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 '' ''.


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.

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.

Programming languages -- C

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.

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).

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.

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.

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

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

3.4

behavior
external appearance or action

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.

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.

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.

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.

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.

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.

3.7

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

3.7.1

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

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.

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

3.8

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

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

3.10

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

3.11

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

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

3.13

implementation limit
restriction imposed upon programs by the implementation

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.

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.

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

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

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.

3.19

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

3.19.1

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

3.19.2

indeterminate value
either an unspecified value or a trap representation

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.

3.19.4

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

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).

3.20

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

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

3.21

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

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

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.

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.

5.1 Conceptual models

5.1.1 Translation environment

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).

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.

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.

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).

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.

5.1.2.2 Hosted environment

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

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.

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).

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.

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.

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.

5.2 Environmental considerations

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).

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.

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:

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).

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.

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.

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).

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).

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.

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.

6. Language

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.

6.2 Concepts

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).

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.

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.

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.

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.

6.2.6 Representations of types

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.

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.

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.

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.

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).

6.3.1 Arithmetic operands

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.

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.

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.

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).

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.

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.

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.

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.

6.3.2 Other operands

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.

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.)

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.

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.

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.

6.4.2 Identifiers

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.

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.

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.

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.

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.

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).

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).

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).

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.

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.

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.

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.

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.

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.

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.

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)

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
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).

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.

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.

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.
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.

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
                 & * + - ~             !
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).

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.

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).

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).

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.

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''.

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.

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.

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''.

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.

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).

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).

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).

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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).

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''.
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).

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.

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.

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];
          }

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.

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).

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).

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).

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.

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.

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.

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.

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.

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.

6.8.5.1 The while statement

The evaluation of the controlling expression takes place before each execution of the loop body.

6.8.5.2 The do statement

The evaluation of the controlling expression takes place after each execution of the loop body.

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.

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.

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.
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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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));

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.

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.

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).

6.10.7 Null directive

Semantics

A preprocessing directive of the form

    # new-line
has no effect.

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).

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.

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).

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.

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 )

6.11 Future language directions

6.11.1 Floating types

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

Declaring an identifier with internal linkage at file scope without the static storage- class specifier is an obsolescent feature.

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.

6.11.4 Character escape sequences

Lowercase letters as escape sequences are reserved for future standardization. Other characters may be used in extensions.

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.

6.11.6 Function declarators

The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.

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.

6.11.8 Pragma directives

Pragmas whose first preprocessing token is STDC are reserved for future standardization.

6.11.9 Predefined macro names

Macro names beginning with __STDC_ are reserved for future standardization.

7. Library

7.1 Introduction

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.

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.

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.

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.

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.

7.2.1 Program diagnostics

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.

7.3 Complex arithmetic <complex.h>

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.

7.3.2 Conventions

Values are interpreted as radians, not degrees. An implementation may set errno but is not required to.

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.

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.

7.3.5 Trigonometric functions

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.

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.

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.

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.

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.

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.

7.3.6 Hyperbolic functions

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.

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.

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.

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.

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.

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.

7.3.7 Exponential and logarithmic functions

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.

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.

7.3.8 Power and absolute-value functions

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.

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.

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).

7.3.9 Manipulation functions

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 ].

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.

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)))
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.

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.

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.

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).

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.

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.

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.

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.

7.4.1.4 The iscntrl function

Synopsis

         #include <ctype.h>
         int iscntrl(int c);

Description

The iscntrl function tests for any control character.

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).

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 (' ').

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).

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 (' ').

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.

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.

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).

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).

7.4.2 Character case mapping functions

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

7.6.3 Rounding

The fegetround and fesetround functions provide control of rounding direction modes.

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.

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);
              /* ... */
        }

7.6.4 Environment

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

        #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.

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.

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.

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;
       }

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.

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).

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.

7.8.2 Functions for greatest-width integer types

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.

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.

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).

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).

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        ^=

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.

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).

7.11.1 Locale control

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.

7.11.2 Numeric formatting convention inquiry

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

7.12.4 Trigonometric functions

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.

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.

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.

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.

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.

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.

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.

7.12.5 Hyperbolic functions

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)].

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.

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.

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.

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.

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.

7.12.6 Exponential and logarithmic functions

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 .

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 .

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.

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.

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).

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 .

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.

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.

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).

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.

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.

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.

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 .

7.12.7 Power and absolute-value functions

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 .

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 |.

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 .

                            -
                            -----
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 .

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.

                           -
                           -

7.12.8 Error and gamma functions

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
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
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) |.

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).

7.12.9 Nearest integer functions

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.

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.

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.

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.

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.

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.

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.

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.

7.12.10 Remainder functions

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.

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.

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.

7.12.11 Manipulation functions

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.

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).

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.

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.

7.12.12 Maximum, minimum, and positive difference functions

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.

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.

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.

7.12.13 Floating multiply-add

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.

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.

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).

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).

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).

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).

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).

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.

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.

7.13.1 Save calling environment

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.

7.13.2 Restore calling environment

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.

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.

7.14.1 Specify signal handling

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.

7.14.2 Send signal

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.

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.

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.

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.

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.

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.

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.

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);
          }

7.17 Atomics <stdatomic.h>

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.

7.17.2 Initialization

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);
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);

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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;
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.

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.

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).

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).

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.

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).

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.

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.
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.

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.
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.

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.

7.20.2.1 Limits of exact-width integer types

7.20.2.2 Limits of minimum-width integer types

7.20.2.3 Limits of fastest minimum-width integer types

7.20.2.4 Limits of integer types capable of holding object pointers

7.20.2.5 Limits of greatest-width integer types

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.

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.

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.

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)

7.21 Input/output <stdio.h>

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.

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.

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.

7.21.4 Operations on files

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.

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.

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).

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.

7.21.5 File access functions

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.

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).

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).

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.

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).

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

7.21.7 Character input/output functions

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.

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.

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.

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.

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.

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. *

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.

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.

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.

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).

7.21.8 Direct input/output functions

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.

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.

7.21.9 File positioning functions

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).

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).

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.

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.

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.

7.21.10 Error-handling functions

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.

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.

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.

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).

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).

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.

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).

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).

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.

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.

7.22.2 Pseudo-random sequence generation functions

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.

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;
         }

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.

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.

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.

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.

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.

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.

7.22.4 Communication with the environment

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.

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.

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.

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.

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.

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.

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.

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.

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
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.

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.

7.22.6 Integer arithmetic functions

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.

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.

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.

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).

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.

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.

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.

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.

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)

7.23 String handling <string.h>

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).

7.23.2 Copying functions

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.

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.

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.

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.

7.23.3 Concatenation functions

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.

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.

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.

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.

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.

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.

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.

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)

7.23.5 Search functions

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.

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.

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.

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.

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.

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.

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.

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

7.23.6 Miscellaneous functions

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.

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.

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.

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.

7.25 Threads <threads.h>

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.

7.25.2 Initialization functions

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.

7.25.3 Condition variable functions

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.

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.

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.

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.

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.

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.

7.25.4 Mutex functions

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.

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.

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.

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.

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.

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.

7.25.5 Thread functions

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.

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.

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.

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.

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.

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.

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.

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.

7.25.6 Thread-specific storage functions

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.

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.

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.

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.

7.25.7 Time functions

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.

7.26 Date and time <time.h>

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.

7.26.2 Time manipulation functions

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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).

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.

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).

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.

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).

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.

7.28 Extended multibyte and wide character utilities <wchar.h>

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

7.28.3 Wide character input/output functions

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

7.28.4.1 Wide string numeric conversion functions
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.

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.

7.28.4.2 Wide string copying functions
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.

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.

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.

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.

7.28.4.3 Wide string concatenation functions
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.

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.

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.

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.

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.

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.

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)
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.

7.28.4.5 Wide string search functions
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.

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.

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.

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.

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.

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.

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
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.

7.28.4.6 Miscellaneous functions
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.

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.

7.28.5 Wide character time conversion functions

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.

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.

7.28.6.1 Single-byte/wide character conversion functions
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.

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.

7.28.6.2 Conversion state functions
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.

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.

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).

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).

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.

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.

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.

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.

7.29 Wide character classification and mapping utilities <wctype.h>

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).

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.

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.

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.

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.

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.

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.

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).

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 ' '.

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.

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.

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)

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.

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.

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).

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).

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).

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.

7.29.3 Wide character case mapping utilities

The header <wctype.h> 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

        #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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Annex A

                                            (informative)
                             Language syntax summary

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

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

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
(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

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

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   .

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 )
(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

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 ) ;

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 ;

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
(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

Annex B

                              (informative)
                          Library summary

B.1 Diagnostics <assert.h>

         NDEBUG
         static_assert
         void assert(scalar expression);

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);

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);

B.4 Errors <errno.h>

         EDOM           EILSEQ            ERANGE           errno
         __STDC_WANT_LIB_EXT1__
         errno_t

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);

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

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);

B.8 Alternative spellings <iso646.h>

         and            bitor             not_eq           xor
         and_eq         compl             or               xor_eq
         bitand         not               or_eq

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

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);

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);

B.12 Nonlocal jumps <setjmp.h>

       jmp_buf
       int setjmp(jmp_buf env);
       _Noreturn void longjmp(jmp_buf env, int val);

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);

B.14 Alignment <stdalign.h>

         alignas
         __alignas_is_defined

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);

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);

B.17 Boolean type and values <stdbool.h>

         bool
         true
         false
         __bool_true_false_are_defined

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

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

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);

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);

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);

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

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);

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);

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);

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);

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);

Annex C

                                     (informative)
                                   Sequence points

The following are the sequence points described in 5.1.2.3:

Annex D

                                     (normative)
                Universal character names for identifiers

This clause lists the hexadecimal code values that are valid in universal character names in identifiers.

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

D.2 Ranges of characters disallowed initially

0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F

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

Annex F

                                           (normative)
                       IEC 60559 floating-point arithmetic

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.

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.

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.

F.3 Operators and functions

C operators and functions provide IEC 60559 required and recommended facilities as listed below.

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>.

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.)

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.

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. *

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.

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).

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.

F.8.3 Execution

At program startup the floating-point environment is initialized as prescribed by IEC 60559:

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;

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.

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''.

F.9 Optimization

This section identifies code transformations that might subvert IEC 60559-specified behavior, and others that do not.

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;

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.

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();

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.

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.

F.10.1 Trigonometric functions

F.10.1.1 The acos functions

F.10.1.2 The asin functions

F.10.1.3 The atan functions

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.

F.10.1.5 The cos functions

F.10.1.6 The sin functions

F.10.1.7 The tan functions

F.10.2 Hyperbolic functions

F.10.2.1 The acosh functions

F.10.2.2 The asinh functions

F.10.2.3 The atanh functions

F.10.2.4 The cosh functions

F.10.2.5 The sinh functions

F.10.2.6 The tanh functions

F.10.3 Exponential and logarithmic functions

F.10.3.1 The exp functions

F.10.3.2 The exp2 functions

F.10.3.3 The expm1 functions

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));
         }
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.

F.10.3.6 The ldexp functions

On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).

F.10.3.7 The log functions

F.10.3.8 The log10 functions

F.10.3.9 The log1p functions

F.10.3.10 The log2 functions

F.10.3.11 The logb functions

The returned value is exact and is independent of the current rounding direction mode.

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);
         }
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.

F.10.4 Power and absolute value functions

F.10.4.1 The cbrt functions

F.10.4.2 The fabs functions

The returned value is exact and is independent of the current rounding direction mode.

F.10.4.3 The hypot functions

F.10.4.4 The pow functions

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.

F.10.5 Error and gamma functions

F.10.5.1 The erf functions

F.10.5.2 The erfc functions

F.10.5.3 The lgamma functions

F.10.5.4 The tgamma functions

F.10.6 Nearest integer functions

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.

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.

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.

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.

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.

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.
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.

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.

F.10.7 Remainder functions

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);
        }
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.

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.

F.10.8 Manipulation functions

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.

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.

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.

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.

F.10.9 Maximum, minimum, and positive difference functions

F.10.9.1 The fdim functions

No additional requirements.

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.

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.

F.10.10 Floating multiply-add

F.10.10.1 The fma functions

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.

Annex G

                                       (normative)
                IEC 60559-compatible complex arithmetic

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.

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.

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.

G.4 Conversions

G.4.1 Imaginary types

Conversions among imaginary types follow rules analogous to those for real floating types.

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.

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.

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.

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'').

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)

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.

G.6.1 Trigonometric functions

G.6.1.1 The cacos functions

G.6.2 Hyperbolic functions

G.6.2.1 The cacosh functions

G.6.2.2 The casinh functions

G.6.2.3 The catanh functions

G.6.2.4 The ccosh functions

G.6.2.5 The csinh functions

G.6.2.6 The ctanh functions

G.6.3 Exponential and logarithmic functions

G.6.3.1 The cexp functions

G.6.3.2 The clog functions

G.6.4 Power and absolute-value functions

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.

G.6.4.2 The csqrt functions

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)

Annex H

                                     (informative)
                     Language independent arithmetic

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.

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).

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>.

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.

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.

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.

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

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.
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.

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.

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.

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.

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.

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.

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.

Annex J

                                      (informative)
                                   Portability issues

This annex collects some information about portability that appears in this International Standard.

J.1 Unspecified behavior

The following are unspecified:

J.2 Undefined behavior

The behavior is undefined in the following circumstances:

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:

J.3.1 Translation

J.3.2 Environment

J.3.3 Identifiers

J.3.4 Characters

J.3.5 Integers

J.3.6 Floating point

J.3.7 Arrays and pointers

J.3.8 Hints

J.3.9 Structures, unions, enumerations, and bit-fields

J.3.10 Qualifiers

J.3.11 Preprocessing directives

J.3.12 Library functions

J.3.13 Architecture

J.4 Locale-specific behavior

The following characteristics of a hosted environment are locale-specific and are required to be documented by the implementation:

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.

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).

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).

J.5.3 Lengths and cases of identifiers

All characters in identifiers (with or without external linkage) are significant (6.4.2).

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).

J.5.5 Writable string literals

String literals are modifiable (in which case, identical string literals should denote distinct objects) (6.4.5).

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.

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).

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).

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).

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 );

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).

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).

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,

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).

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).

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).

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).

Annex K

                                       (normative)
                           Bounds-checking interfaces

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.

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.

K.3 Library

K.3.1 Introduction

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.

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.

K.3.1.3 Use of errno

An implementation may set errno for the functions defined in this annex, but is not required to.

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.

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.

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>.

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.

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.
K.3.5.1 Operations on files
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.

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.

K.3.5.2 File access functions
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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

K.3.5.4 Character input/output functions
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.

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);
K.3.6.1 Runtime-constraint handling
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).

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.

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).

K.3.6.2 Communication with the environment
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.

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
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.

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.

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.

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.

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.

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.

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.

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.
K.3.7.1 Copying functions
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.

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.

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.

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.

K.3.7.2 Concatenation functions
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.

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.

K.3.7.3 Search functions
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
K.3.7.4 Miscellaneous functions
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.

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.

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.

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.

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.
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.

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.

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.

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.

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.

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.

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.

K.3.9.1 Formatted wide character input/output functions
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".

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.

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".

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".

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.

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".

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.

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".

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".

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.

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".

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.

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".

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.

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

         #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.

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.

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.

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.

K.3.9.2.2 Wide string concatenation functions
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.

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.

K.3.9.2.3 Wide string search functions
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
K.3.9.2.4 Miscellaneous functions
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.

K.3.9.3 Extended multibyte/wide character conversion utilities
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.

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.

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.

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.

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.

Annex L

                                            (normative)
                                         Analyzability

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.

L.2 Definitions

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.

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.

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.

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:

Bibliography

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  4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point Arithmetic.
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  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.
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  16. ISO/IEC 9899:1999, Programming languages -- C.
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  18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2.
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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,