returned by the ldiv function, and - lldiv_t - which is a structure type that is the type of the value returned by the lldiv function. -3 The macros defined are NULL (described in 7.19); - EXIT_FAILURE - and - EXIT_SUCCESS - which expand to integer constant expressions that can be used as the argument to the - exit function to return unsuccessful or successful termination status, respectively, to the - host environment; - RAND_MAX - which expands to an integer constant expression that is the maximum value returned by - the rand function; and - MB_CUR_MAX - which expands to a positive integer expression with type size_t that is the maximum - number of bytes in a multibyte character for the extended character set specified by the - current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX. - - - - - 284) See ''future library directions'' (7.30.10). - -[page 340] - - 7.22.1 Numeric conversion functions -1 The functions atof, atoi, atol, and atoll need not affect the value of the integer - expression errno on an error. If the value of the result cannot be represented, the - behavior is undefined. - 7.22.1.1 The atof function - Synopsis -1 #include - double atof(const char *nptr); - Description -2 The atof function converts the initial portion of the string pointed to by nptr to - double representation. Except for the behavior on error, it is equivalent to - strtod(nptr, (char **)NULL) - Returns -3 The atof function returns the converted value. - Forward references: the strtod, strtof, and strtold functions (7.22.1.3). - 7.22.1.2 The atoi, atol, and atoll functions - Synopsis -1 #include - int atoi(const char *nptr); - long int atol(const char *nptr); - long long int atoll(const char *nptr); - Description -2 The atoi, atol, and atoll functions convert the initial portion of the string pointed - to by nptr to int, long int, and long long int representation, respectively. - Except for the behavior on error, they are equivalent to - atoi: (int)strtol(nptr, (char **)NULL, 10) - atol: strtol(nptr, (char **)NULL, 10) - atoll: strtoll(nptr, (char **)NULL, 10) - Returns -3 The atoi, atol, and atoll functions return the converted value. - Forward references: the strtol, strtoll, strtoul, and strtoull functions - (7.22.1.4). - -[page 341] - - 7.22.1.3 The strtod, strtof, and strtold functions - Synopsis -1 #include - double strtod(const char * restrict nptr, - char ** restrict endptr); - float strtof(const char * restrict nptr, - char ** restrict endptr); - long double strtold(const char * restrict nptr, - char ** restrict endptr); - Description -2 The strtod, strtof, and strtold functions convert the initial portion of the string - pointed to by nptr to double, float, and long double representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space characters (as specified by the isspace function), a - subject sequence resembling a floating-point constant or representing an infinity or NaN; - and a final string of one or more unrecognized characters, including the terminating null - character of the input string. Then, they attempt to convert the subject sequence to a - floating-point number, and return the result. -3 The expected form of the subject sequence is an optional plus or minus sign, then one of - the following: - -- a nonempty sequence of decimal digits optionally containing a decimal-point - character, then an optional exponent part as defined in 6.4.4.2; - -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a - decimal-point character, then an optional binary exponent part as defined in 6.4.4.2; - -- INF or INFINITY, ignoring case - -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where: - n-char-sequence: - digit - nondigit - n-char-sequence digit - n-char-sequence nondigit - The subject sequence is defined as the longest initial subsequence of the input string, - starting with the first non-white-space character, that is of the expected form. The subject - sequence contains no characters if the input string is not of the expected form. -4 If the subject sequence has the expected form for a floating-point number, the sequence of - characters starting with the first digit or the decimal-point character (whichever occurs - first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the - -[page 342] - - decimal-point character is used in place of a period, and that if neither an exponent part - nor a decimal-point character appears in a decimal floating point number, or if a binary - exponent part does not appear in a hexadecimal floating point number, an exponent part - of the appropriate type with value zero is assumed to follow the last digit in the string. If - the subject sequence begins with a minus sign, the sequence is interpreted as negated.285) - A character sequence INF or INFINITY is interpreted as an infinity, if representable in - the return type, else like a floating constant that is too large for the range of the return - type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet - NaN, if supported in the return type, else like a subject sequence part that does not have - the expected form; the meaning of the n-char sequences is implementation-defined.286) A - pointer to the final string is stored in the object pointed to by endptr, provided that - endptr is not a null pointer. -5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the - value resulting from the conversion is correctly rounded. -6 In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -7 If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. - Recommended practice -8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and - the result is not exactly representable, the result should be one of the two numbers in the - appropriate internal format that are adjacent to the hexadecimal floating source value, - with the extra stipulation that the error should have a correct sign for the current rounding - direction. -9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in - ) significant digits, the result should be correctly rounded. If the subject - sequence D has the decimal form and more than DECIMAL_DIG significant digits, - consider the two bounding, adjacent decimal strings L and U, both having - DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. - The result should be one of the (equal or adjacent) values that would be obtained by - correctly rounding L and U according to the current rounding direction, with the extra - - 285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two - methods may yield different results if rounding is toward positive or negative infinity. In either case, - the functions honor the sign of zero if floating-point arithmetic supports signed zeros. - 286) An implementation may use the n-char sequence to determine extra information to be represented in - the NaN's significand. - -[page 343] - - stipulation that the error with respect to D should have a correct sign for the current - rounding direction.287) - Returns -10 The functions return the converted value, if any. If no conversion could be performed, - zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), - plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the - return type and sign of the value), and the value of the macro ERANGE is stored in - errno. If the result underflows (7.12.1), the functions return a value whose magnitude is - no greater than the smallest normalized positive number in the return type; whether - errno acquires the value ERANGE is implementation-defined. - 7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions - Synopsis -1 #include - long int strtol( - const char * restrict nptr, - char ** restrict endptr, - int base); - long long int strtoll( - const char * restrict nptr, - char ** restrict endptr, - int base); - unsigned long int strtoul( - const char * restrict nptr, - char ** restrict endptr, - int base); - unsigned long long int strtoull( - const char * restrict nptr, - char ** restrict endptr, - int base); - Description -2 The strtol, strtoll, strtoul, and strtoull functions convert the initial - portion of the string pointed to by nptr to long int, long long int, unsigned - long int, and unsigned long long int representation, respectively. First, - they decompose the input string into three parts: an initial, possibly empty, sequence of - white-space characters (as specified by the isspace function), a subject sequence - - - 287) DECIMAL_DIG, defined in , should be sufficiently large that L and U will usually round - to the same internal floating value, but if not will round to adjacent values. - -[page 344] - - resembling an integer represented in some radix determined by the value of base, and a - final string of one or more unrecognized characters, including the terminating null - character of the input string. Then, they attempt to convert the subject sequence to an - integer, and return the result. -3 If the value of base is zero, the expected form of the subject sequence is that of an - integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but - not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the - expected form of the subject sequence is a sequence of letters and digits representing an - integer with the radix specified by base, optionally preceded by a plus or minus sign, - but not including an integer suffix. The letters from a (or A) through z (or Z) are - ascribed the values 10 through 35; only letters and digits whose ascribed values are less - than that of base are permitted. If the value of base is 16, the characters 0x or 0X may - optionally precede the sequence of letters and digits, following the sign if present. -4 The subject sequence is defined as the longest initial subsequence of the input string, - starting with the first non-white-space character, that is of the expected form. The subject - sequence contains no characters if the input string is empty or consists entirely of white - space, or if the first non-white-space character is other than a sign or a permissible letter - or digit. -5 If the subject sequence has the expected form and the value of base is zero, the sequence - of characters starting with the first digit is interpreted as an integer constant according to - the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base - is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value - as given above. If the subject sequence begins with a minus sign, the value resulting from - the conversion is negated (in the return type). A pointer to the final string is stored in the - object pointed to by endptr, provided that endptr is not a null pointer. -6 In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -7 If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. - Returns -8 The strtol, strtoll, strtoul, and strtoull functions return the converted - value, if any. If no conversion could be performed, zero is returned. If the correct value - is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, - LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type - and sign of the value, if any), and the value of the macro ERANGE is stored in errno. - -[page 345] - - 7.22.2 Pseudo-random sequence generation functions - 7.22.2.1 The rand function - Synopsis -1 #include - int rand(void); - Description -2 The rand function computes a sequence of pseudo-random integers in the range 0 to - RAND_MAX.288) -3 The rand function is not required to avoid data races. The implementation shall behave - as if no library function calls the rand function. - Returns -4 The rand function returns a pseudo-random integer. - Environmental limits -5 The value of the RAND_MAX macro shall be at least 32767. - 7.22.2.2 The srand function - Synopsis -1 #include - void srand(unsigned int seed); - Description -2 The srand function uses the argument as a seed for a new sequence of pseudo-random - numbers to be returned by subsequent calls to rand. If srand is then called with the - same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is - called before any calls to srand have been made, the same sequence shall be generated - as when srand is first called with a seed value of 1. -3 The implementation shall behave as if no library function calls the srand function. - Returns -4 The srand function returns no value. - - - - - 288) There are no guarantees as to the quality of the random sequence produced and some implementations - are known to produce sequences with distressingly non-random low-order bits. Applications with - particular requirements should use a generator that is known to be sufficient for their needs. - -[page 346] - -5 EXAMPLE The following functions define a portable implementation of rand and srand. - static unsigned long int next = 1; - int rand(void) // RAND_MAX assumed to be 32767 - { - next = next * 1103515245 + 12345; - return (unsigned int)(next/65536) % 32768; - } - void srand(unsigned int seed) - { - next = seed; - } - - 7.22.3 Memory management functions -1 The order and contiguity of storage allocated by successive calls to the - aligned_alloc, calloc, malloc, and realloc functions is unspecified. The - pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to - a pointer to any type of object with a fundamental alignment requirement and then used - to access such an object or an array of such objects in the space allocated (until the space - is explicitly deallocated). The lifetime of an allocated object extends from the allocation - until the deallocation. Each such allocation shall yield a pointer to an object disjoint from - any other object. The pointer returned points to the start (lowest byte address) of the - allocated space. If the space cannot be allocated, a null pointer is returned. If the size of - the space requested is zero, the behavior is implementation-defined: either a null pointer - is returned, or the behavior is as if the size were some nonzero value, except that the - returned pointer shall not be used to access an object. - 7.22.3.1 The aligned_alloc function - Synopsis -1 #include - void *aligned_alloc(size_t alignment, size_t size); - Description -2 The aligned_alloc function allocates space for an object whose alignment is - specified by alignment, whose size is specified by size, and whose value is - indeterminate. The value of alignment shall be a valid alignment supported by the - implementation and the value of size shall be an integral multiple of alignment. - Returns -3 The aligned_alloc function returns either a null pointer or a pointer to the allocated - space. - -[page 347] - - 7.22.3.2 The calloc function - Synopsis -1 #include - void *calloc(size_t nmemb, size_t size); - Description -2 The calloc function allocates space for an array of nmemb objects, each of whose size - is size. The space is initialized to all bits zero.289) - Returns -3 The calloc function returns either a null pointer or a pointer to the allocated space. - 7.22.3.3 The free function - Synopsis -1 #include - void free(void *ptr); - Description -2 The free function causes the space pointed to by ptr to be deallocated, that is, made - available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if - the argument does not match a pointer earlier returned by a memory management - function, or if the space has been deallocated by a call to free or realloc, the - behavior is undefined. - Returns -3 The free function returns no value. - 7.22.3.4 The malloc function - Synopsis -1 #include - void *malloc(size_t size); - Description -2 The malloc function allocates space for an object whose size is specified by size and - whose value is indeterminate. - - - - - 289) Note that this need not be the same as the representation of floating-point zero or a null pointer - constant. - -[page 348] - - Returns -3 The malloc function returns either a null pointer or a pointer to the allocated space. - 7.22.3.5 The realloc function - Synopsis -1 #include - void *realloc(void *ptr, size_t size); - Description -2 The realloc function deallocates the old object pointed to by ptr and returns a - pointer to a new object that has the size specified by size. The contents of the new - object shall be the same as that of the old object prior to deallocation, up to the lesser of - the new and old sizes. Any bytes in the new object beyond the size of the old object have - indeterminate values. -3 If ptr is a null pointer, the realloc function behaves like the malloc function for the - specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory - management function, or if the space has been deallocated by a call to the free or - realloc function, the behavior is undefined. If memory for the new object cannot be - allocated, the old object is not deallocated and its value is unchanged. - Returns -4 The realloc function returns a pointer to the new object (which may have the same - value as a pointer to the old object), or a null pointer if the new object could not be - allocated. - 7.22.4 Communication with the environment - 7.22.4.1 The abort function - Synopsis -1 #include - _Noreturn void abort(void); - Description -2 The abort function causes abnormal program termination to occur, unless the signal - SIGABRT is being caught and the signal handler does not return. Whether open streams - with unwritten buffered data are flushed, open streams are closed, or temporary files are - removed is implementation-defined. An implementation-defined form of the status - unsuccessful termination is returned to the host environment by means of the function - call raise(SIGABRT). - -[page 349] - - Returns -3 The abort function does not return to its caller. - 7.22.4.2 The atexit function - Synopsis -1 #include - int atexit(void (*func)(void)); - Description -2 The atexit function registers the function pointed to by func, to be called without - arguments at normal program termination.290) - Environmental limits -3 The implementation shall support the registration of at least 32 functions. - Returns -4 The atexit function returns zero if the registration succeeds, nonzero if it fails. - Forward references: the at_quick_exit function (7.22.4.3), the exit function - (7.22.4.4). - 7.22.4.3 The at_quick_exit function - Synopsis -1 #include - int at_quick_exit(void (*func)(void)); - Description -2 The at_quick_exit function registers the function pointed to by func, to be called - without arguments should quick_exit be called.291) - Environmental limits -3 The implementation shall support the registration of at least 32 functions. - Returns -4 The at_quick_exit function returns zero if the registration succeeds, nonzero if it - fails. - Forward references: the quick_exit function (7.22.4.7). - - - 290) The atexit function registrations are distinct from the at_quick_exit registrations, so - applications may need to call both registration functions with the same argument. - 291) The at_quick_exit function registrations are distinct from the atexit registrations, so - applications may need to call both registration functions with the same argument. - -[page 350] - - 7.22.4.4 The exit function - Synopsis -1 #include - _Noreturn void exit(int status); - Description -2 The exit function causes normal program termination to occur. No functions registered - by the at_quick_exit function are called. If a program calls the exit function - more than once, or calls the quick_exit function in addition to the exit function, the - behavior is undefined. -3 First, all functions registered by the atexit function are called, in the reverse order of - their registration,292) except that a function is called after any previously registered - functions that had already been called at the time it was registered. If, during the call to - any such function, a call to the longjmp function is made that would terminate the call - to the registered function, the behavior is undefined. -4 Next, all open streams with unwritten buffered data are flushed, all open streams are - closed, and all files created by the tmpfile function are removed. -5 Finally, control is returned to the host environment. If the value of status is zero or - EXIT_SUCCESS, an implementation-defined form of the status successful termination is - returned. If the value of status is EXIT_FAILURE, an implementation-defined form - of the status unsuccessful termination is returned. Otherwise the status returned is - implementation-defined. - Returns -6 The exit function cannot return to its caller. - 7.22.4.5 The _Exit function - Synopsis -1 #include - _Noreturn void _Exit(int status); - Description -2 The _Exit function causes normal program termination to occur and control to be - returned to the host environment. No functions registered by the atexit function, the - at_quick_exit function, or signal handlers registered by the signal function are - called. The status returned to the host environment is determined in the same way as for - - - 292) Each function is called as many times as it was registered, and in the correct order with respect to - other registered functions. - -[page 351] - - the exit function (7.22.4.4). Whether open streams with unwritten buffered data are - flushed, open streams are closed, or temporary files are removed is implementation- - defined. - Returns -3 The _Exit function cannot return to its caller. - 7.22.4.6 The getenv function - Synopsis -1 #include - char *getenv(const char *name); - Description -2 The getenv function searches an environment list, provided by the host environment, - for a string that matches the string pointed to by name. The set of environment names - and the method for altering the environment list are implementation-defined. The - getenv function need not avoid data races with other threads of execution that modify - the environment list.293) -3 The implementation shall behave as if no library function calls the getenv function. - Returns -4 The getenv function returns a pointer to a string associated with the matched list - member. The string pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the getenv function. If the specified name cannot - be found, a null pointer is returned. - 7.22.4.7 The quick_exit function - Synopsis -1 #include - _Noreturn void quick_exit(int status); - Description -2 The quick_exit function causes normal program termination to occur. No functions - registered by the atexit function or signal handlers registered by the signal function - are called. If a program calls the quick_exit function more than once, or calls the - exit function in addition to the quick_exit function, the behavior is undefined. -3 The quick_exit function first calls all functions registered by the at_quick_exit - function, in the reverse order of their registration,294) except that a function is called after - - - 293) Many implementations provide non-standard functions that modify the environment list. - -[page 352] - - any previously registered functions that had already been called at the time it was - registered. If, during the call to any such function, a call to the longjmp function is - made that would terminate the call to the registered function, the behavior is undefined. -4 Then control is returned to the host environment by means of the function call - _Exit(status). - Returns -5 The quick_exit function cannot return to its caller. - 7.22.4.8 The system function - Synopsis -1 #include - int system(const char *string); - Description -2 If string is a null pointer, the system function determines whether the host - environment has a command processor. If string is not a null pointer, the system - function passes the string pointed to by string to that command processor to be - executed in a manner which the implementation shall document; this might then cause the - program calling system to behave in a non-conforming manner or to terminate. - Returns -3 If the argument is a null pointer, the system function returns nonzero only if a - command processor is available. If the argument is not a null pointer, and the system - function does return, it returns an implementation-defined value. - 7.22.5 Searching and sorting utilities -1 These utilities make use of a comparison function to search or sort arrays of unspecified - type. Where an argument declared as size_t nmemb specifies the length of the array - for a function, nmemb can have the value zero on a call to that function; the comparison - function is not called, a search finds no matching element, and sorting performs no - rearrangement. Pointer arguments on such a call shall still have valid values, as described - in 7.1.4. -2 The implementation shall ensure that the second argument of the comparison function - (when called from bsearch), or both arguments (when called from qsort), are - pointers to elements of the array.295) The first argument when called from bsearch - shall equal key. - - - - 294) Each function is called as many times as it was registered, and in the correct order with respect to - other registered functions. - -[page 353] - -3 The comparison function shall not alter the contents of the array. The implementation - may reorder elements of the array between calls to the comparison function, but shall not - alter the contents of any individual element. -4 When the same objects (consisting of size bytes, irrespective of their current positions - in the array) are passed more than once to the comparison function, the results shall be - consistent with one another. That is, for qsort they shall define a total ordering on the - array, and for bsearch the same object shall always compare the same way with the - key. -5 A sequence point occurs immediately before and immediately after each call to the - comparison function, and also between any call to the comparison function and any - movement of the objects passed as arguments to that call. - 7.22.5.1 The bsearch function - Synopsis -1 #include - void *bsearch(const void *key, const void *base, - size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - Description -2 The bsearch function searches an array of nmemb objects, the initial element of which - is pointed to by base, for an element that matches the object pointed to by key. The - size of each element of the array is specified by size. -3 The comparison function pointed to by compar is called with two arguments that point - to the key object and to an array element, in that order. The function shall return an - integer less than, equal to, or greater than zero if the key object is considered, - respectively, to be less than, to match, or to be greater than the array element. The array - shall consist of: all the elements that compare less than, all the elements that compare - equal to, and all the elements that compare greater than the key object, in that order.296) - Returns -4 The bsearch function returns a pointer to a matching element of the array, or a null - pointer if no match is found. If two elements compare as equal, which element is - - - 295) That is, if the value passed is p, then the following expressions are always nonzero: - ((char *)p - (char *)base) % size == 0 - (char *)p >= (char *)base - (char *)p < (char *)base + nmemb * size - - 296) In practice, the entire array is sorted according to the comparison function. - -[page 354] - - matched is unspecified. - 7.22.5.2 The qsort function - Synopsis -1 #include - void qsort(void *base, size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - Description -2 The qsort function sorts an array of nmemb objects, the initial element of which is - pointed to by base. The size of each object is specified by size. -3 The contents of the array are sorted into ascending order according to a comparison - function pointed to by compar, which is called with two arguments that point to the - objects being compared. The function shall return an integer less than, equal to, or - greater than zero if the first argument is considered to be respectively less than, equal to, - or greater than the second. -4 If two elements compare as equal, their order in the resulting sorted array is unspecified. - Returns -5 The qsort function returns no value. - 7.22.6 Integer arithmetic functions - 7.22.6.1 The abs, labs and llabs functions - Synopsis -1 #include - int abs(int j); - long int labs(long int j); - long long int llabs(long long int j); - Description -2 The abs, labs, and llabs functions compute the absolute value of an integer j. If the - result cannot be represented, the behavior is undefined.297) - Returns -3 The abs, labs, and llabs, functions return the absolute value. - - - - - 297) The absolute value of the most negative number cannot be represented in two's complement. - -[page 355] - - 7.22.6.2 The div, ldiv, and lldiv functions - Synopsis -1 #include - div_t div(int numer, int denom); - ldiv_t ldiv(long int numer, long int denom); - lldiv_t lldiv(long long int numer, long long int denom); - Description -2 The div, ldiv, and lldiv, functions compute numer / denom and numer % - denom in a single operation. - Returns -3 The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and - lldiv_t, respectively, comprising both the quotient and the remainder. The structures - shall contain (in either order) the members quot (the quotient) and rem (the remainder), - each of which has the same type as the arguments numer and denom. If either part of - the result cannot be represented, the behavior is undefined. - 7.22.7 Multibyte/wide character conversion functions -1 The behavior of the multibyte character functions is affected by the LC_CTYPE category - of the current locale. For a state-dependent encoding, each function is placed into its - initial conversion state at program startup and can be returned to that state by a call for - which its character pointer argument, s, is a null pointer. Subsequent calls with s as - other than a null pointer cause the internal conversion state of the function to be altered as - necessary. A call with s as a null pointer causes these functions to return a nonzero value - if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE - category causes the conversion state of these functions to be indeterminate. - 7.22.7.1 The mblen function - Synopsis -1 #include - int mblen(const char *s, size_t n); - Description -2 If s is not a null pointer, the mblen function determines the number of bytes contained - in the multibyte character pointed to by s. Except that the conversion state of the - mbtowc function is not affected, it is equivalent to - - - - 298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide - character codes, but are grouped with an adjacent multibyte character. - -[page 356] - - mbtowc((wchar_t *)0, (const char *)0, 0); - mbtowc((wchar_t *)0, s, n); -3 The implementation shall behave as if no library function calls the mblen function. - Returns -4 If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the mblen function either returns 0 (if s points to the null character), - or returns the number of bytes that are contained in the multibyte character (if the next n - or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid - multibyte character). - Forward references: the mbtowc function (7.22.7.2). - 7.22.7.2 The mbtowc function - Synopsis -1 #include - int mbtowc(wchar_t * restrict pwc, - const char * restrict s, - size_t n); - Description -2 If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the value of the - corresponding wide character and then, if pwc is not a null pointer, stores that value in - the object pointed to by pwc. If the corresponding wide character is the null wide - character, the function is left in the initial conversion state. -3 The implementation shall behave as if no library function calls the mbtowc function. - Returns -4 If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the mbtowc function either returns 0 (if s points to the null character), - or returns the number of bytes that are contained in the converted multibyte character (if - the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not - form a valid multibyte character). -5 In no case will the value returned be greater than n or the value of the MB_CUR_MAX - macro. - -[page 357] - - 7.22.7.3 The wctomb function - Synopsis -1 #include - int wctomb(char *s, wchar_t wc); - Description -2 The wctomb function determines the number of bytes needed to represent the multibyte - character corresponding to the wide character given by wc (including any shift - sequences), and stores the multibyte character representation in the array whose first - element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters - are stored. If wc is a null wide character, a null byte is stored, preceded by any shift - sequence needed to restore the initial shift state, and the function is left in the initial - conversion state. -3 The implementation shall behave as if no library function calls the wctomb function. - Returns -4 If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte - character encodings, respectively, do or do not have state-dependent encodings. If s is - not a null pointer, the wctomb function returns -1 if the value of wc does not correspond - to a valid multibyte character, or returns the number of bytes that are contained in the - multibyte character corresponding to the value of wc. -5 In no case will the value returned be greater than the value of the MB_CUR_MAX macro. - 7.22.8 Multibyte/wide string conversion functions -1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of - the current locale. - 7.22.8.1 The mbstowcs function - Synopsis -1 #include - size_t mbstowcs(wchar_t * restrict pwcs, - const char * restrict s, - size_t n); - Description -2 The mbstowcs function converts a sequence of multibyte characters that begins in the - initial shift state from the array pointed to by s into a sequence of corresponding wide - characters and stores not more than n wide characters into the array pointed to by pwcs. - No multibyte characters that follow a null character (which is converted into a null wide - character) will be examined or converted. Each multibyte character is converted as if by - a call to the mbtowc function, except that the conversion state of the mbtowc function is - -[page 358] - - not affected. -3 No more than n elements will be modified in the array pointed to by pwcs. If copying - takes place between objects that overlap, the behavior is undefined. - Returns -4 If an invalid multibyte character is encountered, the mbstowcs function returns - (size_t)(-1). Otherwise, the mbstowcs function returns the number of array - elements modified, not including a terminating null wide character, if any.299) - 7.22.8.2 The wcstombs function - Synopsis -1 #include - size_t wcstombs(char * restrict s, - const wchar_t * restrict pwcs, - size_t n); - Description -2 The wcstombs function converts a sequence of wide characters from the array pointed - to by pwcs into a sequence of corresponding multibyte characters that begins in the - initial shift state, and stores these multibyte characters into the array pointed to by s, - stopping if a multibyte character would exceed the limit of n total bytes or if a null - character is stored. Each wide character is converted as if by a call to the wctomb - function, except that the conversion state of the wctomb function is not affected. -3 No more than n bytes will be modified in the array pointed to by s. If copying takes place - between objects that overlap, the behavior is undefined. - Returns -4 If a wide character is encountered that does not correspond to a valid multibyte character, - the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function - returns the number of bytes modified, not including a terminating null character, if - any.299) - - - - - 299) The array will not be null-terminated if the value returned is n. - -[page 359] - - 7.23 String handling - 7.23.1 String function conventions -1 The header declares one type and several functions, and defines one - macro useful for manipulating arrays of character type and other objects treated as arrays - of character type.300) The type is size_t and the macro is NULL (both described in - 7.19). Various methods are used for determining the lengths of the arrays, but in all cases - a char * or void * argument points to the initial (lowest addressed) character of the - array. If an array is accessed beyond the end of an object, the behavior is undefined. -2 Where an argument declared as size_t n specifies the length of the array for a - function, n can have the value zero on a call to that function. Unless explicitly stated - otherwise in the description of a particular function in this subclause, pointer arguments - on such a call shall still have valid values, as described in 7.1.4. On such a call, a - function that locates a character finds no occurrence, a function that compares two - character sequences returns zero, and a function that copies characters copies zero - characters. -3 For all functions in this subclause, each character shall be interpreted as if it had the type - unsigned char (and therefore every possible object representation is valid and has a - different value). - 7.23.2 Copying functions - 7.23.2.1 The memcpy function - Synopsis -1 #include - void *memcpy(void * restrict s1, - const void * restrict s2, - size_t n); - Description -2 The memcpy function copies n characters from the object pointed to by s2 into the - object pointed to by s1. If copying takes place between objects that overlap, the behavior - is undefined. - Returns -3 The memcpy function returns the value of s1. - - - - - 300) See ''future library directions'' (7.30.11). - -[page 360] - - 7.23.2.2 The memmove function - Synopsis -1 #include - void *memmove(void *s1, const void *s2, size_t n); - Description -2 The memmove function copies n characters from the object pointed to by s2 into the - object pointed to by s1. Copying takes place as if the n characters from the object - pointed to by s2 are first copied into a temporary array of n characters that does not - overlap the objects pointed to by s1 and s2, and then the n characters from the - temporary array are copied into the object pointed to by s1. - Returns -3 The memmove function returns the value of s1. - 7.23.2.3 The strcpy function - Synopsis -1 #include - char *strcpy(char * restrict s1, - const char * restrict s2); - Description -2 The strcpy function copies the string pointed to by s2 (including the terminating null - character) into the array pointed to by s1. If copying takes place between objects that - overlap, the behavior is undefined. - Returns -3 The strcpy function returns the value of s1. - 7.23.2.4 The strncpy function - Synopsis -1 #include - char *strncpy(char * restrict s1, - const char * restrict s2, - size_t n); - Description -2 The strncpy function copies not more than n characters (characters that follow a null - character are not copied) from the array pointed to by s2 to the array pointed to by - -[page 361] - - s1.301) If copying takes place between objects that overlap, the behavior is undefined. -3 If the array pointed to by s2 is a string that is shorter than n characters, null characters - are appended to the copy in the array pointed to by s1, until n characters in all have been - written. - Returns -4 The strncpy function returns the value of s1. - 7.23.3 Concatenation functions - 7.23.3.1 The strcat function - Synopsis -1 #include - char *strcat(char * restrict s1, - const char * restrict s2); - Description -2 The strcat function appends a copy of the string pointed to by s2 (including the - terminating null character) to the end of the string pointed to by s1. The initial character - of s2 overwrites the null character at the end of s1. If copying takes place between - objects that overlap, the behavior is undefined. - Returns -3 The strcat function returns the value of s1. - 7.23.3.2 The strncat function - Synopsis -1 #include - char *strncat(char * restrict s1, - const char * restrict s2, - size_t n); - Description -2 The strncat function appends not more than n characters (a null character and - characters that follow it are not appended) from the array pointed to by s2 to the end of - the string pointed to by s1. The initial character of s2 overwrites the null character at the - end of s1. A terminating null character is always appended to the result.302) If copying - - 301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will - not be null-terminated. - 302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is - strlen(s1)+n+1. - -[page 362] - - takes place between objects that overlap, the behavior is undefined. - Returns -3 The strncat function returns the value of s1. - Forward references: the strlen function (7.23.6.3). - 7.23.4 Comparison functions -1 The sign of a nonzero value returned by the comparison functions memcmp, strcmp, - and strncmp is determined by the sign of the difference between the values of the first - pair of characters (both interpreted as unsigned char) that differ in the objects being - compared. - 7.23.4.1 The memcmp function - Synopsis -1 #include - int memcmp(const void *s1, const void *s2, size_t n); - Description -2 The memcmp function compares the first n characters of the object pointed to by s1 to - the first n characters of the object pointed to by s2.303) - Returns -3 The memcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the object pointed to by s1 is greater than, equal to, or less than the object - pointed to by s2. - 7.23.4.2 The strcmp function - Synopsis -1 #include - int strcmp(const char *s1, const char *s2); - Description -2 The strcmp function compares the string pointed to by s1 to the string pointed to by - s2. - Returns -3 The strcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the string pointed to by s1 is greater than, equal to, or less than the string - - 303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are - indeterminate. Strings shorter than their allocated space and unions may also cause problems in - comparison. - -[page 363] - - pointed to by s2. - 7.23.4.3 The strcoll function - Synopsis -1 #include - int strcoll(const char *s1, const char *s2); - Description -2 The strcoll function compares the string pointed to by s1 to the string pointed to by - s2, both interpreted as appropriate to the LC_COLLATE category of the current locale. - Returns -3 The strcoll function returns an integer greater than, equal to, or less than zero, - accordingly as the string pointed to by s1 is greater than, equal to, or less than the string - pointed to by s2 when both are interpreted as appropriate to the current locale. - 7.23.4.4 The strncmp function - Synopsis -1 #include - int strncmp(const char *s1, const char *s2, size_t n); - Description -2 The strncmp function compares not more than n characters (characters that follow a - null character are not compared) from the array pointed to by s1 to the array pointed to - by s2. - Returns -3 The strncmp function returns an integer greater than, equal to, or less than zero, - accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal - to, or less than the possibly null-terminated array pointed to by s2. - 7.23.4.5 The strxfrm function - Synopsis -1 #include - size_t strxfrm(char * restrict s1, - const char * restrict s2, - size_t n); - Description -2 The strxfrm function transforms the string pointed to by s2 and places the resulting - string into the array pointed to by s1. The transformation is such that if the strcmp - function is applied to two transformed strings, it returns a value greater than, equal to, or - -[page 364] - - less than zero, corresponding to the result of the strcoll function applied to the same - two original strings. No more than n characters are placed into the resulting array - pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to - be a null pointer. If copying takes place between objects that overlap, the behavior is - undefined. - Returns -3 The strxfrm function returns the length of the transformed string (not including the - terminating null character). If the value returned is n or more, the contents of the array - pointed to by s1 are indeterminate. -4 EXAMPLE The value of the following expression is the size of the array needed to hold the - transformation of the string pointed to by s. - 1 + strxfrm(NULL, s, 0) - - 7.23.5 Search functions - 7.23.5.1 The memchr function - Synopsis -1 #include - void *memchr(const void *s, int c, size_t n); - Description -2 The memchr function locates the first occurrence of c (converted to an unsigned - char) in the initial n characters (each interpreted as unsigned char) of the object - pointed to by s. The implementation shall behave as if it reads the characters sequentially - and stops as soon as a matching character is found. - Returns -3 The memchr function returns a pointer to the located character, or a null pointer if the - character does not occur in the object. - 7.23.5.2 The strchr function - Synopsis -1 #include - char *strchr(const char *s, int c); - Description -2 The strchr function locates the first occurrence of c (converted to a char) in the - string pointed to by s. The terminating null character is considered to be part of the - string. - -[page 365] - - Returns -3 The strchr function returns a pointer to the located character, or a null pointer if the - character does not occur in the string. - 7.23.5.3 The strcspn function - Synopsis -1 #include - size_t strcspn(const char *s1, const char *s2); - Description -2 The strcspn function computes the length of the maximum initial segment of the string - pointed to by s1 which consists entirely of characters not from the string pointed to by - s2. - Returns -3 The strcspn function returns the length of the segment. - 7.23.5.4 The strpbrk function - Synopsis -1 #include - char *strpbrk(const char *s1, const char *s2); - Description -2 The strpbrk function locates the first occurrence in the string pointed to by s1 of any - character from the string pointed to by s2. - Returns -3 The strpbrk function returns a pointer to the character, or a null pointer if no character - from s2 occurs in s1. - 7.23.5.5 The strrchr function - Synopsis -1 #include - char *strrchr(const char *s, int c); - Description -2 The strrchr function locates the last occurrence of c (converted to a char) in the - string pointed to by s. The terminating null character is considered to be part of the - string. - -[page 366] - - Returns -3 The strrchr function returns a pointer to the character, or a null pointer if c does not - occur in the string. - 7.23.5.6 The strspn function - Synopsis -1 #include - size_t strspn(const char *s1, const char *s2); - Description -2 The strspn function computes the length of the maximum initial segment of the string - pointed to by s1 which consists entirely of characters from the string pointed to by s2. - Returns -3 The strspn function returns the length of the segment. - 7.23.5.7 The strstr function - Synopsis -1 #include - char *strstr(const char *s1, const char *s2); - Description -2 The strstr function locates the first occurrence in the string pointed to by s1 of the - sequence of characters (excluding the terminating null character) in the string pointed to - by s2. - Returns -3 The strstr function returns a pointer to the located string, or a null pointer if the string - is not found. If s2 points to a string with zero length, the function returns s1. - 7.23.5.8 The strtok function - Synopsis -1 #include - char *strtok(char * restrict s1, - const char * restrict s2); - Description -2 A sequence of calls to the strtok function breaks the string pointed to by s1 into a - sequence of tokens, each of which is delimited by a character from the string pointed to - by s2. The first call in the sequence has a non-null first argument; subsequent calls in the - sequence have a null first argument. The separator string pointed to by s2 may be - different from call to call. - -[page 367] - -3 The first call in the sequence searches the string pointed to by s1 for the first character - that is not contained in the current separator string pointed to by s2. If no such character - is found, then there are no tokens in the string pointed to by s1 and the strtok function - returns a null pointer. If such a character is found, it is the start of the first token. -4 The strtok function then searches from there for a character that is contained in the - current separator string. If no such character is found, the current token extends to the - end of the string pointed to by s1, and subsequent searches for a token will return a null - pointer. If such a character is found, it is overwritten by a null character, which - terminates the current token. The strtok function saves a pointer to the following - character, from which the next search for a token will start. -5 Each subsequent call, with a null pointer as the value of the first argument, starts - searching from the saved pointer and behaves as described above. -6 The strtok function is not required to avoid data races. The implementation shall - behave as if no library function calls the strtok function. - Returns -7 The strtok function returns a pointer to the first character of a token, or a null pointer - if there is no token. -8 EXAMPLE - #include - static char str[] = "?a???b,,,#c"; - char *t; - t = strtok(str, "?"); // t points to the token "a" - t = strtok(NULL, ","); // t points to the token "??b" - t = strtok(NULL, "#,"); // t points to the token "c" - t = strtok(NULL, "?"); // t is a null pointer - - 7.23.6 Miscellaneous functions - 7.23.6.1 The memset function - Synopsis -1 #include - void *memset(void *s, int c, size_t n); - Description -2 The memset function copies the value of c (converted to an unsigned char) into - each of the first n characters of the object pointed to by s. - Returns -3 The memset function returns the value of s. - -[page 368] - - 7.23.6.2 The strerror function - Synopsis -1 #include - char *strerror(int errnum); - Description -2 The strerror function maps the number in errnum to a message string. Typically, - the values for errnum come from errno, but strerror shall map any value of type - int to a message. -3 The strerror function is not required to avoid data races. The implementation shall - behave as if no library function calls the strerror function. - Returns -4 The strerror function returns a pointer to the string, the contents of which are locale- - specific. The array pointed to shall not be modified by the program, but may be - overwritten by a subsequent call to the strerror function. - 7.23.6.3 The strlen function - Synopsis -1 #include - size_t strlen(const char *s); - Description -2 The strlen function computes the length of the string pointed to by s. - Returns -3 The strlen function returns the number of characters that precede the terminating null - character. - -[page 369] - - 7.24 Type-generic math -1 The header includes the headers and and - defines several type-generic macros. -2 Of the and functions without an f (float) or l (long - double) suffix, several have one or more parameters whose corresponding real type is - double. For each such function, except modf, there is a corresponding type-generic - macro.304) The parameters whose corresponding real type is double in the function - synopsis are generic parameters. Use of the macro invokes a function whose - corresponding real type and type domain are determined by the arguments for the generic - parameters.305) -3 Use of the macro invokes a function whose generic parameters have the corresponding - real type determined as follows: - -- First, if any argument for generic parameters has type long double, the type - determined is long double. - -- Otherwise, if any argument for generic parameters has type double or is of integer - type, the type determined is double. - -- Otherwise, the type determined is float. -4 For each unsuffixed function in for which there is a function in - with the same name except for a c prefix, the corresponding type- - generic macro (for both functions) has the same name as the function in . The - corresponding type-generic macro for fabs and cabs is fabs. - - - - - 304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to - make available the corresponding ordinary function. - 305) If the type of the argument is not compatible with the type of the parameter for the selected function, - the behavior is undefined. - -[page 370] - - type-generic - function function macro - acos cacos acos - asin casin asin - atan catan atan - acosh cacosh acosh - asinh casinh asinh - atanh catanh atanh - cos ccos cos - sin csin sin - tan ctan tan - cosh ccosh cosh - sinh csinh sinh - tanh ctanh tanh - exp cexp exp - log clog log - pow cpow pow - sqrt csqrt sqrt - fabs cabs fabs - If at least one argument for a generic parameter is complex, then use of the macro invokes - a complex function; otherwise, use of the macro invokes a real function. -5 For each unsuffixed function in without a c-prefixed counterpart in - (except modf), the corresponding type-generic macro has the same - name as the function. These type-generic macros are: - atan2 fma llround remainder - cbrt fmax log10 remquo - ceil fmin log1p rint - copysign fmod log2 round - erf frexp logb scalbn - erfc hypot lrint scalbln - exp2 ilogb lround tgamma - expm1 ldexp nearbyint trunc - fdim lgamma nextafter - floor llrint nexttoward - If all arguments for generic parameters are real, then use of the macro invokes a real - function; otherwise, use of the macro results in undefined behavior. - -[page 371] - -6 For each unsuffixed function in that is not a c-prefixed counterpart to a - function in , the corresponding type-generic macro has the same name as the - function. These type-generic macros are: - carg conj creal - cimag cproj - Use of the macro with any real or complex argument invokes a complex function. -7 EXAMPLE With the declarations - #include - int n; - float f; - double d; - long double ld; - float complex fc; - double complex dc; - long double complex ldc; - functions invoked by use of type-generic macros are shown in the following table: - macro use invokes - exp(n) exp(n), the function - acosh(f) acoshf(f) - sin(d) sin(d), the function - atan(ld) atanl(ld) - log(fc) clogf(fc) - sqrt(dc) csqrt(dc) - pow(ldc, f) cpowl(ldc, f) - remainder(n, n) remainder(n, n), the function - nextafter(d, f) nextafter(d, f), the function - nexttoward(f, ld) nexttowardf(f, ld) - copysign(n, ld) copysignl(n, ld) - ceil(fc) undefined behavior - rint(dc) undefined behavior - fmax(ldc, ld) undefined behavior - carg(n) carg(n), the function - cproj(f) cprojf(f) - creal(d) creal(d), the function - cimag(ld) cimagl(ld) - fabs(fc) cabsf(fc) - carg(dc) carg(dc), the function - cproj(ldc) cprojl(ldc) - -[page 372] - - 7.25 Threads - 7.25.1 Introduction -1 The header defines macros, and declares types, enumeration constants, - and functions that support multiple threads of execution. -2 Implementations that define the macro __STDC_NO_THREADS__ need not provide - this header nor support any of its facilities. -3 The macros are - ONCE_FLAG_INIT - which expands to a value that can be used to initialize an object of type once_flag; - and - TSS_DTOR_ITERATIONS - which expands to an integer constant expression representing the maximum number of - times that destructors will be called when a thread terminates. -4 The types are - cnd_t - which is a complete object type that holds an identifier for a condition variable; - thrd_t - which is a complete object type that holds an identifier for a thread; - tss_t - which is a complete object type that holds an identifier for a thread-specific storage - pointer; - mtx_t - which is a complete object type that holds an identifier for a mutex; - tss_dtor_t - which is the function pointer type void (*)(void*), used for a destructor for a - thread-specific storage pointer; - thrd_start_t - which is the function pointer type int (*)(void*) that is passed to thrd_create - to create a new thread; - once_flag - which is a complete object type that holds a flag for use by call_once; and - -[page 373] - - xtime - which is a structure type that holds a time specified in seconds and nanoseconds. The - structure shall contain at least the following members, in any order. - time_t sec; - long nsec; -5 The enumeration constants are - mtx_plain - which is passed to mtx_init to create a mutex object that supports neither timeout nor - test and return; - mtx_recursive - which is passed to mtx_init to create a mutex object that supports recursive locking; - mtx_timed - which is passed to mtx_init to create a mutex object that supports timeout; - mtx_try - which is passed to mtx_init to create a mutex object that supports test and return; - thrd_timeout - which is returned by a timed wait function to indicate that the time specified in the call - was reached without acquiring the requested resource; - thrd_success - which is returned by a function to indicate that the requested operation succeeded; - thrd_busy - which is returned by a function to indicate that the requested operation failed because a - resource requested by a test and return function is already in use; - thrd_error - which is returned by a function to indicate that the requested operation failed; and - thrd_nomem - which is returned by a function to indicate that the requested operation failed because it - was unable to allocate memory. - -[page 374] - - 7.25.2 Initialization functions - 7.25.2.1 The call_once function - Synopsis -1 #include - void call_once(once_flag *flag, void (*func)(void)); - Description -2 The call_once function uses the once_flag pointed to by flag to ensure that - func is called exactly once, the first time the call_once function is called with that - value of flag. Completion of an effective call to the call_once function synchronizes - with all subsequent calls to the call_once function with the same value of flag. - Returns -3 The call_once function returns no value. - 7.25.3 Condition variable functions - 7.25.3.1 The cnd_broadcast function - Synopsis -1 #include - int cnd_broadcast(cnd_t *cond); - Description -2 The cnd_broadcast function unblocks all of the threads that are blocked on the - condition variable pointed to by cond at the time of the call. If no threads are blocked - on the condition variable pointed to by cond at the time of the call, the function does - nothing. - Returns -3 The cnd_broadcast function returns thrd_success on success, or thrd_error - if the request could not be honored. - 7.25.3.2 The cnd_destroy function - Synopsis -1 #include - void cnd_destroy(cnd_t *cond); - Description -2 The cnd_destroy function releases all resources used by the condition variable - pointed to by cond. The cnd_destroy function requires that no threads be blocked - waiting for the condition variable pointed to by cond. - -[page 375] - - Returns -3 The cnd_destroy function returns no value. - 7.25.3.3 The cnd_init function - Synopsis -1 #include - int cnd_init(cnd_t *cond); - Description -2 The cnd_init function creates a condition variable. If it succeeds it sets the variable - pointed to by cond to a value that uniquely identifies the newly created condition - variable. A thread that calls cnd_wait on a newly created condition variable will - block. - Returns -3 The cnd_init function returns thrd_success on success, or thrd_nomem if no - memory could be allocated for the newly created condition, or thrd_error if the - request could not be honored. - 7.25.3.4 The cnd_signal function - Synopsis -1 #include - int cnd_signal(cnd_t *cond); - Description -2 The cnd_signal function unblocks one of the threads that are blocked on the - condition variable pointed to by cond at the time of the call. If no threads are blocked - on the condition variable at the time of the call, the function does nothing and return - success. - Returns -3 The cnd_signal function returns thrd_success on success or thrd_error if - the request could not be honored. - 7.25.3.5 The cnd_timedwait function - Synopsis -1 #include - int cnd_timedwait(cnd_t *cond, mtx_t *mtx, - const xtime *xt); - -[page 376] - - Description -2 The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and - endeavors to block until the condition variable pointed to by cond is signaled by a call to - cnd_signal or to cnd_broadcast, or until after the time specified by the xtime - object pointed to by xt. When the calling thread becomes unblocked it locks the variable - pointed to by mtx before it returns. The cnd_timedwait function requires that the - mutex pointed to by mtx be locked by the calling thread. - Returns -3 The cnd_timedwait function returns thrd_success upon success, or - thrd_timeout if the time specified in the call was reached without acquiring the - requested resource, or thrd_error if the request could not be honored. - 7.25.3.6 The cnd_wait function - Synopsis -1 #include - int cnd_wait(cnd_t *cond, mtx_t *mtx); - Description -2 The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors - to block until the condition variable pointed to by cond is signaled by a call to - cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it - locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is - not locked by the calling thread, the cnd_wait function will act as if the abort - function is called. - Returns -3 The cnd_wait function returns thrd_success on success or thrd_error if the - request could not be honored. - 7.25.4 Mutex functions - 7.25.4.1 The mtx_destroy function - Synopsis -1 #include - void mtx_destroy(mtx_t *mtx); - Description -2 The mtx_destroy function releases any resources used by the mutex pointed to by - mtx. No threads can be blocked waiting for the mutex pointed to by mtx. - -[page 377] - - Returns -3 The mtx_destroy function returns no value. - 7.25.4.2 The mtx_init function - Synopsis -1 #include - int mtx_init(mtx_t *mtx, int type); - Description -2 The mtx_init function creates a mutex object with properties indicated by type, - which must have one of the six values: - mtx_plain for a simple non-recursive mutex, - mtx_timed for a non-recursive mutex that supports timeout, - mtx_try for a non-recursive mutex that supports test and return, - mtx_plain | mtx_recursive for a simple recursive mutex, - mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or - mtx_try | mtx_recursive for a recursive mutex that supports test and return. -3 If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that - uniquely identifies the newly created mutex. - Returns -4 The mtx_init function returns thrd_success on success, or thrd_error if the - request could not be honored. - 7.25.4.3 The mtx_lock function - Synopsis -1 #include - int mtx_lock(mtx_t *mtx); - Description -2 The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex - is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock - on the same mutex shall synchronize with this operation. - Returns -3 The mtx_lock function returns thrd_success on success, or thrd_busy if the - resource requested is already in use, or thrd_error if the request could not be - honored. - -[page 378] - - 7.25.4.4 The mtx_timedlock function - Synopsis -1 #include - int mtx_timedlock(mtx_t *mtx, const xtime *xt); - Description -2 The mtx_timedlock function endeavors to block until it locks the mutex pointed to by - mtx or until the time specified by the xtime object xt has passed. The specified mutex - shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same - mutex shall synchronize with this operation. - Returns -3 The mtx_timedlock function returns thrd_success on success, or thrd_busy - if the resource requested is already in use, or thrd_timeout if the time specified was - reached without acquiring the requested resource, or thrd_error if the request could - not be honored. - 7.25.4.5 The mtx_trylock function - Synopsis -1 #include - int mtx_trylock(mtx_t *mtx); - Description -2 The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The - specified mutex shall support either test and return or timeout. If the mutex is already - locked, the function returns without blocking. If the operation succeeds, prior calls to - mtx_unlock on the same mutex shall synchronize with this operation. - Returns -3 The mtx_trylock function returns thrd_success on success, or thrd_busy if - the resource requested is already in use, or thrd_error if the request could not be - honored. - 7.25.4.6 The mtx_unlock function - Synopsis -1 #include - int mtx_unlock(mtx_t *mtx); - Description -2 The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to - by mtx shall be locked by the calling thread. - -[page 379] - - Returns -3 The mtx_unlock function returns thrd_success on success or thrd_error if - the request could not be honored. - 7.25.5 Thread functions - 7.25.5.1 The thrd_create function - Synopsis -1 #include - int thrd_create(thrd_t *thr, thrd_start_t func, - void *arg); - Description -2 The thrd_create function creates a new thread executing func(arg). If the - thrd_create function succeeds, it sets the object pointed to by thr to the identifier of - the newly created thread. (A thread's identifier may be reused for a different thread once - the original thread has exited and either been detached or joined to another thread.) The - completion of the thrd_create function synchronizes with the beginning of the - execution of the new thread. - Returns -3 The thrd_create function returns thrd_success on success, or thrd_nomem if - no memory could be allocated for the thread requested, or thrd_error if the request - could not be honored. - 7.25.5.2 The thrd_current function - Synopsis -1 #include - thrd_t thrd_current(void); - Description -2 The thrd_current function identifies the thread that called it. - Returns -3 The thrd_current function returns the identifier of the thread that called it. - 7.25.5.3 The thrd_detach function - Synopsis -1 #include - int thrd_detach(thrd_t thr); - -[page 380] - - Description -2 The thrd_detach function tells the operating system to dispose of any resources - allocated to the thread identified by thr when that thread terminates. The thread - identified by thr shall not have been previously detached or joined with another thread. - Returns -3 The thrd_detach function returns thrd_success on success or thrd_error if - the request could not be honored. - 7.25.5.4 The thrd_equal function - Synopsis -1 #include - int thrd_equal(thrd_t thr0, thrd_t thr1); - Description -2 The thrd_equal function will determine whether the thread identified by thr0 refers - to the thread identified by thr1. - Returns -3 The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to - different threads. Otherwise the thrd_equal function returns a nonzero value. - 7.25.5.5 The thrd_exit function - Synopsis -1 #include - void thrd_exit(int res); - Description -2 The thrd_exit function terminates execution of the calling thread and sets its result - code to res. - Returns -3 The thrd_exit function returns no value. - 7.25.5.6 The thrd_join function - Synopsis -1 #include - int thrd_join(thrd_t thr, int *res); - Description -2 The thrd_join function joins the thread identified by thr with the current thread by - blocking until the other thread has terminated. If the parameter res is not a null pointer, - -[page 381] - - it stores the thread's result code in the integer pointed to by res. The termination of the - other thread synchronizes with the completion of the thrd_join function. The thread - identified by thr shall not have been previously detached or joined with another thread. - Returns -3 The thrd_join function returns thrd_success on success or thrd_error if the - request could not be honored. - 7.25.5.7 The thrd_sleep function - Synopsis -1 #include - void thrd_sleep(const xtime *xt); - Description -2 The thrd_sleep function suspends execution of the calling thread until after the time - specified by the xtime object pointed to by xt. - Returns -3 The thrd_sleep function returns no value. - 7.25.5.8 The thrd_yield function - Synopsis -1 #include - void thrd_yield(void); - Description -2 The thrd_yield function endeavors to permit other threads to run, even if the current - thread would ordinarily continue to run. - Returns -3 The thrd_yield function returns no value. - 7.25.6 Thread-specific storage functions - 7.25.6.1 The tss_create function - Synopsis -1 #include - int tss_create(tss_t *key, tss_dtor_t dtor); - Description -2 The tss_create function creates a thread-specific storage pointer with destructor - dtor, which may be null. - -[page 382] - - Returns -3 If the tss_create function is successful, it sets the thread-specific storage pointed to - by key to a value that uniquely identifies the newly created pointer and returns - thrd_success; otherwise, thrd_error is returned and the thread-specific storage - pointed to by key is set to an undefined value. - 7.25.6.2 The tss_delete function - Synopsis -1 #include - void tss_delete(tss_t key); - Description -2 The tss_delete function releases any resources used by the thread-specific storage - identified by key. - Returns -3 The tss_delete function returns no value. - 7.25.6.3 The tss_get function - Synopsis -1 #include - void *tss_get(tss_t key); - Description -2 The tss_get function returns the value for the current thread held in the thread-specific - storage identified by key. - Returns -3 The tss_get function returns the value for the current thread if successful, or zero if - unsuccessful. - 7.25.6.4 The tss_set function - Synopsis -1 #include - int tss_set(tss_t key, void *val); - Description -2 The tss_set function sets the value for the current thread held in the thread-specific - storage identified by key to val. - -[page 383] - - Returns -3 The tss_set function returns thrd_success on success or thrd_error if the - request could not be honored. - 7.25.7 Time functions - 7.25.7.1 The xtime_get function - Synopsis -1 #include - int xtime_get(xtime *xt, int base); - Description -2 The xtime_get function sets the xtime object pointed to by xt to hold the current - time based on the time base base. - Returns -3 If the xtime_get function is successful it returns the nonzero value base, which must - be TIME_UTC; otherwise, it returns zero.306) - - - - - 306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an - xtime object is system dependent. - -[page 384] - - 7.26 Date and time - 7.26.1 Components of time -1 The header defines two macros, and declares several types and functions for - manipulating time. Many functions deal with a calendar time that represents the current - date (according to the Gregorian calendar) and time. Some functions deal with local - time, which is the calendar time expressed for some specific time zone, and with Daylight - Saving Time, which is a temporary change in the algorithm for determining local time. - The local time zone and Daylight Saving Time are implementation-defined. -2 The macros defined are NULL (described in 7.19); and - CLOCKS_PER_SEC - which expands to an expression with type clock_t (described below) that is the - number per second of the value returned by the clock function. -3 The types declared are size_t (described in 7.19); - clock_t - and - time_t - which are arithmetic types capable of representing times; and - struct tm - which holds the components of a calendar time, called the broken-down time. -4 The range and precision of times representable in clock_t and time_t are - implementation-defined. The tm structure shall contain at least the following members, - in any order. The semantics of the members and their normal ranges are expressed in the - comments.307) - int tm_sec; // seconds after the minute -- [0, 60] - int tm_min; // minutes after the hour -- [0, 59] - int tm_hour; // hours since midnight -- [0, 23] - int tm_mday; // day of the month -- [1, 31] - int tm_mon; // months since January -- [0, 11] - int tm_year; // years since 1900 - int tm_wday; // days since Sunday -- [0, 6] - int tm_yday; // days since January 1 -- [0, 365] - int tm_isdst; // Daylight Saving Time flag - - - - 307) The range [0, 60] for tm_sec allows for a positive leap second. - -[page 385] - - The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight - Saving Time is not in effect, and negative if the information is not available. - 7.26.2 Time manipulation functions - 7.26.2.1 The clock function - Synopsis -1 #include - clock_t clock(void); - Description -2 The clock function determines the processor time used. - Returns -3 The clock function returns the implementation's best approximation to the processor - time used by the program since the beginning of an implementation-defined era related - only to the program invocation. To determine the time in seconds, the value returned by - the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If - the processor time used is not available or its value cannot be represented, the function - returns the value (clock_t)(-1).308) - 7.26.2.2 The difftime function - Synopsis -1 #include - double difftime(time_t time1, time_t time0); - Description -2 The difftime function computes the difference between two calendar times: time1 - - time0. - Returns -3 The difftime function returns the difference expressed in seconds as a double. - - - - - 308) In order to measure the time spent in a program, the clock function should be called at the start of - the program and its return value subtracted from the value returned by subsequent calls. - -[page 386] - - 7.26.2.3 The mktime function - Synopsis -1 #include - time_t mktime(struct tm *timeptr); - Description -2 The mktime function converts the broken-down time, expressed as local time, in the - structure pointed to by timeptr into a calendar time value with the same encoding as - that of the values returned by the time function. The original values of the tm_wday - and tm_yday components of the structure are ignored, and the original values of the - other components are not restricted to the ranges indicated above.309) On successful - completion, the values of the tm_wday and tm_yday components of the structure are - set appropriately, and the other components are set to represent the specified calendar - time, but with their values forced to the ranges indicated above; the final value of - tm_mday is not set until tm_mon and tm_year are determined. - Returns -3 The mktime function returns the specified calendar time encoded as a value of type - time_t. If the calendar time cannot be represented, the function returns the value - (time_t)(-1). -4 EXAMPLE What day of the week is July 4, 2001? - #include - #include - static const char *const wday[] = { - "Sunday", "Monday", "Tuesday", "Wednesday", - "Thursday", "Friday", "Saturday", "-unknown-" - }; - struct tm time_str; - /* ... */ - - - - - 309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that - Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value - causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time. - -[page 387] - - time_str.tm_year = 2001 - 1900; - time_str.tm_mon = 7 - 1; - time_str.tm_mday = 4; - time_str.tm_hour = 0; - time_str.tm_min = 0; - time_str.tm_sec = 1; - time_str.tm_isdst = -1; - if (mktime(&time_str) == (time_t)(-1)) - time_str.tm_wday = 7; - printf("%s\n", wday[time_str.tm_wday]); - - 7.26.2.4 The time function - Synopsis -1 #include - time_t time(time_t *timer); - Description -2 The time function determines the current calendar time. The encoding of the value is - unspecified. - Returns -3 The time function returns the implementation's best approximation to the current - calendar time. The value (time_t)(-1) is returned if the calendar time is not - available. If timer is not a null pointer, the return value is also assigned to the object it - points to. - 7.26.3 Time conversion functions -1 Except for the strftime function, these functions each return a pointer to one of two - types of static objects: a broken-down time structure or an array of char. Execution of - any of the functions that return a pointer to one of these object types may overwrite the - information in any object of the same type pointed to by the value returned from any - previous call to any of them and the functions are not required to avoid data races. The - implementation shall behave as if no other library functions call these functions. - 7.26.3.1 The asctime function - Synopsis -1 #include - char *asctime(const struct tm *timeptr); - Description -2 The asctime function converts the broken-down time in the structure pointed to by - timeptr into a string in the form - Sun Sep 16 01:03:52 1973\n\0 - -[page 388] - - using the equivalent of the following algorithm. - char *asctime(const struct tm *timeptr) - { - static const char wday_name[7][3] = { - "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" - }; - static const char mon_name[12][3] = { - "Jan", "Feb", "Mar", "Apr", "May", "Jun", - "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" - }; - static char result[26]; - sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", - wday_name[timeptr->tm_wday], - mon_name[timeptr->tm_mon], - timeptr->tm_mday, timeptr->tm_hour, - timeptr->tm_min, timeptr->tm_sec, - 1900 + timeptr->tm_year); - return result; - } -3 If any of the fields of the broken-down time contain values that are outside their normal - ranges,310) the behavior of the asctime function is undefined. Likewise, if the - calculated year exceeds four digits or is less than the year 1000, the behavior is - undefined. - Returns -4 The asctime function returns a pointer to the string. - 7.26.3.2 The ctime function - Synopsis -1 #include - char *ctime(const time_t *timer); - Description -2 The ctime function converts the calendar time pointed to by timer to local time in the - form of a string. It is equivalent to - asctime(localtime(timer)) - - - - 310) See 7.26.1. - -[page 389] - - Returns -3 The ctime function returns the pointer returned by the asctime function with that - broken-down time as argument. - Forward references: the localtime function (7.26.3.4). - 7.26.3.3 The gmtime function - Synopsis -1 #include - struct tm *gmtime(const time_t *timer); - Description -2 The gmtime function converts the calendar time pointed to by timer into a broken- - down time, expressed as UTC. - Returns -3 The gmtime function returns a pointer to the broken-down time, or a null pointer if the - specified time cannot be converted to UTC. - 7.26.3.4 The localtime function - Synopsis -1 #include - struct tm *localtime(const time_t *timer); - Description -2 The localtime function converts the calendar time pointed to by timer into a - broken-down time, expressed as local time. - Returns -3 The localtime function returns a pointer to the broken-down time, or a null pointer if - the specified time cannot be converted to local time. - 7.26.3.5 The strftime function - Synopsis -1 #include - size_t strftime(char * restrict s, - size_t maxsize, - const char * restrict format, - const struct tm * restrict timeptr); - -[page 390] - - Description -2 The strftime function places characters into the array pointed to by s as controlled by - the string pointed to by format. The format shall be a multibyte character sequence, - beginning and ending in its initial shift state. The format string consists of zero or - more conversion specifiers and ordinary multibyte characters. A conversion specifier - consists of a % character, possibly followed by an E or O modifier character (described - below), followed by a character that determines the behavior of the conversion specifier. - All ordinary multibyte characters (including the terminating null character) are copied - unchanged into the array. If copying takes place between objects that overlap, the - behavior is undefined. No more than maxsize characters are placed into the array. -3 Each conversion specifier is replaced by appropriate characters as described in the - following list. The appropriate characters are determined using the LC_TIME category - of the current locale and by the values of zero or more members of the broken-down time - structure pointed to by timeptr, as specified in brackets in the description. If any of - the specified values is outside the normal range, the characters stored are unspecified. - %a is replaced by the locale's abbreviated weekday name. [tm_wday] - %A is replaced by the locale's full weekday name. [tm_wday] - %b is replaced by the locale's abbreviated month name. [tm_mon] - %B is replaced by the locale's full month name. [tm_mon] - %c is replaced by the locale's appropriate date and time representation. [all specified - in 7.26.1] - %C is replaced by the year divided by 100 and truncated to an integer, as a decimal - number (00-99). [tm_year] - %d is replaced by the day of the month as a decimal number (01-31). [tm_mday] - %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year] - %e is replaced by the day of the month as a decimal number (1-31); a single digit is - preceded by a space. [tm_mday] - %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon, - tm_mday] - %g is replaced by the last 2 digits of the week-based year (see below) as a decimal - number (00-99). [tm_year, tm_wday, tm_yday] - %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997). - [tm_year, tm_wday, tm_yday] - %h is equivalent to ''%b''. [tm_mon] - %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour] - %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour] - %j is replaced by the day of the year as a decimal number (001-366). [tm_yday] - %m is replaced by the month as a decimal number (01-12). [tm_mon] - %M is replaced by the minute as a decimal number (00-59). [tm_min] - %n is replaced by a new-line character. - -[page 391] - - %p is replaced by the locale's equivalent of the AM/PM designations associated with a - 12-hour clock. [tm_hour] - %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec] - %R is equivalent to ''%H:%M''. [tm_hour, tm_min] - %S is replaced by the second as a decimal number (00-60). [tm_sec] - %t is replaced by a horizontal-tab character. - %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min, - tm_sec] - %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday - is 1. [tm_wday] - %U is replaced by the week number of the year (the first Sunday as the first day of week - 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday] - %V is replaced by the ISO 8601 week number (see below) as a decimal number - (01-53). [tm_year, tm_wday, tm_yday] - %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0. - [tm_wday] - %W is replaced by the week number of the year (the first Monday as the first day of - week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday] - %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1] - %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1] - %y is replaced by the last 2 digits of the year as a decimal number (00-99). - [tm_year] - %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year] - %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4 - hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time - zone is determinable. [tm_isdst] - %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no - time zone is determinable. [tm_isdst] - %% is replaced by %. -4 Some conversion specifiers can be modified by the inclusion of an E or O modifier - character to indicate an alternative format or specification. If the alternative format or - specification does not exist for the current locale, the modifier is ignored. - %Ec is replaced by the locale's alternative date and time representation. - %EC is replaced by the name of the base year (period) in the locale's alternative - representation. - %Ex is replaced by the locale's alternative date representation. - %EX is replaced by the locale's alternative time representation. - %Ey is replaced by the offset from %EC (year only) in the locale's alternative - representation. - %EY is replaced by the locale's full alternative year representation. - -[page 392] - - %Od is replaced by the day of the month, using the locale's alternative numeric symbols - (filled as needed with leading zeros, or with leading spaces if there is no alternative - symbol for zero). - %Oe is replaced by the day of the month, using the locale's alternative numeric symbols - (filled as needed with leading spaces). - %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric - symbols. - %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric - symbols. - %Om is replaced by the month, using the locale's alternative numeric symbols. - %OM is replaced by the minutes, using the locale's alternative numeric symbols. - %OS is replaced by the seconds, using the locale's alternative numeric symbols. - %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative - representation, where Monday is 1. - %OU is replaced by the week number, using the locale's alternative numeric symbols. - %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric - symbols. - %Ow is replaced by the weekday as a number, using the locale's alternative numeric - symbols. - %OW is replaced by the week number of the year, using the locale's alternative numeric - symbols. - %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric - symbols. -5 %g, %G, and %V give values according to the ISO 8601 week-based year. In this system, - weeks begin on a Monday and week 1 of the year is the week that includes January 4th, - which is also the week that includes the first Thursday of the year, and is also the first - week that contains at least four days in the year. If the first Monday of January is the - 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus, - for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If - December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of - the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and - %V is replaced by 01. -6 If a conversion specifier is not one of the above, the behavior is undefined. -7 In the "C" locale, the E and O modifiers are ignored and the replacement strings for the - following specifiers are: - %a the first three characters of %A. - %A one of ''Sunday'', ''Monday'', ... , ''Saturday''. - %b the first three characters of %B. - %B one of ''January'', ''February'', ... , ''December''. - %c equivalent to ''%a %b %e %T %Y''. - -[page 393] - - %p one of ''AM'' or ''PM''. - %r equivalent to ''%I:%M:%S %p''. - %x equivalent to ''%m/%d/%y''. - %X equivalent to %T. - %Z implementation-defined. - Returns -8 If the total number of resulting characters including the terminating null character is not - more than maxsize, the strftime function returns the number of characters placed - into the array pointed to by s not including the terminating null character. Otherwise, - zero is returned and the contents of the array are indeterminate. - -[page 394] - - 7.27 Unicode utilities -1 The header declares types and functions for manipulating Unicode - characters. -2 The types declared are mbstate_t (described in 7.29.1) and size_t (described in - 7.19); - char16_t - which is an unsigned integer type used for 16-bit characters and is the same type as - uint_least16_t (described in 7.20.1.2); and - char32_t - which is an unsigned integer type used for 32-bit characters and is the same type as - uint_least32_t (also described in 7.20.1.2). - 7.27.1 Restartable multibyte/wide character conversion functions -1 These functions have a parameter, ps, of type pointer to mbstate_t that points to an - object that can completely describe the current conversion state of the associated - multibyte character sequence, which the functions alter as necessary. If ps is a null - pointer, each function uses its own internal mbstate_t object instead, which is - initialized at program startup to the initial conversion state; the functions are not required - to avoid data races in this case. The implementation behaves as if no library function - calls these functions with a null pointer for ps. - 7.27.1.1 The mbrtoc16 function - Synopsis -1 #include - size_t mbrtoc16(char16_t * restrict pc16, - const char * restrict s, size_t n, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the mbrtoc16 function is equivalent to the call: - mbrtoc16(NULL, "", 1, ps) - In this case, the values of the parameters pc16 and n are ignored. -3 If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the values of the - corresponding wide characters and then, if pc16 is not a null pointer, stores the value of - the first (or only) such character in the object pointed to by pc16. Subsequent calls will - -[page 395] - - store successive wide characters without consuming any additional input until all the - characters have been stored. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. - Returns -4 The mbrtoc16 function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that - corresponds to the null wide character (which is the value stored). - between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte - character (which is the value stored); the value returned is the number - of bytes that complete the multibyte character. - (size_t)(-3) if the next character resulting from a previous call has been stored (no - bytes from the input have been consumed by this call). - (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) - multibyte character, and all n bytes have been processed (no value is - stored).311) - (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes - do not contribute to a complete and valid multibyte character (no - value is stored); the value of the macro EILSEQ is stored in errno, - and the conversion state is unspecified. - 7.27.1.2 The c16rtomb function - Synopsis -1 #include - size_t c16rtomb(char * restrict s, char16_t c16, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the c16rtomb function is equivalent to the call - c16rtomb(buf, L'\0', ps) - where buf is an internal buffer. -3 If s is not a null pointer, the c16rtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by c16 - (including any shift sequences), and stores the multibyte character representation in the - - - 311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - -[page 396] - - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. - Returns -4 The c16rtomb function returns the number of bytes stored in the array object (including - any shift sequences). When c16 is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - 7.27.1.3 The mbrtoc32 function - Synopsis -1 #include - size_t mbrtoc32(char32_t * restrict pc32, - const char * restrict s, size_t n, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the mbrtoc32 function is equivalent to the call: - mbrtoc32(NULL, "", 1, ps) - In this case, the values of the parameters pc32 and n are ignored. -3 If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the values of the - corresponding wide characters and then, if pc32 is not a null pointer, stores the value of - the first (or only) such character in the object pointed to by pc32. Subsequent calls will - store successive wide characters without consuming any additional input until all the - characters have been stored. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. - Returns -4 The mbrtoc32 function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that - corresponds to the null wide character (which is the value stored). - between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte - character (which is the value stored); the value returned is the number - of bytes that complete the multibyte character. - -[page 397] - - (size_t)(-3) if the next character resulting from a previous call has been stored (no - bytes from the input have been consumed by this call). - (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) - multibyte character, and all n bytes have been processed (no value is - stored).312) - (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes - do not contribute to a complete and valid multibyte character (no - value is stored); the value of the macro EILSEQ is stored in errno, - and the conversion state is unspecified. - 7.27.1.4 The c32rtomb function - Synopsis -1 #include - size_t c32rtomb(char * restrict s, char32_t c32, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the c32rtomb function is equivalent to the call - c32rtomb(buf, L'\0', ps) - where buf is an internal buffer. -3 If s is not a null pointer, the c32rtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by c32 - (including any shift sequences), and stores the multibyte character representation in the - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. - Returns -4 The c32rtomb function returns the number of bytes stored in the array object (including - any shift sequences). When c32 is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - - - - - 312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - -[page 398] - - 7.28 Extended multibyte and wide character utilities - 7.28.1 Introduction -1 The header defines four macros, and declares four data types, one tag, and - many functions.313) -2 The types declared are wchar_t and size_t (both described in 7.19); - mbstate_t - which is a complete object type other than an array type that can hold the conversion state - information necessary to convert between sequences of multibyte characters and wide - characters; - wint_t - which is an integer type unchanged by default argument promotions that can hold any - value corresponding to members of the extended character set, as well as at least one - value that does not correspond to any member of the extended character set (see WEOF - below);314) and - struct tm - which is declared as an incomplete structure type (the contents are described in 7.26.1). -3 The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX - (described in 7.20.3); and - WEOF - which expands to a constant expression of type wint_t whose value does not - correspond to any member of the extended character set.315) It is accepted (and returned) - by several functions in this subclause to indicate end-of-file, that is, no more input from a - stream. It is also used as a wide character value that does not correspond to any member - of the extended character set. -4 The functions declared are grouped as follows: - -- Functions that perform input and output of wide characters, or multibyte characters, - or both; - -- Functions that provide wide string numeric conversion; - -- Functions that perform general wide string manipulation; - - - 313) See ''future library directions'' (7.30.12). - 314) wchar_t and wint_t can be the same integer type. - 315) The value of the macro WEOF may differ from that of EOF and need not be negative. - -[page 399] - - -- Functions for wide string date and time conversion; and - -- Functions that provide extended capabilities for conversion between multibyte and - wide character sequences. -5 Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the behavior is - undefined. - 7.28.2 Formatted wide character input/output functions -1 The formatted wide character input/output functions shall behave as if there is a sequence - point after the actions associated with each specifier.316) - 7.28.2.1 The fwprintf function - Synopsis -1 #include - #include - int fwprintf(FILE * restrict stream, - const wchar_t * restrict format, ...); - Description -2 The fwprintf function writes output to the stream pointed to by stream, under - control of the wide string pointed to by format that specifies how subsequent arguments - are converted for output. If there are insufficient arguments for the format, the behavior - is undefined. If the format is exhausted while arguments remain, the excess arguments - are evaluated (as always) but are otherwise ignored. The fwprintf function returns - when the end of the format string is encountered. -3 The format is composed of zero or more directives: ordinary wide characters (not %), - which are copied unchanged to the output stream; and conversion specifications, each of - which results in fetching zero or more subsequent arguments, converting them, if - applicable, according to the corresponding conversion specifier, and then writing the - result to the output stream. -4 Each conversion specification is introduced by the wide character %. After the %, the - following appear in sequence: - -- Zero or more flags (in any order) that modify the meaning of the conversion - specification. - -- An optional minimum field width. If the converted value has fewer wide characters - than the field width, it is padded with spaces (by default) on the left (or right, if the - - - 316) The fwprintf functions perform writes to memory for the %n specifier. - -[page 400] - - left adjustment flag, described later, has been given) to the field width. The field - width takes the form of an asterisk * (described later) or a nonnegative decimal - integer.317) - -- An optional precision that gives the minimum number of digits to appear for the d, i, - o, u, x, and X conversions, the number of digits to appear after the decimal-point - wide character for a, A, e, E, f, and F conversions, the maximum number of - significant digits for the g and G conversions, or the maximum number of wide - characters to be written for s conversions. The precision takes the form of a period - (.) followed either by an asterisk * (described later) or by an optional decimal - integer; if only the period is specified, the precision is taken as zero. If a precision - appears with any other conversion specifier, the behavior is undefined. - -- An optional length modifier that specifies the size of the argument. - -- A conversion specifier wide character that specifies the type of conversion to be - applied. -5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In - this case, an int argument supplies the field width or precision. The arguments - specifying field width, or precision, or both, shall appear (in that order) before the - argument (if any) to be converted. A negative field width argument is taken as a - flag - followed by a positive field width. A negative precision argument is taken as if the - precision were omitted. -6 The flag wide characters and their meanings are: - - The result of the conversion is left-justified within the field. (It is right-justified if - this flag is not specified.) - + The result of a signed conversion always begins with a plus or minus sign. (It - begins with a sign only when a negative value is converted if this flag is not - specified.)318) - space If the first wide character of a signed conversion is not a sign, or if a signed - conversion results in no wide characters, a space is prefixed to the result. If the - space and + flags both appear, the space flag is ignored. - # The result is converted to an ''alternative form''. For o conversion, it increases - the precision, if and only if necessary, to force the first digit of the result to be a - zero (if the value and precision are both 0, a single 0 is printed). For x (or X) - conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, - - - 317) Note that 0 is taken as a flag, not as the beginning of a field width. - 318) The results of all floating conversions of a negative zero, and of negative values that round to zero, - include a minus sign. - -[page 401] - - and G conversions, the result of converting a floating-point number always - contains a decimal-point wide character, even if no digits follow it. (Normally, a - decimal-point wide character appears in the result of these conversions only if a - digit follows it.) For g and G conversions, trailing zeros are not removed from the - result. For other conversions, the behavior is undefined. - 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros - (following any indication of sign or base) are used to pad to the field width rather - than performing space padding, except when converting an infinity or NaN. If the - 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X - conversions, if a precision is specified, the 0 flag is ignored. For other - conversions, the behavior is undefined. -7 The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - signed char or unsigned char argument (the argument will have - been promoted according to the integer promotions, but its value shall be - converted to signed char or unsigned char before printing); or that - a following n conversion specifier applies to a pointer to a signed char - argument. - h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - short int or unsigned short int argument (the argument will - have been promoted according to the integer promotions, but its value shall - be converted to short int or unsigned short int before printing); - or that a following n conversion specifier applies to a pointer to a short - int argument. - l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - long int or unsigned long int argument; that a following n - conversion specifier applies to a pointer to a long int argument; that a - following c conversion specifier applies to a wint_t argument; that a - following s conversion specifier applies to a pointer to a wchar_t - argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion - specifier. - ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - long long int or unsigned long long int argument; or that a - following n conversion specifier applies to a pointer to a long long int - argument. - j Specifies that a following d, i, o, u, x, or X conversion specifier applies to - an intmax_t or uintmax_t argument; or that a following n conversion - specifier applies to a pointer to an intmax_t argument. - -[page 402] - - z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - size_t or the corresponding signed integer type argument; or that a - following n conversion specifier applies to a pointer to a signed integer type - corresponding to size_t argument. - t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a - ptrdiff_t or the corresponding unsigned integer type argument; or that a - following n conversion specifier applies to a pointer to a ptrdiff_t - argument. - L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier - applies to a long double argument. - If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -8 The conversion specifiers and their meanings are: - d,i The int argument is converted to signed decimal in the style [-]dddd. The - precision specifies the minimum number of digits to appear; if the value - being converted can be represented in fewer digits, it is expanded with - leading zeros. The default precision is 1. The result of converting a zero - value with a precision of zero is no wide characters. - o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned - decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the - letters abcdef are used for x conversion and the letters ABCDEF for X - conversion. The precision specifies the minimum number of digits to appear; - if the value being converted can be represented in fewer digits, it is expanded - with leading zeros. The default precision is 1. The result of converting a - zero value with a precision of zero is no wide characters. - f,F A double argument representing a floating-point number is converted to - decimal notation in the style [-]ddd.ddd, where the number of digits after - the decimal-point wide character is equal to the precision specification. If the - precision is missing, it is taken as 6; if the precision is zero and the # flag is - not specified, no decimal-point wide character appears. If a decimal-point - wide character appears, at least one digit appears before it. The value is - rounded to the appropriate number of digits. - A double argument representing an infinity is converted in one of the styles - [-]inf or [-]infinity -- which style is implementation-defined. A - double argument representing a NaN is converted in one of the styles - [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of - any n-wchar-sequence, is implementation-defined. The F conversion - specifier produces INF, INFINITY, or NAN instead of inf, infinity, or - -[page 403] - - nan, respectively.319) -e,E A double argument representing a floating-point number is converted in the - style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the - argument is nonzero) before the decimal-point wide character and the number - of digits after it is equal to the precision; if the precision is missing, it is taken - as 6; if the precision is zero and the # flag is not specified, no decimal-point - wide character appears. The value is rounded to the appropriate number of - digits. The E conversion specifier produces a number with E instead of e - introducing the exponent. The exponent always contains at least two digits, - and only as many more digits as necessary to represent the exponent. If the - value is zero, the exponent is zero. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -g,G A double argument representing a floating-point number is converted in - style f or e (or in style F or E in the case of a G conversion specifier), - depending on the value converted and the precision. Let P equal the - precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. - Then, if a conversion with style E would have an exponent of X: - -- if P > X >= -4, the conversion is with style f (or F) and precision - P - (X + 1). - -- otherwise, the conversion is with style e (or E) and precision P - 1. - Finally, unless the # flag is used, any trailing zeros are removed from the - fractional portion of the result and the decimal-point wide character is - removed if there is no fractional portion remaining. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -a,A A double argument representing a floating-point number is converted in the - style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is - nonzero if the argument is a normalized floating-point number and is - otherwise unspecified) before the decimal-point wide character320) and the - number of hexadecimal digits after it is equal to the precision; if the precision - is missing and FLT_RADIX is a power of 2, then the precision is sufficient - - -319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual - meaning; the # and 0 flag wide characters have no effect. -320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide - character so that subsequent digits align to nibble (4-bit) boundaries. - -[page 404] - - for an exact representation of the value; if the precision is missing and - FLT_RADIX is not a power of 2, then the precision is sufficient to - distinguish321) values of type double, except that trailing zeros may be - omitted; if the precision is zero and the # flag is not specified, no decimal- - point wide character appears. The letters abcdef are used for a conversion - and the letters ABCDEF for A conversion. The A conversion specifier - produces a number with X and P instead of x and p. The exponent always - contains at least one digit, and only as many more digits as necessary to - represent the decimal exponent of 2. If the value is zero, the exponent is - zero. - A double argument representing an infinity or NaN is converted in the style - of an f or F conversion specifier. -c If no l length modifier is present, the int argument is converted to a wide - character as if by calling btowc and the resulting wide character is written. - If an l length modifier is present, the wint_t argument is converted to - wchar_t and written. -s If no l length modifier is present, the argument shall be a pointer to the initial - element of a character array containing a multibyte character sequence - beginning in the initial shift state. Characters from the array are converted as - if by repeated calls to the mbrtowc function, with the conversion state - described by an mbstate_t object initialized to zero before the first - multibyte character is converted, and written up to (but not including) the - terminating null wide character. If the precision is specified, no more than - that many wide characters are written. If the precision is not specified or is - greater than the size of the converted array, the converted array shall contain a - null wide character. - If an l length modifier is present, the argument shall be a pointer to the initial - element of an array of wchar_t type. Wide characters from the array are - written up to (but not including) a terminating null wide character. If the - precision is specified, no more than that many wide characters are written. If - the precision is not specified or is greater than the size of the array, the array - shall contain a null wide character. -p The argument shall be a pointer to void. The value of the pointer is - converted to a sequence of printing wide characters, in an implementation- - -321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is - FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p - might suffice depending on the implementation's scheme for determining the digit to the left of the - decimal-point wide character. - -[page 405] - - defined manner. - n The argument shall be a pointer to signed integer into which is written the - number of wide characters written to the output stream so far by this call to - fwprintf. No argument is converted, but one is consumed. If the - conversion specification includes any flags, a field width, or a precision, the - behavior is undefined. - % A % wide character is written. No argument is converted. The complete - conversion specification shall be %%. -9 If a conversion specification is invalid, the behavior is undefined.322) If any argument is - not the correct type for the corresponding conversion specification, the behavior is - undefined. -10 In no case does a nonexistent or small field width cause truncation of a field; if the result - of a conversion is wider than the field width, the field is expanded to contain the - conversion result. -11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded - to a hexadecimal floating number with the given precision. - Recommended practice -12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly - representable in the given precision, the result should be one of the two adjacent numbers - in hexadecimal floating style with the given precision, with the extra stipulation that the - error should have a correct sign for the current rounding direction. -13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most - DECIMAL_DIG, then the result should be correctly rounded.323) If the number of - significant decimal digits is more than DECIMAL_DIG but the source value is exactly - representable with DECIMAL_DIG digits, then the result should be an exact - representation with trailing zeros. Otherwise, the source value is bounded by two - adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value - of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that - the error should have a correct sign for the current rounding direction. - Returns -14 The fwprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - - 322) See ''future library directions'' (7.30.12). - 323) For binary-to-decimal conversion, the result format's values are the numbers representable with the - given format specifier. The number of significant digits is determined by the format specifier, and in - the case of fixed-point conversion by the source value as well. - -[page 406] - - Environmental limits -15 The number of wide characters that can be produced by any single conversion shall be at - least 4095. -16 EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal - places: - #include - #include - #include - /* ... */ - wchar_t *weekday, *month; // pointers to wide strings - int day, hour, min; - fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n", - weekday, month, day, hour, min); - fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0)); - - Forward references: the btowc function (7.28.6.1.1), the mbrtowc function - (7.28.6.3.2). - 7.28.2.2 The fwscanf function - Synopsis -1 #include - #include - int fwscanf(FILE * restrict stream, - const wchar_t * restrict format, ...); - Description -2 The fwscanf function reads input from the stream pointed to by stream, under - control of the wide string pointed to by format that specifies the admissible input - sequences and how they are to be converted for assignment, using subsequent arguments - as pointers to the objects to receive the converted input. If there are insufficient - arguments for the format, the behavior is undefined. If the format is exhausted while - arguments remain, the excess arguments are evaluated (as always) but are otherwise - ignored. -3 The format is composed of zero or more directives: one or more white-space wide - characters, an ordinary wide character (neither % nor a white-space wide character), or a - conversion specification. Each conversion specification is introduced by the wide - character %. After the %, the following appear in sequence: - -- An optional assignment-suppressing wide character *. - -- An optional decimal integer greater than zero that specifies the maximum field width - (in wide characters). - -[page 407] - - -- An optional length modifier that specifies the size of the receiving object. - -- A conversion specifier wide character that specifies the type of conversion to be - applied. -4 The fwscanf function executes each directive of the format in turn. When all directives - have been executed, or if a directive fails (as detailed below), the function returns. - Failures are described as input failures (due to the occurrence of an encoding error or the - unavailability of input characters), or matching failures (due to inappropriate input). -5 A directive composed of white-space wide character(s) is executed by reading input up to - the first non-white-space wide character (which remains unread), or until no more wide - characters can be read. -6 A directive that is an ordinary wide character is executed by reading the next wide - character of the stream. If that wide character differs from the directive, the directive - fails and the differing and subsequent wide characters remain unread. Similarly, if end- - of-file, an encoding error, or a read error prevents a wide character from being read, the - directive fails. -7 A directive that is a conversion specification defines a set of matching input sequences, as - described below for each specifier. A conversion specification is executed in the - following steps: -8 Input white-space wide characters (as specified by the iswspace function) are skipped, - unless the specification includes a [, c, or n specifier.324) -9 An input item is read from the stream, unless the specification includes an n specifier. An - input item is defined as the longest sequence of input wide characters which does not - exceed any specified field width and which is, or is a prefix of, a matching input - sequence.325) The first wide character, if any, after the input item remains unread. If the - length of the input item is zero, the execution of the directive fails; this condition is a - matching failure unless end-of-file, an encoding error, or a read error prevented input - from the stream, in which case it is an input failure. -10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the - count of input wide characters) is converted to a type appropriate to the conversion - specifier. If the input item is not a matching sequence, the execution of the directive fails: - this condition is a matching failure. Unless assignment suppression was indicated by a *, - the result of the conversion is placed in the object pointed to by the first argument - following the format argument that has not already received a conversion result. If this - - - 324) These white-space wide characters are not counted against a specified field width. - 325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some - sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf. - -[page 408] - - object does not have an appropriate type, or if the result of the conversion cannot be - represented in the object, the behavior is undefined. -11 The length modifiers and their meanings are: - hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to signed char or unsigned char. - h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to short int or unsigned short - int. - l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to long int or unsigned long - int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to - an argument with type pointer to double; or that a following c, s, or [ - conversion specifier applies to an argument with type pointer to wchar_t. - ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to long long int or unsigned - long long int. - j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to intmax_t or uintmax_t. - z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to size_t or the corresponding signed - integer type. - t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies - to an argument with type pointer to ptrdiff_t or the corresponding - unsigned integer type. - L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier - applies to an argument with type pointer to long double. - If a length modifier appears with any conversion specifier other than as specified above, - the behavior is undefined. -12 The conversion specifiers and their meanings are: - d Matches an optionally signed decimal integer, whose format is the same as - expected for the subject sequence of the wcstol function with the value 10 - for the base argument. The corresponding argument shall be a pointer to - signed integer. - i Matches an optionally signed integer, whose format is the same as expected - for the subject sequence of the wcstol function with the value 0 for the - base argument. The corresponding argument shall be a pointer to signed - -[page 409] - - integer. -o Matches an optionally signed octal integer, whose format is the same as - expected for the subject sequence of the wcstoul function with the value 8 - for the base argument. The corresponding argument shall be a pointer to - unsigned integer. -u Matches an optionally signed decimal integer, whose format is the same as - expected for the subject sequence of the wcstoul function with the value 10 - for the base argument. The corresponding argument shall be a pointer to - unsigned integer. -x Matches an optionally signed hexadecimal integer, whose format is the same - as expected for the subject sequence of the wcstoul function with the value - 16 for the base argument. The corresponding argument shall be a pointer to - unsigned integer. -a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose - format is the same as expected for the subject sequence of the wcstod - function. The corresponding argument shall be a pointer to floating. -c Matches a sequence of wide characters of exactly the number specified by the - field width (1 if no field width is present in the directive). - If no l length modifier is present, characters from the input field are - converted as if by repeated calls to the wcrtomb function, with the - conversion state described by an mbstate_t object initialized to zero - before the first wide character is converted. The corresponding argument - shall be a pointer to the initial element of a character array large enough to - accept the sequence. No null character is added. - If an l length modifier is present, the corresponding argument shall be a - pointer to the initial element of an array of wchar_t large enough to accept - the sequence. No null wide character is added. -s Matches a sequence of non-white-space wide characters. - If no l length modifier is present, characters from the input field are - converted as if by repeated calls to the wcrtomb function, with the - conversion state described by an mbstate_t object initialized to zero - before the first wide character is converted. The corresponding argument - shall be a pointer to the initial element of a character array large enough to - accept the sequence and a terminating null character, which will be added - automatically. - If an l length modifier is present, the corresponding argument shall be a - pointer to the initial element of an array of wchar_t large enough to accept - -[page 410] - - the sequence and the terminating null wide character, which will be added - automatically. -[ Matches a nonempty sequence of wide characters from a set of expected - characters (the scanset). - If no l length modifier is present, characters from the input field are - converted as if by repeated calls to the wcrtomb function, with the - conversion state described by an mbstate_t object initialized to zero - before the first wide character is converted. The corresponding argument - shall be a pointer to the initial element of a character array large enough to - accept the sequence and a terminating null character, which will be added - automatically. - If an l length modifier is present, the corresponding argument shall be a - pointer to the initial element of an array of wchar_t large enough to accept - the sequence and the terminating null wide character, which will be added - automatically. - The conversion specifier includes all subsequent wide characters in the - format string, up to and including the matching right bracket (]). The wide - characters between the brackets (the scanlist) compose the scanset, unless the - wide character after the left bracket is a circumflex (^), in which case the - scanset contains all wide characters that do not appear in the scanlist between - the circumflex and the right bracket. If the conversion specifier begins with - [] or [^], the right bracket wide character is in the scanlist and the next - following right bracket wide character is the matching right bracket that ends - the specification; otherwise the first following right bracket wide character is - the one that ends the specification. If a - wide character is in the scanlist and - is not the first, nor the second where the first wide character is a ^, nor the - last character, the behavior is implementation-defined. -p Matches an implementation-defined set of sequences, which should be the - same as the set of sequences that may be produced by the %p conversion of - the fwprintf function. The corresponding argument shall be a pointer to a - pointer to void. The input item is converted to a pointer value in an - implementation-defined manner. If the input item is a value converted earlier - during the same program execution, the pointer that results shall compare - equal to that value; otherwise the behavior of the %p conversion is undefined. -n No input is consumed. The corresponding argument shall be a pointer to - signed integer into which is to be written the number of wide characters read - from the input stream so far by this call to the fwscanf function. Execution - of a %n directive does not increment the assignment count returned at the - completion of execution of the fwscanf function. No argument is - -[page 411] - - converted, but one is consumed. If the conversion specification includes an - assignment-suppressing wide character or a field width, the behavior is - undefined. - % Matches a single % wide character; no conversion or assignment occurs. The - complete conversion specification shall be %%. -13 If a conversion specification is invalid, the behavior is undefined.326) -14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as, - respectively, a, e, f, g, and x. -15 Trailing white space (including new-line wide characters) is left unread unless matched - by a directive. The success of literal matches and suppressed assignments is not directly - determinable other than via the %n directive. - Returns -16 The fwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the function returns the - number of input items assigned, which can be fewer than provided for, or even zero, in - the event of an early matching failure. -17 EXAMPLE 1 The call: - #include - #include - /* ... */ - int n, i; float x; wchar_t name[50]; - n = fwscanf(stdin, L"%d%f%ls", &i, &x, name); - with the input line: - 25 54.32E-1 thompson - will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -18 EXAMPLE 2 The call: - #include - #include - /* ... */ - int i; float x; double y; - fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y); - with input: - 56789 0123 56a72 - will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value - 56.0. The next wide character read from the input stream will be a. - - - 326) See ''future library directions'' (7.30.12). - -[page 412] - - Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the - wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb - function (7.28.6.3.3). - 7.28.2.3 The swprintf function - Synopsis -1 #include - int swprintf(wchar_t * restrict s, - size_t n, - const wchar_t * restrict format, ...); - Description -2 The swprintf function is equivalent to fwprintf, except that the argument s - specifies an array of wide characters into which the generated output is to be written, - rather than written to a stream. No more than n wide characters are written, including a - terminating null wide character, which is always added (unless n is zero). - Returns -3 The swprintf function returns the number of wide characters written in the array, not - counting the terminating null wide character, or a negative value if an encoding error - occurred or if n or more wide characters were requested to be written. - 7.28.2.4 The swscanf function - Synopsis -1 #include - int swscanf(const wchar_t * restrict s, - const wchar_t * restrict format, ...); - Description -2 The swscanf function is equivalent to fwscanf, except that the argument s specifies a - wide string from which the input is to be obtained, rather than from a stream. Reaching - the end of the wide string is equivalent to encountering end-of-file for the fwscanf - function. - Returns -3 The swscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the swscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - -[page 413] - - 7.28.2.5 The vfwprintf function - Synopsis -1 #include - #include - #include - int vfwprintf(FILE * restrict stream, - const wchar_t * restrict format, - va_list arg); - Description -2 The vfwprintf function is equivalent to fwprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwprintf function does not invoke the - va_end macro.327) - Returns -3 The vfwprintf function returns the number of wide characters transmitted, or a - negative value if an output or encoding error occurred. -4 EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting - routine. - #include - #include - #include - void error(char *function_name, wchar_t *format, ...) - { - va_list args; - va_start(args, format); - // print out name of function causing error - fwprintf(stderr, L"ERROR in %s: ", function_name); - // print out remainder of message - vfwprintf(stderr, format, args); - va_end(args); - } - - - - - 327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf - invoke the va_arg macro, the value of arg after the return is indeterminate. - -[page 414] - - 7.28.2.6 The vfwscanf function - Synopsis -1 #include - #include - #include - int vfwscanf(FILE * restrict stream, - const wchar_t * restrict format, - va_list arg); - Description -2 The vfwscanf function is equivalent to fwscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwscanf function does not invoke the - va_end macro.327) - Returns -3 The vfwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vfwscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.28.2.7 The vswprintf function - Synopsis -1 #include - #include - int vswprintf(wchar_t * restrict s, - size_t n, - const wchar_t * restrict format, - va_list arg); - Description -2 The vswprintf function is equivalent to swprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswprintf function does not invoke the - va_end macro.327) - Returns -3 The vswprintf function returns the number of wide characters written in the array, not - counting the terminating null wide character, or a negative value if an encoding error - occurred or if n or more wide characters were requested to be generated. - -[page 415] - - 7.28.2.8 The vswscanf function - Synopsis -1 #include - #include - int vswscanf(const wchar_t * restrict s, - const wchar_t * restrict format, - va_list arg); - Description -2 The vswscanf function is equivalent to swscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswscanf function does not invoke the - va_end macro.327) - Returns -3 The vswscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vswscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.28.2.9 The vwprintf function - Synopsis -1 #include - #include - int vwprintf(const wchar_t * restrict format, - va_list arg); - Description -2 The vwprintf function is equivalent to wprintf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwprintf function does not invoke the - va_end macro.327) - Returns -3 The vwprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - -[page 416] - - 7.28.2.10 The vwscanf function - Synopsis -1 #include - #include - int vwscanf(const wchar_t * restrict format, - va_list arg); - Description -2 The vwscanf function is equivalent to wscanf, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwscanf function does not invoke the - va_end macro.327) - Returns -3 The vwscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the vwscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.28.2.11 The wprintf function - Synopsis -1 #include - int wprintf(const wchar_t * restrict format, ...); - Description -2 The wprintf function is equivalent to fwprintf with the argument stdout - interposed before the arguments to wprintf. - Returns -3 The wprintf function returns the number of wide characters transmitted, or a negative - value if an output or encoding error occurred. - 7.28.2.12 The wscanf function - Synopsis -1 #include - int wscanf(const wchar_t * restrict format, ...); - Description -2 The wscanf function is equivalent to fwscanf with the argument stdin interposed - before the arguments to wscanf. - -[page 417] - - Returns -3 The wscanf function returns the value of the macro EOF if an input failure occurs - before the first conversion (if any) has completed. Otherwise, the wscanf function - returns the number of input items assigned, which can be fewer than provided for, or even - zero, in the event of an early matching failure. - 7.28.3 Wide character input/output functions - 7.28.3.1 The fgetwc function - Synopsis -1 #include - #include - wint_t fgetwc(FILE *stream); - Description -2 If the end-of-file indicator for the input stream pointed to by stream is not set and a - next wide character is present, the fgetwc function obtains that wide character as a - wchar_t converted to a wint_t and advances the associated file position indicator for - the stream (if defined). - Returns -3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- - of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise, - the fgetwc function returns the next wide character from the input stream pointed to by - stream. If a read error occurs, the error indicator for the stream is set and the fgetwc - function returns WEOF. If an encoding error occurs (including too few bytes), the value of - the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328) - 7.28.3.2 The fgetws function - Synopsis -1 #include - #include - wchar_t *fgetws(wchar_t * restrict s, - int n, FILE * restrict stream); - Description -2 The fgetws function reads at most one less than the number of wide characters - specified by n from the stream pointed to by stream into the array pointed to by s. No - - - 328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. - Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs. - -[page 418] - - additional wide characters are read after a new-line wide character (which is retained) or - after end-of-file. A null wide character is written immediately after the last wide - character read into the array. - Returns -3 The fgetws function returns s if successful. If end-of-file is encountered and no - characters have been read into the array, the contents of the array remain unchanged and a - null pointer is returned. If a read or encoding error occurs during the operation, the array - contents are indeterminate and a null pointer is returned. - 7.28.3.3 The fputwc function - Synopsis -1 #include - #include - wint_t fputwc(wchar_t c, FILE *stream); - Description -2 The fputwc function writes the wide character specified by c to the output stream - pointed to by stream, at the position indicated by the associated file position indicator - for the stream (if defined), and advances the indicator appropriately. If the file cannot - support positioning requests, or if the stream was opened with append mode, the - character is appended to the output stream. - Returns -3 The fputwc function returns the wide character written. If a write error occurs, the - error indicator for the stream is set and fputwc returns WEOF. If an encoding error - occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF. - 7.28.3.4 The fputws function - Synopsis -1 #include - #include - int fputws(const wchar_t * restrict s, - FILE * restrict stream); - Description -2 The fputws function writes the wide string pointed to by s to the stream pointed to by - stream. The terminating null wide character is not written. - Returns -3 The fputws function returns EOF if a write or encoding error occurs; otherwise, it - returns a nonnegative value. - -[page 419] - - 7.28.3.5 The fwide function - Synopsis -1 #include - #include - int fwide(FILE *stream, int mode); - Description -2 The fwide function determines the orientation of the stream pointed to by stream. If - mode is greater than zero, the function first attempts to make the stream wide oriented. If - mode is less than zero, the function first attempts to make the stream byte oriented.329) - Otherwise, mode is zero and the function does not alter the orientation of the stream. - Returns -3 The fwide function returns a value greater than zero if, after the call, the stream has - wide orientation, a value less than zero if the stream has byte orientation, or zero if the - stream has no orientation. - 7.28.3.6 The getwc function - Synopsis -1 #include - #include - wint_t getwc(FILE *stream); - Description -2 The getwc function is equivalent to fgetwc, except that if it is implemented as a - macro, it may evaluate stream more than once, so the argument should never be an - expression with side effects. - Returns -3 The getwc function returns the next wide character from the input stream pointed to by - stream, or WEOF. - 7.28.3.7 The getwchar function - Synopsis -1 #include - wint_t getwchar(void); - - - - - 329) If the orientation of the stream has already been determined, fwide does not change it. - -[page 420] - - Description -2 The getwchar function is equivalent to getwc with the argument stdin. - Returns -3 The getwchar function returns the next wide character from the input stream pointed to - by stdin, or WEOF. - 7.28.3.8 The putwc function - Synopsis -1 #include - #include - wint_t putwc(wchar_t c, FILE *stream); - Description -2 The putwc function is equivalent to fputwc, except that if it is implemented as a - macro, it may evaluate stream more than once, so that argument should never be an - expression with side effects. - Returns -3 The putwc function returns the wide character written, or WEOF. - 7.28.3.9 The putwchar function - Synopsis -1 #include - wint_t putwchar(wchar_t c); - Description -2 The putwchar function is equivalent to putwc with the second argument stdout. - Returns -3 The putwchar function returns the character written, or WEOF. - 7.28.3.10 The ungetwc function - Synopsis -1 #include - #include - wint_t ungetwc(wint_t c, FILE *stream); - Description -2 The ungetwc function pushes the wide character specified by c back onto the input - stream pointed to by stream. Pushed-back wide characters will be returned by - subsequent reads on that stream in the reverse order of their pushing. A successful - -[page 421] - - intervening call (with the stream pointed to by stream) to a file positioning function - (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the - stream. The external storage corresponding to the stream is unchanged. -3 One wide character of pushback is guaranteed, even if the call to the ungetwc function - follows just after a call to a formatted wide character input function fwscanf, - vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times - on the same stream without an intervening read or file positioning operation on that - stream, the operation may fail. -4 If the value of c equals that of the macro WEOF, the operation fails and the input stream is - unchanged. -5 A successful call to the ungetwc function clears the end-of-file indicator for the stream. - The value of the file position indicator for the stream after reading or discarding all - pushed-back wide characters is the same as it was before the wide characters were pushed - back. For a text or binary stream, the value of its file position indicator after a successful - call to the ungetwc function is unspecified until all pushed-back wide characters are - read or discarded. - Returns -6 The ungetwc function returns the wide character pushed back, or WEOF if the operation - fails. - 7.28.4 General wide string utilities -1 The header declares a number of functions useful for wide string - manipulation. Various methods are used for determining the lengths of the arrays, but in - all cases a wchar_t * argument points to the initial (lowest addressed) element of the - array. If an array is accessed beyond the end of an object, the behavior is undefined. -2 Where an argument declared as size_t n determines the length of the array for a - function, n can have the value zero on a call to that function. Unless explicitly stated - otherwise in the description of a particular function in this subclause, pointer arguments - on such a call shall still have valid values, as described in 7.1.4. On such a call, a - function that locates a wide character finds no occurrence, a function that compares two - wide character sequences returns zero, and a function that copies wide characters copies - zero wide characters. - -[page 422] - - 7.28.4.1 Wide string numeric conversion functions - 7.28.4.1.1 The wcstod, wcstof, and wcstold functions - Synopsis -1 #include - double wcstod(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - float wcstof(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - long double wcstold(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - Description -2 The wcstod, wcstof, and wcstold functions convert the initial portion of the wide - string pointed to by nptr to double, float, and long double representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space wide characters (as specified by the iswspace - function), a subject sequence resembling a floating-point constant or representing an - infinity or NaN; and a final wide string of one or more unrecognized wide characters, - including the terminating null wide character of the input wide string. Then, they attempt - to convert the subject sequence to a floating-point number, and return the result. -3 The expected form of the subject sequence is an optional plus or minus sign, then one of - the following: - -- a nonempty sequence of decimal digits optionally containing a decimal-point wide - character, then an optional exponent part as defined for the corresponding single-byte - characters in 6.4.4.2; - -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a - decimal-point wide character, then an optional binary exponent part as defined in - 6.4.4.2; - -- INF or INFINITY, or any other wide string equivalent except for case - -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for - case in the NAN part, where: - n-wchar-sequence: - digit - nondigit - n-wchar-sequence digit - n-wchar-sequence nondigit - The subject sequence is defined as the longest initial subsequence of the input wide - string, starting with the first non-white-space wide character, that is of the expected form. - -[page 423] - - The subject sequence contains no wide characters if the input wide string is not of the - expected form. -4 If the subject sequence has the expected form for a floating-point number, the sequence of - wide characters starting with the first digit or the decimal-point wide character - (whichever occurs first) is interpreted as a floating constant according to the rules of - 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that - if neither an exponent part nor a decimal-point wide character appears in a decimal - floating point number, or if a binary exponent part does not appear in a hexadecimal - floating point number, an exponent part of the appropriate type with value zero is - assumed to follow the last digit in the string. If the subject sequence begins with a minus - sign, the sequence is interpreted as negated.330) A wide character sequence INF or - INFINITY is interpreted as an infinity, if representable in the return type, else like a - floating constant that is too large for the range of the return type. A wide character - sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported - in the return type, else like a subject sequence part that does not have the expected form; - the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the - final wide string is stored in the object pointed to by endptr, provided that endptr is - not a null pointer. -5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the - value resulting from the conversion is correctly rounded. -6 In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -7 If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. - Recommended practice -8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and - the result is not exactly representable, the result should be one of the two numbers in the - appropriate internal format that are adjacent to the hexadecimal floating source value, - with the extra stipulation that the error should have a correct sign for the current rounding - direction. - - - - 330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two - methods may yield different results if rounding is toward positive or negative infinity. In either case, - the functions honor the sign of zero if floating-point arithmetic supports signed zeros. - 331) An implementation may use the n-wchar sequence to determine extra information to be represented in - the NaN's significand. - -[page 424] - -9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in - ) significant digits, the result should be correctly rounded. If the subject - sequence D has the decimal form and more than DECIMAL_DIG significant digits, - consider the two bounding, adjacent decimal strings L and U, both having - DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. - The result should be one of the (equal or adjacent) values that would be obtained by - correctly rounding L and U according to the current rounding direction, with the extra - stipulation that the error with respect to D should have a correct sign for the current - rounding direction.332) - Returns -10 The functions return the converted value, if any. If no conversion could be performed, - zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), - plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the - return type and sign of the value), and the value of the macro ERANGE is stored in - errno. If the result underflows (7.12.1), the functions return a value whose magnitude is - no greater than the smallest normalized positive number in the return type; whether - errno acquires the value ERANGE is implementation-defined. - - - - - 332) DECIMAL_DIG, defined in , should be sufficiently large that L and U will usually round - to the same internal floating value, but if not will round to adjacent values. - -[page 425] - - 7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions - Synopsis -1 #include - long int wcstol( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, - int base); - long long int wcstoll( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, - int base); - unsigned long int wcstoul( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, - int base); - unsigned long long int wcstoull( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, - int base); - Description -2 The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial - portion of the wide string pointed to by nptr to long int, long long int, - unsigned long int, and unsigned long long int representation, - respectively. First, they decompose the input string into three parts: an initial, possibly - empty, sequence of white-space wide characters (as specified by the iswspace - function), a subject sequence resembling an integer represented in some radix determined - by the value of base, and a final wide string of one or more unrecognized wide - characters, including the terminating null wide character of the input wide string. Then, - they attempt to convert the subject sequence to an integer, and return the result. -3 If the value of base is zero, the expected form of the subject sequence is that of an - integer constant as described for the corresponding single-byte characters in 6.4.4.1, - optionally preceded by a plus or minus sign, but not including an integer suffix. If the - value of base is between 2 and 36 (inclusive), the expected form of the subject sequence - is a sequence of letters and digits representing an integer with the radix specified by - base, optionally preceded by a plus or minus sign, but not including an integer suffix. - The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only - letters and digits whose ascribed values are less than that of base are permitted. If the - value of base is 16, the wide characters 0x or 0X may optionally precede the sequence - of letters and digits, following the sign if present. - -[page 426] - -4 The subject sequence is defined as the longest initial subsequence of the input wide - string, starting with the first non-white-space wide character, that is of the expected form. - The subject sequence contains no wide characters if the input wide string is empty or - consists entirely of white space, or if the first non-white-space wide character is other - than a sign or a permissible letter or digit. -5 If the subject sequence has the expected form and the value of base is zero, the sequence - of wide characters starting with the first digit is interpreted as an integer constant - according to the rules of 6.4.4.1. If the subject sequence has the expected form and the - value of base is between 2 and 36, it is used as the base for conversion, ascribing to each - letter its value as given above. If the subject sequence begins with a minus sign, the value - resulting from the conversion is negated (in the return type). A pointer to the final wide - string is stored in the object pointed to by endptr, provided that endptr is not a null - pointer. -6 In other than the "C" locale, additional locale-specific subject sequence forms may be - accepted. -7 If the subject sequence is empty or does not have the expected form, no conversion is - performed; the value of nptr is stored in the object pointed to by endptr, provided - that endptr is not a null pointer. - Returns -8 The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted - value, if any. If no conversion could be performed, zero is returned. If the correct value - is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, - LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type - sign of the value, if any), and the value of the macro ERANGE is stored in errno. - 7.28.4.2 Wide string copying functions - 7.28.4.2.1 The wcscpy function - Synopsis -1 #include - wchar_t *wcscpy(wchar_t * restrict s1, - const wchar_t * restrict s2); - Description -2 The wcscpy function copies the wide string pointed to by s2 (including the terminating - null wide character) into the array pointed to by s1. - Returns -3 The wcscpy function returns the value of s1. - -[page 427] - - 7.28.4.2.2 The wcsncpy function - Synopsis -1 #include - wchar_t *wcsncpy(wchar_t * restrict s1, - const wchar_t * restrict s2, - size_t n); - Description -2 The wcsncpy function copies not more than n wide characters (those that follow a null - wide character are not copied) from the array pointed to by s2 to the array pointed to by - s1.333) -3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null - wide characters are appended to the copy in the array pointed to by s1, until n wide - characters in all have been written. - Returns -4 The wcsncpy function returns the value of s1. - 7.28.4.2.3 The wmemcpy function - Synopsis -1 #include - wchar_t *wmemcpy(wchar_t * restrict s1, - const wchar_t * restrict s2, - size_t n); - Description -2 The wmemcpy function copies n wide characters from the object pointed to by s2 to the - object pointed to by s1. - Returns -3 The wmemcpy function returns the value of s1. - - - - - 333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the - result will not be null-terminated. - -[page 428] - - 7.28.4.2.4 The wmemmove function - Synopsis -1 #include - wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, - size_t n); - Description -2 The wmemmove function copies n wide characters from the object pointed to by s2 to - the object pointed to by s1. Copying takes place as if the n wide characters from the - object pointed to by s2 are first copied into a temporary array of n wide characters that - does not overlap the objects pointed to by s1 or s2, and then the n wide characters from - the temporary array are copied into the object pointed to by s1. - Returns -3 The wmemmove function returns the value of s1. - 7.28.4.3 Wide string concatenation functions - 7.28.4.3.1 The wcscat function - Synopsis -1 #include - wchar_t *wcscat(wchar_t * restrict s1, - const wchar_t * restrict s2); - Description -2 The wcscat function appends a copy of the wide string pointed to by s2 (including the - terminating null wide character) to the end of the wide string pointed to by s1. The initial - wide character of s2 overwrites the null wide character at the end of s1. - Returns -3 The wcscat function returns the value of s1. - 7.28.4.3.2 The wcsncat function - Synopsis -1 #include - wchar_t *wcsncat(wchar_t * restrict s1, - const wchar_t * restrict s2, - size_t n); - Description -2 The wcsncat function appends not more than n wide characters (a null wide character - and those that follow it are not appended) from the array pointed to by s2 to the end of - -[page 429] - - the wide string pointed to by s1. The initial wide character of s2 overwrites the null - wide character at the end of s1. A terminating null wide character is always appended to - the result.334) - Returns -3 The wcsncat function returns the value of s1. - 7.28.4.4 Wide string comparison functions -1 Unless explicitly stated otherwise, the functions described in this subclause order two - wide characters the same way as two integers of the underlying integer type designated - by wchar_t. - 7.28.4.4.1 The wcscmp function - Synopsis -1 #include - int wcscmp(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcscmp function compares the wide string pointed to by s1 to the wide string - pointed to by s2. - Returns -3 The wcscmp function returns an integer greater than, equal to, or less than zero, - accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the - wide string pointed to by s2. - 7.28.4.4.2 The wcscoll function - Synopsis -1 #include - int wcscoll(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcscoll function compares the wide string pointed to by s1 to the wide string - pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the - current locale. - Returns -3 The wcscoll function returns an integer greater than, equal to, or less than zero, - accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the - - - 334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is - wcslen(s1)+n+1. - -[page 430] - - wide string pointed to by s2 when both are interpreted as appropriate to the current - locale. - 7.28.4.4.3 The wcsncmp function - Synopsis -1 #include - int wcsncmp(const wchar_t *s1, const wchar_t *s2, - size_t n); - Description -2 The wcsncmp function compares not more than n wide characters (those that follow a - null wide character are not compared) from the array pointed to by s1 to the array - pointed to by s2. - Returns -3 The wcsncmp function returns an integer greater than, equal to, or less than zero, - accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal - to, or less than the possibly null-terminated array pointed to by s2. - 7.28.4.4.4 The wcsxfrm function - Synopsis -1 #include - size_t wcsxfrm(wchar_t * restrict s1, - const wchar_t * restrict s2, - size_t n); - Description -2 The wcsxfrm function transforms the wide string pointed to by s2 and places the - resulting wide string into the array pointed to by s1. The transformation is such that if - the wcscmp function is applied to two transformed wide strings, it returns a value greater - than, equal to, or less than zero, corresponding to the result of the wcscoll function - applied to the same two original wide strings. No more than n wide characters are placed - into the resulting array pointed to by s1, including the terminating null wide character. If - n is zero, s1 is permitted to be a null pointer. - Returns -3 The wcsxfrm function returns the length of the transformed wide string (not including - the terminating null wide character). If the value returned is n or greater, the contents of - the array pointed to by s1 are indeterminate. -4 EXAMPLE The value of the following expression is the length of the array needed to hold the - transformation of the wide string pointed to by s: - -[page 431] - - 1 + wcsxfrm(NULL, s, 0) - - 7.28.4.4.5 The wmemcmp function - Synopsis -1 #include - int wmemcmp(const wchar_t *s1, const wchar_t *s2, - size_t n); - Description -2 The wmemcmp function compares the first n wide characters of the object pointed to by - s1 to the first n wide characters of the object pointed to by s2. - Returns -3 The wmemcmp function returns an integer greater than, equal to, or less than zero, - accordingly as the object pointed to by s1 is greater than, equal to, or less than the object - pointed to by s2. - 7.28.4.5 Wide string search functions - 7.28.4.5.1 The wcschr function - Synopsis -1 #include - wchar_t *wcschr(const wchar_t *s, wchar_t c); - Description -2 The wcschr function locates the first occurrence of c in the wide string pointed to by s. - The terminating null wide character is considered to be part of the wide string. - Returns -3 The wcschr function returns a pointer to the located wide character, or a null pointer if - the wide character does not occur in the wide string. - 7.28.4.5.2 The wcscspn function - Synopsis -1 #include - size_t wcscspn(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcscspn function computes the length of the maximum initial segment of the wide - string pointed to by s1 which consists entirely of wide characters not from the wide - string pointed to by s2. - -[page 432] - - Returns -3 The wcscspn function returns the length of the segment. - 7.28.4.5.3 The wcspbrk function - Synopsis -1 #include - wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of - any wide character from the wide string pointed to by s2. - Returns -3 The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if - no wide character from s2 occurs in s1. - 7.28.4.5.4 The wcsrchr function - Synopsis -1 #include - wchar_t *wcsrchr(const wchar_t *s, wchar_t c); - Description -2 The wcsrchr function locates the last occurrence of c in the wide string pointed to by - s. The terminating null wide character is considered to be part of the wide string. - Returns -3 The wcsrchr function returns a pointer to the wide character, or a null pointer if c does - not occur in the wide string. - 7.28.4.5.5 The wcsspn function - Synopsis -1 #include - size_t wcsspn(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcsspn function computes the length of the maximum initial segment of the wide - string pointed to by s1 which consists entirely of wide characters from the wide string - pointed to by s2. - Returns -3 The wcsspn function returns the length of the segment. - -[page 433] - - 7.28.4.5.6 The wcsstr function - Synopsis -1 #include - wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2); - Description -2 The wcsstr function locates the first occurrence in the wide string pointed to by s1 of - the sequence of wide characters (excluding the terminating null wide character) in the - wide string pointed to by s2. - Returns -3 The wcsstr function returns a pointer to the located wide string, or a null pointer if the - wide string is not found. If s2 points to a wide string with zero length, the function - returns s1. - 7.28.4.5.7 The wcstok function - Synopsis -1 #include - wchar_t *wcstok(wchar_t * restrict s1, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); - Description -2 A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into - a sequence of tokens, each of which is delimited by a wide character from the wide string - pointed to by s2. The third argument points to a caller-provided wchar_t pointer into - which the wcstok function stores information necessary for it to continue scanning the - same wide string. -3 The first call in a sequence has a non-null first argument and stores an initial value in the - object pointed to by ptr. Subsequent calls in the sequence have a null first argument and - the object pointed to by ptr is required to have the value stored by the previous call in - the sequence, which is then updated. The separator wide string pointed to by s2 may be - different from call to call. -4 The first call in the sequence searches the wide string pointed to by s1 for the first wide - character that is not contained in the current separator wide string pointed to by s2. If no - such wide character is found, then there are no tokens in the wide string pointed to by s1 - and the wcstok function returns a null pointer. If such a wide character is found, it is - the start of the first token. -5 The wcstok function then searches from there for a wide character that is contained in - the current separator wide string. If no such wide character is found, the current token - -[page 434] - - extends to the end of the wide string pointed to by s1, and subsequent searches in the - same wide string for a token return a null pointer. If such a wide character is found, it is - overwritten by a null wide character, which terminates the current token. -6 In all cases, the wcstok function stores sufficient information in the pointer pointed to - by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null wide - character (if any). - Returns -7 The wcstok function returns a pointer to the first wide character of a token, or a null - pointer if there is no token. -8 EXAMPLE - #include - static wchar_t str1[] = L"?a???b,,,#c"; - static wchar_t str2[] = L"\t \t"; - wchar_t *t, *ptr1, *ptr2; - t = wcstok(str1, L"?", &ptr1); // t points to the token L"a" - t = wcstok(NULL, L",", &ptr1); // t points to the token L"??b" - t = wcstok(str2, L" \t", &ptr2); // t is a null pointer - t = wcstok(NULL, L"#,", &ptr1); // t points to the token L"c" - t = wcstok(NULL, L"?", &ptr1); // t is a null pointer - - 7.28.4.5.8 The wmemchr function - Synopsis -1 #include - wchar_t *wmemchr(const wchar_t *s, wchar_t c, - size_t n); - Description -2 The wmemchr function locates the first occurrence of c in the initial n wide characters of - the object pointed to by s. - Returns -3 The wmemchr function returns a pointer to the located wide character, or a null pointer if - the wide character does not occur in the object. - -[page 435] - - 7.28.4.6 Miscellaneous functions - 7.28.4.6.1 The wcslen function - Synopsis -1 #include - size_t wcslen(const wchar_t *s); - Description -2 The wcslen function computes the length of the wide string pointed to by s. - Returns -3 The wcslen function returns the number of wide characters that precede the terminating - null wide character. - 7.28.4.6.2 The wmemset function - Synopsis -1 #include - wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n); - Description -2 The wmemset function copies the value of c into each of the first n wide characters of - the object pointed to by s. - Returns -3 The wmemset function returns the value of s. - 7.28.5 Wide character time conversion functions - 7.28.5.1 The wcsftime function - Synopsis -1 #include - #include - size_t wcsftime(wchar_t * restrict s, - size_t maxsize, - const wchar_t * restrict format, - const struct tm * restrict timeptr); - Description -2 The wcsftime function is equivalent to the strftime function, except that: - -- The argument s points to the initial element of an array of wide characters into which - the generated output is to be placed. - -[page 436] - - -- The argument maxsize indicates the limiting number of wide characters. - -- The argument format is a wide string and the conversion specifiers are replaced by - corresponding sequences of wide characters. - -- The return value indicates the number of wide characters. - Returns -3 If the total number of resulting wide characters including the terminating null wide - character is not more than maxsize, the wcsftime function returns the number of - wide characters placed into the array pointed to by s not including the terminating null - wide character. Otherwise, zero is returned and the contents of the array are - indeterminate. - 7.28.6 Extended multibyte/wide character conversion utilities -1 The header declares an extended set of functions useful for conversion - between multibyte characters and wide characters. -2 Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and - 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used - to describe the current conversion state from a particular multibyte character sequence to - a wide character sequence (or the reverse) under the rules of a particular setting for the - LC_CTYPE category of the current locale. -3 The initial conversion state corresponds, for a conversion in either direction, to the - beginning of a new multibyte character in the initial shift state. A zero-valued - mbstate_t object is (at least) one way to describe an initial conversion state. A zero- - valued mbstate_t object can be used to initiate conversion involving any multibyte - character sequence, in any LC_CTYPE category setting. If an mbstate_t object has - been altered by any of the functions described in this subclause, and is then used with a - different multibyte character sequence, or in the other conversion direction, or with a - different LC_CTYPE category setting than on earlier function calls, the behavior is - undefined.335) -4 On entry, each function takes the described conversion state (either internal or pointed to - by an argument) as current. The conversion state described by the referenced object is - altered as needed to track the shift state, and the position within a multibyte character, for - the associated multibyte character sequence. - - - - - 335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and - mbsrtowcs functions as long as they are used to step sequentially through the same multibyte - character string. - -[page 437] - - 7.28.6.1 Single-byte/wide character conversion functions - 7.28.6.1.1 The btowc function - Synopsis -1 #include * - wint_t btowc(int c); - Description -2 The btowc function determines whether c constitutes a valid single-byte character in the - initial shift state. - Returns -3 The btowc function returns WEOF if c has the value EOF or if (unsigned char)c - does not constitute a valid single-byte character in the initial shift state. Otherwise, it - returns the wide character representation of that character. - 7.28.6.1.2 The wctob function - Synopsis -1 #include * - int wctob(wint_t c); - Description -2 The wctob function determines whether c corresponds to a member of the extended - character set whose multibyte character representation is a single byte when in the initial - shift state. - Returns -3 The wctob function returns EOF if c does not correspond to a multibyte character with - length one in the initial shift state. Otherwise, it returns the single-byte representation of - that character as an unsigned char converted to an int. - 7.28.6.2 Conversion state functions - 7.28.6.2.1 The mbsinit function - Synopsis -1 #include - int mbsinit(const mbstate_t *ps); - Description -2 If ps is not a null pointer, the mbsinit function determines whether the referenced - mbstate_t object describes an initial conversion state. - -[page 438] - - Returns -3 The mbsinit function returns nonzero if ps is a null pointer or if the referenced object - describes an initial conversion state; otherwise, it returns zero. - 7.28.6.3 Restartable multibyte/wide character conversion functions -1 These functions differ from the corresponding multibyte character functions of 7.22.7 - (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type - pointer to mbstate_t that points to an object that can completely describe the current - conversion state of the associated multibyte character sequence. If ps is a null pointer, - each function uses its own internal mbstate_t object instead, which is initialized at - program startup to the initial conversion state; the functions are not required to avoid data - races in this case. The implementation behaves as if no library function calls these - functions with a null pointer for ps. -2 Also unlike their corresponding functions, the return value does not represent whether the - encoding is state-dependent. - 7.28.6.3.1 The mbrlen function - Synopsis -1 #include - size_t mbrlen(const char * restrict s, - size_t n, - mbstate_t * restrict ps); - Description -2 The mbrlen function is equivalent to the call: - mbrtowc(NULL, s, n, ps != NULL ? ps : &internal) - where internal is the mbstate_t object for the mbrlen function, except that the - expression designated by ps is evaluated only once. - Returns -3 The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2), - or (size_t)(-1). - Forward references: the mbrtowc function (7.28.6.3.2). - -[page 439] - - 7.28.6.3.2 The mbrtowc function - Synopsis -1 #include - size_t mbrtowc(wchar_t * restrict pwc, - const char * restrict s, - size_t n, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the mbrtowc function is equivalent to the call: - mbrtowc(NULL, "", 1, ps) - In this case, the values of the parameters pwc and n are ignored. -3 If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with - the byte pointed to by s to determine the number of bytes needed to complete the next - multibyte character (including any shift sequences). If the function determines that the - next multibyte character is complete and valid, it determines the value of the - corresponding wide character and then, if pwc is not a null pointer, stores that value in - the object pointed to by pwc. If the corresponding wide character is the null wide - character, the resulting state described is the initial conversion state. - Returns -4 The mbrtowc function returns the first of the following that applies (given the current - conversion state): - 0 if the next n or fewer bytes complete the multibyte character that - corresponds to the null wide character (which is the value stored). - between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte - character (which is the value stored); the value returned is the number - of bytes that complete the multibyte character. - (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) - multibyte character, and all n bytes have been processed (no value is - stored).336) - (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes - do not contribute to a complete and valid multibyte character (no - value is stored); the value of the macro EILSEQ is stored in errno, - and the conversion state is unspecified. - - 336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a - sequence of redundant shift sequences (for implementations with state-dependent encodings). - -[page 440] - - 7.28.6.3.3 The wcrtomb function - Synopsis -1 #include - size_t wcrtomb(char * restrict s, - wchar_t wc, - mbstate_t * restrict ps); - Description -2 If s is a null pointer, the wcrtomb function is equivalent to the call - wcrtomb(buf, L'\0', ps) - where buf is an internal buffer. -3 If s is not a null pointer, the wcrtomb function determines the number of bytes needed - to represent the multibyte character that corresponds to the wide character given by wc - (including any shift sequences), and stores the multibyte character representation in the - array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If - wc is a null wide character, a null byte is stored, preceded by any shift sequence needed - to restore the initial shift state; the resulting state described is the initial conversion state. - Returns -4 The wcrtomb function returns the number of bytes stored in the array object (including - any shift sequences). When wc is not a valid wide character, an encoding error occurs: - the function stores the value of the macro EILSEQ in errno and returns - (size_t)(-1); the conversion state is unspecified. - 7.28.6.4 Restartable multibyte/wide string conversion functions -1 These functions differ from the corresponding multibyte string functions of 7.22.8 - (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to - mbstate_t that points to an object that can completely describe the current conversion - state of the associated multibyte character sequence. If ps is a null pointer, each function - uses its own internal mbstate_t object instead, which is initialized at program startup - to the initial conversion state; the functions are not required to avoid data races in this - case. The implementation behaves as if no library function calls these functions with a - null pointer for ps. -2 Also unlike their corresponding functions, the conversion source parameter, src, has a - pointer-to-pointer type. When the function is storing the results of conversions (that is, - when dst is not a null pointer), the pointer object pointed to by this parameter is updated - to reflect the amount of the source processed by that invocation. - -[page 441] - - 7.28.6.4.1 The mbsrtowcs function - Synopsis -1 #include - size_t mbsrtowcs(wchar_t * restrict dst, - const char ** restrict src, - size_t len, - mbstate_t * restrict ps); - Description -2 The mbsrtowcs function converts a sequence of multibyte characters that begins in the - conversion state described by the object pointed to by ps, from the array indirectly - pointed to by src into a sequence of corresponding wide characters. If dst is not a null - pointer, the converted characters are stored into the array pointed to by dst. Conversion - continues up to and including a terminating null character, which is also stored. - Conversion stops earlier in two cases: when a sequence of bytes is encountered that does - not form a valid multibyte character, or (if dst is not a null pointer) when len wide - characters have been stored into the array pointed to by dst.337) Each conversion takes - place as if by a call to the mbrtowc function. -3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null character) or the address - just past the last multibyte character converted (if any). If conversion stopped due to - reaching a terminating null character and if dst is not a null pointer, the resulting state - described is the initial conversion state. - Returns -4 If the input conversion encounters a sequence of bytes that do not form a valid multibyte - character, an encoding error occurs: the mbsrtowcs function stores the value of the - macro EILSEQ in errno and returns (size_t)(-1); the conversion state is - unspecified. Otherwise, it returns the number of multibyte characters successfully - converted, not including the terminating null character (if any). - - - - - 337) Thus, the value of len is ignored if dst is a null pointer. - -[page 442] - - 7.28.6.4.2 The wcsrtombs function - Synopsis -1 #include - size_t wcsrtombs(char * restrict dst, - const wchar_t ** restrict src, - size_t len, - mbstate_t * restrict ps); - Description -2 The wcsrtombs function converts a sequence of wide characters from the array - indirectly pointed to by src into a sequence of corresponding multibyte characters that - begins in the conversion state described by the object pointed to by ps. If dst is not a - null pointer, the converted characters are then stored into the array pointed to by dst. - Conversion continues up to and including a terminating null wide character, which is also - stored. Conversion stops earlier in two cases: when a wide character is reached that does - not correspond to a valid multibyte character, or (if dst is not a null pointer) when the - next multibyte character would exceed the limit of len total bytes to be stored into the - array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb - function.338) -3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null wide character) or the - address just past the last wide character converted (if any). If conversion stopped due to - reaching a terminating null wide character, the resulting state described is the initial - conversion state. - Returns -4 If conversion stops because a wide character is reached that does not correspond to a - valid multibyte character, an encoding error occurs: the wcsrtombs function stores the - value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion - state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte - character sequence, not including the terminating null character (if any). - - - - - 338) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. - -[page 443] - - 7.29 Wide character classification and mapping utilities - 7.29.1 Introduction -1 The header defines one macro, and declares three data types and many - functions.339) -2 The types declared are - wint_t - described in 7.28.1; - wctrans_t - which is a scalar type that can hold values which represent locale-specific character - mappings; and - wctype_t - which is a scalar type that can hold values which represent locale-specific character - classifications. -3 The macro defined is WEOF (described in 7.28.1). -4 The functions declared are grouped as follows: - -- Functions that provide wide character classification; - -- Extensible functions that provide wide character classification; - -- Functions that provide wide character case mapping; - -- Extensible functions that provide wide character mapping. -5 For all functions described in this subclause that accept an argument of type wint_t, the - value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If - this argument has any other value, the behavior is undefined. -6 The behavior of these functions is affected by the LC_CTYPE category of the current - locale. - - - - - 339) See ''future library directions'' (7.30.13). - -[page 444] - - 7.29.2 Wide character classification utilities -1 The header declares several functions useful for classifying wide - characters. -2 The term printing wide character refers to a member of a locale-specific set of wide - characters, each of which occupies at least one printing position on a display device. The - term control wide character refers to a member of a locale-specific set of wide characters - that are not printing wide characters. - 7.29.2.1 Wide character classification functions -1 The functions in this subclause return nonzero (true) if and only if the value of the - argument wc conforms to that in the description of the function. -2 Each of the following functions returns true for each wide character that corresponds (as - if by a call to the wctob function) to a single-byte character for which the corresponding - character classification function from 7.4.1 returns true, except that the iswgraph and - iswpunct functions may differ with respect to wide characters other than L' ' that are - both printing and white-space wide characters.340) - Forward references: the wctob function (7.28.6.1.2). - 7.29.2.1.1 The iswalnum function - Synopsis -1 #include - int iswalnum(wint_t wc); - Description -2 The iswalnum function tests for any wide character for which iswalpha or - iswdigit is true. - 7.29.2.1.2 The iswalpha function - Synopsis -1 #include - int iswalpha(wint_t wc); - Description -2 The iswalpha function tests for any wide character for which iswupper or - iswlower is true, or any wide character that is one of a locale-specific set of alphabetic - - 340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call - iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true - (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc) - && iswspace(wc) is true, but not both. - -[page 445] - - wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace - is true.341) - 7.29.2.1.3 The iswblank function - Synopsis -1 #include - int iswblank(wint_t wc); - Description -2 The iswblank function tests for any wide character that is a standard blank wide - character or is one of a locale-specific set of wide characters for which iswspace is true - and that is used to separate words within a line of text. The standard blank wide - characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C" - locale, iswblank returns true only for the standard blank characters. - 7.29.2.1.4 The iswcntrl function - Synopsis -1 #include - int iswcntrl(wint_t wc); - Description -2 The iswcntrl function tests for any control wide character. - 7.29.2.1.5 The iswdigit function - Synopsis -1 #include - int iswdigit(wint_t wc); - Description -2 The iswdigit function tests for any wide character that corresponds to a decimal-digit - character (as defined in 5.2.1). - 7.29.2.1.6 The iswgraph function - Synopsis -1 #include - int iswgraph(wint_t wc); - - - - - 341) The functions iswlower and iswupper test true or false separately for each of these additional - wide characters; all four combinations are possible. - -[page 446] - - Description -2 The iswgraph function tests for any wide character for which iswprint is true and - iswspace is false.342) - 7.29.2.1.7 The iswlower function - Synopsis -1 #include - int iswlower(wint_t wc); - Description -2 The iswlower function tests for any wide character that corresponds to a lowercase - letter or is one of a locale-specific set of wide characters for which none of iswcntrl, - iswdigit, iswpunct, or iswspace is true. - 7.29.2.1.8 The iswprint function - Synopsis -1 #include - int iswprint(wint_t wc); - Description -2 The iswprint function tests for any printing wide character. - 7.29.2.1.9 The iswpunct function - Synopsis -1 #include - int iswpunct(wint_t wc); - Description -2 The iswpunct function tests for any printing wide character that is one of a locale- - specific set of punctuation wide characters for which neither iswspace nor iswalnum - is true.342) - 7.29.2.1.10 The iswspace function - Synopsis -1 #include - int iswspace(wint_t wc); - - - - 342) Note that the behavior of the iswgraph and iswpunct functions may differ from their - corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution - characters other than ' '. - -[page 447] - - Description -2 The iswspace function tests for any wide character that corresponds to a locale-specific - set of white-space wide characters for which none of iswalnum, iswgraph, or - iswpunct is true. - 7.29.2.1.11 The iswupper function - Synopsis -1 #include - int iswupper(wint_t wc); - Description -2 The iswupper function tests for any wide character that corresponds to an uppercase - letter or is one of a locale-specific set of wide characters for which none of iswcntrl, - iswdigit, iswpunct, or iswspace is true. - 7.29.2.1.12 The iswxdigit function - Synopsis -1 #include - int iswxdigit(wint_t wc); - Description -2 The iswxdigit function tests for any wide character that corresponds to a - hexadecimal-digit character (as defined in 6.4.4.1). - 7.29.2.2 Extensible wide character classification functions -1 The functions wctype and iswctype provide extensible wide character classification - as well as testing equivalent to that performed by the functions described in the previous - subclause (7.29.2.1). - 7.29.2.2.1 The iswctype function - Synopsis -1 #include - int iswctype(wint_t wc, wctype_t desc); - Description -2 The iswctype function determines whether the wide character wc has the property - described by desc. The current setting of the LC_CTYPE category shall be the same as - during the call to wctype that returned the value desc. -3 Each of the following expressions has a truth-value equivalent to the call to the wide - character classification function (7.29.2.1) in the comment that follows the expression: - -[page 448] - - iswctype(wc, wctype("alnum")) // iswalnum(wc) - iswctype(wc, wctype("alpha")) // iswalpha(wc) - iswctype(wc, wctype("blank")) // iswblank(wc) - iswctype(wc, wctype("cntrl")) // iswcntrl(wc) - iswctype(wc, wctype("digit")) // iswdigit(wc) - iswctype(wc, wctype("graph")) // iswgraph(wc) - iswctype(wc, wctype("lower")) // iswlower(wc) - iswctype(wc, wctype("print")) // iswprint(wc) - iswctype(wc, wctype("punct")) // iswpunct(wc) - iswctype(wc, wctype("space")) // iswspace(wc) - iswctype(wc, wctype("upper")) // iswupper(wc) - iswctype(wc, wctype("xdigit")) // iswxdigit(wc) - Returns -4 The iswctype function returns nonzero (true) if and only if the value of the wide - character wc has the property described by desc. If desc is zero, the iswctype - function returns zero (false). - Forward references: the wctype function (7.29.2.2.2). - 7.29.2.2.2 The wctype function - Synopsis -1 #include - wctype_t wctype(const char *property); - Description -2 The wctype function constructs a value with type wctype_t that describes a class of - wide characters identified by the string argument property. -3 The strings listed in the description of the iswctype function shall be valid in all - locales as property arguments to the wctype function. - Returns -4 If property identifies a valid class of wide characters according to the LC_CTYPE - category of the current locale, the wctype function returns a nonzero value that is valid - as the second argument to the iswctype function; otherwise, it returns zero. - -[page 449] - - 7.29.3 Wide character case mapping utilities -1 The header declares several functions useful for mapping wide characters. - 7.29.3.1 Wide character case mapping functions - 7.29.3.1.1 The towlower function - Synopsis -1 #include - wint_t towlower(wint_t wc); - Description -2 The towlower function converts an uppercase letter to a corresponding lowercase letter. - Returns -3 If the argument is a wide character for which iswupper is true and there are one or - more corresponding wide characters, as specified by the current locale, for which - iswlower is true, the towlower function returns one of the corresponding wide - characters (always the same one for any given locale); otherwise, the argument is - returned unchanged. - 7.29.3.1.2 The towupper function - Synopsis -1 #include - wint_t towupper(wint_t wc); - Description -2 The towupper function converts a lowercase letter to a corresponding uppercase letter. - Returns -3 If the argument is a wide character for which iswlower is true and there are one or - more corresponding wide characters, as specified by the current locale, for which - iswupper is true, the towupper function returns one of the corresponding wide - characters (always the same one for any given locale); otherwise, the argument is - returned unchanged. - 7.29.3.2 Extensible wide character case mapping functions -1 The functions wctrans and towctrans provide extensible wide character mapping as - well as case mapping equivalent to that performed by the functions described in the - previous subclause (7.29.3.1). - -[page 450] - - 7.29.3.2.1 The towctrans function - Synopsis -1 #include - wint_t towctrans(wint_t wc, wctrans_t desc); - Description -2 The towctrans function maps the wide character wc using the mapping described by - desc. The current setting of the LC_CTYPE category shall be the same as during the call - to wctrans that returned the value desc. -3 Each of the following expressions behaves the same as the call to the wide character case - mapping function (7.29.3.1) in the comment that follows the expression: - towctrans(wc, wctrans("tolower")) // towlower(wc) - towctrans(wc, wctrans("toupper")) // towupper(wc) - Returns -4 The towctrans function returns the mapped value of wc using the mapping described - by desc. If desc is zero, the towctrans function returns the value of wc. - 7.29.3.2.2 The wctrans function - Synopsis -1 #include - wctrans_t wctrans(const char *property); - Description -2 The wctrans function constructs a value with type wctrans_t that describes a - mapping between wide characters identified by the string argument property. -3 The strings listed in the description of the towctrans function shall be valid in all - locales as property arguments to the wctrans function. - Returns -4 If property identifies a valid mapping of wide characters according to the LC_CTYPE - category of the current locale, the wctrans function returns a nonzero value that is valid - as the second argument to the towctrans function; otherwise, it returns zero. - -[page 451] - - 7.30 Future library directions -1 The following names are grouped under individual headers for convenience. All external - names described below are reserved no matter what headers are included by the program. - 7.30.1 Complex arithmetic -1 The function names - cerf cexpm1 clog2 - cerfc clog10 clgamma - cexp2 clog1p ctgamma - and the same names suffixed with f or l may be added to the declarations in the - header. - 7.30.2 Character handling -1 Function names that begin with either is or to, and a lowercase letter may be added to - the declarations in the header. - 7.30.3 Errors -1 Macros that begin with E and a digit or E and an uppercase letter may be added to the - declarations in the header. - 7.30.4 Format conversion of integer types -1 Macro names beginning with PRI or SCN followed by any lowercase letter or X may be - added to the macros defined in the header. - 7.30.5 Localization -1 Macros that begin with LC_ and an uppercase letter may be added to the definitions in - the header. - 7.30.6 Signal handling -1 Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase - letter may be added to the definitions in the header. - 7.30.7 Boolean type and values -1 The ability to undefine and perhaps then redefine the macros bool, true, and false is - an obsolescent feature. - 7.30.8 Integer types -1 Typedef names beginning with int or uint and ending with _t may be added to the - types defined in the header. Macro names beginning with INT or UINT - and ending with _MAX, _MIN, or _C may be added to the macros defined in the - header. - -[page 452] - - 7.30.9 Input/output -1 Lowercase letters may be added to the conversion specifiers and length modifiers in - fprintf and fscanf. Other characters may be used in extensions. -2 The use of ungetc on a binary stream where the file position indicator is zero prior to * - the call is an obsolescent feature. - 7.30.10 General utilities -1 Function names that begin with str and a lowercase letter may be added to the - declarations in the header. - 7.30.11 String handling -1 Function names that begin with str, mem, or wcs and a lowercase letter may be added - to the declarations in the header. - 7.30.12 Extended multibyte and wide character utilities -1 Function names that begin with wcs and a lowercase letter may be added to the - declarations in the header. -2 Lowercase letters may be added to the conversion specifiers and length modifiers in - fwprintf and fwscanf. Other characters may be used in extensions. - 7.30.13 Wide character classification and mapping utilities - -1 Function names that begin with is or to and a lowercase letter may be added to the - declarations in the header. - -[page 453] - - Annex A - (informative) - Language syntax summary -1 NOTE The notation is described in 6.1. - - A.1 Lexical grammar - A.1.1 Lexical elements - (6.4) token: - keyword - identifier - constant - string-literal - punctuator - (6.4) preprocessing-token: - header-name - identifier - pp-number - character-constant - string-literal - punctuator - each non-white-space character that cannot be one of the above - -[page 454] - -A.1.2 Keywords -(6.4.1) keyword: one of - alignof goto union - auto if unsigned - break inline void - case int volatile - char long while - const register _Alignas - continue restrict _Atomic - default return _Bool - do short _Complex - double signed _Generic - else sizeof _Imaginary - enum static _Noreturn - extern struct _Static_assert - float switch _Thread_local - for typedef -A.1.3 Identifiers -(6.4.2.1) identifier: - identifier-nondigit - identifier identifier-nondigit - identifier digit -(6.4.2.1) identifier-nondigit: - nondigit - universal-character-name - other implementation-defined characters -(6.4.2.1) nondigit: one of - _ a b c d e f g h i j k l m - n o p q r s t u v w x y z - A B C D E F G H I J K L M - N O P Q R S T U V W X Y Z -(6.4.2.1) digit: one of - 0 1 2 3 4 5 6 7 8 9 - -[page 455] - -A.1.4 Universal character names -(6.4.3) universal-character-name: - \u hex-quad - \U hex-quad hex-quad -(6.4.3) hex-quad: - hexadecimal-digit hexadecimal-digit - hexadecimal-digit hexadecimal-digit -A.1.5 Constants -(6.4.4) constant: - integer-constant - floating-constant - enumeration-constant - character-constant -(6.4.4.1) integer-constant: - decimal-constant integer-suffixopt - octal-constant integer-suffixopt - hexadecimal-constant integer-suffixopt -(6.4.4.1) decimal-constant: - nonzero-digit - decimal-constant digit -(6.4.4.1) octal-constant: - 0 - octal-constant octal-digit -(6.4.4.1) hexadecimal-constant: - hexadecimal-prefix hexadecimal-digit - hexadecimal-constant hexadecimal-digit -(6.4.4.1) hexadecimal-prefix: one of - 0x 0X -(6.4.4.1) nonzero-digit: one of - 1 2 3 4 5 6 7 8 9 -(6.4.4.1) octal-digit: one of - 0 1 2 3 4 5 6 7 - -[page 456] - -(6.4.4.1) hexadecimal-digit: one of - 0 1 2 3 4 5 6 7 8 9 - a b c d e f - A B C D E F -(6.4.4.1) integer-suffix: - unsigned-suffix long-suffixopt - unsigned-suffix long-long-suffix - long-suffix unsigned-suffixopt - long-long-suffix unsigned-suffixopt -(6.4.4.1) unsigned-suffix: one of - u U -(6.4.4.1) long-suffix: one of - l L -(6.4.4.1) long-long-suffix: one of - ll LL -(6.4.4.2) floating-constant: - decimal-floating-constant - hexadecimal-floating-constant -(6.4.4.2) decimal-floating-constant: - fractional-constant exponent-partopt floating-suffixopt - digit-sequence exponent-part floating-suffixopt -(6.4.4.2) hexadecimal-floating-constant: - hexadecimal-prefix hexadecimal-fractional-constant - binary-exponent-part floating-suffixopt - hexadecimal-prefix hexadecimal-digit-sequence - binary-exponent-part floating-suffixopt -(6.4.4.2) fractional-constant: - digit-sequenceopt . digit-sequence - digit-sequence . -(6.4.4.2) exponent-part: - e signopt digit-sequence - E signopt digit-sequence -(6.4.4.2) sign: one of - + - - -[page 457] - -(6.4.4.2) digit-sequence: - digit - digit-sequence digit -(6.4.4.2) hexadecimal-fractional-constant: - hexadecimal-digit-sequenceopt . - hexadecimal-digit-sequence - hexadecimal-digit-sequence . -(6.4.4.2) binary-exponent-part: - p signopt digit-sequence - P signopt digit-sequence -(6.4.4.2) hexadecimal-digit-sequence: - hexadecimal-digit - hexadecimal-digit-sequence hexadecimal-digit -(6.4.4.2) floating-suffix: one of - f l F L -(6.4.4.3) enumeration-constant: - identifier -(6.4.4.4) character-constant: - ' c-char-sequence ' - L' c-char-sequence ' - u' c-char-sequence ' - U' c-char-sequence ' -(6.4.4.4) c-char-sequence: - c-char - c-char-sequence c-char -(6.4.4.4) c-char: - any member of the source character set except - the single-quote ', backslash \, or new-line character - escape-sequence -(6.4.4.4) escape-sequence: - simple-escape-sequence - octal-escape-sequence - hexadecimal-escape-sequence - universal-character-name - -[page 458] - -(6.4.4.4) simple-escape-sequence: one of - \' \" \? \\ - \a \b \f \n \r \t \v -(6.4.4.4) octal-escape-sequence: - \ octal-digit - \ octal-digit octal-digit - \ octal-digit octal-digit octal-digit -(6.4.4.4) hexadecimal-escape-sequence: - \x hexadecimal-digit - hexadecimal-escape-sequence hexadecimal-digit -A.1.6 String literals -(6.4.5) string-literal: - encoding-prefixopt " s-char-sequenceopt " -(6.4.5) encoding-prefix: - u8 - u - U - L -(6.4.5) s-char-sequence: - s-char - s-char-sequence s-char -(6.4.5) s-char: - any member of the source character set except - the double-quote ", backslash \, or new-line character - escape-sequence -A.1.7 Punctuators -(6.4.6) punctuator: one of - [ ] ( ) { } . -> - ++ -- & * + - ~ ! - / % << >> < > <= >= == != ^ | && || - ? : ; ... - = *= /= %= += -= <<= >>= &= ^= |= - , # ## - <: :> <% %> %: %:%: - -[page 459] - -A.1.8 Header names -(6.4.7) header-name: - < h-char-sequence > - " q-char-sequence " -(6.4.7) h-char-sequence: - h-char - h-char-sequence h-char -(6.4.7) h-char: - any member of the source character set except - the new-line character and > -(6.4.7) q-char-sequence: - q-char - q-char-sequence q-char -(6.4.7) q-char: - any member of the source character set except - the new-line character and " -A.1.9 Preprocessing numbers -(6.4.8) pp-number: - digit - . digit - pp-number digit - pp-number identifier-nondigit - pp-number e sign - pp-number E sign - pp-number p sign - pp-number P sign - pp-number . - -[page 460] - -A.2 Phrase structure grammar -A.2.1 Expressions -(6.5.1) primary-expression: - identifier - constant - string-literal - ( expression ) - generic-selection -(6.5.1.1) generic-selection: - _Generic ( assignment-expression , generic-assoc-list ) -(6.5.1.1) generic-assoc-list: - generic-association - generic-assoc-list , generic-association -(6.5.1.1) generic-association: - type-name : assignment-expression - default : assignment-expression -(6.5.2) postfix-expression: - primary-expression - postfix-expression [ expression ] - postfix-expression ( argument-expression-listopt ) - postfix-expression . identifier - postfix-expression -> identifier - postfix-expression ++ - postfix-expression -- - ( type-name ) { initializer-list } - ( type-name ) { initializer-list , } -(6.5.2) argument-expression-list: - assignment-expression - argument-expression-list , assignment-expression -(6.5.3) unary-expression: - postfix-expression - ++ unary-expression - -- unary-expression - unary-operator cast-expression - sizeof unary-expression - sizeof ( type-name ) - alignof ( type-name ) - -[page 461] - -(6.5.3) unary-operator: one of - & * + - ~ ! -(6.5.4) cast-expression: - unary-expression - ( type-name ) cast-expression -(6.5.5) multiplicative-expression: - cast-expression - multiplicative-expression * cast-expression - multiplicative-expression / cast-expression - multiplicative-expression % cast-expression -(6.5.6) additive-expression: - multiplicative-expression - additive-expression + multiplicative-expression - additive-expression - multiplicative-expression -(6.5.7) shift-expression: - additive-expression - shift-expression << additive-expression - shift-expression >> additive-expression -(6.5.8) relational-expression: - shift-expression - relational-expression < shift-expression - relational-expression > shift-expression - relational-expression <= shift-expression - relational-expression >= shift-expression -(6.5.9) equality-expression: - relational-expression - equality-expression == relational-expression - equality-expression != relational-expression -(6.5.10) AND-expression: - equality-expression - AND-expression & equality-expression -(6.5.11) exclusive-OR-expression: - AND-expression - exclusive-OR-expression ^ AND-expression - -[page 462] - -(6.5.12) inclusive-OR-expression: - exclusive-OR-expression - inclusive-OR-expression | exclusive-OR-expression -(6.5.13) logical-AND-expression: - inclusive-OR-expression - logical-AND-expression && inclusive-OR-expression -(6.5.14) logical-OR-expression: - logical-AND-expression - logical-OR-expression || logical-AND-expression -(6.5.15) conditional-expression: - logical-OR-expression - logical-OR-expression ? expression : conditional-expression -(6.5.16) assignment-expression: - conditional-expression - unary-expression assignment-operator assignment-expression -(6.5.16) assignment-operator: one of - = *= /= %= += -= <<= >>= &= ^= |= -(6.5.17) expression: - assignment-expression - expression , assignment-expression -(6.6) constant-expression: - conditional-expression -A.2.2 Declarations -(6.7) declaration: - declaration-specifiers init-declarator-listopt ; - static_assert-declaration -(6.7) declaration-specifiers: - storage-class-specifier declaration-specifiersopt - type-specifier declaration-specifiersopt - type-qualifier declaration-specifiersopt - function-specifier declaration-specifiersopt - alignment-specifier declaration-specifiersopt -(6.7) init-declarator-list: - init-declarator - init-declarator-list , init-declarator - -[page 463] - -(6.7) init-declarator: - declarator - declarator = initializer -(6.7.1) storage-class-specifier: - typedef - extern - static - _Thread_local - auto - register -(6.7.2) type-specifier: - void - char - short - int - long - float - double - signed - unsigned - _Bool - _Complex - atomic-type-specifier - struct-or-union-specifier - enum-specifier - typedef-name -(6.7.2.1) struct-or-union-specifier: - struct-or-union identifieropt { struct-declaration-list } - struct-or-union identifier -(6.7.2.1) struct-or-union: - struct - union -(6.7.2.1) struct-declaration-list: - struct-declaration - struct-declaration-list struct-declaration -(6.7.2.1) struct-declaration: - specifier-qualifier-list struct-declarator-listopt ; - static_assert-declaration - -[page 464] - -(6.7.2.1) specifier-qualifier-list: - type-specifier specifier-qualifier-listopt - type-qualifier specifier-qualifier-listopt -(6.7.2.1) struct-declarator-list: - struct-declarator - struct-declarator-list , struct-declarator -(6.7.2.1) struct-declarator: - declarator - declaratoropt : constant-expression -(6.7.2.2) enum-specifier: - enum identifieropt { enumerator-list } - enum identifieropt { enumerator-list , } - enum identifier -(6.7.2.2) enumerator-list: - enumerator - enumerator-list , enumerator -(6.7.2.2) enumerator: - enumeration-constant - enumeration-constant = constant-expression -(6.7.2.4) atomic-type-specifier: - _Atomic ( type-name ) -(6.7.3) type-qualifier: - const - restrict - volatile - _Atomic -(6.7.4) function-specifier: - inline - _Noreturn -(6.7.5) alignment-specifier: - _Alignas ( type-name ) - _Alignas ( constant-expression ) -(6.7.6) declarator: - pointeropt direct-declarator - -[page 465] - -(6.7.6) direct-declarator: - identifier - ( declarator ) - direct-declarator [ type-qualifier-listopt assignment-expressionopt ] - direct-declarator [ static type-qualifier-listopt assignment-expression ] - direct-declarator [ type-qualifier-list static assignment-expression ] - direct-declarator [ type-qualifier-listopt * ] - direct-declarator ( parameter-type-list ) - direct-declarator ( identifier-listopt ) -(6.7.6) pointer: - * type-qualifier-listopt - * type-qualifier-listopt pointer -(6.7.6) type-qualifier-list: - type-qualifier - type-qualifier-list type-qualifier -(6.7.6) parameter-type-list: - parameter-list - parameter-list , ... -(6.7.6) parameter-list: - parameter-declaration - parameter-list , parameter-declaration -(6.7.6) parameter-declaration: - declaration-specifiers declarator - declaration-specifiers abstract-declaratoropt -(6.7.6) identifier-list: - identifier - identifier-list , identifier -(6.7.7) type-name: - specifier-qualifier-list abstract-declaratoropt -(6.7.7) abstract-declarator: - pointer - pointeropt direct-abstract-declarator - -[page 466] - -(6.7.7) direct-abstract-declarator: - ( abstract-declarator ) - direct-abstract-declaratoropt [ type-qualifier-listopt - assignment-expressionopt ] - direct-abstract-declaratoropt [ static type-qualifier-listopt - assignment-expression ] - direct-abstract-declaratoropt [ type-qualifier-list static - assignment-expression ] - direct-abstract-declaratoropt [ * ] - direct-abstract-declaratoropt ( parameter-type-listopt ) -(6.7.8) typedef-name: - identifier -(6.7.9) initializer: - assignment-expression - { initializer-list } - { initializer-list , } -(6.7.9) initializer-list: - designationopt initializer - initializer-list , designationopt initializer -(6.7.9) designation: - designator-list = -(6.7.9) designator-list: - designator - designator-list designator -(6.7.9) designator: - [ constant-expression ] - . identifier -(6.7.10) static_assert-declaration: - _Static_assert ( constant-expression , string-literal ) ; - -[page 467] - -A.2.3 Statements -(6.8) statement: - labeled-statement - compound-statement - expression-statement - selection-statement - iteration-statement - jump-statement -(6.8.1) labeled-statement: - identifier : statement - case constant-expression : statement - default : statement -(6.8.2) compound-statement: - { block-item-listopt } -(6.8.2) block-item-list: - block-item - block-item-list block-item -(6.8.2) block-item: - declaration - statement -(6.8.3) expression-statement: - expressionopt ; -(6.8.4) selection-statement: - if ( expression ) statement - if ( expression ) statement else statement - switch ( expression ) statement -(6.8.5) iteration-statement: - while ( expression ) statement - do statement while ( expression ) ; - for ( expressionopt ; expressionopt ; expressionopt ) statement - for ( declaration expressionopt ; expressionopt ) statement -(6.8.6) jump-statement: - goto identifier ; - continue ; - break ; - return expressionopt ; - -[page 468] - -A.2.4 External definitions -(6.9) translation-unit: - external-declaration - translation-unit external-declaration -(6.9) external-declaration: - function-definition - declaration -(6.9.1) function-definition: - declaration-specifiers declarator declaration-listopt compound-statement -(6.9.1) declaration-list: - declaration - declaration-list declaration -A.3 Preprocessing directives -(6.10) preprocessing-file: - groupopt -(6.10) group: - group-part - group group-part -(6.10) group-part: - if-section - control-line - text-line - # non-directive -(6.10) if-section: - if-group elif-groupsopt else-groupopt endif-line -(6.10) if-group: - # if constant-expression new-line groupopt - # ifdef identifier new-line groupopt - # ifndef identifier new-line groupopt -(6.10) elif-groups: - elif-group - elif-groups elif-group -(6.10) elif-group: - # elif constant-expression new-line groupopt - -[page 469] - -(6.10) else-group: - # else new-line groupopt -(6.10) endif-line: - # endif new-line -(6.10) control-line: - # include pp-tokens new-line - # define identifier replacement-list new-line - # define identifier lparen identifier-listopt ) - replacement-list new-line - # define identifier lparen ... ) replacement-list new-line - # define identifier lparen identifier-list , ... ) - replacement-list new-line - # undef identifier new-line - # line pp-tokens new-line - # error pp-tokensopt new-line - # pragma pp-tokensopt new-line - # new-line -(6.10) text-line: - pp-tokensopt new-line -(6.10) non-directive: - pp-tokens new-line -(6.10) lparen: - a ( character not immediately preceded by white-space -(6.10) replacement-list: - pp-tokensopt -(6.10) pp-tokens: - preprocessing-token - pp-tokens preprocessing-token -(6.10) new-line: - the new-line character - -[page 470] - - Annex B - (informative) - Library summary -B.1 Diagnostics - NDEBUG - static_assert - void assert(scalar expression); -B.2 Complex - __STDC_NO_COMPLEX__ imaginary - complex _Imaginary_I - _Complex_I I - #pragma STDC CX_LIMITED_RANGE on-off-switch - double complex cacos(double complex z); - float complex cacosf(float complex z); - long double complex cacosl(long double complex z); - double complex casin(double complex z); - float complex casinf(float complex z); - long double complex casinl(long double complex z); - double complex catan(double complex z); - float complex catanf(float complex z); - long double complex catanl(long double complex z); - double complex ccos(double complex z); - float complex ccosf(float complex z); - long double complex ccosl(long double complex z); - double complex csin(double complex z); - float complex csinf(float complex z); - long double complex csinl(long double complex z); - double complex ctan(double complex z); - float complex ctanf(float complex z); - long double complex ctanl(long double complex z); - double complex cacosh(double complex z); - float complex cacoshf(float complex z); - long double complex cacoshl(long double complex z); - double complex casinh(double complex z); - float complex casinhf(float complex z); - long double complex casinhl(long double complex z); - -[page 471] - - double complex catanh(double complex z); - float complex catanhf(float complex z); - long double complex catanhl(long double complex z); - double complex ccosh(double complex z); - float complex ccoshf(float complex z); - long double complex ccoshl(long double complex z); - double complex csinh(double complex z); - float complex csinhf(float complex z); - long double complex csinhl(long double complex z); - double complex ctanh(double complex z); - float complex ctanhf(float complex z); - long double complex ctanhl(long double complex z); - double complex cexp(double complex z); - float complex cexpf(float complex z); - long double complex cexpl(long double complex z); - double complex clog(double complex z); - float complex clogf(float complex z); - long double complex clogl(long double complex z); - double cabs(double complex z); - float cabsf(float complex z); - long double cabsl(long double complex z); - double complex cpow(double complex x, double complex y); - float complex cpowf(float complex x, float complex y); - long double complex cpowl(long double complex x, - long double complex y); - double complex csqrt(double complex z); - float complex csqrtf(float complex z); - long double complex csqrtl(long double complex z); - double carg(double complex z); - float cargf(float complex z); - long double cargl(long double complex z); - double cimag(double complex z); - float cimagf(float complex z); - long double cimagl(long double complex z); - double complex CMPLX(double x, double y); - float complex CMPLXF(float x, float y); - long double complex CMPLXL(long double x, long double y); - double complex conj(double complex z); - float complex conjf(float complex z); - long double complex conjl(long double complex z); - double complex cproj(double complex z); - -[page 472] - - float complex cprojf(float complex z); - long double complex cprojl(long double complex z); - double creal(double complex z); - float crealf(float complex z); - long double creall(long double complex z); -B.3 Character handling - int isalnum(int c); - int isalpha(int c); - int isblank(int c); - int iscntrl(int c); - int isdigit(int c); - int isgraph(int c); - int islower(int c); - int isprint(int c); - int ispunct(int c); - int isspace(int c); - int isupper(int c); - int isxdigit(int c); - int tolower(int c); - int toupper(int c); -B.4 Errors - EDOM EILSEQ ERANGE errno - __STDC_WANT_LIB_EXT1__ - errno_t -B.5 Floating-point environment - fenv_t FE_OVERFLOW FE_TOWARDZERO - fexcept_t FE_UNDERFLOW FE_UPWARD - FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV - FE_INEXACT FE_DOWNWARD - FE_INVALID FE_TONEAREST - #pragma STDC FENV_ACCESS on-off-switch - int feclearexcept(int excepts); - int fegetexceptflag(fexcept_t *flagp, int excepts); - int feraiseexcept(int excepts); - int fesetexceptflag(const fexcept_t *flagp, - int excepts); - int fetestexcept(int excepts); - -[page 473] - - int fegetround(void); - int fesetround(int round); - int fegetenv(fenv_t *envp); - int feholdexcept(fenv_t *envp); - int fesetenv(const fenv_t *envp); - int feupdateenv(const fenv_t *envp); -B.6 Characteristics of floating types - FLT_ROUNDS DBL_DIG FLT_MAX - FLT_EVAL_METHOD LDBL_DIG DBL_MAX - FLT_HAS_SUBNORM FLT_MIN_EXP LDBL_MAX - DBL_HAS_SUBNORM DBL_MIN_EXP FLT_EPSILON - LDBL_HAS_SUBNORM LDBL_MIN_EXP DBL_EPSILON - FLT_RADIX FLT_MIN_10_EXP LDBL_EPSILON - FLT_MANT_DIG DBL_MIN_10_EXP FLT_MIN - DBL_MANT_DIG LDBL_MIN_10_EXP DBL_MIN - LDBL_MANT_DIG FLT_MAX_EXP LDBL_MIN - FLT_DECIMAL_DIG DBL_MAX_EXP FLT_TRUE_MIN - DBL_DECIMAL_DIG LDBL_MAX_EXP DBL_TRUE_MIN - LDBL_DECIMAL_DIG FLT_MAX_10_EXP LDBL_TRUE_MIN - DECIMAL_DIG DBL_MAX_10_EXP - FLT_DIG LDBL_MAX_10_EXP -B.7 Format conversion of integer types - imaxdiv_t - PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR - PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR - PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR - PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR - PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR - PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR - SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR - SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR - SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR - SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR - SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR - intmax_t imaxabs(intmax_t j); - imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); - intmax_t strtoimax(const char * restrict nptr, - char ** restrict endptr, int base); - -[page 474] - - uintmax_t strtoumax(const char * restrict nptr, - char ** restrict endptr, int base); - intmax_t wcstoimax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - uintmax_t wcstoumax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); -B.8 Alternative spellings - and bitor not_eq xor - and_eq compl or xor_eq - bitand not or_eq -B.9 Sizes of integer types - CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX - SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN - SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX - UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX - CHAR_MIN USHRT_MAX LONG_MAX -B.10 Localization - struct lconv LC_ALL LC_CTYPE LC_NUMERIC - NULL LC_COLLATE LC_MONETARY LC_TIME - char *setlocale(int category, const char *locale); - struct lconv *localeconv(void); -B.11 Mathematics - float_t FP_INFINITE FP_FAST_FMAL - double_t FP_NAN FP_ILOGB0 - HUGE_VAL FP_NORMAL FP_ILOGBNAN - HUGE_VALF FP_SUBNORMAL MATH_ERRNO - HUGE_VALL FP_ZERO MATH_ERREXCEPT - INFINITY FP_FAST_FMA math_errhandling - NAN FP_FAST_FMAF - #pragma STDC FP_CONTRACT on-off-switch - int fpclassify(real-floating x); - int isfinite(real-floating x); - int isinf(real-floating x); - int isnan(real-floating x); - int isnormal(real-floating x); - int signbit(real-floating x); - -[page 475] - - double acos(double x); - float acosf(float x); - long double acosl(long double x); - double asin(double x); - float asinf(float x); - long double asinl(long double x); - double atan(double x); - float atanf(float x); - long double atanl(long double x); - double atan2(double y, double x); - float atan2f(float y, float x); - long double atan2l(long double y, long double x); - double cos(double x); - float cosf(float x); - long double cosl(long double x); - double sin(double x); - float sinf(float x); - long double sinl(long double x); - double tan(double x); - float tanf(float x); - long double tanl(long double x); - double acosh(double x); - float acoshf(float x); - long double acoshl(long double x); - double asinh(double x); - float asinhf(float x); - long double asinhl(long double x); - double atanh(double x); - float atanhf(float x); - long double atanhl(long double x); - double cosh(double x); - float coshf(float x); - long double coshl(long double x); - double sinh(double x); - float sinhf(float x); - long double sinhl(long double x); - double tanh(double x); - float tanhf(float x); - long double tanhl(long double x); - double exp(double x); - float expf(float x); - -[page 476] - - long double expl(long double x); - double exp2(double x); - float exp2f(float x); - long double exp2l(long double x); - double expm1(double x); - float expm1f(float x); - long double expm1l(long double x); - double frexp(double value, int *exp); - float frexpf(float value, int *exp); - long double frexpl(long double value, int *exp); - int ilogb(double x); - int ilogbf(float x); - int ilogbl(long double x); - double ldexp(double x, int exp); - float ldexpf(float x, int exp); - long double ldexpl(long double x, int exp); - double log(double x); - float logf(float x); - long double logl(long double x); - double log10(double x); - float log10f(float x); - long double log10l(long double x); - double log1p(double x); - float log1pf(float x); - long double log1pl(long double x); - double log2(double x); - float log2f(float x); - long double log2l(long double x); - double logb(double x); - float logbf(float x); - long double logbl(long double x); - double modf(double value, double *iptr); - float modff(float value, float *iptr); - long double modfl(long double value, long double *iptr); - double scalbn(double x, int n); - float scalbnf(float x, int n); - long double scalbnl(long double x, int n); - double scalbln(double x, long int n); - float scalblnf(float x, long int n); - long double scalblnl(long double x, long int n); - double cbrt(double x); - -[page 477] - - float cbrtf(float x); - long double cbrtl(long double x); - double fabs(double x); - float fabsf(float x); - long double fabsl(long double x); - double hypot(double x, double y); - float hypotf(float x, float y); - long double hypotl(long double x, long double y); - double pow(double x, double y); - float powf(float x, float y); - long double powl(long double x, long double y); - double sqrt(double x); - float sqrtf(float x); - long double sqrtl(long double x); - double erf(double x); - float erff(float x); - long double erfl(long double x); - double erfc(double x); - float erfcf(float x); - long double erfcl(long double x); - double lgamma(double x); - float lgammaf(float x); - long double lgammal(long double x); - double tgamma(double x); - float tgammaf(float x); - long double tgammal(long double x); - double ceil(double x); - float ceilf(float x); - long double ceill(long double x); - double floor(double x); - float floorf(float x); - long double floorl(long double x); - double nearbyint(double x); - float nearbyintf(float x); - long double nearbyintl(long double x); - double rint(double x); - float rintf(float x); - long double rintl(long double x); - long int lrint(double x); - long int lrintf(float x); - long int lrintl(long double x); - -[page 478] - - long long int llrint(double x); - long long int llrintf(float x); - long long int llrintl(long double x); - double round(double x); - float roundf(float x); - long double roundl(long double x); - long int lround(double x); - long int lroundf(float x); - long int lroundl(long double x); - long long int llround(double x); - long long int llroundf(float x); - long long int llroundl(long double x); - double trunc(double x); - float truncf(float x); - long double truncl(long double x); - double fmod(double x, double y); - float fmodf(float x, float y); - long double fmodl(long double x, long double y); - double remainder(double x, double y); - float remainderf(float x, float y); - long double remainderl(long double x, long double y); - double remquo(double x, double y, int *quo); - float remquof(float x, float y, int *quo); - long double remquol(long double x, long double y, - int *quo); - double copysign(double x, double y); - float copysignf(float x, float y); - long double copysignl(long double x, long double y); - double nan(const char *tagp); - float nanf(const char *tagp); - long double nanl(const char *tagp); - double nextafter(double x, double y); - float nextafterf(float x, float y); - long double nextafterl(long double x, long double y); - double nexttoward(double x, long double y); - float nexttowardf(float x, long double y); - long double nexttowardl(long double x, long double y); - double fdim(double x, double y); - float fdimf(float x, float y); - long double fdiml(long double x, long double y); - double fmax(double x, double y); - -[page 479] - - float fmaxf(float x, float y); - long double fmaxl(long double x, long double y); - double fmin(double x, double y); - float fminf(float x, float y); - long double fminl(long double x, long double y); - double fma(double x, double y, double z); - float fmaf(float x, float y, float z); - long double fmal(long double x, long double y, - long double z); - int isgreater(real-floating x, real-floating y); - int isgreaterequal(real-floating x, real-floating y); - int isless(real-floating x, real-floating y); - int islessequal(real-floating x, real-floating y); - int islessgreater(real-floating x, real-floating y); - int isunordered(real-floating x, real-floating y); -B.12 Nonlocal jumps - jmp_buf - int setjmp(jmp_buf env); - _Noreturn void longjmp(jmp_buf env, int val); -B.13 Signal handling - sig_atomic_t SIG_IGN SIGILL SIGTERM - SIG_DFL SIGABRT SIGINT - SIG_ERR SIGFPE SIGSEGV - void (*signal(int sig, void (*func)(int)))(int); - int raise(int sig); - -[page 480] - -B.14 Alignment - alignas - __alignas_is_defined -B.15 Variable arguments - va_list - type va_arg(va_list ap, type); - void va_copy(va_list dest, va_list src); - void va_end(va_list ap); - void va_start(va_list ap, parmN); -B.16 Atomics - ATOMIC_CHAR_LOCK_FREE atomic_uint - ATOMIC_CHAR16_T_LOCK_FREE atomic_long - ATOMIC_CHAR32_T_LOCK_FREE atomic_ulong - ATOMIC_WCHAR_T_LOCK_FREE atomic_llong - ATOMIC_SHORT_LOCK_FREE atomic_ullong - ATOMIC_INT_LOCK_FREE atomic_char16_t - ATOMIC_LONG_LOCK_FREE atomic_char32_t - ATOMIC_LLONG_LOCK_FREE atomic_wchar_t - ATOMIC_ADDRESS_LOCK_FREE atomic_int_least8_t - ATOMIC_FLAG_INIT atomic_uint_least8_t - memory_order atomic_int_least16_t - atomic_flag atomic_uint_least16_t - atomic_bool atomic_int_least32_t - atomic_address atomic_uint_least32_t - memory_order_relaxed atomic_int_least64_t - memory_order_consume atomic_uint_least64_t - memory_order_acquire atomic_int_fast8_t - memory_order_release atomic_uint_fast8_t - memory_order_acq_rel atomic_int_fast16_t - memory_order_seq_cst atomic_uint_fast16_t - atomic_char atomic_int_fast32_t - atomic_schar atomic_uint_fast32_t - atomic_uchar atomic_int_fast64_t - atomic_short atomic_uint_fast64_t - atomic_ushort atomic_intptr_t - atomic_int atomic_uintptr_t - -[page 481] - - atomic_size_t atomic_intmax_t - atomic_ptrdiff_t atomic_uintmax_t - #define ATOMIC_VAR_INIT(C value) - void atomic_init(volatile A *obj, C value); - type kill_dependency(type y); - void atomic_thread_fence(memory_order order); - void atomic_signal_fence(memory_order order); - _Bool atomic_is_lock_free(atomic_type const volatile *obj); - void atomic_store(volatile A *object, C desired); - void atomic_store_explicit(volatile A *object, - C desired, memory_order order); - C atomic_load(volatile A *object); - C atomic_load_explicit(volatile A *object, - memory_order order); - C atomic_exchange(volatile A *object, C desired); - C atomic_exchange_explicit(volatile A *object, - C desired, memory_order order); - _Bool atomic_compare_exchange_strong(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_strong_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - _Bool atomic_compare_exchange_weak(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_weak_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - C atomic_fetch_key(volatile A *object, M operand); - C atomic_fetch_key_explicit(volatile A *object, - M operand, memory_order order); - bool atomic_flag_test_and_set( - volatile atomic_flag *object); - bool atomic_flag_test_and_set_explicit( - volatile atomic_flag *object, memory_order order); - void atomic_flag_clear(volatile atomic_flag *object); - void atomic_flag_clear_explicit( - volatile atomic_flag *object, memory_order order); - -[page 482] - -B.17 Boolean type and values - bool - true - false - __bool_true_false_are_defined -B.18 Common definitions - ptrdiff_t max_align_t NULL - size_t wchar_t - offsetof(type, member-designator) - __STDC_WANT_LIB_EXT1__ - rsize_t -B.19 Integer types - intN_t INT_LEASTN_MIN PTRDIFF_MAX - uintN_t INT_LEASTN_MAX SIG_ATOMIC_MIN - int_leastN_t UINT_LEASTN_MAX SIG_ATOMIC_MAX - uint_leastN_t INT_FASTN_MIN SIZE_MAX - int_fastN_t INT_FASTN_MAX WCHAR_MIN - uint_fastN_t UINT_FASTN_MAX WCHAR_MAX - intptr_t INTPTR_MIN WINT_MIN - uintptr_t INTPTR_MAX WINT_MAX - intmax_t UINTPTR_MAX INTN_C(value) - uintmax_t INTMAX_MIN UINTN_C(value) - INTN_MIN INTMAX_MAX INTMAX_C(value) - INTN_MAX UINTMAX_MAX UINTMAX_C(value) - UINTN_MAX PTRDIFF_MIN - __STDC_WANT_LIB_EXT1__ - RSIZE_MAX - -[page 483] - -B.20 Input/output - size_t _IOLBF FILENAME_MAX TMP_MAX - FILE _IONBF L_tmpnam stderr - fpos_t BUFSIZ SEEK_CUR stdin - NULL EOF SEEK_END stdout - _IOFBF FOPEN_MAX SEEK_SET - int remove(const char *filename); - int rename(const char *old, const char *new); - FILE *tmpfile(void); - char *tmpnam(char *s); - int fclose(FILE *stream); - int fflush(FILE *stream); - FILE *fopen(const char * restrict filename, - const char * restrict mode); - FILE *freopen(const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - void setbuf(FILE * restrict stream, - char * restrict buf); - int setvbuf(FILE * restrict stream, - char * restrict buf, - int mode, size_t size); - int fprintf(FILE * restrict stream, - const char * restrict format, ...); - int fscanf(FILE * restrict stream, - const char * restrict format, ...); - int printf(const char * restrict format, ...); - int scanf(const char * restrict format, ...); - int snprintf(char * restrict s, size_t n, - const char * restrict format, ...); - int sprintf(char * restrict s, - const char * restrict format, ...); - int sscanf(const char * restrict s, - const char * restrict format, ...); - int vfprintf(FILE * restrict stream, - const char * restrict format, va_list arg); - int vfscanf(FILE * restrict stream, - const char * restrict format, va_list arg); - int vprintf(const char * restrict format, va_list arg); - int vscanf(const char * restrict format, va_list arg); - -[page 484] - - int vsnprintf(char * restrict s, size_t n, - const char * restrict format, va_list arg); - int vsprintf(char * restrict s, - const char * restrict format, va_list arg); - int vsscanf(const char * restrict s, - const char * restrict format, va_list arg); - int fgetc(FILE *stream); - char *fgets(char * restrict s, int n, - FILE * restrict stream); - int fputc(int c, FILE *stream); - int fputs(const char * restrict s, - FILE * restrict stream); - int getc(FILE *stream); - int getchar(void); - int putc(int c, FILE *stream); * - int putchar(int c); - int puts(const char *s); - int ungetc(int c, FILE *stream); - size_t fread(void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - size_t fwrite(const void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - int fgetpos(FILE * restrict stream, - fpos_t * restrict pos); - int fseek(FILE *stream, long int offset, int whence); - int fsetpos(FILE *stream, const fpos_t *pos); - long int ftell(FILE *stream); - void rewind(FILE *stream); - void clearerr(FILE *stream); - int feof(FILE *stream); - int ferror(FILE *stream); - void perror(const char *s); - __STDC_WANT_LIB_EXT1__ - L_tmpnam_s TMP_MAX_S errno_t rsize_t - errno_t tmpfile_s(FILE * restrict * restrict streamptr); - errno_t tmpnam_s(char *s, rsize_t maxsize); - -[page 485] - - errno_t fopen_s(FILE * restrict * restrict streamptr, - const char * restrict filename, - const char * restrict mode); - errno_t freopen_s(FILE * restrict * restrict newstreamptr, - const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - int fprintf_s(FILE * restrict stream, - const char * restrict format, ...); - int fscanf_s(FILE * restrict stream, - const char * restrict format, ...); - int printf_s(const char * restrict format, ...); - int scanf_s(const char * restrict format, ...); - int snprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - int sprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - int sscanf_s(const char * restrict s, - const char * restrict format, ...); - int vfprintf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - int vfscanf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - int vprintf_s(const char * restrict format, - va_list arg); - int vscanf_s(const char * restrict format, - va_list arg); - int vsnprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - int vsprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - int vsscanf_s(const char * restrict s, - const char * restrict format, - va_list arg); - char *gets_s(char *s, rsize_t n); - -[page 486] - -B.21 General utilities - size_t ldiv_t EXIT_FAILURE MB_CUR_MAX - wchar_t lldiv_t EXIT_SUCCESS - div_t NULL RAND_MAX - double atof(const char *nptr); - int atoi(const char *nptr); - long int atol(const char *nptr); - long long int atoll(const char *nptr); - double strtod(const char * restrict nptr, - char ** restrict endptr); - float strtof(const char * restrict nptr, - char ** restrict endptr); - long double strtold(const char * restrict nptr, - char ** restrict endptr); - long int strtol(const char * restrict nptr, - char ** restrict endptr, int base); - long long int strtoll(const char * restrict nptr, - char ** restrict endptr, int base); - unsigned long int strtoul( - const char * restrict nptr, - char ** restrict endptr, int base); - unsigned long long int strtoull( - const char * restrict nptr, - char ** restrict endptr, int base); - int rand(void); - void srand(unsigned int seed); - void *aligned_alloc(size_t alignment, size_t size); - void *calloc(size_t nmemb, size_t size); - void free(void *ptr); - void *malloc(size_t size); - void *realloc(void *ptr, size_t size); - _Noreturn void abort(void); - int atexit(void (*func)(void)); - int at_quick_exit(void (*func)(void)); - _Noreturn void exit(int status); - _Noreturn void _Exit(int status); - char *getenv(const char *name); - _Noreturn void quick_exit(int status); - int system(const char *string); - -[page 487] - - void *bsearch(const void *key, const void *base, - size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - void qsort(void *base, size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - int abs(int j); - long int labs(long int j); - long long int llabs(long long int j); - div_t div(int numer, int denom); - ldiv_t ldiv(long int numer, long int denom); - lldiv_t lldiv(long long int numer, - long long int denom); - int mblen(const char *s, size_t n); - int mbtowc(wchar_t * restrict pwc, - const char * restrict s, size_t n); - int wctomb(char *s, wchar_t wchar); - size_t mbstowcs(wchar_t * restrict pwcs, - const char * restrict s, size_t n); - size_t wcstombs(char * restrict s, - const wchar_t * restrict pwcs, size_t n); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - constraint_handler_t - constraint_handler_t set_constraint_handler_s( - constraint_handler_t handler); - void abort_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - void ignore_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - errno_t getenv_s(size_t * restrict len, - char * restrict value, rsize_t maxsize, - const char * restrict name); - -[page 488] - - void *bsearch_s(const void *key, const void *base, - rsize_t nmemb, rsize_t size, - int (*compar)(const void *k, const void *y, - void *context), - void *context); - errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, - int (*compar)(const void *x, const void *y, - void *context), - void *context); - errno_t wctomb_s(int * restrict status, - char * restrict s, - rsize_t smax, - wchar_t wc); - errno_t mbstowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char * restrict src, rsize_t len); - errno_t wcstombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t * restrict src, rsize_t len); -B.22 String handling - size_t - NULL - void *memcpy(void * restrict s1, - const void * restrict s2, size_t n); - void *memmove(void *s1, const void *s2, size_t n); - char *strcpy(char * restrict s1, - const char * restrict s2); - char *strncpy(char * restrict s1, - const char * restrict s2, size_t n); - char *strcat(char * restrict s1, - const char * restrict s2); - char *strncat(char * restrict s1, - const char * restrict s2, size_t n); - int memcmp(const void *s1, const void *s2, size_t n); - int strcmp(const char *s1, const char *s2); - int strcoll(const char *s1, const char *s2); - int strncmp(const char *s1, const char *s2, size_t n); - size_t strxfrm(char * restrict s1, - const char * restrict s2, size_t n); - void *memchr(const void *s, int c, size_t n); - -[page 489] - - char *strchr(const char *s, int c); - size_t strcspn(const char *s1, const char *s2); - char *strpbrk(const char *s1, const char *s2); - char *strrchr(const char *s, int c); - size_t strspn(const char *s1, const char *s2); - char *strstr(const char *s1, const char *s2); - char *strtok(char * restrict s1, - const char * restrict s2); - void *memset(void *s, int c, size_t n); - char *strerror(int errnum); - size_t strlen(const char *s); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - errno_t memcpy_s(void * restrict s1, rsize_t s1max, - const void * restrict s2, rsize_t n); - errno_t memmove_s(void *s1, rsize_t s1max, - const void *s2, rsize_t n); - errno_t strcpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - errno_t strncpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - errno_t strcat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - errno_t strncat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - char *strtok_s(char * restrict s1, - rsize_t * restrict s1max, - const char * restrict s2, - char ** restrict ptr); - errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) - errno_t strerror_s(char *s, rsize_t maxsize, - errno_t errnum); - size_t strerrorlen_s(errno_t errnum); - -[page 490] - - size_t strnlen_s(const char *s, size_t maxsize); -B.23 Type-generic math - acos sqrt fmod nextafter - asin fabs frexp nexttoward - atan atan2 hypot remainder - acosh cbrt ilogb remquo - asinh ceil ldexp rint - atanh copysign lgamma round - cos erf llrint scalbn - sin erfc llround scalbln - tan exp2 log10 tgamma - cosh expm1 log1p trunc - sinh fdim log2 carg - tanh floor logb cimag - exp fma lrint conj - log fmax lround cproj - pow fmin nearbyint creal -B.24 Threads - ONCE_FLAG_INIT mtx_plain - TSS_DTOR_ITERATIONS mtx_recursive - cnd_t mtx_timed - thrd_t mtx_try - tss_t thrd_timeout - mtx_t thrd_success - tss_dtor_t thrd_busy - thrd_start_t thrd_error - once_flag thrd_nomem - xtime - void call_once(once_flag *flag, void (*func)(void)); - int cnd_broadcast(cnd_t *cond); - void cnd_destroy(cnd_t *cond); - int cnd_init(cnd_t *cond); - int cnd_signal(cnd_t *cond); - int cnd_timedwait(cnd_t *cond, mtx_t *mtx, - const xtime *xt); - int cnd_wait(cnd_t *cond, mtx_t *mtx); - void mtx_destroy(mtx_t *mtx); - int mtx_init(mtx_t *mtx, int type); - int mtx_lock(mtx_t *mtx); - -[page 491] - - int mtx_timedlock(mtx_t *mtx, const xtime *xt); - int mtx_trylock(mtx_t *mtx); - int mtx_unlock(mtx_t *mtx); - int thrd_create(thrd_t *thr, thrd_start_t func, - void *arg); - thrd_t thrd_current(void); - int thrd_detach(thrd_t thr); - int thrd_equal(thrd_t thr0, thrd_t thr1); - void thrd_exit(int res); - int thrd_join(thrd_t thr, int *res); - void thrd_sleep(const xtime *xt); - void thrd_yield(void); - int tss_create(tss_t *key, tss_dtor_t dtor); - void tss_delete(tss_t key); - void *tss_get(tss_t key); - int tss_set(tss_t key, void *val); - int xtime_get(xtime *xt, int base); -B.25 Date and time - NULL size_t time_t - CLOCKS_PER_SEC clock_t struct tm - clock_t clock(void); - double difftime(time_t time1, time_t time0); - time_t mktime(struct tm *timeptr); - time_t time(time_t *timer); - char *asctime(const struct tm *timeptr); - char *ctime(const time_t *timer); - struct tm *gmtime(const time_t *timer); - struct tm *localtime(const time_t *timer); - size_t strftime(char * restrict s, - size_t maxsize, - const char * restrict format, - const struct tm * restrict timeptr); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - errno_t asctime_s(char *s, rsize_t maxsize, - const struct tm *timeptr); - -[page 492] - - errno_t ctime_s(char *s, rsize_t maxsize, - const time_t *timer); - struct tm *gmtime_s(const time_t * restrict timer, - struct tm * restrict result); - struct tm *localtime_s(const time_t * restrict timer, - struct tm * restrict result); -B.26 Unicode utilities - mbstate_t size_t char16_t char32_t - size_t mbrtoc16(char16_t * restrict pc16, - const char * restrict s, size_t n, - mbstate_t * restrict ps); - size_t c16rtomb(char * restrict s, char16_t c16, - mbstate_t * restrict ps); - size_t mbrtoc32(char32_t * restrict pc32, - const char * restrict s, size_t n, - mbstate_t * restrict ps); - size_t c32rtomb(char * restrict s, char32_t c32, - mbstate_t * restrict ps); -B.27 Extended multibyte/wide character utilities - wchar_t wint_t WCHAR_MAX - size_t struct tm WCHAR_MIN - mbstate_t NULL WEOF - int fwprintf(FILE * restrict stream, - const wchar_t * restrict format, ...); - int fwscanf(FILE * restrict stream, - const wchar_t * restrict format, ...); - int swprintf(wchar_t * restrict s, size_t n, - const wchar_t * restrict format, ...); - int swscanf(const wchar_t * restrict s, - const wchar_t * restrict format, ...); - int vfwprintf(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - int vfwscanf(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - int vswprintf(wchar_t * restrict s, size_t n, - const wchar_t * restrict format, va_list arg); - -[page 493] - - int vswscanf(const wchar_t * restrict s, - const wchar_t * restrict format, va_list arg); - int vwprintf(const wchar_t * restrict format, - va_list arg); - int vwscanf(const wchar_t * restrict format, - va_list arg); - int wprintf(const wchar_t * restrict format, ...); - int wscanf(const wchar_t * restrict format, ...); - wint_t fgetwc(FILE *stream); - wchar_t *fgetws(wchar_t * restrict s, int n, - FILE * restrict stream); - wint_t fputwc(wchar_t c, FILE *stream); - int fputws(const wchar_t * restrict s, - FILE * restrict stream); - int fwide(FILE *stream, int mode); - wint_t getwc(FILE *stream); - wint_t getwchar(void); - wint_t putwc(wchar_t c, FILE *stream); - wint_t putwchar(wchar_t c); - wint_t ungetwc(wint_t c, FILE *stream); - double wcstod(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - float wcstof(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - long double wcstold(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - long int wcstol(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - long long int wcstoll(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - unsigned long int wcstoul(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - unsigned long long int wcstoull( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - wchar_t *wcscpy(wchar_t * restrict s1, - const wchar_t * restrict s2); - wchar_t *wcsncpy(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - -[page 494] - - wchar_t *wmemcpy(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, - size_t n); - wchar_t *wcscat(wchar_t * restrict s1, - const wchar_t * restrict s2); - wchar_t *wcsncat(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - int wcscmp(const wchar_t *s1, const wchar_t *s2); - int wcscoll(const wchar_t *s1, const wchar_t *s2); - int wcsncmp(const wchar_t *s1, const wchar_t *s2, - size_t n); - size_t wcsxfrm(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - int wmemcmp(const wchar_t *s1, const wchar_t *s2, - size_t n); - wchar_t *wcschr(const wchar_t *s, wchar_t c); - size_t wcscspn(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcsrchr(const wchar_t *s, wchar_t c); - size_t wcsspn(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcstok(wchar_t * restrict s1, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); - wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n); - size_t wcslen(const wchar_t *s); - wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n); - size_t wcsftime(wchar_t * restrict s, size_t maxsize, - const wchar_t * restrict format, - const struct tm * restrict timeptr); - wint_t btowc(int c); - int wctob(wint_t c); - int mbsinit(const mbstate_t *ps); - size_t mbrlen(const char * restrict s, size_t n, - mbstate_t * restrict ps); - size_t mbrtowc(wchar_t * restrict pwc, - const char * restrict s, size_t n, - mbstate_t * restrict ps); - -[page 495] - - size_t wcrtomb(char * restrict s, wchar_t wc, - mbstate_t * restrict ps); - size_t mbsrtowcs(wchar_t * restrict dst, - const char ** restrict src, size_t len, - mbstate_t * restrict ps); - size_t wcsrtombs(char * restrict dst, - const wchar_t ** restrict src, size_t len, - mbstate_t * restrict ps); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - int fwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - int fwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - int snwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, ...); - int swprintf_s(wchar_t * restrict s, rsize_t n, - const wchar_t * restrict format, ...); - int swscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, ...); - int vfwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, - va_list arg); - int vfwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - int vsnwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - int vswprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - int vswscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, - va_list arg); - -[page 496] - - int vwprintf_s(const wchar_t * restrict format, - va_list arg); - int vwscanf_s(const wchar_t * restrict format, - va_list arg); - int wprintf_s(const wchar_t * restrict format, ...); - int wscanf_s(const wchar_t * restrict format, ...); - errno_t wcscpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - errno_t wcsncpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - errno_t wmemcpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, - const wchar_t *s2, rsize_t n); - errno_t wcscat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - errno_t wcsncat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - wchar_t *wcstok_s(wchar_t * restrict s1, - rsize_t * restrict s1max, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); - size_t wcsnlen_s(const wchar_t *s, size_t maxsize); - errno_t wcrtomb_s(size_t * restrict retval, - char * restrict s, rsize_t smax, - wchar_t wc, mbstate_t * restrict ps); - errno_t mbsrtowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char ** restrict src, rsize_t len, - mbstate_t * restrict ps); - -[page 497] - - errno_t wcsrtombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t ** restrict src, rsize_t len, - mbstate_t * restrict ps); -B.28 Wide character classification and mapping utilities - wint_t wctrans_t wctype_t WEOF - int iswalnum(wint_t wc); - int iswalpha(wint_t wc); - int iswblank(wint_t wc); - int iswcntrl(wint_t wc); - int iswdigit(wint_t wc); - int iswgraph(wint_t wc); - int iswlower(wint_t wc); - int iswprint(wint_t wc); - int iswpunct(wint_t wc); - int iswspace(wint_t wc); - int iswupper(wint_t wc); - int iswxdigit(wint_t wc); - int iswctype(wint_t wc, wctype_t desc); - wctype_t wctype(const char *property); - wint_t towlower(wint_t wc); - wint_t towupper(wint_t wc); - wint_t towctrans(wint_t wc, wctrans_t desc); - wctrans_t wctrans(const char *property); - -[page 498] - - Annex C - (informative) - Sequence points -1 The following are the sequence points described in 5.1.2.3: - -- Between the evaluations of the function designator and actual arguments in a function - call and the actual call. (6.5.2.2). - -- Between the evaluations of the first and second operands of the following operators: - logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17). * - -- Between the evaluations of the first operand of the conditional ? : operator and - whichever of the second and third operands is evaluated (6.5.15). - -- The end of a full declarator: declarators (6.7.6); - -- Between the evaluation of a full expression and the next full expression to be - evaluated. The following are full expressions: an initializer that is not part of a - compound literal (6.7.9); the expression in an expression statement (6.8.3); the - controlling expression of a selection statement (if or switch) (6.8.4); the - controlling expression of a while or do statement (6.8.5); each of the (optional) - expressions of a for statement (6.8.5.3); the (optional) expression in a return - statement (6.8.6.4). - -- Immediately before a library function returns (7.1.4). - -- After the actions associated with each formatted input/output function conversion - specifier (7.21.6, 7.28.2). - -- Immediately before and immediately after each call to a comparison function, and - also between any call to a comparison function and any movement of the objects - passed as arguments to that call (7.22.5). - -[page 499] - - Annex D - (normative) - Universal character names for identifiers -1 This clause lists the hexadecimal code values that are valid in universal character names - in identifiers. - D.1 Ranges of characters allowed -1 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, - 00D8-00F6, 00F8-00FF -2 0100-167F, 1681-180D, 180F-1FFF -3 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F -4 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF -5 3004-3007, 3021-302F, 3031-303F -6 3040-D7FF -7 F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD -8 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, - 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, - B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD - D.2 Ranges of characters disallowed initially -1 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F - -[page 500] - - Annex E - (informative) - Implementation limits -1 The contents of the header are given below, in alphabetical order. The - minimum magnitudes shown shall be replaced by implementation-defined magnitudes - with the same sign. The values shall all be constant expressions suitable for use in #if - preprocessing directives. The components are described further in 5.2.4.2.1. - #define CHAR_BIT 8 - #define CHAR_MAX UCHAR_MAX or SCHAR_MAX - #define CHAR_MIN 0 or SCHAR_MIN - #define INT_MAX +32767 - #define INT_MIN -32767 - #define LONG_MAX +2147483647 - #define LONG_MIN -2147483647 - #define LLONG_MAX +9223372036854775807 - #define LLONG_MIN -9223372036854775807 - #define MB_LEN_MAX 1 - #define SCHAR_MAX +127 - #define SCHAR_MIN -127 - #define SHRT_MAX +32767 - #define SHRT_MIN -32767 - #define UCHAR_MAX 255 - #define USHRT_MAX 65535 - #define UINT_MAX 65535 - #define ULONG_MAX 4294967295 - #define ULLONG_MAX 18446744073709551615 -2 The contents of the header are given below. All integer values, except - FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing - directives; all floating values shall be constant expressions. The components are - described further in 5.2.4.2.2. -3 The values given in the following list shall be replaced by implementation-defined - expressions: - #define FLT_EVAL_METHOD - #define FLT_ROUNDS -4 The values given in the following list shall be replaced by implementation-defined - constant expressions that are greater or equal in magnitude (absolute value) to those - shown, with the same sign: - -[page 501] - - #define DLB_DECIMAL_DIG 10 - #define DBL_DIG 10 - #define DBL_MANT_DIG - #define DBL_MAX_10_EXP +37 - #define DBL_MAX_EXP - #define DBL_MIN_10_EXP -37 - #define DBL_MIN_EXP - #define DECIMAL_DIG 10 - #define FLT_DECIMAL_DIG 6 - #define FLT_DIG 6 - #define FLT_MANT_DIG - #define FLT_MAX_10_EXP +37 - #define FLT_MAX_EXP - #define FLT_MIN_10_EXP -37 - #define FLT_MIN_EXP - #define FLT_RADIX 2 - #define LDLB_DECIMAL_DIG 10 - #define LDBL_DIG 10 - #define LDBL_MANT_DIG - #define LDBL_MAX_10_EXP +37 - #define LDBL_MAX_EXP - #define LDBL_MIN_10_EXP -37 - #define LDBL_MIN_EXP -5 The values given in the following list shall be replaced by implementation-defined - constant expressions with values that are greater than or equal to those shown: - #define DBL_MAX 1E+37 - #define FLT_MAX 1E+37 - #define LDBL_MAX 1E+37 -6 The values given in the following list shall be replaced by implementation-defined - constant expressions with (positive) values that are less than or equal to those shown: - #define DBL_EPSILON 1E-9 - #define DBL_MIN 1E-37 - #define FLT_EPSILON 1E-5 - #define FLT_MIN 1E-37 - #define LDBL_EPSILON 1E-9 - #define LDBL_MIN 1E-37 - -[page 502] - - Annex F - (normative) - IEC 60559 floating-point arithmetic - F.1 Introduction -1 This annex specifies C language support for the IEC 60559 floating-point standard. The - IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for - microprocessor systems, second edition (IEC 60559:1989), previously designated - IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic - (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point - Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove - dependencies on radix and word length. IEC 60559 generally refers to the floating-point - standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that - defines __STDC_IEC_559__ shall conform to the specifications in this annex.343) - Where a binding between the C language and IEC 60559 is indicated, the - IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since - negative and positive infinity are representable in IEC 60559 formats, all real numbers lie - within the range of representable values. - F.2 Types -1 The C floating types match the IEC 60559 formats as follows: - -- The float type matches the IEC 60559 single format. - -- The double type matches the IEC 60559 double format. - -- The long double type matches an IEC 60559 extended format,344) else a - non-IEC 60559 extended format, else the IEC 60559 double format. - Any non-IEC 60559 extended format used for the long double type shall have more - precision than IEC 60559 double and at least the range of IEC 60559 double.345) - - - - - 343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these - specifications. - 344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit - and quadruple 128-bit IEC 60559 formats. - 345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include - all double values. - -[page 503] - - Recommended practice -2 The long double type should match an IEC 60559 extended format. - F.2.1 Infinities, signed zeros, and NaNs -1 This specification does not define the behavior of signaling NaNs.346) It generally uses - the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan - functions in provide designations for IEC 60559 NaNs and infinities. - F.3 Operators and functions -1 C operators and functions provide IEC 60559 required and recommended facilities as - listed below. - -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and - divide operations. - -- The sqrt functions in provide the IEC 60559 square root operation. - -- The remainder functions in provide the IEC 60559 remainder - operation. The remquo functions in provide the same operation but - with additional information. - -- The rint functions in provide the IEC 60559 operation that rounds a - floating-point number to an integer value (in the same precision). The nearbyint - functions in provide the nearbyinteger function recommended in the - Appendix to ANSI/IEEE 854. - -- The conversions for floating types provide the IEC 60559 conversions between - floating-point precisions. - -- The conversions from integer to floating types provide the IEC 60559 conversions - from integer to floating point. - -- The conversions from floating to integer types provide IEC 60559-like conversions - but always round toward zero. - -- The lrint and llrint functions in provide the IEC 60559 - conversions, which honor the directed rounding mode, from floating point to the - long int and long long int integer formats. The lrint and llrint - functions can be used to implement IEC 60559 conversions from floating to other - integer formats. - -- The translation time conversion of floating constants and the strtod, strtof, - strtold, fprintf, fscanf, and related library functions in , - - - 346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are - sufficient for closure of the arithmetic. - -[page 504] - - , and provide IEC 60559 binary-decimal conversions. The - strtold function in provides the conv function recommended in the - Appendix to ANSI/IEEE 854. --- The relational and equality operators provide IEC 60559 comparisons. IEC 60559 - identifies a need for additional comparison predicates to facilitate writing code that - accounts for NaNs. The comparison macros (isgreater, isgreaterequal, - isless, islessequal, islessgreater, and isunordered) in - supplement the language operators to address this need. The islessgreater and - isunordered macros provide respectively a quiet version of the <> predicate and - the unordered predicate recommended in the Appendix to IEC 60559. --- The feclearexcept, feraiseexcept, and fetestexcept functions in - provide the facility to test and alter the IEC 60559 floating-point - exception status flags. The fegetexceptflag and fesetexceptflag - functions in provide the facility to save and restore all five status flags at - one time. These functions are used in conjunction with the type fexcept_t and the - floating-point exception macros (FE_INEXACT, FE_DIVBYZERO, - FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in . --- The fegetround and fesetround functions in provide the facility - to select among the IEC 60559 directed rounding modes represented by the rounding - direction macros in (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD, - FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the - IEC 60559 directed rounding modes. --- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in - provide a facility to manage the floating-point environment, comprising - the IEC 60559 status flags and control modes. --- The copysign functions in provide the copysign function - recommended in the Appendix to IEC 60559. --- The fabs functions in provide the abs function recommended in the - Appendix to IEC 60559. --- The unary minus (-) operator provides the unary minus (-) operation recommended - in the Appendix to IEC 60559. --- The scalbn and scalbln functions in provide the scalb function - recommended in the Appendix to IEC 60559. --- The logb functions in provide the logb function recommended in the - Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854. --- The nextafter and nexttoward functions in provide the nextafter - function recommended in the Appendix to IEC 60559 (but with a minor change to - -[page 505] - - better handle signed zeros). - -- The isfinite macro in provides the finite function recommended in - the Appendix to IEC 60559. - -- The isnan macro in provides the isnan function recommended in the - Appendix to IEC 60559. - -- The signbit macro and the fpclassify macro in , used in - conjunction with the number classification macros (FP_NAN, FP_INFINITE, - FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class - function recommended in the Appendix to IEC 60559 (except that the classification - macros defined in 7.12.3 do not distinguish signaling from quiet NaNs). - F.4 Floating to integer conversion -1 If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised - (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part - of the floating value exceeds the range of the integer type, then the ''invalid'' floating- - point exception is raised and the resulting value is unspecified. Otherwise, the resulting - value is determined by 6.3.1.4. Conversion of an integral floating value that does not - exceed the range of the integer type raises no floating-point exceptions; whether - conversion of a non-integral floating value raises the ''inexact'' floating-point exception is - unspecified.347) - F.5 Binary-decimal conversion -1 Conversion from the widest supported IEC 60559 format to decimal with - DECIMAL_DIG digits and back is the identity function.348) -2 Conversions involving IEC 60559 formats follow all pertinent recommended practice. In - particular, conversion between any supported IEC 60559 format and decimal with - DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current - rounding mode), which assures that conversion from the widest supported IEC 60559 - format to decimal with DECIMAL_DIG digits and back is the identity function. - - - - 347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer - conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those - cases where it matters, library functions can be used to effect such conversions with or without raising - the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in - . - 348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported, - DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest - IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and - DBL_DIG are 18 and 15, respectively, for these formats.) - -[page 506] - -3 Functions such as strtod that convert character sequences to floating types honor the - rounding direction. Hence, if the rounding direction might be upward or downward, the - implementation cannot convert a minus-signed sequence by negating the converted - unsigned sequence. - F.6 The return statement - If the return expression is evaluated in a floating-point format different from the return - type, the expression is converted as if by assignment349) to the return type of the function - and the resulting value is returned to the caller. - F.7 Contracted expressions -1 A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed - zeros, subnormals, and the rounding directions in a manner consistent with the basic - arithmetic operations covered by IEC 60559. - Recommended practice -2 A contracted expression should raise floating-point exceptions in a manner generally - consistent with the basic arithmetic operations. * - F.8 Floating-point environment -1 The floating-point environment defined in includes the IEC 60559 floating- - point exception status flags and directed-rounding control modes. It includes also - IEC 60559 dynamic rounding precision and trap enablement modes, if the - implementation supports them.350) - F.8.1 Environment management -1 IEC 60559 requires that floating-point operations implicitly raise floating-point exception - status flags, and that rounding control modes can be set explicitly to affect result values of - floating-point operations. When the state for the FENV_ACCESS pragma (defined in - ) is ''on'', these changes to the floating-point state are treated as side effects - which respect sequence points.351) - - - - - 349) Assignment removes any extra range and precision. - 350) This specification does not require dynamic rounding precision nor trap enablement modes. - 351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating- - point control modes will be the default ones and the floating-point status flags will not be tested, - which allows certain optimizations (see F.9). - -[page 507] - - F.8.2 Translation -1 During translation the IEC 60559 default modes are in effect: - -- The rounding direction mode is rounding to nearest. - -- The rounding precision mode (if supported) is set so that results are not shortened. - -- Trapping or stopping (if supported) is disabled on all floating-point exceptions. - Recommended practice -2 The implementation should produce a diagnostic message for each translation-time - floating-point exception, other than ''inexact'';352) the implementation should then - proceed with the translation of the program. - F.8.3 Execution -1 At program startup the floating-point environment is initialized as prescribed by - IEC 60559: - -- All floating-point exception status flags are cleared. - -- The rounding direction mode is rounding to nearest. - -- The dynamic rounding precision mode (if supported) is set so that results are not - shortened. - -- Trapping or stopping (if supported) is disabled on all floating-point exceptions. - F.8.4 Constant expressions -1 An arithmetic constant expression of floating type, other than one in an initializer for an - object that has static or thread storage duration, is evaluated (as if) during execution; thus, - it is affected by any operative floating-point control modes and raises floating-point - exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma - is ''on'').353) -2 EXAMPLE - - - - 352) As floating constants are converted to appropriate internal representations at translation time, their - conversion is subject to default rounding modes and raises no execution-time floating-point exceptions - (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example - strtod, provide execution-time conversion of numeric strings. - 353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0 - are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and - 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the - efficiency of translation-time evaluation through static initialization, such as - const static double one_third = 1.0/3.0; - -[page 508] - - #include - #pragma STDC FENV_ACCESS ON - void f(void) - { - float w[] = { 0.0/0.0 }; // raises an exception - static float x = 0.0/0.0; // does not raise an exception - float y = 0.0/0.0; // raises an exception - double z = 0.0/0.0; // raises an exception - /* ... */ - } -3 For the static initialization, the division is done at translation time, raising no (execution-time) floating- - point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at - execution time. - - F.8.5 Initialization -1 All computation for automatic initialization is done (as if) at execution time; thus, it is - affected by any operative modes and raises floating-point exceptions as required by - IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation - for initialization of objects that have static or thread storage duration is done (as if) at - translation time. -2 EXAMPLE - #include - #pragma STDC FENV_ACCESS ON - void f(void) - { - float u[] = { 1.1e75 }; // raises exceptions - static float v = 1.1e75; // does not raise exceptions - float w = 1.1e75; // raises exceptions - double x = 1.1e75; // may raise exceptions - float y = 1.1e75f; // may raise exceptions - long double z = 1.1e75; // does not raise exceptions - /* ... */ - } -3 The static initialization of v raises no (execution-time) floating-point exceptions because its computation is - done at translation time. The automatic initialization of u and w require an execution-time conversion to - float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations - of x and y entail execution-time conversion; however, in some expression evaluation methods, the - conversions is not to a narrower format, in which case no floating-point exception is raised.354) The - automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating- - point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to - - - - 354) Use of float_t and double_t variables increases the likelihood of translation-time computation. - For example, the automatic initialization - double_t x = 1.1e75; - could be done at translation time, regardless of the expression evaluation method. - -[page 509] - - their internal representations occur at translation time in all cases. - - F.8.6 Changing the environment -1 Operations defined in 6.5 and functions and macros defined for the standard libraries - change floating-point status flags and control modes just as indicated by their - specifications (including conformance to IEC 60559). They do not change flags or modes - (so as to be detectable by the user) in any other cases. -2 If the argument to the feraiseexcept function in represents IEC 60559 - valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and - ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised - before ''inexact''. - F.9 Optimization -1 This section identifies code transformations that might subvert IEC 60559-specified - behavior, and others that do not. - F.9.1 Global transformations -1 Floating-point arithmetic operations and external function calls may entail side effects - which optimization shall honor, at least where the state of the FENV_ACCESS pragma is - ''on''. The flags and modes in the floating-point environment may be regarded as global - variables; floating-point operations (+, *, etc.) implicitly read the modes and write the - flags. -2 Concern about side effects may inhibit code motion and removal of seemingly useless - code. For example, in - #include - #pragma STDC FENV_ACCESS ON - void f(double x) - { - /* ... */ - for (i = 0; i < n; i++) x + 1; - /* ... */ - } - x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop - body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of - course these optimizations are valid if the implementation can rule out the nettlesome - cases.) -3 This specification does not require support for trap handlers that maintain information - about the order or count of floating-point exceptions. Therefore, between function calls, - floating-point exceptions need not be precise: the actual order and number of occurrences - of floating-point exceptions (> 1) may vary from what the source code expresses. Thus, - -[page 510] - - the preceding loop could be treated as - if (0 < n) x + 1; - F.9.2 Expression transformations -1 x/2 <-> x x 0.5 Although similar transformations involving inexact constants - generally do not yield numerically equivalent expressions, if the - constants are exact then such transformations can be made on - IEC 60559 machines and others that round perfectly. - 1 x x and x/1 -> x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559 - machines, among others).355) - x/x -> 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero, - infinite, or NaN. - x - y <-> x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on - IEC 60559 machines, among others). - x - y <-> -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1 - is +0 but -(1 - 1) is -0 (in the default rounding direction).356) - x - x -> 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or - infinite. - 0 x x -> 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN, - infinite, or -0. - x+0-> x The expressions x + 0 and x are not equivalent if x is -0, because - (-0) + (+0) yields +0 (in the default rounding direction), not -0. - x-0-> x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but - +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the - FENV_ACCESS pragma is ''off'', promising default rounding, then - the implementation can replace x - 0 by x, even if x might be zero. - -x <-> 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because - -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is - downward). - - 355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and - other transformations that remove arithmetic operators. - 356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities. - Examples include: - 1/(1/ (+-) (inf)) is (+-) (inf) - and - conj(csqrt(z)) is csqrt(conj(z)), - for complex z. - -[page 511] - - F.9.3 Relational operators -1 x != x -> false The expression x != x is true if x is a NaN. - x = x -> true The expression x = x is false if x is a NaN. - x < y -> isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these - expressions are not equivalent because of side effects when x or y is a - NaN and the state of the FENV_ACCESS pragma is ''on''. This - transformation, which would be desirable if extra code were required - to cause the ''invalid'' floating-point exception for unordered cases, - could be performed provided the state of the FENV_ACCESS pragma - is ''off''. - The sense of relational operators shall be maintained. This includes handling unordered - cases as expressed by the source code. -2 EXAMPLE - // calls g and raises ''invalid'' if a and b are unordered - if (a < b) - f(); - else - g(); - is not equivalent to - // calls f and raises ''invalid'' if a and b are unordered - if (a >= b) - g(); - else - f(); - nor to - // calls f without raising ''invalid'' if a and b are unordered - if (isgreaterequal(a,b)) - g(); - else - f(); - nor, unless the state of the FENV_ACCESS pragma is ''off'', to - // calls g without raising ''invalid'' if a and b are unordered - if (isless(a,b)) - f(); - else - g(); - but is equivalent to - -[page 512] - - if (!(a < b)) - g(); - else - f(); - - F.9.4 Constant arithmetic -1 The implementation shall honor floating-point exceptions raised by execution-time - constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4 - and F.8.5.) An operation on constants that raises no floating-point exception can be - folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a - further check is required to assure that changing the rounding direction to downward does - not alter the sign of the result,357) and implementations that support dynamic rounding - precision modes shall assure further that the result of the operation raises no floating- - point exception when converted to the semantic type of the operation. - F.10 Mathematics -1 This subclause contains specifications of facilities that are particularly suited - for IEC 60559 implementations. -2 The Standard C macro HUGE_VAL and its float and long double analogs, - HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive - infinities. -3 Special cases for functions in are covered directly or indirectly by - IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The - other functions in treat infinities, NaNs, signed zeros, subnormals, and - (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags - in a manner consistent with the basic arithmetic operations covered by IEC 60559. -4 The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a - nonzero value. -5 The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in - subsequent subclauses of this annex. -6 The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of - rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value - whose magnitude is too large. -7 The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially - subnormal or zero) and suffers loss of accuracy.358) - - - 357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward. - 358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on - when the floating-point exception is raised. - -[page 513] - -8 Whether or when library functions raise the ''inexact'' floating-point exception is - unspecified, unless explicitly specified otherwise. -9 Whether or when library functions raise an undeserved ''underflow'' floating-point - exception is unspecified.359) Otherwise, as implied by F.8.6, the functions do - not raise spurious floating-point exceptions (detectable by the user), other than the - ''inexact'' floating-point exception. -10 Whether the functions honor the rounding direction mode is implementation-defined, - unless explicitly specified otherwise. -11 Functions with a NaN argument return a NaN result and raise no floating-point exception, - except where stated otherwise. -12 The specifications in the following subclauses append to the definitions in . - For families of functions, the specifications apply to all of the functions even though only - the principal function is shown. Unless otherwise specified, where the symbol ''(+-)'' - occurs in both an argument and the result, the result has the same sign as the argument. - Recommended practice -13 If a function with one or more NaN arguments returns a NaN result, the result should be - the same as one of the NaN arguments (after possible type conversion), except perhaps - for the sign. - F.10.1 Trigonometric functions - F.10.1.1 The acos functions -1 -- acos(1) returns +0. - -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - F.10.1.2 The asin functions -1 -- asin((+-)0) returns (+-)0. - -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - - - - - 359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if - avoiding them would be too costly. - -[page 514] - - F.10.1.3 The atan functions -1 -- atan((+-)0) returns (+-)0. - -- atan((+-)(inf)) returns (+-)pi /2. - F.10.1.4 The atan2 functions -1 -- atan2((+-)0, -0) returns (+-)pi .360) - -- atan2((+-)0, +0) returns (+-)0. - -- atan2((+-)0, x) returns (+-)pi for x < 0. - -- atan2((+-)0, x) returns (+-)0 for x > 0. - -- atan2(y, (+-)0) returns -pi /2 for y < 0. - -- atan2(y, (+-)0) returns pi /2 for y > 0. - -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0. - -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0. - -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x. - -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4. - -- atan2((+-)(inf), +(inf)) returns (+-)pi /4. - F.10.1.5 The cos functions -1 -- cos((+-)0) returns 1. - -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - F.10.1.6 The sin functions -1 -- sin((+-)0) returns (+-)0. - -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - F.10.1.7 The tan functions -1 -- tan((+-)0) returns (+-)0. - -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - - - - - 360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise - the ''divide-by-zero'' floating-point exception. - -[page 515] - - F.10.2 Hyperbolic functions - F.10.2.1 The acosh functions -1 -- acosh(1) returns +0. - -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1. - -- acosh(+(inf)) returns +(inf). - F.10.2.2 The asinh functions -1 -- asinh((+-)0) returns (+-)0. - -- asinh((+-)(inf)) returns (+-)(inf). - F.10.2.3 The atanh functions -1 -- atanh((+-)0) returns (+-)0. - -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception. - -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - F.10.2.4 The cosh functions -1 -- cosh((+-)0) returns 1. - -- cosh((+-)(inf)) returns +(inf). - F.10.2.5 The sinh functions -1 -- sinh((+-)0) returns (+-)0. - -- sinh((+-)(inf)) returns (+-)(inf). - F.10.2.6 The tanh functions -1 -- tanh((+-)0) returns (+-)0. - -- tanh((+-)(inf)) returns (+-)1. - F.10.3 Exponential and logarithmic functions - F.10.3.1 The exp functions -1 -- exp((+-)0) returns 1. - -- exp(-(inf)) returns +0. - -- exp(+(inf)) returns +(inf). - -[page 516] - - F.10.3.2 The exp2 functions -1 -- exp2((+-)0) returns 1. - -- exp2(-(inf)) returns +0. - -- exp2(+(inf)) returns +(inf). - F.10.3.3 The expm1 functions -1 -- expm1((+-)0) returns (+-)0. - -- expm1(-(inf)) returns -1. - -- expm1(+(inf)) returns +(inf). - F.10.3.4 The frexp functions -1 -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp. - -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object - pointed to by exp. - -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp - (and returns a NaN). -2 frexp raises no floating-point exceptions. -3 When the radix of the argument is a power of 2, the returned value is exact and is - independent of the current rounding direction mode. -4 On a binary system, the body of the frexp function might be - { - *exp = (value == 0) ? 0 : (int)(1 + logb(value)); - return scalbn(value, -(*exp)); - } - F.10.3.5 The ilogb functions -1 When the correct result is representable in the range of the return type, the returned value - is exact and is independent of the current rounding direction mode. -2 If the correct result is outside the range of the return type, the numeric result is - unspecified and the ''invalid'' floating-point exception is raised. - -[page 517] - - F.10.3.6 The ldexp functions -1 On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp). - F.10.3.7 The log functions -1 -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log(1) returns +0. - -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log(+(inf)) returns +(inf). - F.10.3.8 The log10 functions -1 -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log10(1) returns +0. - -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log10(+(inf)) returns +(inf). - F.10.3.9 The log1p functions -1 -- log1p((+-)0) returns (+-)0. - -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for - x < -1. - -- log1p(+(inf)) returns +(inf). - F.10.3.10 The log2 functions -1 -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log2(1) returns +0. - -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log2(+(inf)) returns +(inf). - F.10.3.11 The logb functions -1 -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- logb((+-)(inf)) returns +(inf). -2 The returned value is exact and is independent of the current rounding direction mode. - -[page 518] - - F.10.3.12 The modf functions -1 -- modf((+-)x, iptr) returns a result with the same sign as x. - -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr. - -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a - NaN). -2 The returned values are exact and are independent of the current rounding direction - mode. -3 modf behaves as though implemented by - #include - #include - #pragma STDC FENV_ACCESS ON - double modf(double value, double *iptr) - { - int save_round = fegetround(); - fesetround(FE_TOWARDZERO); - *iptr = nearbyint(value); - fesetround(save_round); - return copysign( - isinf(value) ? 0.0 : - value - (*iptr), value); - } - F.10.3.13 The scalbn and scalbln functions -1 -- scalbn((+-)0, n) returns (+-)0. - -- scalbn(x, 0) returns x. - -- scalbn((+-)(inf), n) returns (+-)(inf). -2 If the calculation does not overflow or underflow, the returned value is exact and - independent of the current rounding direction mode. - -[page 519] - - F.10.4 Power and absolute value functions - F.10.4.1 The cbrt functions -1 -- cbrt((+-)0) returns (+-)0. - -- cbrt((+-)(inf)) returns (+-)(inf). - F.10.4.2 The fabs functions -1 -- fabs((+-)0) returns +0. - -- fabs((+-)(inf)) returns +(inf). -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.4.3 The hypot functions -1 -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent. - -- hypot(x, (+-)0) is equivalent to fabs(x). - -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN. - F.10.4.4 The pow functions -1 -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception - for y an odd integer < 0. - -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception - for y < 0, finite, and not an odd integer. - -- pow((+-)0, -(inf)) returns +(inf) and may raise the ''divide-by-zero'' floating-point - exception. - -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0. - -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer. - -- pow(-1, (+-)(inf)) returns 1. - -- pow(+1, y) returns 1 for any y, even a NaN. - -- pow(x, (+-)0) returns 1 for any x, even a NaN. - -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for - finite x < 0 and finite non-integer y. - -- pow(x, -(inf)) returns +(inf) for | x | < 1. - -- pow(x, -(inf)) returns +0 for | x | > 1. - -- pow(x, +(inf)) returns +0 for | x | < 1. - -- pow(x, +(inf)) returns +(inf) for | x | > 1. - -[page 520] - - -- pow(-(inf), y) returns -0 for y an odd integer < 0. - -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer. - -- pow(-(inf), y) returns -(inf) for y an odd integer > 0. - -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer. - -- pow(+(inf), y) returns +0 for y < 0. - -- pow(+(inf), y) returns +(inf) for y > 0. - F.10.4.5 The sqrt functions -1 sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value - is dependent on the current rounding direction mode. - F.10.5 Error and gamma functions - F.10.5.1 The erf functions -1 -- erf((+-)0) returns (+-)0. - -- erf((+-)(inf)) returns (+-)1. - F.10.5.2 The erfc functions -1 -- erfc(-(inf)) returns 2. - -- erfc(+(inf)) returns +0. - F.10.5.3 The lgamma functions -1 -- lgamma(1) returns +0. - -- lgamma(2) returns +0. - -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for - x a negative integer or zero. - -- lgamma(-(inf)) returns +(inf). - -- lgamma(+(inf)) returns +(inf). - F.10.5.4 The tgamma functions -1 -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception. - -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a - negative integer. - -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - -- tgamma(+(inf)) returns +(inf). - -[page 521] - - F.10.6 Nearest integer functions - F.10.6.1 The ceil functions -1 -- ceil((+-)0) returns (+-)0. - -- ceil((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. -3 The double version of ceil behaves as though implemented by - #include - #include - #pragma STDC FENV_ACCESS ON - double ceil(double x) - { - double result; - int save_round = fegetround(); - fesetround(FE_UPWARD); - result = rint(x); // or nearbyint instead of rint - fesetround(save_round); - return result; - } -4 The ceil functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer arguments, as this implementation does. - F.10.6.2 The floor functions -1 -- floor((+-)0) returns (+-)0. - -- floor((+-)(inf)) returns (+-)(inf). -2 The returned value and is independent of the current rounding direction mode. -3 See the sample implementation for ceil in F.10.6.1. The floor functions may, but are - not required to, raise the ''inexact'' floating-point exception for finite non-integer - arguments, as that implementation does. - F.10.6.3 The nearbyint functions -1 The nearbyint functions use IEC 60559 rounding according to the current rounding - direction. They do not raise the ''inexact'' floating-point exception if the result differs in - value from the argument. - -- nearbyint((+-)0) returns (+-)0 (for all rounding directions). - -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions). - -[page 522] - - F.10.6.4 The rint functions -1 The rint functions differ from the nearbyint functions only in that they do raise the - ''inexact'' floating-point exception if the result differs in value from the argument. - F.10.6.5 The lrint and llrint functions -1 The lrint and llrint functions provide floating-to-integer conversion as prescribed - by IEC 60559. They round according to the current rounding direction. If the rounded - value is outside the range of the return type, the numeric result is unspecified and the - ''invalid'' floating-point exception is raised. When they raise no other floating-point - exception and the result differs from the argument, they raise the ''inexact'' floating-point - exception. - F.10.6.6 The round functions -1 -- round((+-)0) returns (+-)0. - -- round((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. -3 The double version of round behaves as though implemented by - #include - #include - #pragma STDC FENV_ACCESS ON - double round(double x) - { - double result; - fenv_t save_env; - feholdexcept(&save_env); - result = rint(x); - if (fetestexcept(FE_INEXACT)) { - fesetround(FE_TOWARDZERO); - result = rint(copysign(0.5 + fabs(x), x)); - } - feupdateenv(&save_env); - return result; - } - The round functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer numeric arguments, as this implementation does. - -[page 523] - - F.10.6.7 The lround and llround functions -1 The lround and llround functions differ from the lrint and llrint functions - with the default rounding direction just in that the lround and llround functions - round halfway cases away from zero and need not raise the ''inexact'' floating-point - exception for non-integer arguments that round to within the range of the return type. - F.10.6.8 The trunc functions -1 The trunc functions use IEC 60559 rounding toward zero (regardless of the current - rounding direction). The returned value is exact. - -- trunc((+-)0) returns (+-)0. - -- trunc((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. The trunc - functions may, but are not required to, raise the ''inexact'' floating-point exception for - finite non-integer arguments. - F.10.7 Remainder functions - F.10.7.1 The fmod functions -1 -- fmod((+-)0, y) returns (+-)0 for y not zero. - -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x - infinite or y zero (and neither is a NaN). - -- fmod(x, (+-)(inf)) returns x for x not infinite. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. -3 The double version of fmod behaves as though implemented by - #include - #include - #pragma STDC FENV_ACCESS ON - double fmod(double x, double y) - { - double result; - result = remainder(fabs(x), (y = fabs(y))); - if (signbit(result)) result += y; - return copysign(result, x); - } - -[page 524] - - F.10.7.2 The remainder functions -1 The remainder functions are fully specified as a basic arithmetic operation in - IEC 60559. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - F.10.7.3 The remquo functions -1 The remquo functions follow the specifications for the remainder functions. They - have no further specifications special to IEC 60559 implementations. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - F.10.8 Manipulation functions - F.10.8.1 The copysign functions -1 copysign is specified in the Appendix to IEC 60559. -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.8.2 The nan functions -1 All IEC 60559 implementations support quiet NaNs, in all floating formats. -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.8.3 The nextafter functions -1 -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions - for x finite and the function value infinite. - -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point - exceptions for the function value subnormal or zero and x != y. -2 Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - F.10.8.4 The nexttoward functions -1 No additional requirements beyond those on nextafter. -2 Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - -[page 525] - - F.10.9 Maximum, minimum, and positive difference functions - F.10.9.1 The fdim functions -1 No additional requirements. - F.10.9.2 The fmax functions -1 If just one argument is a NaN, the fmax functions return the other argument (if both - arguments are NaNs, the functions return a NaN). -2 The returned value is exact and is independent of the current rounding direction mode. -3 The body of the fmax function might be361) - { return (isgreaterequal(x, y) || - isnan(y)) ? x : y; } - F.10.9.3 The fmin functions -1 The fmin functions are analogous to the fmax functions (see F.10.9.2). -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.10 Floating multiply-add - F.10.10.1 The fma functions -1 -- fma(x, y, z) computes xy + z, correctly rounded once. - -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point - exception if one of x and y is infinite, the other is zero, and z is a NaN. - -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if - one of x and y is infinite, the other is zero, and z is not a NaN. - -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x - times y is an exact infinity and z is also an infinity but with the opposite sign. - - - - - 361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would - return +0; however, implementation in software might be impractical. - -[page 526] - - F.10.11 Comparison macros -1 Relational operators and their corresponding comparison macros (7.12.14) produce - equivalent result values, even if argument values are represented in wider formats. Thus, - comparison macro arguments represented in formats wider than their semantic types are - not converted to the semantic types, unless the wide evaluation method converts operands - of relational operators to their semantic types. The standard wide evaluation methods - characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert - operands of relational operators to their semantic types. - -[page 527] - - Annex G - (normative) - IEC 60559-compatible complex arithmetic - G.1 Introduction -1 This annex supplements annex F to specify complex arithmetic for compatibility with - IEC 60559 real floating-point arithmetic. An implementation that defines * - __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362) - G.2 Types -1 There is a new keyword _Imaginary, which is used to specify imaginary types. It is - used as a type specifier within declaration specifiers in the same way as _Complex is - (thus, _Imaginary float is a valid type name). -2 There are three imaginary types, designated as float _Imaginary, double - _Imaginary, and long double _Imaginary. The imaginary types (along with - the real floating and complex types) are floating types. -3 For imaginary types, the corresponding real type is given by deleting the keyword - _Imaginary from the type name. -4 Each imaginary type has the same representation and alignment requirements as the - corresponding real type. The value of an object of imaginary type is the value of the real - representation times the imaginary unit. -5 The imaginary type domain comprises the imaginary types. - G.3 Conventions -1 A complex or imaginary value with at least one infinite part is regarded as an infinity - (even if its other part is a NaN). A complex or imaginary value is a finite number if each - of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is - a zero if each of its parts is a zero. - - - - - 362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform - to these specifications. - -[page 528] - - G.4 Conversions - G.4.1 Imaginary types -1 Conversions among imaginary types follow rules analogous to those for real floating - types. - G.4.2 Real and imaginary -1 When a value of imaginary type is converted to a real type other than _Bool,363) the - result is a positive zero. -2 When a value of real type is converted to an imaginary type, the result is a positive - imaginary zero. - G.4.3 Imaginary and complex -1 When a value of imaginary type is converted to a complex type, the real part of the - complex result value is a positive zero and the imaginary part of the complex result value - is determined by the conversion rules for the corresponding real types. -2 When a value of complex type is converted to an imaginary type, the real part of the - complex value is discarded and the value of the imaginary part is converted according to - the conversion rules for the corresponding real types. - G.5 Binary operators -1 The following subclauses supplement 6.5 in order to specify the type of the result for an - operation with an imaginary operand. -2 For most operand types, the value of the result of a binary operator with an imaginary or - complex operand is completely determined, with reference to real arithmetic, by the usual - mathematical formula. For some operand types, the usual mathematical formula is - problematic because of its treatment of infinities and because of undue overflow or - underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is - not completely determined. - - - - - 363) See 6.3.1.2. - -[page 529] - - G.5.1 Multiplicative operators - Semantics -1 If one operand has real type and the other operand has imaginary type, then the result has - imaginary type. If both operands have imaginary type, then the result has real type. (If - either operand has complex type, then the result has complex type.) -2 If the operands are not both complex, then the result and floating-point exception - behavior of the * operator is defined by the usual mathematical formula: - * u iv u + iv - - x xu i(xv) (xu) + i(xv) - - iy i(yu) -yv (-yv) + i(yu) - - x + iy (xu) + i(yu) (-yv) + i(xv) -3 If the second operand is not complex, then the result and floating-point exception - behavior of the / operator is defined by the usual mathematical formula: - / u iv - - x x/u i(-x/v) - - iy i(y/u) y/v - - x + iy (x/u) + i(y/u) (y/v) + i(-x/v) -4 The * and / operators satisfy the following infinity properties for all real, imaginary, and - complex operands:364) - -- if one operand is an infinity and the other operand is a nonzero finite number or an - infinity, then the result of the * operator is an infinity; - -- if the first operand is an infinity and the second operand is a finite number, then the - result of the / operator is an infinity; - -- if the first operand is a finite number and the second operand is an infinity, then the - result of the / operator is a zero; - - - - - 364) These properties are already implied for those cases covered in the tables, but are required for all cases - (at least where the state for CX_LIMITED_RANGE is ''off''). - -[page 530] - - -- if the first operand is a nonzero finite number or an infinity and the second operand is - a zero, then the result of the / operator is an infinity. -5 If both operands of the * operator are complex or if the second operand of the / operator - is complex, the operator raises floating-point exceptions if appropriate for the calculation - of the parts of the result, and may raise spurious floating-point exceptions. -6 EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note - that the imaginary unit I has imaginary type (see G.6). - #include - #include - /* Multiply z * w ... */ - double complex _Cmultd(double complex z, double complex w) - { - #pragma STDC FP_CONTRACT OFF - double a, b, c, d, ac, bd, ad, bc, x, y; - a = creal(z); b = cimag(z); - c = creal(w); d = cimag(w); - ac = a * c; bd = b * d; - ad = a * d; bc = b * c; - x = ac - bd; y = ad + bc; - if (isnan(x) && isnan(y)) { - /* Recover infinities that computed as NaN+iNaN ... */ - int recalc = 0; - if ( isinf(a) || isinf(b) ) { // z is infinite - /* "Box" the infinity and change NaNs in the other factor to 0 */ - a = copysign(isinf(a) ? 1.0 : 0.0, a); - b = copysign(isinf(b) ? 1.0 : 0.0, b); - if (isnan(c)) c = copysign(0.0, c); - if (isnan(d)) d = copysign(0.0, d); - recalc = 1; - } - if ( isinf(c) || isinf(d) ) { // w is infinite - /* "Box" the infinity and change NaNs in the other factor to 0 */ - c = copysign(isinf(c) ? 1.0 : 0.0, c); - d = copysign(isinf(d) ? 1.0 : 0.0, d); - if (isnan(a)) a = copysign(0.0, a); - if (isnan(b)) b = copysign(0.0, b); - recalc = 1; - } - if (!recalc && (isinf(ac) || isinf(bd) || - isinf(ad) || isinf(bc))) { - /* Recover infinities from overflow by changing NaNs to 0 ... */ - if (isnan(a)) a = copysign(0.0, a); - if (isnan(b)) b = copysign(0.0, b); - if (isnan(c)) c = copysign(0.0, c); - if (isnan(d)) d = copysign(0.0, d); - recalc = 1; - } - if (recalc) { - -[page 531] - - x = INFINITY * ( a * c - b * d ); - y = INFINITY * ( a * d + b * c ); - } - } - return x + I * y; - } -7 This implementation achieves the required treatment of infinities at the cost of only one isnan test in - ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur. - -8 EXAMPLE 2 Division of two double _Complex operands could be implemented as follows. - #include - #include - /* Divide z / w ... */ - double complex _Cdivd(double complex z, double complex w) - { - #pragma STDC FP_CONTRACT OFF - double a, b, c, d, logbw, denom, x, y; - int ilogbw = 0; - a = creal(z); b = cimag(z); - c = creal(w); d = cimag(w); - logbw = logb(fmax(fabs(c), fabs(d))); - if (logbw == INFINITY) { - ilogbw = (int)logbw; - c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw); - } - denom = c * c + d * d; - x = scalbn((a * c + b * d) / denom, -ilogbw); - y = scalbn((b * c - a * d) / denom, -ilogbw); - /* Recover infinities and zeros that computed as NaN+iNaN; */ - /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */ - if (isnan(x) && isnan(y)) { - if ((denom == 0.0) && - (!isnan(a) || !isnan(b))) { - x = copysign(INFINITY, c) * a; - y = copysign(INFINITY, c) * b; - } - else if ((isinf(a) || isinf(b)) && - isfinite(c) && isfinite(d)) { - a = copysign(isinf(a) ? 1.0 : 0.0, a); - b = copysign(isinf(b) ? 1.0 : 0.0, b); - x = INFINITY * ( a * c + b * d ); - y = INFINITY * ( b * c - a * d ); - } - else if (isinf(logbw) && - isfinite(a) && isfinite(b)) { - c = copysign(isinf(c) ? 1.0 : 0.0, c); - d = copysign(isinf(d) ? 1.0 : 0.0, d); - x = 0.0 * ( a * c + b * d ); - y = 0.0 * ( b * c - a * d ); - -[page 532] - - } - } - return x + I * y; - } -9 Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than - for multiplication. In the spirit of the multiplication example above, this code does not defend against - overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of - with division, provides better roundoff characteristics. - - G.5.2 Additive operators - Semantics -1 If both operands have imaginary type, then the result has imaginary type. (If one operand - has real type and the other operand has imaginary type, or if either operand has complex - type, then the result has complex type.) -2 In all cases the result and floating-point exception behavior of a + or - operator is defined - by the usual mathematical formula: - + or - u iv u + iv - - x x(+-)u x (+-) iv (x (+-) u) (+-) iv - - iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v) - - x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v) - G.6 Complex arithmetic -1 The macros - imaginary - and - _Imaginary_I - are defined, respectively, as _Imaginary and a constant expression of type const - float _Imaginary with the value of the imaginary unit. The macro - I - is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding - the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro - imaginary. -2 This subclause contains specifications for the functions that are - particularly suited to IEC 60559 implementations. For families of functions, the - specifications apply to all of the functions even though only the principal function is - -[page 533] - - shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument - and the result, the result has the same sign as the argument. -3 The functions are continuous onto both sides of their branch cuts, taking into account the - sign of zero. For example, csqrt(-2 (+-) i0) = (+-)i(sqrt)2. - -4 Since complex and imaginary values are composed of real values, each function may be - regarded as computing real values from real values. Except as noted, the functions treat - real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a - manner consistent with the specifications for real functions in F.10.365) -5 The functions cimag, conj, cproj, and creal are fully specified for all - implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating- - point exceptions. -6 Each of the functions cabs and carg is specified by a formula in terms of a real - function (whose special cases are covered in annex F): - cabs(x + iy) = hypot(x, y) - carg(x + iy) = atan2(y, x) -7 Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by - a formula in terms of other complex functions (whose special cases are specified below): - casin(z) = -i casinh(iz) - catan(z) = -i catanh(iz) - ccos(z) = ccosh(iz) - csin(z) = -i csinh(iz) - ctan(z) = -i ctanh(iz) -8 For the other functions, the following subclauses specify behavior for special cases, - including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For - families of functions, the specifications apply to all of the functions even though only the - principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the - specifications for the upper half-plane imply the specifications for the lower half-plane; if - the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the - specifications for the first quadrant imply the specifications for the other three quadrants. -9 In the following subclauses, cis(y) is defined as cos(y) + i sin(y). - - - - - 365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its - other part is a NaN. - -[page 534] - - G.6.1 Trigonometric functions - G.6.1.1 The cacos functions -1 -- cacos(conj(z)) = conj(cacos(z)). - -- cacos((+-)0 + i0) returns pi /2 - i0. - -- cacos((+-)0 + iNaN) returns pi /2 + iNaN. - -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x. - -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for nonzero finite x. - -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y. - -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y. - -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf). - -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf). - -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the - result is unspecified). - -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- cacos(NaN + i (inf)) returns NaN - i (inf). - -- cacos(NaN + iNaN) returns NaN + iNaN. - G.6.2 Hyperbolic functions - G.6.2.1 The cacosh functions -1 -- cacosh(conj(z)) = conj(cacosh(z)). - -- cacosh((+-)0 + i0) returns +0 + ipi /2. - -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x. - -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite x. - -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y. - -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y. - -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4. - -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN. - -[page 535] - - -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite y. - -- cacosh(NaN + i (inf)) returns +(inf) + iNaN. - -- cacosh(NaN + iNaN) returns NaN + iNaN. - G.6.2.2 The casinh functions -1 -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd. - -- casinh(+0 + i0) returns 0 + i0. - -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x. - -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite x. - -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y. - -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- casinh(+(inf) + iNaN) returns +(inf) + iNaN. - -- casinh(NaN + i0) returns NaN + i0. - -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite nonzero y. - -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- casinh(NaN + iNaN) returns NaN + iNaN. - G.6.2.3 The catanh functions -1 -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd. - -- catanh(+0 + i0) returns +0 + i0. - -- catanh(+0 + iNaN) returns +0 + iNaN. - -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point - exception. - -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x. - -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for nonzero finite x. - -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y. - -- catanh(+(inf) + i (inf)) returns +0 + ipi /2. - -- catanh(+(inf) + iNaN) returns +0 + iNaN. - -[page 536] - - -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite y. - -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is - unspecified). - -- catanh(NaN + iNaN) returns NaN + iNaN. - G.6.2.4 The ccosh functions -1 -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even. - -- ccosh(+0 + i0) returns 1 + i0. - -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified) and raises the ''invalid'' floating-point exception. - -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite nonzero x. - -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite nonzero x. - -- ccosh(+(inf) + i0) returns +(inf) + i0. - -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y. - -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN. - -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- ccosh(NaN + iNaN) returns NaN + iNaN. - G.6.2.5 The csinh functions -1 -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd. - -- csinh(+0 + i0) returns +0 + i0. - -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is - unspecified). - -[page 537] - - -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for positive finite x. - -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite nonzero x. - -- csinh(+(inf) + i0) returns +(inf) + i0. - -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y. - -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- csinh(NaN + i0) returns NaN + i0. - -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- csinh(NaN + iNaN) returns NaN + iNaN. - G.6.2.6 The ctanh functions -1 -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd. - -- ctanh(+0 + i0) returns +0 + i0. - -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite x. - -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y. - -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result - is unspecified). - -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ctanh(NaN + i0) returns NaN + i0. - -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- ctanh(NaN + iNaN) returns NaN + iNaN. - -[page 538] - - G.6.3 Exponential and logarithmic functions - G.6.3.1 The cexp functions -1 -- cexp(conj(z)) = conj(cexp(z)). - -- cexp((+-)0 + i0) returns 1 + i0. - -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite x. - -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- cexp(+(inf) + i0) returns +(inf) + i0. - -- cexp(-(inf) + iy) returns +0 cis(y), for finite y. - -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y. - -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of - the result are unspecified). - -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point - exception (where the sign of the real part of the result is unspecified). - -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts - of the result are unspecified). - -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- cexp(NaN + i0) returns NaN + i0. - -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- cexp(NaN + iNaN) returns NaN + iNaN. - G.6.3.2 The clog functions -1 -- clog(conj(z)) = conj(clog(z)). - -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point - exception. - -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point - exception. - -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x. - -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -[page 539] - - -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y. - -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y. - -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4. - -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN. - -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- clog(NaN + i (inf)) returns +(inf) + iNaN. - -- clog(NaN + iNaN) returns NaN + iNaN. - G.6.4 Power and absolute-value functions - G.6.4.1 The cpow functions -1 The cpow functions raise floating-point exceptions if appropriate for the calculation of - the parts of the result, and may also raise spurious floating-point exceptions.366) - G.6.4.2 The csqrt functions -1 -- csqrt(conj(z)) = conj(csqrt(z)). - -- csqrt((+-)0 + i0) returns +0 + i0. - -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN). - -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y. - -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y. - -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the - result is unspecified). - -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN. - -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- csqrt(NaN + iNaN) returns NaN + iNaN. - - - - - 366) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding - implementations that treat special cases more carefully. - -[page 540] - - G.7 Type-generic math -1 Type-generic macros that accept complex arguments also accept imaginary arguments. If - an argument is imaginary, the macro expands to an expression whose type is real, - imaginary, or complex, as appropriate for the particular function: if the argument is - imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the - types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and - the types of the others are complex. -2 Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh, - sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real - functions: - cos(iy) = cosh(y) - sin(iy) = i sinh(y) - tan(iy) = i tanh(y) - cosh(iy) = cos(y) - sinh(iy) = i sin(y) - tanh(iy) = i tan(y) - asin(iy) = i asinh(y) - atan(iy) = i atanh(y) - asinh(iy) = i asin(y) - atanh(iy) = i atan(y) - -[page 541] - - Annex H - (informative) - Language independent arithmetic - H.1 Introduction -1 This annex documents the extent to which the C language supports the ISO/IEC 10967-1 - standard for language-independent arithmetic (LIA-1). LIA-1 is more general than - IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics. - H.2 Types -1 The relevant C arithmetic types meet the requirements of LIA-1 types if an - implementation adds notification of exceptional arithmetic operations and meets the 1 - unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8). - H.2.1 Boolean type -1 The LIA-1 data type Boolean is implemented by the C data type bool with values of - true and false, all from . - H.2.2 Integer types -1 The signed C integer types int, long int, long long int, and the corresponding - unsigned types are compatible with LIA-1. If an implementation adds support for the - LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are - LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense - in that overflows or out-of-bounds results silently wrap. An implementation that defines - signed integer types as also being modulo need not detect integer overflow, in which case, - only integer divide-by-zero need be detected. -2 The parameters for the integer data types can be accessed by the following: - maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX, - ULLONG_MAX - minint INT_MIN, LONG_MIN, LLONG_MIN -3 The parameter ''bounded'' is always true, and is not provided. The parameter ''minint'' - is always 0 for the unsigned types, and is not provided for those types. - -[page 542] - - H.2.2.1 Integer operations -1 The integer operations on integer types are the following: - addI x + y - subI x - y - mulI x * y - divI, divtI x / y - remI, remtI x % y - negI -x - absI abs(x), labs(x), llabs(x) - eqI x == y - neqI x != y - lssI x < y - leqI x <= y - gtrI x > y - geqI x >= y - where x and y are expressions of the same integer type. - H.2.3 Floating-point types -1 The C floating-point types float, double, and long double are compatible with - LIA-1. If an implementation adds support for the LIA-1 exceptional values - ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant - with LIA-1. An implementation that uses IEC 60559 floating-point formats and - operations (see annex F) along with IEC 60559 status flags and traps has LIA-1 - conformant types. - H.2.3.1 Floating-point parameters -1 The parameters for a floating point data type can be accessed by the following: - r FLT_RADIX - p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG - emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP - emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP -2 The derived constants for the floating point types are accessed by the following: - -[page 543] - - fmax FLT_MAX, DBL_MAX, LDBL_MAX - fminN FLT_MIN, DBL_MIN, LDBL_MIN - epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON - rnd_style FLT_ROUNDS - H.2.3.2 Floating-point operations -1 The floating-point operations on floating-point types are the following: - addF x + y - subF x - y - mulF x * y - divF x / y - negF -x - absF fabsf(x), fabs(x), fabsl(x) - exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x) - scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n), - scalblnf(x, li), scalbln(x, li), scalblnl(x, li) - intpartF modff(x, &y), modf(x, &y), modfl(x, &y) - fractpartF modff(x, &y), modf(x, &y), modfl(x, &y) - eqF x == y - neqF x != y - lssF x < y - leqF x <= y - gtrF x > y - geqF x >= y - where x and y are expressions of the same floating point type, n is of type int, and li - is of type long int. - H.2.3.3 Rounding styles -1 The C Standard requires all floating types to use the same radix and rounding style, so - that only one identifier for each is provided to map to LIA-1. -2 The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles: - truncate FLT_ROUNDS == 0 - -[page 544] - - nearest FLT_ROUNDS == 1 - other FLT_ROUNDS != 0 && FLT_ROUNDS != 1 - provided that an implementation extends FLT_ROUNDS to cover the rounding style used - in all relevant LIA-1 operations, not just addition as in C. - H.2.4 Type conversions -1 The LIA-1 type conversions are the following type casts: - cvtI' -> I (int)i, (long int)i, (long long int)i, - (unsigned int)i, (unsigned long int)i, - (unsigned long long int)i - cvtF -> I (int)x, (long int)x, (long long int)x, - (unsigned int)x, (unsigned long int)x, - (unsigned long long int)x - cvtI -> F (float)i, (double)i, (long double)i - cvtF' -> F (float)x, (double)x, (long double)x -2 In the above conversions from floating to integer, the use of (cast)x can be replaced with - (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x), - (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer - conversion functions, lrint(), llrint(), lround(), and llround(), can be - used. They all meet LIA-1's requirements on floating to integer rounding for in-range - values. For out-of-range values, the conversions shall silently wrap for the modulo types. -3 The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g., - fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x), - 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0 - to 65535.0 which can then be cast to unsigned short int. But, the - remainder() function is not useful for doing silent wrapping to signed integer types, - e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the - range -32767.0 to +32768.0 which is not, in general, in the range of signed short - int. -4 C's conversions (casts) from floating-point to floating-point can meet LIA-1 - requirements if an implementation uses round-to-nearest (IEC 60559 default). -5 C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an - implementation uses round-to-nearest. - -[page 545] - - H.3 Notification -1 Notification is the process by which a user or program is informed that an exceptional - arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C - allows an implementation to cause a notification to occur when any arithmetic operation - returns an exceptional value as defined in LIA-1 clause 5. - H.3.1 Notification alternatives -1 LIA-1 requires at least the following two alternatives for handling of notifications: - setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and- - resume. -2 An implementation need only support a given notification alternative for the entire - program. An implementation may support the ability to switch between notification - alternatives during execution, but is not required to do so. An implementation can - provide separate selection for each kind of notification, but this is not required. -3 C allows an implementation to provide notification. C's SIGFPE (for traps) and - FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators) - can provide LIA-1 notification. -4 C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can - provide trap-and-terminate behavior, except for those LIA-1 operations implemented by - math library function calls. User-provided signal handlers for SIGFPE allow for trap- - and-resume behavior with the same constraint. - H.3.1.1 Indicators -1 C's status flags are compatible with the LIA-1 indicators. -2 The following mapping is for floating-point types: - undefined FE_INVALID, FE_DIVBYZERO - floating_overflow FE_OVERFLOW - underflow FE_UNDERFLOW -3 The floating-point indicator interrogation and manipulation operations are: - set_indicators feraiseexcept(i) - clear_indicators feclearexcept(i) - test_indicators fetestexcept(i) - current_indicators fetestexcept(FE_ALL_EXCEPT) - where i is an expression of type int representing a subset of the LIA-1 indicators. -4 C allows an implementation to provide the following LIA-1 required behavior: at - program termination if any indicator is set the implementation shall send an unambiguous - -[page 546] - - and ''hard to ignore'' message (see LIA-1 subclause 6.1.2) -5 LIA-1 does not make the distinction between floating-point and integer for ''undefined''. - This documentation makes that distinction because covers only the floating- - point indicators. - H.3.1.2 Traps -1 C is compatible with LIA-1's trap requirements for arithmetic operations, but not for - math library functions (which are not permitted to invoke a user's signal handler for - SIGFPE). An implementation can provide an alternative of notification through - termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3). -2 LIA-1 does not require that traps be precise. -3 C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions, - if there is any signal raised for them. -4 C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic - exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism - allows trap-and-terminate (either default implementation behavior or user replacement for - it) or trap-and-resume, at the programmer's option. - -[page 547] - - Annex I - (informative) - Common warnings -1 An implementation may generate warnings in many situations, none of which are - specified as part of this International Standard. The following are a few of the more - common situations. -2 -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3). - -- A block with initialization of an object that has automatic storage duration is jumped - into (6.2.4). - -- An implicit narrowing conversion is encountered, such as the assignment of a long - int or a double to an int, or a pointer to void to a pointer to any type other than - a character type (6.3). - -- A hexadecimal floating constant cannot be represented exactly in its evaluation format - (6.4.4.2). - -- An integer character constant includes more than one character or a wide character - constant includes more than one multibyte character (6.4.4.4). - -- The characters /* are found in a comment (6.4.7). - -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an - lvalue in one operand, and a side effect to, or an access to the value of, the identical - lvalue in the other operand (6.5). - -- A function is called but no prototype has been supplied (6.5.2.2). - -- The arguments in a function call do not agree in number and type with those of the - parameters in a function definition that is not a prototype (6.5.2.2). - -- An object is defined but not used (6.7). - -- A value is given to an object of an enumerated type other than by assignment of an - enumeration constant that is a member of that type, or an enumeration object that has - the same type, or the value of a function that returns the same enumerated type - (6.7.2.2). - -- An aggregate has a partly bracketed initialization (6.7.8). - -- A statement cannot be reached (6.8). - -- A statement with no apparent effect is encountered (6.8). - -- A constant expression is used as the controlling expression of a selection statement - (6.8.4). - -[page 548] - --- An incorrectly formed preprocessing group is encountered while skipping a - preprocessing group (6.10.1). --- An unrecognized #pragma directive is encountered (6.10.6). - -[page 549] - - Annex J - (informative) - Portability issues -1 This annex collects some information about portability that appears in this International - Standard. - J.1 Unspecified behavior -1 The following are unspecified: - -- The manner and timing of static initialization (5.1.2). - -- The termination status returned to the hosted environment if the return type of main - is not compatible with int (5.1.2.2.3). - -- The behavior of the display device if a printing character is written when the active - position is at the final position of a line (5.2.2). - -- The behavior of the display device if a backspace character is written when the active - position is at the initial position of a line (5.2.2). - -- The behavior of the display device if a horizontal tab character is written when the - active position is at or past the last defined horizontal tabulation position (5.2.2). - -- The behavior of the display device if a vertical tab character is written when the active - position is at or past the last defined vertical tabulation position (5.2.2). - -- How an extended source character that does not correspond to a universal character - name counts toward the significant initial characters in an external identifier (5.2.4.1). - -- Many aspects of the representations of types (6.2.6). - -- The value of padding bytes when storing values in structures or unions (6.2.6.1). - -- The values of bytes that correspond to union members other than the one last stored - into (6.2.6.1). - -- The representation used when storing a value in an object that has more than one - object representation for that value (6.2.6.1). - -- The values of any padding bits in integer representations (6.2.6.2). - -- Whether certain operators can generate negative zeros and whether a negative zero - becomes a normal zero when stored in an object (6.2.6.2). - -- Whether two string literals result in distinct arrays (6.4.5). - -- The order in which subexpressions are evaluated and the order in which side effects - take place, except as specified for the function-call (), &&, ||, ? :, and comma - -[page 550] - - operators (6.5). --- The order in which the function designator, arguments, and subexpressions within the - arguments are evaluated in a function call (6.5.2.2). --- The order of side effects among compound literal initialization list expressions - (6.5.2.5). --- The order in which the operands of an assignment operator are evaluated (6.5.16). --- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1). --- Whether a call to an inline function uses the inline definition or the external definition - of the function (6.7.4). --- Whether or not a size expression is evaluated when it is part of the operand of a - sizeof operator and changing the value of the size expression would not affect the - result of the operator (6.7.6.2). --- The order in which any side effects occur among the initialization list expressions in - an initializer (6.7.9). --- The layout of storage for function parameters (6.9.1). --- When a fully expanded macro replacement list contains a function-like macro name - as its last preprocessing token and the next preprocessing token from the source file is - a (, and the fully expanded replacement of that macro ends with the name of the first - macro and the next preprocessing token from the source file is again a (, whether that - is considered a nested replacement (6.10.3). --- The order in which # and ## operations are evaluated during macro substitution - (6.10.3.2, 6.10.3.3). --- The state of the floating-point status flags when execution passes from a part of the * - program translated with FENV_ACCESS ''off'' to a part translated with - FENV_ACCESS ''on'' (7.6.1). --- The order in which feraiseexcept raises floating-point exceptions, except as - stated in F.8.6 (7.6.2.3). --- Whether math_errhandling is a macro or an identifier with external linkage - (7.12). --- The results of the frexp functions when the specified value is not a floating-point - number (7.12.6.4). --- The numeric result of the ilogb functions when the correct value is outside the - range of the return type (7.12.6.5, F.10.3.5). --- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5). - -[page 551] - --- The value stored by the remquo functions in the object pointed to by quo when y is - zero (7.12.10.3). --- Whether a comparison macro argument that is represented in a format wider than its - semantic type is converted to the semantic type (7.12.14). --- Whether setjmp is a macro or an identifier with external linkage (7.13). --- Whether va_copy and va_end are macros or identifiers with external linkage - (7.16.1). --- The hexadecimal digit before the decimal point when a non-normalized floating-point - number is printed with an a or A conversion specifier (7.21.6.1, 7.28.2.1). --- The value of the file position indicator after a successful call to the ungetc function - for a text stream, or the ungetwc function for any stream, until all pushed-back - characters are read or discarded (7.21.7.10, 7.28.3.10). --- The details of the value stored by the fgetpos function (7.21.9.1). --- The details of the value returned by the ftell function for a text stream (7.21.9.4). --- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold - functions convert a minus-signed sequence to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence - (7.22.1.3, 7.28.4.1.1). --- The order and contiguity of storage allocated by successive calls to the calloc, - malloc, and realloc functions (7.22.3). --- The amount of storage allocated by a successful call to the calloc, malloc, or - realloc function when 0 bytes was requested (7.22.3). --- Which of two elements that compare as equal is matched by the bsearch function - (7.22.5.1). --- The order of two elements that compare as equal in an array sorted by the qsort - function (7.22.5.2). --- The encoding of the calendar time returned by the time function (7.26.2.4). --- The characters stored by the strftime or wcsftime function if any of the time - values being converted is outside the normal range (7.26.3.5, 7.28.5.1). --- The conversion state after an encoding error occurs (7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, - 7.28.6.4.2, --- The resulting value when the ''invalid'' floating-point exception is raised during - IEC 60559 floating to integer conversion (F.4). - -[page 552] - - -- Whether conversion of non-integer IEC 60559 floating values to integer raises the - ''inexact'' floating-point exception (F.4). - -- Whether or when library functions in raise the ''inexact'' floating-point - exception in an IEC 60559 conformant implementation (F.10). - -- Whether or when library functions in raise an undeserved ''underflow'' - floating-point exception in an IEC 60559 conformant implementation (F.10). - -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4). - -- The numeric result returned by the lrint, llrint, lround, and llround - functions if the rounded value is outside the range of the return type (F.10.6.5, - F.10.6.7). - -- The sign of one part of the complex result of several math functions for certain - special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3, - G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2). - J.2 Undefined behavior -1 The behavior is undefined in the following circumstances: - -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated - (clause 4). - -- A nonempty source file does not end in a new-line character which is not immediately - preceded by a backslash character or ends in a partial preprocessing token or - comment (5.1.1.2). - -- Token concatenation produces a character sequence matching the syntax of a - universal character name (5.1.1.2). - -- A program in a hosted environment does not define a function named main using one - of the specified forms (5.1.2.2.1). - -- The execution of a program contains a data race (5.1.2.4). - -- A character not in the basic source character set is encountered in a source file, except - in an identifier, a character constant, a string literal, a header name, a comment, or a - preprocessing token that is never converted to a token (5.2.1). - -- An identifier, comment, string literal, character constant, or header name contains an - invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2). - -- The same identifier has both internal and external linkage in the same translation unit - (6.2.2). - -- An object is referred to outside of its lifetime (6.2.4). - -[page 553] - --- The value of a pointer to an object whose lifetime has ended is used (6.2.4). --- The value of an object with automatic storage duration is used while it is - indeterminate (6.2.4, 6.7.9, 6.8). --- A trap representation is read by an lvalue expression that does not have character type - (6.2.6.1). --- A trap representation is produced by a side effect that modifies any part of the object - using an lvalue expression that does not have character type (6.2.6.1). --- The operands to certain operators are such that they could produce a negative zero - result, but the implementation does not support negative zeros (6.2.6.2). --- Two declarations of the same object or function specify types that are not compatible - (6.2.7). --- A program requires the formation of a composite type from a variable length array - type whose size is specified by an expression that is not evaluated (6.2.7). --- Conversion to or from an integer type produces a value outside the range that can be - represented (6.3.1.4). --- Demotion of one real floating type to another produces a value outside the range that - can be represented (6.3.1.5). --- An lvalue does not designate an object when evaluated (6.3.2.1). --- A non-array lvalue with an incomplete type is used in a context that requires the value - of the designated object (6.3.2.1). --- An lvalue designating an object of automatic storage duration that could have been - declared with the register storage class is used in a context that requires the value - of the designated object, but the object is uninitialized. (6.3.2.1). --- An lvalue having array type is converted to a pointer to the initial element of the - array, and the array object has register storage class (6.3.2.1). --- An attempt is made to use the value of a void expression, or an implicit or explicit - conversion (except to void) is applied to a void expression (6.3.2.2). --- Conversion of a pointer to an integer type produces a value outside the range that can - be represented (6.3.2.3). --- Conversion between two pointer types produces a result that is incorrectly aligned - (6.3.2.3). --- A pointer is used to call a function whose type is not compatible with the referenced - type (6.3.2.3). - -[page 554] - --- An unmatched ' or " character is encountered on a logical source line during - tokenization (6.4). --- A reserved keyword token is used in translation phase 7 or 8 for some purpose other - than as a keyword (6.4.1). --- A universal character name in an identifier does not designate a character whose - encoding falls into one of the specified ranges (6.4.2.1). --- The initial character of an identifier is a universal character name designating a digit - (6.4.2.1). --- Two identifiers differ only in nonsignificant characters (6.4.2.1). --- The identifier __func__ is explicitly declared (6.4.2.2). --- The program attempts to modify a string literal (6.4.5). --- The characters ', \, ", //, or /* occur in the sequence between the < and > - delimiters, or the characters ', \, //, or /* occur in the sequence between the " - delimiters, in a header name preprocessing token (6.4.7). --- A side effect on a scalar object is unsequenced relative to either a different side effect - on the same scalar object or a value computation using the value of the same scalar - object (6.5). --- An exceptional condition occurs during the evaluation of an expression (6.5). --- An object has its stored value accessed other than by an lvalue of an allowable type - (6.5). --- For a call to a function without a function prototype in scope, the number of * - arguments does not equal the number of parameters (6.5.2.2). --- For call to a function without a function prototype in scope where the function is - defined with a function prototype, either the prototype ends with an ellipsis or the - types of the arguments after promotion are not compatible with the types of the - parameters (6.5.2.2). --- For a call to a function without a function prototype in scope where the function is not - defined with a function prototype, the types of the arguments after promotion are not - compatible with those of the parameters after promotion (with certain exceptions) - (6.5.2.2). --- A function is defined with a type that is not compatible with the type (of the - expression) pointed to by the expression that denotes the called function (6.5.2.2). --- A member of an atomic structure or union is accessed (6.5.2.3). --- The operand of the unary * operator has an invalid value (6.5.3.2). - -[page 555] - --- A pointer is converted to other than an integer or pointer type (6.5.4). --- The value of the second operand of the / or % operator is zero (6.5.5). --- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that does not point into, or just beyond, the same array - object (6.5.6). --- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that points just beyond the array object and is used as - the operand of a unary * operator that is evaluated (6.5.6). --- Pointers that do not point into, or just beyond, the same array object are subtracted - (6.5.6). --- An array subscript is out of range, even if an object is apparently accessible with the - given subscript (as in the lvalue expression a[1][7] given the declaration int - a[4][5]) (6.5.6). --- The result of subtracting two pointers is not representable in an object of type - ptrdiff_t (6.5.6). --- An expression is shifted by a negative number or by an amount greater than or equal - to the width of the promoted expression (6.5.7). --- An expression having signed promoted type is left-shifted and either the value of the - expression is negative or the result of shifting would be not be representable in the - promoted type (6.5.7). --- Pointers that do not point to the same aggregate or union (nor just beyond the same - array object) are compared using relational operators (6.5.8). --- An object is assigned to an inexactly overlapping object or to an exactly overlapping - object with incompatible type (6.5.16.1). --- An expression that is required to be an integer constant expression does not have an - integer type; has operands that are not integer constants, enumeration constants, - character constants, sizeof expressions whose results are integer constants, or - immediately-cast floating constants; or contains casts (outside operands to sizeof - operators) other than conversions of arithmetic types to integer types (6.6). --- A constant expression in an initializer is not, or does not evaluate to, one of the - following: an arithmetic constant expression, a null pointer constant, an address - constant, or an address constant for a complete object type plus or minus an integer - constant expression (6.6). --- An arithmetic constant expression does not have arithmetic type; has operands that - are not integer constants, floating constants, enumeration constants, character - constants, or sizeof expressions; or contains casts (outside operands to sizeof - -[page 556] - - operators) other than conversions of arithmetic types to arithmetic types (6.6). --- The value of an object is accessed by an array-subscript [], member-access . or ->, - address &, or indirection * operator or a pointer cast in creating an address constant - (6.6). --- An identifier for an object is declared with no linkage and the type of the object is - incomplete after its declarator, or after its init-declarator if it has an initializer (6.7). --- A function is declared at block scope with an explicit storage-class specifier other - than extern (6.7.1). --- A structure or union is defined as containing no named members, no anonymous - structures, and no anonymous unions (6.7.2.1). --- An attempt is made to access, or generate a pointer to just past, a flexible array - member of a structure when the referenced object provides no elements for that array - (6.7.2.1). --- When the complete type is needed, an incomplete structure or union type is not - completed in the same scope by another declaration of the tag that defines the content - (6.7.2.3). --- An attempt is made to modify an object defined with a const-qualified type through - use of an lvalue with non-const-qualified type (6.7.3). --- An attempt is made to refer to an object defined with a volatile-qualified type through - use of an lvalue with non-volatile-qualified type (6.7.3). --- The specification of a function type includes any type qualifiers (6.7.3). * --- Two qualified types that are required to be compatible do not have the identically - qualified version of a compatible type (6.7.3). --- An object which has been modified is accessed through a restrict-qualified pointer to - a const-qualified type, or through a restrict-qualified pointer and another pointer that - are not both based on the same object (6.7.3.1). --- A restrict-qualified pointer is assigned a value based on another restricted pointer - whose associated block neither began execution before the block associated with this - pointer, nor ended before the assignment (6.7.3.1). --- A function with external linkage is declared with an inline function specifier, but is - not also defined in the same translation unit (6.7.4). --- A function declared with a _Noreturn function specifier returns to its caller (6.7.4). --- The definition of an object has an alignment specifier and another declaration of that - object has a different alignment specifier (6.7.5). - -[page 557] - --- Declarations of an object in different translation units have different alignment - specifiers (6.7.5). --- Two pointer types that are required to be compatible are not identically qualified, or - are not pointers to compatible types (6.7.6.1). --- The size expression in an array declaration is not a constant expression and evaluates - at program execution time to a nonpositive value (6.7.6.2). --- In a context requiring two array types to be compatible, they do not have compatible - element types, or their size specifiers evaluate to unequal values (6.7.6.2). --- A declaration of an array parameter includes the keyword static within the [ and - ] and the corresponding argument does not provide access to the first element of an - array with at least the specified number of elements (6.7.6.3). --- A storage-class specifier or type qualifier modifies the keyword void as a function - parameter type list (6.7.6.3). --- In a context requiring two function types to be compatible, they do not have - compatible return types, or their parameters disagree in use of the ellipsis terminator - or the number and type of parameters (after default argument promotion, when there - is no parameter type list or when one type is specified by a function definition with an - identifier list) (6.7.6.3). --- The value of an unnamed member of a structure or union is used (6.7.9). --- The initializer for a scalar is neither a single expression nor a single expression - enclosed in braces (6.7.9). --- The initializer for a structure or union object that has automatic storage duration is - neither an initializer list nor a single expression that has compatible structure or union - type (6.7.9). --- The initializer for an aggregate or union, other than an array initialized by a string - literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9). --- An identifier with external linkage is used, but in the program there does not exist - exactly one external definition for the identifier, or the identifier is not used and there - exist multiple external definitions for the identifier (6.9). --- A function definition includes an identifier list, but the types of the parameters are not - declared in a following declaration list (6.9.1). --- An adjusted parameter type in a function definition is not a complete object type - (6.9.1). --- A function that accepts a variable number of arguments is defined without a - parameter type list that ends with the ellipsis notation (6.9.1). - -[page 558] - --- The } that terminates a function is reached, and the value of the function call is used - by the caller (6.9.1). --- An identifier for an object with internal linkage and an incomplete type is declared - with a tentative definition (6.9.2). --- The token defined is generated during the expansion of a #if or #elif - preprocessing directive, or the use of the defined unary operator does not match - one of the two specified forms prior to macro replacement (6.10.1). --- The #include preprocessing directive that results after expansion does not match - one of the two header name forms (6.10.2). --- The character sequence in an #include preprocessing directive does not start with a - letter (6.10.2). --- There are sequences of preprocessing tokens within the list of macro arguments that - would otherwise act as preprocessing directives (6.10.3). --- The result of the preprocessing operator # is not a valid character string literal - (6.10.3.2). --- The result of the preprocessing operator ## is not a valid preprocessing token - (6.10.3.3). --- The #line preprocessing directive that results after expansion does not match one of - the two well-defined forms, or its digit sequence specifies zero or a number greater - than 2147483647 (6.10.4). --- A non-STDC #pragma preprocessing directive that is documented as causing - translation failure or some other form of undefined behavior is encountered (6.10.6). --- A #pragma STDC preprocessing directive does not match one of the well-defined - forms (6.10.6). --- The name of a predefined macro, or the identifier defined, is the subject of a - #define or #undef preprocessing directive (6.10.8). --- An attempt is made to copy an object to an overlapping object by use of a library - function, other than as explicitly allowed (e.g., memmove) (clause 7). --- A file with the same name as one of the standard headers, not provided as part of the - implementation, is placed in any of the standard places that are searched for included - source files (7.1.2). --- A header is included within an external declaration or definition (7.1.2). --- A function, object, type, or macro that is specified as being declared or defined by - some standard header is used before any header that declares or defines it is included - (7.1.2). - -[page 559] - --- A standard header is included while a macro is defined with the same name as a - keyword (7.1.2). --- The program attempts to declare a library function itself, rather than via a standard - header, but the declaration does not have external linkage (7.1.2). --- The program declares or defines a reserved identifier, other than as allowed by 7.1.4 - (7.1.3). --- The program removes the definition of a macro whose name begins with an - underscore and either an uppercase letter or another underscore (7.1.3). --- An argument to a library function has an invalid value or a type not expected by a - function with variable number of arguments (7.1.4). --- The pointer passed to a library function array parameter does not have a value such - that all address computations and object accesses are valid (7.1.4). --- The macro definition of assert is suppressed in order to access an actual function - (7.2). --- The argument to the assert macro does not have a scalar type (7.2). --- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in - any context other than outside all external declarations or preceding all explicit - declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2). --- The value of an argument to a character handling function is neither equal to the value - of EOF nor representable as an unsigned char (7.4). --- A macro definition of errno is suppressed in order to access an actual object, or the - program defines an identifier with the name errno (7.5). --- Part of the program tests floating-point status flags, sets floating-point control modes, - or runs under non-default mode settings, but was translated with the state for the - FENV_ACCESS pragma ''off'' (7.6.1). --- The exception-mask argument for one of the functions that provide access to the - floating-point status flags has a nonzero value not obtained by bitwise OR of the - floating-point exception macros (7.6.2). --- The fesetexceptflag function is used to set floating-point status flags that were - not specified in the call to the fegetexceptflag function that provided the value - of the corresponding fexcept_t object (7.6.2.4). --- The argument to fesetenv or feupdateenv is neither an object set by a call to - fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4). --- The value of the result of an integer arithmetic or conversion function cannot be - represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1). - -[page 560] - --- The program modifies the string pointed to by the value returned by the setlocale - function (7.11.1.1). --- The program modifies the structure pointed to by the value returned by the - localeconv function (7.11.2.1). --- A macro definition of math_errhandling is suppressed or the program defines - an identifier with the name math_errhandling (7.12). --- An argument to a floating-point classification or comparison macro is not of real - floating type (7.12.3, 7.12.14). --- A macro definition of setjmp is suppressed in order to access an actual function, or - the program defines an external identifier with the name setjmp (7.13). --- An invocation of the setjmp macro occurs other than in an allowed context - (7.13.2.1). --- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1). --- After a longjmp, there is an attempt to access the value of an object of automatic - storage duration that does not have volatile-qualified type, local to the function - containing the invocation of the corresponding setjmp macro, that was changed - between the setjmp invocation and longjmp call (7.13.2.1). --- The program specifies an invalid pointer to a signal handler function (7.14.1.1). --- A signal handler returns when the signal corresponded to a computational exception - (7.14.1.1). --- A signal occurs as the result of calling the abort or raise function, and the signal - handler calls the raise function (7.14.1.1). --- A signal occurs other than as the result of calling the abort or raise function, and - the signal handler refers to an object with static or thread storage duration that is not a - lock-free atomic object other than by assigning a value to an object declared as - volatile sig_atomic_t, or calls any function in the standard library other - than the abort function, the _Exit function, the quick_exit function, or the - signal function (for the same signal number) (7.14.1.1). --- The value of errno is referred to after a signal occurred other than as the result of - calling the abort or raise function and the corresponding signal handler obtained - a SIG_ERR return from a call to the signal function (7.14.1.1). --- A signal is generated by an asynchronous signal handler (7.14.1.1). --- A function with a variable number of arguments attempts to access its varying - arguments other than through a properly declared and initialized va_list object, or - before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4). - -[page 561] - --- The macro va_arg is invoked using the parameter ap that was passed to a function - that invoked the macro va_arg with the same parameter (7.16). --- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in - order to access an actual function, or the program defines an external identifier with - the name va_copy or va_end (7.16.1). --- The va_start or va_copy macro is invoked without a corresponding invocation - of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3, - 7.16.1.4). --- The type parameter to the va_arg macro is not such that a pointer to an object of - that type can be obtained simply by postfixing a * (7.16.1.1). --- The va_arg macro is invoked when there is no actual next argument, or with a - specified type that is not compatible with the promoted type of the actual next - argument, with certain exceptions (7.16.1.1). --- The va_copy or va_start macro is called to initialize a va_list that was - previously initialized by either macro without an intervening invocation of the - va_end macro for the same va_list (7.16.1.2, 7.16.1.4). --- The parameter parmN of a va_start macro is declared with the register - storage class, with a function or array type, or with a type that is not compatible with - the type that results after application of the default argument promotions (7.16.1.4). --- The member designator parameter of an offsetof macro is an invalid right - operand of the . operator for the type parameter, or designates a bit-field (7.19). --- The argument in an instance of one of the integer-constant macros is not a decimal, - octal, or hexadecimal constant, or it has a value that exceeds the limits for the - corresponding type (7.20.4). --- A byte input/output function is applied to a wide-oriented stream, or a wide character - input/output function is applied to a byte-oriented stream (7.21.2). --- Use is made of any portion of a file beyond the most recent wide character written to - a wide-oriented stream (7.21.2). --- The value of a pointer to a FILE object is used after the associated file is closed - (7.21.3). --- The stream for the fflush function points to an input stream or to an update stream - in which the most recent operation was input (7.21.5.2). --- The string pointed to by the mode argument in a call to the fopen function does not - exactly match one of the specified character sequences (7.21.5.3). --- An output operation on an update stream is followed by an input operation without an - intervening call to the fflush function or a file positioning function, or an input - -[page 562] - - operation on an update stream is followed by an output operation with an intervening - call to a file positioning function (7.21.5.3). --- An attempt is made to use the contents of the array that was supplied in a call to the - setvbuf function (7.21.5.6). --- There are insufficient arguments for the format in a call to one of the formatted - input/output functions, or an argument does not have an appropriate type (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- The format in a call to one of the formatted input/output functions or to the - strftime or wcsftime function is not a valid multibyte character sequence that - begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.26.3.5, 7.28.2.1, 7.28.2.2, - 7.28.5.1). --- In a call to one of the formatted output functions, a precision appears with a - conversion specifier other than those described (7.21.6.1, 7.28.2.1). --- A conversion specification for a formatted output function uses an asterisk to denote - an argument-supplied field width or precision, but the corresponding argument is not - provided (7.21.6.1, 7.28.2.1). --- A conversion specification for a formatted output function uses a # or 0 flag with a - conversion specifier other than those described (7.21.6.1, 7.28.2.1). --- A conversion specification for one of the formatted input/output functions uses a - length modifier with a conversion specifier other than those described (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- An s conversion specifier is encountered by one of the formatted output functions, - and the argument is missing the null terminator (unless a precision is specified that - does not require null termination) (7.21.6.1, 7.28.2.1). --- An n conversion specification for one of the formatted input/output functions includes - any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- A % conversion specifier is encountered by one of the formatted input/output - functions, but the complete conversion specification is not exactly %% (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- An invalid conversion specification is found in the format for one of the formatted - input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2, - 7.26.3.5, 7.28.2.1, 7.28.2.2, 7.28.5.1). --- The number of characters transmitted by a formatted output function is greater than - INT_MAX (7.21.6.1, 7.21.6.3, 7.21.6.8, 7.21.6.10). - -[page 563] - --- The result of a conversion by one of the formatted input functions cannot be - represented in the corresponding object, or the receiving object does not have an - appropriate type (7.21.6.2, 7.28.2.2). --- A c, s, or [ conversion specifier is encountered by one of the formatted input - functions, and the array pointed to by the corresponding argument is not large enough - to accept the input sequence (and a null terminator if the conversion specifier is s or - [) (7.21.6.2, 7.28.2.2). --- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the - formatted input functions, but the input is not a valid multibyte character sequence - that begins in the initial shift state (7.21.6.2, 7.28.2.2). --- The input item for a %p conversion by one of the formatted input functions is not a - value converted earlier during the same program execution (7.21.6.2, 7.28.2.2). --- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, - vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or - vwscanf function is called with an improperly initialized va_list argument, or - the argument is used (other than in an invocation of va_end) after the function - returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, - 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10). --- The contents of the array supplied in a call to the fgets or fgetws function are - used after a read error occurred (7.21.7.2, 7.28.3.2). --- The file position indicator for a binary stream is used after a call to the ungetc - function where its value was zero before the call (7.21.7.10). --- The file position indicator for a stream is used after an error occurred during a call to - the fread or fwrite function (7.21.8.1, 7.21.8.2). --- A partial element read by a call to the fread function is used (7.21.8.1). --- The fseek function is called for a text stream with a nonzero offset and either the - offset was not returned by a previous successful call to the ftell function on a - stream associated with the same file or whence is not SEEK_SET (7.21.9.2). --- The fsetpos function is called to set a position that was not returned by a previous - successful call to the fgetpos function on a stream associated with the same file - (7.21.9.3). --- A non-null pointer returned by a call to the calloc, malloc, or realloc function - with a zero requested size is used to access an object (7.22.3). --- The value of a pointer that refers to space deallocated by a call to the free or - realloc function is used (7.22.3). - -[page 564] - --- The alignment requested of the aligned_alloc function is not valid or not - supported by the implementation, or the size requested is not an integral multiple of - the alignment (7.22.3.1). --- The pointer argument to the free or realloc function does not match a pointer - earlier returned by a memory management function, or the space has been deallocated - by a call to free or realloc (7.22.3.3, 7.22.3.5). --- The value of the object allocated by the malloc function is used (7.22.3.4). --- The value of any bytes in a new object allocated by the realloc function beyond - the size of the old object are used (7.22.3.5). --- The program calls the exit or quick_exit function more than once, or calls both - functions (7.22.4.4, 7.22.4.7). --- During the call to a function registered with the atexit or at_quick_exit - function, a call is made to the longjmp function that would terminate the call to the - registered function (7.22.4.4, 7.22.4.7). --- The string set up by the getenv or strerror function is modified by the program - (7.22.4.6, 7.23.6.2). --- A command is executed through the system function in a way that is documented as - causing termination or some other form of undefined behavior (7.22.4.8). --- A searching or sorting utility function is called with an invalid pointer argument, even - if the number of elements is zero (7.22.5). --- The comparison function called by a searching or sorting utility function alters the - contents of the array being searched or sorted, or returns ordering values - inconsistently (7.22.5). --- The array being searched by the bsearch function does not have its elements in - proper order (7.22.5.1). --- The current conversion state is used by a multibyte/wide character conversion - function after changing the LC_CTYPE category (7.22.7). --- A string or wide string utility function is instructed to access an array beyond the end - of an object (7.23.1, 7.28.4). --- A string or wide string utility function is called with an invalid pointer argument, even - if the length is zero (7.23.1, 7.28.4). --- The contents of the destination array are used after a call to the strxfrm, - strftime, wcsxfrm, or wcsftime function in which the specified length was - too small to hold the entire null-terminated result (7.23.4.5, 7.26.3.5, 7.28.4.4.4, - 7.28.5.1). - -[page 565] - - -- The first argument in the very first call to the strtok or wcstok is a null pointer - (7.23.5.8, 7.28.4.5.7). - -- The type of an argument to a type-generic macro is not compatible with the type of - the corresponding parameter of the selected function (7.24). - -- A complex argument is supplied for a generic parameter of a type-generic macro that - has no corresponding complex function (7.24). - -- At least one field of the broken-down time passed to asctime contains a value - outside its normal range, or the calculated year exceeds four digits or is less than the - year 1000 (7.26.3.1). - -- The argument corresponding to an s specifier without an l qualifier in a call to the - fwprintf function does not point to a valid multibyte character sequence that - begins in the initial shift state (7.28.2.11). - -- In a call to the wcstok function, the object pointed to by ptr does not have the - value stored by the previous call for the same wide string (7.28.4.5.7). - -- An mbstate_t object is used inappropriately (7.28.6). - -- The value of an argument of type wint_t to a wide character classification or case - mapping function is neither equal to the value of WEOF nor representable as a - wchar_t (7.29.1). - -- The iswctype function is called using a different LC_CTYPE category from the - one in effect for the call to the wctype function that returned the description - (7.29.2.2.1). - -- The towctrans function is called using a different LC_CTYPE category from the - one in effect for the call to the wctrans function that returned the description - (7.29.3.2.1). - J.3 Implementation-defined behavior -1 A conforming implementation is required to document its choice of behavior in each of - the areas listed in this subclause. The following are implementation-defined: - -[page 566] - - J.3.1 Translation -1 -- How a diagnostic is identified (3.10, 5.1.1.3). - -- Whether each nonempty sequence of white-space characters other than new-line is - retained or replaced by one space character in translation phase 3 (5.1.1.2). - J.3.2 Environment -1 -- The mapping between physical source file multibyte characters and the source - character set in translation phase 1 (5.1.1.2). - -- The name and type of the function called at program startup in a freestanding - environment (5.1.2.1). - -- The effect of program termination in a freestanding environment (5.1.2.1). - -- An alternative manner in which the main function may be defined (5.1.2.2.1). - -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1). - -- What constitutes an interactive device (5.1.2.3). - -- Whether a program can have more than one thread of execution in a freestanding - environment (5.1.2.4). - -- The set of signals, their semantics, and their default handling (7.14). - -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a - computational exception (7.14.1.1). - -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at - program startup (7.14.1.1). - -- The set of environment names and the method for altering the environment list used - by the getenv function (7.22.4.6). - -- The manner of execution of the string by the system function (7.22.4.8). - J.3.3 Identifiers -1 -- Which additional multibyte characters may appear in identifiers and their - correspondence to universal character names (6.4.2). - -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2). - -[page 567] - - J.3.4 Characters -1 -- The number of bits in a byte (3.6). - -- The values of the members of the execution character set (5.2.1). - -- The unique value of the member of the execution character set produced for each of - the standard alphabetic escape sequences (5.2.2). - -- The value of a char object into which has been stored any character other than a - member of the basic execution character set (6.2.5). - -- Which of signed char or unsigned char has the same range, representation, - and behavior as ''plain'' char (6.2.5, 6.3.1.1). - -- The mapping of members of the source character set (in character constants and string - literals) to members of the execution character set (6.4.4.4, 5.1.1.2). - -- The value of an integer character constant containing more than one character or - containing a character or escape sequence that does not map to a single-byte - execution character (6.4.4.4). - -- The value of a wide character constant containing more than one multibyte character - or a single multibyte character that maps to multiple members of the extended - execution character set, or containing a multibyte character or escape sequence not - represented in the extended execution character set (6.4.4.4). - -- The current locale used to convert a wide character constant consisting of a single - multibyte character that maps to a member of the extended execution character set - into a corresponding wide character code (6.4.4.4). - -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so, - the treatment of the resulting multibyte character sequence (6.4.5). - -- The current locale used to convert a wide string literal into corresponding wide - character codes (6.4.5). - -- The value of a string literal containing a multibyte character or escape sequence not - represented in the execution character set (6.4.5). - -- The encoding of any of wchar_t, char16_t, and char32_t where the - corresponding standard encoding macro (__STDC_ISO_10646__, - __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2). - -[page 568] - - J.3.5 Integers -1 -- Any extended integer types that exist in the implementation (6.2.5). - -- Whether signed integer types are represented using sign and magnitude, two's - complement, or ones' complement, and whether the extraordinary value is a trap - representation or an ordinary value (6.2.6.2). - -- The rank of any extended integer type relative to another extended integer type with - the same precision (6.3.1.1). - -- The result of, or the signal raised by, converting an integer to a signed integer type - when the value cannot be represented in an object of that type (6.3.1.3). - -- The results of some bitwise operations on signed integers (6.5). - J.3.6 Floating point -1 -- The accuracy of the floating-point operations and of the library functions in - and that return floating-point results (5.2.4.2.2). - -- The accuracy of the conversions between floating-point internal representations and - string representations performed by the library functions in , - , and (5.2.4.2.2). - -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS - (5.2.4.2.2). - -- The evaluation methods characterized by non-standard negative values of - FLT_EVAL_METHOD (5.2.4.2.2). - -- The direction of rounding when an integer is converted to a floating-point number that - cannot exactly represent the original value (6.3.1.4). - -- The direction of rounding when a floating-point number is converted to a narrower - floating-point number (6.3.1.5). - -- How the nearest representable value or the larger or smaller representable value - immediately adjacent to the nearest representable value is chosen for certain floating - constants (6.4.4.2). - -- Whether and how floating expressions are contracted when not disallowed by the - FP_CONTRACT pragma (6.5). - -- The default state for the FENV_ACCESS pragma (7.6.1). - -- Additional floating-point exceptions, rounding modes, environments, and - classifications, and their macro names (7.6, 7.12). - -- The default state for the FP_CONTRACT pragma (7.12.2). - -[page 569] - - J.3.7 Arrays and pointers -1 -- The result of converting a pointer to an integer or vice versa (6.3.2.3). - -- The size of the result of subtracting two pointers to elements of the same array - (6.5.6). - J.3.8 Hints -1 -- The extent to which suggestions made by using the register storage-class - specifier are effective (6.7.1). - -- The extent to which suggestions made by using the inline function specifier are - effective (6.7.4). - J.3.9 Structures, unions, enumerations, and bit-fields -1 -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an - unsigned int bit-field (6.7.2, 6.7.2.1). - -- Allowable bit-field types other than _Bool, signed int, and unsigned int - (6.7.2.1). - -- Whether atomic types are permitted for bit-fields (6.7.2.1). - -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1). - -- The order of allocation of bit-fields within a unit (6.7.2.1). - -- The alignment of non-bit-field members of structures (6.7.2.1). This should present - no problem unless binary data written by one implementation is read by another. - -- The integer type compatible with each enumerated type (6.7.2.2). - J.3.10 Qualifiers -1 -- What constitutes an access to an object that has volatile-qualified type (6.7.3). - J.3.11 Preprocessing directives -1 -- The locations within #pragma directives where header name preprocessing tokens - are recognized (6.4, 6.4.7). - -- How sequences in both forms of header names are mapped to headers or external - source file names (6.4.7). - -- Whether the value of a character constant in a constant expression that controls - conditional inclusion matches the value of the same character constant in the - execution character set (6.10.1). - -- Whether the value of a single-character character constant in a constant expression - that controls conditional inclusion may have a negative value (6.10.1). - -[page 570] - - -- The places that are searched for an included < > delimited header, and how the places - are specified or the header is identified (6.10.2). - -- How the named source file is searched for in an included " " delimited header - (6.10.2). - -- The method by which preprocessing tokens (possibly resulting from macro - expansion) in a #include directive are combined into a header name (6.10.2). - -- The nesting limit for #include processing (6.10.2). - -- Whether the # operator inserts a \ character before the \ character that begins a - universal character name in a character constant or string literal (6.10.3.2). - -- The behavior on each recognized non-STDC #pragma directive (6.10.6). - -- The definitions for __DATE__ and __TIME__ when respectively, the date and - time of translation are not available (6.10.8.1). - J.3.12 Library functions -1 -- Any library facilities available to a freestanding program, other than the minimal set - required by clause 4 (5.1.2.1). - -- The format of the diagnostic printed by the assert macro (7.2.1.1). - -- The representation of the floating-point status flags stored by the - fegetexceptflag function (7.6.2.2). - -- Whether the feraiseexcept function raises the ''inexact'' floating-point - exception in addition to the ''overflow'' or ''underflow'' floating-point exception - (7.6.2.3). - -- Strings other than "C" and "" that may be passed as the second argument to the - setlocale function (7.11.1.1). - -- The types defined for float_t and double_t when the value of the - FLT_EVAL_METHOD macro is less than 0 (7.12). - -- Domain errors for the mathematics functions, other than those required by this - International Standard (7.12.1). - -- The values returned by the mathematics functions on domain errors or pole errors - (7.12.1). - -- The values returned by the mathematics functions on underflow range errors, whether - errno is set to the value of the macro ERANGE when the integer expression - math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow'' - floating-point exception is raised when the integer expression math_errhandling - & MATH_ERREXCEPT is nonzero. (7.12.1). - -[page 571] - --- Whether a domain error occurs or zero is returned when an fmod function has a - second argument of zero (7.12.10.1). --- Whether a domain error occurs or zero is returned when a remainder function has - a second argument of zero (7.12.10.2). --- The base-2 logarithm of the modulus used by the remquo functions in reducing the - quotient (7.12.10.3). --- Whether a domain error occurs or zero is returned when a remquo function has a - second argument of zero (7.12.10.3). --- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call - of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1). --- The null pointer constant to which the macro NULL expands (7.19). --- Whether the last line of a text stream requires a terminating new-line character - (7.21.2). --- Whether space characters that are written out to a text stream immediately before a - new-line character appear when read in (7.21.2). --- The number of null characters that may be appended to data written to a binary - stream (7.21.2). --- Whether the file position indicator of an append-mode stream is initially positioned at - the beginning or end of the file (7.21.3). --- Whether a write on a text stream causes the associated file to be truncated beyond that - point (7.21.3). --- The characteristics of file buffering (7.21.3). --- Whether a zero-length file actually exists (7.21.3). --- The rules for composing valid file names (7.21.3). --- Whether the same file can be simultaneously open multiple times (7.21.3). --- The nature and choice of encodings used for multibyte characters in files (7.21.3). --- The effect of the remove function on an open file (7.21.4.1). --- The effect if a file with the new name exists prior to a call to the rename function - (7.21.4.2). --- Whether an open temporary file is removed upon abnormal program termination - (7.21.4.3). --- Which changes of mode are permitted (if any), and under what circumstances - (7.21.5.4). - -[page 572] - --- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar - sequence printed for a NaN (7.21.6.1, 7.28.2.1). --- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1, - 7.28.2.1). --- The interpretation of a - character that is neither the first nor the last character, nor - the second where a ^ character is the first, in the scanlist for %[ conversion in the - fscanf or fwscanf function (7.21.6.2, 7.28.2.1). --- The set of sequences matched by a %p conversion and the interpretation of the - corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.28.2.2). --- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell - functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4). --- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is - converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold - function (7.22.1.3, 7.28.4.1.1). --- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold - function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.28.4.1.1). --- Whether the calloc, malloc, and realloc functions return a null pointer or a - pointer to an allocated object when the size requested is zero (7.22.3). --- Whether open streams with unwritten buffered data are flushed, open streams are - closed, or temporary files are removed when the abort or _Exit function is called - (7.22.4.1, 7.22.4.5). --- The termination status returned to the host environment by the abort, exit, - _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7). --- The value returned by the system function when its argument is not a null pointer - (7.22.4.8). --- The local time zone and Daylight Saving Time (7.26.1). --- The range and precision of times representable in clock_t and time_t (7.26). --- The era for the clock function (7.26.2.1). --- The replacement string for the %Z specifier to the strftime, and wcsftime - functions in the "C" locale (7.26.3.5, 7.28.5.1). --- Whether the functions in honor the rounding direction mode in an - IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10). - -[page 573] - - J.3.13 Architecture -1 -- The values or expressions assigned to the macros specified in the headers - , , and (5.2.4.2, 7.20.2, 7.20.3). - -- The result of attempting to indirectly access an object with automatic or thread - storage duration from a thread other than the one with which it is associated (6.2.4). - -- The number, order, and encoding of bytes in any object (when not explicitly specified - in this International Standard) (6.2.6.1). - -- Whether any extended alignments are supported and the contexts in which they are - supported (6.2.8). - -- Valid alignment values other than those returned by an alignof expression for - fundamental types, if any (6.2.8). - -- The value of the result of the sizeof and alignof operators (6.5.3.4). - J.4 Locale-specific behavior -1 The following characteristics of a hosted environment are locale-specific and are required - to be documented by the implementation: - -- Additional members of the source and execution character sets beyond the basic - character set (5.2.1). - -- The presence, meaning, and representation of additional multibyte characters in the - execution character set beyond the basic character set (5.2.1.2). - -- The shift states used for the encoding of multibyte characters (5.2.1.2). - -- The direction of writing of successive printing characters (5.2.2). - -- The decimal-point character (7.1.1). - -- The set of printing characters (7.4, 7.29.2). - -- The set of control characters (7.4, 7.29.2). - -- The sets of characters tested for by the isalpha, isblank, islower, ispunct, - isspace, isupper, iswalpha, iswblank, iswlower, iswpunct, - iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10, - 7.4.1.11, 7.29.2.1.2, 7.29.2.1.3, 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, 7.29.2.1.11). - -- The native environment (7.11.1.1). - -- Additional subject sequences accepted by the numeric conversion functions (7.22.1, - 7.28.4.1). - -- The collation sequence of the execution character set (7.23.4.3, 7.28.4.4.2). - -[page 574] - - -- The contents of the error message strings set up by the strerror function - (7.23.6.2). - -- The formats for time and date (7.26.3.5, 7.28.5.1). - -- Character mappings that are supported by the towctrans function (7.29.1). - -- Character classifications that are supported by the iswctype function (7.29.1). - J.5 Common extensions -1 The following extensions are widely used in many systems, but are not portable to all - implementations. The inclusion of any extension that may cause a strictly conforming - program to become invalid renders an implementation nonconforming. Examples of such - extensions are new keywords, extra library functions declared in standard headers, or - predefined macros with names that do not begin with an underscore. - J.5.1 Environment arguments -1 In a hosted environment, the main function receives a third argument, char *envp[], - that points to a null-terminated array of pointers to char, each of which points to a string - that provides information about the environment for this execution of the program - (5.1.2.2.1). - J.5.2 Specialized identifiers -1 Characters other than the underscore _, letters, and digits, that are not part of the basic - source character set (such as the dollar sign $, or characters in national character sets) - may appear in an identifier (6.4.2). - J.5.3 Lengths and cases of identifiers -1 All characters in identifiers (with or without external linkage) are significant (6.4.2). - J.5.4 Scopes of identifiers -1 A function identifier, or the identifier of an object the declaration of which contains the - keyword extern, has file scope (6.2.1). - J.5.5 Writable string literals -1 String literals are modifiable (in which case, identical string literals should denote distinct - objects) (6.4.5). - -[page 575] - - J.5.6 Other arithmetic types -1 Additional arithmetic types, such as __int128 or double double, and their - appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have - more range or precision than long double, may be used for evaluating expressions of - other floating types, and may be used to define float_t or double_t. - J.5.7 Function pointer casts -1 A pointer to an object or to void may be cast to a pointer to a function, allowing data to - be invoked as a function (6.5.4). -2 A pointer to a function may be cast to a pointer to an object or to void, allowing a - function to be inspected or modified (for example, by a debugger) (6.5.4). - J.5.8 Extended bit-field types -1 A bit-field may be declared with a type other than _Bool, unsigned int, or - signed int, with an appropriate maximum width (6.7.2.1). - J.5.9 The fortran keyword -1 The fortran function specifier may be used in a function declaration to indicate that - calls suitable for FORTRAN should be generated, or that a different representation for the - external name is to be generated (6.7.4). - J.5.10 The asm keyword -1 The asm keyword may be used to insert assembly language directly into the translator - output (6.8). The most common implementation is via a statement of the form: - asm ( character-string-literal ); - J.5.11 Multiple external definitions -1 There may be more than one external definition for the identifier of an object, with or - without the explicit use of the keyword extern; if the definitions disagree, or more than - one is initialized, the behavior is undefined (6.9.2). - J.5.12 Predefined macro names -1 Macro names that do not begin with an underscore, describing the translation and - execution environments, are defined by the implementation before translation begins - (6.10.8). - -[page 576] - - J.5.13 Floating-point status flags -1 If any floating-point status flags are set on normal termination after all calls to functions - registered by the atexit function have been made (see 7.22.4.4), the implementation - writes some diagnostics indicating the fact to the stderr stream, if it is still open, - J.5.14 Extra arguments for signal handlers -1 Handlers for specific signals are called with extra arguments in addition to the signal - number (7.14.1.1). - J.5.15 Additional stream types and file-opening modes -1 Additional mappings from files to streams are supported (7.21.2). -2 Additional file-opening modes may be specified by characters appended to the mode - argument of the fopen function (7.21.5.3). - J.5.16 Defined file position indicator -1 The file position indicator is decremented by each successful call to the ungetc or - ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10, - 7.28.3.10). - J.5.17 Math error reporting -1 Functions declared in and raise SIGFPE to report errors - instead of, or in addition to, setting errno or raising floating-point exceptions (7.3, - 7.12). - -[page 577] - - Annex K - (normative) - Bounds-checking interfaces - K.1 Background -1 Traditionally, the C Library has contained many functions that trust the programmer to - provide output character arrays big enough to hold the result being produced. Not only - do these functions not check that the arrays are big enough, they frequently lack the - information needed to perform such checks. While it is possible to write safe, robust, and - error-free code using the existing library, the library tends to promote programming styles - that lead to mysterious failures if a result is too big for the provided array. -2 A common programming style is to declare character arrays large enough to handle most - practical cases. However, if these arrays are not large enough to handle the resulting - strings, data can be written past the end of the array overwriting other data and program - structures. The program never gets any indication that a problem exists, and so never has - a chance to recover or to fail gracefully. -3 Worse, this style of programming has compromised the security of computers and - networks. Buffer overflows can often be exploited to run arbitrary code with the - permissions of the vulnerable (defective) program. -4 If the programmer writes runtime checks to verify lengths before calling library - functions, then those runtime checks frequently duplicate work done inside the library - functions, which discover string lengths as a side effect of doing their job. -5 This annex provides alternative library functions that promote safer, more secure - programming. The alternative functions verify that output buffers are large enough for - the intended result and return a failure indicator if they are not. Data is never written past - the end of an array. All string results are null terminated. -6 This annex also addresses another problem that complicates writing robust code: - functions that are not reentrant because they return pointers to static objects owned by the - function. Such functions can be troublesome since a previously returned result can - change if the function is called again, perhaps by another thread. - -[page 578] - - K.2 Scope -1 This annex specifies a series of optional extensions that can be useful in the mitigation of - security vulnerabilities in programs, and comprise new functions, macros, and types - declared or defined in existing standard headers. -2 An implementation that defines __STDC_LIB_EXT1__ shall conform to the - specifications in this annex.367) -3 Subclause K.3 should be read as if it were merged into the parallel structure of named - subclauses of clause 7. - K.3 Library - K.3.1 Introduction - K.3.1.1 Standard headers -1 The functions, macros, and types declared or defined in K.3 and its subclauses are not - declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 0 at the point in the source file - where the appropriate header is first included. -2 The functions, macros, and types declared or defined in K.3 and its subclauses are - declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 1 at the point in the source file - where the appropriate header is first included.368) -3 It is implementation-defined whether the functions, macros, and types declared or defined - in K.3 and its subclauses are declared or defined by their respective headers if - __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file - where the appropriate header is first included.369) -4 Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be - defined identically for all inclusions of any headers from subclause K.3. If - __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the - implementation shall issue a diagnostic as if a preprocessor error directive were used. - - - 367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these - specifications. - 368) Future revisions of this International Standard may define meanings for other values of - __STDC_WANT_LIB_EXT1__. - 369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in - headers. All other names are not reserved, and a conforming implementation is not permitted to use - them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an - unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the - implementation is not conforming. - -[page 579] - - K.3.1.2 Reserved identifiers -1 Each macro name in any of the following subclauses is reserved for use as specified if it - is defined by any of its associated headers when included; unless explicitly stated - otherwise (see 7.1.4). -2 All identifiers with external linkage in any of the following subclauses are reserved for - use as identifiers with external linkage if any of them are used by the program. None of - them are reserved if none of them are used. -3 Each identifier with file scope listed in any of the following subclauses is reserved for use - as a macro name and as an identifier with file scope in the same name space if it is - defined by any of its associated headers when included. - K.3.1.3 Use of errno -1 An implementation may set errno for the functions defined in this annex, but is not - required to. - K.3.1.4 Runtime-constraint violations -1 Most functions in this annex include as part of their specification a list of runtime- - constraints. These runtime-constraints are requirements on the program using the - library.370) -2 Implementations shall verify that the runtime-constraints for a function are not violated - by the program. If a runtime-constraint is violated, the implementation shall call the - currently registered runtime-constraint handler (see set_constraint_handler_s - in ). Multiple runtime-constraint violations in the same call to a library - function result in only one call to the runtime-constraint handler. It is unspecified which - one of the multiple runtime-constraint violations cause the handler to be called. -3 If the runtime-constraints section for a function states an action to be performed when a - runtime-constraint violation occurs, the function shall perform the action before calling - the runtime-constraint handler. If the runtime-constraints section lists actions that are - prohibited when a runtime-constraint violation occurs, then such actions are prohibited to - the function both before calling the handler and after the handler returns. -4 The runtime-constraint handler might not return. If the handler does return, the library - function whose runtime-constraint was violated shall return some indication of failure as - given by the returns section in the function's specification. - - - - 370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still - exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a - runtime-constraint violation by calling the runtime-constraint handler. This license comes directly - from the definition of undefined behavior. - -[page 580] - - K.3.2 Errors -1 The header defines a type. -2 The type is - errno_t - which is type int.371) - K.3.3 Common definitions -1 The header defines a type. -2 The type is - rsize_t - which is the type size_t.372) - K.3.4 Integer types -1 The header defines a macro. -2 The macro is - RSIZE_MAX - which expands to a value373) of type size_t. Functions that have parameters of type - rsize_t consider it a runtime-constraint violation if the values of those parameters are - greater than RSIZE_MAX. - Recommended practice -3 Extremely large object sizes are frequently a sign that an object's size was calculated - incorrectly. For example, negative numbers appear as very large positive numbers when - converted to an unsigned type like size_t. Also, some implementations do not support - objects as large as the maximum value that can be represented by type size_t. -4 For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect - programming errors. For implementations targeting machines with large address spaces, - it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest - object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of - some legitimate, but very large, objects. Implementations targeting machines with small - address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there - - 371) As a matter of programming style, errno_t may be used as the type of something that deals only - with the values that might be found in errno. For example, a function which returns the value of - errno might be declared as having the return type errno_t. - 372) See the description of the RSIZE_MAX macro in . - 373) The macro RSIZE_MAX need not expand to a constant expression. - -[page 581] - - is no object size that is considered a runtime-constraint violation. - K.3.5 Input/output -1 The header defines several macros and two types. -2 The macros are - L_tmpnam_s - which expands to an integer constant expression that is the size needed for an array of - char large enough to hold a temporary file name string generated by the tmpnam_s - function; - TMP_MAX_S - which expands to an integer constant expression that is the maximum number of unique - file names that can be generated by the tmpnam_s function. -3 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.5.1 Operations on files - K.3.5.1.1 The tmpfile_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t tmpfile_s(FILE * restrict * restrict streamptr); - Runtime-constraints -2 streamptr shall not be a null pointer. -3 If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file. - Description -4 The tmpfile_s function creates a temporary binary file that is different from any other - existing file and that will automatically be removed when it is closed or at program - termination. If the program terminates abnormally, whether an open temporary file is - removed is implementation-defined. The file is opened for update with "wb+" mode - with the meaning that mode has in the fopen_s function (including the mode's effect - on exclusive access and file permissions). - -[page 582] - -5 If the file was created successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - to FILE pointed to by streamptr will be set to a null pointer. - Recommended practice - It should be possible to open at least TMP_MAX_S temporary files during the lifetime of - the program (this limit may be shared with tmpnam_s) and there should be no limit on - the number simultaneously open other than this limit and any limit on the number of open - files (FOPEN_MAX). - Returns -6 The tmpfile_s function returns zero if it created the file. If it did not create the file or - there was a runtime-constraint violation, tmpfile_s returns a nonzero value. - K.3.5.1.2 The tmpnam_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t tmpnam_s(char *s, rsize_t maxsize); - Runtime-constraints -2 s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX. - maxsize shall be greater than the length of the generated file name string. - Description -3 The tmpnam_s function generates a string that is a valid file name and that is not the - same as the name of an existing file.374) The function is potentially capable of generating - TMP_MAX_S different strings, but any or all of them may already be in use by existing - files and thus not be suitable return values. The lengths of these strings shall be less than - the value of the L_tmpnam_s macro. -4 The tmpnam_s function generates a different string each time it is called. -5 It is assumed that s points to an array of at least maxsize characters. This array will be - set to generated string, as specified below. - - - - 374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that - their names should not collide with those generated by conventional naming rules for the - implementation. It is still necessary to use the remove function to remove such files when their use - is ended, and before program termination. Implementations should take care in choosing the patterns - used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the - race condition and possible conflict when multiple programs run simultaneously by the same user - generate the same temporary file names. - -[page 583] - -6 The implementation shall behave as if no library function except tmpnam calls the - tmpnam_s function.375) - Recommended practice -7 After a program obtains a file name using the tmpnam_s function and before the - program creates a file with that name, the possibility exists that someone else may create - a file with that same name. To avoid this race condition, the tmpfile_s function - should be used instead of tmpnam_s when possible. One situation that requires the use - of the tmpnam_s function is when the program needs to create a temporary directory - rather than a temporary file. - Returns -8 If no suitable string can be generated, or if there is a runtime-constraint violation, the - tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize - is greater than zero) and returns a nonzero value. -9 Otherwise, the tmpnam_s function writes the string in the array pointed to by s and - returns zero. - Environmental limits -10 The value of the macro TMP_MAX_S shall be at least 25. - K.3.5.2 File access functions - K.3.5.2.1 The fopen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t fopen_s(FILE * restrict * restrict streamptr, - const char * restrict filename, - const char * restrict mode); - Runtime-constraints -2 None of streamptr, filename, or mode shall be a null pointer. -3 If there is a runtime-constraint violation, fopen_s does not attempt to open a file. - Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the - null pointer. - - - - - 375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming - convention for temporary files), but this is not required. - -[page 584] - - Description -4 The fopen_s function opens the file whose name is the string pointed to by - filename, and associates a stream with it. -5 The mode string shall be as described for fopen, with the addition that modes starting - with the character 'w' or 'a' may be preceded by the character 'u', see below: - uw truncate to zero length or create text file for writing, default - permissions - uwx create text file for writing, default permissions - ua append; open or create text file for writing at end-of-file, default - permissions - uwb truncate to zero length or create binary file for writing, default - permissions - uwbx create binary file for writing, default permissions - uab append; open or create binary file for writing at end-of-file, default - permissions - uw+ truncate to zero length or create text file for update, default - permissions - uw+x create text file for update, default permissions - ua+ append; open or create text file for update, writing at end-of-file, - default permissions - uw+b or uwb+ truncate to zero length or create binary file for update, default - permissions - uw+bx or uwb+x create binary file for update, default permissions - ua+b or uab+ append; open or create binary file for update, writing at end-of-file, - default permissions -6 Opening a file with exclusive mode ('x' as the last character in the mode argument) - fails if the file already exists or cannot be created. -7 To the extent that the underlying system supports the concepts, files opened for writing - shall be opened with exclusive (also known as non-shared) access. If the file is being - created, and the first character of the mode string is not 'u', to the extent that the - underlying system supports it, the file shall have a file permission that prevents other - users on the system from accessing the file. If the file is being created and first character - of the mode string is 'u', then by the time the file has been closed, it shall have the - system default file access permissions.376) -8 If the file was opened successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - - - 376) These are the same permissions that the file would have been created with by fopen. - -[page 585] - - to FILE pointed to by streamptr will be set to a null pointer. - Returns -9 The fopen_s function returns zero if it opened the file. If it did not open the file or if - there was a runtime-constraint violation, fopen_s returns a nonzero value. - K.3.5.2.2 The freopen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t freopen_s(FILE * restrict * restrict newstreamptr, - const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - Runtime-constraints -2 None of newstreamptr, mode, and stream shall be a null pointer. -3 If there is a runtime-constraint violation, freopen_s neither attempts to close any file - associated with stream nor attempts to open a file. Furthermore, if newstreamptr is - not a null pointer, fopen_s sets *newstreamptr to the null pointer. - Description -4 The freopen_s function opens the file whose name is the string pointed to by - filename and associates the stream pointed to by stream with it. The mode - argument has the same meaning as in the fopen_s function (including the mode's effect - on exclusive access and file permissions). -5 If filename is a null pointer, the freopen_s function attempts to change the mode of - the stream to that specified by mode, as if the name of the file currently associated with - the stream had been used. It is implementation-defined which changes of mode are - permitted (if any), and under what circumstances. -6 The freopen_s function first attempts to close any file that is associated with stream. - Failure to close the file is ignored. The error and end-of-file indicators for the stream are - cleared. -7 If the file was opened successfully, then the pointer to FILE pointed to by - newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE - pointed to by newstreamptr will be set to a null pointer. - Returns -8 The freopen_s function returns zero if it opened the file. If it did not open the file or - there was a runtime-constraint violation, freopen_s returns a nonzero value. - -[page 586] - - K.3.5.3 Formatted input/output functions -1 Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - K.3.5.3.1 The fprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int fprintf_s(FILE * restrict stream, - const char * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier377) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to fprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation,378) the fprintf_s function does not attempt - to produce further output, and it is unspecified to what extent fprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The fprintf_s function is equivalent to the fprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The fprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - 377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - 378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - -[page 587] - - K.3.5.3.2 The fscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int fscanf_s(FILE * restrict stream, - const char * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion - specifiers apply to a pair of arguments (unless assignment suppression is indicated by a - *). The first of these arguments is the same as for fscanf. That argument is - immediately followed in the argument list by the second argument, which has type - rsize_t and gives the number of elements in the array pointed to by the first argument - of the pair. If the first argument points to a scalar object, it is considered to be an array of - one element.380) -5 A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). - Returns -6 The fscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - - 379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - 380) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - -[page 588] - - fscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. -7 EXAMPLE 1 The call: - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - int n, i; float x; char name[50]; - n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50); - with the input line: - 25 54.32E-1 thompson - will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -8 EXAMPLE 2 The call: - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - int n; char s[5]; - n = fscanf_s(stdin, "%s", s, sizeof s); - with the input line: - hello - will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an - array of six characters to store it. - - K.3.5.3.3 The printf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int printf_s(const char * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier381) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to printf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the printf_s function does not attempt to - produce further output, and it is unspecified to what extent printf_s produced output - before discovering the runtime-constraint violation. - - - 381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 589] - - Description -4 The printf_s function is equivalent to the printf function except for the explicit - runtime-constraints listed above. - Returns -5 The printf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.4 The scanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int scanf_s(const char * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the scanf_s function does not attempt to - perform further input, and it is unspecified to what extent scanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The scanf_s function is equivalent to fscanf_s with the argument stdin - interposed before the arguments to scanf_s. - Returns -5 The scanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - scanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - K.3.5.3.5 The snprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int snprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to - -[page 590] - - snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the - null character. - Description -4 The snprintf_s function is equivalent to the snprintf function except for the - explicit runtime-constraints listed above. -5 The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the - array pointed to by s. - Returns -6 The snprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - K.3.5.3.6 The sprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int sprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier383) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to sprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. - - - - 382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - 383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 591] - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the - null character. - Description -4 The sprintf_s function is equivalent to the sprintf function except for the - parameter n and the explicit runtime-constraints listed above. -5 The sprintf_s function, unlike snprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the sprintf_s function returns the number - of characters written in the array, not counting the terminating null character. If an - encoding error occurred, sprintf_s returns a negative value. If any other runtime- - constraint violation occurred, sprintf_s returns zero. - K.3.5.3.7 The sscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int sscanf_s(const char * restrict s, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the sscanf_s function does not attempt to - perform further input, and it is unspecified to what extent sscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The sscanf_s function is equivalent to fscanf_s, except that input is obtained from - a string (specified by the argument s) rather than from a stream. Reaching the end of the - string is equivalent to encountering end-of-file for the fscanf_s function. If copying - takes place between objects that overlap, the objects take on unspecified values. - Returns -5 The sscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - sscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - -[page 592] - - K.3.5.3.8 The vfprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vfprintf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier384) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation, the vfprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vfprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vfprintf_s function is equivalent to the vfprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vfprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.9 The vfscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vfscanf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - - - - - 384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 593] - - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vfscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vfscanf_s function is equivalent to fscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfscanf_s function does not invoke the - va_end macro.385) - Returns -5 The vfscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.5.3.10 The vprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vprintf_s(const char * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier386) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to vprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the vprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vprintf_s produced output - before discovering the runtime-constraint violation. - - 385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - 386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 594] - - Description -4 The vprintf_s function is equivalent to the vprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The vprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.11 The vscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vscanf_s(const char * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vscanf_s function is equivalent to scanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vscanf_s function does not invoke the - va_end macro.387) - Returns -5 The vscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - - - - 387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - -[page 595] - - K.3.5.3.12 The vsnprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vsnprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to - vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the - null character. - Description -4 The vsnprintf_s function is equivalent to the vsnprintf function except for the - explicit runtime-constraints listed above. -5 The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within - the array pointed to by s. - Returns -6 The vsnprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - - - - - 388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 596] - - K.3.5.3.13 The vsprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vsprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier389) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to vsprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the - null character. - Description -4 The vsprintf_s function is equivalent to the vsprintf function except for the - parameter n and the explicit runtime-constraints listed above. -5 The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the vsprintf_s function returns the - number of characters written in the array, not counting the terminating null character. If - an encoding error occurred, vsprintf_s returns a negative value. If any other - runtime-constraint violation occurred, vsprintf_s returns zero. - - - - - 389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 597] - - K.3.5.3.14 The vsscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vsscanf_s(const char * restrict s, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vsscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vsscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vsscanf_s function is equivalent to sscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsscanf_s function does not invoke the - va_end macro.390) - Returns -5 The vsscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - K.3.5.4 Character input/output functions - K.3.5.4.1 The gets_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - char *gets_s(char *s, rsize_t n); - - - - - 390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - -[page 598] - - Runtime-constraints -2 s shall not be a null pointer. n shall neither be equal to zero nor be greater than - RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading - n-1 characters from stdin.391) -3 If there is a runtime-constraint violation, s[0] is set to the null character, and characters - are read and discarded from stdin until a new-line character is read, or end-of-file or a - read error occurs. - Description -4 The gets_s function reads at most one less than the number of characters specified by n - from the stream pointed to by stdin, into the array pointed to by s. No additional - characters are read after a new-line character (which is discarded) or after end-of-file. - The discarded new-line character does not count towards number of characters read. A - null character is written immediately after the last character read into the array. -5 If end-of-file is encountered and no characters have been read into the array, or if a read - error occurs during the operation, then s[0] is set to the null character, and the other - elements of s take unspecified values. - Recommended practice -6 The fgets function allows properly-written programs to safely process input lines too - long to store in the result array. In general this requires that callers of fgets pay - attention to the presence or absence of a new-line character in the result array. Consider - using fgets (along with any needed processing based on new-line characters) instead of - gets_s. - Returns -7 The gets_s function returns s if successful. If there was a runtime-constraint violation, - or if end-of-file is encountered and no characters have been read into the array, or if a - read error occurs during the operation, then a null pointer is returned. - - - - - 391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for - a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a - one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets - expect such a relationship. - -[page 599] - - K.3.6 General utilities -1 The header defines three types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t; and - constraint_handler_t - which has the following definition - typedef void (*constraint_handler_t)( - const char * restrict msg, - void * restrict ptr, - errno_t error); - K.3.6.1 Runtime-constraint handling - K.3.6.1.1 The set_constraint_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - constraint_handler_t set_constraint_handler_s( - constraint_handler_t handler); - Description -2 The set_constraint_handler_s function sets the runtime-constraint handler to - be handler. The runtime-constraint handler is the function to be called when a library - function detects a runtime-constraint violation. Only the most recent handler registered - with set_constraint_handler_s is called when a runtime-constraint violation - occurs. -3 When the handler is called, it is passed the following arguments in the following order: - 1. A pointer to a character string describing the runtime-constraint violation. - 2. A null pointer or a pointer to an implementation defined object. - 3. If the function calling the handler has a return type declared as errno_t, the - return value of the function is passed. Otherwise, a positive value of type - errno_t is passed. - -[page 600] - -4 The implementation has a default constraint handler that is used if no calls to the - set_constraint_handler_s function have been made. The behavior of the - default handler is implementation-defined, and it may cause the program to exit or abort. -5 If the handler argument to set_constraint_handler_s is a null pointer, the - implementation default handler becomes the current constraint handler. - Returns -6 The set_constraint_handler_s function returns a pointer to the previously - registered handler.392) - K.3.6.1.2 The abort_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - void abort_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - Description -2 A pointer to the abort_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -3 The abort_handler_s function writes a message on the standard error stream in an - implementation-defined format. The message shall include the string pointed to by msg. - The abort_handler_s function then calls the abort function.393) - Returns -4 The abort_handler_s function does not return to its caller. - - - - - 392) If the previous handler was registered by calling set_constraint_handler_s with a null - pointer argument, a pointer to the implementation default handler is returned (not NULL). - 393) Many implementations invoke a debugger when the abort function is called. - -[page 601] - - K.3.6.1.3 The ignore_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - void ignore_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - Description -2 A pointer to the ignore_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -3 The ignore_handler_s function simply returns to its caller.394) - Returns -4 The ignore_handler_s function returns no value. - K.3.6.2 Communication with the environment - K.3.6.2.1 The getenv_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t getenv_s(size_t * restrict len, - char * restrict value, rsize_t maxsize, - const char * restrict name); - Runtime-constraints -2 name shall not be a null pointer. maxsize shall neither equal zero nor be greater than - RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer. -3 If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len - is not null), and the environment list is not searched. - Description -4 The getenv_s function searches an environment list, provided by the host environment, - for a string that matches the string pointed to by name. - - - 394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in - which a runtime-constraint violation occurs will return to its caller. The caller can determine whether - a runtime-constraint violation occurred based on the library function's specification (usually, the - library function returns a nonzero errno_t). - -[page 602] - -5 If that name is found then getenv_s performs the following actions. If len is not a - null pointer, the length of the string associated with the matched list member is stored in - the integer pointed to by len. If the length of the associated string is less than maxsize, - then the associated string is copied to the array pointed to by value. -6 If that name is not found then getenv_s performs the following actions. If len is not - a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than - zero, then value[0] is set to the null character. -7 The set of environment names and the method for altering the environment list are - implementation-defined. - Returns -8 The getenv_s function returns zero if the specified name is found and the associated - string was successfully stored in value. Otherwise, a nonzero value is returned. - K.3.6.3 Searching and sorting utilities -1 These utilities make use of a comparison function to search or sort arrays of unspecified - type. Where an argument declared as size_t nmemb specifies the length of the array - for a function, if nmemb has the value zero on a call to that function, then the comparison - function is not called, a search finds no matching element, sorting performs no - rearrangement, and the pointer to the array may be null. -2 The implementation shall ensure that the second argument of the comparison function - (when called from bsearch_s), or both arguments (when called from qsort_s), are - pointers to elements of the array.395) The first argument when called from bsearch_s - shall equal key. -3 The comparison function shall not alter the contents of either the array or search key. The - implementation may reorder elements of the array between calls to the comparison - function, but shall not otherwise alter the contents of any individual element. -4 When the same objects (consisting of size bytes, irrespective of their current positions - in the array) are passed more than once to the comparison function, the results shall be - consistent with one another. That is, for qsort_s they shall define a total ordering on - the array, and for bsearch_s the same object shall always compare the same way with - the key. - - - - - 395) That is, if the value passed is p, then the following expressions are always valid and nonzero: - ((char *)p - (char *)base) % size == 0 - (char *)p >= (char *)base - (char *)p < (char *)base + nmemb * size - -[page 603] - -5 A sequence point occurs immediately before and immediately after each call to the - comparison function, and also between any call to the comparison function and any - movement of the objects passed as arguments to that call. - K.3.6.3.1 The bsearch_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - void *bsearch_s(const void *key, const void *base, - rsize_t nmemb, rsize_t size, - int (*compar)(const void *k, const void *y, - void *context), - void *context); - Runtime-constraints -2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then none of key, base, or compar shall be a null pointer. -3 If there is a runtime-constraint violation, the bsearch_s function does not search the - array. - Description -4 The bsearch_s function searches an array of nmemb objects, the initial element of - which is pointed to by base, for an element that matches the object pointed to by key. - The size of each element of the array is specified by size. -5 The comparison function pointed to by compar is called with three arguments. The first - two point to the key object and to an array element, in that order. The function shall - return an integer less than, equal to, or greater than zero if the key object is considered, - respectively, to be less than, to match, or to be greater than the array element. The array - shall consist of: all the elements that compare less than, all the elements that compare - equal to, and all the elements that compare greater than the key object, in that order.396) - The third argument to the comparison function is the context argument passed to - bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison - function.397) - - - - - 396) In practice, this means that the entire array has been sorted according to the comparison function. - 397) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - -[page 604] - - Returns -6 The bsearch_s function returns a pointer to a matching element of the array, or a null - pointer if no match is found or there is a runtime-constraint violation. If two elements - compare as equal, which element is matched is unspecified. - K.3.6.3.2 The qsort_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, - int (*compar)(const void *x, const void *y, - void *context), - void *context); - Runtime-constraints -2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then neither base nor compar shall be a null pointer. -3 If there is a runtime-constraint violation, the qsort_s function does not sort the array. - Description -4 The qsort_s function sorts an array of nmemb objects, the initial element of which is - pointed to by base. The size of each object is specified by size. -5 The contents of the array are sorted into ascending order according to a comparison - function pointed to by compar, which is called with three arguments. The first two - point to the objects being compared. The function shall return an integer less than, equal - to, or greater than zero if the first argument is considered to be respectively less than, - equal to, or greater than the second. The third argument to the comparison function is the - context argument passed to qsort_s. The sole use of context by qsort_s is to - pass it to the comparison function.398) -6 If two elements compare as equal, their relative order in the resulting sorted array is - unspecified. - Returns -7 The qsort_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - 398) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - -[page 605] - - K.3.6.4 Multibyte/wide character conversion functions -1 The behavior of the multibyte character functions is affected by the LC_CTYPE category - of the current locale. For a state-dependent encoding, each function is placed into its - initial conversion state by a call for which its character pointer argument, s, is a null - pointer. Subsequent calls with s as other than a null pointer cause the internal conversion - state of the function to be altered as necessary. A call with s as a null pointer causes - these functions to set the int pointed to by their status argument to a nonzero value if - encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE - category causes the conversion state of these functions to be indeterminate. - K.3.6.4.1 The wctomb_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wctomb_s(int * restrict status, - char * restrict s, - rsize_t smax, - wchar_t wc); - Runtime-constraints -2 Let n denote the number of bytes needed to represent the multibyte character - corresponding to the wide character given by wc (including any shift sequences). -3 If s is not a null pointer, then smax shall not be less than n, and smax shall not be - greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero. -4 If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to - by status, and if s is not a null pointer, no more than smax elements in the array - pointed to by s will be accessed. - Description -5 The wctomb_s function determines n and stores the multibyte character representation - of wc in the array whose first element is pointed to by s (if s is not a null pointer). The - number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide - character, a null byte is stored, preceded by any shift sequence needed to restore the - initial shift state, and the function is left in the initial conversion state. -6 The implementation shall behave as if no library function calls the wctomb_s function. - - - - - 399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide - character codes, but are grouped with an adjacent multibyte character. - -[page 606] - -7 If s is a null pointer, the wctomb_s function stores into the int pointed to by status a - nonzero or zero value, if multibyte character encodings, respectively, do or do not have - state-dependent encodings. -8 If s is not a null pointer, the wctomb_s function stores into the int pointed to by - status either n or -1 if wc, respectively, does or does not correspond to a valid - multibyte character. -9 In no case will the int pointed to by status be set to a value greater than the - MB_CUR_MAX macro. - Returns -10 The wctomb_s function returns zero if successful, and a nonzero value if there was a - runtime-constraint violation or wc did not correspond to a valid multibyte character. - K.3.6.5 Multibyte/wide string conversion functions -1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of - the current locale. - K.3.6.5.1 The mbstowcs_s function - Synopsis -1 #include - errno_t mbstowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char * restrict src, rsize_t len); - Runtime-constraints -2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then a null character - shall occur within the first dstmax multibyte characters of the array pointed to by src. -3 If there is a runtime-constraint violation, then mbstowcs_s does the following. If - retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbstowcs_s sets dst[0] to the null wide character. - Description -4 The mbstowcs_s function converts a sequence of multibyte characters that begins in - the initial shift state from the array pointed to by src into a sequence of corresponding - wide characters. If dst is not a null pointer, the converted characters are stored into the - array pointed to by dst. Conversion continues up to and including a terminating null - character, which is also stored. Conversion stops earlier in two cases: when a sequence of - -[page 607] - - bytes is encountered that does not form a valid multibyte character, or (if dst is not a - null pointer) when len wide characters have been stored into the array pointed to by - dst.400) If dst is not a null pointer and no null wide character was stored into the array - pointed to by dst, then dst[len] is set to the null wide character. Each conversion - takes place as if by a call to the mbrtowc function. -5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbstowcs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the mbstowcs_s function stores into *retval the number of multibyte - characters successfully converted, not including the terminating null character (if any). -6 All elements following the terminating null wide character (if any) written by - mbstowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbstowcs_s returns.401) -7 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -8 The mbstowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.6.5.2 The wcstombs_s function - Synopsis -1 #include - errno_t wcstombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t * restrict src, rsize_t len); - Runtime-constraints -2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then the conversion - shall have been stopped (see below) because a terminating null wide character was - reached or because an encoding error occurred. - - - - - 400) Thus, the value of len is ignored if dst is a null pointer. - 401) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - -[page 608] - -3 If there is a runtime-constraint violation, then wcstombs_s does the following. If - retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcstombs_s sets dst[0] to the null character. - Description -4 The wcstombs_s function converts a sequence of wide characters from the array - pointed to by src into a sequence of corresponding multibyte characters that begins in - the initial shift state. If dst is not a null pointer, the converted characters are then stored - into the array pointed to by dst. Conversion continues up to and including a terminating - null wide character, which is also stored. Conversion stops earlier in two cases: - -- when a wide character is reached that does not correspond to a valid multibyte - character; - -- (if dst is not a null pointer) when the next multibyte character would exceed the - limit of n total bytes to be stored into the array pointed to by dst. If the wide - character being converted is the null wide character, then n is the lesser of len or - dstmax. Otherwise, n is the lesser of len or dstmax-1. - If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.402) -5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the wcstombs_s function stores into *retval the number of bytes in the - resulting multibyte character sequence, not including the terminating null character (if - any). -6 All elements following the terminating null character (if any) written by wcstombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcstombs_s returns.403) -7 If copying takes place between objects that overlap, the objects take on unspecified - values. - - - 402) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - 403) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - -[page 609] - - Returns -8 The wcstombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.7 String handling -1 The header defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.7.1 Copying functions - K.3.7.1.1 The memcpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t memcpy_s(void * restrict s1, rsize_t s1max, - const void * restrict s2, rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -3 If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first - s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is - not greater than RSIZE_MAX. - Description -4 The memcpy_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. - Returns -5 The memcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -[page 610] - - K.3.7.1.2 The memmove_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t memmove_s(void *s1, rsize_t s1max, - const void *s2, rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -3 If there is a runtime-constraint violation, the memmove_s function stores zeros in the - first s1max characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -4 The memmove_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. This copying takes place as if the n characters from the object - pointed to by s2 are first copied into a temporary array of n characters that does not - overlap the objects pointed to by s1 or s2, and then the n characters from the temporary - array are copied into the object pointed to by s1. - Returns -5 The memmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.1.3 The strcpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t strcpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the - null character. - -[page 611] - - Description -4 The strcpy_s function copies the string pointed to by s2 (including the terminating - null character) into the array pointed to by s1. -5 All elements following the terminating null character (if any) written by strcpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcpy_s returns.404) - Returns -6 The strcpy_s function returns zero405) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.1.4 The strncpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t strncpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than strnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the - null character. - Description -4 The strncpy_s function copies not more than n successive characters (characters that - follow a null character are not copied) from the array pointed to by s2 to the array - pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null - character. - - - 404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 612] - -5 All elements following the terminating null character (if any) written by strncpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncpy_s returns.406) - Returns -6 The strncpy_s function returns zero407) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -7 EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - char src1[100] = "hello"; - char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'}; - char dst1[6], dst2[5], dst3[5]; - int r1, r2, r3; - r1 = strncpy_s(dst1, 6, src1, 100); - r2 = strncpy_s(dst2, 5, src2, 7); - r3 = strncpy_s(dst3, 5, src2, 4); - The first call will assign to r1 the value zero and to dst1 the sequence hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence \0. - The third call will assign to r3 the value zero and to dst3 the sequence good\0. - - K.3.7.2 Concatenation functions - K.3.7.2.1 The strcat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t strcat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - Runtime-constraints -2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strcat_s. - - - - - 406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 613] - -3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.408) m shall be greater than - strnlen_s(s2, m). Copying shall not take place between objects that overlap. -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the - null character. - Description -5 The strcat_s function appends a copy of the string pointed to by s2 (including the - terminating null character) to the end of the string pointed to by s1. The initial character - from s2 overwrites the null character at the end of s1. -6 All elements following the terminating null character (if any) written by strcat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcat_s returns.409) - Returns -7 The strcat_s function returns zero410) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.2.2 The strncat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t strncat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - Runtime-constraints -2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strncat_s. -3 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less - - - 408) Zero means that s1 was not null terminated upon entry to strcat_s. - 409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 410) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - -[page 614] - - than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take - place between objects that overlap. -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the - null character. - Description -5 The strncat_s function appends not more than n successive characters (characters - that follow a null character are not copied) from the array pointed to by s2 to the end of - the string pointed to by s1. The initial character from s2 overwrites the null character at - the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to - a null character. -6 All elements following the terminating null character (if any) written by strncat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncat_s returns.412) - Returns -7 The strncat_s function returns zero413) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -8 EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - char s1[100] = "good"; - char s2[6] = "hello"; - char s3[6] = "hello"; - char s4[7] = "abc"; - char s5[1000] = "bye"; - int r1, r2, r3, r4; - r1 = strncat_s(s1, 100, s5, 1000); - r2 = strncat_s(s2, 6, "", 1); - r3 = strncat_s(s3, 6, "X", 2); - r4 = strncat_s(s4, 7, "defghijklmn", 3); - After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0. - - - - 411) Zero means that s1 was not null terminated upon entry to strncat_s. - 412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 413) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - -[page 615] - - After the second call r2 will have the value zero and s2 will contain the sequence hello\0. - After the third call r3 will have a nonzero value and s3 will contain the sequence \0. - After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0. - - K.3.7.3 Search functions - K.3.7.3.1 The strtok_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - char *strtok_s(char * restrict s1, - rsize_t * restrict s1max, - const char * restrict s2, - char ** restrict ptr); - Runtime-constraints -2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max characters of s1 for the - first call, and shall occur within the first *s1max characters of where searching resumes - on subsequent calls. -3 If there is a runtime-constraint violation, the strtok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. - Description -4 A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a - sequence of tokens, each of which is delimited by a character from the string pointed to - by s2. The fourth argument points to a caller-provided char pointer into which the - strtok_s function stores information necessary for it to continue scanning the same - string. -5 The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator string pointed to by - s2 may be different from call to call. -6 The first call in the sequence searches the string pointed to by s1 for the first character - that is not contained in the current separator string pointed to by s2. If no such character - is found, then there are no tokens in the string pointed to by s1 and the strtok_s - function returns a null pointer. If such a character is found, it is the start of the first token. - -[page 616] - -7 The strtok_s function then searches from there for the first character in s1 that is - contained in the current separator string. If no such character is found, the current token - extends to the end of the string pointed to by s1, and subsequent searches in the same - string for a token return a null pointer. If such a character is found, it is overwritten by a - null character, which terminates the current token. -8 In all cases, the strtok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null character - (if any). - Returns -9 The strtok_s function returns a pointer to the first character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -10 EXAMPLE - #define __STDC_WANT_LIB_EXT1__ 1 - #include - static char str1[] = "?a???b,,,#c"; - static char str2[] = "\t \t"; - char *t, *ptr1, *ptr2; - rsize_t max1 = sizeof(str1); - rsize_t max2 = sizeof(str2); - t = strtok_s(str1, &max1, "?", &ptr1); // t points to the token "a" - t = strtok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" - t = strtok_s(str2, &max2, " \t", &ptr2); // t is a null pointer - t = strtok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" - t = strtok_s(NULL, &max1, "?", &ptr1); // t is a null pointer - - K.3.7.4 Miscellaneous functions - K.3.7.4.1 The memset_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) - Runtime-constraints -2 s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n - shall not be greater than smax. -3 If there is a runtime-constraint violation, then if s is not a null pointer and smax is not - greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an - unsigned char) into each of the first smax characters of the object pointed to by s. - -[page 617] - - Description -4 The memset_s function copies the value of c (converted to an unsigned char) into - each of the first n characters of the object pointed to by s. Unlike memset, any call to - the memset_s function shall be evaluated strictly according to the rules of the abstract - machine as described in (5.1.2.3). That is, any call to the memset_s function shall - assume that the memory indicated by s and n may be accessible in the future and thus - must contain the values indicated by c. - Returns -5 The memset_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.4.2 The strerror_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t strerror_s(char *s, rsize_t maxsize, - errno_t errnum); - Runtime-constraints -2 s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. - maxsize shall not equal zero. -3 If there is a runtime-constraint violation, then the array (if any) pointed to by s is not - modified. - Description -4 The strerror_s function maps the number in errnum to a locale-specific message - string. Typically, the values for errnum come from errno, but strerror_s shall - map any value of type int to a message. -5 If the length of the desired string is less than maxsize, then the string is copied to the - array pointed to by s. -6 Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied - from the string to the array pointed to by s and then s[maxsize-1] is set to the null - character. Then, if maxsize is greater than 3, then s[maxsize-2], - s[maxsize-3], and s[maxsize-4] are set to the character period (.). - Returns -7 The strerror_s function returns zero if the length of the desired string was less than - maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s - function returns a nonzero value. - -[page 618] - - K.3.7.4.3 The strerrorlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - size_t strerrorlen_s(errno_t errnum); - Description -2 The strerrorlen_s function calculates the length of the (untruncated) locale-specific - message string that the strerror_s function maps to errnum. - Returns -3 The strerrorlen_s function returns the number of characters (not including the null - character) in the full message string. - K.3.7.4.4 The strnlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - size_t strnlen_s(const char *s, size_t maxsize); - Description -2 The strnlen_s function computes the length of the string pointed to by s. - Returns -3 If s is a null pointer,414) then the strnlen_s function returns zero. -4 Otherwise, the strnlen_s function returns the number of characters that precede the - terminating null character. If there is no null character in the first maxsize characters of - s then strnlen_s returns maxsize. At most the first maxsize characters of s shall - be accessed by strnlen_s. - - - - - 414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated string argument make - strnlen_s useful in algorithms that gracefully handle such exceptional data. - -[page 619] - - K.3.8 Date and time -1 The header defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.8.1 Components of time -1 A broken-down time is normalized if the values of the members of the tm structure are in - their normal rages.415) - K.3.8.2 Time conversion functions -1 Like the strftime function, the asctime_s and ctime_s functions do not return a - pointer to a static object, and other library functions are permitted to call them. - K.3.8.2.1 The asctime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t asctime_s(char *s, rsize_t maxsize, - const struct tm *timeptr); - Runtime-constraints -2 Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr - shall be normalized. The calendar year represented by the broken-down time pointed to - by timeptr shall not be less than calendar year 0 and shall not be greater than calendar - year 9999. -3 If there is a runtime-constraint violation, there is no attempt to convert the time, and - s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is - not greater than RSIZE_MAX. - Description -4 The asctime_s function converts the normalized broken-down time in the structure - pointed to by timeptr into a 26 character (including the null character) string in the - - - 415) The normal ranges are defined in 7.26.1. - -[page 620] - - form - Sun Sep 16 01:03:52 1973\n\0 - The fields making up this string are (in order): - 1. The name of the day of the week represented by timeptr->tm_wday using the - following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat. - 2. The character space. - 3. The name of the month represented by timeptr->tm_mon using the following - three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, - Nov, and Dec. - 4. The character space. - 5. The value of timeptr->tm_mday as if printed using the fprintf format - "%2d". - 6. The character space. - 7. The value of timeptr->tm_hour as if printed using the fprintf format - "%.2d". - 8. The character colon. - 9. The value of timeptr->tm_min as if printed using the fprintf format - "%.2d". - 10. The character colon. - 11. The value of timeptr->tm_sec as if printed using the fprintf format - "%.2d". - 12. The character space. - 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf - format "%4d". - 14. The character new line. - 15. The null character. - Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - asctime_s function, consider using the strftime function instead. - Returns -5 The asctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. - -[page 621] - - K.3.8.2.2 The ctime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t ctime_s(char *s, rsize_t maxsize, - const time_t *timer); - Runtime-constraints -2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. -3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null - pointer and maxsize is not equal zero and is not greater than RSIZE_MAX. - Description -4 The ctime_s function converts the calendar time pointed to by timer to local time in - the form of a string. It is equivalent to - asctime_s(s, maxsize, localtime_s(timer)) - Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - ctime_s function, consider using the strftime function instead. - Returns -5 The ctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. - K.3.8.2.3 The gmtime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - struct tm *gmtime_s(const time_t * restrict timer, - struct tm * restrict result); - Runtime-constraints -2 Neither timer nor result shall be a null pointer. -3 If there is a runtime-constraint violation, there is no attempt to convert the time. - Description -4 The gmtime_s function converts the calendar time pointed to by timer into a broken- - down time, expressed as UTC. The broken-down time is stored in the structure pointed - -[page 622] - - to by result. - Returns -5 The gmtime_s function returns result, or a null pointer if the specified time cannot - be converted to UTC or there is a runtime-constraint violation. - K.3.8.2.4 The localtime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - struct tm *localtime_s(const time_t * restrict timer, - struct tm * restrict result); - Runtime-constraints -2 Neither timer nor result shall be a null pointer. -3 If there is a runtime-constraint violation, there is no attempt to convert the time. - Description -4 The localtime_s function converts the calendar time pointed to by timer into a - broken-down time, expressed as local time. The broken-down time is stored in the - structure pointed to by result. - Returns -5 The localtime_s function returns result, or a null pointer if the specified time - cannot be converted to local time or there is a runtime-constraint violation. - K.3.9 Extended multibyte and wide character utilities -1 The header defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. -3 Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - -[page 623] - - K.3.9.1 Formatted wide character input/output functions - K.3.9.1.1 The fwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int fwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier416) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation, the fwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent fwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The fwprintf_s function is equivalent to the fwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The fwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.2 The fwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int fwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. - - - 416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 624] - -3 If there is a runtime-constraint violation, the fwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The fwscanf_s function is equivalent to fwscanf except that the c, s, and [ - conversion specifiers apply to a pair of arguments (unless assignment suppression is - indicated by a *). The first of these arguments is the same as for fwscanf. That - argument is immediately followed in the argument list by the second argument, which has - type size_t and gives the number of elements in the array pointed to by the first - argument of the pair. If the first argument points to a scalar object, it is considered to be - an array of one element.417) -5 A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). - Returns -6 The fwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - fwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.3 The snwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int snwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or - - 417) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - -[page 625] - - precision) shall not appear in the wide string pointed to by format. Any argument to - snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the - null wide character. - Description -4 The snwprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -5 The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within - the array pointed to by s. - Returns -6 The snwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating wide null - character, or a negative value if a runtime-constraint violation occurred. Thus, the null- - terminated output has been completely written if and only if the returned value is - nonnegative and less than n. - K.3.9.1.4 The swprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int swprintf_s(wchar_t * restrict s, rsize_t n, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier419) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to swprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. - - - 418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - 419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 626] - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the - null wide character. - Description -4 The swprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -5 The swprintf_s function, unlike snwprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the swprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, swprintf_s returns a negative value. If any other runtime-constraint - violation occurred, swprintf_s returns zero. - K.3.9.1.5 The swscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int swscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the swscanf_s function does not attempt to - perform further input, and it is unspecified to what extent swscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The swscanf_s function is equivalent to fwscanf_s, except that the argument s - specifies a wide string from which the input is to be obtained, rather than from a stream. - Reaching the end of the wide string is equivalent to encountering end-of-file for the - fwscanf_s function. - Returns -5 The swscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - swscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - -[page 627] - - K.3.9.1.6 The vfwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - #include - int vfwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier420) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be - a null pointer. -3 If there is a runtime-constraint violation, the vfwprintf_s function does not attempt - to produce further output, and it is unspecified to what extent vfwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vfwprintf_s function is equivalent to the vfwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vfwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.7 The vfwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - #include - int vfwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - - - - 420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 628] - - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the - va_end macro.421) - Returns -5 The vfwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.8 The vsnwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vsnwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or - precision) shall not appear in the wide string pointed to by format. Any argument to - vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No - encoding error shall occur. - - 421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - 422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 629] - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to - the null wide character. - Description -4 The vsnwprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -5 The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit - within the array pointed to by s. - Returns -6 The vsnwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating null character, or - a negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - K.3.9.1.9 The vswprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vswprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier423) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to vswprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the - null wide character. - - 423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 630] - - Description -4 The vswprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -5 The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the - array pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the vswprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, vswprintf_s returns a negative value. If any other runtime-constraint - violation occurred, vswprintf_s returns zero. - K.3.9.1.10 The vswscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vswscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vswscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vswscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vswscanf_s function is equivalent to swscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswscanf_s function does not invoke the - va_end macro.424) - - - - - 424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - -[page 631] - - Returns -5 The vswscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vswscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.11 The vwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vwprintf_s(const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier425) (modified or not by flags, field - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the vwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vwprintf_s function is equivalent to the vwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - 425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 632] - - K.3.9.1.12 The vwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - #include - int vwscanf_s(const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vwscanf_s function is equivalent to wscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwscanf_s function does not invoke the - va_end macro.426) - Returns -5 The vwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.13 The wprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int wprintf_s(const wchar_t * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier427) (modified or not by flags, field - - 426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - 427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 633] - - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to wprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the wprintf_s function does not attempt to - produce further output, and it is unspecified to what extent wprintf_s produced output - before discovering the runtime-constraint violation. - Description -4 The wprintf_s function is equivalent to the wprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The wprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.14 The wscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - int wscanf_s(const wchar_t * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the wscanf_s function does not attempt to - perform further input, and it is unspecified to what extent wscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The wscanf_s function is equivalent to fwscanf_s with the argument stdin - interposed before the arguments to wscanf_s. - Returns -5 The wscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - wscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - -[page 634] - - K.3.9.2 General wide string utilities - K.3.9.2.1 Wide string copying functions - K.3.9.2.1.1 The wcscpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wcscpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the - null wide character. - Description -4 The wcscpy_s function copies the wide string pointed to by s2 (including the - terminating null wide character) into the array pointed to by s1. -5 All elements following the terminating null wide character (if any) written by - wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscpy_s returns.428) - Returns -6 The wcscpy_s function returns zero429) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - 428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - 429) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 635] - - K.3.9.2.1.2 The wcsncpy_s function - Synopsis -7 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wcsncpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -8 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -9 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the - null wide character. - Description -10 The wcsncpy_s function copies not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the array pointed to by s1. If no null wide character was copied from s2, then - s1[n] is set to a null wide character. -11 All elements following the terminating null wide character (if any) written by - wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncpy_s returns.430) - Returns -12 The wcsncpy_s function returns zero431) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -13 EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. - - - - - 430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - 431) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 636] - - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - wchar_t src1[100] = L"hello"; - wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'}; - wchar_t dst1[6], dst2[5], dst3[5]; - int r1, r2, r3; - r1 = wcsncpy_s(dst1, 6, src1, 100); - r2 = wcsncpy_s(dst2, 5, src2, 7); - r3 = wcsncpy_s(dst3, 5, src2, 4); - The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0. - The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0. - - K.3.9.2.1.3 The wmemcpy_s function - Synopsis -14 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wmemcpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -15 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -16 If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -17 The wmemcpy_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. - Returns -18 The wmemcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - -[page 637] - - K.3.9.2.1.4 The wmemmove_s function - Synopsis -19 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, - const wchar_t *s2, rsize_t n); - Runtime-constraints -20 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -21 If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -22 The wmemmove_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. This copying takes place as if the n wide - characters from the object pointed to by s2 are first copied into a temporary array of n - wide characters that does not overlap the objects pointed to by s1 or s2, and then the n - wide characters from the temporary array are copied into the object pointed to by s1. - Returns -23 The wmemmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.9.2.2 Wide string concatenation functions - K.3.9.2.2.1 The wcscat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wcscat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - Runtime-constraints -2 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcscat_s. -3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.432) m shall be greater than - wcsnlen_s(s2, m). Copying shall not take place between objects that overlap. - -[page 638] - -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the - null wide character. - Description -5 The wcscat_s function appends a copy of the wide string pointed to by s2 (including - the terminating null wide character) to the end of the wide string pointed to by s1. The - initial wide character from s2 overwrites the null wide character at the end of s1. -6 All elements following the terminating null wide character (if any) written by - wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscat_s returns.433) - Returns -7 The wcscat_s function returns zero434) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.9.2.2.2 The wcsncat_s function - Synopsis -8 #define __STDC_WANT_LIB_EXT1__ 1 - #include - errno_t wcsncat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -9 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcsncat_s. -10 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less - than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take - place between objects that overlap. - - - 432) Zero means that s1 was not null terminated upon entry to wcscat_s. - 433) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - 434) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - 435) Zero means that s1 was not null terminated upon entry to wcsncat_s. - -[page 639] - -11 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the - null wide character. - Description -12 The wcsncat_s function appends not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the end of the wide string pointed to by s1. The initial wide character from s2 - overwrites the null wide character at the end of s1. If no null wide character was copied - from s2, then s1[s1max-m+n] is set to a null wide character. -13 All elements following the terminating null wide character (if any) written by - wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncat_s returns.436) - Returns -14 The wcsncat_s function returns zero437) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -15 EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include - /* ... */ - wchar_t s1[100] = L"good"; - wchar_t s2[6] = L"hello"; - wchar_t s3[6] = L"hello"; - wchar_t s4[7] = L"abc"; - wchar_t s5[1000] = L"bye"; - int r1, r2, r3, r4; - r1 = wcsncat_s(s1, 100, s5, 1000); - r2 = wcsncat_s(s2, 6, L"", 1); - r3 = wcsncat_s(s3, 6, L"X", 2); - r4 = wcsncat_s(s4, 7, L"defghijklmn", 3); - After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0. - After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0. - After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0. - After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0. - - - - - 436) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - 437) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - -[page 640] - - K.3.9.2.3 Wide string search functions - K.3.9.2.3.1 The wcstok_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - wchar_t *wcstok_s(wchar_t * restrict s1, - rsize_t * restrict s1max, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); - Runtime-constraints -2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max wide characters of s1 for - the first call, and shall occur within the first *s1max wide characters of where searching - resumes on subsequent calls. -3 If there is a runtime-constraint violation, the wcstok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. - Description -4 A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1 - into a sequence of tokens, each of which is delimited by a wide character from the wide - string pointed to by s2. The fourth argument points to a caller-provided wchar_t - pointer into which the wcstok_s function stores information necessary for it to - continue scanning the same wide string. -5 The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the wide character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator wide string pointed - to by s2 may be different from call to call. -6 The first call in the sequence searches the wide string pointed to by s1 for the first wide - character that is not contained in the current separator wide string pointed to by s2. If no - such wide character is found, then there are no tokens in the wide string pointed to by s1 - and the wcstok_s function returns a null pointer. If such a wide character is found, it is - the start of the first token. - -[page 641] - -7 The wcstok_s function then searches from there for the first wide character in s1 that - is contained in the current separator wide string. If no such wide character is found, the - current token extends to the end of the wide string pointed to by s1, and subsequent - searches in the same wide string for a token return a null pointer. If such a wide character - is found, it is overwritten by a null wide character, which terminates the current token. -8 In all cases, the wcstok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null wide - character (if any). - Returns -9 The wcstok_s function returns a pointer to the first wide character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -10 EXAMPLE - #define __STDC_WANT_LIB_EXT1__ 1 - #include - static wchar_t str1[] = L"?a???b,,,#c"; - static wchar_t str2[] = L"\t \t"; - wchar_t *t, *ptr1, *ptr2; - rsize_t max1 = wcslen(str1)+1; - rsize_t max2 = wcslen(str2)+1; - t = wcstok_s(str1, &max1, "?", &ptr1); // t points to the token "a" - t = wcstok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" - t = wcstok_s(str2, &max2, " \t", &ptr2); // t is a null pointer - t = wcstok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" - t = wcstok_s(NULL, &max1, "?", &ptr1); // t is a null pointer - - K.3.9.2.4 Miscellaneous functions - K.3.9.2.4.1 The wcsnlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include - size_t wcsnlen_s(const wchar_t *s, size_t maxsize); - Description -2 The wcsnlen_s function computes the length of the wide string pointed to by s. - Returns -3 If s is a null pointer,438) then the wcsnlen_s function returns zero. -4 Otherwise, the wcsnlen_s function returns the number of wide characters that precede - the terminating null wide character. If there is no null wide character in the first - maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first - -[page 642] - - maxsize wide characters of s shall be accessed by wcsnlen_s. - K.3.9.3 Extended multibyte/wide character conversion utilities - K.3.9.3.1 Restartable multibyte/wide character conversion functions -1 Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the - conversion state) to be a null pointer. - K.3.9.3.1.1 The wcrtomb_s function - Synopsis -2 #include - errno_t wcrtomb_s(size_t * restrict retval, - char * restrict s, rsize_t smax, - wchar_t wc, mbstate_t * restrict ps); - Runtime-constraints -3 Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax - shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer, - then smax shall be not be less than the number of bytes to be stored in the array pointed - to by s. If s is a null pointer, then smax shall equal zero. -4 If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is - not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then - wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then - wcrtomb_s sets *retval to (size_t)(-1). - Description -5 If s is a null pointer, the wcrtomb_s function is equivalent to the call - wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps) - where retval and buf are internal variables of the appropriate types, and the size of - buf is greater than MB_CUR_MAX. -6 If s is not a null pointer, the wcrtomb_s function determines the number of bytes - needed to represent the multibyte character that corresponds to the wide character given - by wc (including any shift sequences), and stores the multibyte character representation - in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are - stored. If wc is a null wide character, a null byte is stored, preceded by any shift - sequence needed to restore the initial shift state; the resulting state described is the initial - conversion state. - - 438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated wide string argument make - wcsnlen_s useful in algorithms that gracefully handle such exceptional data. - -[page 643] - -7 If wc does not correspond to a valid multibyte character, an encoding error occurs: the - wcrtomb_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the wcrtomb_s function stores into - *retval the number of bytes (including any shift sequences) stored in the array pointed - to by s. - Returns -8 The wcrtomb_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.9.3.2 Restartable multibyte/wide string conversion functions -1 Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not - permit the ps parameter (the pointer to the conversion state) to be a null pointer. - K.3.9.3.2.1 The mbsrtowcs_s function - Synopsis -2 #include - errno_t mbsrtowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char ** restrict src, rsize_t len, - mbstate_t * restrict ps); - Runtime-constraints -3 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null - character shall occur within the first dstmax multibyte characters of the array pointed to - by *src. -4 If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If - retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbsrtowcs_s sets dst[0] to the null wide character. - Description -5 The mbsrtowcs_s function converts a sequence of multibyte characters that begins in - the conversion state described by the object pointed to by ps, from the array indirectly - pointed to by src into a sequence of corresponding wide characters. If dst is not a null - pointer, the converted characters are stored into the array pointed to by dst. Conversion - continues up to and including a terminating null character, which is also stored. - Conversion stops earlier in two cases: when a sequence of bytes is encountered that does - not form a valid multibyte character, or (if dst is not a null pointer) when len wide - -[page 644] - - characters have been stored into the array pointed to by dst.439) If dst is not a null - pointer and no null wide character was stored into the array pointed to by dst, then - dst[len] is set to the null wide character. Each conversion takes place as if by a call - to the mbrtowc function. -6 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null character) or the address - just past the last multibyte character converted (if any). If conversion stopped due to - reaching a terminating null character and if dst is not a null pointer, the resulting state - described is the initial conversion state. -7 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into - *retval the number of multibyte characters successfully converted, not including the - terminating null character (if any). -8 All elements following the terminating null wide character (if any) written by - mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbsrtowcs_s returns.440) -9 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -10 The mbsrtowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.9.3.2.2 The wcsrtombs_s function - Synopsis -11 #include - errno_t wcsrtombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t ** restrict src, rsize_t len, - mbstate_t * restrict ps); - - - - - 439) Thus, the value of len is ignored if dst is a null pointer. - 440) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - -[page 645] - - Runtime-constraints -12 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then the - conversion shall have been stopped (see below) because a terminating null wide character - was reached or because an encoding error occurred. -13 If there is a runtime-constraint violation, then wcsrtombs_s does the following. If - retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcsrtombs_s sets dst[0] to the null character. - Description -14 The wcsrtombs_s function converts a sequence of wide characters from the array - indirectly pointed to by src into a sequence of corresponding multibyte characters that - begins in the conversion state described by the object pointed to by ps. If dst is not a - null pointer, the converted characters are then stored into the array pointed to by dst. - Conversion continues up to and including a terminating null wide character, which is also - stored. Conversion stops earlier in two cases: - -- when a wide character is reached that does not correspond to a valid multibyte - character; - -- (if dst is not a null pointer) when the next multibyte character would exceed the - limit of n total bytes to be stored into the array pointed to by dst. If the wide - character being converted is the null wide character, then n is the lesser of len or - dstmax. Otherwise, n is the lesser of len or dstmax-1. - If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.441) -15 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null wide character) or the - address just past the last wide character converted (if any). If conversion stopped due to - reaching a terminating null wide character, the resulting state described is the initial - conversion state. - - - 441) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - -[page 646] - -16 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval - and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores - into *retval the number of bytes in the resulting multibyte character sequence, not - including the terminating null character (if any). -17 All elements following the terminating null character (if any) written by wcsrtombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcsrtombs_s returns.442) -18 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -19 The wcsrtombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - - - - - 442) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - -[page 647] - - Annex L - (normative) - Analyzability - L.1 Scope -1 This annex specifies optional behavior that can aid in the analyzability of C programs. -2 An implementation that defines __STDC_ANALYZABLE__ shall conform to the - specifications in this annex.443) - L.2 Definitions - L.2.1 -1 out-of-bounds store - an (attempted) access (3.1) that, at run time, for a given computational state, would - modify (or, for an object declared volatile, fetch) one or more bytes that lie outside - the bounds permitted by this Standard. - L.2.2 -1 bounded undefined behavior - undefined behavior (3.4.3) that does not perform an out-of-bounds store. -2 NOTE 1 The behavior might perform a trap. - -3 NOTE 2 Any values produced or stored might be indeterminate values. - - L.2.3 -1 critical undefined behavior - undefined behavior that is not bounded undefined behavior. -2 NOTE The behavior might perform an out-of-bounds store or perform a trap. - - - - - 443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these - specifications. - -[page 648] - - L.3 Requirements -1 If the program performs a trap (3.19.5), the implementation is permitted to invoke a - runtime-constraint handler. Any such semantics are implementation-defined. -2 All undefined behavior shall be limited to bounded undefined behavior, except for the - following which are permitted to result in critical undefined behavior: - -- An object is referred to outside of its lifetime (6.2.4). - -- An lvalue does not designate an object when evaluated (6.3.2.1). - -- A pointer is used to call a function whose type is not compatible with the referenced - type (6.3.2.3). - -- The operand of the unary * operator has an invalid value (6.5.3.2). - -- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that points just beyond the array object and is used as - the operand of a unary * operator that is evaluated (6.5.6). - -- An argument to a library function has an invalid value or a type not expected by a - function with variable number of arguments (7.1.4). - -- The value of a pointer that refers to space deallocated by a call to the free or realloc - function is used (7.22.3). - -- A string or wide string utility function is instructed to access an array beyond the end - of an object (7.23.1, 7.28.4). - -[page 649] - - - Bibliography - 1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was - published in The C Programming Language by Brian W. Kernighan and Dennis - M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T. - 2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara, - California, USA, November 1984. - 3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information - Processing Systems, Information Processing Systems Technical Report. - 4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point - Arithmetic. - 5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent - Floating-Point Arithmetic. - 6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems, - second edition (previously designated IEC 559:1989). - 7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and - symbols for use in the physical sciences and technology. - 8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for - information interchange. - 9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: - Fundamental terms. - 10. ISO 4217:1995, Codes for the representation of currencies and funds. - 11. ISO 8601:1988, Data elements and interchange formats -- Information - interchange -- Representation of dates and times. - 12. ISO/IEC 9899:1990, Programming languages -- C. - 13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1. - 14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2. - 15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity. - 16. ISO/IEC 9899:1999, Programming languages -- C. - 17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1. - 18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2. - 19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3. - -[page 650] - - 20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System - Interface (POSIX) -- Part 2: Shell and Utilities. - 21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the - preparation of programming language standards. - 22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet - Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. - 23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to - ISO/IEC 10646-1:1993. - 24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to - ISO/IEC 10646-1:1993. - 25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993 - Transformation Format for 16 planes of group 00 (UTF-16). - 26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS - Transformation Format 8 (UTF-8). - 27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993. - 28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993. - 29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul - syllables. - 30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993 - Tibetan. - 31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33 - additional characters. - 32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993. - 33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993 - Identifiers for characters. - 34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993 - Ethiopic. - 35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993 - Unified Canadian Aboriginal Syllabics. - 36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993 - Cherokee. - 37. ISO/IEC 10967-1:1994, Information technology -- Language independent - arithmetic -- Part 1: Integer and floating point arithmetic. - -[page 651] - - 38. ISO/IEC TR 19769:2004, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions for the - programming language C to support new character data types. - 39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions to the C library - -- Part 1: Bounds-checking interfaces. - -[page 652] - - -Index -[^ x ^], 3.20 , (comma operator), 5.1.2.4, 6.5.17 - , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, -[_ x _], 3.21 6.7.2.3, 6.7.9 -! (logical negation operator), 6.5.3.3 - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2 -!= (inequality operator), 6.5.9 - (unary minus operator), 6.5.3.3, F.3 -# operator, 6.10.3.2 -- (postfix decrement operator), 6.3.2.1, 6.5.2.4 -# preprocessing directive, 6.10.7 -- (prefix decrement operator), 6.3.2.1, 6.5.3.1 -# punctuator, 6.10 -= (subtraction assignment operator), 6.5.16.2 -## operator, 6.10.3.3 -> (structure/union pointer operator), 6.5.2.3 -#define preprocessing directive, 6.10.3 . (structure/union member operator), 6.3.2.1, -#elif preprocessing directive, 6.10.1 6.5.2.3 -#else preprocessing directive, 6.10.1 . punctuator, 6.7.9 -#endif preprocessing directive, 6.10.1 ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3 -#error preprocessing directive, 4, 6.10.5 / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1 -#if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, /* */ (comment delimiters), 6.4.9 - 6.10.1, 7.1.4 // (comment delimiter), 6.4.9 -#ifdef preprocessing directive, 6.10.1 /= (division assignment operator), 6.5.16.2 -#ifndef preprocessing directive, 6.10.1 : (colon punctuator), 6.7.2.1 -#include preprocessing directive, 5.1.1.2, :> (alternative spelling of ]), 6.4.6 - 6.10.2 ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3, -#line preprocessing directive, 6.10.4 6.8.5, 6.8.6 -#pragma preprocessing directive, 6.10.6 < (less-than operator), 6.5.8 -#undef preprocessing directive, 6.10.3.5, 7.1.3, <% (alternative spelling of {), 6.4.6 - 7.1.4 <: (alternative spelling of [), 6.4.6 -% (remainder operator), 6.2.6.2, 6.5.5 << (left-shift operator), 6.2.6.2, 6.5.7 -%: (alternative spelling of #), 6.4.6 <<= (left-shift assignment operator), 6.5.16.2 -%:%: (alternative spelling of ##), 6.4.6 <= (less-than-or-equal-to operator), 6.5.8 -%= (remainder assignment operator), 6.5.16.2 header, 7.2 -%> (alternative spelling of }), 6.4.6 header, 5.2.4.2.2, 6.10.8.3, 7.1.2, -& (address operator), 6.3.2.1, 6.5.3.2 7.3, 7.24, 7.30.1, G.6, J.5.17 -& (bitwise AND operator), 6.2.6.2, 6.5.10 header, 7.4, 7.30.2 -&& (logical AND operator), 5.1.2.4, 6.5.13 header, 7.5, 7.30.3, K.3.2 -&= (bitwise AND assignment operator), 6.5.16.2 header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, -' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, H - 7.4.1.10, 7.29.2.1.3 header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, -( ) (cast operator), 6.5.4 7.28.4.1.1 -( ) (function-call operator), 6.5.2.2 header, 7.8, 7.30.4 -( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5 header, 4, 7.9 -( ){ } (compound-literal operator), 6.5.2.5 header, 4, 5.2.4.2.1, 6.2.5, 7.10 -* (asterisk punctuator), 6.7.6.1, 6.7.6.2 header, 7.11, 7.30.5 -* (indirection operator), 6.5.2.1, 6.5.3.2 header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, -* (multiplication operator), 6.2.6.2, 6.5.5, F.3, F.10, J.5.17 - G.5.1 header, 7.13 -*= (multiplication assignment operator), 6.5.16.2 header, 7.14, 7.30.6 -+ (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2, header, 4, 7.15 - 6.5.6, F.3, G.5.2 header, 4, 6.7.6.3, 7.16 -+ (unary plus operator), 6.5.3.3 header, 6.10.8.3, 7.1.2, 7.17 -++ (postfix increment operator), 6.3.2.1, 6.5.2.4 header, 4, 7.18, 7.30.7, H -++ (prefix increment operator), 6.3.2.1, 6.5.3.1 header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, -+= (addition assignment operator), 6.5.16.2 - -[page 653] - - 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \x hexadecimal digits (hexadecimal-character - header, 4, 5.2.4.2, 6.10.1, 7.8, escape sequence), 6.4.4.4 - 7.20, 7.30.8, K.3.3, K.3.4 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11 - header, 5.2.4.2.2, 7.21, 7.30.9, F, ^= (bitwise exclusive OR assignment operator), - K.3.5 6.5.16.2 - header, 5.2.4.2.2, 7.22, 7.30.10, F, __alignas_is_defined macro, 7.15 - K.3.1.4, K.3.6 __bool_true_false_are_defined - header, 7.23, 7.30.11, K.3.7 macro, 7.18 - header, 7.24, G.7 __cplusplus macro, 6.10.8 - header, 6.10.8.3, 7.1.2, 7.25 __DATE__ macro, 6.10.8.1 - header, 7.26, K.3.8 __FILE__ macro, 6.10.8.1, 7.2.1.1 - header, 6.4.4.4, 6.4.5, 7.27 __func__ identifier, 6.4.2.2, 7.2.1.1 - header, 5.2.4.2.2, 7.21.1, 7.28, __LINE__ macro, 6.10.8.1, 7.2.1.1 - 7.30.12, F, K.3.9 __STDC_, 6.11.9 - header, 7.29, 7.30.13 __STDC__ macro, 6.10.8.1 -= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1 -= (simple assignment operator), 6.5.16.1 __STDC_HOSTED__ macro, 6.10.8.1 -== (equality operator), 6.5.9 __STDC_IEC_559__ macro, 6.10.8.3, F.1 -> (greater-than operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro, ->= (greater-than-or-equal-to operator), 6.5.8 6.10.8.3, G.1 ->> (right-shift operator), 6.2.6.2, 6.5.7 __STDC_ISO_10646__ macro, 6.10.8.2 ->>= (right-shift assignment operator), 6.5.16.2 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2 -? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_MB_MIGHT_NEQ_WC__ macro, -?? (trigraph sequences), 5.2.1.1 6.10.8.2, 7.19 -[ ] (array subscript operator), 6.5.2.1, 6.5.3.2 __STDC_NO_COMPLEX__ macro, 6.10.8.3, -[ ] (brackets punctuator), 6.7.6.2, 6.7.9 7.3.1 -\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 __STDC_NO_THREADS__ macro, 6.10.8.3, -\ (escape character), 6.4.4.4 7.17.1, 7.25.1 -\" (double-quote escape sequence), 6.4.4.4, __STDC_NO_VLA__ macro, 6.10.8.3 - 6.4.5, 6.10.9 __STDC_UTF_16__ macro, 6.10.8.2 -\\ (backslash escape sequence), 6.4.4.4, 6.10.9 __STDC_UTF_32__ macro, 6.10.8.2 -\' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_VERSION__ macro, 6.10.8.1 -\0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1 - padding of binary stream, 7.21.2 __TIME__ macro, 6.10.8.1 -\? (question-mark escape sequence), 6.4.4.4 __VA_ARGS__ identifier, 6.10.3, 6.10.3.1 -\a (alert escape sequence), 5.2.2, 6.4.4.4 _Alignas, 6.7.5 -\b (backspace escape sequence), 5.2.2, 6.4.4.4 _Atomic type qualifier, 6.7.3 -\f (form-feed escape sequence), 5.2.2, 6.4.4.4, _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1, - 7.4.1.10 F.4 -\n (new-line escape sequence), 5.2.2, 6.4.4.4, _Bool type conversions, 6.3.1.2 - 7.4.1.10 _Complex types, 6.2.5, 6.7.2, 7.3.1, G -\octal digits (octal-character escape sequence), _Complex_I macro, 7.3.1 - 6.4.4.4 _Exit function, 7.22.4.5, 7.22.4.7 -\r (carriage-return escape sequence), 5.2.2, _Imaginary keyword, G.2 - 6.4.4.4, 7.4.1.10 _Imaginary types, 7.3.1, G -\t (horizontal-tab escape sequence), 5.2.2, _Imaginary_I macro, 7.3.1, G.6 - 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3 _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 -\U (universal character names), 6.4.3 _IOLBF macro, 7.21.1, 7.21.5.6 -\u (universal character names), 6.4.3 _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 -\v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, _Noreturn, 6.7.4 - 7.4.1.10 _Pragma operator, 5.1.1.2, 6.10.9 - -[page 654] - -_Static_assert, 6.7.10, 7.2 allocated storage, order and contiguity, 7.22.3 -_Thread_local storage-class specifier, 6.2.4, and macro, 7.9 - 6.7.1 AND operators -{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, bitwise (&), 6.2.6.2, 6.5.10 - 6.8.2 bitwise assignment (&=), 6.5.16.2 -{ } (compound-literal operator), 6.5.2.5 logical (&&), 5.1.2.4, 6.5.13 -| (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 and_eq macro, 7.9 -|= (bitwise inclusive OR assignment operator), anonymous structure, 6.7.2.1 - 6.5.16.2 anonymous union, 6.7.2.1 -|| (logical OR operator), 5.1.2.4, 6.5.14 ANSI/IEEE 754, F.1 -~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 ANSI/IEEE 854, F.1 - argc (main function parameter), 5.1.2.2.1 -abort function, 7.2.1.1, 7.14.1.1, 7.21.3, argument, 3.3 - 7.22.4.1, 7.25.3.6, K.3.6.1.2 array, 6.9.1 -abort_handler_s function, K.3.6.1.2 default promotions, 6.5.2.2 -abs function, 7.22.6.1 function, 6.5.2.2, 6.9.1 -absolute-value functions macro, substitution, 6.10.3.1 - complex, 7.3.8, G.6.4 argument, complex, 7.3.9.1 - integer, 7.8.2.1, 7.22.6.1 argv (main function parameter), 5.1.2.2.1 - real, 7.12.7, F.10.4 arithmetic constant expression, 6.6 -abstract declarator, 6.7.7 arithmetic conversions, usual, see usual arithmetic -abstract machine, 5.1.2.3 conversions -access, 3.1, 6.7.3, L.2.1 arithmetic operators -accuracy, see floating-point accuracy additive, 6.2.6.2, 6.5.6, G.5.2 -acos functions, 7.12.4.1, F.10.1.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12 -acos type-generic macro, 7.24 increment and decrement, 6.5.2.4, 6.5.3.1 -acosh functions, 7.12.5.1, F.10.2.1 multiplicative, 6.2.6.2, 6.5.5, G.5.1 -acosh type-generic macro, 7.24 shift, 6.2.6.2, 6.5.7 -acquire fence, 7.17.4 unary, 6.5.3.3 -acquire operation, 5.1.2.4 arithmetic types, 6.2.5 -active position, 5.2.2 arithmetic, pointer, 6.5.6 -actual argument, 3.3 array -actual parameter (deprecated), 3.3 argument, 6.9.1 -addition assignment operator (+=), 6.5.16.2 declarator, 6.7.6.2 -addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, initialization, 6.7.9 - 6.5.6, F.3, G.5.2 multidimensional, 6.5.2.1 -additive expressions, 6.5.6, G.5.2 parameter, 6.9.1 -address constant, 6.6 storage order, 6.5.2.1 -address operator (&), 6.3.2.1, 6.5.3.2 subscript operator ([ ]), 6.5.2.1, 6.5.3.2 -address-free, 7.17.5 subscripting, 6.5.2.1 -aggregate initialization, 6.7.9 type, 6.2.5 -aggregate types, 6.2.5 type conversion, 6.3.2.1 -alert escape sequence (\a), 5.2.2, 6.4.4.4 variable length, 6.7.6, 6.7.6.2, 6.10.8.3 -aliasing, 6.5 arrow operator (->), 6.5.2.3 -alignas macro, 7.15 as-if rule, 5.1.2.3 -aligned_alloc function, 7.22.3, 7.22.3.1 ASCII code set, 5.2.1.1 -alignment, 3.2, 6.2.8, 7.22.3.1 asctime function, 7.26.3.1 - pointer, 6.2.5, 6.3.2.3 asctime_s function, K.3.8.2, K.3.8.2.1 - structure/union member, 6.7.2.1 asin functions, 7.12.4.2, F.10.1.2 -alignment specifier, 6.7.5 asin type-generic macro, 7.24, G.7 -alignof operator, 6.5.3, 6.5.3.4 asinh functions, 7.12.5.2, F.10.2.2 - -[page 655] - -asinh type-generic macro, 7.24, G.7 atomic_is_lock_free generic function, -asm keyword, J.5.10 7.17.5.1 -assert macro, 7.2.1.1 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1 -assert.h header, 7.2 atomic_load generic functions, 7.17.7.2 -assignment ATOMIC_LONG_LOCK_FREE macro, 7.17.1 - compound, 6.5.16.2 ATOMIC_SHORT_LOCK_FREE macro, 7.17.1 - conversion, 6.5.16.1 atomic_signal_fence function, 7.17.4.2 - expression, 6.5.16 atomic_store generic functions, 7.17.7.1 - operators, 6.3.2.1, 6.5.16 atomic_thread_fence function, 7.17.4.1 - simple, 6.5.16.1 ATOMIC_VAR_INIT macro, 7.17.2.1 -associativity of operators, 6.5 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1 -asterisk punctuator (*), 6.7.6.1, 6.7.6.2 atomics header, 7.17 -at_quick_exit function, 7.22.4.2, 7.22.4.3, auto storage-class specifier, 6.7.1, 6.9 - 7.22.4.4, 7.22.4.5, 7.22.4.7 automatic storage duration, 5.2.3, 6.2.4 -atan functions, 7.12.4.3, F.10.1.3 -atan type-generic macro, 7.24, G.7 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4 -atan2 functions, 7.12.4.4, F.10.1.4 backslash escape sequence (\\), 6.4.4.4, 6.10.9 -atan2 type-generic macro, 7.24 backspace escape sequence (\b), 5.2.2, 6.4.4.4 -atanh functions, 7.12.5.3, F.10.2.3 basic character set, 3.6, 3.7.2, 5.2.1 -atanh type-generic macro, 7.24, G.7 basic types, 6.2.5 -atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, behavior, 3.4 - 7.22.4.5, 7.22.4.7, J.5.13 binary streams, 7.21.2, 7.21.7.10, 7.21.9.2, -atof function, 7.22.1, 7.22.1.1 7.21.9.4 -atoi function, 7.22.1, 7.22.1.2 bit, 3.5 -atol function, 7.22.1, 7.22.1.2 high order, 3.6 -atoll function, 7.22.1, 7.22.1.2 low order, 3.6 -atomic lock-free macros, 7.17.1, 7.17.5 bit-field, 6.7.2.1 -atomic operations, 5.1.2.4 bitand macro, 7.9 -atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, bitor macro, 7.9 - 6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, bitwise operators, 6.5 - 7.17.6 AND, 6.2.6.2, 6.5.10 -atomic_address type, 7.17.1, 7.17.6 AND assignment (&=), 6.5.16.2 -ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3 -atomic_bool type, 7.17.1, 7.17.6 exclusive OR, 6.2.6.2, 6.5.11 -ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR assignment (^=), 6.5.16.2 - 7.17.1 inclusive OR, 6.2.6.2, 6.5.12 -ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR assignment (|=), 6.5.16.2 - 7.17.1 shift, 6.2.6.2, 6.5.7 -ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 blank character, 7.4.1.3 -atomic_compare_exchange generic block, 6.8, 6.8.2, 6.8.4, 6.8.5 - functions, 7.17.7.4 block scope, 6.2.1 -atomic_exchange generic functions, 7.17.7.3 block structure, 6.2.1 -atomic_fetch and modify generic functions, bold type convention, 6.1 - 7.17.7.5 bool macro, 7.18 -atomic_flag type, 7.17.1, 7.17.8 boolean type, 6.3.1.2 -atomic_flag_clear functions, 7.17.8.2 boolean type conversion, 6.3.1.1, 6.3.1.2 -ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8 bounded undefined behavior, L.2.2 -atomic_flag_test_and_set functions, braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9, - 7.17.8.1 6.8.2 -atomic_init generic function, 7.17.2.2 brackets operator ([ ]), 6.5.2.1, 6.5.3.2 -ATOMIC_INT_LOCK_FREE macro, 7.17.1 brackets punctuator ([ ]), 6.7.6.2, 6.7.9 - -[page 656] - -branch cuts, 7.3.3 type-generic macro for, 7.24 -break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4 -broken-down time, 7.26.1, 7.26.2.3, 7.26.3, type-generic macro for, 7.24 - 7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5, ceil functions, 7.12.9.1, F.10.6.1 - K.3.8.2.1, K.3.8.2.3, K.3.8.2.4 ceil type-generic macro, 7.24 -bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.30.1 -bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.30.1 -btowc function, 7.28.6.1.1 cexp functions, 7.3.7.1, G.6.3.1 -BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5 type-generic macro for, 7.24 -byte, 3.6, 6.5.3.4 cexp2 function, 7.30.1 -byte input/output functions, 7.21.1 cexpm1 function, 7.30.1 -byte-oriented stream, 7.21.2 char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2, - K.3.9.1.2 -C program, 5.1.1.1 char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, -c16rtomb function, 7.27.1.2 6.3.1.8 -c32rtomb function, 7.27.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 -cabs functions, 7.3.8.1, G.6 char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 - type-generic macro for, 7.24 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1 -cacos functions, 7.3.5.1, G.6.1.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1 - type-generic macro for, 7.24 CHAR_MIN macro, 5.2.4.2.1 -cacosh functions, 7.3.6.1, G.6.2.1 character, 3.7, 3.7.1 - type-generic macro for, 7.24 character array initialization, 6.7.9 -calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, character case mapping functions, 7.4.2 - 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, wide character, 7.29.3.1 - K.3.8.2.3, K.3.8.2.4 extensible, 7.29.3.2 -call by value, 6.5.2.2 character classification functions, 7.4.1 -call_once function, 7.25.1, 7.25.2.1 wide character, 7.29.2.1 -calloc function, 7.22.3, 7.22.3.2 extensible, 7.29.2.2 -carg functions, 7.3.9.1, G.6 character constant, 5.1.1.2, 5.2.1, 6.4.4.4 -carg type-generic macro, 7.24, G.7 character display semantics, 5.2.2 -carriage-return escape sequence (\r), 5.2.2, character handling header, 7.4, 7.11.1.1 - 6.4.4.4, 7.4.1.10 character input/output functions, 7.21.7, K.3.5.4 -carries a dependency, 5.1.2.4 wide character, 7.28.3 -case label, 6.8.1, 6.8.4.2 character sets, 5.2.1 -case mapping functions character string literal, see string literal - character, 7.4.2 character type conversion, 6.3.1.1 - wide character, 7.29.3.1 character types, 6.2.5, 6.7.9 - extensible, 7.29.3.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6 -casin functions, 7.3.5.2, G.6 cimag type-generic macro, 7.24, G.7 - type-generic macro for, 7.24 cis function, G.6 -casinh functions, 7.3.6.2, G.6.2.2 classification functions - type-generic macro for, 7.24 character, 7.4.1 -cast expression, 6.5.4 floating-point, 7.12.3 -cast operator (( )), 6.5.4 wide character, 7.29.2.1 -catan functions, 7.3.5.3, G.6 extensible, 7.29.2.2 - type-generic macro for, 7.24 clearerr function, 7.21.10.1 -catanh functions, 7.3.6.3, G.6.2.3 clgamma function, 7.30.1 - type-generic macro for, 7.24 clock function, 7.26.2.1 -cbrt functions, 7.12.7.1, F.10.4.1 clock_t type, 7.26.1, 7.26.2.1 -cbrt type-generic macro, 7.24 CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1 -ccos functions, 7.3.5.4, G.6 clog functions, 7.3.7.2, G.6.3.2 - -[page 657] - - type-generic macro for, 7.24 string, 7.23.3, K.3.7.2 -clog10 function, 7.30.1 wide string, 7.28.4.3, K.3.9.2.2 -clog1p function, 7.30.1 concatenation, preprocessing, see preprocessing -clog2 function, 7.30.1 concatenation -CMPLX macros, 7.3.9.3 conceptual models, 5.1 -cnd_broadcast function, 7.25.3.1, 7.25.3.5, conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3, - 7.25.3.6 7.1.2, F.1, G.1, K.2, L.1 -cnd_destroy function, 7.25.3.2 conditional inclusion, 6.10.1 -cnd_init function, 7.25.3.3 conditional operator (? :), 5.1.2.4, 6.5.15 -cnd_signal function, 7.25.3.4, 7.25.3.5, conflict, 5.1.2.4 - 7.25.3.6 conformance, 4 -cnd_t type, 7.25.1 conj functions, 7.3.9.4, G.6 -cnd_timedwait function, 7.25.3.5 conj type-generic macro, 7.24 -cnd_wait function, 7.25.3.3, 7.25.3.6 const type qualifier, 6.7.3 -collating sequences, 5.2.1 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3 -colon punctuator (:), 6.7.2.1 constant expression, 6.6, F.8.4 -comma operator (,), 5.1.2.4, 6.5.17 constants, 6.4.4 -comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, as primary expression, 6.5.1 - 6.7.2.3, 6.7.9 character, 6.4.4.4 -command processor, 7.22.4.8 enumeration, 6.2.1, 6.4.4.3 -comment delimiters (/* */ and //), 6.4.9 floating, 6.4.4.2 -comments, 5.1.1.2, 6.4, 6.4.9 hexadecimal, 6.4.4.1 -common extensions, J.5 integer, 6.4.4.1 -common initial sequence, 6.5.2.3 octal, 6.4.4.1 -common real type, 6.3.1.8 constraint, 3.8, 4 -common warnings, I constraint_handler_t type, K.3.6 -comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, consume operation, 5.1.2.4 - K.3.6.3, K.3.6.3.1, K.3.6.3.2 content of structure/union/enumeration, 6.7.2.3 - string, 7.23.4 contiguity of allocated storage, 7.22.3 - wide string, 7.28.4.4 continue statement, 6.8.6.2 -comparison macros, 7.12.14 contracted expression, 6.5, 7.12.2, F.7 -comparison, pointer, 6.5.8 control character, 5.2.1, 7.4 -compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control wide character, 7.29.2 -compl macro, 7.9 conversion, 6.3 -complement operator (~), 6.2.6.2, 6.5.3.3 arithmetic operands, 6.3.1 -complete type, 6.2.5 array argument, 6.9.1 -complex macro, 7.3.1 array parameter, 6.9.1 -complex numbers, 6.2.5, G arrays, 6.3.2.1 -complex type conversion, 6.3.1.6, 6.3.1.7 boolean, 6.3.1.2 -complex type domain, 6.2.5 boolean, characters, and integers, 6.3.1.1 -complex types, 6.2.5, 6.7.2, 6.10.8.3, G by assignment, 6.5.16.1 -complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2, by return statement, 6.8.6.4 - 7.3, 7.24, 7.30.1, G.6, J.5.17 complex types, 6.3.1.6 -compliance, see conformance explicit, 6.3 -components of time, 7.26.1, K.3.8.1 function, 6.3.2.1 -composite type, 6.2.7 function argument, 6.5.2.2, 6.9.1 -compound assignment, 6.5.16.2 function designators, 6.3.2.1 -compound literals, 6.5.2.5 function parameter, 6.9.1 -compound statement, 6.8.2 imaginary, G.4.1 -compound-literal operator (( ){ }), 6.5.2.5 imaginary and complex, G.4.3 -concatenation functions implicit, 6.3 - -[page 658] - - lvalues, 6.3.2.1 csinh functions, 7.3.6.5, G.6.2.5 - pointer, 6.3.2.1, 6.3.2.3 type-generic macro for, 7.24 - real and complex, 6.3.1.7 csqrt functions, 7.3.8.3, G.6.4.2 - real and imaginary, G.4.2 type-generic macro for, 7.24 - real floating and integer, 6.3.1.4, F.3, F.4 ctan functions, 7.3.5.6, G.6 - real floating types, 6.3.1.5, F.3 type-generic macro for, 7.24 - signed and unsigned integers, 6.3.1.3 ctanh functions, 7.3.6.6, G.6.2.6 - usual arithmetic, see usual arithmetic type-generic macro for, 7.24 - conversions ctgamma function, 7.30.1 - void type, 6.3.2.2 ctime function, 7.26.3.2 -conversion functions ctime_s function, K.3.8.2, K.3.8.2.2 - multibyte/wide character, 7.22.7, K.3.6.4 ctype.h header, 7.4, 7.30.2 - extended, 7.28.6, K.3.9.3 current object, 6.7.9 - restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4 - multibyte/wide string, 7.22.8, K.3.6.5 - restartable, 7.28.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6, - numeric, 7.8.2.3, 7.22.1 7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3, - wide string, 7.8.2.4, 7.28.4.1 7.28.6.4 - single byte/wide character, 7.28.6.1 data stream, see streams - time, 7.26.3, K.3.8.2 date and time header, 7.26, K.3.8 - wide character, 7.28.5 Daylight Saving Time, 7.26.1 -conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2 - 7.28.2.2 DBL_DIG macro, 5.2.4.2.2 -conversion state, 7.22.7, 7.27.1, 7.27.1.1, DBL_EPSILON macro, 5.2.4.2.2 - 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2 - 7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2 - 7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4, DBL_MAX macro, 5.2.4.2.2 - K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1, DBL_MAX_10_EXP macro, 5.2.4.2.2 - K.3.9.3.2.2 DBL_MAX_EXP macro, 5.2.4.2.2 -conversion state functions, 7.28.6.2 DBL_MIN macro, 5.2.4.2.2 -copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2 - string, 7.23.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2 - wide string, 7.28.4.2, K.3.9.2.1 DBL_TRUE_MIN macro, 5.2.4.2.2 -copysign functions, 7.3.9.5, 7.12.11.1, F.3, decimal constant, 6.4.4.1 - F.10.8.1 decimal digit, 5.2.1 -copysign type-generic macro, 7.24 decimal-point character, 7.1.1, 7.11.2.1 -correctly rounded result, 3.9 DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1, -corresponding real type, 6.2.5 7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5 -cos functions, 7.12.4.5, F.10.1.5 declaration specifiers, 6.7 -cos type-generic macro, 7.24, G.7 declarations, 6.7 -cosh functions, 7.12.5.4, F.10.2.4 function, 6.7.6.3 -cosh type-generic macro, 7.24, G.7 pointer, 6.7.6.1 -cpow functions, 7.3.8.2, G.6.4.1 structure/union, 6.7.2.1 - type-generic macro for, 7.24 typedef, 6.7.8 -cproj functions, 7.3.9.5, G.6 declarator, 6.7.6 -cproj type-generic macro, 7.24 abstract, 6.7.7 -creal functions, 7.3.9.6, G.6 declarator type derivation, 6.2.5, 6.7.6 -creal type-generic macro, 7.24, G.7 decrement operators, see arithmetic operators, -critical undefined behavior, L.2.3 increment and decrement -csin functions, 7.3.5.5, G.6 default argument promotions, 6.5.2.2 - type-generic macro for, 7.24 default initialization, 6.7.9 - -[page 659] - -default label, 6.8.1, 6.8.4.2 elif preprocessing directive, 6.10.1 -define preprocessing directive, 6.10.3 ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3 -defined operator, 6.10.1, 6.10.8 else preprocessing directive, 6.10.1 -definition, 6.7 else statement, 6.8.4.1 - function, 6.9.1 empty statement, 6.8.3 -dependency-ordered before, 5.1.2.4 encoding error, 7.21.3, 7.27.1.1, 7.27.1.2, -derived declarator types, 6.2.5 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, -derived types, 6.2.5 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, -designated initializer, 6.7.9 K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1, -destringizing, 6.10.9 K.3.9.3.2.2 -device input/output, 5.1.2.3 end-of-file, 7.28.1 -diagnostic message, 3.10, 5.1.1.3 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1, -diagnostics, 5.1.1.3 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2, -diagnostics header, 7.2 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1, -difftime function, 7.26.2.2 7.28.3.10 -digit, 5.2.1, 7.4 end-of-file macro, see EOF macro -digraphs, 6.4.6 end-of-line indicator, 5.2.1 -direct input/output functions, 7.21.8 endif preprocessing directive, 6.10.1 -display device, 5.2.2 enum type, 6.2.5, 6.7.2, 6.7.2.2 -div function, 7.22.6.2 enumerated type, 6.2.5 -div_t type, 7.22 enumeration, 6.2.5, 6.7.2.2 -division assignment operator (/=), 6.5.16.2 enumeration constant, 6.2.1, 6.4.4.3 -division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enumeration content, 6.7.2.3 -do statement, 6.8.5.2 enumeration members, 6.7.2.2 -documentation of implementation, 4 enumeration specifiers, 6.7.2.2 -domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration tag, 6.2.3, 6.7.2.3 - 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumerator, 6.7.2.2 - 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, environment, 5 - 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, environment functions, 7.22.4, K.3.6.2 - 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 environment list, 7.22.4.6, K.3.6.2.1 -dot operator (.), 6.5.2.3 environmental considerations, 5.2 -double _Complex type, 6.2.5 environmental limits, 5.2.4, 7.13.1.1, 7.21.2, -double _Complex type conversion, 6.3.1.6, 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2, - 6.3.1.7, 6.3.1.8 7.22.4.3, 7.28.2.1, K.3.5.1.2 -double _Imaginary type, G.2 EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2, -double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11, - 7.28.2.2, F.2 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4, -double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9, - 6.3.1.8 7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4, -double-precision arithmetic, 5.1.2.3 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12, -double-quote escape sequence (\"), 6.4.4.4, 7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7, - 6.4.5, 6.10.9 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, -double_t type, 7.12, J.5.6 K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, - K.3.9.1.14 -EDOM macro, 7.5, 7.12.1, see also domain error equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9 -effective type, 6.5 equal-to operator, see equality operator -EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2, equality expressions, 6.5.9 - 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, equality operator (==), 6.5.9 - 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1, - see also encoding error 7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see -element type, 6.2.5 also range error, pole error - -[page 660] - -erf functions, 7.12.8.1, F.10.5.1 exp2 functions, 7.12.6.2, F.10.3.2 -erf type-generic macro, 7.24 exp2 type-generic macro, 7.24 -erfc functions, 7.12.8.2, F.10.5.2 explicit conversion, 6.3 -erfc type-generic macro, 7.24 expm1 functions, 7.12.6.3, F.10.3.3 -errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4, expm1 type-generic macro, 7.24 - 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, exponent part, 6.4.4.2 - 7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1, exponential functions - 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1, complex, 7.3.7, G.6.3 - 7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2, real, 7.12.6, F.10.3 - 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17, expression, 6.5 - K.3.1.3, K.3.7.4.2 assignment, 6.5.16 -errno.h header, 7.5, 7.30.3, K.3.2 cast, 6.5.4 -errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, constant, 6.6 - K.3.7, K.3.8, K.3.9 evaluation, 5.1.2.3 -error full, 6.8 - domain, see domain error order of evaluation, see order of evaluation - encoding, see encoding error parenthesized, 6.5.1 - pole, see pole error primary, 6.5.1 - range, see range error unary, 6.5.3 -error conditions, 7.12.1 expression statement, 6.8.3 -error functions, 7.12.8, F.10.5 extended alignment, 6.2.8 -error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended character set, 3.7.2, 5.2.1, 5.2.1.2 - 7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7, extended characters, 5.2.1 - 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1, - 7.28.3.1, 7.28.3.3 7.20 -error preprocessing directive, 4, 6.10.5 extended multibyte/wide character conversion -error-handling functions, 7.21.10, 7.23.6.2, utilities, 7.28.6, K.3.9.3 - K.3.7.4.2, K.3.7.4.3 extensible wide character case mapping functions, -escape character (\), 6.4.4.4 7.29.3.2 -escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 extensible wide character classification functions, -evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12 7.29.2.2 -evaluation method, 5.2.4.2.2, 6.5, F.8.5 extern storage-class specifier, 6.2.2, 6.7.1 -evaluation of expression, 5.1.2.3 external definition, 6.9 -evaluation order, see order of evaluation external identifiers, underscore, 7.1.3 -exceptional condition, 6.5 external linkage, 6.2.2 -excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external name, 6.4.2.1 -excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external object definitions, 6.9.2 -exclusive OR operators - bitwise (^), 6.2.6.2, 6.5.11 fabs functions, 7.12.7.2, F.3, F.10.4.2 - bitwise assignment (^=), 6.5.16.2 fabs type-generic macro, 7.24, G.7 -executable program, 5.1.1.1 false macro, 7.18 -execution character set, 5.2.1 fclose function, 7.21.5.1 -execution environment, 5, 5.1.2, see also fdim functions, 7.12.12.1, F.10.9.1 - environmental limits fdim type-generic macro, 7.24 -execution sequence, 5.1.2.3, 6.8 FE_ALL_EXCEPT macro, 7.6 -exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4, FE_DFL_ENV macro, 7.6 - 7.22.4.5, 7.22.4.7 FE_DIVBYZERO macro, 7.6, 7.12, F.3 -EXIT_FAILURE macro, 7.22, 7.22.4.4 FE_DOWNWARD macro, 7.6, F.3 -EXIT_SUCCESS macro, 7.22, 7.22.4.4 FE_INEXACT macro, 7.6, F.3 -exp functions, 7.12.6.1, F.10.3.1 FE_INVALID macro, 7.6, 7.12, F.3 -exp type-generic macro, 7.24 FE_OVERFLOW macro, 7.6, 7.12, F.3 - -[page 661] - -FE_TONEAREST macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6, -FE_TOWARDZERO macro, 7.6, F.3 6.3.1.7, 6.3.1.8 -FE_UNDERFLOW macro, 7.6, F.3 float _Imaginary type, G.2 -FE_UPWARD macro, 7.6, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2 -feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, -fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 6.3.1.8 -fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, -fegetround function, 7.6, 7.6.3.1, F.3 7.28.4.1.1 -feholdexcept function, 7.6.4.2, 7.6.4.3, float_t type, 7.12, J.5.6 - 7.6.4.4, F.3 floating constant, 6.4.4.2 -fence, 5.1.2.4 floating suffix, f or F, 6.4.4.2 -fences, 7.17.4 floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, -fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H F.3, F.4 -FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9, floating types, 6.2.5, 6.11.1 - F.10 floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5, -fenv_t type, 7.6 7.22.1.3, F.5, see also contracted expression -feof function, 7.21.10.2 floating-point arithmetic functions, 7.12, F.10 -feraiseexcept function, 7.6.2, 7.6.2.3, F.3 floating-point classification functions, 7.12.3 -ferror function, 7.21.10.3 floating-point control mode, 7.6, F.8.6 -fesetenv function, 7.6.4.3, F.3 floating-point environment, 7.6, F.8, F.8.6 -fesetexceptflag function, 7.6.2, 7.6.2.4, F.3 floating-point exception, 7.6, 7.6.2, F.10 -fesetround function, 7.6, 7.6.3.2, F.3 floating-point number, 5.2.4.2.2, 6.2.5 -fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point rounding mode, 5.2.4.2.2 -feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point status flag, 7.6, F.8.6 -fexcept_t type, 7.6, F.3 floor functions, 7.12.9.2, F.10.6.2 -fflush function, 7.21.5.2, 7.21.5.3 floor type-generic macro, 7.24 -fgetc function, 7.21.1, 7.21.3, 7.21.7.1, FLT_DECIMAL_DIG macro, 5.2.4.2.2 - 7.21.7.5, 7.21.8.1 FLT_DIG macro, 5.2.4.2.2 -fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3 FLT_EPSILON macro, 5.2.4.2.2 -fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1 FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12, -fgetwc function, 7.21.1, 7.21.3, 7.28.3.1, F.10.11 - 7.28.3.6 FLT_HAS_SUBNORM macro, 5.2.4.2.2 -fgetws function, 7.21.1, 7.28.3.2 FLT_MANT_DIG macro, 5.2.4.2.2 -field width, 7.21.6.1, 7.28.2.1 FLT_MAX macro, 5.2.4.2.2 -file, 7.21.3 FLT_MAX_10_EXP macro, 5.2.4.2.2 - access functions, 7.21.5, K.3.5.2 FLT_MAX_EXP macro, 5.2.4.2.2 - name, 7.21.3 FLT_MIN macro, 5.2.4.2.2 - operations, 7.21.4, K.3.5.1 FLT_MIN_10_EXP macro, 5.2.4.2.2 - position indicator, 7.21.1, 7.21.2, 7.21.3, FLT_MIN_EXP macro, 5.2.4.2.2 - 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10, FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3, - 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2, 7.28.2.1, 7.28.4.1.1 - 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1, FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3 - 7.28.3.3, 7.28.3.10 FLT_TRUE_MIN macro, 5.2.4.2.2 - positioning functions, 7.21.9 fma functions, 7.12, 7.12.13.1, F.10.10.1 -file scope, 6.2.1, 6.9 fma type-generic macro, 7.24 -FILE type, 7.21.1, 7.21.3 fmax functions, 7.12.12.2, F.10.9.2 -FILENAME_MAX macro, 7.21.1 fmax type-generic macro, 7.24 -flags, 7.21.6.1, 7.28.2.1, see also floating-point fmin functions, 7.12.12.3, F.10.9.3 - status flag fmin type-generic macro, 7.24 -flexible array member, 6.7.2.1 fmod functions, 7.12.10.1, F.10.7.1 -float _Complex type, 6.2.5 fmod type-generic macro, 7.24 - -[page 662] - -fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 K.3.5.3.7, K.3.5.3.9 -FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10, - K.3.5.1.1 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10 -fopen_s function, K.3.5.1.1, K.3.5.2.1, fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10, - K.3.5.2.2 7.21.9.1, 7.21.9.3, 7.28.3.10 -for statement, 6.8.5, 6.8.5.3 ftell function, 7.21.9.2, 7.21.9.4 -form-feed character, 5.2.1, 6.4 full declarator, 6.7.6 -form-feed escape sequence (\f), 5.2.2, 6.4.4.4, full expression, 6.8 - 7.4.1.10 fully buffered stream, 7.21.3 -formal argument (deprecated), 3.16 function -formal parameter, 3.16 argument, 6.5.2.2, 6.9.1 -formatted input/output functions, 7.11.1.1, 7.21.6, body, 6.9.1 - K.3.5.3 call, 6.5.2.2 - wide character, 7.28.2, K.3.9.1 library, 7.1.4 -fortran keyword, J.5.9 declarator, 6.7.6.3, 6.11.6 -forward reference, 3.11 definition, 6.7.6.3, 6.9.1, 6.11.7 -FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see designator, 6.3.2.1 - also contracted expression image, 5.2.3 -FP_FAST_FMA macro, 7.12 inline, 6.7.4 -FP_FAST_FMAF macro, 7.12 library, 5.1.1.1, 7.1.4 -FP_FAST_FMAL macro, 7.12 name length, 5.2.4.1, 6.4.2.1, 6.11.3 -FP_ILOGB0 macro, 7.12, 7.12.6.5 no-return, 6.7.4 -FP_ILOGBNAN macro, 7.12, 7.12.6.5 parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1 -FP_INFINITE macro, 7.12, F.3 prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7, -FP_NAN macro, 7.12, F.3 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12 -FP_NORMAL macro, 7.12, F.3 prototype scope, 6.2.1, 6.7.6.2 -FP_SUBNORMAL macro, 7.12, F.3 recursive call, 6.5.2.2 -FP_ZERO macro, 7.12, F.3 return, 6.8.6.4, F.6 -fpclassify macro, 7.12.3.1, F.3 scope, 6.2.1 -fpos_t type, 7.21.1, 7.21.2 type, 6.2.5 -fprintf function, 7.8.1, 7.21.1, 7.21.6.1, type conversion, 6.3.2.1 - 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6, function specifiers, 6.7.4 - 7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1 function type, 6.2.5 -fprintf_s function, K.3.5.3.1 function-call operator (( )), 6.5.2.2 -fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3, function-like macro, 6.10.3 - 7.21.7.7, 7.21.8.2 fundamental alignment, 6.2.8 -fputs function, 7.21.1, 7.21.7.4 future directions -fputwc function, 7.21.1, 7.21.3, 7.28.3.3, language, 6.11 - 7.28.3.8 library, 7.30 -fputws function, 7.21.1, 7.28.3.4 fwide function, 7.21.2, 7.28.3.5 -fread function, 7.21.1, 7.21.8.1 fwprintf function, 7.8.1, 7.21.1, 7.21.6.2, -free function, 7.22.3.3, 7.22.3.5 7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5, -freestanding execution environment, 4, 5.1.2, 7.28.2.11, K.3.9.1.1 - 5.1.2.1 fwprintf_s function, K.3.9.1.1 -freopen function, 7.21.2, 7.21.5.4 fwrite function, 7.21.1, 7.21.8.2 -freopen_s function, K.3.5.2.2 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2, -frexp functions, 7.12.6.4, F.10.3.4 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10, -frexp type-generic macro, 7.24 K.3.9.1.2 -fscanf function, 7.8.1, 7.21.1, 7.21.6.2, fwscanf_s function, K.3.9.1.2, K.3.9.1.5, - 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2 K.3.9.1.7, K.3.9.1.14 -fscanf_s function, K.3.5.3.2, K.3.5.3.4, - -[page 663] - -gamma functions, 7.12.8, F.10.5 name spaces, 6.2.3 -general utilities, 7.22, K.3.6 reserved, 6.4.1, 7.1.3, K.3.1.2 - wide string, 7.28.4, K.3.9.2 scope, 6.2.1 -general wide string utilities, 7.28.4, K.3.9.2 type, 6.2.5 -generic parameters, 7.24 identifier list, 6.7.6 -generic selection, 6.5.1.1 identifier nondigit, 6.4.2.1 -getc function, 7.21.1, 7.21.7.5, 7.21.7.6 IEC 559, F.1 -getchar function, 7.21.1, 7.21.7.6 IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3, -getenv function, 7.22.4.6 7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G, -getenv_s function, K.3.6.2.1 H.1 -gets function, K.3.5.4.1 IEEE 754, F.1 -gets_s function, K.3.5.4.1 IEEE 854, F.1 -getwc function, 7.21.1, 7.28.3.6, 7.28.3.7 IEEE floating-point arithmetic standard, see -getwchar function, 7.21.1, 7.28.3.7 IEC 60559, ANSI/IEEE 754, -gmtime function, 7.26.3.3 ANSI/IEEE 854 -gmtime_s function, K.3.8.2.3 if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, -goto statement, 6.2.1, 6.8.1, 6.8.6.1 6.10.1, 7.1.4 -graphic characters, 5.2.1 if statement, 6.8.4.1 -greater-than operator (>), 6.5.8 ifdef preprocessing directive, 6.10.1 -greater-than-or-equal-to operator (>=), 6.5.8 ifndef preprocessing directive, 6.10.1 - ignore_handler_s function, K.3.6.1.3 -happens before, 5.1.2.4 ilogb functions, 7.12, 7.12.6.5, F.10.3.5 -header, 5.1.1.1, 7.1.2, see also standard headers ilogb type-generic macro, 7.24 -header names, 6.4, 6.4.7, 6.10.2 imaginary macro, 7.3.1, G.6 -hexadecimal constant, 6.4.4.1 imaginary numbers, G -hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4 imaginary type domain, G.2 -hexadecimal prefix, 6.4.4.1 imaginary types, G -hexadecimal-character escape sequence imaxabs function, 7.8.2.1 - (\x hexadecimal digits), 6.4.4.4 imaxdiv function, 7.8, 7.8.2.2 -high-order bit, 3.6 imaxdiv_t type, 7.8 -horizontal-tab character, 5.2.1, 6.4 implementation, 3.12 -horizontal-tab escape sequence (\r), 7.29.2.1.3 implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1, -horizontal-tab escape sequence (\t), 5.2.2, 6.7.6, 6.8.4.2, E, see also environmental - 6.4.4.4, 7.4.1.3, 7.4.1.10 limits -hosted execution environment, 4, 5.1.2, 5.1.2.2 implementation-defined behavior, 3.4.1, 4, J.3 -HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3, implementation-defined value, 3.19.1 - 7.28.4.1.1, F.10 implicit conversion, 6.3 -HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3, implicit initialization, 6.7.9 - 7.28.4.1.1, F.10 include preprocessing directive, 5.1.1.2, 6.10.2 -HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3, inclusive OR operators - 7.28.4.1.1, F.10 bitwise (|), 6.2.6.2, 6.5.12 -hyperbolic functions bitwise assignment (|=), 6.5.16.2 - complex, 7.3.6, G.6.2 incomplete type, 6.2.5 - real, 7.12.5, F.10.2 increment operators, see arithmetic operators, -hypot functions, 7.12.7.3, F.10.4.3 increment and decrement -hypot type-generic macro, 7.24 indeterminate value, 3.19.2 - indeterminately sequenced, 5.1.2.3, 6.5.2.2, -I macro, 7.3.1, 7.3.9.5, G.6 6.5.2.4, 6.5.16.2, see also sequenced before, -identifier, 6.4.2.1, 6.5.1 unsequenced - linkage, see linkage indirection operator (*), 6.5.2.1, 6.5.3.2 - maximum length, 6.4.2.1 inequality operator (!=), 6.5.9 - -[page 664] - -infinitary, 7.12.1 extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20 -INFINITY macro, 7.3.9.5, 7.12, F.2.1 inter-thread happens before, 5.1.2.4 -initial position, 5.2.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3 -initial shift state, 5.2.1.2 internal linkage, 6.2.2 -initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal name, 6.4.2.1 - F.8.5 interrupt, 5.2.3 - in blocks, 6.8 INTMAX_C macro, 7.20.4.2 -initializer, 6.7.9 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 - permitted form, 6.6 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 - string literal, 6.3.2.1 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, -inline, 6.7.4 7.28.2.1, 7.28.2.2 -inner scope, 6.2.1 INTN_C macros, 7.20.4.1 -input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, INTN_MAX macros, 7.20.2.1 - K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MIN macros, 7.20.2.1 - K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5, intN_t types, 7.20.1.1 - K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 INTPTR_MAX macro, 7.20.2.4 -input/output functions INTPTR_MIN macro, 7.20.2.4 - character, 7.21.7, K.3.5.4 intptr_t type, 7.20.1.4 - direct, 7.21.8 inttypes.h header, 7.8, 7.30.4 - formatted, 7.21.6, K.3.5.3 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10 - wide character, 7.28.2, K.3.9.1 isalpha function, 7.4.1.1, 7.4.1.2 - wide character, 7.28.3 isblank function, 7.4.1.3 - formatted, 7.28.2, K.3.9.1 iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7, -input/output header, 7.21, K.3.5 7.4.1.11 -input/output, device, 5.1.2.3 isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5, -int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 7.4.1.7, 7.4.1.11, 7.11.1.1 -int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isfinite macro, 7.12.3.2, F.3 - 6.3.1.8 isgraph function, 7.4.1.6 -INT_FASTN_MAX macros, 7.20.2.3 isgreater macro, 7.12.14.1, F.3 -INT_FASTN_MIN macros, 7.20.2.3 isgreaterequal macro, 7.12.14.2, F.3 -int_fastN_t types, 7.20.1.3 isinf macro, 7.12.3.3 -INT_LEASTN_MAX macros, 7.20.2.2 isless macro, 7.12.14.3, F.3 -INT_LEASTN_MIN macros, 7.20.2.2 islessequal macro, 7.12.14.4, F.3 -int_leastN_t types, 7.20.1.2 islessgreater macro, 7.12.14.5, F.3 -INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5 islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1, -INT_MIN macro, 5.2.4.2.1, 7.12 7.4.2.2 -integer arithmetic functions, 7.8.2.1, 7.8.2.2, isnan macro, 7.12.3.4, F.3 - 7.22.6 isnormal macro, 7.12.3.5 -integer character constant, 6.4.4.4 ISO 31-11, 2, 3 -integer constant, 6.4.4.1 ISO 4217, 2, 7.11.2.1 -integer constant expression, 6.3.2.3, 6.6, 6.7.2.1, ISO 8601, 2, 7.26.3.5 - 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1, ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2 - 7.1.4 ISO/IEC 10976-1, H.1 -integer conversion rank, 6.3.1.1 ISO/IEC 2382-1, 2, 3 -integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, ISO/IEC 646, 2, 5.2.1.1 - 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3, ISO/IEC 9945-2, 7.11 - 7.21.6.1, 7.28.2.1 iso646.h header, 4, 7.9 * -integer suffix, 6.4.4.1 isprint function, 5.2.2, 7.4.1.8 -integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9, - F.3, F.4 7.4.1.11 -integer types, 6.2.5, 7.20 isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9, - -[page 665] - - 7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3, LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1 - 7.22.1.4, 7.28.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3, -isunordered macro, 7.12.14.6, F.3 7.28.4.4.2 -isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1, LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7, - 7.4.2.2 7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2, -iswalnum function, 7.29.2.1.1, 7.29.2.1.9, 7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5 - 7.29.2.1.10, 7.29.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1 -iswalpha function, 7.29.2.1.1, 7.29.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1 - 7.29.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5 -iswblank function, 7.29.2.1.3, 7.29.2.2.1 lconv structure type, 7.11 -iswcntrl function, 7.29.2.1.2, 7.29.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2 - 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_DIG macro, 5.2.4.2.2 -iswctype function, 7.29.2.2.1, 7.29.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2 -iswdigit function, 7.29.2.1.1, 7.29.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2 - 7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2 -iswgraph function, 7.29.2.1, 7.29.2.1.6, LDBL_MAX macro, 5.2.4.2.2 - 7.29.2.1.10, 7.29.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2 -iswlower function, 7.29.2.1.2, 7.29.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2 - 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 LDBL_MIN macro, 5.2.4.2.2 -iswprint function, 7.29.2.1.6, 7.29.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2 - 7.29.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2 -iswpunct function, 7.29.2.1, 7.29.2.1.2, LDBL_TRUE_MIN macro, 5.2.4.2.2 - 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, ldexp functions, 7.12.6.6, F.10.3.6 - 7.29.2.1.11, 7.29.2.2.1 ldexp type-generic macro, 7.24 -iswspace function, 7.21.6.2, 7.28.2.2, ldiv function, 7.22.6.2 - 7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6, ldiv_t type, 7.22 - 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, leading underscore in identifiers, 7.1.3 - 7.29.2.1.11, 7.29.2.2.1 left-shift assignment operator (<<=), 6.5.16.2 -iswupper function, 7.29.2.1.2, 7.29.2.1.11, left-shift operator (<<), 6.2.6.2, 6.5.7 - 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 length -iswxdigit function, 7.29.2.1.12, 7.29.2.2.1 external name, 5.2.4.1, 6.4.2.1, 6.11.3 -isxdigit function, 7.4.1.12, 7.11.1.1 function name, 5.2.4.1, 6.4.2.1, 6.11.3 -italic type convention, 3, 6.1 identifier, 6.4.2.1 -iteration statements, 6.8.5 internal name, 5.2.4.1, 6.4.2.1 - length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1, -jmp_buf type, 7.13 7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1 -jump statements, 6.8.6 length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, - 7.28.2.2 -keywords, 6.4.1, G.2, J.5.9, J.5.10 less-than operator (<), 6.5.8 -kill_dependency macro, 5.1.2.4, 7.17.3.1 less-than-or-equal-to operator (<=), 6.5.8 -known constant size, 6.2.5 letter, 5.2.1, 7.4 - lexical elements, 5.1.1.2, 6.4 -L_tmpnam macro, 7.21.1, 7.21.4.4 lgamma functions, 7.12.8.3, F.10.5.3 -L_tmpnam_s macro, K.3.5, K.3.5.1.2 lgamma type-generic macro, 7.24 -label name, 6.2.1, 6.2.3 library, 5.1.1.1, 7, K.3 -labeled statement, 6.8.1 future directions, 7.30 -labs function, 7.22.6.1 summary, B -language, 6 terms, 7.1.1 - future directions, 6.11 use of functions, 7.1.4 - syntax summary, A lifetime, 6.2.4 -Latin alphabet, 5.2.1, 6.4.2.1 limits - -[page 666] - - environmental, see environmental limits 6.3.1.6, 6.3.1.7, 6.3.1.8 - implementation, see implementation limits long double _Imaginary type, G.2 - numerical, see numerical limits long double suffix, l or L, 6.4.4.2 - translation, see translation limits long double type, 6.2.5, 6.4.4.2, 6.7.2, -limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2 -line buffered stream, 7.21.3 long double type conversion, 6.3.1.4, 6.3.1.5, -line number, 6.10.4, 6.10.8.1 6.3.1.7, 6.3.1.8 -line preprocessing directive, 6.10.4 long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, -lines, 5.1.1.2, 7.21.2 7.21.6.2, 7.28.2.1, 7.28.2.2 - preprocessing directive, 6.10 long int type conversion, 6.3.1.1, 6.3.1.3, -linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2, 6.3.1.4, 6.3.1.8 - 6.11.2 long integer suffix, l or L, 6.4.4.1 -llabs function, 7.22.6.1 long long int type, 6.2.5, 6.3.1.1, 6.7.2, -lldiv function, 7.22.6.2 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2 -lldiv_t type, 7.22 long long int type conversion, 6.3.1.1, -LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.3.1.3, 6.3.1.4, 6.3.1.8 - 7.28.4.1.2 long long integer suffix, ll or LL, 6.4.4.1 -LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4, LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 - 7.28.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 -llrint functions, 7.12.9.5, F.3, F.10.6.5 longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4, -llrint type-generic macro, 7.24 7.22.4.7 -llround functions, 7.12.9.7, F.10.6.7 loop body, 6.8.5 -llround type-generic macro, 7.24 low-order bit, 3.6 -local time, 7.26.1 lowercase letter, 5.2.1 -locale, 3.4.2 lrint functions, 7.12.9.5, F.3, F.10.6.5 -locale-specific behavior, 3.4.2, J.4 lrint type-generic macro, 7.24 -locale.h header, 7.11, 7.30.5 lround functions, 7.12.9.7, F.10.6.7 -localeconv function, 7.11.1.1, 7.11.2.1 lround type-generic macro, 7.24 -localization, 7.11 lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16, -localtime function, 7.26.3.4 6.7.2.4 -localtime_s function, K.3.8.2.4 lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1, -log functions, 7.12.6.7, F.10.3.7 6.5.16.2 -log type-generic macro, 7.24 -log10 functions, 7.12.6.8, F.10.3.8 macro argument substitution, 6.10.3.1 -log10 type-generic macro, 7.24 macro definition -log1p functions, 7.12.6.9, F.10.3.9 library function, 7.1.4 -log1p type-generic macro, 7.24 macro invocation, 6.10.3 -log2 functions, 7.12.6.10, F.10.3.10 macro name, 6.10.3 -log2 type-generic macro, 7.24 length, 5.2.4.1 -logarithmic functions predefined, 6.10.8, 6.11.9 - complex, 7.3.7, G.6.3 redefinition, 6.10.3 - real, 7.12.6, F.10.3 scope, 6.10.3.5 -logb functions, 7.12.6.11, F.3, F.10.3.11 macro parameter, 6.10.3 -logb type-generic macro, 7.24 macro preprocessor, 6.10 -logical operators macro replacement, 6.10.3 - AND (&&), 5.1.2.4, 6.5.13 magnitude, complex, 7.3.8.1 - negation (!), 6.5.3.3 main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4, - OR (||), 5.1.2.4, 6.5.14 7.21.3 -logical source lines, 5.1.1.2 malloc function, 7.22.3, 7.22.3.4, 7.22.3.5 -long double _Complex type, 6.2.5 manipulation functions -long double _Complex type conversion, complex, 7.3.9 - -[page 667] - - real, 7.12.11, F.10.8 modf functions, 7.12.6.12, F.10.3.12 -matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, modifiable lvalue, 6.3.2.1 - K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modification order, 5.1.2.4 -math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, modulus functions, 7.12.6.12 - F.10, J.5.17 modulus, complex, 7.3.8.1 -MATH_ERREXCEPT macro, 7.12, F.10 mtx_destroy function, 7.25.4.1 -math_errhandling macro, 7.1.3, 7.12, F.10 mtx_init function, 7.25.1, 7.25.4.2 -MATH_ERRNO macro, 7.12 mtx_lock function, 7.25.4.3 -max_align_t type, 7.19 mtx_t type, 7.25.1 -maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.25.4.4 -MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.25.4.5 - 7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3, mtx_unlock function, 7.25.4.3, 7.25.4.4, - K.3.6.4.1, K.3.9.3.1.1 7.25.4.5, 7.25.4.6 -MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22 multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4 -mblen function, 7.22.7.1, 7.28.6.3 multibyte conversion functions -mbrlen function, 7.28.6.3.1 wide character, 7.22.7, K.3.6.4 -mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1 extended, 7.28.6, K.3.9.3 -mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 -mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2, wide string, 7.22.8, K.3.6.5 - 7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2, restartable, 7.28.6.4, K.3.9.3.2 - 7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1 multibyte string, 7.1.1 -mbsinit function, 7.28.6.2.1 multibyte/wide character conversion functions, -mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2 7.22.7, K.3.6.4 -mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1 extended, 7.28.6, K.3.9.3 -mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1, restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 - 7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1, multibyte/wide string conversion functions, - 7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3, 7.22.8, K.3.6.5 - 7.28.6.3.1, 7.28.6.4 restartable, 7.28.6.4, K.3.9.3.2 -mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4 multidimensional array, 6.5.2.1 -mbstowcs_s function, K.3.6.5.1 multiplication assignment operator (*=), 6.5.16.2 -mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2, multiplication operator (*), 6.2.6.2, 6.5.5, F.3, - 7.22.8.1, 7.28.6.3 G.5.1 -member access operators (. and ->), 6.5.2.3 multiplicative expressions, 6.5.5, G.5.1 -member alignment, 6.7.2.1 -memchr function, 7.23.5.1 n-char sequence, 7.22.1.3 -memcmp function, 7.23.4, 7.23.4.1 n-wchar sequence, 7.28.4.1.1 -memcpy function, 7.23.2.1 name -memcpy_s function, K.3.7.1.1 external, 5.2.4.1, 6.4.2.1, 6.11.3 -memmove function, 7.23.2.2 file, 7.21.3 -memmove_s function, K.3.7.1.2 internal, 5.2.4.1, 6.4.2.1 -memory location, 3.14 label, 6.2.3 -memory management functions, 7.22.3 structure/union member, 6.2.3 -memory_order type, 7.17.1, 7.17.3 name spaces, 6.2.3 -memset function, 7.23.6.1, K.3.7.4.1 named label, 6.8.1 -memset_s function, K.3.7.4.1 NaN, 5.2.4.2.2 -minimum functions, 7.12.12, F.10.9 nan functions, 7.12.11.2, F.2.1, F.10.8.2 -minus operator, unary, 6.5.3.3 NAN macro, 7.12, F.2.1 -miscellaneous functions NDEBUG macro, 7.2 - string, 7.23.6, K.3.7.4 nearbyint functions, 7.12.9.3, 7.12.9.4, F.3, - wide string, 7.28.4.6, K.3.9.2.4 F.10.6.3 -mktime function, 7.26.2.3 nearbyint type-generic macro, 7.24 - -[page 668] - -nearest integer functions, 7.12.9, F.10.6 operating system, 5.1.2.1, 7.22.4.8 -negation operator (!), 6.5.3.3 operations on files, 7.21.4, K.3.5.1 -negative zero, 6.2.6.2, 7.12.11.1 operator, 6.4.6 -new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operators, 6.5 -new-line escape sequence (\n), 5.2.2, 6.4.4.4, additive, 6.2.6.2, 6.5.6 - 7.4.1.10 alignof, 6.5.3.4 -nextafter functions, 7.12.11.3, 7.12.11.4, F.3, assignment, 6.5.16 - F.10.8.3 associativity, 6.5 -nextafter type-generic macro, 7.24 equality, 6.5.9 -nexttoward functions, 7.12.11.4, F.3, F.10.8.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1 -nexttoward type-generic macro, 7.24 postfix, 6.5.2 -no linkage, 6.2.2 precedence, 6.5 -no-return function, 6.7.4 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9 -non-stop floating-point control mode, 7.6.4.2 relational, 6.5.8 -nongraphic characters, 5.2.2, 6.4.4.4 shift, 6.5.7 -nonlocal jumps header, 7.13 sizeof, 6.5.3.4 -norm, complex, 7.3.8.1 unary, 6.5.3 -normalized broken-down time, K.3.8.1, K.3.8.2.1 unary arithmetic, 6.5.3.3 -not macro, 7.9 optional features, see conditional features -not-equal-to operator, see inequality operator or macro, 7.9 -not_eq macro, 7.9 OR operators -null character (\0), 5.2.1, 6.4.4.4, 6.4.5 bitwise exclusive (^), 6.2.6.2, 6.5.11 - padding of binary stream, 7.21.2 bitwise exclusive assignment (^=), 6.5.16.2 -NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1, bitwise inclusive (|), 6.2.6.2, 6.5.12 - 7.26.1, 7.28.1 bitwise inclusive assignment (|=), 6.5.16.2 -null pointer, 6.3.2.3 logical (||), 5.1.2.4, 6.5.14 -null pointer constant, 6.3.2.3 or_eq macro, 7.9 -null preprocessing directive, 6.10.7 order of allocated storage, 7.22.3 -null statement, 6.8.3 order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3, -null wide character, 7.1.1 see also sequence points -number classification macros, 7.12, 7.12.3.1 ordinary identifier name space, 6.2.3 -numeric conversion functions, 7.8.2.3, 7.22.1 orientation of stream, 7.21.2, 7.28.3.5 - wide string, 7.8.2.4, 7.28.4.1 out-of-bounds store, L.2.1 -numerical limits, 5.2.4.2 outer scope, 6.2.1 - over-aligned, 6.2.8 -object, 3.15 -object representation, 6.2.6.1 padding -object type, 6.2.5 binary stream, 7.21.2 -object-like macro, 6.10.3 bits, 6.2.6.2, 7.20.1.1 -observable behavior, 5.1.2.3 structure/union, 6.2.6.1, 6.7.2.1 -obsolescence, 6.11, 7.30 parameter, 3.16 -octal constant, 6.4.4.1 array, 6.9.1 -octal digit, 6.4.4.1, 6.4.4.4 ellipsis, 6.7.6.3, 6.10.3 -octal-character escape sequence (\octal digits), function, 6.5.2.2, 6.7, 6.9.1 - 6.4.4.4 macro, 6.10.3 -offsetof macro, 7.19 main function, 5.1.2.2.1 -on-off switch, 6.10.6 program, 5.1.2.2.1 -once_flag type, 7.25.1 parameter type list, 6.7.6.3 -ONCE_FLAG_INIT macro, 7.25.1 parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5 -ones' complement, 6.2.6.2 parenthesized expression, 6.5.1 -operand, 6.4.6, 6.5 parse state, 7.21.2 - -[page 669] - -perform a trap, 3.19.5 preprocessor, 6.10 -permitted form of initializer, 6.6 PRIcFASTN macros, 7.8.1 -perror function, 7.21.10.4 PRIcLEASTN macros, 7.8.1 -phase angle, complex, 7.3.9.1 PRIcMAX macros, 7.8.1 -physical source lines, 5.1.1.2 PRIcN macros, 7.8.1 -placemarker, 6.10.3.3 PRIcPTR macros, 7.8.1 -plus operator, unary, 6.5.3.3 primary expression, 6.5.1 -pointer arithmetic, 6.5.6 printf function, 7.21.1, 7.21.6.3, 7.21.6.10, -pointer comparison, 6.5.8 K.3.5.3.3 -pointer declarator, 6.7.6.1 printf_s function, K.3.5.3.3 -pointer operator (->), 6.5.2.3 printing character, 5.2.2, 7.4, 7.4.1.8 -pointer to function, 6.5.2.2 printing wide character, 7.29.2 -pointer type, 6.2.5 program diagnostics, 7.2.1 -pointer type conversion, 6.3.2.1, 6.3.2.3 program execution, 5.1.2.2.2, 5.1.2.3 -pointer, null, 6.3.2.3 program file, 5.1.1.1 -pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, program image, 5.1.1.2 - 7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4, program name (argv[0]), 5.1.2.2.1 - 7.12.8.3, 7.12.8.4 program parameters, 5.1.2.2.1 -portability, 4, J program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1 -position indicator, file, see file position indicator program structure, 5.1.1.1 -positive difference, 7.12.12.1 program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3, -positive difference functions, 7.12.12, F.10.9 5.1.2.3 -postfix decrement operator (--), 6.3.2.1, 6.5.2.4 program, conforming, 4 -postfix expressions, 6.5.2 program, strictly conforming, 4 -postfix increment operator (++), 6.3.2.1, 6.5.2.4 promotions -pow functions, 7.12.7.4, F.10.4.4 default argument, 6.5.2.2 -pow type-generic macro, 7.24 integer, 5.1.2.3, 6.3.1.1 -power functions prototype, see function prototype - complex, 7.3.8, G.6.4 pseudo-random sequence functions, 7.22.2 - real, 7.12.7, F.10.4 PTRDIFF_MAX macro, 7.20.3 -pp-number, 6.4.8 PTRDIFF_MIN macro, 7.20.3 -pragma operator, 6.10.9 ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1, -pragma preprocessing directive, 6.10.6, 6.11.8 7.21.6.2, 7.28.2.1, 7.28.2.2 -precedence of operators, 6.5 punctuators, 6.4.6 -precedence of syntax rules, 5.1.1.2 putc function, 7.21.1, 7.21.7.7, 7.21.7.8 -precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1 putchar function, 7.21.1, 7.21.7.8 - excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 puts function, 7.21.1, 7.21.7.9 -predefined macro names, 6.10.8, 6.11.9 putwc function, 7.21.1, 7.28.3.8, 7.28.3.9 -prefix decrement operator (--), 6.3.2.1, 6.5.3.1 putwchar function, 7.21.1, 7.28.3.9 -prefix increment operator (++), 6.3.2.1, 6.5.3.1 -preprocessing concatenation, 6.10.3.3 qsort function, 7.22.5, 7.22.5.2 -preprocessing directives, 5.1.1.2, 6.10 qsort_s function, K.3.6.3, K.3.6.3.2 -preprocessing file, 5.1.1.1, 6.10 qualified types, 6.2.5 -preprocessing numbers, 6.4, 6.4.8 qualified version of type, 6.2.5 -preprocessing operators question-mark escape sequence (\?), 6.4.4.4 - #, 6.10.3.2 quick_exit function, 7.22.4.3, 7.22.4.4, - ##, 6.10.3.3 7.22.4.7 - _Pragma, 5.1.1.2, 6.10.9 quiet NaN, 5.2.4.2.2 - defined, 6.10.1 -preprocessing tokens, 5.1.1.2, 6.4, 6.10 raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1 -preprocessing translation unit, 5.1.1.1 rand function, 7.22, 7.22.2.1, 7.22.2.2 - -[page 670] - -RAND_MAX macro, 7.22, 7.22.2.1 restrict-qualified type, 6.2.5, 6.7.3 -range return statement, 6.8.6.4, F.6 - excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5, -range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1, 7.28.3.10 - 7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, right-shift assignment operator (>>=), 6.5.16.2 - 7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2, right-shift operator (>>), 6.2.6.2, 6.5.7 - 7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7, rint functions, 7.12.9.4, F.3, F.10.6.4 - 7.12.11.3, 7.12.12.1, 7.12.13.1 rint type-generic macro, 7.24 -rank, see integer conversion rank round functions, 7.12.9.6, F.10.6.6 -read-modify-write operations, 5.1.2.4 round type-generic macro, 7.24 -real floating type conversion, 6.3.1.4, 6.3.1.5, rounding mode, floating point, 5.2.4.2.2 - 6.3.1.7, F.3, F.4 RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2, -real floating types, 6.2.5 K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13, -real type domain, 6.2.5 K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2, -real types, 6.2.5 K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1, -real-floating, 7.12.3 K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1, -realloc function, 7.22.3, 7.22.3.5 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2, -recommended practice, 3.17 K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4, -recursion, 6.5.2.2 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2, -recursive function call, 6.5.2.2 K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1, -redefinition of macro, 6.10.3 K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1, -reentrancy, 5.1.2.3, 5.2.3 K.3.9.3.2.1, K.3.9.3.2.2 - library functions, 7.1.4 rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2, -referenced type, 6.2.5 K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 -register storage-class specifier, 6.7.1, 6.9 runtime-constraint, 3.18 -relational expressions, 6.5.8 Runtime-constraint handling functions, K.3.6.1 -relaxed atomic operations, 5.1.2.4 rvalue, 6.3.2.1 -release fence, 7.17.4 -release operation, 5.1.2.4 same scope, 6.2.1 -release sequence, 5.1.2.4 save calling environment function, 7.13.1 -reliability of data, interrupted, 5.1.2.3 scalar types, 6.2.5 -remainder assignment operator (%=), 6.5.16.2 scalbln function, 7.12.6.13, F.3, F.10.3.13 -remainder functions, 7.12.10, F.10.7 scalbln type-generic macro, 7.24 -remainder functions, 7.12.10.2, 7.12.10.3, F.3, scalbn function, 7.12.6.13, F.3, F.10.3.13 - F.10.7.2 scalbn type-generic macro, 7.24 -remainder operator (%), 6.2.6.2, 6.5.5 scanf function, 7.21.1, 7.21.6.4, 7.21.6.11 -remainder type-generic macro, 7.24 scanf_s function, K.3.5.3.4, K.3.5.3.11 -remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2 scanlist, 7.21.6.2, 7.28.2.2 -remquo functions, 7.12.10.3, F.3, F.10.7.3 scanset, 7.21.6.2, 7.28.2.2 -remquo type-generic macro, 7.24 SCHAR_MAX macro, 5.2.4.2.1 -rename function, 7.21.4.2 SCHAR_MIN macro, 5.2.4.2.1 -representations of types, 6.2.6 SCNcFASTN macros, 7.8.1 - pointer, 6.2.5 SCNcLEASTN macros, 7.8.1 -rescanning and replacement, 6.10.3.4 SCNcMAX macros, 7.8.1 -reserved identifiers, 6.4.1, 7.1.3, K.3.1.2 SCNcN macros, 7.8.1 -restartable multibyte/wide character conversion SCNcPTR macros, 7.8.1 - functions, 7.27.1, 7.28.6.3, K.3.9.3.1 scope of identifier, 6.2.1, 6.9.2 -restartable multibyte/wide string conversion search functions - functions, 7.28.6.4, K.3.9.3.2 string, 7.23.5, K.3.7.3 -restore calling environment function, 7.13.2 utility, 7.22.5, K.3.6.3 -restrict type qualifier, 6.7.3, 6.7.3.1 wide string, 7.28.4.5, K.3.9.2.3 - -[page 671] - -SEEK_CUR macro, 7.21.1, 7.21.9.2 sign and magnitude, 6.2.6.2 -SEEK_END macro, 7.21.1, 7.21.9.2 sign bit, 6.2.6.2 -SEEK_SET macro, 7.21.1, 7.21.9.2 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7 -selection statements, 6.8.4 signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1 -self-referential structure, 6.7.2.3 signal handling functions, 7.14.1 -semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, signal.h header, 7.14, 7.30.6 - 6.8.5, 6.8.6 signaling NaN, 5.2.4.2.2, F.2.1 -separate compilation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1 -separate translation, 5.1.1.1 signbit macro, 7.12.3.6, F.3 -sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2, - 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, 7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2 - 7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3 signed character, 6.3.1.1 -sequenced after, see sequenced before signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1 -sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, - 6.5.16, see also indeterminately sequenced, 6.3.1.8 - unsequenced signed types, 6.2.5, 6.7.2 -sequencing of statements, 6.8 significand part, 6.4.4.2 -set_constraint_handler_s function, SIGSEGV macro, 7.14, 7.14.1.1 - K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3 SIGTERM macro, 7.14 -setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5 simple assignment operator (=), 6.5.16.1 -setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1 sin functions, 7.12.4.6, F.10.1.6 -setjmp.h header, 7.13 sin type-generic macro, 7.24, G.7 -setlocale function, 7.11.1.1, 7.11.2.1 single-byte character, 3.7.1, 5.2.1.2 -setvbuf function, 7.21.1, 7.21.3, 7.21.5.1, single-byte/wide character conversion functions, - 7.21.5.5, 7.21.5.6 7.28.6.1 -shall, 4 single-precision arithmetic, 5.1.2.3 -shift expressions, 6.5.7 single-quote escape sequence (\'), 6.4.4.4, 6.4.5 -shift sequence, 7.1.1 singularity, 7.12.1 -shift states, 5.2.1.2 sinh functions, 7.12.5.5, F.10.2.5 -short identifier, character, 5.2.4.1, 6.4.3 sinh type-generic macro, 7.24, G.7 -short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, SIZE_MAX macro, 7.20.3 - 7.21.6.2, 7.28.2.1, 7.28.2.2 size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1, -short int type conversion, 6.3.1.1, 6.3.1.3, 7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27, - 6.3.1.4, 6.3.1.8 7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4, -SHRT_MAX macro, 5.2.4.2.1 K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 -SHRT_MIN macro, 5.2.4.2.1 sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4 -side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4, snprintf function, 7.21.6.5, 7.21.6.12, - 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5, K.3.5.3.5 - 7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1, snprintf_s function, K.3.5.3.5, K.3.5.3.6 - F.9.3 snwprintf_s function, K.3.9.1.3, K.3.9.1.4 -SIG_ATOMIC_MAX macro, 7.20.3 sorting utility functions, 7.22.5, K.3.6.3 -SIG_ATOMIC_MIN macro, 7.20.3 source character set, 5.1.1.2, 5.2.1 -sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1, source file, 5.1.1.1 - 7.20.3 name, 6.10.4, 6.10.8.1 -SIG_DFL macro, 7.14, 7.14.1.1 source file inclusion, 6.10.2 -SIG_ERR macro, 7.14, 7.14.1.1 source lines, 5.1.1.2 -SIG_IGN macro, 7.14, 7.14.1.1 source text, 5.1.1.2 -SIGABRT macro, 7.14, 7.22.4.1 space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, -SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17 7.4.1.10, 7.29.2.1.3 -SIGILL macro, 7.14, 7.14.1.1 sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6 -SIGINT macro, 7.14 sprintf_s function, K.3.5.3.5, K.3.5.3.6 - -[page 672] - -sqrt functions, 7.12.7.5, F.3, F.10.4.5 do, 6.8.5.2 -sqrt type-generic macro, 7.24 else, 6.8.4.1 -srand function, 7.22.2.2 expression, 6.8.3 -sscanf function, 7.21.6.7, 7.21.6.14 for, 6.8.5.3 -sscanf_s function, K.3.5.3.7, K.3.5.3.14 goto, 6.8.6.1 -standard error stream, 7.21.1, 7.21.3, 7.21.10.4 if, 6.8.4.1 -standard headers, 4, 7.1.2 iteration, 6.8.5 - , 7.2 jump, 6.8.6 - , 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, labeled, 6.8.1 - 7.24, 7.30.1, G.6, J.5.17 null, 6.8.3 - , 7.4, 7.30.2 return, 6.8.6.4, F.6 - , 7.5, 7.30.3, K.3.2 selection, 6.8.4 - , 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H sequencing, 6.8 - , 4, 5.2.4.2.2, 7.7, 7.22.1.3, switch, 6.8.4.2 - 7.28.4.1.1 while, 6.8.5.1 - , 7.8, 7.30.4 static assertions, 6.7.10 - , 4, 7.9 static storage duration, 6.2.4 - , 4, 5.2.4.2.1, 6.2.5, 7.10 static storage-class specifier, 6.2.2, 6.2.4, 6.7.1 - , 7.11, 7.30.5 static, in array declarators, 6.7.6.2, 6.7.6.3 - , 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10, static_assert declaration, 6.7.10 - J.5.17 static_assert macro, 7.2 - , 7.13 stdalign.h header, 4, 7.15 - , 7.14, 7.30.6 stdarg.h header, 4, 6.7.6.3, 7.16 - , 4, 7.15 stdatomic.h header, 6.10.8.3, 7.1.2, 7.17 - , 4, 6.7.6.3, 7.16 stdbool.h header, 4, 7.18, 7.30.7, H - , 6.10.8.3, 7.1.2, 7.17 STDC, 6.10.6, 6.11.8 - , 4, 7.18, 7.30.7, H stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, - , 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 - 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 stderr macro, 7.21.1, 7.21.2, 7.21.3 - , 4, 5.2.4.2, 6.10.1, 7.8, 7.20, stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4, - 7.30.8, K.3.3, K.3.4 7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4, - , 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 K.3.5.4.1, K.3.9.1.14 - , 5.2.4.2.2, 7.22, 7.30.10, F, stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, - K.3.1.4, K.3.6 7.30.8, K.3.3, K.3.4 - , 7.23, 7.30.11, K.3.7 stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 - , 7.24, G.7 stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F, - , 6.10.8.3, 7.1.2, 7.25 K.3.1.4, K.3.6 - , 7.26, K.3.8 stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3, - , 6.4.4.4, 6.4.5, 7.27 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9 - , 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, storage duration, 6.2.4 - F, K.3.9 storage order of array, 6.5.2.1 - , 7.29, 7.30.13 storage unit (bit-field), 6.2.6.1, 6.7.2.1 -standard input stream, 7.21.1, 7.21.3 storage-class specifiers, 6.7.1, 6.11.5 -standard integer types, 6.2.5 strcat function, 7.23.3.1 -standard output stream, 7.21.1, 7.21.3 strcat_s function, K.3.7.2.1 -standard signed integer types, 6.2.5 strchr function, 7.23.5.2 -state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4 strcmp function, 7.23.4, 7.23.4.2 -statements, 6.8 strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5 - break, 6.8.6.3 strcpy function, 7.23.2.3 - compound, 6.8.2 strcpy_s function, K.3.7.1.3 - continue, 6.8.6.2 strcspn function, 7.23.5.3 - -[page 673] - -streams, 7.21.2, 7.22.4.4 7.22.1.4, 7.28.2.2 - fully buffered, 7.21.3 strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4 - line buffered, 7.21.3 strtoumax function, 7.8.2.3 - orientation, 7.21.2 struct hack, see flexible array member - standard error, 7.21.1, 7.21.3 struct lconv, 7.11 - standard input, 7.21.1, 7.21.3 struct tm, 7.26.1 - standard output, 7.21.1, 7.21.3 structure - unbuffered, 7.21.3 arrow operator (->), 6.5.2.3 -strerror function, 7.21.10.4, 7.23.6.2 content, 6.7.2.3 -strerror_s function, K.3.7.4.2, K.3.7.4.3 dot operator (.), 6.5.2.3 -strerrorlen_s function, K.3.7.4.3 initialization, 6.7.9 -strftime function, 7.11.1.1, 7.26.3, 7.26.3.5, member alignment, 6.7.2.1 - 7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2 member name space, 6.2.3 -stricter, 6.2.8 member operator (.), 6.3.2.1, 6.5.2.3 -strictly conforming program, 4 pointer operator (->), 6.5.2.3 -string, 7.1.1 specifier, 6.7.2.1 - comparison functions, 7.23.4 tag, 6.2.3, 6.7.2.3 - concatenation functions, 7.23.3, K.3.7.2 type, 6.2.5, 6.7.2.1 - conversion functions, 7.11.1.1 strxfrm function, 7.11.1.1, 7.23.4.5 - copying functions, 7.23.2, K.3.7.1 subnormal floating-point numbers, 5.2.4.2.2 - library function conventions, 7.23.1 subscripting, 6.5.2.1 - literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9 subtraction assignment operator (-=), 6.5.16.2 - miscellaneous functions, 7.23.6, K.3.7.4 subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2 - numeric conversion functions, 7.8.2.3, 7.22.1 suffix - search functions, 7.23.5, K.3.7.3 floating constant, 6.4.4.2 -string handling header, 7.23, K.3.7 integer constant, 6.4.4.1 -string.h header, 7.23, 7.30.11, K.3.7 switch body, 6.8.4.2 -stringizing, 6.10.3.2, 6.10.9 switch case label, 6.8.1, 6.8.4.2 -strlen function, 7.23.6.3 switch default label, 6.8.1, 6.8.4.2 -strncat function, 7.23.3.2 switch statement, 6.8.1, 6.8.4.2 -strncat_s function, K.3.7.2.2 swprintf function, 7.28.2.3, 7.28.2.7, -strncmp function, 7.23.4, 7.23.4.4 K.3.9.1.3, K.3.9.1.4 -strncpy function, 7.23.2.4 swprintf_s function, K.3.9.1.3, K.3.9.1.4 -strncpy_s function, K.3.7.1.4 swscanf function, 7.28.2.4, 7.28.2.8 -strnlen_s function, K.3.7.4.4 swscanf_s function, K.3.9.1.5, K.3.9.1.10 -stronger, 6.2.8 symbols, 3 -strpbrk function, 7.23.5.4 synchronization operation, 5.1.2.4 -strrchr function, 7.23.5.5 synchronize with, 5.1.2.4 -strspn function, 7.23.5.6 syntactic categories, 6.1 -strstr function, 7.23.5.7 syntax notation, 6.1 -strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3, syntax rule precedence, 5.1.1.2 - 7.28.2.2, F.3 syntax summary, language, A -strtof function, 7.12.11.2, 7.22.1.3, F.3 system function, 7.22.4.8 -strtoimax function, 7.8.2.3 -strtok function, 7.23.5.8 tab characters, 5.2.1, 6.4 -strtok_s function, K.3.7.3.1 tag compatibility, 6.2.7 -strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tag name space, 6.2.3 - 7.22.1.4, 7.28.2.2 tags, 6.7.2.3 -strtold function, 7.12.11.2, 7.22.1.3, F.3 tan functions, 7.12.4.7, F.10.1.7 -strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4 tan type-generic macro, 7.24, G.7 -strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tanh functions, 7.12.5.6, F.10.2.6 - -[page 674] - -tanh type-generic macro, 7.24, G.7 toupper function, 7.4.2.2 -temporary lifetime, 6.2.4 towctrans function, 7.29.3.2.1, 7.29.3.2.2 -tentative definition, 6.9.2 towlower function, 7.29.3.1.1, 7.29.3.2.1 -terms, 3 towupper function, 7.29.3.1.2, 7.29.3.2.1 -text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 translation environment, 5, 5.1.1 -tgamma functions, 7.12.8.4, F.10.5.4 translation limits, 5.2.4.1 -tgamma type-generic macro, 7.24 translation phases, 5.1.1.2 -tgmath.h header, 7.24, G.7 translation unit, 5.1.1.1, 6.9 -thrd_create function, 7.25.1, 7.25.5.1 trap, see perform a trap -thrd_current function, 7.25.5.2 trap representation, 3.19.4, 6.2.6.1, 6.2.6.2, -thrd_detach function, 7.25.5.3 6.3.2.3, 6.5.2.3 -thrd_equal function, 7.25.5.4 trigonometric functions -thrd_exit function, 7.25.5.5 complex, 7.3.5, G.6.1 -thrd_join function, 7.25.5.6 real, 7.12.4, F.10.1 -thrd_sleep function, 7.25.5.7 trigraph sequences, 5.1.1.2, 5.2.1.1 -thrd_start_t type, 7.25.1 true macro, 7.18 -thrd_t type, 7.25.1 trunc functions, 7.12.9.8, F.10.6.8 -thrd_yield function, 7.25.5.8 trunc type-generic macro, 7.24 -thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6 truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3 -thread storage duration, 6.2.4, 7.6 truncation toward zero, 6.5.5 -threads header, 7.25 tss_create function, 7.25.6.1 -threads.h header, 6.10.8.3, 7.1.2, 7.25 tss_delete function, 7.25.6.2 -time TSS_DTOR_ITERATIONS macro, 7.25.1 - broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1, tss_dtor_t type, 7.25.1 - 7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1, tss_get function, 7.25.6.3 - K.3.8.2.3, K.3.8.2.4 tss_set function, 7.25.6.4 - calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, tss_t type, 7.25.1 - 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, two's complement, 6.2.6.2, 7.20.1.1 - K.3.8.2.3, K.3.8.2.4 type category, 6.2.5 - components, 7.26.1, K.3.8.1 type conversion, 6.3 - conversion functions, 7.26.3, K.3.8.2 type definitions, 6.7.8 - wide character, 7.28.5 type domain, 6.2.5, G.2 - local, 7.26.1 type names, 6.7.7 - manipulation functions, 7.26.2 type punning, 6.5.2.3 - normalized broken down, K.3.8.1, K.3.8.2.1 type qualifiers, 6.7.3 -time function, 7.26.2.4 type specifiers, 6.7.2 -time.h header, 7.26, K.3.8 type-generic macro, 7.24, G.7 -time_t type, 7.26.1 typedef declaration, 6.7.8 -TIME_UTC macro, 7.25.7.1 typedef storage-class specifier, 6.7.1, 6.7.8 -tm structure type, 7.26.1, 7.28.1, K.3.8.1 types, 6.2.5 -TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4 atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3, -TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6 -tmpfile function, 7.21.4.3, 7.22.4.4 character, 6.7.9 -tmpfile_s function, K.3.5.1.1, K.3.5.1.2 compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6 -tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4, complex, 6.2.5, G - K.3.5.1.2 composite, 6.2.7 -tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2 const qualified, 6.7.3 -token, 5.1.1.2, 6.4, see also preprocessing tokens conversions, 6.3 -token concatenation, 6.10.3.3 imaginary, G -token pasting, 6.10.3.3 restrict qualified, 6.7.3 -tolower function, 7.4.2.1 volatile qualified, 6.7.3 - -[page 675] - -uchar.h header, 6.4.4.4, 6.4.5, 7.27 universal character name, 6.4.3 -UCHAR_MAX macro, 5.2.4.2.1 unnormalized floating-point numbers, 5.2.4.2.2 -UINT_FASTN_MAX macros, 7.20.2.3 unqualified type, 6.2.5 -uint_fastN_t types, 7.20.1.3 unqualified version of type, 6.2.5 -uint_least16_t type, 7.27 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also -uint_least32_t type, 7.27 indeterminately sequenced, sequenced -UINT_LEASTN_MAX macros, 7.20.2.2 before -uint_leastN_t types, 7.20.1.2 unsigned char type, K.3.5.3.2, K.3.9.1.2 -UINT_MAX macro, 5.2.4.2.1 unsigned integer suffix, u or U, 6.4.4.1 -UINTMAX_C macro, 7.20.4.2 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1 -UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 unsigned type conversion, 6.3.1.1, 6.3.1.3, -uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, 6.3.1.4, 6.3.1.8 - 7.28.2.1, 7.28.2.2 unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2, -UINTN_C macros, 7.20.4.1 7.28.2.1, 7.28.2.2 -UINTN_MAX macros, 7.20.2.1 unspecified behavior, 3.4.4, 4, J.1 -uintN_t types, 7.20.1.1 unspecified value, 3.19.3 -UINTPTR_MAX macro, 7.20.2.4 uppercase letter, 5.2.1 -uintptr_t type, 7.20.1.4 use of library functions, 7.1.4 -ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, USHRT_MAX macro, 5.2.4.2.1 - 7.28.4.1.2 usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6, -ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15 - 7.28.4.1.2 UTF-16, 6.10.8.2 -unary arithmetic operators, 6.5.3.3 UTF-32, 6.10.8.2 -unary expression, 6.5.3 UTF-8 string literal, see string literal -unary minus operator (-), 6.5.3.3, F.3 utilities, general, 7.22, K.3.6 -unary operators, 6.5.3 wide string, 7.28.4, K.3.9.2 -unary plus operator (+), 6.5.3.3 -unbuffered stream, 7.21.3 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2, -undef preprocessing directive, 6.10.3.5, 7.1.3, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, - 7.1.4 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, -undefined behavior, 3.4.3, 4, J.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, -underscore character, 6.4.2.1 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, -underscore, leading, in identifier, 7.1.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 -ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2, va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1, - 7.21.9.3 7.16.1.2, 7.16.1.3 -ungetwc function, 7.21.1, 7.28.3.10 va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3, -Unicode, 7.27, see also char16_t type, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, - char32_t type, wchar_t type 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, -Unicode required set, 6.10.8.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, -union 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, - arrow operator (->), 6.5.2.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 - content, 6.7.2.3 va_list type, 7.16, 7.16.1.3 - dot operator (.), 6.5.2.3 va_start macro, 7.16, 7.16.1, 7.16.1.1, - initialization, 6.7.9 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8, - member alignment, 6.7.2.1 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, - member name space, 6.2.3 7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6, - member operator (.), 6.3.2.1, 6.5.2.3 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10, - pointer operator (->), 6.5.2.3 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7, - specifier, 6.7.2.1 K.3.9.1.10, K.3.9.1.12 - tag, 6.2.3, 6.7.2.3 value, 3.19 - type, 6.2.5, 6.7.2.1 value bits, 6.2.6.2 - -[page 676] - -variable arguments, 6.10.3, 7.16 vswscanf function, 7.28.2.8 -variable arguments header, 7.16 vswscanf_s function, K.3.9.1.10 -variable length array, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11 -variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf_s function, K.3.9.1.11 -vertical-tab character, 5.2.1, 6.4 vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10 -vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, vwscanf_s function, K.3.9.1.12 - 7.4.1.10 -vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8 warnings, I -vfprintf_s function, K.3.5.3.8, K.3.5.3.9, wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, - K.3.5.3.11, K.3.5.3.14 F, K.3.9 -vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9 WCHAR_MAX macro, 7.20.3, 7.28.1 -vfscanf_s function, K.3.5.3.9, K.3.5.3.11, WCHAR_MIN macro, 7.20.3, 7.28.1 - K.3.5.3.14 wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19, -vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1, -vfwprintf_s function, K.3.9.1.6 7.28.2.1, 7.28.2.2 -vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10 wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2, -vfwscanf_s function, K.3.9.1.7 7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1, -visibility of identifier, 6.2.1 K.3.9.3.2.2 -visible sequence of side effects, 5.1.2.4 wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1 -visible side effect, 5.1.2.4 wcscat function, 7.28.4.3.1 -VLA, see variable length array wcscat_s function, K.3.9.2.2.1 -void expression, 6.3.2.2 wcschr function, 7.28.4.5.1 -void function parameter, 6.7.6.3 wcscmp function, 7.28.4.4.1, 7.28.4.4.4 -void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2, wcscoll function, 7.28.4.4.2, 7.28.4.4.4 - K.3.9.1.2 wcscpy function, 7.28.4.2.1 -void type conversion, 6.3.2.2 wcscpy_s function, K.3.9.2.1.1 -volatile storage, 5.1.2.3 wcscspn function, 7.28.4.5.2 -volatile type qualifier, 6.7.3 wcsftime function, 7.11.1.1, 7.28.5.1 -volatile-qualified type, 6.2.5, 6.7.3 wcslen function, 7.28.4.6.1 -vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10, wcsncat function, 7.28.4.3.2 - K.3.5.3.10 wcsncat_s function, K.3.9.2.2.2 -vprintf_s function, K.3.5.3.9, K.3.5.3.10, wcsncmp function, 7.28.4.4.3 - K.3.5.3.11, K.3.5.3.14 wcsncpy function, 7.28.4.2.2 -vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11 wcsncpy_s function, K.3.9.2.1.2 -vscanf_s function, K.3.5.3.9, K.3.5.3.11, wcsnlen_s function, K.3.9.2.4.1 - K.3.5.3.14 wcspbrk function, 7.28.4.5.3 -vsnprintf function, 7.21.6.8, 7.21.6.12, wcsrchr function, 7.28.4.5.4 - K.3.5.3.12 wcsrtombs function, 7.28.6.4.2, K.3.9.3.2 -vsnprintf_s function, K.3.5.3.9, K.3.5.3.11, wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2 - K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcsspn function, 7.28.4.5.5 -vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9 wcsstr function, 7.28.4.5.6 -vsprintf function, 7.21.6.8, 7.21.6.13, wcstod function, 7.21.6.2, 7.28.2.2 - K.3.5.3.13 wcstod function, 7.28.4.1.1 -vsprintf_s function, K.3.5.3.9, K.3.5.3.11, wcstof function, 7.28.4.1.1 - K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcstoimax function, 7.8.2.4 -vsscanf function, 7.21.6.8, 7.21.6.14 wcstok function, 7.28.4.5.7 -vsscanf_s function, K.3.5.3.9, K.3.5.3.11, wcstok_s function, K.3.9.2.3.1 - K.3.5.3.14 wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2, -vswprintf function, 7.28.2.7, K.3.9.1.8, 7.28.4.1.2 - K.3.9.1.9 wcstold function, 7.28.4.1.1 -vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.28.4.1.2 - -[page 677] - -wcstombs function, 7.22.8.2, 7.28.6.4 7.29.1 -wcstombs_s function, K.3.6.5.2 wmemchr function, 7.28.4.5.8 -wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2, wmemcmp function, 7.28.4.4.5 - 7.28.4.1.2 wmemcpy function, 7.28.4.2.3 -wcstoull function, 7.8.2.4, 7.28.4.1.2 wmemcpy_s function, K.3.9.2.1.3 -wcstoumax function, 7.8.2.4 wmemmove function, 7.28.4.2.4 -wcsxfrm function, 7.28.4.4.4 wmemmove_s function, K.3.9.2.1.4 -wctob function, 7.28.6.1.2, 7.29.2.1 wmemset function, 7.28.4.6.2 -wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3 wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11, -wctomb_s function, K.3.6.4.1 K.3.9.1.13 -wctrans function, 7.29.3.2.1, 7.29.3.2.2 wprintf_s function, K.3.9.1.13 -wctrans_t type, 7.29.1, 7.29.3.2.2 wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12, -wctype function, 7.29.2.2.1, 7.29.2.2.2 7.28.3.10 -wctype.h header, 7.29, 7.30.13 wscanf_s function, K.3.9.1.12, K.3.9.1.14 -wctype_t type, 7.29.1, 7.29.2.2.2 -weaker, 6.2.8 xor macro, 7.9 -WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6, xor_eq macro, 7.9 - 7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10, xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7, - 7.28.6.1.1, 7.29.1 7.25.7.1 -while statement, 6.8.5.1 xtime_get function, 7.25.7.1 -white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10, - 7.29.2.1.10 -white-space characters, 6.4 -wide character, 3.7.3 - case mapping functions, 7.29.3.1 - extensible, 7.29.3.2 - classification functions, 7.29.2.1 - extensible, 7.29.2.2 - constant, 6.4.4.4 - formatted input/output functions, 7.28.2, - K.3.9.1 - input functions, 7.21.1 - input/output functions, 7.21.1, 7.28.3 - output functions, 7.21.1 - single-byte conversion functions, 7.28.6.1 -wide string, 7.1.1 -wide string comparison functions, 7.28.4.4 -wide string concatenation functions, 7.28.4.3, - K.3.9.2.2 -wide string copying functions, 7.28.4.2, K.3.9.2.1 -wide string literal, see string literal -wide string miscellaneous functions, 7.28.4.6, - K.3.9.2.4 -wide string numeric conversion functions, 7.8.2.4, - 7.28.4.1 -wide string search functions, 7.28.4.5, K.3.9.2.3 -wide-oriented stream, 7.21.2 -width, 6.2.6.2 -WINT_MAX macro, 7.20.3 -WINT_MIN macro, 7.20.3 -wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1, - -[page 678] -- 2.20.1