--- /dev/null
+N1570 Committee Draft -- April 12, 2011 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 (N1539) are indicated by ''diff marks'' in the right
+margin: deleted text is marked with ''*'', new or changed text with '' ''.
+
+[page i]
+
+
+[page ii]
+
+Contents
+Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
+Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
+1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
+2. Normative references . . . . . . . . . . . . . . . . . . . . . . . 2
+3. Terms, definitions, and symbols . . . . . . . . . . . . . . . . . . . 3
+4. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . 8
+5. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 10
+ 5.1 Conceptual models . . . . . . . . . . . . . . . . . . . . . 10
+ 5.1.1 Translation environment . . . . . . . . . . . . . . . . 10
+ 5.1.2 Execution environments . . . . . . . . . . . . . . . . 12
+ 5.2 Environmental considerations . . . . . . . . . . . . . . . . . 22
+ 5.2.1 Character sets . . . . . . . . . . . . . . . . . . . . 22
+ 5.2.2 Character display semantics . . . . . . . . . . . . . . 24
+ 5.2.3 Signals and interrupts . . . . . . . . . . . . . . . . . 25
+ 5.2.4 Environmental limits . . . . . . . . . . . . . . . . . 25
+6. Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
+ 6.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 35
+ 6.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 35
+ 6.2.1 Scopes of identifiers . . . . . . . . . . . . . . . . . 35
+ 6.2.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 36
+ 6.2.3 Name spaces of identifiers . . . . . . . . . . . . . . . 37
+ 6.2.4 Storage durations of objects . . . . . . . . . . . . . . 38
+ 6.2.5 Types . . . . . . . . . . . . . . . . . . . . . . . 39
+ 6.2.6 Representations of types . . . . . . . . . . . . . . . . 44
+ 6.2.7 Compatible type and composite type . . . . . . . . . . . 47
+ 6.2.8 Alignment of objects . . . . . . . . . . . . . . . . . 48
+ 6.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 50
+ 6.3.1 Arithmetic operands . . . . . . . . . . . . . . . . . 50
+ 6.3.2 Other operands . . . . . . . . . . . . . . . . . . . 54
+ 6.4 Lexical elements . . . . . . . . . . . . . . . . . . . . . . 57
+ 6.4.1 Keywords . . . . . . . . . . . . . . . . . . . . . . 58
+ 6.4.2 Identifiers . . . . . . . . . . . . . . . . . . . . . . 59
+ 6.4.3 Universal character names . . . . . . . . . . . . . . . 61
+ 6.4.4 Constants . . . . . . . . . . . . . . . . . . . . . . 62
+ 6.4.5 String literals . . . . . . . . . . . . . . . . . . . . 70
+ 6.4.6 Punctuators . . . . . . . . . . . . . . . . . . . . . 72
+ 6.4.7 Header names . . . . . . . . . . . . . . . . . . . . 73
+ 6.4.8 Preprocessing numbers . . . . . . . . . . . . . . . . 74
+ 6.4.9 Comments . . . . . . . . . . . . . . . . . . . . . 75
+
+[page iii]
+
+ 6.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . 76
+ 6.5.1 Primary expressions . . . . . . . . . . . . . . . . . 78
+ 6.5.2 Postfix operators . . . . . . . . . . . . . . . . . . . 79
+ 6.5.3 Unary operators . . . . . . . . . . . . . . . . . . . 88
+ 6.5.4 Cast operators . . . . . . . . . . . . . . . . . . . . 91
+ 6.5.5 Multiplicative operators . . . . . . . . . . . . . . . . 92
+ 6.5.6 Additive operators . . . . . . . . . . . . . . . . . . 92
+ 6.5.7 Bitwise shift operators . . . . . . . . . . . . . . . . . 94
+ 6.5.8 Relational operators . . . . . . . . . . . . . . . . . . 95
+ 6.5.9 Equality operators . . . . . . . . . . . . . . . . . . 96
+ 6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . 97
+ 6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . 98
+ 6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . 98
+ 6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . 99
+ 6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . 99
+ 6.5.15 Conditional operator . . . . . . . . . . . . . . . . . 100
+ 6.5.16 Assignment operators . . . . . . . . . . . . . . . . . 101
+ 6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . 105
+ 6.6 Constant expressions . . . . . . . . . . . . . . . . . . . . . 106
+ 6.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . 108
+ 6.7.1 Storage-class specifiers . . . . . . . . . . . . . . . . 109
+ 6.7.2 Type specifiers . . . . . . . . . . . . . . . . . . . . 111
+ 6.7.3 Type qualifiers . . . . . . . . . . . . . . . . . . . . 121
+ 6.7.4 Function specifiers . . . . . . . . . . . . . . . . . . 125
+ 6.7.5 Alignment specifier . . . . . . . . . . . . . . . . . . 127
+ 6.7.6 Declarators . . . . . . . . . . . . . . . . . . . . . 128
+ 6.7.7 Type names . . . . . . . . . . . . . . . . . . . . . 136
+ 6.7.8 Type definitions . . . . . . . . . . . . . . . . . . . 137
+ 6.7.9 Initialization . . . . . . . . . . . . . . . . . . . . 139
+ 6.7.10 Static assertions . . . . . . . . . . . . . . . . . . . 145
+ 6.8 Statements and blocks . . . . . . . . . . . . . . . . . . . . 146
+ 6.8.1 Labeled statements . . . . . . . . . . . . . . . . . . 146
+ 6.8.2 Compound statement . . . . . . . . . . . . . . . . . 147
+ 6.8.3 Expression and null statements . . . . . . . . . . . . . 147
+ 6.8.4 Selection statements . . . . . . . . . . . . . . . . . 148
+ 6.8.5 Iteration statements . . . . . . . . . . . . . . . . . . 150
+ 6.8.6 Jump statements . . . . . . . . . . . . . . . . . . . 151
+ 6.9 External definitions . . . . . . . . . . . . . . . . . . . . . 155
+ 6.9.1 Function definitions . . . . . . . . . . . . . . . . . . 156
+ 6.9.2 External object definitions . . . . . . . . . . . . . . . 158
+ 6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . 160
+ 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . 162
+ 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . 164
+ 6.10.3 Macro replacement . . . . . . . . . . . . . . . . . . 166
+
+[page iv]
+
+ 6.10.4 Line control . . . . . . . . . . . . . . . . . . . . . 173
+ 6.10.5 Error directive . . . . . . . . . . . . . . . . . . . . 174
+ 6.10.6 Pragma directive . . . . . . . . . . . . . . . . . . . 174
+ 6.10.7 Null directive . . . . . . . . . . . . . . . . . . . . 175
+ 6.10.8 Predefined macro names . . . . . . . . . . . . . . . . 175
+ 6.10.9 Pragma operator . . . . . . . . . . . . . . . . . . . 178
+ 6.11 Future language directions . . . . . . . . . . . . . . . . . . 179
+ 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . 179
+ 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 179
+ 6.11.3 External names . . . . . . . . . . . . . . . . . . . 179
+ 6.11.4 Character escape sequences . . . . . . . . . . . . . . 179
+ 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . 179
+ 6.11.6 Function declarators . . . . . . . . . . . . . . . . . 179
+ 6.11.7 Function definitions . . . . . . . . . . . . . . . . . . 179
+ 6.11.8 Pragma directives . . . . . . . . . . . . . . . . . . 179
+ 6.11.9 Predefined macro names . . . . . . . . . . . . . . . . 179
+7. Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
+ 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 180
+ 7.1.1 Definitions of terms . . . . . . . . . . . . . . . . . . 180
+ 7.1.2 Standard headers . . . . . . . . . . . . . . . . . . . 181
+ 7.1.3 Reserved identifiers . . . . . . . . . . . . . . . . . . 182
+ 7.1.4 Use of library functions . . . . . . . . . . . . . . . . 183
+ 7.2 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 186
+ 7.2.1 Program diagnostics . . . . . . . . . . . . . . . . . 186
+ 7.3 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 188
+ 7.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 188
+ 7.3.2 Conventions . . . . . . . . . . . . . . . . . . . . . 189
+ 7.3.3 Branch cuts . . . . . . . . . . . . . . . . . . . . . 189
+ 7.3.4 The CX_LIMITED_RANGE pragma . . . . . . . . . . . 189
+ 7.3.5 Trigonometric functions . . . . . . . . . . . . . . . . 190
+ 7.3.6 Hyperbolic functions . . . . . . . . . . . . . . . . . 192
+ 7.3.7 Exponential and logarithmic functions . . . . . . . . . . 194
+ 7.3.8 Power and absolute-value functions . . . . . . . . . . . 195
+ 7.3.9 Manipulation functions . . . . . . . . . . . . . . . . 196
+ 7.4 Character handling <ctype.h> . . . . . . . . . . . . . . . . 200
+ 7.4.1 Character classification functions . . . . . . . . . . . . 200
+ 7.4.2 Character case mapping functions . . . . . . . . . . . . 203
+ 7.5 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 205
+ 7.6 Floating-point environment <fenv.h> . . . . . . . . . . . . . 206
+ 7.6.1 The FENV_ACCESS pragma . . . . . . . . . . . . . . 208
+ 7.6.2 Floating-point exceptions . . . . . . . . . . . . . . . 209
+ 7.6.3 Rounding . . . . . . . . . . . . . . . . . . . . . . 212
+ 7.6.4 Environment . . . . . . . . . . . . . . . . . . . . 213
+ 7.7 Characteristics of floating types <float.h> . . . . . . . . . . . 216
+
+[page v]
+
+ 7.8 Format conversion of integer types <inttypes.h> . . . . . . . . 217
+ 7.8.1 Macros for format specifiers . . . . . . . . . . . . . . 217
+ 7.8.2 Functions for greatest-width integer types . . . . . . . . . 218
+ 7.9 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 221
+ 7.10 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 222
+ 7.11 Localization <locale.h> . . . . . . . . . . . . . . . . . . 223
+ 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . 224
+ 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . 225
+ 7.12 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 231
+ 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . 233
+ 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . 235
+ 7.12.3 Classification macros . . . . . . . . . . . . . . . . . 235
+ 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . 238
+ 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . 240
+ 7.12.6 Exponential and logarithmic functions . . . . . . . . . . 242
+ 7.12.7 Power and absolute-value functions . . . . . . . . . . . 247
+ 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . 249
+ 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . 251
+ 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . 254
+ 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . 255
+ 7.12.12 Maximum, minimum, and positive difference functions . . . 257
+ 7.12.13 Floating multiply-add . . . . . . . . . . . . . . . . . 258
+ 7.12.14 Comparison macros . . . . . . . . . . . . . . . . . . 259
+ 7.13 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 262
+ 7.13.1 Save calling environment . . . . . . . . . . . . . . . 262
+ 7.13.2 Restore calling environment . . . . . . . . . . . . . . 263
+ 7.14 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 265
+ 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . 266
+ 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . 267
+ 7.15 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 268
+ 7.16 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 269
+ 7.16.1 Variable argument list access macros . . . . . . . . . . . 269
+ 7.17 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 273
+ 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . 273
+ 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . 274
+ 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . 275
+ 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . 278
+ 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . 279
+ 7.17.6 Atomic integer types . . . . . . . . . . . . . . . . . 280
+ 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . 282
+ 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . 285
+ 7.18 Boolean type and values <stdbool.h> . . . . . . . . . . . . 287
+ 7.19 Common definitions <stddef.h> . . . . . . . . . . . . . . . 288
+ 7.20 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 289
+
+[page vi]
+
+ 7.20.1 Integer types . . . . . . . . . . . . . . . . . . . . 289
+ 7.20.2 Limits of specified-width integer types . . . . . . . . . . 291
+ 7.20.3 Limits of other integer types . . . . . . . . . . . . . . 293
+ 7.20.4 Macros for integer constants . . . . . . . . . . . . . . 294
+ 7.21 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 296
+ 7.21.1 Introduction . . . . . . . . . . . . . . . . . . . . . 296
+ 7.21.2 Streams . . . . . . . . . . . . . . . . . . . . . . 298
+ 7.21.3 Files . . . . . . . . . . . . . . . . . . . . . . . . 300
+ 7.21.4 Operations on files . . . . . . . . . . . . . . . . . . 302
+ 7.21.5 File access functions . . . . . . . . . . . . . . . . . 304
+ 7.21.6 Formatted input/output functions . . . . . . . . . . . . 309
+ 7.21.7 Character input/output functions . . . . . . . . . . . . . 330
+ 7.21.8 Direct input/output functions . . . . . . . . . . . . . . 335
+ 7.21.9 File positioning functions . . . . . . . . . . . . . . . 336
+ 7.21.10 Error-handling functions . . . . . . . . . . . . . . . . 338
+ 7.22 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 340
+ 7.22.1 Numeric conversion functions . . . . . . . . . . . . . . 341
+ 7.22.2 Pseudo-random sequence generation functions . . . . . . . 346
+ 7.22.3 Memory management functions . . . . . . . . . . . . . 347
+ 7.22.4 Communication with the environment . . . . . . . . . . 350
+ 7.22.5 Searching and sorting utilities . . . . . . . . . . . . . . 354
+ 7.22.6 Integer arithmetic functions . . . . . . . . . . . . . . 356
+ 7.22.7 Multibyte/wide character conversion functions . . . . . . . 357
+ 7.22.8 Multibyte/wide string conversion functions . . . . . . . . 359
+ 7.23 _Noreturn <stdnoreturn.h> . . . . . . . . . . . . . . 361
+ 7.24 String handling <string.h> . . . . . . . . . . . . . . . . . 362
+ 7.24.1 String function conventions . . . . . . . . . . . . . . . 362
+ 7.24.2 Copying functions . . . . . . . . . . . . . . . . . . 362
+ 7.24.3 Concatenation functions . . . . . . . . . . . . . . . . 364
+ 7.24.4 Comparison functions . . . . . . . . . . . . . . . . . 365
+ 7.24.5 Search functions . . . . . . . . . . . . . . . . . . . 367
+ 7.24.6 Miscellaneous functions . . . . . . . . . . . . . . . . 371
+ 7.25 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 373
+ 7.26 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 376
+ 7.26.1 Introduction . . . . . . . . . . . . . . . . . . . . . 376
+ 7.26.2 Initialization functions . . . . . . . . . . . . . . . . . 378
+ 7.26.3 Condition variable functions . . . . . . . . . . . . . . 378
+ 7.26.4 Mutex functions . . . . . . . . . . . . . . . . . . . 380
+ 7.26.5 Thread functions . . . . . . . . . . . . . . . . . . . 383
+ 7.26.6 Thread-specific storage functions . . . . . . . . . . . . 386
+ 7.27 Date and time <time.h> . . . . . . . . . . . . . . . . . . 388
+ 7.27.1 Components of time . . . . . . . . . . . . . . . . . 388
+ 7.27.2 Time manipulation functions . . . . . . . . . . . . . . 389
+ 7.27.3 Time conversion functions . . . . . . . . . . . . . . . 392
+
+[page vii]
+
+ 7.28 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 398
+ 7.28.1 Restartable multibyte/wide character conversion functions . . 398
+ 7.29 Extended multibyte and wide character utilities <wchar.h> . . . . . 402
+ 7.29.1 Introduction . . . . . . . . . . . . . . . . . . . . . 402
+ 7.29.2 Formatted wide character input/output functions . . . . . . 403
+ 7.29.3 Wide character input/output functions . . . . . . . . . . 421
+ 7.29.4 General wide string utilities . . . . . . . . . . . . . . 426
+ 7.29.4.1 Wide string numeric conversion functions . . . . . 426
+ 7.29.4.2 Wide string copying functions . . . . . . . . . . 430
+ 7.29.4.3 Wide string concatenation functions . . . . . . . 432
+ 7.29.4.4 Wide string comparison functions . . . . . . . . 433
+ 7.29.4.5 Wide string search functions . . . . . . . . . . 435
+ 7.29.4.6 Miscellaneous functions . . . . . . . . . . . . 439
+ 7.29.5 Wide character time conversion functions . . . . . . . . . 439
+ 7.29.6 Extended multibyte/wide character conversion utilities . . . . 440
+ 7.29.6.1 Single-byte/wide character conversion functions . . . 441
+ 7.29.6.2 Conversion state functions . . . . . . . . . . . 441
+ 7.29.6.3 Restartable multibyte/wide character conversion
+ functions . . . . . . . . . . . . . . . . . . 442
+ 7.29.6.4 Restartable multibyte/wide string conversion
+ functions . . . . . . . . . . . . . . . . . . 444
+ 7.30 Wide character classification and mapping utilities <wctype.h> . . . 447
+ 7.30.1 Introduction . . . . . . . . . . . . . . . . . . . . . 447
+ 7.30.2 Wide character classification utilities . . . . . . . . . . . 448
+ 7.30.2.1 Wide character classification functions . . . . . . 448
+ 7.30.2.2 Extensible wide character classification
+ functions . . . . . . . . . . . . . . . . . . 451
+ 7.30.3 Wide character case mapping utilities . . . . . . . . . . . 453
+ 7.30.3.1 Wide character case mapping functions . . . . . . 453
+ 7.30.3.2 Extensible wide character case mapping
+ functions . . . . . . . . . . . . . . . . . . 453
+ 7.31 Future library directions . . . . . . . . . . . . . . . . . . . 455
+ 7.31.1 Complex arithmetic <complex.h> . . . . . . . . . . . 455
+ 7.31.2 Character handling <ctype.h> . . . . . . . . . . . . 455
+ 7.31.3 Errors <errno.h> . . . . . . . . . . . . . . . . . 455
+ 7.31.4 Floating-point environment <fenv.h> . . . . . . . . . . 455
+ 7.31.5 Format conversion of integer types <inttypes.h> . . . . 455
+ 7.31.6 Localization <locale.h> . . . . . . . . . . . . . . 455
+ 7.31.7 Signal handling <signal.h> . . . . . . . . . . . . . 455
+ 7.31.8 Atomics <stdatomic.h> . . . . . . . . . . . . . . 455
+ 7.31.9 Boolean type and values <stdbool.h> . . . . . . . . . 456
+ 7.31.10 Integer types <stdint.h> . . . . . . . . . . . . . . 456
+ 7.31.11 Input/output <stdio.h> . . . . . . . . . . . . . . . 456
+ 7.31.12 General utilities <stdlib.h> . . . . . . . . . . . . . 456
+
+[page viii]
+
+ 7.31.13 String handling <string.h> . . . . . . . . . . . . . 456
+ 7.31.14 Date and time <time.h> . . . . . . . . . . . . . . . 456
+ 7.31.15 Threads <threads.h> . . . . . . . . . . . . . . . . 456
+ 7.31.16 Extended multibyte and wide character utilities
+ <wchar.h> . . . . . . . . . . . . . . . . . . . . 456
+ 7.31.17 Wide character classification and mapping utilities
+ <wctype.h> . . . . . . . . . . . . . . . . . . . . 457
+Annex A (informative) Language syntax summary . . . . . . . . . . . . 458
+ A.1 Lexical grammar . . . . . . . . . . . . . . . . . . . . . . 458
+ A.2 Phrase structure grammar . . . . . . . . . . . . . . . . . . . 465
+ A.3 Preprocessing directives . . . . . . . . . . . . . . . . . . . 473
+Annex B (informative) Library summary . . . . . . . . . . . . . . . . 475
+ B.1 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 475
+ B.2 Complex <complex.h> . . . . . . . . . . . . . . . . . . . 475
+ B.3 Character handling <ctype.h> . . . . . . . . . . . . . . . . 477
+ B.4 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 477
+ B.5 Floating-point environment <fenv.h> . . . . . . . . . . . . . 477
+ B.6 Characteristics of floating types <float.h> . . . . . . . . . . . 478
+ B.7 Format conversion of integer types <inttypes.h> . . . . . . . . 478
+ B.8 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 479
+ B.9 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 479
+ B.10 Localization <locale.h> . . . . . . . . . . . . . . . . . . 479
+ B.11 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 479
+ B.12 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 484
+ B.13 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 484
+ B.14 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 485
+ B.15 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 485
+ B.16 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 485
+ B.17 Boolean type and values <stdbool.h> . . . . . . . . . . . . 487
+ B.18 Common definitions <stddef.h> . . . . . . . . . . . . . . . 487
+ B.19 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 487
+ B.20 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 488
+ B.21 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 491
+ B.22 _Noreturn <stdnoreturn.h> . . . . . . . . . . . . . . 493
+ B.23 String handling <string.h> . . . . . . . . . . . . . . . . . 493
+ B.24 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 495
+ B.25 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 495
+ B.26 Date and time <time.h> . . . . . . . . . . . . . . . . . . 496
+ B.27 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 497
+ B.28 Extended multibyte/wide character utilities <wchar.h> . . . . . . 497
+ B.29 Wide character classification and mapping utilities <wctype.h> . . . 502
+Annex C (informative) Sequence points . . . . . . . . . . . . . . . . . 503
+
+[page ix]
+
+Annex D (normative) Universal character names for identifiers . . . . . . . 504
+ D.1 Ranges of characters allowed . . . . . . . . . . . . . . . . . 504
+ D.2 Ranges of characters disallowed initially . . . . . . . . . . . . . 504
+Annex E (informative) Implementation limits . . . . . . . . . . . . . . 505
+Annex F (normative) IEC 60559 floating-point arithmetic . . . . . . . . . . 507
+ F.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 507
+ F.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
+ F.3 Operators and functions . . . . . . . . . . . . . . . . . . . 508
+ F.4 Floating to integer conversion . . . . . . . . . . . . . . . . . 510
+ F.5 Binary-decimal conversion . . . . . . . . . . . . . . . . . . 510
+ F.6 The return statement . . . . . . . . . . . . . . . . . . . . 511
+ F.7 Contracted expressions . . . . . . . . . . . . . . . . . . . . 511
+ F.8 Floating-point environment . . . . . . . . . . . . . . . . . . 511
+ F.9 Optimization . . . . . . . . . . . . . . . . . . . . . . . . 514
+ F.10 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 517
+ F.10.1 Trigonometric functions . . . . . . . . . . . . . . . . 518
+ F.10.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 520
+ F.10.3 Exponential and logarithmic functions . . . . . . . . . . 520
+ F.10.4 Power and absolute value functions . . . . . . . . . . . 524
+ F.10.5 Error and gamma functions . . . . . . . . . . . . . . . 525
+ F.10.6 Nearest integer functions . . . . . . . . . . . . . . . . 526
+ F.10.7 Remainder functions . . . . . . . . . . . . . . . . . 528
+ F.10.8 Manipulation functions . . . . . . . . . . . . . . . . 529
+ F.10.9 Maximum, minimum, and positive difference functions . . . 530
+ F.10.10 Floating multiply-add . . . . . . . . . . . . . . . . . 530
+ F.10.11 Comparison macros . . . . . . . . . . . . . . . . . . 531
+Annex G (normative) IEC 60559-compatible complex arithmetic . . . . . . . 532
+ G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 532
+ G.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
+ G.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . 532
+ G.4 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 533
+ G.4.1 Imaginary types . . . . . . . . . . . . . . . . . . . 533
+ G.4.2 Real and imaginary . . . . . . . . . . . . . . . . . . 533
+ G.4.3 Imaginary and complex . . . . . . . . . . . . . . . . 533
+ G.5 Binary operators . . . . . . . . . . . . . . . . . . . . . . 533
+ G.5.1 Multiplicative operators . . . . . . . . . . . . . . . . 534
+ G.5.2 Additive operators . . . . . . . . . . . . . . . . . . 537
+ G.6 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 537
+ G.6.1 Trigonometric functions . . . . . . . . . . . . . . . . 539
+ G.6.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 539
+ G.6.3 Exponential and logarithmic functions . . . . . . . . . . 543
+ G.6.4 Power and absolute-value functions . . . . . . . . . . . 544
+ G.7 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 545
+
+[page x]
+
+Annex H (informative) Language independent arithmetic . . . . . . . . . . 546
+ H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 546
+ H.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
+ H.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 550
+Annex I (informative) Common warnings . . . . . . . . . . . . . . . . 552
+Annex J (informative) Portability issues . . . . . . . . . . . . . . . . . 554
+ J.1 Unspecified behavior . . . . . . . . . . . . . . . . . . . . . 554
+ J.2 Undefined behavior . . . . . . . . . . . . . . . . . . . . . 557
+ J.3 Implementation-defined behavior . . . . . . . . . . . . . . . . 571
+ J.4 Locale-specific behavior . . . . . . . . . . . . . . . . . . . 578
+ J.5 Common extensions . . . . . . . . . . . . . . . . . . . . . 579
+Annex K (normative) Bounds-checking interfaces . . . . . . . . . . . . . 582
+ K.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 582
+ K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
+ K.3 Library . . . . . . . . . . . . . . . . . . . . . . . . . . 583
+ K.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 583
+ K.3.1.1 Standard headers . . . . . . . . . . . . . . . 583
+ K.3.1.2 Reserved identifiers . . . . . . . . . . . . . . 584
+ K.3.1.3 Use of errno . . . . . . . . . . . . . . . . . 584
+ K.3.1.4 Runtime-constraint violations . . . . . . . . . . 584
+ K.3.2 Errors <errno.h> . . . . . . . . . . . . . . . . . 585
+ K.3.3 Common definitions <stddef.h> . . . . . . . . . . . 585
+ K.3.4 Integer types <stdint.h> . . . . . . . . . . . . . . 585
+ K.3.5 Input/output <stdio.h> . . . . . . . . . . . . . . . 586
+ K.3.5.1 Operations on files . . . . . . . . . . . . . . 586
+ K.3.5.2 File access functions . . . . . . . . . . . . . . 588
+ K.3.5.3 Formatted input/output functions . . . . . . . . . 591
+ K.3.5.4 Character input/output functions . . . . . . . . . 602
+ K.3.6 General utilities <stdlib.h> . . . . . . . . . . . . . 604
+ K.3.6.1 Runtime-constraint handling . . . . . . . . . . 604
+ K.3.6.2 Communication with the environment . . . . . . . 606
+ K.3.6.3 Searching and sorting utilities . . . . . . . . . . 607
+ K.3.6.4 Multibyte/wide character conversion functions . . . 610
+ K.3.6.5 Multibyte/wide string conversion functions . . . . . 611
+ K.3.7 String handling <string.h> . . . . . . . . . . . . . 614
+ K.3.7.1 Copying functions . . . . . . . . . . . . . . 614
+ K.3.7.2 Concatenation functions . . . . . . . . . . . . 617
+ K.3.7.3 Search functions . . . . . . . . . . . . . . . 620
+ K.3.7.4 Miscellaneous functions . . . . . . . . . . . . 621
+ K.3.8 Date and time <time.h> . . . . . . . . . . . . . . . 624
+ K.3.8.1 Components of time . . . . . . . . . . . . . . 624
+ K.3.8.2 Time conversion functions . . . . . . . . . . . 624
+
+[page xi]
+
+ K.3.9 Extended multibyte and wide character utilities
+ <wchar.h> . . . . . . . . . . . . . . . . . . . . 627
+ K.3.9.1 Formatted wide character input/output functions . . . 628
+ K.3.9.2 General wide string utilities . . . . . . . . . . . 639
+ K.3.9.3 Extended multibyte/wide character conversion
+ utilities . . . . . . . . . . . . . . . . . . . 647
+Annex L (normative) Analyzability . . . . . . . . . . . . . . . . . . 652
+ L.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
+ L.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 652
+ L.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 653
+Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
+Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657
+
+[page xii]
+
+ Foreword
+1 ISO (the International Organization for Standardization) and IEC (the International
+ Electrotechnical Commission) form the specialized system for worldwide
+ standardization. National bodies that are member of ISO or IEC participate in the
+ development of International Standards through technical committees established by the
+ respective organization to deal with particular fields of technical activity. ISO and IEC
+ technical committees collaborate in fields of mutual interest. Other international
+ organizations, governmental and non-governmental, in liaison with ISO and IEC, also
+ take part in the work.
+2 International Standards are drafted in accordance with the rules given in the ISO/IEC
+ Directives, Part 2. This International Standard was drafted in accordance with the fifth
+ edition (2004).
+3 In the field of information technology, ISO and IEC have established a joint technical
+ committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
+ committee are circulated to national bodies for voting. Publication as an International
+ Standard requires approval by at least 75% of the national bodies casting a vote.
+4 Attention is drawn to the possibility that some of the elements of this document may be
+ the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
+ or all such patent rights.
+5 This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
+ Information technology, Subcommittee SC 22, Programming languages, their
+ environments and system software interfaces. The Working Group responsible for this
+ standard (WG 14) maintains a site on the World Wide Web at http://www.open-
+ std.org/JTC1/SC22/WG14/ containing additional information relevant to this
+ standard such as a Rationale for many of the decisions made during its preparation and a
+ log of Defect Reports and Responses.
+6 This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
+ corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
+ ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
+ -- conditional (optional) features (including some that were previously mandatory)
+ -- support for multiple threads of execution including an improved memory sequencing
+ model, atomic objects, and thread-local storage (<stdatomic.h> and
+ <threads.h>)
+ -- additional floating-point characteristic macros (<float.h>)
+ -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
+ -- Unicode characters and strings (<uchar.h>) (originally specified in
+ ISO/IEC TR 19769:2004)
+ -- type-generic expressions
+
+[page xiii]
+
+ -- static assertions
+ -- anonymous structures and unions
+ -- no-return functions
+ -- macros to create complex numbers (<complex.h>)
+ -- support for opening files for exclusive access
+ -- removed the gets function (<stdio.h>)
+ -- added the aligned_alloc, at_quick_exit, and quick_exit functions
+ (<stdlib.h>)
+ -- (conditional) support for bounds-checking interfaces (originally specified in
+ ISO/IEC TR 24731-1:2007)
+ -- (conditional) support for analyzability
+7 Major changes in the second edition included:
+ -- restricted character set support via digraphs and <iso646.h> (originally specified
+ in AMD1)
+ -- wide character library support in <wchar.h> and <wctype.h> (originally
+ specified in AMD1)
+ -- more precise aliasing rules via effective type
+ -- restricted pointers
+ -- variable length arrays
+ -- flexible array members
+ -- static and type qualifiers in parameter array declarators
+ -- complex (and imaginary) support in <complex.h>
+ -- type-generic math macros in <tgmath.h>
+ -- the long long int type and library functions
+ -- increased minimum translation limits
+ -- additional floating-point characteristics in <float.h>
+ -- remove implicit int
+ -- reliable integer division
+ -- universal character names (\u and \U)
+ -- extended identifiers
+ -- hexadecimal floating-point constants and %a and %A printf/scanf conversion
+ specifiers
+
+[page xiv]
+
+-- compound literals
+-- designated initializers
+-- // comments
+-- extended integer types and library functions in <inttypes.h> and <stdint.h>
+-- remove implicit function declaration
+-- preprocessor arithmetic done in intmax_t/uintmax_t
+-- mixed declarations and code
+-- new block scopes for selection and iteration statements
+-- integer constant type rules
+-- integer promotion rules
+-- macros with a variable number of arguments
+-- the vscanf family of functions in <stdio.h> and <wchar.h>
+-- additional math library functions in <math.h>
+-- treatment of error conditions by math library functions (math_errhandling)
+-- floating-point environment access in <fenv.h>
+-- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
+-- trailing comma allowed in enum declaration
+-- %lf conversion specifier allowed in printf
+-- inline functions
+-- the snprintf family of functions in <stdio.h>
+-- boolean type in <stdbool.h>
+-- idempotent type qualifiers
+-- empty macro arguments
+-- new structure type compatibility rules (tag compatibility)
+-- additional predefined macro names
+-- _Pragma preprocessing operator
+-- standard pragmas
+-- __func__ predefined identifier
+-- va_copy macro
+-- additional strftime conversion specifiers
+-- LIA compatibility annex
+
+[page xv]
+
+ -- deprecate ungetc at the beginning of a binary file
+ -- remove deprecation of aliased array parameters
+ -- conversion of array to pointer not limited to lvalues
+ -- relaxed constraints on aggregate and union initialization
+ -- relaxed restrictions on portable header names
+ -- return without expression not permitted in function that returns a value (and vice
+ versa)
+8 Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H,
+ I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
+ the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
+ are also for information only.
+
+[page xvi]
+
+ Introduction
+1 With the introduction of new devices and extended character sets, new features may be
+ added to this International Standard. Subclauses in the language and library clauses warn
+ implementors and programmers of usages which, though valid in themselves, may
+ conflict with future additions.
+2 Certain features are obsolescent, which means that they may be considered for
+ withdrawal in future revisions of this International Standard. They are retained because
+ of their widespread use, but their use in new implementations (for implementation
+ features) or new programs (for language [6.11] or library features [7.31]) is discouraged.
+3 This International Standard is divided into four major subdivisions:
+ -- preliminary elements (clauses 1-4);
+ -- the characteristics of environments that translate and execute C programs (clause 5);
+ -- the language syntax, constraints, and semantics (clause 6);
+ -- the library facilities (clause 7).
+4 Examples are provided to illustrate possible forms of the constructions described.
+ Footnotes are provided to emphasize consequences of the rules described in that
+ subclause or elsewhere in this International Standard. References are used to refer to
+ other related subclauses. Recommendations are provided to give advice or guidance to
+ implementors. Annexes provide additional information and summarize the information
+ contained in this International Standard. A bibliography lists documents that were
+ referred to during the preparation of the standard.
+5 The language clause (clause 6) is derived from ''The C Reference Manual''.
+6 The library clause (clause 7) is based on the 1984 /usr/group Standard.
+
+[page xvii]
+
+
+[page xviii]
+
+
+
+ Programming languages -- C
+
+
+
+ 1. Scope
+1 This International Standard specifies the form and establishes the interpretation of
+ programs written in the C programming language.1) It specifies
+ -- the representation of C programs;
+ -- the syntax and constraints of the C language;
+ -- the semantic rules for interpreting C programs;
+ -- the representation of input data to be processed by C programs;
+ -- the representation of output data produced by C programs;
+ -- the restrictions and limits imposed by a conforming implementation of C.
+2 This International Standard does not specify
+ -- the mechanism by which C programs are transformed for use by a data-processing
+ system;
+ -- the mechanism by which C programs are invoked for use by a data-processing
+ system;
+ -- the mechanism by which input data are transformed for use by a C program;
+ -- the mechanism by which output data are transformed after being produced by a C
+ program;
+ -- the size or complexity of a program and its data that will exceed the capacity of any
+ specific data-processing system or the capacity of a particular processor;
+ -- all minimal requirements of a data-processing system that is capable of supporting a
+ conforming implementation.
+
+
+ 1) This International Standard is designed to promote the portability of C programs among a variety of
+ data-processing systems. It is intended for use by implementors and programmers.
+
+[page 1]
+
+
+ 2. Normative references
+1 The following referenced documents are indispensable for the application of this
+ document. For dated references, only the edition cited applies. For undated references,
+ the latest edition of the referenced document (including any amendments) applies.
+2 ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for
+ use in the physical sciences and technology.
+3 ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information
+ interchange.
+4 ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental
+ terms.
+5 ISO 4217, Codes for the representation of currencies and funds.
+6 ISO 8601, Data elements and interchange formats -- Information interchange --
+ Representation of dates and times.
+7 ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded
+ Character Set (UCS).
+8 IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
+ designated IEC 559:1989).
+
+[page 2]
+
+
+ 3. Terms, definitions, and symbols
+1 For the purposes of this International Standard, the following definitions apply. Other
+ terms are defined where they appear in italic type or on the left side of a syntax rule.
+ Terms explicitly defined in this International Standard are not to be presumed to refer
+ implicitly to similar terms defined elsewhere. Terms not defined in this International
+ Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not
+ defined in this International Standard are to be interpreted according to ISO 31-11.
+ 3.1
+1 access
+ <execution-time action> to read or modify the value of an object
+2 NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used.
+
+3 NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value.
+
+4 NOTE 3 Expressions that are not evaluated do not access objects.
+
+ 3.2
+1 alignment
+ requirement that objects of a particular type be located on storage boundaries with
+ addresses that are particular multiples of a byte address
+ 3.3
+1 argument
+ actual argument
+ actual parameter (deprecated)
+ expression in the comma-separated list bounded by the parentheses in a function call
+ expression, or a sequence of preprocessing tokens in the comma-separated list bounded
+ by the parentheses in a function-like macro invocation
+ 3.4
+1 behavior
+ external appearance or action
+ 3.4.1
+1 implementation-defined behavior
+ unspecified behavior where each implementation documents how the choice is made
+2 EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
+ when a signed integer is shifted right.
+
+ 3.4.2
+1 locale-specific behavior
+ behavior that depends on local conventions of nationality, culture, and language that each
+ implementation documents
+
+[page 3]
+
+2 EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
+ characters other than the 26 lowercase Latin letters.
+
+ 3.4.3
+1 undefined behavior
+ behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
+ for which this International Standard imposes no requirements
+2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
+ results, to behaving during translation or program execution in a documented manner characteristic of the
+ environment (with or without the issuance of a diagnostic message), to terminating a translation or
+ execution (with the issuance of a diagnostic message).
+
+3 EXAMPLE An example of undefined behavior is the behavior on integer overflow.
+
+ 3.4.4
+1 unspecified behavior
+ use of an unspecified value, or other behavior where this International Standard provides
+ two or more possibilities and imposes no further requirements on which is chosen in any
+ instance
+2 EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are
+ evaluated.
+
+ 3.5
+1 bit
+ unit of data storage in the execution environment large enough to hold an object that may
+ have one of two values
+2 NOTE It need not be possible to express the address of each individual bit of an object.
+
+ 3.6
+1 byte
+ addressable unit of data storage large enough to hold any member of the basic character
+ set of the execution environment
+2 NOTE 1 It is possible to express the address of each individual byte of an object uniquely.
+
+3 NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
+ defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
+ bit.
+
+ 3.7
+1 character
+ <abstract> member of a set of elements used for the organization, control, or
+ representation of data
+ 3.7.1
+1 character
+ single-byte character
+ <C> bit representation that fits in a byte
+
+[page 4]
+
+ 3.7.2
+1 multibyte character
+ sequence of one or more bytes representing a member of the extended character set of
+ either the source or the execution environment
+2 NOTE The extended character set is a superset of the basic character set.
+
+ 3.7.3
+1 wide character
+ value representable by an object of type wchar_t, capable of representing any character
+ in the current locale
+ 3.8
+1 constraint
+ restriction, either syntactic or semantic, by which the exposition of language elements is
+ to be interpreted
+ 3.9
+1 correctly rounded result
+ representation in the result format that is nearest in value, subject to the current rounding
+ mode, to what the result would be given unlimited range and precision
+ 3.10
+1 diagnostic message
+ message belonging to an implementation-defined subset of the implementation's message
+ output
+ 3.11
+1 forward reference
+ reference to a later subclause of this International Standard that contains additional
+ information relevant to this subclause
+ 3.12
+1 implementation
+ particular set of software, running in a particular translation environment under particular
+ control options, that performs translation of programs for, and supports execution of
+ functions in, a particular execution environment
+ 3.13
+1 implementation limit
+ restriction imposed upon programs by the implementation
+ 3.14
+1 memory location
+ either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
+ nonzero width
+
+[page 5]
+
+2 NOTE 1 Two threads of execution can update and access separate memory locations without interfering
+ with each other.
+
+3 NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
+ applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
+ two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
+ declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
+ members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
+ intervening bit-fields happen to be.
+
+4 EXAMPLE A structure declared as
+ struct {
+ char a;
+ int b:5, c:11, :0, d:8;
+ struct { int ee:8; } e;
+ }
+ contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
+ memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
+ and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
+ modified, but b and a, for example, can be.
+
+ 3.15
+1 object
+ region of data storage in the execution environment, the contents of which can represent
+ values
+2 NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.
+
+ 3.16
+1 parameter
+ formal parameter
+ formal argument (deprecated)
+ object declared as part of a function declaration or definition that acquires a value on
+ entry to the function, or an identifier from the comma-separated list bounded by the
+ parentheses immediately following the macro name in a function-like macro definition
+ 3.17
+1 recommended practice
+ specification that is strongly recommended as being in keeping with the intent of the
+ standard, but that may be impractical for some implementations
+ 3.18
+1 runtime-constraint
+ requirement on a program when calling a library function
+2 NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
+ need not be diagnosed at translation time.
+
+3 NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
+ constraints for a library function are not violated by the program; see K.3.1.4.
+
+[page 6]
+
+ 3.19
+1 value
+ precise meaning of the contents of an object when interpreted as having a specific type
+ 3.19.1
+1 implementation-defined value
+ unspecified value where each implementation documents how the choice is made
+ 3.19.2
+1 indeterminate value
+ either an unspecified value or a trap representation
+ 3.19.3
+1 unspecified value
+ valid value of the relevant type where this International Standard imposes no
+ requirements on which value is chosen in any instance
+2 NOTE An unspecified value cannot be a trap representation.
+
+ 3.19.4
+1 trap representation
+ an object representation that need not represent a value of the object type
+ 3.19.5
+1 perform a trap
+ interrupt execution of the program such that no further operations are performed
+2 NOTE In this International Standard, when the word ''trap'' is not immediately followed by
+ ''representation'', this is the intended usage.2)
+
+ 3.20
+1 [^ x^]
+ ceiling of x: the least integer greater than or equal to x
+2 EXAMPLE [^2.4^] is 3, [^-2.4^] is -2.
+
+ 3.21
+1 [_ x_]
+ floor of x: the greatest integer less than or equal to x
+2 EXAMPLE [_2.4_] is 2, [_-2.4_] is -3.
+
+
+
+
+ 2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap
+ representation might perform a trap but is not required to (see 6.2.6.1).
+
+[page 7]
+
+
+ 4. Conformance
+1 In this International Standard, ''shall'' is to be interpreted as a requirement on an
+ implementation or on a program; conversely, ''shall not'' is to be interpreted as a
+ prohibition.
+2 If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime-
+ constraint is violated, the behavior is undefined. Undefined behavior is otherwise
+ indicated in this International Standard by the words ''undefined behavior'' or by the
+ omission of any explicit definition of behavior. There is no difference in emphasis among
+ these three; they all describe ''behavior that is undefined''.
+3 A program that is correct in all other aspects, operating on correct data, containing
+ unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
+4 The implementation shall not successfully translate a preprocessing translation unit
+ containing a #error preprocessing directive unless it is part of a group skipped by
+ conditional inclusion.
+5 A strictly conforming program shall use only those features of the language and library
+ specified in this International Standard.3) It shall not produce output dependent on any
+ unspecified, undefined, or implementation-defined behavior, and shall not exceed any
+ minimum implementation limit.
+6 The two forms of conforming implementation are hosted and freestanding. A conforming
+ hosted implementation shall accept any strictly conforming program. A conforming
+ freestanding implementation shall accept any strictly conforming program 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>, <stdint.h>, and
+ <stdnoreturn.h>. A conforming implementation may have extensions (including
+ additional library functions), provided they do not alter the behavior of any strictly
+ conforming program.4)
+
+
+
+ 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
+ by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
+ #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
+ /* ... */
+ fesetround(FE_UPWARD);
+ /* ... */
+ #endif
+
+ 4) This implies that a conforming implementation reserves no identifiers other than those explicitly
+ reserved in this International Standard.
+
+[page 8]
+
+7 A conforming program is one that is acceptable to a conforming implementation.5)
+8 An implementation shall be accompanied by a document that defines all implementation-
+ defined and locale-specific characteristics and all extensions.
+ Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
+ characteristics of floating types <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),
+ <stdnoreturn.h> (7.23).
+
+
+
+
+ 5) Strictly conforming programs are intended to be maximally portable among conforming
+ implementations. Conforming programs may depend upon nonportable features of a conforming
+ implementation.
+
+[page 9]
+
+
+ 5. Environment
+1 An implementation translates C source files and executes C programs in two data-
+ processing-system environments, which will be called the translation environment and
+ the execution environment in this International Standard. Their characteristics define and
+ constrain the results of executing conforming C programs constructed according to the
+ syntactic and semantic rules for conforming implementations.
+ Forward references: In this clause, only a few of many possible forward references
+ have been noted.
+ 5.1 Conceptual models
+ 5.1.1 Translation environment
+ 5.1.1.1 Program structure
+1 A C program need not all be translated at the same time. The text of the program is kept
+ in units called source files, (or preprocessing files) in this International Standard. A
+ source file together with all the headers and source files included via the preprocessing
+ directive #include is known as a preprocessing translation unit. After preprocessing, a
+ preprocessing translation unit is called a translation unit. Previously translated translation
+ units may be preserved individually or in libraries. The separate translation units of a
+ program communicate by (for example) calls to functions whose identifiers have external
+ linkage, manipulation of objects whose identifiers have external linkage, or manipulation
+ of data files. Translation units may be separately translated and then later linked to
+ produce an executable program.
+ Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
+ preprocessing directives (6.10).
+ 5.1.1.2 Translation phases
+1 The precedence among the syntax rules of translation is specified by the following
+ phases.6)
+ 1. Physical source file multibyte characters are mapped, in an implementation-
+ defined manner, to the source character set (introducing new-line characters for
+ end-of-line indicators) if necessary. Trigraph sequences are replaced by
+ corresponding single-character internal representations.
+
+
+
+ 6) Implementations shall behave as if these separate phases occur, even though many are typically folded
+ together in practice. Source files, translation units, and translated translation units need not
+ necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
+ and any external representation. The description is conceptual only, and does not specify any
+ particular implementation.
+
+[page 10]
+
+ 2. Each instance of a backslash character (\) immediately followed by a new-line
+ character is deleted, splicing physical source lines to form logical source lines.
+ Only the last backslash on any physical source line shall be eligible for being part
+ of such a splice. A source file that is not empty shall end in a new-line character,
+ which shall not be immediately preceded by a backslash character before any such
+ splicing takes place.
+ 3. The source file is decomposed into preprocessing tokens7) and sequences of
+ white-space characters (including comments). A source file shall not end in a
+ partial preprocessing token or in a partial comment. Each comment is replaced by
+ one space character. New-line characters are retained. Whether each nonempty
+ sequence of white-space characters other than new-line is retained or replaced by
+ one space character is implementation-defined.
+ 4. Preprocessing directives are executed, macro invocations are expanded, and
+ _Pragma unary operator expressions are executed. If a character sequence that
+ matches the syntax of a universal character name is produced by token
+ concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
+ directive causes the named header or source file to be processed from phase 1
+ through phase 4, recursively. All preprocessing directives are then deleted.
+ 5. Each source character set member and escape sequence in character constants and
+ string literals is converted to the corresponding member of the execution character
+ set; if there is no corresponding member, it is converted to an implementation-
+ defined member other than the null (wide) character.8)
+ 6. Adjacent string literal tokens are concatenated.
+ 7. White-space characters separating tokens are no longer significant. Each
+ preprocessing token is converted into a token. The resulting tokens are
+ syntactically and semantically analyzed and translated as a translation unit.
+ 8. All external object and function references are resolved. Library components are
+ linked to satisfy external references to functions and objects not defined in the
+ current translation. All such translator output is collected into a program image
+ which contains information needed for execution in its execution environment.
+Forward references: universal character names (6.4.3), lexical elements (6.4),
+preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).
+
+
+
+7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is
+ context-dependent. For example, see the handling of < within a #include preprocessing directive.
+8) An implementation need not convert all non-corresponding source characters to the same execution
+ character.
+
+[page 11]
+
+ 5.1.1.3 Diagnostics
+1 A conforming implementation shall produce at least one diagnostic message (identified in
+ an implementation-defined manner) if a preprocessing translation unit or translation unit
+ contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
+ specified as undefined or implementation-defined. Diagnostic messages need not be
+ produced in other circumstances.9)
+2 EXAMPLE An implementation shall issue a diagnostic for the translation unit:
+ char i;
+ int i;
+ because in those cases where wording in this International Standard describes the behavior for a construct
+ as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.
+
+ 5.1.2 Execution environments
+1 Two execution environments are defined: freestanding and hosted. In both cases,
+ program startup occurs when a designated C function is called by the execution
+ environment. All objects with static storage duration shall be initialized (set to their
+ initial values) before program startup. The manner and timing of such initialization are
+ otherwise unspecified. Program termination returns control to the execution
+ environment.
+ Forward references: storage durations of objects (6.2.4), initialization (6.7.9).
+ 5.1.2.1 Freestanding environment
+1 In a freestanding environment (in which C program execution may take place without any
+ benefit of an operating system), the name and type of the function called at program
+ startup are implementation-defined. Any library facilities available to a freestanding
+ program, other than the minimal set required by clause 4, are implementation-defined.
+2 The effect of program termination in a freestanding environment is implementation-
+ defined.
+ 5.1.2.2 Hosted environment
+1 A hosted environment need not be provided, but shall conform to the following
+ specifications if present.
+
+
+
+
+ 9) The intent is that an implementation should identify the nature of, and where possible localize, each
+ violation. Of course, an implementation is free to produce any number of diagnostics as long as a
+ valid program is still correctly translated. It may also successfully translate an invalid program.
+
+[page 12]
+
+ 5.1.2.2.1 Program startup
+1 The function called at program startup is named main. The implementation declares no
+ prototype for this function. It shall be defined with a return type of int and with no
+ parameters:
+ int main(void) { /* ... */ }
+ or with two parameters (referred to here as argc and argv, though any names may be
+ used, as they are local to the function in which they are declared):
+ int main(int argc, char *argv[]) { /* ... */ }
+ or equivalent;10) or in some other implementation-defined manner.
+2 If they are declared, the parameters to the main function shall obey the following
+ constraints:
+ -- The value of argc shall be nonnegative.
+ -- argv[argc] shall be a null pointer.
+ -- If the value of argc is greater than zero, the array members argv[0] through
+ argv[argc-1] inclusive shall contain pointers to strings, which are given
+ implementation-defined values by the host environment prior to program startup. The
+ intent is to supply to the program information determined prior to program startup
+ from elsewhere in the hosted environment. If the host environment is not capable of
+ supplying strings with letters in both uppercase and lowercase, the implementation
+ shall ensure that the strings are received in lowercase.
+ -- If the value of argc is greater than zero, the string pointed to by argv[0]
+ represents the program name; argv[0][0] shall be the null character if the
+ program name is not available from the host environment. If the value of argc is
+ greater than one, the strings pointed to by argv[1] through argv[argc-1]
+ represent the program parameters.
+ -- The parameters argc and argv and the strings pointed to by the argv array shall
+ be modifiable by the program, and retain their last-stored values between program
+ startup and program termination.
+ 5.1.2.2.2 Program execution
+1 In a hosted environment, a program may use all the functions, macros, type definitions,
+ and objects described in the library clause (clause 7).
+
+
+
+
+ 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
+ char ** argv, and so on.
+
+[page 13]
+
+ 5.1.2.2.3 Program termination
+1 If the return type of the main function is a type compatible with int, a return from the
+ initial call to the main function is equivalent to calling the exit function with the value
+ returned by the main function as its argument;11) reaching the } that terminates the
+ main function returns a value of 0. If the return type is not compatible with int, the
+ termination status returned to the host environment is unspecified.
+ Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).
+ 5.1.2.3 Program execution
+1 The semantic descriptions in this International Standard describe the behavior of an
+ abstract machine in which issues of optimization are irrelevant.
+2 Accessing a volatile object, modifying an object, modifying a file, or calling a function
+ that does any of those operations are all side effects,12) which are changes in the state of
+ the execution environment. Evaluation of an expression in general includes both value
+ computations and initiation of side effects. Value computation for an lvalue expression
+ includes determining the identity of the designated object.
+3 Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
+ executed by a single thread, which induces a partial order among those evaluations.
+ Given any two evaluations A and B, if A is sequenced before B, then the execution of A
+ shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
+ sequenced after A.) If A is not sequenced before or after B, then A and B are
+ unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced
+ either before or after B, but it is unspecified which.13) The presence of a sequence point
+ between the evaluation of expressions A and B implies that every value computation and
+ side effect associated with A is sequenced before every value computation and side effect
+ associated with B. (A summary of the sequence points is given in annex C.)
+4 In the abstract machine, all expressions are evaluated as specified by the semantics. An
+ actual implementation need not evaluate part of an expression if it can deduce that its
+ value is not used and that no needed side effects are produced (including any caused by
+
+ 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
+ will have ended in the former case, even where they would not have in the latter.
+ 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
+ flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
+ values of floating-point operations. Implementations that support such floating-point state are
+ required to regard changes to it as side effects -- see annex F for details. The floating-point
+ environment library <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.
+
+[page 14]
+
+ calling a function or accessing a volatile object).
+5 When the processing of the abstract machine is interrupted by receipt of a signal, the
+ values of objects that are neither lock-free atomic objects nor of type volatile
+ sig_atomic_t are unspecified, as is the state of the floating-point environment. The
+ value of any object modified by the handler that is neither a lock-free atomic object nor of
+ type volatile sig_atomic_t becomes indeterminate when the handler exits, as
+ does the state of the floating-point environment if it is modified by the handler and not
+ restored to its original state.
+6 The least requirements on a conforming implementation are:
+ -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract
+ machine.
+ -- At program termination, all data written into files shall be identical to the result that
+ execution of the program according to the abstract semantics would have produced.
+ -- The input and output dynamics of interactive devices shall take place as specified in
+ 7.21.3. The intent of these requirements is that unbuffered or line-buffered output
+ appear as soon as possible, to ensure that prompting messages actually appear prior to
+ a program waiting for input.
+ This is the observable behavior of the program.
+7 What constitutes an interactive device is implementation-defined.
+8 More stringent correspondences between abstract and actual semantics may be defined by
+ each implementation.
+9 EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
+ semantics: at every sequence point, the values of the actual objects would agree with those specified by the
+ abstract semantics. The keyword volatile would then be redundant.
+10 Alternatively, an implementation might perform various optimizations within each translation unit, such
+ that the actual semantics would agree with the abstract semantics only when making function calls across
+ translation unit boundaries. In such an implementation, at the time of each function entry and function
+ return where the calling function and the called function are in different translation units, the values of all
+ externally linked objects and of all objects accessible via pointers therein would agree with the abstract
+ semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
+ function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
+ type of implementation, objects referred to by interrupt service routines activated by the signal function
+ would require explicit specification of volatile storage, as well as other implementation-defined
+ restrictions.
+
+11 EXAMPLE 2 In executing the fragment
+ char c1, c2;
+ /* ... */
+ c1 = c1 + c2;
+ the ''integer promotions'' require that the abstract machine promote the value of each variable to int size
+ and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
+
+[page 15]
+
+ overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
+ produce the same result, possibly omitting the promotions.
+
+12 EXAMPLE 3 Similarly, in the fragment
+ float f1, f2;
+ double d;
+ /* ... */
+ f1 = f2 * d;
+ the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
+ that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
+ were replaced by the constant 2.0, which has type double).
+
+13 EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
+ semantics. Values are independent of whether they are represented in a register or in memory. For
+ example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
+ is required to round to the precision of the storage type. In particular, casts and assignments are required to
+ perform their specified conversion. For the fragment
+ double d1, d2;
+ float f;
+ d1 = f = expression;
+ d2 = (float) expression;
+ the values assigned to d1 and d2 are required to have been converted to float.
+
+14 EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
+ precision as well as range. The implementation cannot generally apply the mathematical associative rules
+ for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
+ overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
+ rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
+ numbers are often not valid (see F.9).
+ double x, y, z;
+ /* ... */
+ x = (x * y) * z; // not equivalent to x *= y * z;
+ z = (x - y) + y ; // not equivalent to z = x;
+ z = x + x * y; // not equivalent to z = x * (1.0 + y);
+ y = x / 5.0; // not equivalent to y = x * 0.2;
+
+15 EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment
+ int a, b;
+ /* ... */
+ a = a + 32760 + b + 5;
+ the expression statement behaves exactly the same as
+ a = (((a + 32760) + b) + 5);
+ due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
+ next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
+ which overflows produce an explicit trap and in which the range of values representable by an int is
+ [-32768, +32767], the implementation cannot rewrite this expression as
+ a = ((a + b) + 32765);
+ since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap
+
+[page 16]
+
+ 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.
+
+16 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), floating-
+ point environment <fenv.h> (7.6), the signal function (7.14), files (7.21.3).
+ 5.1.2.4 Multi-threaded executions and data races
+1 Under a hosted implementation, a program can have more than one thread of execution
+ (or thread) running concurrently. The execution of each thread proceeds as defined by
+ the remainder of this standard. The execution of the entire program consists of an
+ execution of all of its threads.14) Under a freestanding implementation, it is
+ implementation-defined whether a program can have more than one thread of execution.
+2 The value of an object visible to a thread T at a particular point is the initial value of the
+ object, a value stored in the object by T , or a value stored in the object by another thread,
+ according to the rules below.
+3 NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
+ the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
+ implicitly supports a simpler view for more restricted programs.
+
+4 Two expression evaluations conflict if one of them modifies a memory location and the
+ other one reads or modifies the same memory location.
+
+
+ 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
+ atomic operations, for example, allow executions inconsistent with a simple interleaving as described
+ below.
+
+[page 17]
+
+5 The library defines a number of atomic operations (7.17) and operations on mutexes
+ (7.26.4) that are specially identified as synchronization operations. These operations play
+ a special role in making assignments in one thread visible to another. A synchronization
+ operation on one or more memory locations is either an acquire operation, a release
+ operation, both an acquire and release operation, or a consume operation. A
+ synchronization operation without an associated memory location is a fence and can be
+ either an acquire fence, a release fence, or both an acquire and release fence. In addition,
+ there are relaxed atomic operations, which are not synchronization operations, and
+ atomic read-modify-write operations, which have special characteristics.
+6 NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
+ composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
+ operation on those same locations. Informally, performing a release operation on A forces prior side effects
+ on other memory locations to become visible to other threads that later perform an acquire or consume
+ operation on A. We do not include relaxed atomic operations as synchronization operations although, like
+ synchronization operations, they cannot contribute to data races.
+
+7 All modifications to a particular atomic object M occur in some particular total order,
+ called the modification order of M. If A and B are modifications of an atomic object M,
+ and A happens before B, then A shall precede B in the modification order of M, which is
+ defined below.
+8 NOTE 3 This states that the modification orders must respect the ''happens before'' relation.
+
+9 NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
+ combined into a single total order for all objects. In general this will be impossible since different threads
+ may observe modifications to different variables in inconsistent orders.
+
+10 A release sequence headed by a release operation A 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 and every subsequent operation either is performed by the same thread that
+ performed the release or is an atomic read-modify-write operation.
+11 Certain library calls synchronize with other library calls performed by another thread. In
+ particular, an atomic operation A that performs a release operation on an object M
+ synchronizes with an atomic operation B that performs an acquire operation on M and
+ reads a value written by any side effect in the release sequence headed by A.
+12 NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
+ described below. Such a requirement would sometimes interfere with efficient implementation.
+
+13 NOTE 6 The specifications of the synchronization operations define when one reads the value written by
+ another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
+ order. Each mutex acquisition ''reads the value written'' by the last mutex release.
+
+14 An evaluation A carries a dependency 15) to an evaluation B if:
+
+
+ 15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly
+ strictly intra-thread.
+
+[page 18]
+
+ -- the value of A is used as an operand of B, unless:
+ o B is an invocation of the kill_dependency macro,
+
+ o A is the left operand of a && or || operator,
+
+ o A is the left operand of a ? : operator, or
+
+ o A is the left operand of a , operator;
+ or
+ -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A
+ is sequenced before B, or
+ -- for some evaluation X, A carries a dependency to X and X carries a dependency to B.
+15 An evaluation A is dependency-ordered before16) an evaluation B if:
+ -- A performs a release operation on an atomic object M, and, in another thread, B
+ performs a consume operation on M and reads a value written by any side effect in
+ the release sequence headed by A, or
+ -- for some evaluation X, A is dependency-ordered before X and X carries a
+ dependency to B.
+16 An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
+ is dependency-ordered before B, or, for some evaluation X:
+ -- A synchronizes with X and X is sequenced before B,
+ -- A is sequenced before X and X inter-thread happens before B, or
+ -- A inter-thread happens before X and X inter-thread happens before B.
+17 NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced
+ before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The
+ first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed
+ by ''sequenced before''. The reason for this limitation is that a consume operation participating in a
+ ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this
+ consume operation actually carries a dependency. The reason that this limitation applies only to the end of
+ such a concatenation is that any subsequent release operation will provide the required ordering for a prior
+ consume operation. The second exception is that a concatenation is not permitted to consist entirely of
+ ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be
+ transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships
+ consisting entirely of ''sequenced before''.
+
+18 An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
+ thread happens before B.
+
+
+
+ 16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses
+ release/consume in place of release/acquire.
+
+[page 19]
+
+19 A visible side effect A on an object M with respect to a value computation B of M
+ satisfies the conditions:
+ -- A happens before B, and
+ -- there is no other side effect X to M such that A happens before X and X happens
+ before B.
+ The value of a non-atomic scalar object M, as determined by evaluation B, shall be the
+ value stored by the visible side effect A.
+20 NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
+ race and the behavior is undefined.
+
+21 NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
+ detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
+ restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
+ execution.
+
+22 The visible sequence of side effects on an atomic object M, with respect to a value
+ computation B of M, is a maximal contiguous sub-sequence of side effects in the
+ modification order of M, where the first side effect is visible with respect to B, and for
+ every subsequent side effect, it is not the case that B happens before it. The value of an
+ atomic object M, as determined by evaluation B, shall be the value stored by some
+ operation in the visible sequence of M with respect to B. Furthermore, if a value
+ computation A of an atomic object M happens before a value computation B of M, and
+ the value computed by A corresponds to the value stored by side effect X, then the value
+ computed by B shall either equal the value computed by A, or be the value stored by side
+ effect Y , where Y follows X in the modification order of M.
+23 NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
+ both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee
+ provided by most hardware available to C atomic operations.
+
+24 NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the
+ values observed by loads of atomics, which we are restricting here. The intended reading is that there must
+ exist an association of atomic loads with modifications they observe that, together with suitably chosen
+ modification orders and the ''happens before'' relation derived as described above, satisfy the resulting
+ constraints as imposed here.
+
+25 The execution of a program contains a data race if it contains two conflicting actions in
+ different threads, at least one of which is not atomic, and neither happens before the
+ other. Any such data race results in undefined behavior.
+26 NOTE 12 It can be shown that programs that correctly use simple mutexes and
+ memory_order_seq_cst operations to prevent all data races, and use no other synchronization
+ operations, behave as though the operations executed by their constituent threads were simply interleaved,
+ with each value computation of an object being the last value stored in that interleaving. This is normally
+ referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data-
+ race-free programs cannot observe most program transformations that do not change single-threaded
+ program semantics. In fact, most single-threaded program transformations continue to be allowed, since
+ any program that behaves differently as a result must contain undefined behavior.
+
+[page 20]
+
+27 NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
+ that would not be modified by the abstract machine are generally precluded by this standard, since such an
+ assignment might overwrite another assignment by a different thread in cases in which an abstract machine
+ execution would not have encountered a data race. This includes implementations of data member
+ assignment that overwrite adjacent members in separate memory locations. We also generally preclude
+ reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
+ "visible sequence" rules.
+
+28 NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
+ not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
+ race. However, they are typically valid in the context of an optimizing compiler that targets a specific
+ machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
+ is not tolerant of races or provides hardware race detection.
+
+[page 21]
+
+ 5.2 Environmental considerations
+ 5.2.1 Character sets
+1 Two sets of characters and their associated collating sequences shall be defined: the set in
+ which source files are written (the source character set), and the set interpreted in the
+ execution environment (the execution character set). Each set is further divided into a
+ basic character set, whose contents are given by this subclause, and a set of zero or more
+ locale-specific members (which are not members of the basic character set) called
+ extended characters. The combined set is also called the extended character set. The
+ values of the members of the execution character set are implementation-defined.
+2 In a character constant or string literal, members of the execution character set shall be
+ represented by corresponding members of the source character set or by escape
+ sequences consisting of the backslash \ followed by one or more characters. A byte with
+ all bits set to 0, called the null character, shall exist in the basic execution character set; it
+ is used to terminate a character string.
+3 Both the basic source and basic execution character sets shall have the following
+ members: the 26 uppercase letters of the Latin alphabet
+ A B C D E F G H I J K L M
+ N O P Q R S T U V W X Y Z
+ the 26 lowercase letters of the Latin alphabet
+ a b c d e f g h i j k l m
+ n o p q r s t u v w x y z
+ the 10 decimal digits
+ 0 1 2 3 4 5 6 7 8 9
+ the following 29 graphic characters
+ ! " # % & ' ( ) * + , - . / :
+ ; < = > ? [ \ ] ^ _ { | } ~
+ the space character, and control characters representing horizontal tab, vertical tab, and
+ form feed. The representation of each member of the source and execution basic
+ character sets shall fit in a byte. In both the source and execution basic character sets, the
+ value of each character after 0 in the above list of decimal digits shall be one greater than
+ the value of the previous. In source files, there shall be some way of indicating the end of
+ each line of text; this International Standard treats such an end-of-line indicator as if it
+ were a single new-line character. In the basic execution character set, there shall be
+ control characters representing alert, backspace, carriage return, and new line. If any
+ other characters are encountered in a source file (except in an identifier, a character
+ constant, a string literal, a header name, a comment, or a preprocessing token that is never
+
+[page 22]
+
+ converted to a token), the behavior is undefined.
+4 A letter is an uppercase letter or a lowercase letter as defined above; in this International
+ Standard the term does not include other characters that are letters in other alphabets.
+5 The universal character name construct provides a way to name other characters.
+ Forward references: universal character names (6.4.3), character constants (6.4.4.4),
+ preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
+ 5.2.1.1 Trigraph sequences
+1 Before any other processing takes place, each occurrence of one of the following
+ sequences of three characters (called trigraph sequences17)) is replaced with the
+ corresponding single character.
+ ??= # ??) ] ??! |
+ ??( [ ??' ^ ??> }
+ ??/ \ ??< { ??- ~
+ No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
+ above is not changed.
+2 EXAMPLE 1
+ ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
+ becomes
+ #define arraycheck(a, b) a[b] || b[a]
+
+3 EXAMPLE 2 The following source line
+ printf("Eh???/n");
+ becomes (after replacement of the trigraph sequence ??/)
+ printf("Eh?\n");
+
+ 5.2.1.2 Multibyte characters
+1 The source character set may contain multibyte characters, used to represent members of
+ the extended character set. The execution character set may also contain multibyte
+ characters, which need not have the same encoding as for the source character set. For
+ both character sets, the following shall hold:
+ -- The basic character set shall be present and each character shall be encoded as a
+ single byte.
+ -- The presence, meaning, and representation of any additional members is locale-
+ specific.
+
+ 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
+ described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.
+
+[page 23]
+
+ -- A multibyte character set may have a state-dependent encoding, wherein each
+ sequence of multibyte characters begins in an initial shift state and enters other
+ locale-specific shift states when specific multibyte characters are encountered in the
+ sequence. While in the initial shift state, all single-byte characters retain their usual
+ interpretation and do not alter the shift state. The interpretation for subsequent bytes
+ in the sequence is a function of the current shift state.
+ -- A byte with all bits zero shall be interpreted as a null character independent of shift
+ state. Such a byte shall not occur as part of any other multibyte character.
+2 For source files, the following shall hold:
+ -- An identifier, comment, string literal, character constant, or header name shall begin
+ and end in the initial shift state.
+ -- An identifier, comment, string literal, character constant, or header name shall consist
+ of a sequence of valid multibyte characters.
+ 5.2.2 Character display semantics
+1 The active position is that location on a display device where the next character output by
+ the fputc function would appear. The intent of writing a printing character (as defined
+ by the isprint function) to a display device is to display a graphic representation of
+ that character at the active position and then advance the active position to the next
+ position on the current line. The direction of writing is locale-specific. If the active
+ position is at the final position of a line (if there is one), the behavior of the display device
+ is unspecified.
+2 Alphabetic escape sequences representing nongraphic characters in the execution
+ character set are intended to produce actions on display devices as follows:
+ \a (alert) Produces an audible or visible alert without changing the active position.
+ \b (backspace) Moves the active position to the previous position on the current line. If
+ the active position is at the initial position of a line, the behavior of the display
+ device is unspecified.
+ \f ( form feed) Moves the active position to the initial position at the start of the next
+ logical page.
+ \n (new line) Moves the active position to the initial position of the next line.
+ \r (carriage return) Moves the active position to the initial position of the current line.
+ \t (horizontal tab) Moves the active position to the next horizontal tabulation position
+ on the current line. If the active position is at or past the last defined horizontal
+ tabulation position, the behavior of the display device is unspecified.
+ \v (vertical tab) Moves the active position to the initial position of the next vertical
+ tabulation position. If the active position is at or past the last defined vertical
+
+[page 24]
+
+ tabulation position, the behavior of the display device is unspecified.
+3 Each of these escape sequences shall produce a unique implementation-defined value
+ which can be stored in a single char object. The external representations in a text file
+ need not be identical to the internal representations, and are outside the scope of this
+ International Standard.
+ Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).
+ 5.2.3 Signals and interrupts
+1 Functions shall be implemented such that they may be interrupted at any time by a signal,
+ or may be called by a signal handler, or both, with no alteration to earlier, but still active,
+ invocations' control flow (after the interruption), function return values, or objects with
+ automatic storage duration. All such objects shall be maintained outside the function
+ image (the instructions that compose the executable representation of a function) on a
+ per-invocation basis.
+ 5.2.4 Environmental limits
+1 Both the translation and execution environments constrain the implementation of
+ language translators and libraries. The following summarizes the language-related
+ environmental limits on a conforming implementation; the library-related limits are
+ discussed in clause 7.
+ 5.2.4.1 Translation limits
+1 The implementation shall be able to translate and execute at least one program that
+ contains at least one instance of every one of the following limits:18)
+ -- 127 nesting levels of blocks
+ -- 63 nesting levels of conditional inclusion
+ -- 12 pointer, array, and function declarators (in any combinations) modifying an
+ arithmetic, structure, union, or void type in a declaration
+ -- 63 nesting levels of parenthesized declarators within a full declarator
+ -- 63 nesting levels of parenthesized expressions within a full expression
+ -- 63 significant initial characters in an internal identifier or a macro name (each
+ universal character name or extended source character is considered a single
+ character)
+ -- 31 significant initial characters in an external identifier (each universal character name
+ specifying a short identifier of 0000FFFF or less is considered 6 characters, each
+
+
+ 18) Implementations should avoid imposing fixed translation limits whenever possible.
+
+[page 25]
+
+ universal character name specifying a short identifier of 00010000 or more is
+ considered 10 characters, and each extended source character is considered the same
+ number of characters as the corresponding universal character name, if any)19)
+ -- 4095 external identifiers in one translation unit
+ -- 511 identifiers with block scope declared in one block
+ -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
+ -- 127 parameters in one function definition
+ -- 127 arguments in one function call
+ -- 127 parameters in one macro definition
+ -- 127 arguments in one macro invocation
+ -- 4095 characters in a logical source line
+ -- 4095 characters in a string literal (after concatenation)
+ -- 65535 bytes in an object (in a hosted environment only)
+ -- 15 nesting levels for #included files
+ -- 1023 case labels for a switch statement (excluding those for any nested switch
+ statements)
+ -- 1023 members in a single structure or union
+ -- 1023 enumeration constants in a single enumeration
+ -- 63 levels of nested structure or union definitions in a single struct-declaration-list
+ 5.2.4.2 Numerical limits
+1 An implementation is required to document all the limits specified in this subclause,
+ which are specified in the headers <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>
+1 The values given below shall be replaced by constant expressions suitable for use in #if
+ preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
+ following shall be replaced by expressions that have the same type as would an
+ expression that is an object of the corresponding type converted according to the integer
+ promotions. Their implementation-defined values shall be equal or greater in magnitude
+
+
+ 19) See ''future language directions'' (6.11.3).
+
+[page 26]
+
+(absolute value) to those shown, with the same sign.
+-- number of bits for smallest object that is not a bit-field (byte)
+ CHAR_BIT 8
+-- minimum value for an object of type signed char
+ SCHAR_MIN -127 // -(27 - 1)
+-- maximum value for an object of type signed char
+ SCHAR_MAX +127 // 27 - 1
+-- maximum value for an object of type unsigned char
+ UCHAR_MAX 255 // 28 - 1
+-- minimum value for an object of type char
+ CHAR_MIN see below
+-- maximum value for an object of type char
+ CHAR_MAX see below
+-- maximum number of bytes in a multibyte character, for any supported locale
+ MB_LEN_MAX 1
+-- minimum value for an object of type short int
+ SHRT_MIN -32767 // -(215 - 1)
+-- maximum value for an object of type short int
+ SHRT_MAX +32767 // 215 - 1
+-- maximum value for an object of type unsigned short int
+ USHRT_MAX 65535 // 216 - 1
+-- minimum value for an object of type int
+ INT_MIN -32767 // -(215 - 1)
+-- maximum value for an object of type int
+ INT_MAX +32767 // 215 - 1
+-- maximum value for an object of type unsigned int
+ UINT_MAX 65535 // 216 - 1
+-- minimum value for an object of type long int
+ LONG_MIN -2147483647 // -(231 - 1)
+-- maximum value for an object of type long int
+ LONG_MAX +2147483647 // 231 - 1
+-- maximum value for an object of type unsigned long int
+ ULONG_MAX 4294967295 // 232 - 1
+
+[page 27]
+
+ -- minimum value for an object of type long long int
+ LLONG_MIN -9223372036854775807 // -(263 - 1)
+ -- maximum value for an object of type long long int
+ LLONG_MAX +9223372036854775807 // 263 - 1
+ -- maximum value for an object of type unsigned long long int
+ ULLONG_MAX 18446744073709551615 // 264 - 1
+2 If the value of an object of type char is treated as a signed integer when used in an
+ expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
+ value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
+ CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
+ UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1.
+ Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).
+ 5.2.4.2.2 Characteristics of floating types <float.h>
+1 The characteristics of floating types are defined in terms of a model that describes a
+ representation of floating-point numbers and values that provide information about an
+ implementation's floating-point arithmetic.21) The following parameters are used to
+ define the model for each floating-point type:
+ s sign ((+-)1)
+ b base or radix of exponent representation (an integer > 1)
+ e exponent (an integer between a minimum emin and a maximum emax )
+ p precision (the number of base-b digits in the significand)
+ fk nonnegative integers less than b (the significand digits)
+2 A floating-point number (x) is defined by the following model:
+ p
+ x = sb e (Sum) f k b-k ,
+ k=1
+ emin <= e <= emax
+
+3 In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be
+ able to contain other kinds of floating-point numbers, such as subnormal floating-point
+ numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0,
+ e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
+ NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
+ through almost every arithmetic operation without raising a floating-point exception; a
+ signaling NaN generally raises a floating-point exception when occurring as an
+
+
+ 20) See 6.2.5.
+ 21) The floating-point model is intended to clarify the description of each floating-point characteristic and
+ does not require the floating-point arithmetic of the implementation to be identical.
+
+[page 28]
+
+ arithmetic operand.22)
+4 An implementation may give zero and values that are not floating-point numbers (such as
+ infinities and NaNs) a sign or may leave them unsigned. Wherever such values are
+ unsigned, any requirement in this International Standard to retrieve the sign shall produce
+ an unspecified sign, and any requirement to set the sign shall be ignored.
+5 The minimum range of representable values for a floating type is the most negative finite
+ floating-point number representable in that type through the most positive finite floating-
+ point number representable in that type. In addition, if negative infinity is representable
+ in a type, the range of that type is extended to all negative real numbers; likewise, if
+ positive infinity is representable in a type, the range of that type is extended to all positive
+ real numbers.
+6 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
+ <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.
+7 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.
+8 The rounding mode for floating-point addition is characterized by the implementation-
+ defined value of FLT_ROUNDS:23)
+ -1 indeterminable
+ 0 toward zero
+ 1 to nearest
+ 2 toward positive infinity
+ 3 toward negative infinity
+ All other values for FLT_ROUNDS characterize implementation-defined rounding
+ behavior.
+
+
+ 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
+ IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
+ similar behavior.
+ 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
+ the function fesetround in <fenv.h>.
+
+[page 29]
+
+9 Except for assignment and cast (which remove all extra range and precision), the values
+ yielded by operators with floating operands and values subject to the usual arithmetic
+ conversions and of floating constants are evaluated to a format whose range and precision
+ may be greater than required by the type. The use of evaluation formats is characterized
+ by the implementation-defined value of FLT_EVAL_METHOD:24)
+ -1 indeterminable;
+ 0 evaluate all operations and constants just to the range and precision of the
+ type;
+ 1 evaluate operations and constants of type float and double to the
+ range and precision of the double type, evaluate long double
+ operations and constants to the range and precision of the long double
+ type;
+ 2 evaluate all operations and constants to the range and precision of the
+ long double type.
+ All other negative values for FLT_EVAL_METHOD characterize implementation-defined
+ behavior.
+10 The presence or absence of subnormal numbers is characterized by the implementation-
+ defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and
+ LDBL_HAS_SUBNORM:
+ -1 indeterminable25)
+ 0 absent26) (type does not support subnormal numbers)
+ 1 present (type does support subnormal numbers)
+11 The values given in the following list shall be replaced by constant expressions with
+ implementation-defined values that are greater or equal in magnitude (absolute value) to
+ those shown, with the same sign:
+ -- radix of exponent representation, b
+ FLT_RADIX 2
+
+
+
+
+ 24) The evaluation method determines evaluation formats of expressions involving all floating types, not
+ just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
+ _Complex operands is represented in the double _Complex format, and its parts are evaluated to
+ double.
+ 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
+ subnormal representations as zero, nor as nonzero.
+ 26) Characterization as absent is intended if no floating-point operations produce subnormal results from
+ non-subnormal inputs, even if the type format includes representations of subnormal numbers.
+
+[page 30]
+
+-- number of base-FLT_RADIX digits in the floating-point significand, p
+ FLT_MANT_DIG
+ DBL_MANT_DIG
+ LDBL_MANT_DIG
+-- number of decimal digits, n, such that any floating-point number with p radix b digits
+ can be rounded to a floating-point number with n decimal digits and back again
+ without change to the value,
+ { p log10 b if b is a power of 10
+ {
+ { [^1 + p log10 b^] otherwise
+ FLT_DECIMAL_DIG 6
+ DBL_DECIMAL_DIG 10
+ LDBL_DECIMAL_DIG 10
+-- number of decimal digits, n, such that any floating-point number in the widest
+ supported floating type with pmax radix b digits can be rounded to a floating-point
+ number with n decimal digits and back again without change to the value,
+ { pmax log10 b if b is a power of 10
+ {
+ { [^1 + pmax log10 b^] otherwise
+ DECIMAL_DIG 10
+-- number of decimal digits, q, such that any floating-point number with q decimal digits
+ can be rounded into a floating-point number with p radix b digits and back again
+ without change to the q decimal digits,
+ { p log10 b if b is a power of 10
+ {
+ { [_( p - 1) log10 b_] otherwise
+ FLT_DIG 6
+ DBL_DIG 10
+ LDBL_DIG 10
+-- minimum negative integer such that FLT_RADIX raised to one less than that power is
+ a normalized floating-point number, emin
+ FLT_MIN_EXP
+ DBL_MIN_EXP
+ LDBL_MIN_EXP
+
+[page 31]
+
+ -- minimum negative integer such that 10 raised to that power is in the range of
+ normalized floating-point numbers, [^log10 b emin -1 ^]
+ [ ]
+ FLT_MIN_10_EXP -37
+ DBL_MIN_10_EXP -37
+ LDBL_MIN_10_EXP -37
+ -- maximum integer such that FLT_RADIX raised to one less than that power is a
+ representable finite floating-point number, emax
+ FLT_MAX_EXP
+ DBL_MAX_EXP
+ LDBL_MAX_EXP
+ -- maximum integer such that 10 raised to that power is in the range of representable
+ finite floating-point numbers, [_log10 ((1 - b- p )b emax )_]
+ FLT_MAX_10_EXP +37
+ DBL_MAX_10_EXP +37
+ LDBL_MAX_10_EXP +37
+12 The values given in the following list shall be replaced by constant expressions with
+ implementation-defined values that are greater than or equal to those shown:
+ -- maximum representable finite floating-point number, (1 - b- p )b emax
+ FLT_MAX 1E+37
+ DBL_MAX 1E+37
+ LDBL_MAX 1E+37
+13 The values given in the following list shall be replaced by constant expressions with
+ implementation-defined (positive) values that are less than or equal to those shown:
+ -- the difference between 1 and the least value greater than 1 that is representable in the
+ given floating point type, b1- p
+ FLT_EPSILON 1E-5
+ DBL_EPSILON 1E-9
+ LDBL_EPSILON 1E-9
+ -- minimum normalized positive floating-point number, b emin -1
+ FLT_MIN 1E-37
+ DBL_MIN 1E-37
+ LDBL_MIN 1E-37
+
+[page 32]
+
+ -- minimum positive floating-point number27)
+ FLT_TRUE_MIN 1E-37
+ DBL_TRUE_MIN 1E-37
+ LDBL_TRUE_MIN 1E-37
+ Recommended practice
+14 Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
+ should be the identity function.
+15 EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
+ requirements of this International Standard, and the appropriate values in a <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
+
+16 EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
+ single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a
+ <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
+
+
+ 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
+ positive number no greater than the minimum normalized positive number for the type.
+ 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
+ limits are one less than shown here.
+
+[page 33]
+
+ FLT_DIG 6
+ FLT_MIN_EXP -125
+ FLT_MIN 1.17549435E-38F // decimal constant
+ FLT_MIN 0X1P-126F // hex constant
+ FLT_TRUE_MIN 1.40129846E-45F // decimal constant
+ FLT_TRUE_MIN 0X1P-149F // hex constant
+ FLT_HAS_SUBNORM 1
+ FLT_MIN_10_EXP -37
+ FLT_MAX_EXP +128
+ FLT_MAX 3.40282347E+38F // decimal constant
+ FLT_MAX 0X1.fffffeP127F // hex constant
+ FLT_MAX_10_EXP +38
+ DBL_MANT_DIG 53
+ DBL_EPSILON 2.2204460492503131E-16 // decimal constant
+ DBL_EPSILON 0X1P-52 // hex constant
+ DBL_DECIMAL_DIG 17
+ DBL_DIG 15
+ DBL_MIN_EXP -1021
+ DBL_MIN 2.2250738585072014E-308 // decimal constant
+ DBL_MIN 0X1P-1022 // hex constant
+ DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant
+ DBL_TRUE_MIN 0X1P-1074 // hex constant
+ DBL_HAS_SUBNORM 1
+ DBL_MIN_10_EXP -307
+ DBL_MAX_EXP +1024
+ DBL_MAX 1.7976931348623157E+308 // decimal constant
+ DBL_MAX 0X1.fffffffffffffP1023 // hex constant
+ DBL_MAX_10_EXP +308
+If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
+example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
+precision), then DECIMAL_DIG would be 21.
+
+Forward references: conditional inclusion (6.10.1), complex arithmetic
+<complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
+(7.29), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
+(7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).
+
+[page 34]
+
+
+ 6. Language
+ 6.1 Notation
+1 In the syntax notation used in this clause, syntactic categories (nonterminals) are
+ indicated by italic type, and literal words and character set members (terminals) by bold
+ type. A colon (:) following a nonterminal introduces its definition. Alternative
+ definitions are listed on separate lines, except when prefaced by the words ''one of''. An
+ optional symbol is indicated by the subscript ''opt'', so that
+ { expressionopt }
+ indicates an optional expression enclosed in braces.
+2 When syntactic categories are referred to in the main text, they are not italicized and
+ words are separated by spaces instead of hyphens.
+3 A summary of the language syntax is given in annex A.
+ 6.2 Concepts
+ 6.2.1 Scopes of identifiers
+1 An identifier can denote an object; a function; a tag or a member of a structure, union, or
+ enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
+ same identifier can denote different entities at different points in the program. A member
+ of an enumeration is called an enumeration constant. Macro names and macro
+ parameters are not considered further here, because prior to the semantic phase of
+ program translation any occurrences of macro names in the source file are replaced by the
+ preprocessing token sequences that constitute their macro definitions.
+2 For each different entity that an identifier designates, the identifier is visible (i.e., can be
+ used) only within a region of program text called its scope. Different entities designated
+ by the same identifier either have different scopes, or are in different name spaces. There
+ are four kinds of scopes: function, file, block, and function prototype. (A function
+ prototype is a declaration of a function that declares the types of its parameters.)
+3 A label name is the only kind of identifier that has function scope. It can be used (in a
+ goto statement) anywhere in the function in which it appears, and is declared implicitly
+ by its syntactic appearance (followed by a : and a statement).
+4 Every other identifier has scope determined by the placement of its declaration (in a
+ declarator or type specifier). If the declarator or type specifier that declares the identifier
+ appears outside of any block or list of parameters, the identifier has file scope, which
+ terminates at the end of the translation unit. If the declarator or type specifier that
+ declares the identifier appears inside a block or within the list of parameter declarations in
+ a function definition, the identifier has block scope, which terminates at the end of the
+ associated block. If the declarator or type specifier that declares the identifier appears
+
+[page 35]
+
+ within the list of parameter declarations in a function prototype (not part of a function
+ definition), the identifier has function prototype scope, which terminates at the end of the
+ function declarator. If an identifier designates two different entities in the same name
+ space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
+ strictly before the scope of the other entity (the outer scope). Within the inner scope, the
+ identifier designates the entity declared in the inner scope; the entity declared in the outer
+ scope is hidden (and not visible) within the inner scope.
+5 Unless explicitly stated otherwise, where this International Standard uses the term
+ ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the
+ entity in the relevant name space whose declaration is visible at the point the identifier
+ occurs.
+6 Two identifiers have the same scope if and only if their scopes terminate at the same
+ point.
+7 Structure, union, and enumeration tags have scope that begins just after the appearance of
+ the tag in a type specifier that declares the tag. Each enumeration constant has scope that
+ begins just after the appearance of its defining enumerator in an enumerator list. Any
+ other identifier has scope that begins just after the completion of its declarator.
+8 As a special case, a type name (which is not a declaration of an identifier) is considered to
+ have a scope that begins just after the place within the type name where the omitted
+ identifier would appear were it not omitted.
+ Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
+ (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
+ source file inclusion (6.10.2), statements (6.8).
+ 6.2.2 Linkages of identifiers
+1 An identifier declared in different scopes or in the same scope more than once can be
+ made to refer to the same object or function by a process called linkage.29) There are
+ three kinds of linkage: external, internal, and none.
+2 In the set of translation units and libraries that constitutes an entire program, each
+ declaration of a particular identifier with external linkage denotes the same object or
+ function. Within one translation unit, each declaration of an identifier with internal
+ linkage denotes the same object or function. Each declaration of an identifier with no
+ linkage denotes a unique entity.
+3 If the declaration of a file scope identifier for an object or a function contains the storage-
+ class specifier static, the identifier has internal linkage.30)
+
+
+
+ 29) There is no linkage between different identifiers.
+
+[page 36]
+
+4 For an identifier declared with the storage-class specifier extern in a scope in which a
+ prior declaration of that identifier is visible,31) if the prior declaration specifies internal or
+ external linkage, the linkage of the identifier at the later declaration is the same as the
+ linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
+ declaration specifies no linkage, then the identifier has external linkage.
+5 If the declaration of an identifier for a function has no storage-class specifier, its linkage
+ is determined exactly as if it were declared with the storage-class specifier extern. If
+ the declaration of an identifier for an object has file scope and no storage-class specifier,
+ its linkage is external.
+6 The following identifiers have no linkage: an identifier declared to be anything other than
+ an object or a function; an identifier declared to be a function parameter; a block scope
+ identifier for an object declared without the storage-class specifier extern.
+7 If, within a translation unit, the same identifier appears with both internal and external
+ linkage, the behavior is undefined.
+ Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
+ statements (6.8).
+ 6.2.3 Name spaces of identifiers
+1 If more than one declaration of a particular identifier is visible at any point in a
+ translation unit, the syntactic context disambiguates uses that refer to different entities.
+ Thus, there are separate name spaces for various categories of identifiers, as follows:
+ -- label names (disambiguated by the syntax of the label declaration and use);
+ -- the tags of structures, unions, and enumerations (disambiguated by following any32)
+ of the keywords struct, union, or enum);
+ -- the members of structures or unions; each structure or union has a separate name
+ space for its members (disambiguated by the type of the expression used to access the
+ member via the . or -> operator);
+ -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
+ enumeration constants).
+ Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
+ structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
+ (6.7.2.3), the goto statement (6.8.6.1).
+
+ 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
+ 6.7.1.
+ 31) As specified in 6.2.1, the later declaration might hide the prior declaration.
+ 32) There is only one name space for tags even though three are possible.
+
+[page 37]
+
+ 6.2.4 Storage durations of objects
+1 An object has a storage duration that determines its lifetime. There are four storage
+ durations: static, thread, automatic, and allocated. Allocated storage is described in
+ 7.22.3.
+2 The lifetime of an object is the portion of program execution during which storage is
+ guaranteed to be reserved for it. An object exists, has a constant address,33) and retains
+ its last-stored value throughout its lifetime.34) If an object is referred to outside of its
+ lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
+ the object it points to (or just past) reaches the end of its lifetime.
+3 An object whose identifier is declared without the storage-class specifier
+ _Thread_local, and either with external or internal linkage or with the storage-class
+ specifier static, has static storage duration. Its lifetime is the entire execution of the
+ program and its stored value is initialized only once, prior to program startup.
+4 An object whose identifier is declared with the storage-class specifier _Thread_local
+ has thread storage duration. Its lifetime is the entire execution of the thread for which it
+ is created, and its stored value is initialized when the thread is started. There is a distinct
+ object per thread, and use of the declared name in an expression refers to the object
+ associated with the thread evaluating the expression. The result of attempting to
+ indirectly access an object with thread storage duration from a thread other than the one
+ with which the object is associated is implementation-defined.
+5 An object whose identifier is declared with no linkage and without the storage-class
+ specifier static has automatic storage duration, as do some compound literals. The
+ result of attempting to indirectly access an object with automatic storage duration from a
+ thread other than the one with which the object is associated is implementation-defined.
+6 For such an object that does not have a variable length array type, its lifetime extends
+ from entry into the block with which it is associated until execution of that block ends in
+ any way. (Entering an enclosed block or calling a function suspends, but does not end,
+ execution of the current block.) If the block is entered recursively, a new instance of the
+ object is created each time. The initial value of the object is indeterminate. If an
+ initialization is specified for the object, it is performed each time the declaration or
+ compound literal is reached in the execution of the block; otherwise, the value becomes
+ indeterminate each time the declaration is reached.
+
+
+
+ 33) The term ''constant address'' means that two pointers to the object constructed at possibly different
+ times will compare equal. The address may be different during two different executions of the same
+ program.
+ 34) In the case of a volatile object, the last store need not be explicit in the program.
+
+[page 38]
+
+7 For such an object that does have a variable length array type, its lifetime extends from
+ the declaration of the object until execution of the program leaves the scope of the
+ declaration.35) If the scope is entered recursively, a new instance of the object is created
+ each time. The initial value of the object is indeterminate.
+8 A non-lvalue expression with structure or union type, where the structure or union
+ contains a member with array type (including, recursively, members of all contained
+ structures and unions) refers to an object with automatic storage duration and temporary
+ lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the
+ value of the expression. Its lifetime ends when the evaluation of the containing full
+ expression or full declarator ends. Any attempt to modify an object with temporary
+ lifetime results in undefined behavior.
+ Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
+ (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).
+ 6.2.5 Types
+1 The meaning of a value stored in an object or returned by a function is determined by the
+ type of the expression used to access it. (An identifier declared to be an object is the
+ simplest such expression; the type is specified in the declaration of the identifier.) Types
+ are partitioned into object types (types that describe objects) and function types (types
+ that describe functions). At various points within a translation unit an object type may be
+ incomplete (lacking sufficient information to determine the size of objects of that type) or
+ complete (having sufficient information).37)
+2 An object declared as type _Bool is large enough to store the values 0 and 1.
+3 An object declared as type char is large enough to store any member of the basic
+ execution character set. If a member of the basic execution character set is stored in a
+ char object, its value is guaranteed to be nonnegative. If any other character is stored in
+ a char object, the resulting value is implementation-defined but shall be within the range
+ of values that can be represented in that type.
+4 There are five standard signed integer types, designated as signed char, short
+ int, int, long int, and long long int. (These and other types may be
+ designated in several additional ways, as described in 6.7.2.) There may also be
+ implementation-defined extended signed integer types.38) The standard and extended
+ signed integer types are collectively called signed integer types.39)
+
+ 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
+ embedded block prior to the declaration, leaves the scope of the declaration.
+ 36) The address of such an object is taken implicitly when an array member is accessed.
+ 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
+ different points within a translation unit.
+
+[page 39]
+
+5 An object declared as type signed char occupies the same amount of storage as a
+ ''plain'' char object. A ''plain'' int object has the natural size suggested by the
+ architecture of the execution environment (large enough to contain any value in the range
+ INT_MIN to INT_MAX as defined in the header <limits.h>).
+6 For each of the signed integer types, there is a corresponding (but different) unsigned
+ integer type (designated with the keyword unsigned) that uses the same amount of
+ storage (including sign information) and has the same alignment requirements. The type
+ _Bool and the unsigned integer types that correspond to the standard signed integer
+ types are the standard unsigned integer types. The unsigned integer types that
+ correspond to the extended signed integer types are the extended unsigned integer types.
+ The standard and extended unsigned integer types are collectively called unsigned integer
+ types.40)
+7 The standard signed integer types and standard unsigned integer types are collectively
+ called the standard integer types, the extended signed integer types and extended
+ unsigned integer types are collectively called the extended integer types.
+8 For any two integer types with the same signedness and different integer conversion rank
+ (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
+ subrange of the values of the other type.
+9 The range of nonnegative values of a signed integer type is a subrange of the
+ corresponding unsigned integer type, and the representation of the same value in each
+ type is the same.41) A computation involving unsigned operands can never overflow,
+ because a result that cannot be represented by the resulting unsigned integer type is
+ reduced modulo the number that is one greater than the largest value that can be
+ represented by the resulting type.
+10 There are three real floating types, designated as float, double, and long
+ double.42) The set of values of the type float is a subset of the set of values of the
+ type double; the set of values of the type double is a subset of the set of values of the
+ type long double.
+
+
+ 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
+ described in 7.1.3.
+ 39) Therefore, any statement in this Standard about signed integer types also applies to the extended
+ signed integer types.
+ 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
+ unsigned integer types.
+ 41) The same representation and alignment requirements are meant to imply interchangeability as
+ arguments to functions, return values from functions, and members of unions.
+ 42) See ''future language directions'' (6.11.1).
+
+[page 40]
+
+11 There are three complex types, designated as float _Complex, double
+ _Complex, and long double _Complex.43) (Complex types are a conditional
+ feature that implementations need not support; see 6.10.8.3.) The real floating and
+ complex types are collectively called the floating types.
+12 For each floating type there is a corresponding real type, which is always a real floating
+ type. For real floating types, it is the same type. For complex types, it is the type given
+ by deleting the keyword _Complex from the type name.
+13 Each complex type has the same representation and alignment requirements as an array
+ type containing exactly two elements of the corresponding real type; the first element is
+ equal to the real part, and the second element to the imaginary part, of the complex
+ number.
+14 The type char, the signed and unsigned integer types, and the floating types are
+ collectively called the basic types. The basic types are complete object types. Even if the
+ implementation defines two or more basic types to have the same representation, they are
+ nevertheless different types.44)
+15 The three types char, signed char, and unsigned char are collectively called
+ the character types. The implementation shall define char to have the same range,
+ representation, and behavior as either signed char or unsigned char.45)
+16 An enumeration comprises a set of named integer constant values. Each distinct
+ enumeration constitutes a different enumerated type.
+17 The type char, the signed and unsigned integer types, and the enumerated types are
+ collectively called integer types. The integer and real floating types are collectively called
+ real types.
+18 Integer and floating types are collectively called arithmetic types. Each arithmetic type
+ belongs to one type domain: the real type domain comprises the real types, the complex
+ type domain comprises the complex types.
+19 The void type comprises an empty set of values; it is an incomplete object type that
+ cannot be completed.
+
+
+
+ 43) A specification for imaginary types is in annex G.
+ 44) An implementation may define new keywords that provide alternative ways to designate a basic (or
+ any other) type; this does not violate the requirement that all basic types be different.
+ Implementation-defined keywords shall have the form of an identifier reserved for any use as
+ described in 7.1.3.
+ 45) CHAR_MIN, defined in <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.
+
+[page 41]
+
+20 Any number of derived types can be constructed from the object and function types, as
+ follows:
+ -- An array type describes a contiguously allocated nonempty set of objects with a
+ particular member object type, called the element type. The element type shall be
+ complete whenever the array type is specified. Array types are characterized by their
+ element type and by the number of elements in the array. An array type is said to be
+ derived from its element type, and if its element type is T , the array type is sometimes
+ called ''array of T ''. The construction of an array type from an element type is called
+ ''array type derivation''.
+ -- A structure type describes a sequentially allocated nonempty set of member objects
+ (and, in certain circumstances, an incomplete array), each of which has an optionally
+ specified name and possibly distinct type.
+ -- A union type describes an overlapping nonempty set of member objects, each of
+ which has an optionally specified name and possibly distinct type.
+ -- A function type describes a function with specified return type. A function type is
+ characterized by its return type and the number and types of its parameters. A
+ function type is said to be derived from its return type, and if its return type is T , the
+ function type is sometimes called ''function returning T ''. The construction of a
+ function type from a return type is called ''function type derivation''.
+ -- A pointer type may be derived from a function type or an object type, called the
+ referenced type. A pointer type describes an object whose value provides a reference
+ to an entity of the referenced type. A pointer type derived from the referenced type T
+ is sometimes called ''pointer to T ''. The construction of a pointer type from a
+ referenced type is called ''pointer type derivation''. A pointer type is a complete
+ object type.
+ -- An atomic type describes the type designated by the construct _Atomic ( type-
+ name ). (Atomic types are a conditional feature that implementations need not
+ support; see 6.10.8.3.)
+ These methods of constructing derived types can be applied recursively.
+21 Arithmetic types and pointer types are collectively called scalar types. Array and
+ structure types are collectively called aggregate types.46)
+22 An array type of unknown size is an incomplete type. It is completed, for an identifier of
+ that type, by specifying the size in a later declaration (with internal or external linkage).
+ A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete
+
+
+ 46) Note that aggregate type does not include union type because an object with union type can only
+ contain one member at a time.
+
+[page 42]
+
+ type. It is completed, for all declarations of that type, by declaring the same structure or
+ union tag with its defining content later in the same scope.
+23 A type has known constant size if the type is not incomplete and is not a variable length
+ array type.
+24 Array, function, and pointer types are collectively called derived declarator types. A
+ declarator type derivation from a type T is the construction of a derived declarator type
+ from T by the application of an array-type, a function-type, or a pointer-type derivation to
+ T.
+25 A type is characterized by its type category, which is either the outermost derivation of a
+ derived type (as noted above in the construction of derived types), or the type itself if the
+ type consists of no derived types.
+26 Any type so far mentioned is an unqualified type. Each unqualified type has several
+ qualified versions of its type,47) corresponding to the combinations of one, two, or all
+ three of the const, volatile, and restrict qualifiers. The qualified or unqualified
+ versions of a type are distinct types that belong to the same type category and have the
+ same representation and alignment requirements.48) A derived type is not qualified by the
+ qualifiers (if any) of the type from which it is derived.
+27 Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier
+ designates an atomic type. The size, representation, and alignment of an atomic type
+ need not be the same as those of the corresponding unqualified type. Therefore, this
+ Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the
+ atomic version of a type is permitted along with the other qualified versions of a type.
+ The phrase ''qualified or unqualified type'', without specific mention of atomic, does not
+ include the atomic types.
+28 A pointer to void shall have the same representation and alignment requirements as a
+ pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of
+ compatible types shall have the same representation and alignment requirements. All
+ pointers to structure types shall have the same representation and alignment requirements
+ as each other. All pointers to union types shall have the same representation and
+ alignment requirements as each other. Pointers to other types need not have the same
+ representation or alignment requirements.
+29 EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is
+ pointer, not a floating type. The const-qualified version of this type is designated as ''float * const''
+ whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const-
+
+
+ 47) See 6.7.3 regarding qualified array and function types.
+ 48) The same representation and alignment requirements are meant to imply interchangeability as
+ arguments to functions, return values from functions, and members of unions.
+
+[page 43]
+
+ qualified float'' and is a pointer to a qualified type.
+
+30 EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to
+ function returning struct tag''. The array has length five and the function has a single parameter of type
+ float. Its type category is array.
+
+ Forward references: compatible type and composite type (6.2.7), declarations (6.7).
+ 6.2.6 Representations of types
+ 6.2.6.1 General
+1 The representations of all types are unspecified except as stated in this subclause.
+2 Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
+ the number, order, and encoding of which are either explicitly specified or
+ implementation-defined.
+3 Values stored in unsigned bit-fields and objects of type unsigned char shall be
+ represented using a pure binary notation.49)
+4 Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT
+ bits, where n is the size of an object of that type, in bytes. The value may be copied into
+ an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
+ called the object representation of the value. Values stored in bit-fields consist of m bits,
+ where m is the size specified for the bit-field. The object representation is the set of m
+ bits the bit-field comprises in the addressable storage unit holding it. Two values (other
+ than NaNs) with the same object representation compare equal, but values that compare
+ equal may have different object representations.
+5 Certain object representations need not represent a value of the object type. If the stored
+ value of an object has such a representation and is read by an lvalue expression that does
+ not have character type, the behavior is undefined. If such a representation is produced
+ by a side effect that modifies all or any part of the object by an lvalue expression that
+ does not have character type, the behavior is undefined.50) Such a representation is called
+ a trap representation.
+6 When a value is stored in an object of structure or union type, including in a member
+ object, the bytes of the object representation that correspond to any padding bytes take
+ unspecified values.51) The value of a structure or union object is never a trap
+
+
+ 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
+ represented by successive bits are additive, begin with 1, and are multiplied by successive integral
+ powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
+ Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
+ type unsigned char range from 0 to 2
+ CHAR_BIT
+ - 1.
+ 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
+ behavior, but the value of the variable cannot be used until a proper value is stored in it.
+
+[page 44]
+
+ representation, even though the value of a member of the structure or union object may be
+ a trap representation.
+7 When a value is stored in a member of an object of union type, the bytes of the object
+ representation that do not correspond to that member but do correspond to other members
+ take unspecified values.
+8 Where an operator is applied to a value that has more than one object representation,
+ which object representation is used shall not affect the value of the result.52) Where a
+ value is stored in an object using a type that has more than one object representation for
+ that value, it is unspecified which representation is used, but a trap representation shall
+ not be generated.
+9 Loads and stores of objects with atomic types are done with
+ memory_order_seq_cst semantics.
+ Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
+ designators (6.3.2.1), order and consistency (7.17.3).
+ 6.2.6.2 Integer types
+1 For unsigned integer types other than unsigned char, the bits of the object
+ representation shall be divided into two groups: value bits and padding bits (there need
+ not be any of the latter). If there are N value bits, each bit shall represent a different
+ power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of
+ representing values from 0 to 2 N - 1 using a pure binary representation; this shall be
+ known as the value representation. The values of any padding bits are unspecified.53)
+2 For signed integer types, the bits of the object representation shall be divided into three
+ groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
+ signed char shall not have any padding bits. There shall be exactly one sign bit.
+ Each bit that is a value bit shall have the same value as the same bit in the object
+ representation of the corresponding unsigned type (if there are M value bits in the signed
+ type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect
+
+ 51) Thus, for example, structure assignment need not copy any padding bits.
+ 52) It is possible for objects x and y with the same effective type T to have the same value when they are
+ accessed as objects of type T, but to have different values in other contexts. In particular, if == is
+ defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
+ Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
+ on values of type T may distinguish between them.
+ 53) Some combinations of padding bits might generate trap representations, for example, if one padding
+ bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
+ representation other than as part of an exceptional condition such as an overflow, and this cannot occur
+ with unsigned types. All other combinations of padding bits are alternative object representations of
+ the value specified by the value bits.
+
+[page 45]
+
+ the resulting value. If the sign bit is one, the value shall be modified in one of the
+ following ways:
+ -- the corresponding value with sign bit 0 is negated (sign and magnitude);
+ -- the sign bit has the value -(2 M ) (two's complement);
+ -- the sign bit has the value -(2 M - 1) (ones' complement).
+ Which of these applies is implementation-defined, as is whether the value with sign bit 1
+ and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones'
+ complement), is a trap representation or a normal value. In the case of sign and
+ magnitude and ones' complement, if this representation is a normal value it is called a
+ negative zero.
+3 If the implementation supports negative zeros, they shall be generated only by:
+ -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
+ -- the +, -, *, /, and % operators where one operand is a negative zero and the result is
+ zero;
+ -- compound assignment operators based on the above cases.
+ It is unspecified whether these cases actually generate a negative zero or a normal zero,
+ and whether a negative zero becomes a normal zero when stored in an object.
+4 If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
+ and >> operators with operands that would produce such a value is undefined.
+5 The values of any padding bits are unspecified.54) A valid (non-trap) object representation
+ of a signed integer type where the sign bit is zero is a valid object representation of the
+ corresponding unsigned type, and shall represent the same value. For any integer type,
+ the object representation where all the bits are zero shall be a representation of the value
+ zero in that type.
+6 The precision of an integer type is the number of bits it uses to represent values,
+ excluding any sign and padding bits. The width of an integer type is the same but
+ including any sign bit; thus for unsigned integer types the two values are the same, while
+ for signed integer types the width is one greater than the precision.
+
+
+
+
+ 54) Some combinations of padding bits might generate trap representations, for example, if one padding
+ bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
+ representation other than as part of an exceptional condition such as an overflow. All other
+ combinations of padding bits are alternative object representations of the value specified by the value
+ bits.
+
+[page 46]
+
+ 6.2.7 Compatible type and composite type
+1 Two types have compatible type if their types are the same. Additional rules for
+ determining whether two types are compatible are described in 6.7.2 for type specifiers,
+ in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure,
+ union, or enumerated types declared in separate translation units are compatible if their
+ tags and members satisfy the following requirements: If one is declared with a tag, the
+ other shall be declared with the same tag. If both are completed anywhere within their
+ respective translation units, then the following additional requirements apply: there shall
+ be a one-to-one correspondence between their members such that each pair of
+ corresponding members are declared with compatible types; if one member of the pair is
+ declared with an alignment specifier, the other is declared with an equivalent alignment
+ specifier; and if one member of the pair is declared with a name, the other is declared
+ with the same name. For two structures, corresponding members shall be declared in the
+ same order. For two structures or unions, corresponding bit-fields shall have the same
+ widths. For two enumerations, corresponding members shall have the same values.
+2 All declarations that refer to the same object or function shall have compatible type;
+ otherwise, the behavior is undefined.
+3 A composite type can be constructed from two types that are compatible; it is a type that
+ is compatible with both of the two types and satisfies the following conditions:
+ -- If both types are array types, the following rules are applied:
+ o If one type is an array of known constant size, the composite type is an array of
+ that size.
+ o Otherwise, if one type is a variable length array whose size is specified by an
+ expression that is not evaluated, the behavior is undefined.
+ o Otherwise, if one type is a variable length array whose size is specified, the
+ composite type is a variable length array of that size.
+ o Otherwise, if one type is a variable length array of unspecified size, the composite
+ type is a variable length array of unspecified size.
+ o Otherwise, both types are arrays of unknown size and the composite type is an
+ array of unknown size.
+ The element type of the composite type is the composite type of the two element
+ types.
+ -- If only one type is a function type with a parameter type list (a function prototype),
+ the composite type is a function prototype with the parameter type list.
+
+
+ 55) Two types need not be identical to be compatible.
+
+[page 47]
+
+ -- If both types are function types with parameter type lists, the type of each parameter
+ in the composite parameter type list is the composite type of the corresponding
+ parameters.
+ These rules apply recursively to the types from which the two types are derived.
+4 For an identifier with internal or external linkage declared in a scope in which a prior
+ declaration of that identifier is visible,56) if the prior declaration specifies internal or
+ external linkage, the type of the identifier at the later declaration becomes the composite
+ type.
+ Forward references: array declarators (6.7.6.2).
+5 EXAMPLE Given the following two file scope declarations:
+ int f(int (*)(), double (*)[3]);
+ int f(int (*)(char *), double (*)[]);
+ The resulting composite type for the function is:
+ int f(int (*)(char *), double (*)[3]);
+
+ 6.2.8 Alignment of objects
+1 Complete object types have alignment requirements which place restrictions on the
+ addresses at which objects of that type may be allocated. An alignment is an
+ implementation-defined integer value representing the number of bytes between
+ successive addresses at which a given object can be allocated. An object type imposes an
+ alignment requirement on every object of that type: stricter alignment can be requested
+ using the _Alignas keyword.
+2 A fundamental alignment is represented by an alignment less than or equal to the greatest
+ alignment supported by the implementation in all contexts, which is equal to
+ _Alignof (max_align_t).
+3 An extended alignment is represented by an alignment greater than
+ _Alignof (max_align_t). It is implementation-defined whether any extended
+ alignments are supported and the contexts in which they are supported. A type having an
+ extended alignment requirement is an over-aligned type.57)
+4 Alignments are represented as values of the type size_t. Valid alignments include only
+ those values returned by an _Alignof expression for fundamental types, plus an
+ additional implementation-defined set of values, which may be empty. Every valid
+ alignment value shall be a nonnegative integral power of two.
+
+
+ 56) As specified in 6.2.1, the later declaration might hide the prior declaration.
+ 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
+ alignment has been applied.
+
+[page 48]
+
+5 Alignments have an order from weaker to stronger or stricter alignments. Stricter
+ alignments have larger alignment values. An address that satisfies an alignment
+ requirement also satisfies any weaker valid alignment requirement.
+6 The alignment requirement of a complete type can be queried using an _Alignof
+ expression. The types char, signed char, and unsigned char shall have the
+ weakest alignment requirement.
+7 Comparing alignments is meaningful and provides the obvious results:
+ -- Two alignments are equal when their numeric values are equal.
+ -- Two alignments are different when their numeric values are not equal.
+ -- When an alignment is larger than another it represents a stricter alignment.
+
+[page 49]
+
+ 6.3 Conversions
+1 Several operators convert operand values from one type to another automatically. This
+ subclause specifies the result required from such an implicit conversion, as well as those
+ that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
+ the conversions performed by most ordinary operators; it is supplemented as required by
+ the discussion of each operator in 6.5.
+2 Conversion of an operand value to a compatible type causes no change to the value or the
+ representation.
+ Forward references: cast operators (6.5.4).
+ 6.3.1 Arithmetic operands
+ 6.3.1.1 Boolean, characters, and integers
+1 Every integer type has an integer conversion rank defined as follows:
+ -- No two signed integer types shall have the same rank, even if they have the same
+ representation.
+ -- The rank of a signed integer type shall be greater than the rank of any signed integer
+ type with less precision.
+ -- The rank of long long int shall be greater than the rank of long int, which
+ shall be greater than the rank of int, which shall be greater than the rank of short
+ int, which shall be greater than the rank of signed char.
+ -- The rank of any unsigned integer type shall equal the rank of the corresponding
+ signed integer type, if any.
+ -- The rank of any standard integer type shall be greater than the rank of any extended
+ integer type with the same width.
+ -- The rank of char shall equal the rank of signed char and unsigned char.
+ -- The rank of _Bool shall be less than the rank of all other standard integer types.
+ -- The rank of any enumerated type shall equal the rank of the compatible integer type
+ (see 6.7.2.2).
+ -- The rank of any extended signed integer type relative to another extended signed
+ integer type with the same precision is implementation-defined, but still subject to the
+ other rules for determining the integer conversion rank.
+ -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
+ greater rank than T3, then T1 has greater rank than T3.
+2 The following may be used in an expression wherever an int or unsigned int may
+ be used:
+
+[page 50]
+
+ -- An object or expression with an integer type (other than int or unsigned int)
+ whose integer conversion rank is less than or equal to the rank of int and
+ unsigned int.
+ -- A bit-field of type _Bool, int, signed int, or unsigned int.
+ If an int can represent all values of the original type (as restricted by the width, for a
+ bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
+ int. These are called the integer promotions.58) All other types are unchanged by the
+ integer promotions.
+3 The integer promotions preserve value including sign. As discussed earlier, whether a
+ ''plain'' char is treated as signed is implementation-defined.
+ Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
+ (6.7.2.1).
+ 6.3.1.2 Boolean type
+1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal
+ to 0; otherwise, the result is 1.59)
+ 6.3.1.3 Signed and unsigned integers
+1 When a value with integer type is converted to another integer type other than _Bool, if
+ the value can be represented by the new type, it is unchanged.
+2 Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
+ subtracting one more than the maximum value that can be represented in the new type
+ until the value is in the range of the new type.60)
+3 Otherwise, the new type is signed and the value cannot be represented in it; either the
+ result is implementation-defined or an implementation-defined signal is raised.
+ 6.3.1.4 Real floating and integer
+1 When a finite value of real floating type is converted to an integer type other than _Bool,
+ the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
+ the integral part cannot be represented by the integer type, the behavior is undefined.61)
+
+
+ 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
+ argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
+ shift operators, as specified by their respective subclauses.
+ 59) NaNs do not compare equal to 0 and thus convert to 1.
+ 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
+ 61) The remaindering operation performed when a value of integer type is converted to unsigned type
+ need not be performed when a value of real floating type is converted to unsigned type. Thus, the
+ range of portable real floating values is (-1, Utype_MAX+1).
+
+[page 51]
+
+2 When a value of integer type is converted to a real floating type, if the value being
+ converted can be represented exactly in the new type, it is unchanged. If the value being
+ converted is in the range of values that can be represented but cannot be represented
+ exactly, the result is either the nearest higher or nearest lower representable value, chosen
+ in an implementation-defined manner. If the value being converted is outside the range of
+ values that can be represented, the behavior is undefined. Results of some implicit
+ conversions may be represented in greater range and precision than that required by the
+ new type (see 6.3.1.8 and 6.8.6.4).
+ 6.3.1.5 Real floating types
+1 When a value of real floating type is converted to a real floating type, if the value being
+ converted can be represented exactly in the new type, it is unchanged. If the value being
+ converted is in the range of values that can be represented but cannot be represented
+ exactly, the result is either the nearest higher or nearest lower representable value, chosen
+ in an implementation-defined manner. If the value being converted is outside the range of
+ values that can be represented, the behavior is undefined. Results of some implicit
+ conversions may be represented in greater range and precision than that required by the
+ new type (see 6.3.1.8 and 6.8.6.4).
+ 6.3.1.6 Complex types
+1 When a value of complex type is converted to another complex type, both the real and
+ imaginary parts follow the conversion rules for the corresponding real types.
+ 6.3.1.7 Real and complex
+1 When a value of real type is converted to a complex type, the real part of the complex
+ result value is determined by the rules of conversion to the corresponding real type and
+ the imaginary part of the complex result value is a positive zero or an unsigned zero.
+2 When a value of complex type is converted to a real type, the imaginary part of the
+ complex value is discarded and the value of the real part is converted according to the
+ conversion rules for the corresponding real type.
+ 6.3.1.8 Usual arithmetic conversions
+1 Many operators that expect operands of arithmetic type cause conversions and yield result
+ types in a similar way. The purpose is to determine a common real type for the operands
+ and result. For the specified operands, each operand is converted, without change of type
+ domain, to a type whose corresponding real type is the common real type. Unless
+ explicitly stated otherwise, the common real type is also the corresponding real type of
+ the result, whose type domain is the type domain of the operands if they are the same,
+ and complex otherwise. This pattern is called the usual arithmetic conversions:
+ First, if the corresponding real type of either operand is long double, the other
+ operand is converted, without change of type domain, to a type whose
+
+[page 52]
+
+ corresponding real type is long double.
+ Otherwise, if the corresponding real type of either operand is double, the other
+ operand is converted, without change of type domain, to a type whose
+ corresponding real type is double.
+ Otherwise, if the corresponding real type of either operand is float, the other
+ operand is converted, without change of type domain, to a type whose
+ corresponding real type is float.62)
+ Otherwise, the integer promotions are performed on both operands. Then the
+ following rules are applied to the promoted operands:
+ If both operands have the same type, then no further conversion is needed.
+ Otherwise, if both operands have signed integer types or both have unsigned
+ integer types, the operand with the type of lesser integer conversion rank is
+ converted to the type of the operand with greater rank.
+ Otherwise, if the operand that has unsigned integer type has rank greater or
+ equal to the rank of the type of the other operand, then the operand with
+ signed integer type is converted to the type of the operand with unsigned
+ integer type.
+ Otherwise, if the type of the operand with signed integer type can represent
+ all of the values of the type of the operand with unsigned integer type, then
+ the operand with unsigned integer type is converted to the type of the
+ operand with signed integer type.
+ Otherwise, both operands are converted to the unsigned integer type
+ corresponding to the type of the operand with signed integer type.
+2 The values of floating operands and of the results of floating expressions may be
+ represented in greater range and precision than that required by the type; the types are not
+ changed thereby.63)
+
+
+
+
+ 62) For example, addition of a double _Complex and a float entails just the conversion of the
+ float operand to double (and yields a double _Complex result).
+ 63) The cast and assignment operators are still required to remove extra range and precision.
+
+[page 53]
+
+ 6.3.2 Other operands
+ 6.3.2.1 Lvalues, arrays, and function designators
+1 An lvalue is an expression (with an object type other than void) that potentially
+ designates an object;64) if an lvalue does not designate an object when it is evaluated, the
+ behavior is undefined. When an object is said to have a particular type, the type is
+ specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
+ does not have array type, does not have an incomplete type, does not have a const-
+ qualified type, and if it is a structure or union, does not have any member (including,
+ recursively, any member or element of all contained aggregates or unions) with a const-
+ qualified type.
+2 Except when it is the operand of the sizeof operator, the _Alignof operator, the
+ unary & operator, the ++ operator, the -- operator, or the left operand of the . operator
+ or an assignment operator, an lvalue that does not have array type is converted to the
+ value stored in the designated object (and is no longer an lvalue); this is called lvalue
+ conversion. If the lvalue has qualified type, the value has the unqualified version of the
+ type of the lvalue; additionally, if the lvalue has atomic type, the value has the non-atomic
+ version of the type of the lvalue; otherwise, the value has the type of the lvalue. If the
+ lvalue has an incomplete type and does not have array type, the behavior is undefined. If
+ the lvalue designates an object of automatic storage duration that could have been
+ declared with the register storage class (never had its address taken), and that object
+ is uninitialized (not declared with an initializer and no assignment to it has been
+ performed prior to use), the behavior is undefined.
+3 Except when it is the operand of the sizeof operator, the _Alignof operator, or the
+ unary & operator, or is a string literal used to initialize an array, an expression that has
+ type ''array of type'' is converted to an expression with type ''pointer to type'' that points
+ to the initial element of the array object and is not an lvalue. If the array object has
+ register storage class, the behavior is undefined.
+4 A function designator is an expression that has function type. Except when it is the
+ operand of the sizeof operator, the _Alignof operator,65) or the unary & operator, a
+ function designator with type ''function returning type'' is converted to an expression that
+
+
+ 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 or _Alignof operator remains
+ a function designator and violates the constraints in 6.5.3.4.
+
+[page 54]
+
+ 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 and _Alignof operators (6.5.3.4), structure and union members
+ (6.5.2.3).
+ 6.3.2.2 void
+1 The (nonexistent) value of a void expression (an expression that has type void) shall not
+ be used in any way, and implicit or explicit conversions (except to void) shall not be
+ applied to such an expression. If an expression of any other type is evaluated as a void
+ expression, its value or designator is discarded. (A void expression is evaluated for its
+ side effects.)
+ 6.3.2.3 Pointers
+1 A pointer to void may be converted to or from a pointer to any object type. A pointer to
+ any object type may be converted to a pointer to void and back again; the result shall
+ compare equal to the original pointer.
+2 For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to
+ the q-qualified version of the type; the values stored in the original and converted pointers
+ shall compare equal.
+3 An integer constant expression with the value 0, or such an expression cast to type
+ void *, is called a null pointer constant.66) If a null pointer constant is converted to a
+ pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
+ to a pointer to any object or function.
+4 Conversion of a null pointer to another pointer type yields a null pointer of that type.
+ Any two null pointers shall compare equal.
+5 An integer may be converted to any pointer type. Except as previously specified, the
+ result is implementation-defined, might not be correctly aligned, might not point to an
+ entity of the referenced type, and might be a trap representation.67)
+6 Any pointer type may be converted to an integer type. Except as previously specified, the
+ result is implementation-defined. If the result cannot be represented in the integer type,
+ the behavior is undefined. The result need not be in the range of values of any integer
+ type.
+
+
+ 66) The macro NULL is defined in <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.
+
+[page 55]
+
+7 A pointer to an object type may be converted to a pointer to a different object type. If the
+ resulting pointer is not correctly aligned68) for the referenced type, the behavior is
+ undefined. Otherwise, when converted back again, the result shall compare equal to the
+ original pointer. When a pointer to an object is converted to a pointer to a character type,
+ the result points to the lowest addressed byte of the object. Successive increments of the
+ result, up to the size of the object, yield pointers to the remaining bytes of the object.
+8 A pointer to a function of one type may be converted to a pointer to a function of another
+ type and back again; the result shall compare equal to the original pointer. If a converted
+ pointer is used to call a function whose type is not compatible with the referenced type,
+ the behavior is undefined.
+ Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
+ capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).
+
+
+
+
+ 68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a
+ pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
+ correctly aligned for a pointer to type C.
+
+[page 56]
+
+ 6.4 Lexical elements
+ Syntax
+1 token:
+ keyword
+ identifier
+ constant
+ string-literal
+ punctuator
+ preprocessing-token:
+ header-name
+ identifier
+ pp-number
+ character-constant
+ string-literal
+ punctuator
+ each non-white-space character that cannot be one of the above
+ Constraints
+2 Each preprocessing token that is converted to a token shall have the lexical form of a
+ keyword, an identifier, a constant, a string literal, or a punctuator.
+ Semantics
+3 A token is the minimal lexical element of the language in translation phases 7 and 8. The
+ categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
+ A preprocessing token is the minimal lexical element of the language in translation
+ phases 3 through 6. The categories of preprocessing tokens are: header names,
+ identifiers, preprocessing numbers, character constants, string literals, punctuators, and
+ single non-white-space characters that do not lexically match the other preprocessing
+ token categories.69) If a ' or a " character matches the last category, the behavior is
+ undefined. Preprocessing tokens can be separated by white space; this consists of
+ comments (described later), or white-space characters (space, horizontal tab, new-line,
+ vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
+ during translation phase 4, white space (or the absence thereof) serves as more than
+ preprocessing token separation. White space may appear within a preprocessing token
+ only as part of a header name or between the quotation characters in a character constant
+ or string literal.
+
+
+
+ 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
+ occur in source files.
+
+[page 57]
+
+4 If the input stream has been parsed into preprocessing tokens up to a given character, the
+ next preprocessing token is the longest sequence of characters that could constitute a
+ preprocessing token. There is one exception to this rule: header name preprocessing
+ tokens are recognized only within #include preprocessing directives and in
+ implementation-defined locations within #pragma directives. In such contexts, a
+ sequence of characters that could be either a header name or a string literal is recognized
+ as the former.
+5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
+ valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
+ might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
+ fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
+ not E is a macro name.
+
+6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
+ increment operators, even though the parse x ++ + ++ y might yield a correct expression.
+
+ Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
+ floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
+ increment and decrement operators (6.5.2.4), prefix increment and decrement operators
+ (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
+ (6.4.5).
+ 6.4.1 Keywords
+ Syntax
+1 keyword: one of
+ auto * if unsigned
+ break inline void
+ case int volatile
+ char long while
+ const register _Alignas
+ continue restrict _Alignof
+ default return _Atomic
+ do short _Bool
+ double signed _Complex
+ else sizeof _Generic
+ enum static _Imaginary
+ extern struct _Noreturn
+ float switch _Static_assert
+ for typedef _Thread_local
+ goto union
+ Semantics
+2 The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
+ keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for
+
+[page 58]
+
+ specifying imaginary types.70)
+ 6.4.2 Identifiers
+ 6.4.2.1 General
+ Syntax
+1 identifier:
+ identifier-nondigit
+ identifier identifier-nondigit
+ identifier digit
+ identifier-nondigit:
+ nondigit
+ universal-character-name
+ other implementation-defined characters
+ nondigit: one of
+ _ a b c d e f g h i j k l m
+ n o p q r s t u v w x y z
+ A B C D E F G H I J K L M
+ N O P Q R S T U V W X Y Z
+ digit: one of
+ 0 1 2 3 4 5 6 7 8 9
+ Semantics
+2 An identifier is a sequence of nondigit characters (including the underscore _, the
+ lowercase and uppercase Latin letters, and other characters) and digits, which designates
+ one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
+ There is no specific limit on the maximum length of an identifier.
+3 Each universal character name in an identifier shall designate a character whose encoding
+ in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character
+ shall not be a universal character name designating a character whose encoding falls into
+ one of the ranges specified in D.2. An implementation may allow multibyte characters
+ that are not part of the basic source character set to appear in identifiers; which characters
+ and their correspondence to universal character names is implementation-defined.
+
+
+
+ 70) One possible specification for imaginary types appears in annex G.
+ 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
+ name may be used in forming valid external identifiers. For example, some otherwise unused
+ character or sequence of characters may be used to encode the \u in a universal character name.
+ Extended characters may produce a long external identifier.
+
+[page 59]
+
+4 When preprocessing tokens are converted to tokens during translation phase 7, if a
+ preprocessing token could be converted to either a keyword or an identifier, it is converted
+ to a keyword.
+ Implementation limits
+5 As discussed in 5.2.4.1, an implementation may limit the number of significant initial
+ characters in an identifier; the limit for an external name (an identifier that has external
+ linkage) may be more restrictive than that for an internal name (a macro name or an
+ identifier that does not have external linkage). The number of significant characters in an
+ identifier is implementation-defined.
+6 Any identifiers that differ in a significant character are different identifiers. If two
+ identifiers differ only in nonsignificant characters, the behavior is undefined.
+ Forward references: universal character names (6.4.3), macro replacement (6.10.3).
+ 6.4.2.2 Predefined identifiers
+ Semantics
+1 The identifier __func__ shall be implicitly declared by the translator as if,
+ immediately following the opening brace of each function definition, the declaration
+ static const char __func__[] = "function-name";
+ appeared, where function-name is the name of the lexically-enclosing function.72)
+2 This name is encoded as if the implicit declaration had been written in the source
+ character set and then translated into the execution character set as indicated in translation
+ phase 5.
+3 EXAMPLE Consider the code fragment:
+ #include <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).
+
+
+
+
+ 72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other
+ identifier is explicitly declared using the name __func__, the behavior is undefined.
+
+[page 60]
+
+ 6.4.3 Universal character names
+ Syntax
+1 universal-character-name:
+ \u hex-quad
+ \U hex-quad hex-quad
+ hex-quad:
+ hexadecimal-digit hexadecimal-digit
+ hexadecimal-digit hexadecimal-digit
+ Constraints
+2 A universal character name shall not specify a character whose short identifier is less than
+ 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through
+ DFFF inclusive.73)
+ Description
+3 Universal character names may be used in identifiers, character constants, and string
+ literals to designate characters that are not in the basic character set.
+ Semantics
+4 The universal character name \Unnnnnnnn designates the character whose eight-digit
+ short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal
+ character name \unnnn designates the character whose four-digit short identifier is nnnn
+ (and whose eight-digit short identifier is 0000nnnn).
+
+
+
+
+ 73) The disallowed characters are the characters in the basic character set and the code positions reserved
+ by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
+ UTF-16).
+
+ 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997.
+
+[page 61]
+
+ 6.4.4 Constants
+ Syntax
+1 constant:
+ integer-constant
+ floating-constant
+ enumeration-constant
+ character-constant
+ Constraints
+2 Each constant shall have a type and the value of a constant shall be in the range of
+ representable values for its type.
+ Semantics
+3 Each constant has a type, determined by its form and value, as detailed later.
+ 6.4.4.1 Integer constants
+ Syntax
+1 integer-constant:
+ decimal-constant integer-suffixopt
+ octal-constant integer-suffixopt
+ hexadecimal-constant integer-suffixopt
+ decimal-constant:
+ nonzero-digit
+ decimal-constant digit
+ octal-constant:
+ 0
+ octal-constant octal-digit
+ hexadecimal-constant:
+ hexadecimal-prefix hexadecimal-digit
+ hexadecimal-constant hexadecimal-digit
+ hexadecimal-prefix: one of
+ 0x 0X
+ nonzero-digit: one of
+ 1 2 3 4 5 6 7 8 9
+ octal-digit: one of
+ 0 1 2 3 4 5 6 7
+
+[page 62]
+
+ hexadecimal-digit: one of
+ 0 1 2 3 4 5 6 7 8 9
+ a b c d e f
+ A B C D E F
+ integer-suffix:
+ unsigned-suffix long-suffixopt
+ unsigned-suffix long-long-suffix
+ long-suffix unsigned-suffixopt
+ long-long-suffix unsigned-suffixopt
+ unsigned-suffix: one of
+ u U
+ long-suffix: one of
+ l L
+ long-long-suffix: one of
+ ll LL
+ Description
+2 An integer constant begins with a digit, but has no period or exponent part. It may have a
+ prefix that specifies its base and a suffix that specifies its type.
+3 A decimal constant begins with a nonzero digit and consists of a sequence of decimal
+ digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
+ digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
+ by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
+ 10 through 15 respectively.
+ Semantics
+4 The value of a decimal constant is computed base 10; that of an octal constant, base 8;
+ that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
+5 The type of an integer constant is the first of the corresponding list in which its value can
+ be represented.
+
+[page 63]
+
+ Octal or Hexadecimal
+ Suffix Decimal Constant Constant
+
+ none int int
+ long int unsigned int
+ long long int long int
+ unsigned long int
+ long long int
+ unsigned long long int
+
+ u or U unsigned int unsigned int
+ unsigned long int unsigned long int
+ unsigned long long int unsigned long long int
+
+ l or L long int long int
+ long long int unsigned long int
+ long long int
+ unsigned long long int
+
+ Both u or U unsigned long int unsigned long int
+ and l or L unsigned long long int unsigned long long int
+
+ ll or LL long long int long long int
+ unsigned long long int
+
+ Both u or U unsigned long long int unsigned long long int
+ and ll or LL
+6 If an integer constant cannot be represented by any type in its list, it may have an
+ extended integer type, if the extended integer type can represent its value. If all of the
+ types in the list for the constant are signed, the extended integer type shall be signed. If
+ all of the types in the list for the constant are unsigned, the extended integer type shall be
+ unsigned. If the list contains both signed and unsigned types, the extended integer type
+ may be signed or unsigned. If an integer constant cannot be represented by any type in
+ its list and has no extended integer type, then the integer constant has no type.
+
+[page 64]
+
+ 6.4.4.2 Floating constants
+ Syntax
+1 floating-constant:
+ decimal-floating-constant
+ hexadecimal-floating-constant
+ decimal-floating-constant:
+ fractional-constant exponent-partopt floating-suffixopt
+ digit-sequence exponent-part floating-suffixopt
+ hexadecimal-floating-constant:
+ hexadecimal-prefix hexadecimal-fractional-constant
+ binary-exponent-part floating-suffixopt
+ hexadecimal-prefix hexadecimal-digit-sequence
+ binary-exponent-part floating-suffixopt
+ fractional-constant:
+ digit-sequenceopt . digit-sequence
+ digit-sequence .
+ exponent-part:
+ e signopt digit-sequence
+ E signopt digit-sequence
+ sign: one of
+ + -
+ digit-sequence:
+ digit
+ digit-sequence digit
+ hexadecimal-fractional-constant:
+ hexadecimal-digit-sequenceopt .
+ hexadecimal-digit-sequence
+ hexadecimal-digit-sequence .
+ binary-exponent-part:
+ p signopt digit-sequence
+ P signopt digit-sequence
+ hexadecimal-digit-sequence:
+ hexadecimal-digit
+ hexadecimal-digit-sequence hexadecimal-digit
+ floating-suffix: one of
+ f l F L
+
+[page 65]
+
+ Description
+2 A floating constant has a significand part that may be followed by an exponent part and a
+ suffix that specifies its type. The components of the significand part may include a digit
+ sequence representing the whole-number part, followed by a period (.), followed by a
+ digit sequence representing the fraction part. The components of the exponent part are an
+ e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
+ Either the whole-number part or the fraction part has to be present; for decimal floating
+ constants, either the period or the exponent part has to be present.
+ Semantics
+3 The significand part is interpreted as a (decimal or hexadecimal) rational number; the
+ digit sequence in the exponent part is interpreted as a decimal integer. For decimal
+ floating constants, the exponent indicates the power of 10 by which the significand part is
+ to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
+ by which the significand part is to be scaled. For decimal floating constants, and also for
+ hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
+ the nearest representable value, or the larger or smaller representable value immediately
+ adjacent to the nearest representable value, chosen in an implementation-defined manner.
+ For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
+ correctly rounded.
+4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
+ type float. If suffixed by the letter l or L, it has type long double.
+5 Floating constants are converted to internal format as if at translation-time. The
+ conversion of a floating constant shall not raise an exceptional condition or a floating-
+ point exception at execution time. All floating constants of the same source form75) shall
+ convert to the same internal format with the same value.
+ Recommended practice
+6 The implementation should produce a diagnostic message if a hexadecimal constant
+ cannot be represented exactly in its evaluation format; the implementation should then
+ proceed with the translation of the program.
+7 The translation-time conversion of floating constants should match the execution-time
+ conversion of character strings by library functions, such as strtod, given matching
+ inputs suitable for both conversions, the same result format, and default execution-time
+ rounding.76)
+
+ 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not
+ convert to the same internal format and value.
+ 76) The specification for the library functions recommends more accurate conversion than required for
+ floating constants (see 7.22.1.3).
+
+[page 66]
+
+ 6.4.4.3 Enumeration constants
+ Syntax
+1 enumeration-constant:
+ identifier
+ Semantics
+2 An identifier declared as an enumeration constant has type int.
+ Forward references: enumeration specifiers (6.7.2.2).
+ 6.4.4.4 Character constants
+ Syntax
+1 character-constant:
+ ' c-char-sequence '
+ L' c-char-sequence '
+ u' c-char-sequence '
+ U' c-char-sequence '
+ c-char-sequence:
+ c-char
+ c-char-sequence c-char
+ c-char:
+ any member of the source character set except
+ the single-quote ', backslash \, or new-line character
+ escape-sequence
+ escape-sequence:
+ simple-escape-sequence
+ octal-escape-sequence
+ hexadecimal-escape-sequence
+ universal-character-name
+ simple-escape-sequence: one of
+ \' \" \? \\
+ \a \b \f \n \r \t \v
+ octal-escape-sequence:
+ \ octal-digit
+ \ octal-digit octal-digit
+ \ octal-digit octal-digit octal-digit
+
+[page 67]
+
+ hexadecimal-escape-sequence:
+ \x hexadecimal-digit
+ hexadecimal-escape-sequence hexadecimal-digit
+ Description
+2 An integer character constant is a sequence of one or more multibyte characters enclosed
+ in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
+ letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
+ any members of the source character set; they are mapped in an implementation-defined
+ manner to members of the execution character set.
+3 The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
+ arbitrary integer values are representable according to the following table of escape
+ sequences:
+ single quote ' \'
+ double quote " \"
+ question mark ? \?
+ backslash \ \\
+ octal character \octal digits
+ hexadecimal character \x hexadecimal digits
+4 The double-quote " and question-mark ? are representable either by themselves or by the
+ escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
+ shall be represented, respectively, by the escape sequences \' and \\.
+5 The octal digits that follow the backslash in an octal escape sequence are taken to be part
+ of the construction of a single character for an integer character constant or of a single
+ wide character for a wide character constant. The numerical value of the octal integer so
+ formed specifies the value of the desired character or wide character.
+6 The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
+ sequence are taken to be part of the construction of a single character for an integer
+ character constant or of a single wide character for a wide character constant. The
+ numerical value of the hexadecimal integer so formed specifies the value of the desired
+ character or wide character.
+7 Each octal or hexadecimal escape sequence is the longest sequence of characters that can
+ constitute the escape sequence.
+8 In addition, characters not in the basic character set are representable by universal
+ character names and certain nongraphic characters are representable by escape sequences
+ consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
+ and \v.77)
+
+[page 68]
+
+ Constraints
+9 The value of an octal or hexadecimal escape sequence shall be in the range of
+ representable values for the corresponding type:
+ Prefix Corresponding Type
+ none unsigned char
+ L the unsigned type corresponding to wchar_t
+ u char16_t
+ U char32_t
+ Semantics
+10 An integer character constant has type int. The value of an integer character constant
+ containing a single character that maps to a single-byte execution character is the
+ numerical value of the representation of the mapped character interpreted as an integer.
+ The value of an integer character constant containing more than one character (e.g.,
+ 'ab'), or containing a character or escape sequence that does not map to a single-byte
+ execution character, is implementation-defined. If an integer character constant contains
+ a single character or escape sequence, its value is the one that results when an object with
+ type char whose value is that of the single character or escape sequence is converted to
+ type int.
+11 A wide character constant prefixed by the letter L has type wchar_t, an integer type
+ defined in the <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.
+12 EXAMPLE 1 The construction '\0' is commonly used to represent the null character.
+
+13 EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight
+ bits for objects that have type char. In an implementation in which type char has the same range of
+ values as signed char, the integer character constant '\xFF' has the value -1; if type char has the
+ same range of values as unsigned char, the character constant '\xFF' has the value +255.
+
+
+
+
+ 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
+ the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4).
+
+[page 69]
+
+14 EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
+ specifies an integer character constant containing only one character, since a hexadecimal escape sequence
+ is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
+ two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
+ escape sequence is terminated after three octal digits. (The value of this two-character integer character
+ constant is implementation-defined.)
+
+15 EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
+ L'\1234' specifies the implementation-defined value that results from the combination of the values
+ 0123 and '4'.
+
+ Forward references: common definitions <stddef.h> (7.19), the mbtowc function
+ (7.22.7.2), Unicode utilities <uchar.h> (7.28).
+ 6.4.5 String literals
+ Syntax
+1 string-literal:
+ encoding-prefixopt " s-char-sequenceopt "
+ encoding-prefix:
+ u8
+ u
+ U
+ L
+ s-char-sequence:
+ s-char
+ s-char-sequence s-char
+ s-char:
+ any member of the source character set except
+ the double-quote ", backslash \, or new-line character
+ escape-sequence
+ Constraints
+2 A sequence of adjacent string literal tokens shall not include both a wide string literal and
+ a UTF-8 string literal.
+ Description
+3 A character string literal is a sequence of zero or more multibyte characters enclosed in
+ double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8.
+ A wide string literal is the same, except prefixed by the letter L, u, or U.
+4 The same considerations apply to each element of the sequence in a string literal as if it
+ were in an integer character constant (for a character or UTF-8 string literal) or a wide
+ character constant (for a wide string literal), except that the single-quote ' is
+ representable either by itself or by the escape sequence \', but the double-quote " shall
+
+[page 70]
+
+ be represented by the escape sequence \".
+ Semantics
+5 In translation phase 6, the multibyte character sequences specified by any sequence of
+ adjacent character and identically-prefixed string literal tokens are concatenated into a
+ single multibyte character sequence. If any of the tokens has an encoding prefix, the
+ resulting multibyte character sequence is treated as having the same prefix; otherwise, it
+ is treated as a character string literal. Whether differently-prefixed wide string literal
+ tokens can be concatenated and, if so, the treatment of the resulting multibyte character
+ sequence are implementation-defined.
+6 In translation phase 7, a byte or code of value zero is appended to each multibyte
+ character sequence that results from a string literal or literals.78) The multibyte character
+ sequence is then used to initialize an array of static storage duration and length just
+ sufficient to contain the sequence. For character string literals, the array elements have
+ type char, and are initialized with the individual bytes of the multibyte character
+ sequence. For UTF-8 string literals, the array elements have type char, and are
+ initialized with the characters of the multibyte character sequence, as encoded in UTF-8.
+ For wide string literals prefixed by the letter L, the array elements have type wchar_t
+ and are initialized with the sequence of wide characters corresponding to the multibyte
+ character sequence, as defined by the mbstowcs function with an implementation-
+ defined current locale. For wide string literals prefixed by the letter u or U, the array
+ elements have type char16_t or char32_t, respectively, and are initialized with the
+ sequence of wide characters corresponding to the multibyte character sequence, as
+ defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
+ its type, with an implementation-defined current locale. The value of a string literal
+ containing a multibyte character or escape sequence not represented in the execution
+ character set is implementation-defined.
+7 It is unspecified whether these arrays are distinct provided their elements have the
+ appropriate values. If the program attempts to modify such an array, the behavior is
+ undefined.
+8 EXAMPLE 1 This pair of adjacent character string literals
+ "\x12" "3"
+ produces a single character string literal containing the two characters whose values are '\x12' and '3',
+ because escape sequences are converted into single members of the execution character set just prior to
+ adjacent string literal concatenation.
+
+9 EXAMPLE 2 Each of the sequences of adjacent string literal tokens
+
+
+
+ 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
+ \0 escape sequence.
+
+[page 71]
+
+ "a" "b" L"c"
+ "a" L"b" "c"
+ L"a" "b" L"c"
+ L"a" L"b" L"c"
+ is equivalent to the string literal
+ L"abc"
+ Likewise, each of the sequences
+ "a" "b" u"c"
+ "a" u"b" "c"
+ u"a" "b" u"c"
+ u"a" u"b" u"c"
+ is equivalent to
+ u"abc"
+
+ Forward references: common definitions <stddef.h> (7.19), the mbstowcs
+ function (7.22.8.1), Unicode utilities <uchar.h> (7.28).
+ 6.4.6 Punctuators
+ Syntax
+1 punctuator: one of
+ [ ] ( ) { } . ->
+ ++ -- & * + - ~ !
+ / % << >> < > <= >= == != ^ | && ||
+ ? : ; ...
+ = *= /= %= += -= <<= >>= &= ^= |=
+ , # ##
+ <: :> <% %> %: %:%:
+ Semantics
+2 A punctuator is a symbol that has independent syntactic and semantic significance.
+ Depending on context, it may specify an operation to be performed (which in turn may
+ yield a value or a function designator, produce a side effect, or some combination thereof)
+ in which case it is known as an operator (other forms of operator also exist in some
+ contexts). An operand is an entity on which an operator acts.
+
+[page 72]
+
+3 In all aspects of the language, the six tokens79)
+ <: :> <% %> %: %:%:
+ behave, respectively, the same as the six tokens
+ [ ] { } # ##
+ except for their spelling.80)
+ Forward references: expressions (6.5), declarations (6.7), preprocessing directives
+ (6.10), statements (6.8).
+ 6.4.7 Header names
+ Syntax
+1 header-name:
+ < h-char-sequence >
+ " q-char-sequence "
+ h-char-sequence:
+ h-char
+ h-char-sequence h-char
+ h-char:
+ any member of the source character set except
+ the new-line character and >
+ q-char-sequence:
+ q-char
+ q-char-sequence q-char
+ q-char:
+ any member of the source character set except
+ the new-line character and "
+ Semantics
+2 The sequences in both forms of header names are mapped in an implementation-defined
+ manner to headers or external source file names as specified in 6.10.2.
+3 If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
+ the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the
+
+
+
+
+ 79) These tokens are sometimes called ''digraphs''.
+ 80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely
+ interchanged.
+
+[page 73]
+
+ sequence between the " delimiters, the behavior is undefined.81) Header name
+ preprocessing tokens are recognized only within #include preprocessing directives and
+ in implementation-defined locations within #pragma directives.82)
+4 EXAMPLE The following sequence of characters:
+ 0x3<1/a.h>1e2
+ #include <1/a.h>
+ #define const.member@$
+ forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
+ by a { on the left and a } on the right).
+ {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
+ {#}{include} {<1/a.h>}
+ {#}{define} {const}{.}{member}{@}{$}
+
+ Forward references: source file inclusion (6.10.2).
+ 6.4.8 Preprocessing numbers
+ Syntax
+1 pp-number:
+ digit
+ . digit
+ pp-number digit
+ pp-number identifier-nondigit
+ pp-number e sign
+ pp-number E sign
+ pp-number p sign
+ pp-number P sign
+ pp-number .
+ Description
+2 A preprocessing number begins with a digit optionally preceded by a period (.) and may
+ be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
+ p+, p-, P+, or P-.
+3 Preprocessing number tokens lexically include all floating and integer constant tokens.
+ Semantics
+4 A preprocessing number does not have type or a value; it acquires both after a successful
+ conversion (as part of translation phase 7) to a floating constant token or an integer
+ constant token.
+
+
+ 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
+ 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.
+
+[page 74]
+
+ 6.4.9 Comments
+1 Except within a character constant, a string literal, or a comment, the characters /*
+ introduce a comment. The contents of such a comment are examined only to identify
+ multibyte characters and to find the characters */ that terminate it.83)
+2 Except within a character constant, a string literal, or a comment, the characters //
+ introduce a comment that includes all multibyte characters up to, but not including, the
+ next new-line character. The contents of such a comment are examined only to identify
+ multibyte characters and to find the terminating new-line character.
+3 EXAMPLE
+ "a//b" // four-character string literal
+ #include "//e" // undefined behavior
+ // */ // comment, not syntax error
+ f = g/**//h; // equivalent to f = g / h;
+ //\
+ i(); // part of a two-line comment
+ /\
+ / j(); // part of a two-line comment
+ #define glue(x,y) x##y
+ glue(/,/) k(); // syntax error, not comment
+ /*//*/ l(); // equivalent to l();
+ m = n//**/o
+ + p; // equivalent to m = n + p;
+
+
+
+
+ 83) Thus, /* ... */ comments do not nest.
+
+[page 75]
+
+ 6.5 Expressions
+1 An expression is a sequence of operators and operands that specifies computation of a
+ value, or that designates an object or a function, or that generates side effects, or that
+ performs a combination thereof. The value computations of the operands of an operator
+ are sequenced before the value computation of the result of the operator.
+2 If a side effect on a scalar object is unsequenced relative to either a different side effect
+ on the same scalar object or a value computation using the value of the same scalar
+ object, the behavior is undefined. If there are multiple allowable orderings of the
+ subexpressions of an expression, the behavior is undefined if such an unsequenced side
+ effect occurs in any of the orderings.84)
+3 The grouping of operators and operands is indicated by the syntax.85) Except as specified
+ later, side effects and value computations of subexpressions are unsequenced.86)
+4 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
+ collectively described as bitwise operators) are required to have operands that have
+ integer type. These operators yield values that depend on the internal representations of
+ integers, and have implementation-defined and undefined aspects for signed types.
+5 If an exceptional condition occurs during the evaluation of an expression (that is, if the
+ result is not mathematically defined or not in the range of representable values for its
+ type), the behavior is undefined.
+
+
+
+ 84) This paragraph renders undefined statement expressions such as
+ i = ++i + 1;
+ a[i++] = i;
+ while allowing
+ i = i + 1;
+ a[i] = i;
+
+ 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
+ as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
+ expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
+ 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
+ (6.5.3), and an operand contained between any of the following pairs of operators: grouping
+ parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
+ the conditional operator ? : (6.5.15).
+ Within each major subclause, the operators have the same precedence. Left- or right-associativity is
+ indicated in each subclause by the syntax for the expressions discussed therein.
+ 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and
+ indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
+ different evaluations.
+
+[page 76]
+
+6 The effective type of an object for an access to its stored value is the declared type of the
+ object, if any.87) If a value is stored into an object having no declared type through an
+ lvalue having a type that is not a character type, then the type of the lvalue becomes the
+ effective type of the object for that access and for subsequent accesses that do not modify
+ the stored value. If a value is copied into an object having no declared type using
+ memcpy or memmove, or is copied as an array of character type, then the effective type
+ of the modified object for that access and for subsequent accesses that do not modify the
+ value is the effective type of the object from which the value is copied, if it has one. For
+ all other accesses to an object having no declared type, the effective type of the object is
+ simply the type of the lvalue used for the access.
+7 An object shall have its stored value accessed only by an lvalue expression that has one of
+ the following types:88)
+ -- a type compatible with the effective type of the object,
+ -- a qualified version of a type compatible with the effective type of the object,
+ -- a type that is the signed or unsigned type corresponding to the effective type of the
+ object,
+ -- a type that is the signed or unsigned type corresponding to a qualified version of the
+ effective type of the object,
+ -- an aggregate or union type that includes one of the aforementioned types among its
+ members (including, recursively, a member of a subaggregate or contained union), or
+ -- a character type.
+8 A floating expression may be contracted, that is, evaluated as though it were a single
+ operation, thereby omitting rounding errors implied by the source code and the
+ expression evaluation method.89) The FP_CONTRACT pragma in <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 (7.24.2).
+
+
+ 87) Allocated objects have no declared type.
+ 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
+ 89) The intermediate operations in the contracted expression are evaluated as if to infinite range and
+ precision, while the final operation is rounded to the format determined by the expression evaluation
+ method. A contracted expression might also omit the raising of floating-point exceptions.
+ 90) This license is specifically intended to allow implementations to exploit fast machine instructions that
+ combine multiple C operators. As contractions potentially undermine predictability, and can even
+ decrease accuracy for containing expressions, their use needs to be well-defined and clearly
+ documented.
+
+[page 77]
+
+ 6.5.1 Primary expressions
+ Syntax
+1 primary-expression:
+ identifier
+ constant
+ string-literal
+ ( expression )
+ generic-selection
+ Semantics
+2 An identifier is a primary expression, provided it has been declared as designating an
+ object (in which case it is an lvalue) or a function (in which case it is a function
+ designator).91)
+3 A constant is a primary expression. Its type depends on its form and value, as detailed in
+ 6.4.4.
+4 A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
+5 A parenthesized expression is a primary expression. Its type and value are identical to
+ those of the unparenthesized expression. It is an lvalue, a function designator, or a void
+ expression if the unparenthesized expression is, respectively, an lvalue, a function
+ designator, or a void expression.
+6 A generic selection is a primary expression. Its type and value depend on the selected
+ generic association, as detailed in the following subclause.
+ Forward references: declarations (6.7).
+ 6.5.1.1 Generic selection
+ Syntax
+1 generic-selection:
+ _Generic ( assignment-expression , generic-assoc-list )
+ generic-assoc-list:
+ generic-association
+ generic-assoc-list , generic-association
+ generic-association:
+ type-name : assignment-expression
+ default : assignment-expression
+
+
+
+ 91) Thus, an undeclared identifier is a violation of the syntax.
+
+[page 78]
+
+ Constraints
+2 A generic selection shall have no more than one default generic association. The type
+ name in a generic association shall specify a complete object type other than a variably
+ modified type. No two generic associations in the same generic selection shall specify
+ compatible types. The controlling expression of a generic selection shall have type
+ compatible with at most one of the types named in its generic association list. If a
+ generic selection has no default generic association, its controlling expression shall
+ have type compatible with exactly one of the types named in its generic association list.
+ Semantics
+3 The controlling expression of a generic selection is not evaluated. If a generic selection
+ has a generic association with a type name that is compatible with the type of the
+ controlling expression, then the result expression of the generic selection is the
+ expression in that generic association. Otherwise, the result expression of the generic
+ selection is the expression in the default generic association. None of the expressions
+ from any other generic association of the generic selection is evaluated.
+4 The type and value of a generic selection are identical to those of its result expression. It
+ is an lvalue, a function designator, or a void expression if its result expression is,
+ respectively, an lvalue, a function designator, or a void expression.
+5 EXAMPLE The cbrt type-generic macro could be implemented as follows:
+ #define cbrt(X) _Generic((X), \
+ long double: cbrtl, \
+ default: cbrt, \
+ float: cbrtf \
+ )(X)
+
+ 6.5.2 Postfix operators
+ Syntax
+1 postfix-expression:
+ primary-expression
+ postfix-expression [ expression ]
+ postfix-expression ( argument-expression-listopt )
+ postfix-expression . identifier
+ postfix-expression -> identifier
+ postfix-expression ++
+ postfix-expression --
+ ( type-name ) { initializer-list }
+ ( type-name ) { initializer-list , }
+
+[page 79]
+
+ argument-expression-list:
+ assignment-expression
+ argument-expression-list , assignment-expression
+ 6.5.2.1 Array subscripting
+ Constraints
+1 One of the expressions shall have type ''pointer to complete object type'', the other
+ expression shall have integer type, and the result has type ''type''.
+ Semantics
+2 A postfix expression followed by an expression in square brackets [] is a subscripted
+ designation of an element of an array object. The definition of the subscript operator []
+ is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
+ apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
+ initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
+ element of E1 (counting from zero).
+3 Successive subscript operators designate an element of a multidimensional array object.
+ If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as
+ other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with
+ dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or
+ implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional
+ array, which itself is converted into a pointer if used as other than an lvalue. It follows
+ from this that arrays are stored in row-major order (last subscript varies fastest).
+4 EXAMPLE Consider the array object defined by the declaration
+ int x[3][5];
+ Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an
+ array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
+ a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
+ entails multiplying i by the size of the object to which the pointer points, namely an array of five int
+ objects. The results are added and indirection is applied to yield an array of five ints. When used in the
+ expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
+ yields an int.
+
+ Forward references: additive operators (6.5.6), address and indirection operators
+ (6.5.3.2), array declarators (6.7.6.2).
+
+[page 80]
+
+ 6.5.2.2 Function calls
+ Constraints
+1 The expression that denotes the called function92) shall have type pointer to function
+ returning void or returning a complete object type other than an array type.
+2 If the expression that denotes the called function has a type that includes a prototype, the
+ number of arguments shall agree with the number of parameters. Each argument shall
+ have a type such that its value may be assigned to an object with the unqualified version
+ of the type of its corresponding parameter.
+ Semantics
+3 A postfix expression followed by parentheses () containing a possibly empty, comma-
+ separated list of expressions is a function call. The postfix expression denotes the called
+ function. The list of expressions specifies the arguments to the function.
+4 An argument may be an expression of any complete object type. In preparing for the call
+ to a function, the arguments are evaluated, and each parameter is assigned the value of the
+ corresponding argument.93)
+5 If the expression that denotes the called function has type pointer to function returning an
+ object type, the function call expression has the same type as that object type, and has the
+ value determined as specified in 6.8.6.4. Otherwise, the function call has type void.
+6 If the expression that denotes the called function has a type that does not include a
+ prototype, the integer promotions are performed on each argument, and arguments that
+ have type float are promoted to double. These are called the default argument
+ promotions. If the number of arguments does not equal the number of parameters, the
+ behavior is undefined. If the function is defined with a type that includes a prototype, and
+ either the prototype ends with an ellipsis (, ...) or the types of the arguments after
+ promotion are not compatible with the types of the parameters, the behavior is undefined.
+ If the function is defined with a type that does not include a prototype, and the types of
+ the arguments after promotion are not compatible with those of the parameters after
+ promotion, the behavior is undefined, except for the following cases:
+ -- one promoted type is a signed integer type, the other promoted type is the
+ corresponding unsigned integer type, and the value is representable in both types;
+
+
+
+ 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.
+
+[page 81]
+
+ -- both types are pointers to qualified or unqualified versions of a character type or
+ void.
+7 If the expression that denotes the called function has a type that does include a prototype,
+ the arguments are implicitly converted, as if by assignment, to the types of the
+ corresponding parameters, taking the type of each parameter to be the unqualified version
+ of its declared type. The ellipsis notation in a function prototype declarator causes
+ argument type conversion to stop after the last declared parameter. The default argument
+ promotions are performed on trailing arguments.
+8 No other conversions are performed implicitly; in particular, the number and types of
+ arguments are not compared with those of the parameters in a function definition that
+ does not include a function prototype declarator.
+9 If the function is defined with a type that is not compatible with the type (of the
+ expression) pointed to by the expression that denotes the called function, the behavior is
+ undefined.
+10 There is a sequence point after the evaluations of the function designator and the actual
+ arguments but before the actual call. Every evaluation in the calling function (including
+ other function calls) that is not otherwise specifically sequenced before or after the
+ execution of the body of the called function is indeterminately sequenced with respect to
+ the execution of the called function.94)
+11 Recursive function calls shall be permitted, both directly and indirectly through any chain
+ of other functions.
+12 EXAMPLE In the function call
+ (*pf[f1()]) (f2(), f3() + f4())
+ the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
+ the function pointed to by pf[f1()] is called.
+
+ Forward references: function declarators (including prototypes) (6.7.6.3), function
+ definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
+ 6.5.2.3 Structure and union members
+ Constraints
+1 The first operand of the . operator shall have an atomic, qualified, or unqualified
+ structure or union type, and the second operand shall name a member of that type.
+2 The first operand of the -> operator shall have type ''pointer to atomic, qualified, or
+ unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the
+ second operand shall name a member of the type pointed to.
+
+
+ 94) In other words, function executions do not ''interleave'' with each other.
+
+[page 82]
+
+ Semantics
+3 A postfix expression followed by the . operator and an identifier designates a member of
+ a structure or union object. The value is that of the named member,95) and is an lvalue if
+ the first expression is an lvalue. If the first expression has qualified type, the result has
+ the so-qualified version of the type of the designated member.
+4 A postfix expression followed by the -> operator and an identifier designates a member
+ of a structure or union object. The value is that of the named member of the object to
+ which the first expression points, and is an lvalue.96) If the first expression is a pointer to
+ a qualified type, the result has the so-qualified version of the type of the designated
+ member.
+5 Accessing a member of an atomic structure or union object results in undefined
+ behavior.97)
+6 One special guarantee is made in order to simplify the use of unions: if a union contains
+ several structures that share a common initial sequence (see below), and if the union
+ object currently contains one of these structures, it is permitted to inspect the common
+ initial part of any of them anywhere that a declaration of the completed type of the union
+ is visible. Two structures share a common initial sequence if corresponding members
+ have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
+ initial members.
+7 EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
+ union, f().x is a valid postfix expression but is not an lvalue.
+
+8 EXAMPLE 2 In:
+ struct s { int i; const int ci; };
+ struct s s;
+ const struct s cs;
+ volatile struct s vs;
+ the various members have the types:
+
+
+
+
+ 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.
+
+[page 83]
+
+ s.i int
+ s.ci const int
+ cs.i const int
+ cs.ci const int
+ vs.i volatile int
+ vs.ci volatile const int
+
+9 EXAMPLE 3 The following is a valid fragment:
+ union {
+ struct {
+ int alltypes;
+ } n;
+ struct {
+ int type;
+ int intnode;
+ } ni;
+ struct {
+ int type;
+ double doublenode;
+ } nf;
+ } u;
+ u.nf.type = 1;
+ u.nf.doublenode = 3.14;
+ /* ... */
+ if (u.n.alltypes == 1)
+ if (sin(u.nf.doublenode) == 0.0)
+ /* ... */
+ The following is not a valid fragment (because the union type is not visible within function f):
+ struct t1 { int m; };
+ struct t2 { int m; };
+ int f(struct t1 *p1, struct t2 *p2)
+ {
+ if (p1->m < 0)
+ p2->m = -p2->m;
+ return p1->m;
+ }
+ int g()
+ {
+ union {
+ struct t1 s1;
+ struct t2 s2;
+ } u;
+ /* ... */
+ return f(&u.s1, &u.s2);
+ }
+
+ Forward references: address and indirection operators (6.5.3.2), structure and union
+ specifiers (6.7.2.1).
+
+[page 84]
+
+ 6.5.2.4 Postfix increment and decrement operators
+ Constraints
+1 The operand of the postfix increment or decrement operator shall have atomic, qualified,
+ or unqualified real or pointer type, and shall be a modifiable lvalue.
+ Semantics
+2 The result of the postfix ++ operator is the value of the operand. As a side effect, the
+ value of the operand object is incremented (that is, the value 1 of the appropriate type is
+ added to it). See the discussions of additive operators and compound assignment for
+ information on constraints, types, and conversions and the effects of operations on
+ pointers. The value computation of the result is sequenced before the side effect of
+ updating the stored value of the operand. With respect to an indeterminately-sequenced
+ function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
+ with atomic type is a read-modify-write operation with memory_order_seq_cst
+ memory order semantics.98)
+3 The postfix -- operator is analogous to the postfix ++ operator, except that the value of
+ the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
+ it).
+ Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
+ 6.5.2.5 Compound literals
+ Constraints
+1 The type name shall specify a complete object type or an array of unknown size, but not a
+ variable length array type.
+2 All the constraints for initializer lists in 6.7.9 also apply to compound literals.
+ Semantics
+3 A postfix expression that consists of a parenthesized type name followed by a brace-
+ enclosed list of initializers is a compound literal. It provides an unnamed object whose
+
+ 98) Where a pointer to an atomic object can be formed and E has integer type, E++ is equivalent to the
+ following code sequence where T is the type of E:
+ T *addr = &E;
+ T old = *addr;
+ T new;
+ do {
+ new = old + 1;
+ } while (!atomic_compare_exchange_strong(addr, &old, new));
+ with old being the result of the operation.
+ Special care must be taken if E has floating type; see 6.5.16.2.
+
+[page 85]
+
+ value is given by the initializer list.99)
+4 If the type name specifies an array of unknown size, the size is determined by the
+ initializer list as specified in 6.7.9, and the type of the compound literal is that of the
+ completed array type. Otherwise (when the type name specifies an object type), the type
+ of the compound literal is that specified by the type name. In either case, the result is an
+ lvalue.
+5 The value of the compound literal is that of an unnamed object initialized by the
+ initializer list. If the compound literal occurs outside the body of a function, the object
+ has static storage duration; otherwise, it has automatic storage duration associated with
+ the enclosing block.
+6 All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100)
+7 String literals, and compound literals with const-qualified types, need not designate
+ distinct objects.101)
+8 EXAMPLE 1 The file scope definition
+ int *p = (int []){2, 4};
+ initializes p to point to the first element of an array of two ints, the first having the value two and the
+ second, four. The expressions in this compound literal are required to be constant. The unnamed object
+ has static storage duration.
+
+9 EXAMPLE 2 In contrast, in
+ void f(void)
+ {
+ int *p;
+ /*...*/
+ p = (int [2]){*p};
+ /*...*/
+ }
+ p is assigned the address of the first element of an array of two ints, the first having the value previously
+ pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
+ unnamed object has automatic storage duration.
+
+10 EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
+ created using compound literals can be passed to functions without depending on member order:
+ drawline((struct point){.x=1, .y=1},
+ (struct point){.x=3, .y=4});
+
+
+
+ 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
+ or void only, and the result of a cast expression is not an lvalue.
+ 100) For example, subobjects without explicit initializers are initialized to zero.
+ 101) This allows implementations to share storage for string literals and constant compound literals with
+ the same or overlapping representations.
+
+[page 86]
+
+ Or, if drawline instead expected pointers to struct point:
+ drawline(&(struct point){.x=1, .y=1},
+ &(struct point){.x=3, .y=4});
+
+11 EXAMPLE 4 A read-only compound literal can be specified through constructions like:
+ (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
+
+12 EXAMPLE 5 The following three expressions have different meanings:
+ "/tmp/fileXXXXXX"
+ (char []){"/tmp/fileXXXXXX"}
+ (const char []){"/tmp/fileXXXXXX"}
+ The first always has static storage duration and has type array of char, but need not be modifiable; the last
+ two have automatic storage duration when they occur within the body of a function, and the first of these
+ two is modifiable.
+
+13 EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
+ and can even be shared. For example,
+ (const char []){"abc"} == "abc"
+ might yield 1 if the literals' storage is shared.
+
+14 EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
+ linked object. For example, there is no way to write a self-referential compound literal that could be used
+ as the function argument in place of the named object endless_zeros below:
+ struct int_list { int car; struct int_list *cdr; };
+ struct int_list endless_zeros = {0, &endless_zeros};
+ eval(endless_zeros);
+
+15 EXAMPLE 8 Each compound literal creates only a single object in a given scope:
+ struct s { int i; };
+ int f (void)
+ {
+ struct s *p = 0, *q;
+ int j = 0;
+ again:
+ q = p, p = &((struct s){ j++ });
+ if (j < 2) goto again;
+ return p == q && q->i == 1;
+ }
+ The function f() always returns the value 1.
+16 Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
+ lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
+ have an indeterminate value, which would result in undefined behavior.
+
+ Forward references: type names (6.7.7), initialization (6.7.9).
+
+[page 87]
+
+ 6.5.3 Unary operators
+ Syntax
+1 unary-expression:
+ postfix-expression
+ ++ unary-expression
+ -- unary-expression
+ unary-operator cast-expression
+ sizeof unary-expression
+ sizeof ( type-name )
+ _Alignof ( type-name )
+ unary-operator: one of
+ & * + - ~ !
+ 6.5.3.1 Prefix increment and decrement operators
+ Constraints
+1 The operand of the prefix increment or decrement operator shall have atomic, qualified,
+ or unqualified real or pointer type, and shall be a modifiable lvalue.
+ Semantics
+2 The value of the operand of the prefix ++ operator is incremented. The result is the new
+ value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
+ See the discussions of additive operators and compound assignment for information on
+ constraints, types, side effects, and conversions and the effects of operations on pointers.
+3 The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
+ operand is decremented.
+ Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
+ 6.5.3.2 Address and indirection operators
+ Constraints
+1 The operand of the unary & operator shall be either a function designator, the result of a
+ [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
+ not declared with the register storage-class specifier.
+2 The operand of the unary * operator shall have pointer type.
+ Semantics
+3 The unary & operator yields the address of its operand. If the operand has type ''type'',
+ the result has type ''pointer to type''. If the operand is the result of a unary * operator,
+ neither that operator nor the & operator is evaluated and the result is as if both were
+ omitted, except that the constraints on the operators still apply and the result is not an
+
+[page 88]
+
+ lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
+ the unary * that is implied by the [] is evaluated and the result is as if the & operator
+ were removed and the [] operator were changed to a + operator. Otherwise, the result is
+ a pointer to the object or function designated by its operand.
+4 The unary * operator denotes indirection. If the operand points to a function, the result is
+ a function designator; if it points to an object, the result is an lvalue designating the
+ object. If the operand has type ''pointer to type'', the result has type ''type''. If an
+ invalid value has been assigned to the pointer, the behavior of the unary * operator is
+ undefined.102)
+ Forward references: storage-class specifiers (6.7.1), structure and union specifiers
+ (6.7.2.1).
+ 6.5.3.3 Unary arithmetic operators
+ Constraints
+1 The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
+ integer type; of the ! operator, scalar type.
+ Semantics
+2 The result of the unary + operator is the value of its (promoted) operand. The integer
+ promotions are performed on the operand, and the result has the promoted type.
+3 The result of the unary - operator is the negative of its (promoted) operand. The integer
+ promotions are performed on the operand, and the result has the promoted type.
+4 The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
+ each bit in the result is set if and only if the corresponding bit in the converted operand is
+ not set). The integer promotions are performed on the operand, and the result has the
+ promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
+ to the maximum value representable in that type minus E.
+5 The result of the logical negation operator ! is 0 if the value of its operand compares
+ unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
+ The expression !E is equivalent to (0==E).
+
+
+
+ 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
+ always true that if E is a function designator or an lvalue that is a valid operand of the unary &
+ operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
+ an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
+ Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
+ address inappropriately aligned for the type of object pointed to, and the address of an object after the
+ end of its lifetime.
+
+[page 89]
+
+ 6.5.3.4 The sizeof and _Alignof operators
+ Constraints
+1 The sizeof operator shall not be applied to an expression that has function type or an
+ incomplete type, to the parenthesized name of such a type, or to an expression that
+ designates a bit-field member. The _Alignof operator shall not be applied to a
+ function type or an incomplete type.
+ Semantics
+2 The sizeof operator yields the size (in bytes) of its operand, which may be an
+ expression or the parenthesized name of a type. The size is determined from the type of
+ the operand. The result is an integer. If the type of the operand is a variable length array
+ type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
+ integer constant.
+3 The _Alignof operator yields the alignment requirement of its operand type. The
+ operand is not evaluated and the result is an integer constant. When applied to an array
+ type, the result is the alignment requirement of the element type.
+4 When sizeof is applied to an operand that has type char, unsigned char, or
+ signed char, (or a qualified version thereof) the result is 1. When applied to an
+ operand that has array type, the result is the total number of bytes in the array.103) When
+ applied to an operand that has structure or union type, the result is the total number of
+ bytes in such an object, including internal and trailing padding.
+5 The value of the result of both operators is implementation-defined, and its type (an
+ unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
+6 EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
+ allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
+ allocate and return a pointer to void. For example:
+ extern void *alloc(size_t);
+ double *dp = alloc(sizeof *dp);
+ The implementation of the alloc function should ensure that its return value is aligned suitably for
+ conversion to a pointer to double.
+
+7 EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array:
+ sizeof array / sizeof array[0]
+
+8 EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a
+ function:
+ #include <stddef.h>
+
+
+
+ 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the
+ size of the adjusted (pointer) type (see 6.9.1).
+
+[page 90]
+
+ size_t fsize3(int n)
+ {
+ char b[n+3]; // variable length array
+ return sizeof b; // execution time sizeof
+ }
+ int main()
+ {
+ size_t size;
+ size = fsize3(10); // fsize3 returns 13
+ return 0;
+ }
+
+ Forward references: common definitions <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).
+ 6.5.4 Cast operators
+ Syntax
+1 cast-expression:
+ unary-expression
+ ( type-name ) cast-expression
+ Constraints
+2 Unless the type name specifies a void type, the type name shall specify atomic, qualified,
+ or unqualified scalar type, and the operand shall have scalar type.
+3 Conversions that involve pointers, other than where permitted by the constraints of
+ 6.5.16.1, shall be specified by means of an explicit cast.
+4 A pointer type shall not be converted to any floating type. A floating type shall not be
+ converted to any pointer type.
+ Semantics
+5 Preceding an expression by a parenthesized type name converts the value of the
+ expression to the named type. This construction is called a cast.104) A cast that specifies
+ no conversion has no effect on the type or value of an expression.
+6 If the value of the expression is represented with greater range or precision than required
+ by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
+ type of the expression is the same as the named type and removes any extra range and
+ precision.
+ Forward references: equality operators (6.5.9), function declarators (including
+ prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).
+
+ 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
+ unqualified version of the type.
+
+[page 91]
+
+ 6.5.5 Multiplicative operators
+ Syntax
+1 multiplicative-expression:
+ cast-expression
+ multiplicative-expression * cast-expression
+ multiplicative-expression / cast-expression
+ multiplicative-expression % cast-expression
+ Constraints
+2 Each of the operands shall have arithmetic type. The operands of the % operator shall
+ have integer type.
+ Semantics
+3 The usual arithmetic conversions are performed on the operands.
+4 The result of the binary * operator is the product of the operands.
+5 The result of the / operator is the quotient from the division of the first operand by the
+ second; the result of the % operator is the remainder. In both operations, if the value of
+ the second operand is zero, the behavior is undefined.
+6 When integers are divided, the result of the / operator is the algebraic quotient with any
+ fractional part discarded.105) If the quotient a/b is representable, the expression
+ (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
+ undefined.
+ 6.5.6 Additive operators
+ Syntax
+1 additive-expression:
+ multiplicative-expression
+ additive-expression + multiplicative-expression
+ additive-expression - multiplicative-expression
+ Constraints
+2 For addition, either both operands shall have arithmetic type, or one operand shall be a
+ pointer to a complete object type and the other shall have integer type. (Incrementing is
+ equivalent to adding 1.)
+3 For subtraction, one of the following shall hold:
+
+
+
+
+ 105) This is often called ''truncation toward zero''.
+
+[page 92]
+
+ -- both operands have arithmetic type;
+ -- both operands are pointers to qualified or unqualified versions of compatible complete
+ object types; or
+ -- the left operand is a pointer to a complete object type and the right operand has
+ integer type.
+ (Decrementing is equivalent to subtracting 1.)
+ Semantics
+4 If both operands have arithmetic type, the usual arithmetic conversions are performed on
+ them.
+5 The result of the binary + operator is the sum of the operands.
+6 The result of the binary - operator is the difference resulting from the subtraction of the
+ second operand from the first.
+7 For the purposes of these operators, a pointer to an object that is not an element of an
+ array behaves the same as a pointer to the first element of an array of length one with the
+ type of the object as its element type.
+8 When an expression that has integer type is added to or subtracted from a pointer, the
+ result has the type of the pointer operand. If the pointer operand points to an element of
+ an array object, and the array is large enough, the result points to an element offset from
+ the original element such that the difference of the subscripts of the resulting and original
+ array elements equals the integer expression. In other words, if the expression P points to
+ the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
+ (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
+ the array object, provided they exist. Moreover, if the expression P points to the last
+ element of an array object, the expression (P)+1 points one past the last element of the
+ array object, and if the expression Q points one past the last element of an array object,
+ the expression (Q)-1 points to the last element of the array object. If both the pointer
+ operand and the result point to elements of the same array object, or one past the last
+ element of the array object, the evaluation shall not produce an overflow; otherwise, the
+ behavior is undefined. If the result points one past the last element of the array object, it
+ shall not be used as the operand of a unary * operator that is evaluated.
+9 When two pointers are subtracted, both shall point to elements of the same array object,
+ or one past the last element of the array object; the result is the difference of the
+ subscripts of the two array elements. The size of the result is implementation-defined,
+ and its type (a signed integer type) is ptrdiff_t defined in the <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
+
+[page 93]
+
+ object of type ptrdiff_t. Moreover, if the expression P points either to an element of
+ an array object or one past the last element of an array object, and the expression Q points
+ to the last element of the same array object, the expression ((Q)+1)-(P) has the same
+ value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
+ expression P points one past the last element of the array object, even though the
+ expression (Q)+1 does not point to an element of the array object.106)
+10 EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types.
+ {
+ int n = 4, m = 3;
+ int a[n][m];
+ int (*p)[m] = a; // p == &a[0]
+ p += 1; // p == &a[1]
+ (*p)[2] = 99; // a[1][2] == 99
+ n = p - a; // n == 1
+ }
+11 If array a in the above example were declared to be an array of known constant size, and pointer p were
+ declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
+ the same.
+
+ Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
+ (7.19).
+ 6.5.7 Bitwise shift operators
+ Syntax
+1 shift-expression:
+ additive-expression
+ shift-expression << additive-expression
+ shift-expression >> additive-expression
+ Constraints
+2 Each of the operands shall have integer type.
+ Semantics
+3 The integer promotions are performed on each of the operands. The type of the result is
+ that of the promoted left operand. If the value of the right operand is negative or is
+
+ 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
+ this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
+ by the size of the object originally pointed to, and the resulting pointer is converted back to the
+ original type. For pointer subtraction, the result of the difference between the character pointers is
+ similarly divided by the size of the object originally pointed to.
+ When viewed in this way, an implementation need only provide one extra byte (which may overlap
+ another object in the program) just after the end of the object in order to satisfy the ''one past the last
+ element'' requirements.
+
+[page 94]
+
+ greater than or equal to the width of the promoted left operand, the behavior is undefined.
+4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
+ zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo
+ one more than the maximum value representable in the result type. If E1 has a signed
+ type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is
+ the resulting value; otherwise, the behavior is undefined.
+5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
+ or if E1 has a signed type and a nonnegative value, the value of the result is the integral
+ part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
+ resulting value is implementation-defined.
+ 6.5.8 Relational operators
+ Syntax
+1 relational-expression:
+ shift-expression
+ relational-expression < shift-expression
+ relational-expression > shift-expression
+ relational-expression <= shift-expression
+ relational-expression >= shift-expression
+ Constraints
+2 One of the following shall hold:
+ -- both operands have real type; or
+ -- both operands are pointers to qualified or unqualified versions of compatible object
+ types.
+ Semantics
+3 If both of the operands have arithmetic type, the usual arithmetic conversions are
+ performed.
+4 For the purposes of these operators, a pointer to an object that is not an element of an
+ array behaves the same as a pointer to the first element of an array of length one with the
+ type of the object as its element type.
+5 When two pointers are compared, the result depends on the relative locations in the
+ address space of the objects pointed to. If two pointers to object types both point to the
+ same object, or both point one past the last element of the same array object, they
+ compare equal. If the objects pointed to are members of the same aggregate object,
+ pointers to structure members declared later compare greater than pointers to members
+ declared earlier in the structure, and pointers to array elements with larger subscript
+ values compare greater than pointers to elements of the same array with lower subscript
+
+[page 95]
+
+ values. All pointers to members of the same union object compare equal. If the
+ expression P points to an element of an array object and the expression Q points to the
+ last element of the same array object, the pointer expression Q+1 compares greater than
+ P. In all other cases, the behavior is undefined.
+6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
+ (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
+ false.107) The result has type int.
+ 6.5.9 Equality operators
+ Syntax
+1 equality-expression:
+ relational-expression
+ equality-expression == relational-expression
+ equality-expression != relational-expression
+ Constraints
+2 One of the following shall hold:
+ -- both operands have arithmetic type;
+ -- both operands are pointers to qualified or unqualified versions of compatible types;
+ -- one operand is a pointer to an object type and the other is a pointer to a qualified or
+ unqualified version of void; or
+ -- one operand is a pointer and the other is a null pointer constant.
+ Semantics
+3 The == (equal to) and != (not equal to) operators are analogous to the relational
+ operators except for their lower precedence.108) Each of the operators yields 1 if the
+ specified relation is true and 0 if it is false. The result has type int. For any pair of
+ operands, exactly one of the relations is true.
+4 If both of the operands have arithmetic type, the usual arithmetic conversions are
+ performed. Values of complex types are equal if and only if both their real parts are equal
+ and also their imaginary parts are equal. Any two values of arithmetic types from
+ different type domains are equal if and only if the results of their conversions to the
+ (complex) result type determined by the usual arithmetic conversions are equal.
+
+
+
+ 107) The expression a<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''.
+ 108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.
+
+[page 96]
+
+5 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.
+6 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)
+7 For the purposes of these operators, a pointer to an object that is not an element of an
+ array behaves the same as a pointer to the first element of an array of length one with the
+ type of the object as its element type.
+ 6.5.10 Bitwise AND operator
+ Syntax
+1 AND-expression:
+ equality-expression
+ AND-expression & equality-expression
+ Constraints
+2 Each of the operands shall have integer type.
+ Semantics
+3 The usual arithmetic conversions are performed on the operands.
+4 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).
+
+
+
+
+ 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.
+
+[page 97]
+
+ 6.5.11 Bitwise exclusive OR operator
+ Syntax
+1 exclusive-OR-expression:
+ AND-expression
+ exclusive-OR-expression ^ AND-expression
+ Constraints
+2 Each of the operands shall have integer type.
+ Semantics
+3 The usual arithmetic conversions are performed on the operands.
+4 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
+1 inclusive-OR-expression:
+ exclusive-OR-expression
+ inclusive-OR-expression | exclusive-OR-expression
+ Constraints
+2 Each of the operands shall have integer type.
+ Semantics
+3 The usual arithmetic conversions are performed on the operands.
+4 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).
+
+[page 98]
+
+ 6.5.13 Logical AND operator
+ Syntax
+1 logical-AND-expression:
+ inclusive-OR-expression
+ logical-AND-expression && inclusive-OR-expression
+ Constraints
+2 Each of the operands shall have scalar type.
+ Semantics
+3 The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
+ yields 0. The result has type int.
+4 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
+1 logical-OR-expression:
+ logical-AND-expression
+ logical-OR-expression || logical-AND-expression
+ Constraints
+2 Each of the operands shall have scalar type.
+ Semantics
+3 The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
+ yields 0. The result has type int.
+4 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.
+
+[page 99]
+
+ 6.5.15 Conditional operator
+ Syntax
+1 conditional-expression:
+ logical-OR-expression
+ logical-OR-expression ? expression : conditional-expression
+ Constraints
+2 The first operand shall have scalar type.
+3 One of the following shall hold for the second and third operands:
+ -- both operands have arithmetic type;
+ -- both operands have the same structure or union type;
+ -- both operands have void type;
+ -- both operands are pointers to qualified or unqualified versions of compatible types;
+ -- one operand is a pointer and the other is a null pointer constant; or
+ -- one operand is a pointer to an object type and the other is a pointer to a qualified or
+ unqualified version of void.
+ Semantics
+4 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)
+5 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.
+6 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.
+
+ 110) A conditional expression does not yield an lvalue.
+
+[page 100]
+
+7 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.
+8 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 *
+
+ 6.5.16 Assignment operators
+ Syntax
+1 assignment-expression:
+ conditional-expression
+ unary-expression assignment-operator assignment-expression
+ assignment-operator: one of
+ = *= /= %= += -= <<= >>= &= ^= |=
+ Constraints
+2 An assignment operator shall have a modifiable lvalue as its left operand.
+ Semantics
+3 An assignment operator stores a value in the object designated by the left operand. An
+ assignment expression has the value of the left operand after the assignment,111) but is not
+ an lvalue. The type of an assignment expression is the type the left operand would have
+ after lvalue conversion. The side effect of updating the stored value of the left operand is
+ sequenced after the value computations of the left and right operands. The evaluations of
+ the operands are unsequenced.
+
+
+
+
+ 111) The implementation is permitted to read the object to determine the value but is not required to, even
+ when the object has volatile-qualified type.
+
+[page 101]
+
+ 6.5.16.1 Simple assignment
+ Constraints
+1 One of the following shall hold:112)
+ -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has
+ arithmetic type;
+ -- the left operand has an atomic, qualified, or unqualified version of a structure or union
+ type compatible with the type of the right;
+ -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
+ the type the left operand would have after lvalue conversion) both operands are
+ pointers to qualified or unqualified versions of compatible types, and the type pointed
+ to by the left has all the qualifiers of the type pointed to by the right;
+ -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
+ the type the left operand would have after lvalue conversion) one operand is a pointer
+ to an object type, and the other is a pointer to a qualified or unqualified version of
+ void, and the type pointed to by the left has all the qualifiers of the type pointed to
+ by the right;
+ -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null
+ pointer constant; or
+ -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a
+ pointer.
+ Semantics
+2 In simple assignment (=), the value of the right operand is converted to the type of the
+ assignment expression and replaces the value stored in the object designated by the left
+ operand.
+3 If the value being stored in an object is read from another object that overlaps in any way
+ the storage of the first object, then the overlap shall be exact and the two objects shall
+ have qualified or unqualified versions of a compatible type; otherwise, the behavior is
+ undefined.
+4 EXAMPLE 1 In the program fragment
+
+
+
+
+ 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
+ (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type
+ qualifiers that were applied to the type category of the expression (for example, it removes const but
+ not volatile from the type int volatile * const).
+
+[page 102]
+
+ int f(void);
+ char c;
+ /* ... */
+ if ((c = f()) == -1)
+ /* ... */
+ the int value returned by the function may be truncated when stored in the char, and then converted back
+ to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
+ values as unsigned char (and char is narrower than int), the result of the conversion cannot be
+ negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
+ variable c should be declared as int.
+
+5 EXAMPLE 2 In the fragment:
+ char c;
+ int i;
+ long l;
+ l = (c = i);
+ the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
+ of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
+ that is, long int type.
+
+6 EXAMPLE 3 Consider the fragment:
+ const char **cpp;
+ char *p;
+ const char c = 'A';
+ cpp = &p; // constraint violation
+ *cpp = &c; // valid
+ *p = 0; // valid
+ The first assignment is unsafe because it would allow the following valid code to attempt to change the
+ value of the const object c.
+
+ 6.5.16.2 Compound assignment
+ Constraints
+1 For the operators += and -= only, either the left operand shall be an atomic, qualified, or
+ unqualified pointer to a complete object type, and the right shall have integer type; or the
+ left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
+ shall have arithmetic type.
+2 For the other operators, the left operand shall have atomic, qualified, or unqualified
+ arithmetic type, and (considering the type the left operand would have after lvalue
+ conversion) each operand shall have arithmetic type consistent with those allowed by the
+ corresponding binary operator.
+ Semantics
+3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
+ expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
+ respect to an indeterminately-sequenced function call, the operation of a compound
+
+[page 103]
+
+assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
+read-modify-write operation with memory_order_seq_cst memory order
+semantics.113)
+
+
+
+
+113) Where a pointer to an atomic object can be formed and E1 and E2 have integer type, this is equivalent
+ to the following code sequence where T1 is the type of E1 and T2 is the type of E2:
+ T1 *addr = &E1;
+ T2 val = (E2);
+ T1 old = *addr;
+ T1 new;
+ do {
+ new = old op val;
+ } while (!atomic_compare_exchange_strong(addr, &old, new));
+ with new being the result of the operation.
+ If E1 or E2 has floating type, then exceptional conditions or floating-point exceptions encountered
+ during discarded evaluations of new should also be discarded in order to satisfy the equivalence of E1
+ op = E2 and E1 = E1 op (E2). For example, if annex F is in effect, the floating types involved have
+ IEC 60559 formats, and FLT_EVAL_METHOD is 0, the equivalent code would be:
+ #include <fenv.h>
+ #pragma STDC FENV_ACCESS ON
+ /* ... */
+ fenv_t fenv;
+ T1 *addr = &E1;
+ T2 val = E2;
+ T1 old = *addr;
+ T1 new;
+ feholdexcept(&fenv);
+ for (;;) {
+ new = old op val;
+ if (atomic_compare_exchange_strong(addr, &old, new))
+ break;
+ feclearexcept(FE_ALL_EXCEPT);
+ }
+ feupdateenv(&fenv);
+ If FLT_EVAL_METHOD is not 0, then T2 must be a type with the range and precision to which E2 is
+ evaluated in order to satisfy the equivalence.
+
+[page 104]
+
+ 6.5.17 Comma operator
+ Syntax
+1 expression:
+ assignment-expression
+ expression , assignment-expression
+ Semantics
+2 The left operand of a comma operator is evaluated as a void expression; there is a
+ sequence point between its evaluation and that of the right operand. Then the right
+ operand is evaluated; the result has its type and value.114)
+3 EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
+ appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
+ of initializers). On the other hand, it can be used within a parenthesized expression or within the second
+ expression of a conditional operator in such contexts. In the function call
+ f(a, (t=3, t+2), c)
+ the function has three arguments, the second of which has the value 5.
+
+ Forward references: initialization (6.7.9).
+
+
+
+
+ 114) A comma operator does not yield an lvalue.
+
+[page 105]
+
+ 6.6 Constant expressions
+ Syntax
+1 constant-expression:
+ conditional-expression
+ Description
+2 A constant expression can be evaluated during translation rather than runtime, and
+ accordingly may be used in any place that a constant may be.
+ Constraints
+3 Constant expressions shall not contain assignment, increment, decrement, function-call,
+ or comma operators, except when they are contained within a subexpression that is not
+ evaluated.115)
+4 Each constant expression shall evaluate to a constant that is in the range of representable
+ values for its type.
+ Semantics
+5 An expression that evaluates to a constant is required in several contexts. If a floating
+ expression is evaluated in the translation environment, the arithmetic range and precision
+ shall be at least as great as if the expression were being evaluated in the execution
+ environment.116)
+6 An integer constant expression117) shall have integer type and shall only have operands
+ that are integer constants, enumeration constants, character constants, sizeof
+ expressions whose results are integer constants, _Alignof expressions, 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 or _Alignof operator.
+7 More latitude is permitted for constant expressions in initializers. Such a constant
+ expression shall be, or evaluate to, one of the following:
+ -- an arithmetic constant expression,
+
+
+
+ 115) The operand of a sizeof or _Alignof operator is usually not evaluated (6.5.3.4).
+ 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
+ the translation environment.
+ 117) An integer constant expression is required in a number of contexts such as the size of a bit-field
+ member of a structure, the value of an enumeration constant, and the size of a non-variable length
+ array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
+ preprocessing directives are discussed in 6.10.1.
+
+[page 106]
+
+ -- a null pointer constant,
+ -- an address constant, or
+ -- an address constant for a complete object type plus or minus an integer constant
+ expression.
+8 An arithmetic constant expression shall have arithmetic type and shall only have
+ operands that are integer constants, floating constants, enumeration constants, character
+ constants, sizeof expressions whose results are integer constants, and _Alignof
+ 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 or
+ _Alignof operator.
+9 An address constant is a null pointer, a pointer to an lvalue designating an object of static
+ storage duration, or a pointer to a function designator; it shall be created explicitly using
+ the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
+ an expression of array or function type. The array-subscript [] and member-access .
+ and -> operators, the address & and indirection * unary operators, and pointer casts may
+ be used in the creation of an address constant, but the value of an object shall not be
+ accessed by use of these operators.
+10 An implementation may accept other forms of constant expressions.
+11 The semantic rules for the evaluation of a constant expression are the same as for
+ nonconstant expressions.118)
+ Forward references: array declarators (6.7.6.2), initialization (6.7.9).
+
+
+
+
+ 118) Thus, in the following initialization,
+ static int i = 2 || 1 / 0;
+ the expression is a valid integer constant expression with value one.
+
+[page 107]
+
+ 6.7 Declarations
+ Syntax
+1 declaration:
+ declaration-specifiers init-declarator-listopt ;
+ static_assert-declaration
+ declaration-specifiers:
+ storage-class-specifier declaration-specifiersopt
+ type-specifier declaration-specifiersopt
+ type-qualifier declaration-specifiersopt
+ function-specifier declaration-specifiersopt
+ alignment-specifier declaration-specifiersopt
+ init-declarator-list:
+ init-declarator
+ init-declarator-list , init-declarator
+ init-declarator:
+ declarator
+ declarator = initializer
+ Constraints
+2 A declaration other than a static_assert declaration shall declare at least a declarator
+ (other than the parameters of a function or the members of a structure or union), a tag, or
+ the members of an enumeration.
+3 If an identifier has no linkage, there shall be no more than one declaration of the identifier
+ (in a declarator or type specifier) with the same scope and in the same name space, except
+ that:
+ -- a typedef name may be redefined to denote the same type as it currently does,
+ provided that type is not a variably modified type;
+ -- tags may be redeclared as specified in 6.7.2.3.
+4 All declarations in the same scope that refer to the same object or function shall specify
+ compatible types.
+ Semantics
+5 A declaration specifies the interpretation and attributes of a set of identifiers. A definition
+ of an identifier is a declaration for that identifier that:
+ -- for an object, causes storage to be reserved for that object;
+ -- for a function, includes the function body;119)
+
+[page 108]
+
+ -- for an enumeration constant, is the (only) declaration of the identifier;
+ -- for a typedef name, is the first (or only) declaration of the identifier.
+6 The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
+ storage duration, and part of the type of the entities that the declarators denote. The init-
+ declarator-list is a comma-separated sequence of declarators, each of which may have
+ additional type information, or an initializer, or both. The declarators contain the
+ identifiers (if any) being declared.
+7 If an identifier for an object is declared with no linkage, the type for the object shall be
+ complete by the end of its declarator, or by the end of its init-declarator if it has an
+ initializer; in the case of function parameters (including in prototypes), it is the adjusted
+ type (see 6.7.6.3) that is required to be complete.
+ Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
+ (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
+ 6.7.1 Storage-class specifiers
+ Syntax
+1 storage-class-specifier:
+ typedef
+ extern
+ static
+ _Thread_local
+ auto
+ register
+ Constraints
+2 At most, one storage-class specifier may be given in the declaration specifiers in a
+ declaration, except that _Thread_local may appear with static or extern.120)
+3 In the declaration of an object with block scope, if the declaration specifiers include
+ _Thread_local, they shall also include either static or extern. If
+ _Thread_local appears in any declaration of an object, it shall be present in every
+ declaration of that object.
+4 _Thread_local shall not appear in the declaration specifiers of a function declaration.
+
+
+
+
+ 119) Function definitions have a different syntax, described in 6.9.1.
+ 120) See ''future language directions'' (6.11.5).
+
+[page 109]
+
+ Semantics
+5 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.
+6 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)
+7 The declaration of an identifier for a function that has block scope shall have no explicit
+ storage-class specifier other than extern.
+8 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).
+
+
+
+
+ 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 operators that can be applied to an array declared with storage-class specifier
+ register are sizeof and _Alignof.
+
+[page 110]
+
+ 6.7.2 Type specifiers
+ Syntax
+1 type-specifier:
+ void
+ char
+ short
+ int
+ long
+ float
+ double
+ signed
+ unsigned
+ _Bool
+ _Complex
+ atomic-type-specifier
+ struct-or-union-specifier
+ enum-specifier
+ typedef-name
+ Constraints
+2 At least one type specifier shall be given in the declaration specifiers in each declaration,
+ and in the specifier-qualifier list in each struct declaration and type name. Each list of
+ type specifiers shall be one of the following multisets (delimited by commas, when there
+ is more than one multiset per item); the type specifiers may occur in any order, possibly
+ intermixed with the other declaration specifiers.
+ -- void
+ -- char
+ -- signed char
+ -- unsigned char
+ -- short, signed short, short int, or signed short int
+ -- unsigned short, or unsigned short int
+ -- int, signed, or signed int
+ -- unsigned, or unsigned int
+ -- long, signed long, long int, or signed long int
+ -- unsigned long, or unsigned long int
+
+[page 111]
+
+ -- long long, signed long long, long long int, or
+ signed long long int
+ -- unsigned long long, or unsigned long long int
+ -- float
+ -- double
+ -- long double
+ -- _Bool
+ -- float _Complex
+ -- double _Complex
+ -- long double _Complex
+ -- atomic type specifier
+ -- struct or union specifier
+ -- enum specifier
+ -- typedef name
+3 The type specifier _Complex shall not be used if the implementation does not support
+ complex types (see 6.10.8.3).
+ Semantics
+4 Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
+ through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
+ characteristics of the other types are discussed in 6.2.5.
+5 Each of the comma-separated multisets designates the same type, except that for bit-
+ fields, it is implementation-defined whether the specifier int designates the same type as
+ signed int or the same type as unsigned int.
+ Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
+ structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
+ 6.7.2.1 Structure and union specifiers
+ Syntax
+1 struct-or-union-specifier:
+ struct-or-union identifieropt { struct-declaration-list }
+ struct-or-union identifier
+
+[page 112]
+
+ struct-or-union:
+ struct
+ union
+ struct-declaration-list:
+ struct-declaration
+ struct-declaration-list struct-declaration
+ struct-declaration:
+ specifier-qualifier-list struct-declarator-listopt ;
+ static_assert-declaration
+ specifier-qualifier-list:
+ type-specifier specifier-qualifier-listopt
+ type-qualifier specifier-qualifier-listopt
+ struct-declarator-list:
+ struct-declarator
+ struct-declarator-list , struct-declarator
+ struct-declarator:
+ declarator
+ declaratoropt : constant-expression
+ Constraints
+2 A struct-declaration that does not declare an anonymous structure or anonymous union
+ shall contain a struct-declarator-list.
+3 A structure or union shall not contain a member with incomplete or function type (hence,
+ a structure shall not contain an instance of itself, but may contain a pointer to an instance
+ of itself), except that the last member of a structure with more than one named member
+ may have incomplete array type; such a structure (and any union containing, possibly
+ recursively, a member that is such a structure) shall not be a member of a structure or an
+ element of an array.
+4 The expression that specifies the width of a bit-field shall be an integer constant
+ expression with a nonnegative value that does not exceed the width of an object of the
+ type that would be specified were the colon and expression omitted.122) If the value is
+ zero, the declaration shall have no declarator.
+5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
+ int, unsigned int, or some other implementation-defined type. It is
+ implementation-defined whether atomic types are permitted.
+
+ 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.
+
+[page 113]
+
+ Semantics
+6 As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
+ storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
+ of members whose storage overlap.
+7 Structure and union specifiers have the same form. The keywords struct and union
+ indicate that the type being specified is, respectively, a structure type or a union type.
+8 The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
+ within a translation unit. The struct-declaration-list is a sequence of declarations for the
+ members of the structure or union. If the struct-declaration-list does not contain any
+ named members, either directly or via an anonymous structure or anonymous union, the
+ behavior is undefined. The type is incomplete until immediately after the } that
+ terminates the list, and complete thereafter.
+9 A member of a structure or union may have any complete object type other than a
+ variably modified type.123) In addition, a member may be declared to consist of a
+ specified number of bits (including a sign bit, if any). Such a member is called a
+ bit-field;124) its width is preceded by a colon.
+10 A bit-field is interpreted as having a signed or unsigned integer type consisting of the
+ specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of
+ type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
+ bit-field has the semantics of a _Bool.
+11 An implementation may allocate any addressable storage unit large enough to hold a bit-
+ field. If enough space remains, a bit-field that immediately follows another bit-field in a
+ structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
+ whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
+ implementation-defined. The order of allocation of bit-fields within a unit (high-order to
+ low-order or low-order to high-order) is implementation-defined. The alignment of the
+ addressable storage unit is unspecified.
+12 A bit-field declaration with no declarator, but only a colon and a width, indicates an
+ unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0
+
+
+ 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.
+
+[page 114]
+
+ indicates that no further bit-field is to be packed into the unit in which the previous bit-
+ field, if any, was placed.
+13 An unnamed member whose type specifier is a structure specifier with no tag is called an
+ anonymous structure; an unnamed member whose type specifier is a union specifier with
+ no tag is called an anonymous union. The members of an anonymous structure or union
+ are considered to be members of the containing structure or union. This applies
+ recursively if the containing structure or union is also anonymous.
+14 Each non-bit-field member of a structure or union object is aligned in an implementation-
+ defined manner appropriate to its type.
+15 Within a structure object, the non-bit-field members and the units in which bit-fields
+ reside have addresses that increase in the order in which they are declared. A pointer to a
+ structure object, suitably converted, points to its initial member (or if that member is a
+ bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
+ padding within a structure object, but not at its beginning.
+16 The size of a union is sufficient to contain the largest of its members. The value of at
+ most one of the members can be stored in a union object at any time. A pointer to a
+ union object, suitably converted, points to each of its members (or if a member is a bit-
+ field, then to the unit in which it resides), and vice versa.
+17 There may be unnamed padding at the end of a structure or union.
+18 As a special case, the last element of a structure with more than one named member may
+ have an incomplete array type; this is called a flexible array member. In most situations,
+ the flexible array member is ignored. In particular, the size of the structure is as if the
+ flexible array member were omitted except that it may have more trailing padding than
+ the omission would imply. However, when a . (or ->) operator has a left operand that is
+ (a pointer to) a structure with a flexible array member and the right operand names that
+ member, it behaves as if that member were replaced with the longest array (with the same
+ element type) that would not make the structure larger than the object being accessed; the
+ offset of the array shall remain that of the flexible array member, even if this would differ
+ from that of the replacement array. If this array would have no elements, it behaves as if
+ it had one element but the behavior is undefined if any attempt is made to access that
+ element or to generate a pointer one past it.
+19 EXAMPLE 1 The following illustrates anonymous structures and unions:
+ struct v {
+ union { // anonymous union
+ struct { int i, j; }; // anonymous structure
+ struct { long k, l; } w;
+ };
+ int m;
+ } v1;
+
+[page 115]
+
+ v1.i = 2; // valid
+ v1.k = 3; // invalid: inner structure is not anonymous
+ v1.w.k = 5; // valid
+
+20 EXAMPLE 2 After the declaration:
+ struct s { int n; double d[]; };
+ the structure struct s has a flexible array member d. A typical way to use this is:
+ int m = /* some value */;
+ struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
+ and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
+ p had been declared as:
+ struct { int n; double d[m]; } *p;
+ (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
+ not be the same).
+21 Following the above declaration:
+ struct s t1 = { 0 }; // valid
+ struct s t2 = { 1, { 4.2 }}; // invalid
+ t1.n = 4; // valid
+ t1.d[0] = 4.2; // might be undefined behavior
+ The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
+ contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
+ sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
+ in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
+ code.
+22 After the further declaration:
+ struct ss { int n; };
+ the expressions:
+ sizeof (struct s) >= sizeof (struct ss)
+ sizeof (struct s) >= offsetof(struct s, d)
+ are always equal to 1.
+23 If sizeof (double) is 8, then after the following code is executed:
+ struct s *s1;
+ struct s *s2;
+ s1 = malloc(sizeof (struct s) + 64);
+ s2 = malloc(sizeof (struct s) + 46);
+ and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
+ purposes, as if the identifiers had been declared as:
+ struct { int n; double d[8]; } *s1;
+ struct { int n; double d[5]; } *s2;
+24 Following the further successful assignments:
+
+[page 116]
+
+ s1 = malloc(sizeof (struct s) + 10);
+ s2 = malloc(sizeof (struct s) + 6);
+ they then behave as if the declarations were:
+ struct { int n; double d[1]; } *s1, *s2;
+ and:
+ double *dp;
+ dp = &(s1->d[0]); // valid
+ *dp = 42; // valid
+ dp = &(s2->d[0]); // valid
+ *dp = 42; // undefined behavior
+25 The assignment:
+ *s1 = *s2;
+ only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
+ of the structure, they might be copied or simply overwritten with indeterminate values.
+
+26 EXAMPLE 3 Because members of anonymous structures and unions are considered to be members of the
+ containing structure or union, struct s in the following example has more than one named member and
+ thus the use of a flexible array member is valid:
+ struct s {
+ struct { int i; };
+ int a[];
+ };
+
+ Forward references: declarators (6.7.6), tags (6.7.2.3).
+ 6.7.2.2 Enumeration specifiers
+ Syntax
+1 enum-specifier:
+ enum identifieropt { enumerator-list }
+ enum identifieropt { enumerator-list , }
+ enum identifier
+ enumerator-list:
+ enumerator
+ enumerator-list , enumerator
+ enumerator:
+ enumeration-constant
+ enumeration-constant = constant-expression
+ Constraints
+2 The expression that defines the value of an enumeration constant shall be an integer
+ constant expression that has a value representable as an int.
+
+[page 117]
+
+ Semantics
+3 The identifiers in an enumerator list are declared as constants that have type int and
+ may appear wherever such are permitted.127) An enumerator with = defines its
+ enumeration constant as the value of the constant expression. If the first enumerator has
+ no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
+ defines its enumeration constant as the value of the constant expression obtained by
+ adding 1 to the value of the previous enumeration constant. (The use of enumerators with
+ = may produce enumeration constants with values that duplicate other values in the same
+ enumeration.) The enumerators of an enumeration are also known as its members.
+4 Each enumerated type shall be compatible with char, a signed integer type, or an
+ unsigned integer type. The choice of type is implementation-defined,128) but shall be
+ capable of representing the values of all the members of the enumeration. The
+ enumerated type is incomplete until immediately after the } that terminates the list of
+ enumerator declarations, and complete thereafter.
+5 EXAMPLE The following fragment:
+ enum hue { chartreuse, burgundy, claret=20, winedark };
+ enum hue col, *cp;
+ col = claret;
+ cp = &col;
+ if (*cp != burgundy)
+ /* ... */
+ makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
+ pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.
+
+ Forward references: tags (6.7.2.3).
+ 6.7.2.3 Tags
+ Constraints
+1 A specific type shall have its content defined at most once.
+2 Where two declarations that use the same tag declare the same type, they shall both use
+ the same choice of struct, union, or enum.
+3 A type specifier of the form
+ enum identifier
+ without an enumerator list shall only appear after the type it specifies is complete.
+
+
+ 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
+ each other and from other identifiers declared in ordinary declarators.
+ 128) An implementation may delay the choice of which integer type until all enumeration constants have
+ been seen.
+
+[page 118]
+
+ Semantics
+4 All declarations of structure, union, or enumerated types that have the same scope and
+ use the same tag declare the same type. Irrespective of whether there is a tag or what
+ other declarations of the type are in the same translation unit, the type is incomplete129)
+ until immediately after the closing brace of the list defining the content, and complete
+ thereafter.
+5 Two declarations of structure, union, or enumerated types which are in different scopes or
+ use different tags declare distinct types. Each declaration of a structure, union, or
+ enumerated type which does not include a tag declares a distinct type.
+6 A type specifier of the form
+ struct-or-union identifieropt { struct-declaration-list }
+ or
+ enum identifieropt { enumerator-list }
+ or
+ enum identifieropt { enumerator-list , }
+ declares a structure, union, or enumerated type. The list defines the structure content,
+ union content, or enumeration content. If an identifier is provided,130) the type specifier
+ also declares the identifier to be the tag of that type.
+7 A declaration of the form
+ struct-or-union identifier ;
+ specifies a structure or union type and declares the identifier as a tag of that type.131)
+8 If a type specifier of the form
+ struct-or-union identifier
+ occurs other than as part of one of the above forms, and no other declaration of the
+ identifier as a tag is visible, then it declares an incomplete structure or union type, and
+ declares the identifier as the tag of that type.131)
+
+
+
+ 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.
+
+[page 119]
+
+9 If a type specifier of the form
+ struct-or-union identifier
+ or
+ enum identifier
+ occurs other than as part of one of the above forms, and a declaration of the identifier as a
+ tag is visible, then it specifies the same type as that other declaration, and does not
+ redeclare the tag.
+10 EXAMPLE 1 This mechanism allows declaration of a self-referential structure.
+ struct tnode {
+ int count;
+ struct tnode *left, *right;
+ };
+ specifies a structure that contains an integer and two pointers to objects of the same type. Once this
+ declaration has been given, the declaration
+ struct tnode s, *sp;
+ declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
+ these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
+ which sp points; the expression s.right->count designates the count member of the right struct
+ tnode pointed to from s.
+11 The following alternative formulation uses the typedef mechanism:
+ typedef struct tnode TNODE;
+ struct tnode {
+ int count;
+ TNODE *left, *right;
+ };
+ TNODE s, *sp;
+
+12 EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
+ structures, the declarations
+ struct s1 { struct s2 *s2p; /* ... */ }; // D1
+ struct s2 { struct s1 *s1p; /* ... */ }; // D2
+ specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
+ declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
+ D2. To eliminate this context sensitivity, the declaration
+ struct s2;
+ may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
+ completes the specification of the new type.
+
+ Forward references: declarators (6.7.6), type definitions (6.7.8).
+
+[page 120]
+
+ 6.7.2.4 Atomic type specifiers
+ Syntax
+1 atomic-type-specifier:
+ _Atomic ( type-name )
+ Constraints
+2 Atomic type specifiers shall not be used if the implementation does not support atomic
+ types (see 6.10.8.3).
+3 The type name in an atomic type specifier shall not refer to an array type, a function type,
+ an atomic type, or a qualified type.
+ Semantics
+4 The properties associated with atomic types are meaningful only for expressions that are
+ lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
+ interpreted as a type specifier (with a type name), not as a type qualifier.
+ 6.7.3 Type qualifiers
+ Syntax
+1 type-qualifier:
+ const
+ restrict
+ volatile
+ _Atomic
+ Constraints
+2 Types other than pointer types whose referenced type is an object type shall not be
+ restrict-qualified.
+3 The type modified by the _Atomic qualifier shall not be an array type or a function
+ type.
+ Semantics
+4 The properties associated with qualified types are meaningful only for expressions that
+ are lvalues.132)
+5 If the same qualifier appears more than once in the same specifier-qualifier-list, either
+ directly or via one or more typedefs, the behavior is the same as if it appeared only
+ once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-
+
+ 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.
+
+[page 121]
+
+ list, the resulting type is the so-qualified atomic type.
+6 If an attempt is made to modify an object defined with a const-qualified type through use
+ of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
+ made to refer to an object defined with a volatile-qualified type through use of an lvalue
+ with non-volatile-qualified type, the behavior is undefined.133)
+7 An object that has volatile-qualified type may be modified in ways unknown to the
+ implementation or have other unknown side effects. Therefore any expression referring
+ to such an object shall be evaluated strictly according to the rules of the abstract machine,
+ as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
+ object shall agree with that prescribed by the abstract machine, except as modified by the
+ unknown factors mentioned previously.134) What constitutes an access to an object that
+ has volatile-qualified type is implementation-defined.
+8 An object that is accessed through a restrict-qualified pointer has a special association
+ with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
+ that object use, directly or indirectly, the value of that particular pointer.135) The intended
+ use of the restrict qualifier (like the register storage class) is to promote
+ optimization, and deleting all instances of the qualifier from all preprocessing translation
+ units composing a conforming program does not change its meaning (i.e., observable
+ behavior).
+9 If the specification of an array type includes any type qualifiers, the element type is so-
+ qualified, not the array type. If the specification of a function type includes any type
+ qualifiers, the behavior is undefined.136)
+10 For two qualified types to be compatible, both shall have the identically qualified version
+ of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
+ does not affect the specified type.
+11 EXAMPLE 1 An object declared
+ extern const volatile int real_time_clock;
+
+
+
+ 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.
+
+[page 122]
+
+ may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
+
+12 EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
+ modify an aggregate type:
+ const struct s { int mem; } cs = { 1 };
+ struct s ncs; // the object ncs is modifiable
+ typedef int A[2][3];
+ const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
+ int *pi;
+ const int *pci;
+ ncs = cs; // valid
+ cs = ncs; // violates modifiable lvalue constraint for =
+ pi = &ncs.mem; // valid
+ pi = &cs.mem; // violates type constraints for =
+ pci = &cs.mem; // valid
+ pi = a[0]; // invalid: a[0] has type ''const int *''
+
+13 EXAMPLE 3 The declaration
+ _Atomic volatile int *p;
+ specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type.
+
+ 6.7.3.1 Formal definition of restrict
+1 Let D be a declaration of an ordinary identifier that provides a means of designating an
+ object P as a restrict-qualified pointer to type T.
+2 If D appears inside a block and does not have storage class extern, let B denote the
+ block. If D appears in the list of parameter declarations of a function definition, let B
+ denote the associated block. Otherwise, let B denote the block of main (or the block of
+ whatever function is called at program startup in a freestanding environment).
+3 In what follows, a pointer expression E is said to be based on object P if (at some
+ sequence point in the execution of B prior to the evaluation of E) modifying P to point to
+ a copy of the array object into which it formerly pointed would change the value of E.137)
+ Note that ''based'' is defined only for expressions with pointer types.
+4 During each execution of B, let L be any lvalue that has &L based on P. If L is used to
+ access the value of the object X that it designates, and X is also modified (by any means),
+ then the following requirements apply: T shall not be const-qualified. Every other lvalue
+ used to access the value of X shall also have its address based on P. Every access that
+ modifies X shall be considered also to modify P, for the purposes of this subclause. If P
+ is assigned the value of a pointer expression E that is based on another restricted pointer
+
+
+ 137) In other words, E depends on the value of P itself rather than on the value of an object referenced
+ indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
+ expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
+ expressions *p and p[1] are not.
+
+[page 123]
+
+ object P2, associated with block B2, then either the execution of B2 shall begin before
+ the execution of B, or the execution of B2 shall end prior to the assignment. If these
+ requirements are not met, then the behavior is undefined.
+5 Here an execution of B means that portion of the execution of the program that would
+ correspond to the lifetime of an object with scalar type and automatic storage duration
+ associated with B.
+6 A translator is free to ignore any or all aliasing implications of uses of restrict.
+7 EXAMPLE 1 The file scope declarations
+ int * restrict a;
+ int * restrict b;
+ extern int c[];
+ assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
+ program, then it is never accessed using either of the other two.
+
+8 EXAMPLE 2 The function parameter declarations in the following example
+ void f(int n, int * restrict p, int * restrict q)
+ {
+ while (n-- > 0)
+ *p++ = *q++;
+ }
+ assert that, during each execution of the function, if an object is accessed through one of the pointer
+ parameters, then it is not also accessed through the other.
+9 The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
+ analysis of function f without examining any of the calls of f in the program. The cost is that the
+ programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
+ second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
+ both p and q.
+ void g(void)
+ {
+ extern int d[100];
+ f(50, d + 50, d); // valid
+ f(50, d + 1, d); // undefined behavior
+ }
+
+10 EXAMPLE 3 The function parameter declarations
+ void h(int n, int * restrict p, int * restrict q, int * restrict r)
+ {
+ int i;
+ for (i = 0; i < n; i++)
+ p[i] = q[i] + r[i];
+ }
+ illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
+ are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
+ modified within function h.
+
+[page 124]
+
+11 EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
+ function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments
+ between restricted pointers declared in nested blocks have defined behavior.
+ {
+ int * restrict p1;
+ int * restrict q1;
+ p1 = q1; // undefined behavior
+ {
+ int * restrict p2 = p1; // valid
+ int * restrict q2 = q1; // valid
+ p1 = q2; // undefined behavior
+ p2 = q2; // undefined behavior
+ }
+ }
+12 The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
+ precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
+ example, this permits new_vector to return a vector.
+ typedef struct { int n; float * restrict v; } vector;
+ vector new_vector(int n)
+ {
+ vector t;
+ t.n = n;
+ t.v = malloc(n * sizeof (float));
+ return t;
+ }
+
+ 6.7.4 Function specifiers
+ Syntax
+1 function-specifier:
+ inline
+ _Noreturn
+ Constraints
+2 Function specifiers shall be used only in the declaration of an identifier for a function.
+3 An inline definition of a function with external linkage shall not contain a definition of a
+ modifiable object with static or thread storage duration, and shall not contain a reference
+ to an identifier with internal linkage.
+4 In a hosted environment, no function specifier(s) shall appear in a declaration of main.
+ Semantics
+5 A function specifier may appear more than once; the behavior is the same as if it
+ appeared only once.
+6 A function declared with an inline function specifier is an inline function. Making a
+ function an inline function suggests that calls to the function be as fast as possible.138)
+
+[page 125]
+
+ The extent to which such suggestions are effective is implementation-defined.139)
+7 Any function with internal linkage can be an inline function. For a function with external
+ linkage, the following restrictions apply: If a function is declared with an inline
+ function specifier, then it shall also be defined in the same translation unit. If all of the
+ file scope declarations for a function in a translation unit include the inline function
+ specifier without extern, then the definition in that translation unit is an inline
+ definition. An inline definition does not provide an external definition for the function,
+ and does not forbid an external definition in another translation unit. An inline definition
+ provides an alternative to an external definition, which a translator may use to implement
+ any call to the function in the same translation unit. It is unspecified whether a call to the
+ function uses the inline definition or the external definition.140)
+8 A function declared with a _Noreturn function specifier shall not return to its caller.
+ Recommended practice
+9 The implementation should produce a diagnostic message for a function declared with a
+ _Noreturn function specifier that appears to be capable of returning to its caller.
+10 EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
+ definition, or a definition available for use only within the translation unit. A file scope declaration with
+ extern creates an external definition. The following example shows an entire translation unit.
+ inline double fahr(double t)
+ {
+ return (9.0 * t) / 5.0 + 32.0;
+ }
+ inline double cels(double t)
+ {
+ return (5.0 * (t - 32.0)) / 9.0;
+ }
+ extern double fahr(double); // creates an external definition
+
+
+
+
+ 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.
+
+[page 126]
+
+ double convert(int is_fahr, double temp)
+ {
+ /* A translator may perform inline substitutions */
+ return is_fahr ? cels(temp) : fahr(temp);
+ }
+11 Note that the definition of fahr is an external definition because fahr is also declared with extern, but
+ the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
+ external definition has to appear in another translation unit (see 6.9); the inline definition and the external
+ definition are distinct and either may be used for the call.
+
+12 EXAMPLE 2
+ _Noreturn void f () {
+ abort(); // ok
+ }
+ _Noreturn void g (int i) { // causes undefined behavior if i <= 0
+ if (i > 0) abort();
+ }
+
+ Forward references: function definitions (6.9.1).
+ 6.7.5 Alignment specifier
+ Syntax
+1 alignment-specifier:
+ _Alignas ( type-name )
+ _Alignas ( constant-expression )
+ Constraints
+2 An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
+ a function, or a parameter, or an object declared with the register storage-class
+ specifier.
+3 The constant expression shall be an integer constant expression. It shall evaluate to a
+ valid fundamental alignment, or to a valid extended alignment supported by the
+ implementation in the context in which it appears, or to zero.
+4 The combined effect of all alignment attributes in a declaration shall not specify an
+ alignment that is less strict than the alignment that would otherwise be required for the
+ type of the object or member being declared.
+ Semantics
+5 The first form is equivalent to _Alignas (_Alignof (type-name)).
+6 The alignment requirement of the declared object or member is taken to be the specified
+ alignment. An alignment specification of zero has no effect.141) When multiple
+ alignment specifiers occur in a declaration, the effective alignment requirement is the
+ strictest specified alignment.
+
+[page 127]
+
+7 If the definition of an object has an alignment specifier, any other declaration of that
+ object shall either specify equivalent alignment or have no alignment specifier. If the
+ definition of an object does not have an alignment specifier, any other declaration of that
+ object shall also have no alignment specifier. If declarations of an object in different
+ translation units have different alignment specifiers, the behavior is undefined.
+ 6.7.6 Declarators
+ Syntax
+1 declarator:
+ pointeropt direct-declarator
+ direct-declarator:
+ identifier
+ ( declarator )
+ direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
+ direct-declarator [ static type-qualifier-listopt assignment-expression ]
+ direct-declarator [ type-qualifier-list static assignment-expression ]
+ direct-declarator [ type-qualifier-listopt * ]
+ direct-declarator ( parameter-type-list )
+ direct-declarator ( identifier-listopt )
+ pointer:
+ * type-qualifier-listopt
+ * type-qualifier-listopt pointer
+ type-qualifier-list:
+ type-qualifier
+ type-qualifier-list type-qualifier
+ parameter-type-list:
+ parameter-list
+ parameter-list , ...
+ parameter-list:
+ parameter-declaration
+ parameter-list , parameter-declaration
+ parameter-declaration:
+ declaration-specifiers declarator
+ declaration-specifiers abstract-declaratoropt
+
+
+
+ 141) An alignment specification of zero also does not affect other alignment specifications in the same
+ declaration.
+
+[page 128]
+
+ identifier-list:
+ identifier
+ identifier-list , identifier
+ Semantics
+2 Each declarator declares one identifier, and asserts that when an operand of the same
+ form as the declarator appears in an expression, it designates a function or object with the
+ scope, storage duration, and type indicated by the declaration specifiers.
+3 A full declarator is a declarator that is not part of another declarator. The end of a full
+ declarator is a sequence point. If, in the nested sequence of declarators in a full
+ declarator, there is a declarator specifying a variable length array type, the type specified
+ by the full declarator is said to be variably modified. Furthermore, any type derived by
+ declarator type derivation from a variably modified type is itself variably modified.
+4 In the following subclauses, consider a declaration
+ T D1
+ where T contains the declaration specifiers that specify a type T (such as int) and D1 is
+ a declarator that contains an identifier ident. The type specified for the identifier ident in
+ the various forms of declarator is described inductively using this notation.
+5 If, in the declaration ''T D1'', D1 has the form
+ identifier
+ then the type specified for ident is T .
+6 If, in the declaration ''T D1'', D1 has the form
+ ( D )
+ then ident has the type specified by the declaration ''T D''. Thus, a declarator in
+ parentheses is identical to the unparenthesized declarator, but the binding of complicated
+ declarators may be altered by parentheses.
+ Implementation limits
+7 As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
+ function declarators that modify an arithmetic, structure, union, or void type, either
+ directly or via one or more typedefs.
+ Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
+
+[page 129]
+
+ 6.7.6.1 Pointer declarators
+ Semantics
+1 If, in the declaration ''T D1'', D1 has the form
+ * type-qualifier-listopt D
+ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
+ T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list
+ pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
+2 For two pointer types to be compatible, both shall be identically qualified and both shall
+ be pointers to compatible types.
+3 EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer
+ to a constant value'' and a ''constant pointer to a variable value''.
+ const int *ptr_to_constant;
+ int *const constant_ptr;
+ The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
+ but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
+ int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
+ same location.
+4 The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
+ type ''pointer to int''.
+ typedef int *int_ptr;
+ const int_ptr constant_ptr;
+ declares constant_ptr as an object that has type ''const-qualified pointer to int''.
+
+ 6.7.6.2 Array declarators
+ Constraints
+1 In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
+ an expression or *. If they delimit an expression (which specifies the size of an array), the
+ expression shall have an integer type. If the expression is a constant expression, it shall
+ have a value greater than zero. The element type shall not be an incomplete or function
+ type. The optional type qualifiers and the keyword static shall appear only in a
+ declaration of a function parameter with an array type, and then only in the outermost
+ array type derivation.
+2 If an identifier is declared as having a variably modified type, it shall be an ordinary
+ identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
+ prototype scope. If an identifier is declared to be an object with static or thread storage
+ duration, it shall not have a variable length array type.
+
+[page 130]
+
+ Semantics
+3 If, in the declaration ''T D1'', D1 has one of the forms:
+ D[ type-qualifier-listopt assignment-expressionopt ]
+ D[ static type-qualifier-listopt assignment-expression ]
+ D[ type-qualifier-list static assignment-expression ]
+ D[ type-qualifier-listopt * ]
+ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
+ T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142)
+ (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
+4 If the size is not present, the array type is an incomplete type. If the size is * instead of
+ being an expression, the array type is a variable length array type of unspecified size,
+ which can only be used in declarations or type names with function prototype scope;143)
+ such arrays are nonetheless complete types. If the size is an integer constant expression
+ and the element type has a known constant size, the array type is not a variable length
+ array type; otherwise, the array type is a variable length array type. (Variable length
+ arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
+5 If the size is an expression that is not an integer constant expression: if it occurs in a
+ declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
+ each time it is evaluated it shall have a value greater than zero. The size of each instance
+ of a variable length array type does not change during its lifetime. Where a size
+ expression is part of the operand of a sizeof operator and changing the value of the
+ size expression would not affect the result of the operator, it is unspecified whether or not
+ the size expression is evaluated.
+6 For two array types to be compatible, both shall have compatible element types, and if
+ both size specifiers are present, and are integer constant expressions, then both size
+ specifiers shall have the same constant value. If the two array types are used in a context
+ which requires them to be compatible, it is undefined behavior if the two size specifiers
+ evaluate to unequal values.
+7 EXAMPLE 1
+ float fa[11], *afp[17];
+ declares an array of float numbers and an array of pointers to float numbers.
+
+8 EXAMPLE 2 Note the distinction between the declarations
+
+
+
+
+ 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).
+
+[page 131]
+
+ extern int *x;
+ extern int y[];
+ The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
+ (an incomplete type), the storage for which is defined elsewhere.
+
+9 EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types.
+ extern int n;
+ extern int m;
+ void fcompat(void)
+ {
+ int a[n][6][m];
+ int (*p)[4][n+1];
+ int c[n][n][6][m];
+ int (*r)[n][n][n+1];
+ p = a; // invalid: not compatible because 4 != 6
+ r = c; // compatible, but defined behavior only if
+ // n == 6 and m == n+1
+ }
+
+10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
+ function prototype scope. Array objects declared with the _Thread_local, static, or extern
+ storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
+ the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
+ identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
+ structures or unions.
+ extern int n;
+ int A[n]; // invalid: file scope VLA
+ extern int (*p2)[n]; // invalid: file scope VM
+ int B[100]; // valid: file scope but not VM
+ void fvla(int m, int C[m][m]); // valid: VLA with prototype scope
+ void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA
+ {
+ typedef int VLA[m][m]; // valid: block scope typedef VLA
+ struct tag {
+ int (*y)[n]; // invalid: y not ordinary identifier
+ int z[n]; // invalid: z not ordinary identifier
+ };
+ int D[m]; // valid: auto VLA
+ static int E[m]; // invalid: static block scope VLA
+ extern int F[m]; // invalid: F has linkage and is VLA
+ int (*s)[m]; // valid: auto pointer to VLA
+ extern int (*r)[m]; // invalid: r has linkage and points to VLA
+ static int (*q)[m] = &B; // valid: q is a static block pointer to VLA
+ }
+
+ Forward references: function declarators (6.7.6.3), function definitions (6.9.1),
+ initialization (6.7.9).
+
+[page 132]
+
+ 6.7.6.3 Function declarators (including prototypes)
+ Constraints
+1 A function declarator shall not specify a return type that is a function type or an array
+ type.
+2 The only storage-class specifier that shall occur in a parameter declaration is register.
+3 An identifier list in a function declarator that is not part of a definition of that function
+ shall be empty.
+4 After adjustment, the parameters in a parameter type list in a function declarator that is
+ part of a definition of that function shall not have incomplete type.
+ Semantics
+5 If, in the declaration ''T D1'', D1 has the form
+ D( parameter-type-list )
+ or
+ D( identifier-listopt )
+ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
+ T '', then the type specified for ident is ''derived-declarator-type-list function returning
+ T ''.
+6 A parameter type list specifies the types of, and may declare identifiers for, the
+ parameters of the function.
+7 A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to
+ type'', where the type qualifiers (if any) are those specified within the [ and ] of the
+ array type derivation. If the keyword static also appears within the [ and ] of the
+ array type derivation, then for each call to the function, the value of the corresponding
+ actual argument shall provide access to the first element of an array with at least as many
+ elements as specified by the size expression.
+8 A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to
+ function returning type'', as in 6.3.2.1.
+9 If the list terminates with an ellipsis (, ...), no information about the number or types
+ of the parameters after the comma is supplied.144)
+10 The special case of an unnamed parameter of type void as the only item in the list
+ specifies that the function has no parameters.
+
+
+
+ 144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
+ correspond to the ellipsis.
+
+[page 133]
+
+11 If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
+ parameter name, it shall be taken as a typedef name.
+12 If the function declarator is not part of a definition of that function, parameters may have
+ incomplete type and may use the [*] notation in their sequences of declarator specifiers
+ to specify variable length array types.
+13 The storage-class specifier in the declaration specifiers for a parameter declaration, if
+ present, is ignored unless the declared parameter is one of the members of the parameter
+ type list for a function definition.
+14 An identifier list declares only the identifiers of the parameters of the function. An empty
+ list in a function declarator that is part of a definition of that function specifies that the
+ function has no parameters. The empty list in a function declarator that is not part of a
+ definition of that function specifies that no information about the number or types of the
+ parameters is supplied.145)
+15 For two function types to be compatible, both shall specify compatible return types.146)
+ Moreover, the parameter type lists, if both are present, shall agree in the number of
+ parameters and in use of the ellipsis terminator; corresponding parameters shall have
+ compatible types. If one type has a parameter type list and the other type is specified by a
+ function declarator that is not part of a function definition and that contains an empty
+ identifier list, the parameter list shall not have an ellipsis terminator and the type of each
+ parameter shall be compatible with the type that results from the application of the
+ default argument promotions. If one type has a parameter type list and the other type is
+ specified by a function definition that contains a (possibly empty) identifier list, both shall
+ agree in the number of parameters, and the type of each prototype parameter shall be
+ compatible with the type that results from the application of the default argument
+ promotions to the type of the corresponding identifier. (In the determination of type
+ compatibility and of a composite type, each parameter declared with function or array
+ type is taken as having the adjusted type and each parameter declared with qualified type
+ is taken as having the unqualified version of its declared type.)
+16 EXAMPLE 1 The declaration
+ int f(void), *fip(), (*pfi)();
+ declares a function f with no parameters returning an int, a function fip with no parameter specification
+ returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
+ int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
+ declaration suggests, and the same construction in an expression requires, the calling of a function fip,
+ and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
+ extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
+
+
+ 145) See ''future language directions'' (6.11.6).
+ 146) If both function types are ''old style'', parameter types are not compared.
+
+[page 134]
+
+ designator, which is then used to call the function; it returns an int.
+17 If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
+ declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
+ internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
+ the identifier of the pointer pfi has block scope and no linkage.
+
+18 EXAMPLE 2 The declaration
+ int (*apfi[3])(int *x, int *y);
+ declares an array apfi of three pointers to functions returning int. Each of these functions has two
+ parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
+ go out of scope at the end of the declaration of apfi.
+
+19 EXAMPLE 3 The declaration
+ int (*fpfi(int (*)(long), int))(int, ...);
+ declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
+ parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
+ The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
+ additional arguments of any type.
+
+20 EXAMPLE 4 The following prototype has a variably modified parameter.
+ void addscalar(int n, int m,
+ double a[n][n*m+300], double x);
+ int main()
+ {
+ double b[4][308];
+ addscalar(4, 2, b, 2.17);
+ return 0;
+ }
+ void addscalar(int n, int m,
+ double a[n][n*m+300], double x)
+ {
+ for (int i = 0; i < n; i++)
+ for (int j = 0, k = n*m+300; j < k; j++)
+ // a is a pointer to a VLA with n*m+300 elements
+ a[i][j] += x;
+ }
+
+21 EXAMPLE 5 The following are all compatible function prototype declarators.
+ double maximum(int n, int m, double a[n][m]);
+ double maximum(int n, int m, double a[*][*]);
+ double maximum(int n, int m, double a[ ][*]);
+ double maximum(int n, int m, double a[ ][m]);
+ as are:
+ void f(double (* restrict a)[5]);
+ void f(double a[restrict][5]);
+ void f(double a[restrict 3][5]);
+ void f(double a[restrict static 3][5]);
+
+[page 135]
+
+ (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).
+ 6.7.7 Type names
+ Syntax
+1 type-name:
+ specifier-qualifier-list abstract-declaratoropt
+ abstract-declarator:
+ pointer
+ pointeropt direct-abstract-declarator
+ direct-abstract-declarator:
+ ( abstract-declarator )
+ direct-abstract-declaratoropt [ type-qualifier-listopt
+ assignment-expressionopt ]
+ direct-abstract-declaratoropt [ static type-qualifier-listopt
+ assignment-expression ]
+ direct-abstract-declaratoropt [ type-qualifier-list static
+ assignment-expression ]
+ direct-abstract-declaratoropt [ * ]
+ direct-abstract-declaratoropt ( parameter-type-listopt )
+ Semantics
+2 In several contexts, it is necessary to specify a type. This is accomplished using a type
+ name, which is syntactically a declaration for a function or an object of that type that
+ omits the identifier.147)
+3 EXAMPLE The constructions
+ (a) int
+ (b) int *
+ (c) int *[3]
+ (d) int (*)[3]
+ (e) int (*)[*]
+ (f) int *()
+ (g) int (*)(void)
+ (h) int (*const [])(unsigned int, ...)
+ name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
+ array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
+ with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
+
+
+ 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no
+ parameter specification'', rather than redundant parentheses around the omitted identifier.
+
+[page 136]
+
+ 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.
+
+ 6.7.8 Type definitions
+ Syntax
+1 typedef-name:
+ identifier
+ Constraints
+2 If a typedef name specifies a variably modified type then it shall have block scope.
+ Semantics
+3 In a declaration whose storage-class specifier is typedef, each declarator defines an
+ identifier to be a typedef name that denotes the type specified for the identifier in the way
+ described in 6.7.6. Any array size expressions associated with variable length array
+ declarators are evaluated each time the declaration of the typedef name is reached in the
+ order of execution. A typedef declaration does not introduce a new type, only a
+ synonym for the type so specified. That is, in the following declarations:
+ typedef T type_ident;
+ type_ident D;
+ type_ident is defined as a typedef name with the type specified by the declaration
+ specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator-
+ type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
+ typedef name shares the same name space as other identifiers declared in ordinary
+ declarators.
+4 EXAMPLE 1 After
+ typedef int MILES, KLICKSP();
+ typedef struct { double hi, lo; } range;
+ the constructions
+ MILES distance;
+ extern KLICKSP *metricp;
+ range x;
+ range z, *zp;
+ are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no
+ parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
+ such a structure. The object distance has a type compatible with any other int object.
+
+5 EXAMPLE 2 After the declarations
+ typedef struct s1 { int x; } t1, *tp1;
+ typedef struct s2 { int x; } t2, *tp2;
+ type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
+
+[page 137]
+
+ s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.
+
+6 EXAMPLE 3 The following obscure constructions
+ typedef signed int t;
+ typedef int plain;
+ struct tag {
+ unsigned t:4;
+ const t:5;
+ plain r:5;
+ };
+ declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
+ with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
+ qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
+ [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
+ (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
+ unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
+ type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
+ in an inner scope by
+ t f(t (t));
+ long t;
+ then a function f is declared with type ''function returning signed int with one unnamed parameter
+ with type pointer to function returning signed int with one unnamed parameter with type signed
+ int'', and an identifier t with type long int.
+
+7 EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
+ following declarations of the signal function specify exactly the same type, the first without making use
+ of any typedef names.
+ typedef void fv(int), (*pfv)(int);
+ void (*signal(int, void (*)(int)))(int);
+ fv *signal(int, fv *);
+ pfv signal(int, pfv);
+
+8 EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
+ time the typedef name is defined, not each time it is used:
+ void copyt(int n)
+ {
+ typedef int B[n]; // B is n ints, n evaluated now
+ n += 1;
+ B a; // a is n ints, n without += 1
+ int b[n]; // a and b are different sizes
+ for (int i = 1; i < n; i++)
+ a[i-1] = b[i];
+ }
+
+[page 138]
+
+ 6.7.9 Initialization
+ Syntax
+1 initializer:
+ assignment-expression
+ { initializer-list }
+ { initializer-list , }
+ initializer-list:
+ designationopt initializer
+ initializer-list , designationopt initializer
+ designation:
+ designator-list =
+ designator-list:
+ designator
+ designator-list designator
+ designator:
+ [ constant-expression ]
+ . identifier
+ Constraints
+2 No initializer shall attempt to provide a value for an object not contained within the entity
+ being initialized.
+3 The type of the entity to be initialized shall be an array of unknown size or a complete
+ object type that is not a variable length array type.
+4 All the expressions in an initializer for an object that has static or thread storage duration
+ shall be constant expressions or string literals.
+5 If the declaration of an identifier has block scope, and the identifier has external or
+ internal linkage, the declaration shall have no initializer for the identifier.
+6 If a designator has the form
+ [ constant-expression ]
+ then the current object (defined below) shall have array type and the expression shall be
+ an integer constant expression. If the array is of unknown size, any nonnegative value is
+ valid.
+7 If a designator has the form
+ . identifier
+ then the current object (defined below) shall have structure or union type and the
+ identifier shall be the name of a member of that type.
+
+[page 139]
+
+ Semantics
+8 An initializer specifies the initial value stored in an object.
+9 Except where explicitly stated otherwise, for the purposes of this subclause unnamed
+ members of objects of structure and union type do not participate in initialization.
+ Unnamed members of structure objects have indeterminate value even after initialization.
+10 If an object that has automatic storage duration is not initialized explicitly, its value is
+ indeterminate. If an object that has static or thread storage duration is not initialized
+ explicitly, then:
+ -- if it has pointer type, it is initialized to a null pointer;
+ -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
+ -- if it is an aggregate, every member is initialized (recursively) according to these rules,
+ and any padding is initialized to zero bits;
+ -- if it is a union, the first named member is initialized (recursively) according to these
+ rules, and any padding is initialized to zero bits;
+11 The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
+ initial value of the object is that of the expression (after conversion); the same type
+ constraints and conversions as for simple assignment apply, taking the type of the scalar
+ to be the unqualified version of its declared type.
+12 The rest of this subclause deals with initializers for objects that have aggregate or union
+ type.
+13 The initializer for a structure or union object that has automatic storage duration shall be
+ either an initializer list as described below, or a single expression that has compatible
+ structure or union type. In the latter case, the initial value of the object, including
+ unnamed members, is that of the expression.
+14 An array of character type may be initialized by a character string literal or UTF-8 string
+ literal, optionally enclosed in braces. Successive bytes of the string literal (including the
+ terminating null character if there is room or if the array is of unknown size) initialize the
+ elements of the array.
+15 An array with element type compatible with a qualified or unqualified version of
+ wchar_t, char16_t, or char32_t may be initialized by a wide string literal with
+ the corresponding encoding prefix (L, u, or U, respectively), optionally enclosed in
+ braces. Successive wide characters of the wide string literal (including the terminating
+ null wide character if there is room or if the array is of unknown size) initialize the
+ elements of the array.
+16 Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
+ enclosed list of initializers for the elements or named members.
+
+[page 140]
+
+17 Each brace-enclosed initializer list has an associated current object. When no
+ designations are present, subobjects of the current object are initialized in order according
+ to the type of the current object: array elements in increasing subscript order, structure
+ members in declaration order, and the first named member of a union.148) In contrast, a
+ designation causes the following initializer to begin initialization of the subobject
+ described by the designator. Initialization then continues forward in order, beginning
+ with the next subobject after that described by the designator.149)
+18 Each designator list begins its description with the current object associated with the
+ closest surrounding brace pair. Each item in the designator list (in order) specifies a
+ particular member of its current object and changes the current object for the next
+ designator (if any) to be that member.150) The current object that results at the end of the
+ designator list is the subobject to be initialized by the following initializer.
+19 The initialization shall occur in initializer list order, each initializer provided for a
+ particular subobject overriding any previously listed initializer for the same subobject;151)
+ all subobjects that are not initialized explicitly shall be initialized implicitly the same as
+ objects that have static storage duration.
+20 If the aggregate or union contains elements or members that are aggregates or unions,
+ these rules apply recursively to the subaggregates or contained unions. If the initializer of
+ a subaggregate or contained union begins with a left brace, the initializers enclosed by
+ that brace and its matching right brace initialize the elements or members of the
+ subaggregate or the contained union. Otherwise, only enough initializers from the list are
+ taken to account for the elements or members of the subaggregate or the first member of
+ the contained union; any remaining initializers are left to initialize the next element or
+ member of the aggregate of which the current subaggregate or contained union is a part.
+21 If there are fewer initializers in a brace-enclosed list than there are elements or members
+ of an aggregate, or fewer characters in a string literal used to initialize an array of known
+ size than there are elements in the array, the remainder of the aggregate shall be
+ initialized implicitly the same as objects that have static storage duration.
+
+
+
+ 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
+ subobjects are initialized as usual, but the subaggregate or contained union does not become the
+ current object: current objects are associated only with brace-enclosed initializer lists.
+ 149) After a union member is initialized, the next object is not the next member of the union; instead, it is
+ the next subobject of an object containing the union.
+ 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
+ the surrounding brace pair. Note, too, that each separate designator list is independent.
+ 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
+ not be evaluated at all.
+
+[page 141]
+
+22 If an array of unknown size is initialized, its size is determined by the largest indexed
+ element with an explicit initializer. The array type is completed at the end of its
+ initializer list.
+23 The evaluations of the initialization list expressions are indeterminately sequenced with
+ respect to one another and thus the order in which any side effects occur is
+ unspecified.152)
+24 EXAMPLE 1 Provided that <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.
+
+25 EXAMPLE 2 The declaration
+ int x[] = { 1, 3, 5 };
+ defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
+ and there are three initializers.
+
+26 EXAMPLE 3 The declaration
+ int y[4][3] = {
+ { 1, 3, 5 },
+ { 2, 4, 6 },
+ { 3, 5, 7 },
+ };
+ is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
+ y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
+ y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
+ been achieved by
+ int y[4][3] = {
+ 1, 3, 5, 2, 4, 6, 3, 5, 7
+ };
+ The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
+ next three are taken successively for y[1] and y[2].
+
+27 EXAMPLE 4 The declaration
+ int z[4][3] = {
+ { 1 }, { 2 }, { 3 }, { 4 }
+ };
+ initializes the first column of z as specified and initializes the rest with zeros.
+
+28 EXAMPLE 5 The declaration
+ struct { int a[3], b; } w[] = { { 1 }, 2 };
+ is a definition with an inconsistently bracketed initialization. It defines an array with two element
+
+
+
+ 152) In particular, the evaluation order need not be the same as the order of subobject initialization.
+
+[page 142]
+
+ structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
+
+29 EXAMPLE 6 The declaration
+ short q[4][3][2] = {
+ { 1 },
+ { 2, 3 },
+ { 4, 5, 6 }
+ };
+ contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
+ object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
+ q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
+ q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
+ only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
+ for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
+ respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
+ diagnostic message would have been issued. The same initialization result could have been achieved by:
+ short q[4][3][2] = {
+ 1, 0, 0, 0, 0, 0,
+ 2, 3, 0, 0, 0, 0,
+ 4, 5, 6
+ };
+ or by:
+ short q[4][3][2] = {
+ {
+ { 1 },
+ },
+ {
+ { 2, 3 },
+ },
+ {
+ { 4, 5 },
+ { 6 },
+ }
+ };
+ in a fully bracketed form.
+30 Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
+ cause confusion.
+
+31 EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the
+ declaration
+ typedef int A[]; // OK - declared with block scope
+ the declaration
+ A a = { 1, 2 }, b = { 3, 4, 5 };
+ is identical to
+ int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
+ due to the rules for incomplete types.
+
+[page 143]
+
+32 EXAMPLE 8 The declaration
+ char s[] = "abc", t[3] = "abc";
+ defines ''plain'' char array objects s and t whose elements are initialized with character string literals.
+ This declaration is identical to
+ char s[] = { 'a', 'b', 'c', '\0' },
+ t[] = { 'a', 'b', 'c' };
+ The contents of the arrays are modifiable. On the other hand, the declaration
+ char *p = "abc";
+ defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char''
+ with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
+ modify the contents of the array, the behavior is undefined.
+
+33 EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using
+ designators:
+ enum { member_one, member_two };
+ const char *nm[] = {
+ [member_two] = "member two",
+ [member_one] = "member one",
+ };
+
+34 EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order:
+ div_t answer = { .quot = 2, .rem = -1 };
+
+35 EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
+ might be misunderstood:
+ struct { int a[3], b; } w[] =
+ { [0].a = {1}, [1].a[0] = 2 };
+
+36 EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator:
+ int a[MAX] = {
+ 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
+ };
+37 In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
+ than ten, some of the values provided by the first five initializers will be overridden by the second five.
+
+38 EXAMPLE 13 Any member of a union can be initialized:
+ union { /* ... */ } u = { .any_member = 42 };
+
+ Forward references: common definitions <stddef.h> (7.19).
+
+[page 144]
+
+ 6.7.10 Static assertions
+ Syntax
+1 static_assert-declaration:
+ _Static_assert ( constant-expression , string-literal ) ;
+ Constraints
+2 The constant expression shall compare unequal to 0.
+ Semantics
+3 The constant expression shall be an integer constant expression. If the value of the
+ constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
+ constraint is violated and the implementation shall produce a diagnostic message that
+ includes the text of the string literal, except that characters not in the basic source
+ character set are not required to appear in the message.
+ Forward references: diagnostics (7.2).
+
+[page 145]
+
+ 6.8 Statements and blocks
+ Syntax
+1 statement:
+ labeled-statement
+ compound-statement
+ expression-statement
+ selection-statement
+ iteration-statement
+ jump-statement
+ Semantics
+2 A statement specifies an action to be performed. Except as indicated, statements are
+ executed in sequence.
+3 A block allows a set of declarations and statements to be grouped into one syntactic unit.
+ The initializers of objects that have automatic storage duration, and the variable length
+ array declarators of ordinary identifiers with block scope, are evaluated and the values are
+ stored in the objects (including storing an indeterminate value in objects without an
+ initializer) each time the declaration is reached in the order of execution, as if it were a
+ statement, and within each declaration in the order that declarators appear.
+4 A full expression is an expression that is not part of another expression or of a declarator.
+ Each of the following is a full expression: an initializer that is not part of a compound
+ literal; the expression in an expression statement; the controlling expression of a selection
+ statement (if or switch); the controlling expression of a while or do statement; each
+ of the (optional) expressions of a for statement; the (optional) expression in a return
+ statement. There is a sequence point between the evaluation of a full expression and the
+ evaluation of the next full expression to be evaluated.
+ Forward references: expression and null statements (6.8.3), selection statements
+ (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
+ 6.8.1 Labeled statements
+ Syntax
+1 labeled-statement:
+ identifier : statement
+ case constant-expression : statement
+ default : statement
+ Constraints
+2 A case or default label shall appear only in a switch statement. Further
+ constraints on such labels are discussed under the switch statement.
+
+[page 146]
+
+3 Label names shall be unique within a function.
+ Semantics
+4 Any statement may be preceded by a prefix that declares an identifier as a label name.
+ Labels in themselves do not alter the flow of control, which continues unimpeded across
+ them.
+ Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).
+ 6.8.2 Compound statement
+ Syntax
+1 compound-statement:
+ { block-item-listopt }
+ block-item-list:
+ block-item
+ block-item-list block-item
+ block-item:
+ declaration
+ statement
+ Semantics
+2 A compound statement is a block.
+ 6.8.3 Expression and null statements
+ Syntax
+1 expression-statement:
+ expressionopt ;
+ Semantics
+2 The expression in an expression statement is evaluated as a void expression for its side
+ effects.153)
+3 A null statement (consisting of just a semicolon) performs no operations.
+4 EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
+ discarding of its value may be made explicit by converting the expression to a void expression by means of
+ a cast:
+ int p(int);
+ /* ... */
+ (void)p(0);
+
+
+
+ 153) Such as assignments, and function calls which have side effects.
+
+[page 147]
+
+5 EXAMPLE 2 In the program fragment
+ char *s;
+ /* ... */
+ while (*s++ != '\0')
+ ;
+ a null statement is used to supply an empty loop body to the iteration statement.
+
+6 EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound
+ statement.
+ while (loop1) {
+ /* ... */
+ while (loop2) {
+ /* ... */
+ if (want_out)
+ goto end_loop1;
+ /* ... */
+ }
+ /* ... */
+ end_loop1: ;
+ }
+
+ Forward references: iteration statements (6.8.5).
+ 6.8.4 Selection statements
+ Syntax
+1 selection-statement:
+ if ( expression ) statement
+ if ( expression ) statement else statement
+ switch ( expression ) statement
+ Semantics
+2 A selection statement selects among a set of statements depending on the value of a
+ controlling expression.
+3 A selection statement is a block whose scope is a strict subset of the scope of its
+ enclosing block. Each associated substatement is also a block whose scope is a strict
+ subset of the scope of the selection statement.
+ 6.8.4.1 The if statement
+ Constraints
+1 The controlling expression of an if statement shall have scalar type.
+ Semantics
+2 In both forms, the first substatement is executed if the expression compares unequal to 0.
+ In the else form, the second substatement is executed if the expression compares equal
+
+[page 148]
+
+ to 0. If the first substatement is reached via a label, the second substatement is not
+ executed.
+3 An else is associated with the lexically nearest preceding if that is allowed by the
+ syntax.
+ 6.8.4.2 The switch statement
+ Constraints
+1 The controlling expression of a switch statement shall have integer type.
+2 If a switch statement has an associated case or default label within the scope of an
+ identifier with a variably modified type, the entire switch statement shall be within the
+ scope of that identifier.154)
+3 The expression of each case label shall be an integer constant expression and no two of
+ the case constant expressions in the same switch statement shall have the same value
+ after conversion. There may be at most one default label in a switch statement.
+ (Any enclosed switch statement may have a default label or case constant
+ expressions with values that duplicate case constant expressions in the enclosing
+ switch statement.)
+ Semantics
+4 A switch statement causes control to jump to, into, or past the statement that is the
+ switch body, depending on the value of a controlling expression, and on the presence of a
+ default label and the values of any case labels on or in the switch body. A case or
+ default label is accessible only within the closest enclosing switch statement.
+5 The integer promotions are performed on the controlling expression. The constant
+ expression in each case label is converted to the promoted type of the controlling
+ expression. If a converted value matches that of the promoted controlling expression,
+ control jumps to the statement following the matched case label. Otherwise, if there is
+ a default label, control jumps to the labeled statement. If no converted case constant
+ expression matches and there is no default label, no part of the switch body is
+ executed.
+ Implementation limits
+6 As discussed in 5.2.4.1, the implementation may limit the number of case values in a
+ switch statement.
+
+
+
+
+ 154) That is, the declaration either precedes the switch statement, or it follows the last case or
+ default label associated with the switch that is in the block containing the declaration.
+
+[page 149]
+
+7 EXAMPLE In the artificial program fragment
+ switch (expr)
+ {
+ int i = 4;
+ f(i);
+ case 0:
+ i = 17;
+ /* falls through into default code */
+ default:
+ printf("%d\n", i);
+ }
+ the object whose identifier is i exists with automatic storage duration (within the block) but is never
+ initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
+ access an indeterminate value. Similarly, the call to the function f cannot be reached.
+
+ 6.8.5 Iteration statements
+ Syntax
+1 iteration-statement:
+ while ( expression ) statement
+ do statement while ( expression ) ;
+ for ( expressionopt ; expressionopt ; expressionopt ) statement
+ for ( declaration expressionopt ; expressionopt ) statement
+ Constraints
+2 The controlling expression of an iteration statement shall have scalar type.
+3 The declaration part of a for statement shall only declare identifiers for objects having
+ storage class auto or register.
+ Semantics
+4 An iteration statement causes a statement called the loop body to be executed repeatedly
+ until the controlling expression compares equal to 0. The repetition occurs regardless of
+ whether the loop body is entered from the iteration statement or by a jump.155)
+5 An iteration statement is a block whose scope is a strict subset of the scope of its
+ enclosing block. The loop body is also a block whose scope is a strict subset of the scope
+ of the iteration statement.
+6 An iteration statement whose controlling expression is not a constant expression,156) that
+ performs no input/output operations, does not access volatile objects, and performs no
+ synchronization or atomic operations in its body, controlling expression, or (in the case of
+
+ 155) Code jumped over is not executed. In particular, the controlling expression of a for or while
+ statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
+ 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.
+
+[page 150]
+
+ a for statement) its expression-3, may be assumed by the implementation to
+ terminate.157)
+ 6.8.5.1 The while statement
+1 The evaluation of the controlling expression takes place before each execution of the loop
+ body.
+ 6.8.5.2 The do statement
+1 The evaluation of the controlling expression takes place after each execution of the loop
+ body.
+ 6.8.5.3 The for statement
+1 The statement
+ for ( clause-1 ; expression-2 ; expression-3 ) statement
+ behaves as follows: The expression expression-2 is the controlling expression that is
+ evaluated before each execution of the loop body. The expression expression-3 is
+ evaluated as a void expression after each execution of the loop body. If clause-1 is a
+ declaration, the scope of any identifiers it declares is the remainder of the declaration and
+ the entire loop, including the other two expressions; it is reached in the order of execution
+ before the first evaluation of the controlling expression. If clause-1 is an expression, it is
+ evaluated as a void expression before the first evaluation of the controlling expression.158)
+2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
+ nonzero constant.
+ 6.8.6 Jump statements
+ Syntax
+1 jump-statement:
+ goto identifier ;
+ continue ;
+ break ;
+ return expressionopt ;
+
+
+
+
+ 157) This is intended to allow compiler transformations such as removal of empty loops even when
+ termination cannot be proven.
+ 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
+ the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
+ such that execution of the loop continues until the expression compares equal to 0; and expression-3
+ specifies an operation (such as incrementing) that is performed after each iteration.
+
+[page 151]
+
+ Semantics
+2 A jump statement causes an unconditional jump to another place.
+ 6.8.6.1 The goto statement
+ Constraints
+1 The identifier in a goto statement shall name a label located somewhere in the enclosing
+ function. A goto statement shall not jump from outside the scope of an identifier having
+ a variably modified type to inside the scope of that identifier.
+ Semantics
+2 A goto statement causes an unconditional jump to the statement prefixed by the named
+ label in the enclosing function.
+3 EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
+ following outline presents one possible approach to a problem based on these three assumptions:
+ 1. The general initialization code accesses objects only visible to the current function.
+ 2. The general initialization code is too large to warrant duplication.
+ 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
+ continue statements, for example.)
+ /* ... */
+ goto first_time;
+ for (;;) {
+ // determine next operation
+ /* ... */
+ if (need to reinitialize) {
+ // reinitialize-only code
+ /* ... */
+ first_time:
+ // general initialization code
+ /* ... */
+ continue;
+ }
+ // handle other operations
+ /* ... */
+ }
+
+[page 152]
+
+4 EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
+ modified types. A jump within the scope, however, is permitted.
+ goto lab3; // invalid: going INTO scope of VLA.
+ {
+ double a[n];
+ a[j] = 4.4;
+ lab3:
+ a[j] = 3.3;
+ goto lab4; // valid: going WITHIN scope of VLA.
+ a[j] = 5.5;
+ lab4:
+ a[j] = 6.6;
+ }
+ goto lab4; // invalid: going INTO scope of VLA.
+
+ 6.8.6.2 The continue statement
+ Constraints
+1 A continue statement shall appear only in or as a loop body.
+ Semantics
+2 A continue statement causes a jump to the loop-continuation portion of the smallest
+ enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
+ of the statements
+ while (/* ... */) { do { for (/* ... */) {
+ /* ... */ /* ... */ /* ... */
+ continue; continue; continue;
+ /* ... */ /* ... */ /* ... */
+ contin: ; contin: ; contin: ;
+ } } while (/* ... */); }
+ unless the continue statement shown is in an enclosed iteration statement (in which
+ case it is interpreted within that statement), it is equivalent to goto contin;.159)
+ 6.8.6.3 The break statement
+ Constraints
+1 A break statement shall appear only in or as a switch body or loop body.
+ Semantics
+2 A break statement terminates execution of the smallest enclosing switch or iteration
+ statement.
+
+
+
+ 159) Following the contin: label is a null statement.
+
+[page 153]
+
+ 6.8.6.4 The return statement
+ Constraints
+1 A return statement with an expression shall not appear in a function whose return type
+ is void. A return statement without an expression shall only appear in a function
+ whose return type is void.
+ Semantics
+2 A return statement terminates execution of the current function and returns control to
+ its caller. A function may have any number of return statements.
+3 If a return statement with an expression is executed, the value of the expression is
+ returned to the caller as the value of the function call expression. If the expression has a
+ type different from the return type of the function in which it appears, the value is
+ converted as if by assignment to an object having the return type of the function.160)
+4 EXAMPLE In:
+ struct s { double i; } f(void);
+ union {
+ struct {
+ int f1;
+ struct s f2;
+ } u1;
+ struct {
+ struct s f3;
+ int f4;
+ } u2;
+ } g;
+ struct s f(void)
+ {
+ return g.u1.f2;
+ }
+ /* ... */
+ g.u2.f3 = f();
+ there is no undefined behavior, although there would be if the assignment were done directly (without using
+ a function call to fetch the value).
+
+
+
+
+ 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
+ apply to the case of function return. The representation of floating-point values may have wider range
+ or precision than implied by the type; a cast may be used to remove this extra range and precision.
+
+[page 154]
+
+ 6.9 External definitions
+ Syntax
+1 translation-unit:
+ external-declaration
+ translation-unit external-declaration
+ external-declaration:
+ function-definition
+ declaration
+ Constraints
+2 The storage-class specifiers auto and register shall not appear in the declaration
+ specifiers in an external declaration.
+3 There shall be no more than one external definition for each identifier declared with
+ internal linkage in a translation unit. Moreover, if an identifier declared with internal
+ linkage is used in an expression (other than as a part of the operand of a sizeof or
+ _Alignof operator whose result is an integer constant), there shall be exactly one
+ external definition for the identifier in the translation unit.
+ Semantics
+4 As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
+ which consists of a sequence of external declarations. These are described as ''external''
+ because they appear outside any function (and hence have file scope). As discussed in
+ 6.7, a declaration that also causes storage to be reserved for an object or a function named
+ by the identifier is a definition.
+5 An external definition is an external declaration that is also a definition of a function
+ (other than an inline definition) or an object. If an identifier declared with external
+ linkage is used in an expression (other than as part of the operand of a sizeof or
+ _Alignof operator whose result is an integer constant), somewhere in the entire
+ program there shall be exactly one external definition for the identifier; otherwise, there
+ shall be no more than one.161)
+
+
+
+
+ 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
+ external definition for it.
+
+[page 155]
+
+ 6.9.1 Function definitions
+ Syntax
+1 function-definition:
+ declaration-specifiers declarator declaration-listopt compound-statement
+ declaration-list:
+ declaration
+ declaration-list declaration
+ Constraints
+2 The identifier declared in a function definition (which is the name of the function) shall
+ have a function type, as specified by the declarator portion of the function definition.162)
+3 The return type of a function shall be void or a complete object type other than array
+ type.
+4 The storage-class specifier, if any, in the declaration specifiers shall be either extern or
+ static.
+5 If the declarator includes a parameter type list, the declaration of each parameter shall
+ include an identifier, except for the special case of a parameter list consisting of a single
+ parameter of type void, in which case there shall not be an identifier. No declaration list
+ shall follow.
+6 If the declarator includes an identifier list, each declaration in the declaration list shall
+ have at least one declarator, those declarators shall declare only identifiers from the
+ identifier list, and every identifier in the identifier list shall be declared. An identifier
+ declared as a typedef name shall not be redeclared as a parameter. The declarations in the
+ declaration list shall contain no storage-class specifier other than register and no
+ initializations.
+
+
+
+ 162) The intent is that the type category in a function definition cannot be inherited from a typedef:
+ typedef int F(void); // type F is ''function with no parameters
+ // returning int''
+ F f, g; // f and g both have type compatible with F
+ F f { /* ... */ } // WRONG: syntax/constraint error
+ F g() { /* ... */ } // WRONG: declares that g returns a function
+ int f(void) { /* ... */ } // RIGHT: f has type compatible with F
+ int g() { /* ... */ } // RIGHT: g has type compatible with F
+ F *e(void) { /* ... */ } // e returns a pointer to a function
+ F *((e))(void) { /* ... */ } // same: parentheses irrelevant
+ int (*fp)(void); // fp points to a function that has type F
+ F *Fp; // Fp points to a function that has type F
+
+[page 156]
+
+ Semantics
+7 The declarator in a function definition specifies the name of the function being defined
+ and the identifiers of its parameters. If the declarator includes a parameter type list, the
+ list also specifies the types of all the parameters; such a declarator also serves as a
+ function prototype for later calls to the same function in the same translation unit. If the
+ declarator includes an identifier list,163) the types of the parameters shall be declared in a
+ following declaration list. In either case, the type of each parameter is adjusted as
+ described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
+ type.
+8 If a function that accepts a variable number of arguments is defined without a parameter
+ type list that ends with the ellipsis notation, the behavior is undefined.
+9 Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout
+ of the storage for parameters is unspecified.
+10 On entry to the function, the size expressions of each variably modified parameter are
+ evaluated and the value of each argument expression is converted to the type of the
+ corresponding parameter as if by assignment. (Array expressions and function
+ designators as arguments were converted to pointers before the call.)
+11 After all parameters have been assigned, the compound statement that constitutes the
+ body of the function definition is executed.
+12 If the } that terminates a function is reached, and the value of the function call is used by
+ the caller, the behavior is undefined.
+13 EXAMPLE 1 In the following:
+ extern int max(int a, int b)
+ {
+ return a > b ? a : b;
+ }
+ extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
+ function declarator; and
+ { return a > b ? a : b; }
+ is the function body. The following similar definition uses the identifier-list form for the parameter
+ declarations:
+
+
+
+
+ 163) See ''future language directions'' (6.11.7).
+ 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
+
+[page 157]
+
+ extern int max(a, b)
+ int a, b;
+ {
+ return a > b ? a : b;
+ }
+ Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
+ that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
+ to the function, whereas the second form does not.
+
+14 EXAMPLE 2 To pass one function to another, one might say
+ int f(void);
+ /* ... */
+ g(f);
+ Then the definition of g might read
+ void g(int (*funcp)(void))
+ {
+ /* ... */
+ (*funcp)(); /* or funcp(); ... */
+ }
+ or, equivalently,
+ void g(int func(void))
+ {
+ /* ... */
+ func(); /* or (*func)(); ... */
+ }
+
+ 6.9.2 External object definitions
+ Semantics
+1 If the declaration of an identifier for an object has file scope and an initializer, the
+ declaration is an external definition for the identifier.
+2 A declaration of an identifier for an object that has file scope without an initializer, and
+ without a storage-class specifier or with the storage-class specifier static, constitutes a
+ tentative definition. If a translation unit contains one or more tentative definitions for an
+ identifier, and the translation unit contains no external definition for that identifier, then
+ the behavior is exactly as if the translation unit contains a file scope declaration of that
+ identifier, with the composite type as of the end of the translation unit, with an initializer
+ equal to 0.
+3 If the declaration of an identifier for an object is a tentative definition and has internal
+ linkage, the declared type shall not be an incomplete type.
+
+[page 158]
+
+4 EXAMPLE 1
+ int i1 = 1; // definition, external linkage
+ static int i2 = 2; // definition, internal linkage
+ extern int i3 = 3; // definition, external linkage
+ int i4; // tentative definition, external linkage
+ static int i5; // tentative definition, internal linkage
+ int i1; // valid tentative definition, refers to previous
+ int i2; // 6.2.2 renders undefined, linkage disagreement
+ int i3; // valid tentative definition, refers to previous
+ int i4; // valid tentative definition, refers to previous
+ int i5; // 6.2.2 renders undefined, linkage disagreement
+ extern int i1; // refers to previous, whose linkage is external
+ extern int i2; // refers to previous, whose linkage is internal
+ extern int i3; // refers to previous, whose linkage is external
+ extern int i4; // refers to previous, whose linkage is external
+ extern int i5; // refers to previous, whose linkage is internal
+
+5 EXAMPLE 2 If at the end of the translation unit containing
+ int i[];
+ the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
+ zero on program startup.
+
+[page 159]
+
+ 6.10 Preprocessing directives
+ Syntax
+1 preprocessing-file:
+ groupopt
+ group:
+ group-part
+ group group-part
+ group-part:
+ if-section
+ control-line
+ text-line
+ # non-directive
+ if-section:
+ if-group elif-groupsopt else-groupopt endif-line
+ if-group:
+ # if constant-expression new-line groupopt
+ # ifdef identifier new-line groupopt
+ # ifndef identifier new-line groupopt
+ elif-groups:
+ elif-group
+ elif-groups elif-group
+ elif-group:
+ # elif constant-expression new-line groupopt
+ else-group:
+ # else new-line groupopt
+ endif-line:
+ # endif new-line
+
+[page 160]
+
+ control-line:
+ # include pp-tokens new-line
+ # define identifier replacement-list new-line
+ # define identifier lparen identifier-listopt )
+ replacement-list new-line
+ # define identifier lparen ... ) replacement-list new-line
+ # define identifier lparen identifier-list , ... )
+ replacement-list new-line
+ # undef identifier new-line
+ # line pp-tokens new-line
+ # error pp-tokensopt new-line
+ # pragma pp-tokensopt new-line
+ # new-line
+ text-line:
+ pp-tokensopt new-line
+ non-directive:
+ pp-tokens new-line
+ lparen:
+ a ( character not immediately preceded by white-space
+ replacement-list:
+ pp-tokensopt
+ pp-tokens:
+ preprocessing-token
+ pp-tokens preprocessing-token
+ new-line:
+ the new-line character
+ Description
+2 A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
+ following constraints: The first token in the sequence is a # preprocessing token that (at
+ the start of translation phase 4) is either the first character in the source file (optionally
+ after white space containing no new-line characters) or that follows white space
+ containing at least one new-line character. The last token in the sequence is the first new-
+ line character that follows the first token in the sequence.165) A new-line character ends
+ the preprocessing directive even if it occurs within what would otherwise be an
+
+ 165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic
+ significance, as all white space is equivalent except in certain situations during preprocessing (see the
+ # character string literal creation operator in 6.10.3.2, for example).
+
+[page 161]
+
+ invocation of a function-like macro.
+3 A text line shall not begin with a # preprocessing token. A non-directive shall not begin
+ with any of the directive names appearing in the syntax.
+4 When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
+ sequence of preprocessing tokens to occur between the directive name and the following
+ new-line character.
+ Constraints
+5 The only white-space characters that shall appear between preprocessing tokens within a
+ preprocessing directive (from just after the introducing # preprocessing token through
+ just before the terminating new-line character) are space and horizontal-tab (including
+ spaces that have replaced comments or possibly other white-space characters in
+ translation phase 3).
+ Semantics
+6 The implementation can process and skip sections of source files conditionally, include
+ other source files, and replace macros. These capabilities are called preprocessing,
+ because conceptually they occur before translation of the resulting translation unit.
+7 The preprocessing tokens within a preprocessing directive are not subject to macro
+ expansion unless otherwise stated.
+8 EXAMPLE In:
+ #define EMPTY
+ EMPTY # include <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.
+
+ 6.10.1 Conditional inclusion
+ Constraints
+1 The expression that controls conditional inclusion shall be an integer constant expression
+ except that: identifiers (including those lexically identical to keywords) are interpreted as
+ described below;166) and it may contain unary operator expressions of the form
+ defined identifier
+ or
+ defined ( identifier )
+ which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is
+
+
+ 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
+ either are or are not macro names -- there simply are no keywords, enumeration constants, etc.
+
+[page 162]
+
+ predefined or if it has been the subject of a #define preprocessing directive without an
+ intervening #undef directive with the same subject identifier), 0 if it is not.
+2 Each preprocessing token that remains (in the list of preprocessing tokens that will
+ become the controlling expression) after all macro replacements have occurred shall be in
+ the lexical form of a token (6.4).
+ Semantics
+3 Preprocessing directives of the forms
+ # if constant-expression new-line groupopt
+ # elif constant-expression new-line groupopt
+ check whether the controlling constant expression evaluates to nonzero.
+4 Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
+ the controlling constant expression are replaced (except for those macro names modified
+ by the defined unary operator), just as in normal text. If the token defined is
+ generated as a result of this replacement process or use of the defined unary operator
+ does not match one of the two specified forms prior to macro replacement, the behavior is
+ undefined. After all replacements due to macro expansion and the defined unary
+ operator have been performed, all remaining identifiers (including those lexically
+ identical to keywords) are replaced with the pp-number 0, and then each preprocessing
+ token is converted into a token. The resulting tokens compose the controlling constant
+ expression which is evaluated according to the rules of 6.6. For the purposes of this
+ token conversion and evaluation, all signed integer types and all unsigned integer types
+ act as if they have the same representation as, respectively, the types intmax_t and
+ uintmax_t defined in the header <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.
+
+
+
+
+ 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
+ 0x8000 is signed and positive within a #if expression even though it would be unsigned in
+ translation phase 7.
+ 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
+ evaluate to the same value in these two contexts.
+ #if 'z' - 'a' == 25
+ if ('z' - 'a' == 25)
+
+[page 163]
+
+5 Preprocessing directives of the forms
+ # ifdef identifier new-line groupopt
+ # ifndef identifier new-line groupopt
+ check whether the identifier is or is not currently defined as a macro name. Their
+ conditions are equivalent to #if defined identifier and #if !defined identifier
+ respectively.
+6 Each directive's condition is checked in order. If it evaluates to false (zero), the group
+ that it controls is skipped: directives are processed only through the name that determines
+ the directive in order to keep track of the level of nested conditionals; the rest of the
+ directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
+ group. Only the first group whose control condition evaluates to true (nonzero) is
+ processed. If none of the conditions evaluates to true, and there is a #else directive, the
+ group controlled by the #else is processed; lacking a #else directive, all the groups
+ until the #endif are skipped.169)
+ Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
+ integer types (7.20.1.5).
+ 6.10.2 Source file inclusion
+ Constraints
+1 A #include directive shall identify a header or source file that can be processed by the
+ implementation.
+ Semantics
+2 A preprocessing directive of the form
+ # include <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.
+3 A preprocessing directive of the form
+ # include "q-char-sequence" new-line
+ causes the replacement of that directive by the entire contents of the source file identified
+ by the specified sequence between the " delimiters. The named source file is searched
+
+
+ 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
+ before the terminating new-line character. However, comments may appear anywhere in a source file,
+ including within a preprocessing directive.
+
+[page 164]
+
+ 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.
+4 A preprocessing directive of the form
+ # include pp-tokens new-line
+ (that does not match one of the two previous forms) is permitted. The preprocessing
+ tokens after include in the directive are processed just as in normal text. (Each
+ identifier currently defined as a macro name is replaced by its replacement list of
+ preprocessing tokens.) The directive resulting after all replacements shall match one of
+ the two previous forms.170) The method by which a sequence of preprocessing tokens
+ between a < and a > preprocessing token pair or a pair of " characters is combined into a
+ single header name preprocessing token is implementation-defined.
+5 The implementation shall provide unique mappings for sequences consisting of one or
+ more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
+ first character shall not be a digit. The implementation may ignore distinctions of
+ alphabetical case and restrict the mapping to eight significant characters before the
+ period.
+6 A #include preprocessing directive may appear in a source file that has been read
+ because of a #include directive in another file, up to an implementation-defined
+ nesting limit (see 5.2.4.1).
+7 EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following:
+ #include <stdio.h>
+ #include "myprog.h"
+
+
+
+
+ 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
+ phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
+
+[page 165]
+
+8 EXAMPLE 2 This illustrates macro-replaced #include directives:
+ #if VERSION == 1
+ #define INCFILE "vers1.h"
+ #elif VERSION == 2
+ #define INCFILE "vers2.h" // and so on
+ #else
+ #define INCFILE "versN.h"
+ #endif
+ #include INCFILE
+
+ Forward references: macro replacement (6.10.3).
+ 6.10.3 Macro replacement
+ Constraints
+1 Two replacement lists are identical if and only if the preprocessing tokens in both have
+ the same number, ordering, spelling, and white-space separation, where all white-space
+ separations are considered identical.
+2 An identifier currently defined as an object-like macro shall not be redefined by another
+ #define preprocessing directive unless the second definition is an object-like macro
+ definition and the two replacement lists are identical. Likewise, an identifier currently
+ defined as a function-like macro shall not be redefined by another #define
+ preprocessing directive unless the second definition is a function-like macro definition
+ that has the same number and spelling of parameters, and the two replacement lists are
+ identical.
+3 There shall be white-space between the identifier and the replacement list in the definition
+ of an object-like macro.
+4 If the identifier-list in the macro definition does not end with an ellipsis, the number of
+ arguments (including those arguments consisting of no preprocessing tokens) in an
+ invocation of a function-like macro shall equal the number of parameters in the macro
+ definition. Otherwise, there shall be more arguments in the invocation than there are
+ parameters in the macro definition (excluding the ...). There shall exist a )
+ preprocessing token that terminates the invocation.
+5 The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like
+ macro that uses the ellipsis notation in the parameters.
+6 A parameter identifier in a function-like macro shall be uniquely declared within its
+ scope.
+ Semantics
+7 The identifier immediately following the define is called the macro name. There is one
+ name space for macro names. Any white-space characters preceding or following the
+ replacement list of preprocessing tokens are not considered part of the replacement list
+
+[page 166]
+
+ for either form of macro.
+8 If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
+ a preprocessing directive could begin, the identifier is not subject to macro replacement.
+9 A preprocessing directive of the form
+ # define identifier replacement-list new-line
+ defines an object-like macro that causes each subsequent instance of the macro name171)
+ to be replaced by the replacement list of preprocessing tokens that constitute the
+ remainder of the directive. The replacement list is then rescanned for more macro names
+ as specified below.
+10 A preprocessing directive of the form
+ # define identifier lparen identifier-listopt ) replacement-list new-line
+ # define identifier lparen ... ) replacement-list new-line
+ # define identifier lparen identifier-list , ... ) replacement-list new-line
+ defines a function-like macro with parameters, whose use is similar syntactically to a
+ function call. The parameters are specified by the optional list of identifiers, whose scope
+ extends from their declaration in the identifier list until the new-line character that
+ terminates the #define preprocessing directive. Each subsequent instance of the
+ function-like macro name followed by a ( as the next preprocessing token introduces the
+ sequence of preprocessing tokens that is replaced by the replacement list in the definition
+ (an invocation of the macro). The replaced sequence of preprocessing tokens is
+ terminated by the matching ) preprocessing token, skipping intervening matched pairs of
+ left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
+ tokens making up an invocation of a function-like macro, new-line is considered a normal
+ white-space character.
+11 The sequence of preprocessing tokens bounded by the outside-most matching parentheses
+ forms the list of arguments for the function-like macro. The individual arguments within
+ the list are separated by comma preprocessing tokens, but comma preprocessing tokens
+ between matching inner parentheses do not separate arguments. If there are sequences of
+ preprocessing tokens within the list of arguments that would otherwise act as
+ preprocessing directives,172) the behavior is undefined.
+12 If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
+ including any separating comma preprocessing tokens, are merged to form a single item:
+
+
+ 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
+ not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
+ are never scanned for macro names or parameters.
+ 172) Despite the name, a non-directive is a preprocessing directive.
+
+[page 167]
+
+ the variable arguments. The number of arguments so combined is such that, following
+ merger, the number of arguments is one more than the number of parameters in the macro
+ definition (excluding the ...).
+ 6.10.3.1 Argument substitution
+1 After the arguments for the invocation of a function-like macro have been identified,
+ argument substitution takes place. A parameter in the replacement list, unless preceded
+ by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
+ replaced by the corresponding argument after all macros contained therein have been
+ expanded. Before being substituted, each argument's preprocessing tokens are
+ completely macro replaced as if they formed the rest of the preprocessing file; no other
+ preprocessing tokens are available.
+2 An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it
+ were a parameter, and the variable arguments shall form the preprocessing tokens used to
+ replace it.
+ 6.10.3.2 The # operator
+ Constraints
+1 Each # preprocessing token in the replacement list for a function-like macro shall be
+ followed by a parameter as the next preprocessing token in the replacement list.
+ Semantics
+2 If, in the replacement list, a parameter is immediately preceded by a # preprocessing
+ token, both are replaced by a single character string literal preprocessing token that
+ contains the spelling of the preprocessing token sequence for the corresponding
+ argument. Each occurrence of white space between the argument's preprocessing tokens
+ becomes a single space character in the character string literal. White space before the
+ first preprocessing token and after the last preprocessing token composing the argument
+ is deleted. Otherwise, the original spelling of each preprocessing token in the argument
+ is retained in the character string literal, except for special handling for producing the
+ spelling of string literals and character constants: a \ character is inserted before each "
+ and \ character of a character constant or string literal (including the delimiting "
+ characters), except that it is implementation-defined whether a \ character is inserted
+ before the \ character beginning a universal character name. If the replacement that
+ results is not a valid character string literal, the behavior is undefined. The character
+ string literal corresponding to an empty argument is "". The order of evaluation of # and
+ ## operators is unspecified.
+
+[page 168]
+
+ 6.10.3.3 The ## operator
+ Constraints
+1 A ## preprocessing token shall not occur at the beginning or at the end of a replacement
+ list for either form of macro definition.
+ Semantics
+2 If, in the replacement list of a function-like macro, a parameter is immediately preceded
+ or followed by a ## preprocessing token, the parameter is replaced by the corresponding
+ argument's preprocessing token sequence; however, if an argument consists of no
+ preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
+ instead.173)
+3 For both object-like and function-like macro invocations, before the replacement list is
+ reexamined for more macro names to replace, each instance of a ## preprocessing token
+ in the replacement list (not from an argument) is deleted and the preceding preprocessing
+ token is concatenated with the following preprocessing token. Placemarker
+ preprocessing tokens are handled specially: concatenation of two placemarkers results in
+ a single placemarker preprocessing token, and concatenation of a placemarker with a
+ non-placemarker preprocessing token results in the non-placemarker preprocessing token.
+ If the result is not a valid preprocessing token, the behavior is undefined. The resulting
+ token is available for further macro replacement. The order of evaluation of ## operators
+ is unspecified.
+4 EXAMPLE In the following fragment:
+ #define hash_hash # ## #
+ #define mkstr(a) # a
+ #define in_between(a) mkstr(a)
+ #define join(c, d) in_between(c hash_hash d)
+ char p[] = join(x, y); // equivalent to
+ // char p[] = "x ## y";
+ The expansion produces, at various stages:
+ join(x, y)
+ in_between(x hash_hash y)
+ in_between(x ## y)
+ mkstr(x ## y)
+ "x ## y"
+ In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
+ this new token is not the ## operator.
+
+
+ 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
+ exist only within translation phase 4.
+
+[page 169]
+
+ 6.10.3.4 Rescanning and further replacement
+1 After all parameters in the replacement list have been substituted and # and ##
+ processing has taken place, all placemarker preprocessing tokens are removed. The
+ resulting preprocessing token sequence is then rescanned, along with all subsequent
+ preprocessing tokens of the source file, for more macro names to replace.
+2 If the name of the macro being replaced is found during this scan of the replacement list
+ (not including the rest of the source file's preprocessing tokens), it is not replaced.
+ Furthermore, if any nested replacements encounter the name of the macro being replaced,
+ it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
+ available for further replacement even if they are later (re)examined in contexts in which
+ that macro name preprocessing token would otherwise have been replaced.
+3 The resulting completely macro-replaced preprocessing token sequence is not processed
+ as a preprocessing directive even if it resembles one, but all pragma unary operator
+ expressions within it are then processed as specified in 6.10.9 below.
+4 EXAMPLE There are cases where it is not clear whether a replacement is nested or not. For example,
+ given the following macro definitions:
+ #define f(a) a*g
+ #define g(a) f(a)
+ the invocation
+ f(2)(9)
+ may expand to either
+ 2*f(9)
+ or
+ 2*9*g
+ Strictly conforming programs are not permitted to depend on such unspecified behavior.
+
+ 6.10.3.5 Scope of macro definitions
+1 A macro definition lasts (independent of block structure) until a corresponding #undef
+ directive is encountered or (if none is encountered) until the end of the preprocessing
+ translation unit. Macro definitions have no significance after translation phase 4.
+2 A preprocessing directive of the form
+ # undef identifier new-line
+ causes the specified identifier no longer to be defined as a macro name. It is ignored if
+ the specified identifier is not currently defined as a macro name.
+3 EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in
+ #define TABSIZE 100
+
+[page 170]
+
+ int table[TABSIZE];
+
+4 EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
+ It has the advantages of working for any compatible types of the arguments and of generating in-line code
+ without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
+ arguments a second time (including side effects) and generating more code than a function if invoked
+ several times. It also cannot have its address taken, as it has none.
+ #define max(a, b) ((a) > (b) ? (a) : (b))
+ The parentheses ensure that the arguments and the resulting expression are bound properly.
+
+5 EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence
+ #define x 3
+ #define f(a) f(x * (a))
+ #undef x
+ #define x 2
+ #define g f
+ #define z z[0]
+ #define h g(~
+ #define m(a) a(w)
+ #define w 0,1
+ #define t(a) a
+ #define p() int
+ #define q(x) x
+ #define r(x,y) x ## y
+ #define str(x) # x
+ f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
+ g(x+(3,4)-w) | h 5) & m
+ (f)^m(m);
+ p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
+ char c[2][6] = { str(hello), str() };
+ results in
+ f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
+ f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
+ int i[] = { 1, 23, 4, 5, };
+ char c[2][6] = { "hello", "" };
+
+6 EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the
+ sequence
+ #define str(s) # s
+ #define xstr(s) str(s)
+ #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
+ x ## s, x ## t)
+ #define INCFILE(n) vers ## n
+ #define glue(a, b) a ## b
+ #define xglue(a, b) glue(a, b)
+ #define HIGHLOW "hello"
+ #define LOW LOW ", world"
+
+[page 171]
+
+ 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.
+
+7 EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence
+ #define t(x,y,z) x ## y ## z
+ int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
+ t(10,,), t(,11,), t(,,12), t(,,) };
+ results in
+ int j[] = { 123, 45, 67, 89,
+ 10, 11, 12, };
+
+8 EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid.
+ #define OBJ_LIKE (1-1)
+ #define OBJ_LIKE /* white space */ (1-1) /* other */
+ #define FUNC_LIKE(a) ( a )
+ #define FUNC_LIKE( a )( /* note the white space */ \
+ a /* other stuff on this line
+ */ )
+ But the following redefinitions are invalid:
+ #define OBJ_LIKE (0) // different token sequence
+ #define OBJ_LIKE (1 - 1) // different white space
+ #define FUNC_LIKE(b) ( a ) // different parameter usage
+ #define FUNC_LIKE(b) ( b ) // different parameter spelling
+
+9 EXAMPLE 7 Finally, to show the variable argument list macro facilities:
+
+[page 172]
+
+ #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
+1 The string literal of a #line directive, if present, shall be a character string literal.
+ Semantics
+2 The line number of the current source line is one greater than the number of new-line
+ characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
+ file to the current token.
+3 A preprocessing directive of the form
+ # line digit-sequence new-line
+ causes the implementation to behave as if the following sequence of source lines begins
+ with a source line that has a line number as specified by the digit sequence (interpreted as
+ a decimal integer). The digit sequence shall not specify zero, nor a number greater than
+ 2147483647.
+4 A preprocessing directive of the form
+ # line digit-sequence "s-char-sequenceopt" new-line
+ sets the presumed line number similarly and changes the presumed name of the source
+ file to be the contents of the character string literal.
+5 A preprocessing directive of the form
+ # line pp-tokens new-line
+ (that does not match one of the two previous forms) is permitted. The preprocessing
+ tokens after line on the directive are processed just as in normal text (each identifier
+ currently defined as a macro name is replaced by its replacement list of preprocessing
+ tokens). The directive resulting after all replacements shall match one of the two
+ previous forms and is then processed as appropriate.
+
+[page 173]
+
+ 6.10.5 Error directive
+ Semantics
+1 A preprocessing directive of the form
+ # error pp-tokensopt new-line
+ causes the implementation to produce a diagnostic message that includes the specified
+ sequence of preprocessing tokens.
+ 6.10.6 Pragma directive
+ Semantics
+1 A preprocessing directive of the form
+ # pragma pp-tokensopt new-line
+ where the preprocessing token STDC does not immediately follow pragma in the
+ directive (prior to any macro replacement)174) causes the implementation to behave in an
+ implementation-defined manner. The behavior might cause translation to fail or cause the
+ translator or the resulting program to behave in a non-conforming manner. Any such
+ pragma that is not recognized by the implementation is ignored.
+2 If the preprocessing token STDC does immediately follow pragma in the directive (prior
+ to any macro replacement), then no macro replacement is performed on the directive, and
+ the directive shall have one of the following forms175) whose meanings are described
+ elsewhere:
+ #pragma STDC FP_CONTRACT on-off-switch
+ #pragma STDC FENV_ACCESS on-off-switch
+ #pragma STDC CX_LIMITED_RANGE on-off-switch
+ on-off-switch: one of
+ ON OFF DEFAULT
+ Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
+ (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).
+
+
+
+
+ 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
+ except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
+ replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
+ implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
+ but is not required to.
+ 175) See ''future language directions'' (6.11.8).
+
+[page 174]
+
+ 6.10.7 Null directive
+ Semantics
+1 A preprocessing directive of the form
+ # new-line
+ has no effect.
+ 6.10.8 Predefined macro names
+1 The values of the predefined macros listed in the following subclauses176) (except for
+ __FILE__ and __LINE__) remain constant throughout the translation unit.
+2 None of these macro names, nor the identifier defined, shall be the subject of a
+ #define or a #undef preprocessing directive. Any other predefined macro names
+ shall begin with a leading underscore followed by an uppercase letter or a second
+ underscore.
+3 The implementation shall not predefine the macro __cplusplus, nor shall it define it
+ in any standard header.
+ Forward references: standard headers (7.1.2).
+ 6.10.8.1 Mandatory macros
+1 The following macro names shall be defined by the implementation:
+ __DATE__ The date of translation of the preprocessing translation unit: a character
+ string literal of the form "Mmm dd yyyy", where the names of the
+ months are the same as those generated by the asctime function, and the
+ first character of dd is a space character if the value is less than 10. If the
+ date of translation is not available, an implementation-defined valid date
+ shall be supplied.
+ __FILE__ The presumed name of the current source file (a character string literal).177)
+ __LINE__ The presumed line number (within the current source file) of the current
+ source line (an integer constant).177)
+ __STDC__ The integer constant 1, intended to indicate a conforming implementation.
+ __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted
+ implementation or the integer constant 0 if it is not.
+
+
+
+
+ 176) See ''future language directions'' (6.11.9).
+ 177) The presumed source file name and line number can be changed by the #line directive.
+
+[page 175]
+
+ __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 (7.27.3.1).
+ 6.10.8.2 Environment macros
+1 The following macro names are conditionally defined by the implementation:
+ __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example,
+ 199712L). If this symbol is defined, then every character in the Unicode
+ required set, when stored in an object of type wchar_t, has the same
+ value as the short identifier of that character. The Unicode required set
+ consists of all the characters that are defined by ISO/IEC 10646, along with
+ all amendments and technical corrigenda, as of the specified year and
+ month. If some other encoding is used, the macro shall not be defined and
+ the actual encoding used is implementation-defined.
+ __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in
+ the encoding for wchar_t, a member of the basic character set need not
+ have a code value equal to its value when used as the lone character in an
+ integer character constant.
+ __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type
+ char16_t are UTF-16 encoded. If some other encoding is used, the
+ macro shall not be defined and the actual encoding used is implementation-
+ defined.
+ __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type
+ char32_t are UTF-32 encoded. If some other encoding is used, the
+ macro shall not be defined and the actual encoding used is implementation-
+ defined.
+ Forward references: common definitions (7.19), unicode utilities (7.28).
+
+
+
+
+ 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
+ ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
+ remain an integer constant of type long int that is increased with each revision of this International
+ Standard.
+
+[page 176]
+
+ 6.10.8.3 Conditional feature macros
+1 The following macro names are conditionally defined by the implementation:
+ __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to
+ the specifications in annex L (Analyzability).
+ __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the
+ specifications in annex F (IEC 60559 floating-point arithmetic).
+ __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate
+ adherence to the specifications in annex G (IEC 60559 compatible complex
+ arithmetic).
+ __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support
+ for the extensions defined in annex K (Bounds-checking interfaces).179)
+ __STDC_NO_ATOMICS__ 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.
+ __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 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.
+2 An implementation that defines __STDC_NO_COMPLEX__ shall not define
+ __STDC_IEC_559_COMPLEX__.
+
+
+
+
+ 179) The intention is that this will remain an integer constant of type long int that is increased with
+ each revision of this International Standard.
+
+[page 177]
+
+ 6.10.9 Pragma operator
+ Semantics
+1 A unary operator expression of the form:
+ _Pragma ( string-literal )
+ is processed as follows: The string literal is destringized by deleting any encoding prefix,
+ 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.
+2 EXAMPLE A directive of the form:
+ #pragma listing on "..\listing.dir"
+ can also be expressed as:
+ _Pragma ( "listing on \"..\\listing.dir\"" )
+ The latter form is processed in the same way whether it appears literally as shown, or results from macro
+ replacement, as in:
+ #define LISTING(x) PRAGMA(listing on #x)
+ #define PRAGMA(x) _Pragma(#x)
+ LISTING ( ..\listing.dir )
+
+[page 178]
+
+ 6.11 Future language directions
+ 6.11.1 Floating types
+1 Future standardization may include additional floating-point types, including those with
+ greater range, precision, or both than long double.
+ 6.11.2 Linkages of identifiers
+1 Declaring an identifier with internal linkage at file scope without the static storage-
+ class specifier is an obsolescent feature.
+ 6.11.3 External names
+1 Restriction of the significance of an external name to fewer than 255 characters
+ (considering each universal character name or extended source character as a single
+ character) is an obsolescent feature that is a concession to existing implementations.
+ 6.11.4 Character escape sequences
+1 Lowercase letters as escape sequences are reserved for future standardization. Other
+ characters may be used in extensions.
+ 6.11.5 Storage-class specifiers
+1 The placement of a storage-class specifier other than at the beginning of the declaration
+ specifiers in a declaration is an obsolescent feature.
+ 6.11.6 Function declarators
+1 The use of function declarators with empty parentheses (not prototype-format parameter
+ type declarators) is an obsolescent feature.
+ 6.11.7 Function definitions
+1 The use of function definitions with separate parameter identifier and declaration lists
+ (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
+ 6.11.8 Pragma directives
+1 Pragmas whose first preprocessing token is STDC are reserved for future standardization.
+ 6.11.9 Predefined macro names
+1 Macro names beginning with __STDC_ are reserved for future standardization.
+
+[page 179]
+
+
+ 7. Library
+ 7.1 Introduction
+ 7.1.1 Definitions of terms
+1 A string is a contiguous sequence of characters terminated by and including the first null
+ character. The term multibyte string is sometimes used instead to emphasize special
+ processing given to multibyte characters contained in the string or to avoid confusion
+ with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
+ character. The length of a string is the number of bytes preceding the null character and
+ the value of a string is the sequence of the values of the contained characters, in order.
+2 The decimal-point character is the character used by functions that convert floating-point
+ numbers to or from character sequences to denote the beginning of the fractional part of
+ such character sequences.180) It is represented in the text and examples by a period, but
+ may be changed by the setlocale function.
+3 A null wide character is a wide character with code value zero.
+4 A wide string is a contiguous sequence of wide characters terminated by and including
+ the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
+ addressed) wide character. The length of a wide string is the number of wide characters
+ preceding the null wide character and the value of a wide string is the sequence of code
+ values of the contained wide characters, in order.
+5 A shift sequence is a contiguous sequence of bytes within a multibyte string that
+ (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
+ corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
+ character.181)
+ Forward references: character handling (7.4), the setlocale function (7.11.1.1).
+
+
+
+
+ 180) The functions that make use of the decimal-point character are the numeric conversion functions
+ (7.22.1, 7.29.4.1) and the formatted input/output functions (7.21.6, 7.29.2).
+ 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
+ enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
+ sequence of maximum length. Whether these counts provide for more than one shift sequence is the
+ implementation's choice.
+
+[page 180]
+
+ 7.1.2 Standard headers
+1 Each library function is declared, with a type that includes a prototype, in a header,182)
+ whose contents are made available by the #include preprocessing directive. The
+ header declares a set of related functions, plus any necessary types and additional macros
+ needed to facilitate their use. Declarations of types described in this clause shall not
+ include type qualifiers, unless explicitly stated otherwise.
+2 The standard headers are183)
+ <assert.h> <math.h> <stdlib.h>
+ <complex.h> <setjmp.h> <stdnoreturn.h>
+ <ctype.h> <signal.h> <string.h>
+ <errno.h> <stdalign.h> <tgmath.h>
+ <fenv.h> <stdarg.h> <threads.h>
+ <float.h> <stdatomic.h> <time.h>
+ <inttypes.h> <stdbool.h> <uchar.h>
+ <iso646.h> <stddef.h> <wchar.h>
+ <limits.h> <stdint.h> <wctype.h>
+ <locale.h> <stdio.h>
+3 If a file with the same name as one of the above < and > delimited sequences, not
+ provided as part of the implementation, is placed in any of the standard places that are
+ searched for included source files, the behavior is undefined.
+4 Standard headers may be included in any order; each may be included more than once in
+ a given scope, with no effect different from being included only once, except that the
+ effect of including <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
+ of the header or when any macro defined in the header is expanded.
+5 Any definition of an object-like macro described in this clause shall expand to code that is
+ fully protected by parentheses where necessary, so that it groups in an arbitrary
+ expression as if it were a single identifier.
+
+
+ 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.
+
+[page 181]
+
+6 Any declaration of a library function shall have external linkage.
+7 A summary of the contents of the standard headers is given in annex B.
+ Forward references: diagnostics (7.2).
+ 7.1.3 Reserved identifiers
+1 Each header declares or defines all identifiers listed in its associated subclause, and
+ optionally declares or defines identifiers listed in its associated future library directions
+ subclause and identifiers which are always reserved either for any use or for use as file
+ scope identifiers.
+ -- All identifiers that begin with an underscore and either an uppercase letter or another
+ underscore are always reserved for any use.
+ -- All identifiers that begin with an underscore are always reserved for use as identifiers
+ with file scope in both the ordinary and tag name spaces.
+ -- Each macro name in any of the following subclauses (including the future library
+ directions) is reserved for use as specified if any of its associated headers is included;
+ unless explicitly stated otherwise (see 7.1.4).
+ -- All identifiers with external linkage in any of the following subclauses (including the
+ future library directions) and errno are always reserved for use as identifiers with
+ external linkage.184)
+ -- Each identifier with file scope listed in any of the following subclauses (including the
+ future library directions) is reserved for use as a macro name and as an identifier with
+ file scope in the same name space if any of its associated headers is included.
+2 No other identifiers are reserved. If the program declares or defines an identifier in a
+ context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
+ identifier as a macro name, the behavior is undefined.
+3 If the program removes (with #undef) any macro definition of an identifier in the first
+ group listed above, the behavior is undefined.
+
+
+
+
+ 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
+ va_copy, and va_end.
+
+[page 182]
+
+ 7.1.4 Use of library functions
+1 Each of the following statements applies unless explicitly stated otherwise in the detailed
+ descriptions that follow: If an argument to a function has an invalid value (such as a value
+ outside the domain of the function, or a pointer outside the address space of the program,
+ or a null pointer, or a pointer to non-modifiable storage when the corresponding
+ parameter is not const-qualified) or a type (after promotion) not expected by a function
+ with variable number of arguments, the behavior is undefined. If a function argument is
+ described as being an array, the pointer actually passed to the function shall have a value
+ such that all address computations and accesses to objects (that would be valid if the
+ pointer did point to the first element of such an array) are in fact valid. Any function
+ declared in a header may be additionally implemented as a function-like macro defined in
+ the header, so if a library function is declared explicitly when its header is included, one
+ of the techniques shown below can be used to ensure the declaration is not affected by
+ such a macro. Any macro definition of a function can be suppressed locally by enclosing
+ the name of the function in parentheses, because the name is then not followed by the left
+ parenthesis that indicates expansion of a macro function name. For the same syntactic
+ reason, it is permitted to take the address of a library function even if it is also defined as
+ a macro.185) The use of #undef to remove any macro definition will also ensure that an
+ actual function is referred to. Any invocation of a library function that is implemented as
+ a macro shall expand to code that evaluates each of its arguments exactly once, fully
+ protected by parentheses where necessary, so it is generally safe to use arbitrary
+ expressions as arguments.186) Likewise, those function-like macros described in the
+ following subclauses may be invoked in an expression anywhere a function with a
+ compatible return type could be called.187) All object-like macros listed as expanding to
+
+
+ 185) This means that an implementation shall provide an actual function for each library function, even if it
+ also provides a macro for that function.
+ 186) Such macros might not contain the sequence points that the corresponding function calls do.
+ 187) Because external identifiers and some macro names beginning with an underscore are reserved,
+ implementations may provide special semantics for such names. For example, the identifier
+ _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
+ appropriate header could specify
+ #define abs(x) _BUILTIN_abs(x)
+ for a compiler whose code generator will accept it.
+ In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
+ function may write
+ #undef abs
+ whether the implementation's header provides a macro implementation of abs or a built-in
+ implementation. The prototype for the function, which precedes and is hidden by any macro
+ definition, is thereby revealed also.
+
+[page 183]
+
+ integer constant expressions shall additionally be suitable for use in #if preprocessing
+ directives.
+2 Provided that a library function can be declared without reference to any type defined in a
+ header, it is also permissible to declare the function and use it without including its
+ associated header.
+3 There is a sequence point immediately before a library function returns.
+4 The functions in the standard library are not guaranteed to be reentrant and may modify
+ objects with static or thread storage duration.188)
+5 Unless explicitly stated otherwise in the detailed descriptions that follow, library
+ functions shall prevent data races as follows: A library function shall not directly or
+ indirectly access objects accessible by threads other than the current thread unless the
+ objects are accessed directly or indirectly via the function's arguments. A library
+ function shall not directly or indirectly modify objects accessible by threads other than
+ the current thread unless the objects are accessed directly or indirectly via the function's
+ non-const arguments.189) Implementations may share their own internal objects between
+ threads if the objects are not visible to users and are protected against data races.
+6 Unless otherwise specified, library functions shall perform all operations solely within the
+ current thread if those operations have effects that are visible to users.190)
+7 EXAMPLE The function atoi may be used in any of several ways:
+ -- by use of its associated header (possibly generating a macro expansion)
+ #include <stdlib.h>
+ const char *str;
+ /* ... */
+ i = atoi(str);
+ -- by use of its associated header (assuredly generating a true function reference)
+
+
+
+
+ 188) Thus, a signal handler cannot, in general, call standard library functions.
+ 189) This means, for example, that an implementation is not permitted to use a static object for internal
+ purposes without synchronization because it could cause a data race even in programs that do not
+ explicitly share objects between threads. Similarly, an implementation of memcpy is not permitted to
+ copy bytes beyond the specified length of the destination object and then restore the original values
+ because it could cause a data race if the program shared those bytes between threads.
+ 190) This allows implementations to parallelize operations if there are no visible side effects.
+
+[page 184]
+
+ #include <stdlib.h>
+ #undef atoi
+ const char *str;
+ /* ... */
+ i = atoi(str);
+ or
+ #include <stdlib.h>
+ const char *str;
+ /* ... */
+ i = (atoi)(str);
+-- by explicit declaration
+ extern int atoi(const char *);
+ const char *str;
+ /* ... */
+ i = atoi(str);
+
+[page 185]
+
+ 7.2 Diagnostics <assert.h>
+1 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.
+2 The assert macro shall be implemented as a macro, not as an actual function. If the
+ macro definition is suppressed in order to access an actual function, the behavior is
+ undefined.
+3 The macro
+ static_assert
+ expands to _Static_assert.
+ 7.2.1 Program diagnostics
+ 7.2.1.1 The assert macro
+ Synopsis
+1 #include <assert.h>
+ void assert(scalar expression);
+ Description
+2 The assert macro puts diagnostic tests into programs; it expands to a void expression.
+ When it is executed, if expression (which shall have a scalar type) is false (that is,
+ compares equal to 0), the assert macro writes information about the particular call that
+ failed (including the text of the argument, the name of the source file, the source line
+ number, and the name of the enclosing function -- the latter are respectively the values of
+ the preprocessing macros __FILE__ and __LINE__ and of the identifier
+ __func__) on the standard error stream in an implementation-defined format.191) It
+ then calls the abort function.
+
+
+
+ 191) The message written might be of the form:
+ Assertion failed: expression, function abc, file xyz, line nnn.
+
+[page 186]
+
+ Returns
+3 The assert macro returns no value.
+ Forward references: the abort function (7.22.4.1).
+
+[page 187]
+
+ 7.3 Complex arithmetic <complex.h>
+ 7.3.1 Introduction
+1 The header <complex.h> defines macros and declares functions that support complex
+ arithmetic.192)
+2 Implementations that define the macro __STDC_NO_COMPLEX__ need not provide
+ this header nor support any of its facilities.
+3 Each synopsis specifies a family of functions consisting of a principal function with one
+ or more double complex parameters and a double complex or double return
+ value; and other functions with the same name but with f and l suffixes which are
+ corresponding functions with float and long double parameters and return values.
+4 The macro
+ complex
+ expands to _Complex; the macro
+ _Complex_I
+ expands to a constant expression of type const float _Complex, with the value of
+ the imaginary unit.193)
+5 The macros
+ imaginary
+ and
+ _Imaginary_I
+ are defined if and only if the implementation supports imaginary types;194) if defined,
+ they expand to _Imaginary and a constant expression of type const float
+ _Imaginary with the value of the imaginary unit.
+6 The macro
+ I
+ expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
+ defined, I shall expand to _Complex_I.
+7 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
+ redefine the macros complex, imaginary, and I.
+
+ 192) See ''future library directions'' (7.31.1).
+ 193) The imaginary unit is a number i such that i 2 = -1.
+ 194) A specification for imaginary types is in informative annex G.
+
+[page 188]
+
+ Forward references: IEC 60559-compatible complex arithmetic (annex G).
+ 7.3.2 Conventions
+1 Values are interpreted as radians, not degrees. An implementation may set errno but is
+ not required to.
+ 7.3.3 Branch cuts
+1 Some of the functions below have branch cuts, across which the function is
+ discontinuous. For implementations with a signed zero (including all IEC 60559
+ implementations) that follow the specifications of annex G, the sign of zero distinguishes
+ one side of a cut from another so the function is continuous (except for format
+ limitations) as the cut is approached from either side. For example, for the square root
+ function, which has a branch cut along the negative real axis, the top of the cut, with
+ imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
+ imaginary part -0, maps to the negative imaginary axis.
+2 Implementations that do not support a signed zero (see annex F) cannot distinguish the
+ sides of branch cuts. These implementations shall map a cut so the function is continuous
+ as the cut is approached coming around the finite endpoint of the cut in a counter
+ clockwise direction. (Branch cuts for the functions specified here have just one finite
+ endpoint.) For example, for the square root function, coming counter clockwise around
+ the finite endpoint of the cut along the negative real axis approaches the cut from above,
+ so the cut maps to the positive imaginary axis.
+ 7.3.4 The CX_LIMITED_RANGE pragma
+ Synopsis
+1 #include <complex.h>
+ #pragma STDC CX_LIMITED_RANGE on-off-switch
+ Description
+2 The usual mathematical formulas for complex multiply, divide, and absolute value are
+ problematic because of their treatment of infinities and because of undue overflow and
+ underflow. The CX_LIMITED_RANGE pragma can be used to inform the
+ implementation that (where the state is ''on'') the usual mathematical formulas are
+ acceptable.195) The pragma can occur either outside external declarations or preceding all
+ explicit declarations and statements inside a compound statement. When outside external
+ declarations, the pragma takes effect from its occurrence until another
+ CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
+ When inside a compound statement, the pragma takes effect from its occurrence until
+ another CX_LIMITED_RANGE pragma is encountered (including within a nested
+ compound statement), or until the end of the compound statement; at the end of a
+ compound statement the state for the pragma is restored to its condition just before the
+
+[page 189]
+
+ compound statement. If this pragma is used in any other context, the behavior is
+ undefined. The default state for the pragma is ''off''.
+ 7.3.5 Trigonometric functions
+ 7.3.5.1 The cacos functions
+ Synopsis
+1 #include <complex.h>
+ double complex cacos(double complex z);
+ float complex cacosf(float complex z);
+ long double complex cacosl(long double complex z);
+ Description
+2 The cacos functions compute the complex arc cosine of z, with branch cuts outside the
+ interval [-1, +1] along the real axis.
+ Returns
+3 The cacos functions return the complex arc cosine value, in the range of a strip
+ mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the
+ real axis.
+ 7.3.5.2 The casin functions
+ Synopsis
+1 #include <complex.h>
+ double complex casin(double complex z);
+ float complex casinf(float complex z);
+ long double complex casinl(long double complex z);
+ Description
+2 The casin functions compute the complex arc sine of z, with branch cuts outside the
+ interval [-1, +1] along the real axis.
+ Returns
+3 The casin functions return the complex arc sine value, in the range of a strip
+ mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
+
+ 195) The purpose of the pragma is to allow the implementation to use the formulas:
+ (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
+ (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
+ | x + iy | = (sqrt) x 2 + y 2
+ -----
+ where the programmer can determine they are safe.
+
+[page 190]
+
+ along the real axis.
+ 7.3.5.3 The catan functions
+ Synopsis
+1 #include <complex.h>
+ double complex catan(double complex z);
+ float complex catanf(float complex z);
+ long double complex catanl(long double complex z);
+ Description
+2 The catan functions compute the complex arc tangent of z, with branch cuts outside the
+ interval [-i, +i] along the imaginary axis.
+ Returns
+3 The catan functions return the complex arc tangent value, in the range of a strip
+ mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
+ along the real axis.
+ 7.3.5.4 The ccos functions
+ Synopsis
+1 #include <complex.h>
+ double complex ccos(double complex z);
+ float complex ccosf(float complex z);
+ long double complex ccosl(long double complex z);
+ Description
+2 The ccos functions compute the complex cosine of z.
+ Returns
+3 The ccos functions return the complex cosine value.
+ 7.3.5.5 The csin functions
+ Synopsis
+1 #include <complex.h>
+ double complex csin(double complex z);
+ float complex csinf(float complex z);
+ long double complex csinl(long double complex z);
+ Description
+2 The csin functions compute the complex sine of z.
+
+[page 191]
+
+ Returns
+3 The csin functions return the complex sine value.
+ 7.3.5.6 The ctan functions
+ Synopsis
+1 #include <complex.h>
+ double complex ctan(double complex z);
+ float complex ctanf(float complex z);
+ long double complex ctanl(long double complex z);
+ Description
+2 The ctan functions compute the complex tangent of z.
+ Returns
+3 The ctan functions return the complex tangent value.
+ 7.3.6 Hyperbolic functions
+ 7.3.6.1 The cacosh functions
+ Synopsis
+1 #include <complex.h>
+ double complex cacosh(double complex z);
+ float complex cacoshf(float complex z);
+ long double complex cacoshl(long double complex z);
+ Description
+2 The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
+ cut at values less than 1 along the real axis.
+ Returns
+3 The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
+ half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the
+ imaginary axis.
+ 7.3.6.2 The casinh functions
+ Synopsis
+1 #include <complex.h>
+ double complex casinh(double complex z);
+ float complex casinhf(float complex z);
+ long double complex casinhl(long double complex z);
+
+[page 192]
+
+ Description
+2 The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
+ outside the interval [-i, +i] along the imaginary axis.
+ Returns
+3 The casinh functions return the complex arc hyperbolic sine value, in the range of a
+ strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
+ along the imaginary axis.
+ 7.3.6.3 The catanh functions
+ Synopsis
+1 #include <complex.h>
+ double complex catanh(double complex z);
+ float complex catanhf(float complex z);
+ long double complex catanhl(long double complex z);
+ Description
+2 The catanh functions compute the complex arc hyperbolic tangent of z, with branch
+ cuts outside the interval [-1, +1] along the real axis.
+ Returns
+3 The catanh functions return the complex arc hyperbolic tangent value, in the range of a
+ strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
+ along the imaginary axis.
+ 7.3.6.4 The ccosh functions
+ Synopsis
+1 #include <complex.h>
+ double complex ccosh(double complex z);
+ float complex ccoshf(float complex z);
+ long double complex ccoshl(long double complex z);
+ Description
+2 The ccosh functions compute the complex hyperbolic cosine of z.
+ Returns
+3 The ccosh functions return the complex hyperbolic cosine value.
+
+[page 193]
+
+ 7.3.6.5 The csinh functions
+ Synopsis
+1 #include <complex.h>
+ double complex csinh(double complex z);
+ float complex csinhf(float complex z);
+ long double complex csinhl(long double complex z);
+ Description
+2 The csinh functions compute the complex hyperbolic sine of z.
+ Returns
+3 The csinh functions return the complex hyperbolic sine value.
+ 7.3.6.6 The ctanh functions
+ Synopsis
+1 #include <complex.h>
+ double complex ctanh(double complex z);
+ float complex ctanhf(float complex z);
+ long double complex ctanhl(long double complex z);
+ Description
+2 The ctanh functions compute the complex hyperbolic tangent of z.
+ Returns
+3 The ctanh functions return the complex hyperbolic tangent value.
+ 7.3.7 Exponential and logarithmic functions
+ 7.3.7.1 The cexp functions
+ Synopsis
+1 #include <complex.h>
+ double complex cexp(double complex z);
+ float complex cexpf(float complex z);
+ long double complex cexpl(long double complex z);
+ Description
+2 The cexp functions compute the complex base-e exponential of z.
+ Returns
+3 The cexp functions return the complex base-e exponential value.
+
+[page 194]
+
+ 7.3.7.2 The clog functions
+ Synopsis
+1 #include <complex.h>
+ double complex clog(double complex z);
+ float complex clogf(float complex z);
+ long double complex clogl(long double complex z);
+ Description
+2 The clog functions compute the complex natural (base-e) logarithm of z, with a branch
+ cut along the negative real axis.
+ Returns
+3 The clog functions return the complex natural logarithm value, in the range of a strip
+ mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the
+ imaginary axis.
+ 7.3.8 Power and absolute-value functions
+ 7.3.8.1 The cabs functions
+ Synopsis
+1 #include <complex.h>
+ double cabs(double complex z);
+ float cabsf(float complex z);
+ long double cabsl(long double complex z);
+ Description
+2 The cabs functions compute the complex absolute value (also called norm, modulus, or
+ magnitude) of z.
+ Returns
+3 The cabs functions return the complex absolute value.
+ 7.3.8.2 The cpow functions
+ Synopsis
+1 #include <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);
+
+[page 195]
+
+ Description
+2 The cpow functions compute the complex power function xy , with a branch cut for the
+ first parameter along the negative real axis.
+ Returns
+3 The cpow functions return the complex power function value.
+ 7.3.8.3 The csqrt functions
+ Synopsis
+1 #include <complex.h>
+ double complex csqrt(double complex z);
+ float complex csqrtf(float complex z);
+ long double complex csqrtl(long double complex z);
+ Description
+2 The csqrt functions compute the complex square root of z, with a branch cut along the
+ negative real axis.
+ Returns
+3 The csqrt functions return the complex square root value, in the range of the right half-
+ plane (including the imaginary axis).
+ 7.3.9 Manipulation functions
+ 7.3.9.1 The carg functions
+ Synopsis
+1 #include <complex.h>
+ double carg(double complex z);
+ float cargf(float complex z);
+ long double cargl(long double complex z);
+ Description
+2 The carg functions compute the argument (also called phase angle) of z, with a branch
+ cut along the negative real axis.
+ Returns
+3 The carg functions return the value of the argument in the interval [-pi , +pi ].
+
+[page 196]
+
+ 7.3.9.2 The cimag functions
+ Synopsis
+1 #include <complex.h>
+ double cimag(double complex z);
+ float cimagf(float complex z);
+ long double cimagl(long double complex z);
+ Description
+2 The cimag functions compute the imaginary part of z.196)
+ Returns
+3 The cimag functions return the imaginary part value (as a real).
+ 7.3.9.3 The CMPLX macros
+ Synopsis
+1 #include <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
+2 The CMPLX macros expand to an expression of the specified complex type, with the real
+ part having the (converted) value of x and the imaginary part having the (converted)
+ value of y. The resulting expression shall be suitable for use as an initializer for an object
+ with static or thread storage duration, provided both arguments are likewise suitable.
+ Returns
+3 The CMPLX macros return the complex value x + i y.
+4 NOTE These macros act as if the implementation supported imaginary types and the definitions were:
+ #define CMPLX(x, y) ((double complex)((double)(x) + \
+ _Imaginary_I * (double)(y)))
+ #define CMPLXF(x, y) ((float complex)((float)(x) + \
+ _Imaginary_I * (float)(y)))
+ #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
+ _Imaginary_I * (long double)(y)))
+
+
+
+
+ 196) For a variable z of complex type, z == creal(z) + cimag(z)*I.
+
+[page 197]
+
+ 7.3.9.4 The conj functions
+ Synopsis
+1 #include <complex.h>
+ double complex conj(double complex z);
+ float complex conjf(float complex z);
+ long double complex conjl(long double complex z);
+ Description
+2 The conj functions compute the complex conjugate of z, by reversing the sign of its
+ imaginary part.
+ Returns
+3 The conj functions return the complex conjugate value.
+ 7.3.9.5 The cproj functions
+ Synopsis
+1 #include <complex.h>
+ double complex cproj(double complex z);
+ float complex cprojf(float complex z);
+ long double complex cprojl(long double complex z);
+ Description
+2 The cproj functions compute a projection of z onto the Riemann sphere: z projects to
+ z except that all complex infinities (even those with one infinite part and one NaN part)
+ project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
+ equivalent to
+ INFINITY + I * copysign(0.0, cimag(z))
+ Returns
+3 The cproj functions return the value of the projection onto the Riemann sphere.
+ 7.3.9.6 The creal functions
+ Synopsis
+1 #include <complex.h>
+ double creal(double complex z);
+ float crealf(float complex z);
+ long double creall(long double complex z);
+ Description
+2 The creal functions compute the real part of z.197)
+
+[page 198]
+
+ Returns
+3 The creal functions return the real part value.
+
+
+
+
+ 197) For a variable z of complex type, z == creal(z) + cimag(z)*I.
+
+[page 199]
+
+ 7.4 Character handling <ctype.h>
+1 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.
+2 The behavior of these functions is affected by the current locale. Those functions that
+ have locale-specific aspects only when not in the "C" locale are noted below.
+3 The term printing character refers to a member of a locale-specific set of characters, each
+ of which occupies one printing position on a display device; the term control character
+ refers to a member of a locale-specific set of characters that are not printing
+ characters.199) All letters and digits are printing characters.
+ Forward references: EOF (7.21.1), localization (7.11).
+ 7.4.1 Character classification functions
+1 The functions in this subclause return nonzero (true) if and only if the value of the
+ argument c conforms to that in the description of the function.
+ 7.4.1.1 The isalnum function
+ Synopsis
+1 #include <ctype.h>
+ int isalnum(int c);
+ Description
+2 The isalnum function tests for any character for which isalpha or isdigit is true.
+ 7.4.1.2 The isalpha function
+ Synopsis
+1 #include <ctype.h>
+ int isalpha(int c);
+ Description
+2 The isalpha function tests for any character for which isupper or islower is true,
+ or any character that is one of a locale-specific set of alphabetic characters for which
+
+
+
+ 198) See ''future library directions'' (7.31.2).
+ 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
+ whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
+ values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
+
+[page 200]
+
+ none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale,
+ isalpha returns true only for the characters for which isupper or islower is true.
+ 7.4.1.3 The isblank function
+ Synopsis
+1 #include <ctype.h>
+ int isblank(int c);
+ Description
+2 The isblank function tests for any character that is a standard blank character or is one
+ of a locale-specific set of characters for which isspace is true and that is used to
+ separate words within a line of text. The standard blank characters are the following:
+ space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
+ for the standard blank characters.
+ 7.4.1.4 The iscntrl function
+ Synopsis
+1 #include <ctype.h>
+ int iscntrl(int c);
+ Description
+2 The iscntrl function tests for any control character.
+ 7.4.1.5 The isdigit function
+ Synopsis
+1 #include <ctype.h>
+ int isdigit(int c);
+ Description
+2 The isdigit function tests for any decimal-digit character (as defined in 5.2.1).
+ 7.4.1.6 The isgraph function
+ Synopsis
+1 #include <ctype.h>
+ int isgraph(int c);
+
+
+
+
+ 200) The functions islower and isupper test true or false separately for each of these additional
+ characters; all four combinations are possible.
+
+[page 201]
+
+ Description
+2 The isgraph function tests for any printing character except space (' ').
+ 7.4.1.7 The islower function
+ Synopsis
+1 #include <ctype.h>
+ int islower(int c);
+ Description
+2 The islower function tests for any character that is a lowercase letter or is one of a
+ locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
+ isspace is true. In the "C" locale, islower returns true only for the lowercase
+ letters (as defined in 5.2.1).
+ 7.4.1.8 The isprint function
+ Synopsis
+1 #include <ctype.h>
+ int isprint(int c);
+ Description
+2 The isprint function tests for any printing character including space (' ').
+ 7.4.1.9 The ispunct function
+ Synopsis
+1 #include <ctype.h>
+ int ispunct(int c);
+ Description
+2 The ispunct function tests for any printing character that is one of a locale-specific set
+ of punctuation characters for which neither isspace nor isalnum is true. In the "C"
+ locale, ispunct returns true for every printing character for which neither isspace
+ nor isalnum is true.
+ 7.4.1.10 The isspace function
+ Synopsis
+1 #include <ctype.h>
+ int isspace(int c);
+ Description
+2 The isspace function tests for any character that is a standard white-space character or
+ is one of a locale-specific set of characters for which isalnum is false. The standard
+
+[page 202]
+
+ white-space characters are the following: space (' '), form feed ('\f'), new-line
+ ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
+ "C" locale, isspace returns true only for the standard white-space characters.
+ 7.4.1.11 The isupper function
+ Synopsis
+1 #include <ctype.h>
+ int isupper(int c);
+ Description
+2 The isupper function tests for any character that is an uppercase letter or is one of a
+ locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
+ isspace is true. In the "C" locale, isupper returns true only for the uppercase
+ letters (as defined in 5.2.1).
+ 7.4.1.12 The isxdigit function
+ Synopsis
+1 #include <ctype.h>
+ int isxdigit(int c);
+ Description
+2 The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
+ 7.4.2 Character case mapping functions
+ 7.4.2.1 The tolower function
+ Synopsis
+1 #include <ctype.h>
+ int tolower(int c);
+ Description
+2 The tolower function converts an uppercase letter to a corresponding lowercase letter.
+ Returns
+3 If the argument is a character for which isupper is true and there are one or more
+ corresponding characters, as specified by the current locale, for which islower is true,
+ the tolower function returns one of the corresponding characters (always the same one
+ for any given locale); otherwise, the argument is returned unchanged.
+
+[page 203]
+
+ 7.4.2.2 The toupper function
+ Synopsis
+1 #include <ctype.h>
+ int toupper(int c);
+ Description
+2 The toupper function converts a lowercase letter to a corresponding uppercase letter.
+ Returns
+3 If the argument is a character for which islower is true and there are one or more
+ corresponding characters, as specified by the current locale, for which isupper is true,
+ the toupper function returns one of the corresponding characters (always the same one
+ for any given locale); otherwise, the argument is returned unchanged.
+
+[page 204]
+
+ 7.5 Errors <errno.h>
+1 The header <errno.h> defines several macros, all relating to the reporting of error
+ conditions.
+2 The macros are
+ EDOM
+ EILSEQ
+ ERANGE
+ which expand to integer constant expressions with type int, distinct positive values, and
+ which are suitable for use in #if preprocessing directives; and
+ errno
+ which expands to a modifiable lvalue201) that has type int and thread local storage
+ duration, the value of which is set to a positive error number by several library functions.
+ If a macro definition is suppressed in order to access an actual object, or a program
+ defines an identifier with the name errno, the behavior is undefined.
+3 The value of errno in the initial thread is zero at program startup (the initial value of
+ errno in other threads is an indeterminate value), but is never set to zero by any library
+ function.202) The value of errno may be set to nonzero by a library function call
+ whether or not there is an error, provided the use of errno is not documented in the
+ description of the function in this International Standard.
+4 Additional macro definitions, beginning with E and a digit or E and an uppercase
+ letter,203) may also be specified by the implementation.
+
+
+
+
+ 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
+ resulting from a function call (for example, *errno()).
+ 202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
+ then inspect it before a subsequent library function call. Of course, a library function can save the
+ value of errno on entry and then set it to zero, as long as the original value is restored if errno's
+ value is still zero just before the return.
+ 203) See ''future library directions'' (7.31.3).
+
+[page 205]
+
+ 7.6 Floating-point environment <fenv.h>
+1 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.
+2 The floating-point environment has thread storage duration. The initial state for a
+ thread's floating-point environment is the current state of the floating-point environment
+ of the thread that creates it at the time of creation.
+3 Certain programming conventions support the intended model of use for the floating-
+ point environment:206)
+ -- a function call does not alter its caller's floating-point control modes, clear its caller's
+ floating-point status flags, nor depend on the state of its caller's floating-point status
+ flags unless the function is so documented;
+ -- a function call is assumed to require default floating-point control modes, unless its
+ documentation promises otherwise;
+ -- a function call is assumed to have the potential for raising floating-point exceptions,
+ unless its documentation promises otherwise.
+4 The type
+ fenv_t
+ represents the entire floating-point environment.
+5 The type
+ fexcept_t
+ represents the floating-point status flags collectively, including any status the
+ implementation associates with the flags.
+
+
+ 204) This header is designed to support the floating-point exception status flags and directed-rounding
+ control modes required by IEC 60559, and other similar floating-point state information. It is also
+ designed to facilitate code portability among all systems.
+ 205) A floating-point status flag is not an object and can be set more than once within an expression.
+ 206) With these conventions, a programmer can safely assume default floating-point control modes (or be
+ unaware of them). The responsibilities associated with accessing the floating-point environment fall
+ on the programmer or program that does so explicitly.
+
+[page 206]
+
+6 Each of the macros
+ FE_DIVBYZERO
+ FE_INEXACT
+ FE_INVALID
+ FE_OVERFLOW
+ FE_UNDERFLOW
+ is defined if and only if the implementation supports the floating-point exception by
+ means of the functions in 7.6.2.207) Additional implementation-defined floating-point
+ exceptions, with macro definitions beginning with FE_ and an uppercase letter,208) 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.209)
+7 The macro
+ FE_ALL_EXCEPT
+ is simply the bitwise OR of all floating-point exception macros defined by the
+ implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
+8 Each of the macros
+ FE_DOWNWARD
+ FE_TONEAREST
+ FE_TOWARDZERO
+ FE_UPWARD
+ is defined if and only if the implementation supports getting and setting the represented
+ rounding direction by means of the fegetround and fesetround functions.
+ Additional implementation-defined rounding directions, with macro definitions beginning
+ with FE_ and an uppercase letter,210) may also be specified by the implementation. The
+ defined macros expand to integer constant expressions whose values are distinct
+ nonnegative values.211)
+
+
+ 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) See ''future library directions'' (7.31.4).
+ 209) The macros should be distinct powers of two.
+ 210) See ''future library directions'' (7.31.4).
+ 211) Even though the rounding direction macros may expand to constants corresponding to the values of
+ FLT_ROUNDS, they are not required to do so.
+
+[page 207]
+
+9 The macro
+ FE_DFL_ENV
+ represents the default floating-point environment -- the one installed at program startup
+ -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to
+ <fenv.h> functions that manage the floating-point environment.
+10 Additional implementation-defined environments, with macro definitions beginning with
+ FE_ and an uppercase letter,212) and having type ''pointer to const-qualified fenv_t'',
+ may also be specified by the implementation.
+ 7.6.1 The FENV_ACCESS pragma
+ Synopsis
+1 #include <fenv.h>
+ #pragma STDC FENV_ACCESS on-off-switch
+ Description
+2 The FENV_ACCESS pragma provides a means to inform the implementation when a
+ program might access the floating-point environment to test floating-point status flags or
+ run under non-default floating-point control modes.213) 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.)
+
+
+
+ 212) See ''future library directions'' (7.31.4).
+ 213) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
+ tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
+ folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default
+ modes are in effect and the flags are not tested.
+
+[page 208]
+
+3 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);
+ /* ... */
+ }
+4 If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
+ x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
+ contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.214)
+
+ 7.6.2 Floating-point exceptions
+1 The following functions provide access to the floating-point status flags.215) The int
+ input argument for the functions represents a subset of floating-point exceptions, and can
+ be zero or the bitwise OR of one or more floating-point exception macros, for example
+ FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
+ functions is undefined.
+ 7.6.2.1 The feclearexcept function
+ Synopsis
+1 #include <fenv.h>
+ int feclearexcept(int excepts);
+ Description
+2 The feclearexcept function attempts to clear the supported floating-point exceptions
+ represented by its argument.
+ Returns
+3 The feclearexcept function returns zero if the excepts argument is zero or if all
+ the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.
+
+
+ 214) 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.
+ 215) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
+ abstraction of flags that are either set or clear. An implementation may endow floating-point status
+ flags with more information -- for example, the address of the code which first raised the floating-
+ point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
+ content of flags.
+
+[page 209]
+
+ 7.6.2.2 The fegetexceptflag function
+ Synopsis
+1 #include <fenv.h>
+ int fegetexceptflag(fexcept_t *flagp,
+ int excepts);
+ Description
+2 The fegetexceptflag function attempts to store an implementation-defined
+ representation of the states of the floating-point status flags indicated by the argument
+ excepts in the object pointed to by the argument flagp.
+ Returns
+3 The fegetexceptflag function returns zero if the representation was successfully
+ stored. Otherwise, it returns a nonzero value.
+ 7.6.2.3 The feraiseexcept function
+ Synopsis
+1 #include <fenv.h>
+ int feraiseexcept(int excepts);
+ Description
+2 The feraiseexcept function attempts to raise the supported floating-point exceptions
+ represented by its argument.216) The order in which these floating-point exceptions are
+ raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
+ additionally raises the ''inexact'' floating-point exception whenever it raises the
+ ''overflow'' or ''underflow'' floating-point exception is implementation-defined.
+ Returns
+3 The feraiseexcept function returns zero if the excepts argument is zero or if all
+ the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.
+
+
+
+
+ 216) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
+ Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
+ in F.8.6 is in the same spirit.
+
+[page 210]
+
+ 7.6.2.4 The fesetexceptflag function
+ Synopsis
+1 #include <fenv.h>
+ int fesetexceptflag(const fexcept_t *flagp,
+ int excepts);
+ Description
+2 The fesetexceptflag function attempts to set the floating-point status flags
+ indicated by the argument excepts to the states stored in the object pointed to by
+ flagp. The value of *flagp shall have been set by a previous call to
+ fegetexceptflag whose second argument represented at least those floating-point
+ exceptions represented by the argument excepts. This function does not raise floating-
+ point exceptions, but only sets the state of the flags.
+ Returns
+3 The fesetexceptflag function returns zero if the excepts argument is zero or if
+ all the specified flags were successfully set to the appropriate state. Otherwise, it returns
+ a nonzero value.
+ 7.6.2.5 The fetestexcept function
+ Synopsis
+1 #include <fenv.h>
+ int fetestexcept(int excepts);
+ Description
+2 The fetestexcept function determines which of a specified subset of the floating-
+ point exception flags are currently set. The excepts argument specifies the floating-
+ point status flags to be queried.217)
+ Returns
+3 The fetestexcept function returns the value of the bitwise OR of the floating-point
+ exception macros corresponding to the currently set floating-point exceptions included in
+ excepts.
+4 EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set:
+
+
+
+
+ 217) This mechanism allows testing several floating-point exceptions with just one function call.
+
+[page 211]
+
+ #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();
+ /* ... */
+ }
+
+ 7.6.3 Rounding
+1 The fegetround and fesetround functions provide control of rounding direction
+ modes.
+ 7.6.3.1 The fegetround function
+ Synopsis
+1 #include <fenv.h>
+ int fegetround(void);
+ Description
+2 The fegetround function gets the current rounding direction.
+ Returns
+3 The fegetround function returns the value of the rounding direction macro
+ representing the current rounding direction or a negative value if there is no such
+ rounding direction macro or the current rounding direction is not determinable.
+ 7.6.3.2 The fesetround function
+ Synopsis
+1 #include <fenv.h>
+ int fesetround(int round);
+ Description
+2 The fesetround function establishes the rounding direction represented by its
+ argument round. If the argument is not equal to the value of a rounding direction macro,
+ the rounding direction is not changed.
+ Returns
+3 The fesetround function returns zero if and only if the requested rounding direction
+ was established.
+
+[page 212]
+
+4 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
+1 The functions in this section manage the floating-point environment -- status flags and
+ control modes -- as one entity.
+ 7.6.4.1 The fegetenv function
+ Synopsis
+1 #include <fenv.h>
+ int fegetenv(fenv_t *envp);
+ Description
+2 The fegetenv function attempts to store the current floating-point environment in the
+ object pointed to by envp.
+ Returns
+3 The fegetenv function returns zero if the environment was successfully stored.
+ Otherwise, it returns a nonzero value.
+ 7.6.4.2 The feholdexcept function
+ Synopsis
+1 #include <fenv.h>
+ int feholdexcept(fenv_t *envp);
+ Description
+2 The feholdexcept function saves the current floating-point environment in the object
+ pointed to by envp, clears the floating-point status flags, and then installs a non-stop
+ (continue on floating-point exceptions) mode, if available, for all floating-point
+ exceptions.218)
+
+[page 213]
+
+ Returns
+3 The feholdexcept function returns zero if and only if non-stop floating-point
+ exception handling was successfully installed.
+ 7.6.4.3 The fesetenv function
+ Synopsis
+1 #include <fenv.h>
+ int fesetenv(const fenv_t *envp);
+ Description
+2 The fesetenv function attempts to establish the floating-point environment represented
+ by the object pointed to by envp. The argument envp shall point to an object set by a
+ call to fegetenv or feholdexcept, or equal a floating-point environment macro.
+ Note that fesetenv merely installs the state of the floating-point status flags
+ represented through its argument, and does not raise these floating-point exceptions.
+ Returns
+3 The fesetenv function returns zero if the environment was successfully established.
+ Otherwise, it returns a nonzero value.
+ 7.6.4.4 The feupdateenv function
+ Synopsis
+1 #include <fenv.h>
+ int feupdateenv(const fenv_t *envp);
+ Description
+2 The feupdateenv function attempts to save the currently raised floating-point
+ exceptions in its automatic storage, install the floating-point environment represented by
+ the object pointed to by envp, and then raise the saved floating-point exceptions. The
+ argument envp shall point to an object set by a call to feholdexcept or fegetenv,
+ or equal a floating-point environment macro.
+ Returns
+3 The feupdateenv function returns zero if all the actions were successfully carried out.
+ Otherwise, it returns a nonzero value.
+
+
+
+
+ 218) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
+ handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
+ such systems, the feholdexcept function can be used in conjunction with the feupdateenv
+ function to write routines that hide spurious floating-point exceptions from their callers.
+
+[page 214]
+
+4 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;
+ }
+
+[page 215]
+
+ 7.7 Characteristics of floating types <float.h>
+1 The header <float.h> defines several macros that expand to various limits and
+ parameters of the standard floating-point types.
+2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
+ in 5.2.4.2.2.
+
+[page 216]
+
+ 7.8 Format conversion of integer types <inttypes.h>
+1 The header <inttypes.h> includes the header <stdint.h> and extends it with
+ additional facilities provided by hosted implementations.
+2 It declares functions for manipulating greatest-width integers and converting numeric
+ character strings to greatest-width integers, and it declares the type
+ imaxdiv_t
+ which is a structure type that is the type of the value returned by the imaxdiv function.
+ For each type declared in <stdint.h>, it defines corresponding macros for conversion
+ specifiers for use with the formatted input/output functions.219)
+ Forward references: integer types <stdint.h> (7.20), formatted input/output
+ functions (7.21.6), formatted wide character input/output functions (7.29.2).
+ 7.8.1 Macros for format specifiers
+1 Each of the following object-like macros expands to a character string literal containing a
+ conversion specifier, possibly modified by a length modifier, suitable for use within the
+ format argument of a formatted input/output function when converting the corresponding
+ integer type. These macro names have the general form of PRI (character string literals
+ for the fprintf and fwprintf family) or SCN (character string literals for the
+ fscanf and fwscanf family),220) followed by the conversion specifier, followed by a
+ name corresponding to a similar type name in 7.20.1. In these names, N represents the
+ width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
+ format string to print the value of an integer of type int_fast32_t.
+2 The fprintf macros for signed integers are:
+ PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
+ PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
+3 The fprintf macros for unsigned integers are:
+ PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
+ PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
+ PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
+ PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
+4 The fscanf macros for signed integers are:
+
+
+
+ 219) See ''future library directions'' (7.31.5).
+ 220) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
+ different format specifiers may be required for fprintf and fscanf, even when the type is the
+ same.
+
+[page 217]
+
+ SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
+ SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
+5 The fscanf macros for unsigned integers are:
+ SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
+ SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
+ SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
+6 For each type that the implementation provides in <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.
+7 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;
+ }
+
+ 7.8.2 Functions for greatest-width integer types
+ 7.8.2.1 The imaxabs function
+ Synopsis
+1 #include <inttypes.h>
+ intmax_t imaxabs(intmax_t j);
+ Description
+2 The imaxabs function computes the absolute value of an integer j. If the result cannot
+ be represented, the behavior is undefined.221)
+ Returns
+3 The imaxabs function returns the absolute value.
+
+
+
+
+ 221) The absolute value of the most negative number cannot be represented in two's complement.
+
+[page 218]
+
+ 7.8.2.2 The imaxdiv function
+ Synopsis
+1 #include <inttypes.h>
+ imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
+ Description
+2 The imaxdiv function computes numer / denom and numer % denom in a single
+ operation.
+ Returns
+3 The imaxdiv function returns a structure of type imaxdiv_t comprising both the
+ quotient and the remainder. The structure shall contain (in either order) the members
+ quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
+ either part of the result cannot be represented, the behavior is undefined.
+ 7.8.2.3 The strtoimax and strtoumax functions
+ Synopsis
+1 #include <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
+2 The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
+ strtoul, and strtoull functions, except that the initial portion of the string is
+ converted to intmax_t and uintmax_t representation, respectively.
+ Returns
+3 The strtoimax and strtoumax functions return the converted value, if any. If no
+ conversion could be performed, zero is returned. If the correct value is outside the range
+ of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
+ (according to the return type and sign of the value, if any), and the value of the macro
+ ERANGE is stored in errno.
+ Forward references: the strtol, strtoll, strtoul, and strtoull functions
+ (7.22.1.4).
+
+[page 219]
+
+ 7.8.2.4 The wcstoimax and wcstoumax functions
+ Synopsis
+1 #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
+2 The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
+ wcstoul, and wcstoull functions except that the initial portion of the wide string is
+ converted to intmax_t and uintmax_t representation, respectively.
+ Returns
+3 The wcstoimax function returns the converted value, if any. If no conversion could be
+ performed, zero is returned. If the correct value is outside the range of representable
+ values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
+ return type and sign of the value, if any), and the value of the macro ERANGE is stored in
+ errno.
+ Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
+ (7.29.4.1.2).
+
+[page 220]
+
+ 7.9 Alternative spellings <iso646.h>
+1 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 ^=
+
+[page 221]
+
+ 7.10 Sizes of integer types <limits.h>
+1 The header <limits.h> defines several macros that expand to various limits and
+ parameters of the standard integer types.
+2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
+ in 5.2.4.2.1.
+
+[page 222]
+
+ 7.11 Localization <locale.h>
+1 The header <locale.h> declares two functions, one type, and defines several macros.
+2 The type is
+ struct lconv
+ which contains members related to the formatting of numeric values. The structure shall
+ contain at least the following members, in any order. The semantics of the members and
+ their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
+ the values specified in the comments.
+ char *decimal_point; // "."
+ char *thousands_sep; // ""
+ char *grouping; // ""
+ char *mon_decimal_point; // ""
+ char *mon_thousands_sep; // ""
+ char *mon_grouping; // ""
+ char *positive_sign; // ""
+ char *negative_sign; // ""
+ char *currency_symbol; // ""
+ char frac_digits; // CHAR_MAX
+ char p_cs_precedes; // CHAR_MAX
+ char n_cs_precedes; // CHAR_MAX
+ char p_sep_by_space; // CHAR_MAX
+ char n_sep_by_space; // CHAR_MAX
+ char p_sign_posn; // CHAR_MAX
+ char n_sign_posn; // CHAR_MAX
+ char *int_curr_symbol; // ""
+ char int_frac_digits; // CHAR_MAX
+ char int_p_cs_precedes; // CHAR_MAX
+ char int_n_cs_precedes; // CHAR_MAX
+ char int_p_sep_by_space; // CHAR_MAX
+ char int_n_sep_by_space; // CHAR_MAX
+ char int_p_sign_posn; // CHAR_MAX
+ char int_n_sign_posn; // CHAR_MAX
+
+[page 223]
+
+3 The macros defined are NULL (described in 7.19); and
+ LC_ALL
+ LC_COLLATE
+ LC_CTYPE
+ LC_MONETARY
+ LC_NUMERIC
+ LC_TIME
+ which expand to integer constant expressions with distinct values, suitable for use as the
+ first argument to the setlocale function.222) Additional macro definitions, beginning
+ with the characters LC_ and an uppercase letter,223) may also be specified by the
+ implementation.
+ 7.11.1 Locale control
+ 7.11.1.1 The setlocale function
+ Synopsis
+1 #include <locale.h>
+ char *setlocale(int category, const char *locale);
+ Description
+2 The setlocale function selects the appropriate portion of the program's locale as
+ specified by the category and locale arguments. The setlocale function may be
+ used to change or query the program's entire current locale or portions thereof. The value
+ LC_ALL for category names the program's entire locale; the other values for
+ category name only a portion of the program's locale. LC_COLLATE affects the
+ behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
+ the character handling functions224) and the multibyte and wide character functions.
+ LC_MONETARY affects the monetary formatting information returned by the
+ localeconv function. LC_NUMERIC affects the decimal-point character for the
+ formatted input/output functions and the string conversion functions, as well as the
+ nonmonetary formatting information returned by the localeconv function. LC_TIME
+ affects the behavior of the strftime and wcsftime functions.
+3 A value of "C" for locale specifies the minimal environment for C translation; a value
+ of "" for locale specifies the locale-specific native environment. Other
+ implementation-defined strings may be passed as the second argument to setlocale.
+
+ 222) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
+ 223) See ''future library directions'' (7.31.6).
+ 224) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
+ isxdigit.
+
+[page 224]
+
+4 At program startup, the equivalent of
+ setlocale(LC_ALL, "C");
+ is executed.
+5 A call to the setlocale function may introduce a data race with other calls to the
+ setlocale function or with calls to functions that are affected by the current locale.
+ The implementation shall behave as if no library function calls the setlocale function.
+ Returns
+6 If a pointer to a string is given for locale and the selection can be honored, the
+ setlocale function returns a pointer to the string associated with the specified
+ category for the new locale. If the selection cannot be honored, the setlocale
+ function returns a null pointer and the program's locale is not changed.
+7 A null pointer for locale causes the setlocale function to return a pointer to the
+ string associated with the category for the program's current locale; the program's
+ locale is not changed.225)
+8 The pointer to string returned by the setlocale function is such that a subsequent call
+ with that string value and its associated category will restore that part of the program's
+ locale. The string pointed to shall not be modified by the program, but may be
+ overwritten by a subsequent call to the setlocale function.
+ Forward references: formatted input/output functions (7.21.6), multibyte/wide
+ character conversion functions (7.22.7), multibyte/wide string conversion functions
+ (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.24.4.3), the
+ strftime function (7.27.3.5), the strxfrm function (7.24.4.5).
+ 7.11.2 Numeric formatting convention inquiry
+ 7.11.2.1 The localeconv function
+ Synopsis
+1 #include <locale.h>
+ struct lconv *localeconv(void);
+ Description
+2 The localeconv function sets the components of an object with type struct lconv
+ with values appropriate for the formatting of numeric quantities (monetary and otherwise)
+ according to the rules of the current locale.
+
+
+
+ 225) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
+ locale when category has the value LC_ALL.
+
+[page 225]
+
+3 The members of the structure with type char * are pointers to strings, any of which
+ (except decimal_point) can point to "", to indicate that the value is not available in
+ the current locale or is of zero length. Apart from grouping and mon_grouping, the
+ strings shall start and end in the initial shift state. The members with type char are
+ nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
+ available in the current locale. The members include the following:
+ char *decimal_point
+ The decimal-point character used to format nonmonetary quantities.
+ char *thousands_sep
+ The character used to separate groups of digits before the decimal-point
+ character in formatted nonmonetary quantities.
+ char *grouping
+ A string whose elements indicate the size of each group of digits in
+ formatted nonmonetary quantities.
+ char *mon_decimal_point
+ The decimal-point used to format monetary quantities.
+ char *mon_thousands_sep
+ The separator for groups of digits before the decimal-point in formatted
+ monetary quantities.
+ char *mon_grouping
+ A string whose elements indicate the size of each group of digits in
+ formatted monetary quantities.
+ char *positive_sign
+ The string used to indicate a nonnegative-valued formatted monetary
+ quantity.
+ char *negative_sign
+ The string used to indicate a negative-valued formatted monetary quantity.
+ char *currency_symbol
+ The local currency symbol applicable to the current locale.
+ char frac_digits
+ The number of fractional digits (those after the decimal-point) to be
+ displayed in a locally formatted monetary quantity.
+ char p_cs_precedes
+ Set to 1 or 0 if the currency_symbol respectively precedes or
+ succeeds the value for a nonnegative locally formatted monetary quantity.
+
+[page 226]
+
+char n_cs_precedes
+ Set to 1 or 0 if the currency_symbol respectively precedes or
+ succeeds the value for a negative locally formatted monetary quantity.
+char p_sep_by_space
+ Set to a value indicating the separation of the currency_symbol, the
+ sign string, and the value for a nonnegative locally formatted monetary
+ quantity.
+char n_sep_by_space
+ Set to a value indicating the separation of the currency_symbol, the
+ sign string, and the value for a negative locally formatted monetary
+ quantity.
+char p_sign_posn
+ Set to a value indicating the positioning of the positive_sign for a
+ nonnegative locally formatted monetary quantity.
+char n_sign_posn
+ Set to a value indicating the positioning of the negative_sign for a
+ negative locally formatted monetary quantity.
+char *int_curr_symbol
+ The international currency symbol applicable to the current locale. The
+ first three characters contain the alphabetic international currency symbol
+ in accordance with those specified in ISO 4217. The fourth character
+ (immediately preceding the null character) is the character used to separate
+ the international currency symbol from the monetary quantity.
+char int_frac_digits
+ The number of fractional digits (those after the decimal-point) to be
+ displayed in an internationally formatted monetary quantity.
+char int_p_cs_precedes
+ Set to 1 or 0 if the int_curr_symbol respectively precedes or
+ succeeds the value for a nonnegative internationally formatted monetary
+ quantity.
+char int_n_cs_precedes
+ Set to 1 or 0 if the int_curr_symbol respectively precedes or
+ succeeds the value for a negative internationally formatted monetary
+ quantity.
+char int_p_sep_by_space
+ Set to a value indicating the separation of the int_curr_symbol, the
+ sign string, and the value for a nonnegative internationally formatted
+ monetary quantity.
+
+[page 227]
+
+ char int_n_sep_by_space
+ Set to a value indicating the separation of the int_curr_symbol, the
+ sign string, and the value for a negative internationally formatted monetary
+ quantity.
+ char int_p_sign_posn
+ Set to a value indicating the positioning of the positive_sign for a
+ nonnegative internationally formatted monetary quantity.
+ char int_n_sign_posn
+ Set to a value indicating the positioning of the negative_sign for a
+ negative internationally formatted monetary quantity.
+4 The elements of grouping and mon_grouping are interpreted according to the
+ following:
+ CHAR_MAX No further grouping is to be performed.
+ 0 The previous element is to be repeatedly used for the remainder of the
+ digits.
+ other The integer value is the number of digits that compose the current group.
+ The next element is examined to determine the size of the next group of
+ digits before the current group.
+5 The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
+ and int_n_sep_by_space are interpreted according to the following:
+ 0 No space separates the currency symbol and value.
+ 1 If the currency symbol and sign string are adjacent, a space separates them from the
+ value; otherwise, a space separates the currency symbol from the value.
+ 2 If the currency symbol and sign string are adjacent, a space separates them;
+ otherwise, a space separates the sign string from the value.
+ For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
+ int_curr_symbol is used instead of a space.
+6 The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and
+ int_n_sign_posn are interpreted according to the following:
+ 0 Parentheses surround the quantity and currency symbol.
+ 1 The sign string precedes the quantity and currency symbol.
+ 2 The sign string succeeds the quantity and currency symbol.
+ 3 The sign string immediately precedes the currency symbol.
+ 4 The sign string immediately succeeds the currency symbol.
+
+[page 228]
+
+7 The implementation shall behave as if no library function calls the localeconv
+ function.
+ Returns
+8 The localeconv function returns a pointer to the filled-in object. The structure
+ pointed to by the return value shall not be modified by the program, but may be
+ overwritten by a subsequent call to the localeconv function. In addition, calls to the
+ setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
+ overwrite the contents of the structure.
+9 EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
+ monetary quantities.
+ Local format International format
+
+ Country Positive Negative Positive Negative
+
+ Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56
+ Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234
+ Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56
+ Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C
+10 For these four countries, the respective values for the monetary members of the structure returned by
+ localeconv could be:
+ Country1 Country2 Country3 Country4
+
+ mon_decimal_point "," "" "," "."
+ mon_thousands_sep "." "." "." ","
+ mon_grouping "\3" "\3" "\3" "\3"
+ positive_sign "" "" "" ""
+ negative_sign "-" "-" "-" "C"
+ currency_symbol "mk" "L." "\u0192" "SFrs."
+ frac_digits 2 0 2 2
+ p_cs_precedes 0 1 1 1
+ n_cs_precedes 0 1 1 1
+ p_sep_by_space 1 0 1 0
+ n_sep_by_space 1 0 2 0
+ p_sign_posn 1 1 1 1
+ n_sign_posn 1 1 4 2
+ int_curr_symbol "FIM " "ITL " "NLG " "CHF "
+ int_frac_digits 2 0 2 2
+ int_p_cs_precedes 1 1 1 1
+ int_n_cs_precedes 1 1 1 1
+ int_p_sep_by_space 1 1 1 1
+ int_n_sep_by_space 2 1 2 1
+ int_p_sign_posn 1 1 1 1
+ int_n_sign_posn 4 1 4 2
+
+[page 229]
+
+11 EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
+ affect the formatted value.
+ p_sep_by_space
+
+ p_cs_precedes p_sign_posn 0 1 2
+
+ 0 0 (1.25$) (1.25 $) (1.25$)
+ 1 +1.25$ +1.25 $ + 1.25$
+ 2 1.25$+ 1.25 $+ 1.25$ +
+ 3 1.25+$ 1.25 +$ 1.25+ $
+ 4 1.25$+ 1.25 $+ 1.25$ +
+
+ 1 0 ($1.25) ($ 1.25) ($1.25)
+ 1 +$1.25 +$ 1.25 + $1.25
+ 2 $1.25+ $ 1.25+ $1.25 +
+ 3 +$1.25 +$ 1.25 + $1.25
+ 4 $+1.25 $+ 1.25 $ +1.25
+
+[page 230]
+
+ 7.12 Mathematics <math.h>
+1 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.226)
+ Integer arithmetic functions and conversion functions are discussed later.
+2 The types
+ float_t
+ double_t
+ are floating types at least as wide as float and double, respectively, and such that
+ double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
+ float_t and double_t are float and double, respectively; if
+ FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
+ 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
+ otherwise implementation-defined.227)
+3 The macro
+ HUGE_VAL
+ expands to a positive double constant expression, not necessarily representable as a
+ float. The macros
+ HUGE_VALF
+ HUGE_VALL
+ are respectively float and long double analogs of HUGE_VAL.228)
+4 The macro
+ INFINITY
+ expands to a constant expression of type float representing positive or unsigned
+ infinity, if available; else to a positive constant of type float that overflows at
+
+
+
+ 226) 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.
+ 227) 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.
+ 228) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
+ supports infinities.
+
+[page 231]
+
+ translation time.229)
+5 The macro
+ NAN
+ is defined if and only if the implementation supports quiet NaNs for the float type. It
+ expands to a constant expression of type float representing a quiet NaN.
+6 The number classification macros
+ FP_INFINITE
+ FP_NAN
+ FP_NORMAL
+ FP_SUBNORMAL
+ FP_ZERO
+ represent the mutually exclusive kinds of floating-point values. They expand to integer
+ constant expressions with distinct values. Additional implementation-defined floating-
+ point classifications, with macro definitions beginning with FP_ and an uppercase letter,
+ may also be specified by the implementation.
+7 The macro
+ FP_FAST_FMA
+ is optionally defined. If defined, it indicates that the fma function generally executes
+ about as fast as, or faster than, a multiply and an add of double operands.230) The
+ macros
+ FP_FAST_FMAF
+ FP_FAST_FMAL
+ are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
+ these macros expand to the integer constant 1.
+8 The macros
+ FP_ILOGB0
+ FP_ILOGBNAN
+ expand to integer constant expressions whose values are returned by ilogb(x) if x is
+ zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
+ -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
+
+
+ 229) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
+ 230) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
+ directly with a hardware multiply-add instruction. Software implementations are expected to be
+ substantially slower.
+
+[page 232]
+
+9 The macros
+ MATH_ERRNO
+ MATH_ERREXCEPT
+ expand to the integer constants 1 and 2, respectively; the macro
+ math_errhandling
+ expands to an expression that has type int and the value MATH_ERRNO,
+ MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
+ constant for the duration of the program. It is unspecified whether
+ math_errhandling is a macro or an identifier with external linkage. If a macro
+ definition is suppressed or a program defines an identifier with the name
+ math_errhandling, the behavior is undefined. If the expression
+ math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
+ shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
+ <fenv.h>.
+ 7.12.1 Treatment of error conditions
+1 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.
+2 For all functions, a domain error occurs if an input argument is outside the domain over
+ which the mathematical function is defined. The description of each function lists any
+ required domain errors; an implementation may define additional domain errors, provided
+ that such errors are consistent with the mathematical definition of the function.231) On a
+ domain error, the function returns an implementation-defined value; if the integer
+ expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
+ errno acquires the value EDOM; if the integer expression math_errhandling &
+ MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised.
+3 Similarly, a pole error (also known as a singularity or infinitary) occurs if the
+ mathematical function has an exact infinite result as the finite input argument(s) are
+ approached in the limit (for example, log(0.0)). The description of each function lists
+ any required pole errors; an implementation may define additional pole errors, provided
+ that such errors are consistent with the mathematical definition of the function. On a pole
+ error, the function returns an implementation-defined value; if the integer expression
+
+
+ 231) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
+ error if the mathematical domain of the function does not include the infinity.
+
+[page 233]
+
+ math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
+ acquires the value ERANGE; if the integer expression math_errhandling &
+ MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised.
+4 Likewise, a range error occurs if the mathematical result of the function cannot be
+ represented in an object of the specified type, due to extreme magnitude.
+5 A floating result overflows if the magnitude of the mathematical result is finite but so
+ large that the mathematical result cannot be represented without extraordinary roundoff
+ error in an object of the specified type. If a floating result overflows and default rounding
+ is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or
+ HUGE_VALL according to the return type, with the same sign as the correct value of the
+ function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
+ the integer expression errno acquires the value ERANGE; if the integer expression
+ math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating-
+ point exception is raised.
+6 The result underflows if the magnitude of the mathematical result is so small that the
+ mathematical result cannot be represented, without extraordinary roundoff error, in an
+ object of the specified type.232) If the result underflows, the function returns an
+ implementation-defined value whose magnitude is no greater than the smallest
+ normalized positive number in the specified type; if the integer expression
+ math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
+ value ERANGE is implementation-defined; if the integer expression
+ math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow''
+ floating-point exception is raised is implementation-defined.
+7 If a domain, pole, or range error occurs and the integer expression
+ math_errhandling & MATH_ERRNO is zero,233) 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.
+
+
+
+
+ 232) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and
+ also ''flush-to-zero'' underflow.
+ 233) Math errors are being indicated by the floating-point exception flags rather than by errno.
+
+[page 234]
+
+ 7.12.2 The FP_CONTRACT pragma
+ Synopsis
+1 #include <math.h>
+ #pragma STDC FP_CONTRACT on-off-switch
+ Description
+2 The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the
+ state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur
+ either outside external declarations or preceding all explicit declarations and statements
+ inside a compound statement. When outside external declarations, the pragma takes
+ effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
+ the end of the translation unit. When inside a compound statement, the pragma takes
+ effect from its occurrence until another FP_CONTRACT pragma is encountered
+ (including within a nested compound statement), or until the end of the compound
+ statement; at the end of a compound statement the state for the pragma is restored to its
+ condition just before the compound statement. If this pragma is used in any other
+ context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is
+ implementation-defined.
+ 7.12.3 Classification macros
+1 In the synopses in this subclause, real-floating indicates that the argument shall be an
+ expression of real floating type.
+ 7.12.3.1 The fpclassify macro
+ Synopsis
+1 #include <math.h>
+ int fpclassify(real-floating x);
+ Description
+2 The fpclassify macro classifies its argument value as NaN, infinite, normal,
+ subnormal, zero, or into another implementation-defined category. First, an argument
+ represented in a format wider than its semantic type is converted to its semantic type.
+ Then classification is based on the type of the argument.234)
+ Returns
+3 The fpclassify macro returns the value of the number classification macro
+ appropriate to the value of its argument.
+
+
+ 234) Since an expression can be evaluated with more range and precision than its type has, it is important to
+ know the type that classification is based on. For example, a normal long double value might
+ become subnormal when converted to double, and zero when converted to float.
+
+[page 235]
+
+ 7.12.3.2 The isfinite macro
+ Synopsis
+1 #include <math.h>
+ int isfinite(real-floating x);
+ Description
+2 The isfinite macro determines whether its argument has a finite value (zero,
+ subnormal, or normal, and not infinite or NaN). First, an argument represented in a
+ format wider than its semantic type is converted to its semantic type. Then determination
+ is based on the type of the argument.
+ Returns
+3 The isfinite macro returns a nonzero value if and only if its argument has a finite
+ value.
+ 7.12.3.3 The isinf macro
+ Synopsis
+1 #include <math.h>
+ int isinf(real-floating x);
+ Description
+2 The isinf macro determines whether its argument value is an infinity (positive or
+ negative). First, an argument represented in a format wider than its semantic type is
+ converted to its semantic type. Then determination is based on the type of the argument.
+ Returns
+3 The isinf macro returns a nonzero value if and only if its argument has an infinite
+ value.
+ 7.12.3.4 The isnan macro
+ Synopsis
+1 #include <math.h>
+ int isnan(real-floating x);
+ Description
+2 The isnan macro determines whether its argument value is a NaN. First, an argument
+ represented in a format wider than its semantic type is converted to its semantic type.
+ Then determination is based on the type of the argument.235)
+
+
+ 235) For the isnan macro, the type for determination does not matter unless the implementation supports
+ NaNs in the evaluation type but not in the semantic type.
+
+[page 236]
+
+ Returns
+3 The isnan macro returns a nonzero value if and only if its argument has a NaN value.
+ 7.12.3.5 The isnormal macro
+ Synopsis
+1 #include <math.h>
+ int isnormal(real-floating x);
+ Description
+2 The isnormal macro determines whether its argument value is normal (neither zero,
+ subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
+ semantic type is converted to its semantic type. Then determination is based on the type
+ of the argument.
+ Returns
+3 The isnormal macro returns a nonzero value if and only if its argument has a normal
+ value.
+ 7.12.3.6 The signbit macro
+ Synopsis
+1 #include <math.h>
+ int signbit(real-floating x);
+ Description
+2 The signbit macro determines whether the sign of its argument value is negative.236)
+ Returns
+3 The signbit macro returns a nonzero value if and only if the sign of its argument value
+ is negative.
+
+
+
+
+ 236) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
+ unsigned, it is treated as positive.
+
+[page 237]
+
+ 7.12.4 Trigonometric functions
+ 7.12.4.1 The acos functions
+ Synopsis
+1 #include <math.h>
+ double acos(double x);
+ float acosf(float x);
+ long double acosl(long double x);
+ Description
+2 The acos functions compute the principal value of the arc cosine of x. A domain error
+ occurs for arguments not in the interval [-1, +1].
+ Returns
+3 The acos functions return arccos x in the interval [0, pi ] radians.
+ 7.12.4.2 The asin functions
+ Synopsis
+1 #include <math.h>
+ double asin(double x);
+ float asinf(float x);
+ long double asinl(long double x);
+ Description
+2 The asin functions compute the principal value of the arc sine of x. A domain error
+ occurs for arguments not in the interval [-1, +1].
+ Returns
+3 The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians.
+ 7.12.4.3 The atan functions
+ Synopsis
+1 #include <math.h>
+ double atan(double x);
+ float atanf(float x);
+ long double atanl(long double x);
+ Description
+2 The atan functions compute the principal value of the arc tangent of x.
+
+[page 238]
+
+ Returns
+3 The atan functions return arctan x in the interval [-pi /2, +pi /2] radians.
+ 7.12.4.4 The atan2 functions
+ Synopsis
+1 #include <math.h>
+ double atan2(double y, double x);
+ float atan2f(float y, float x);
+ long double atan2l(long double y, long double x);
+ Description
+2 The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
+ arguments to determine the quadrant of the return value. A domain error may occur if
+ both arguments are zero.
+ Returns
+3 The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians.
+ 7.12.4.5 The cos functions
+ Synopsis
+1 #include <math.h>
+ double cos(double x);
+ float cosf(float x);
+ long double cosl(long double x);
+ Description
+2 The cos functions compute the cosine of x (measured in radians).
+ Returns
+3 The cos functions return cos x.
+ 7.12.4.6 The sin functions
+ Synopsis
+1 #include <math.h>
+ double sin(double x);
+ float sinf(float x);
+ long double sinl(long double x);
+ Description
+2 The sin functions compute the sine of x (measured in radians).
+
+[page 239]
+
+ Returns
+3 The sin functions return sin x.
+ 7.12.4.7 The tan functions
+ Synopsis
+1 #include <math.h>
+ double tan(double x);
+ float tanf(float x);
+ long double tanl(long double x);
+ Description
+2 The tan functions return the tangent of x (measured in radians).
+ Returns
+3 The tan functions return tan x.
+ 7.12.5 Hyperbolic functions
+ 7.12.5.1 The acosh functions
+ Synopsis
+1 #include <math.h>
+ double acosh(double x);
+ float acoshf(float x);
+ long double acoshl(long double x);
+ Description
+2 The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
+ error occurs for arguments less than 1.
+ Returns
+3 The acosh functions return arcosh x in the interval [0, +(inf)].
+ 7.12.5.2 The asinh functions
+ Synopsis
+1 #include <math.h>
+ double asinh(double x);
+ float asinhf(float x);
+ long double asinhl(long double x);
+ Description
+2 The asinh functions compute the arc hyperbolic sine of x.
+
+[page 240]
+
+ Returns
+3 The asinh functions return arsinh x.
+ 7.12.5.3 The atanh functions
+ Synopsis
+1 #include <math.h>
+ double atanh(double x);
+ float atanhf(float x);
+ long double atanhl(long double x);
+ Description
+2 The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
+ for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
+ -1 or +1.
+ Returns
+3 The atanh functions return artanh x.
+ 7.12.5.4 The cosh functions
+ Synopsis
+1 #include <math.h>
+ double cosh(double x);
+ float coshf(float x);
+ long double coshl(long double x);
+ Description
+2 The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
+ magnitude of x is too large.
+ Returns
+3 The cosh functions return cosh x.
+ 7.12.5.5 The sinh functions
+ Synopsis
+1 #include <math.h>
+ double sinh(double x);
+ float sinhf(float x);
+ long double sinhl(long double x);
+ Description
+2 The sinh functions compute the hyperbolic sine of x. A range error occurs if the
+ magnitude of x is too large.
+
+[page 241]
+
+ Returns
+3 The sinh functions return sinh x.
+ 7.12.5.6 The tanh functions
+ Synopsis
+1 #include <math.h>
+ double tanh(double x);
+ float tanhf(float x);
+ long double tanhl(long double x);
+ Description
+2 The tanh functions compute the hyperbolic tangent of x.
+ Returns
+3 The tanh functions return tanh x.
+ 7.12.6 Exponential and logarithmic functions
+ 7.12.6.1 The exp functions
+ Synopsis
+1 #include <math.h>
+ double exp(double x);
+ float expf(float x);
+ long double expl(long double x);
+ Description
+2 The exp functions compute the base-e exponential of x. A range error occurs if the
+ magnitude of x is too large.
+ Returns
+3 The exp functions return ex .
+ 7.12.6.2 The exp2 functions
+ Synopsis
+1 #include <math.h>
+ double exp2(double x);
+ float exp2f(float x);
+ long double exp2l(long double x);
+ Description
+2 The exp2 functions compute the base-2 exponential of x. A range error occurs if the
+ magnitude of x is too large.
+
+[page 242]
+
+ Returns
+3 The exp2 functions return 2x .
+ 7.12.6.3 The expm1 functions
+ Synopsis
+1 #include <math.h>
+ double expm1(double x);
+ float expm1f(float x);
+ long double expm1l(long double x);
+ Description
+2 The expm1 functions compute the base-e exponential of the argument, minus 1. A range
+ error occurs if x is too large.237)
+ Returns
+3 The expm1 functions return ex - 1.
+ 7.12.6.4 The frexp functions
+ Synopsis
+1 #include <math.h>
+ double frexp(double value, int *exp);
+ float frexpf(float value, int *exp);
+ long double frexpl(long double value, int *exp);
+ Description
+2 The frexp functions break a floating-point number into a normalized fraction and an
+ integral power of 2. They store the integer in the int object pointed to by exp.
+ Returns
+3 If value is not a floating-point number or if the integral power of 2 is outside the range
+ of int, the results are unspecified. Otherwise, the frexp functions return the value x,
+ such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp .
+ If value is zero, both parts of the result are zero.
+
+
+
+
+ 237) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.
+
+[page 243]
+
+ 7.12.6.5 The ilogb functions
+ Synopsis
+1 #include <math.h>
+ int ilogb(double x);
+ int ilogbf(float x);
+ int ilogbl(long double x);
+ Description
+2 The ilogb functions extract the exponent of x as a signed int value. If x is zero they
+ compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
+ a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
+ the corresponding logb function and casting the returned value to type int. A domain
+ error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
+ the range of the return type, the numeric result is unspecified.
+ Returns
+3 The ilogb functions return the exponent of x as a signed int value.
+ Forward references: the logb functions (7.12.6.11).
+ 7.12.6.6 The ldexp functions
+ Synopsis
+1 #include <math.h>
+ double ldexp(double x, int exp);
+ float ldexpf(float x, int exp);
+ long double ldexpl(long double x, int exp);
+ Description
+2 The ldexp functions multiply a floating-point number by an integral power of 2. A
+ range error may occur.
+ Returns
+3 The ldexp functions return x x 2exp .
+ 7.12.6.7 The log functions
+ Synopsis
+1 #include <math.h>
+ double log(double x);
+ float logf(float x);
+ long double logl(long double x);
+
+[page 244]
+
+ Description
+2 The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
+ the argument is negative. A pole error may occur if the argument is zero.
+ Returns
+3 The log functions return loge x.
+ 7.12.6.8 The log10 functions
+ Synopsis
+1 #include <math.h>
+ double log10(double x);
+ float log10f(float x);
+ long double log10l(long double x);
+ Description
+2 The log10 functions compute the base-10 (common) logarithm of x. A domain error
+ occurs if the argument is negative. A pole error may occur if the argument is zero.
+ Returns
+3 The log10 functions return log10 x.
+ 7.12.6.9 The log1p functions
+ Synopsis
+1 #include <math.h>
+ double log1p(double x);
+ float log1pf(float x);
+ long double log1pl(long double x);
+ Description
+2 The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.238)
+ A domain error occurs if the argument is less than -1. A pole error may occur if the
+ argument equals -1.
+ Returns
+3 The log1p functions return loge (1 + x).
+
+
+
+
+ 238) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).
+
+[page 245]
+
+ 7.12.6.10 The log2 functions
+ Synopsis
+1 #include <math.h>
+ double log2(double x);
+ float log2f(float x);
+ long double log2l(long double x);
+ Description
+2 The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
+ argument is less than zero. A pole error may occur if the argument is zero.
+ Returns
+3 The log2 functions return log2 x.
+ 7.12.6.11 The logb functions
+ Synopsis
+1 #include <math.h>
+ double logb(double x);
+ float logbf(float x);
+ long double logbl(long double x);
+ Description
+2 The logb functions extract the exponent of x, as a signed integer value in floating-point
+ format. If x is subnormal it is treated as though it were normalized; thus, for positive
+ finite x,
+ 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
+ A domain error or pole error may occur if the argument is zero.
+ Returns
+3 The logb functions return the signed exponent of x.
+ 7.12.6.12 The modf functions
+ Synopsis
+1 #include <math.h>
+ double modf(double value, double *iptr);
+ float modff(float value, float *iptr);
+ long double modfl(long double value, long double *iptr);
+ Description
+2 The modf functions break the argument value into integral and fractional parts, each of
+ which has the same type and sign as the argument. They store the integral part (in
+
+[page 246]
+
+ floating-point format) in the object pointed to by iptr.
+ Returns
+3 The modf functions return the signed fractional part of value.
+ 7.12.6.13 The scalbn and scalbln functions
+ Synopsis
+1 #include <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
+2 The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not
+ normally by computing FLT_RADIXn explicitly. A range error may occur.
+ Returns
+3 The scalbn and scalbln functions return x x FLT_RADIXn .
+ 7.12.7 Power and absolute-value functions
+ 7.12.7.1 The cbrt functions
+ Synopsis
+1 #include <math.h>
+ double cbrt(double x);
+ float cbrtf(float x);
+ long double cbrtl(long double x);
+ Description
+2 The cbrt functions compute the real cube root of x.
+ Returns
+3 The cbrt functions return x1/3 .
+
+[page 247]
+
+ 7.12.7.2 The fabs functions
+ Synopsis
+1 #include <math.h>
+ double fabs(double x);
+ float fabsf(float x);
+ long double fabsl(long double x);
+ Description
+2 The fabs functions compute the absolute value of a floating-point number x.
+ Returns
+3 The fabs functions return | x |.
+ 7.12.7.3 The hypot functions
+ Synopsis
+1 #include <math.h>
+ double hypot(double x, double y);
+ float hypotf(float x, float y);
+ long double hypotl(long double x, long double y);
+ Description
+2 The hypot functions compute the square root of the sum of the squares of x and y,
+ without undue overflow or underflow. A range error may occur.
+3 Returns
+4 The hypot functions return (sqrt)x2 + y2 .
+ -
+ -----
+ 7.12.7.4 The pow functions
+ Synopsis
+1 #include <math.h>
+ double pow(double x, double y);
+ float powf(float x, float y);
+ long double powl(long double x, long double y);
+ Description
+2 The pow functions compute x raised to the power y. A domain error occurs if x is finite
+ and negative and y is finite and not an integer value. A range error may occur. A domain
+ error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
+ zero and y is less than zero.
+
+[page 248]
+
+ Returns
+3 The pow functions return xy .
+ 7.12.7.5 The sqrt functions
+ Synopsis
+1 #include <math.h>
+ double sqrt(double x);
+ float sqrtf(float x);
+ long double sqrtl(long double x);
+ Description
+2 The sqrt functions compute the nonnegative square root of x. A domain error occurs if
+ the argument is less than zero.
+ Returns
+3 The sqrt functions return (sqrt)x.
+ -
+ -
+ 7.12.8 Error and gamma functions
+ 7.12.8.1 The erf functions
+ Synopsis
+1 #include <math.h>
+ double erf(double x);
+ float erff(float x);
+ long double erfl(long double x);
+ Description
+2 The erf functions compute the error function of x.
+ Returns
+3 2 x
+ (integral) e-t dt.
+ 2
+ The erf functions return erf x =
+ (sqrt)pi
+ -
+ - 0
+
+ 7.12.8.2 The erfc functions
+ Synopsis
+1 #include <math.h>
+ double erfc(double x);
+ float erfcf(float x);
+ long double erfcl(long double x);
+ Description
+2 The erfc functions compute the complementary error function of x. A range error
+ occurs if x is too large.
+
+[page 249]
+
+ Returns
+3 2 (inf)
+ (integral) e-t dt.
+ 2
+ The erfc functions return erfc x = 1 - erf x =
+ (sqrt)pi
+ -
+ - x
+
+ 7.12.8.3 The lgamma functions
+ Synopsis
+1 #include <math.h>
+ double lgamma(double x);
+ float lgammaf(float x);
+ long double lgammal(long double x);
+ Description
+2 The lgamma functions compute the natural logarithm of the absolute value of gamma of
+ x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
+ or zero.
+ Returns
+3 The lgamma functions return loge | (Gamma)(x) |.
+ 7.12.8.4 The tgamma functions
+ Synopsis
+1 #include <math.h>
+ double tgamma(double x);
+ float tgammaf(float x);
+ long double tgammal(long double x);
+ Description
+2 The tgamma functions compute the gamma function of x. A domain error or pole error
+ may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
+ too large and may occur if the magnitude of x is too small.
+ Returns
+3 The tgamma functions return (Gamma)(x).
+
+[page 250]
+
+ 7.12.9 Nearest integer functions
+ 7.12.9.1 The ceil functions
+ Synopsis
+1 #include <math.h>
+ double ceil(double x);
+ float ceilf(float x);
+ long double ceill(long double x);
+ Description
+2 The ceil functions compute the smallest integer value not less than x.
+ Returns
+3 The ceil functions return [^x^], expressed as a floating-point number.
+ 7.12.9.2 The floor functions
+ Synopsis
+1 #include <math.h>
+ double floor(double x);
+ float floorf(float x);
+ long double floorl(long double x);
+ Description
+2 The floor functions compute the largest integer value not greater than x.
+ Returns
+3 The floor functions return [_x_], expressed as a floating-point number.
+ 7.12.9.3 The nearbyint functions
+ Synopsis
+1 #include <math.h>
+ double nearbyint(double x);
+ float nearbyintf(float x);
+ long double nearbyintl(long double x);
+ Description
+2 The nearbyint functions round their argument to an integer value in floating-point
+ format, using the current rounding direction and without raising the ''inexact'' floating-
+ point exception.
+
+[page 251]
+
+ Returns
+3 The nearbyint functions return the rounded integer value.
+ 7.12.9.4 The rint functions
+ Synopsis
+1 #include <math.h>
+ double rint(double x);
+ float rintf(float x);
+ long double rintl(long double x);
+ Description
+2 The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
+ rint functions may raise the ''inexact'' floating-point exception if the result differs in
+ value from the argument.
+ Returns
+3 The rint functions return the rounded integer value.
+ 7.12.9.5 The lrint and llrint functions
+ Synopsis
+1 #include <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
+2 The lrint and llrint functions round their argument to the nearest integer value,
+ rounding according to the current rounding direction. If the rounded value is outside the
+ range of the return type, the numeric result is unspecified and a domain error or range
+ error may occur.
+ Returns
+3 The lrint and llrint functions return the rounded integer value.
+
+[page 252]
+
+ 7.12.9.6 The round functions
+ Synopsis
+1 #include <math.h>
+ double round(double x);
+ float roundf(float x);
+ long double roundl(long double x);
+ Description
+2 The round functions round their argument to the nearest integer value in floating-point
+ format, rounding halfway cases away from zero, regardless of the current rounding
+ direction.
+ Returns
+3 The round functions return the rounded integer value.
+ 7.12.9.7 The lround and llround functions
+ Synopsis
+1 #include <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
+2 The lround and llround functions round their argument to the nearest integer value,
+ rounding halfway cases away from zero, regardless of the current rounding direction. If
+ the rounded value is outside the range of the return type, the numeric result is unspecified
+ and a domain error or range error may occur.
+ Returns
+3 The lround and llround functions return the rounded integer value.
+ 7.12.9.8 The trunc functions
+ Synopsis
+1 #include <math.h>
+ double trunc(double x);
+ float truncf(float x);
+ long double truncl(long double x);
+
+[page 253]
+
+ Description
+2 The trunc functions round their argument to the integer value, in floating format,
+ nearest to but no larger in magnitude than the argument.
+ Returns
+3 The trunc functions return the truncated integer value.
+ 7.12.10 Remainder functions
+ 7.12.10.1 The fmod functions
+ Synopsis
+1 #include <math.h>
+ double fmod(double x, double y);
+ float fmodf(float x, float y);
+ long double fmodl(long double x, long double y);
+ Description
+2 The fmod functions compute the floating-point remainder of x/y.
+ Returns
+3 The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
+ the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
+ whether a domain error occurs or the fmod functions return zero is implementation-
+ defined.
+ 7.12.10.2 The remainder functions
+ Synopsis
+1 #include <math.h>
+ double remainder(double x, double y);
+ float remainderf(float x, float y);
+ long double remainderl(long double x, long double y);
+ Description
+2 The remainder functions compute the remainder x REM y required by IEC 60559.239)
+
+
+
+
+ 239) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the
+ mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever
+ | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for
+ all implementations.
+
+[page 254]
+
+ Returns
+3 The remainder functions return x REM y. If y is zero, whether a domain error occurs
+ or the functions return zero is implementation defined.
+ 7.12.10.3 The remquo functions
+ Synopsis
+1 #include <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
+2 The remquo functions compute the same remainder as the remainder functions. In
+ the object pointed to by quo they store a value whose sign is the sign of x/y and whose
+ magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
+ n is an implementation-defined integer greater than or equal to 3.
+ Returns
+3 The remquo functions return x REM y. If y is zero, the value stored in the object
+ pointed to by quo is unspecified and whether a domain error occurs or the functions
+ return zero is implementation defined.
+ 7.12.11 Manipulation functions
+ 7.12.11.1 The copysign functions
+ Synopsis
+1 #include <math.h>
+ double copysign(double x, double y);
+ float copysignf(float x, float y);
+ long double copysignl(long double x, long double y);
+ Description
+2 The copysign functions produce a value with the magnitude of x and the sign of y.
+ They produce a NaN (with the sign of y) if x is a NaN. On implementations that
+ represent a signed zero but do not treat negative zero consistently in arithmetic
+ operations, the copysign functions regard the sign of zero as positive.
+ Returns
+3 The copysign functions return a value with the magnitude of x and the sign of y.
+
+[page 255]
+
+ 7.12.11.2 The nan functions
+ Synopsis
+1 #include <math.h>
+ double nan(const char *tagp);
+ float nanf(const char *tagp);
+ long double nanl(const char *tagp);
+ Description
+2 The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
+ sequence)", (char**) NULL); the call nan("") is equivalent to
+ strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
+ sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
+ NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
+ and strtold.
+ Returns
+3 The nan functions return a quiet NaN, if available, with content indicated through tagp.
+ If the implementation does not support quiet NaNs, the functions return zero.
+ Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
+ 7.12.11.3 The nextafter functions
+ Synopsis
+1 #include <math.h>
+ double nextafter(double x, double y);
+ float nextafterf(float x, float y);
+ long double nextafterl(long double x, long double y);
+ Description
+2 The nextafter functions determine the next representable value, in the type of the
+ function, after x in the direction of y, where x and y are first converted to the type of the
+ function.240) The nextafter functions return y if x equals y. A range error may occur
+ if the magnitude of x is the largest finite value representable in the type and the result is
+ infinite or not representable in the type.
+ Returns
+3 The nextafter functions return the next representable value in the specified format
+ after x in the direction of y.
+
+
+ 240) The argument values are converted to the type of the function, even by a macro implementation of the
+ function.
+
+[page 256]
+
+ 7.12.11.4 The nexttoward functions
+ Synopsis
+1 #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
+2 The nexttoward functions are equivalent to the nextafter functions except that the
+ second parameter has type long double and the functions return y converted to the
+ type of the function if x equals y.241)
+ 7.12.12 Maximum, minimum, and positive difference functions
+ 7.12.12.1 The fdim functions
+ Synopsis
+1 #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
+2 The fdim functions determine the positive difference between their arguments:
+ {x - y if x > y
+ {
+ {+0 if x <= y
+ A range error may occur.
+ Returns
+3 The fdim functions return the positive difference value.
+ 7.12.12.2 The fmax functions
+ Synopsis
+1 #include <math.h>
+ double fmax(double x, double y);
+ float fmaxf(float x, float y);
+ long double fmaxl(long double x, long double y);
+
+
+
+ 241) The result of the nexttoward functions is determined in the type of the function, without loss of
+ range or precision in a floating second argument.
+
+[page 257]
+
+ Description
+2 The fmax functions determine the maximum numeric value of their arguments.242)
+ Returns
+3 The fmax functions return the maximum numeric value of their arguments.
+ 7.12.12.3 The fmin functions
+ Synopsis
+1 #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
+2 The fmin functions determine the minimum numeric value of their arguments.243)
+ Returns
+3 The fmin functions return the minimum numeric value of their arguments.
+ 7.12.13 Floating multiply-add
+ 7.12.13.1 The fma functions
+ Synopsis
+1 #include <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
+2 The fma functions compute (x x y) + z, rounded as one ternary operation: they compute
+ the value (as if) to infinite precision and round once to the result format, according to the
+ current rounding mode. A range error may occur.
+ Returns
+3 The fma functions return (x x y) + z, rounded as one ternary operation.
+
+
+
+
+ 242) 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.
+ 243) The fmin functions are analogous to the fmax functions in their treatment of NaNs.
+
+[page 258]
+
+ 7.12.14 Comparison macros
+1 The relational and equality operators support the usual mathematical relationships
+ between numeric values. For any ordered pair of numeric values exactly one of the
+ relationships -- less, greater, and equal -- is true. Relational operators may raise the
+ ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a
+ numeric value, or for two NaNs, just the unordered relationship is true.244) 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 type245) (both arguments need not have the same type).246)
+ 7.12.14.1 The isgreater macro
+ Synopsis
+1 #include <math.h>
+ int isgreater(real-floating x, real-floating y);
+ Description
+2 The isgreater macro determines whether its first argument is greater than its second
+ argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
+ unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point
+ exception when x and y are unordered.
+ Returns
+3 The isgreater macro returns the value of (x) > (y).
+ 7.12.14.2 The isgreaterequal macro
+ Synopsis
+1 #include <math.h>
+ int isgreaterequal(real-floating x, real-floating y);
+
+
+
+
+ 244) 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.
+ 245) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
+ undefined.
+ 246) Whether an argument represented in a format wider than its semantic type is converted to the semantic
+ type is unspecified.
+
+[page 259]
+
+ Description
+2 The isgreaterequal macro determines whether its first argument is greater than or
+ equal to its second argument. The value of isgreaterequal(x, y) is always equal
+ to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
+ not raise the ''invalid'' floating-point exception when x and y are unordered.
+ Returns
+3 The isgreaterequal macro returns the value of (x) >= (y).
+ 7.12.14.3 The isless macro
+ Synopsis
+1 #include <math.h>
+ int isless(real-floating x, real-floating y);
+ Description
+2 The isless macro determines whether its first argument is less than its second
+ argument. The value of isless(x, y) is always equal to (x) < (y); however,
+ unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point
+ exception when x and y are unordered.
+ Returns
+3 The isless macro returns the value of (x) < (y).
+ 7.12.14.4 The islessequal macro
+ Synopsis
+1 #include <math.h>
+ int islessequal(real-floating x, real-floating y);
+ Description
+2 The islessequal macro determines whether its first argument is less than or equal to
+ its second argument. The value of islessequal(x, y) is always equal to
+ (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
+ the ''invalid'' floating-point exception when x and y are unordered.
+ Returns
+3 The islessequal macro returns the value of (x) <= (y).
+
+[page 260]
+
+ 7.12.14.5 The islessgreater macro
+ Synopsis
+1 #include <math.h>
+ int islessgreater(real-floating x, real-floating y);
+ Description
+2 The islessgreater macro determines whether its first argument is less than or
+ greater than its second argument. The islessgreater(x, y) macro is similar to
+ (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
+ the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
+ and y twice).
+ Returns
+3 The islessgreater macro returns the value of (x) < (y) || (x) > (y).
+ 7.12.14.6 The isunordered macro
+ Synopsis
+1 #include <math.h>
+ int isunordered(real-floating x, real-floating y);
+ Description
+2 The isunordered macro determines whether its arguments are unordered.
+ Returns
+3 The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.
+
+[page 261]
+
+ 7.13 Nonlocal jumps <setjmp.h>
+1 The header <setjmp.h> defines the macro setjmp, and declares one function and
+ one type, for bypassing the normal function call and return discipline.247)
+2 The type declared is
+ jmp_buf
+ which is an array type suitable for holding the information needed to restore a calling
+ environment. The environment of a call to the setjmp macro consists of information
+ sufficient for a call to the longjmp function to return execution to the correct block and
+ invocation of that block, were it called recursively. It does not include the state of the
+ floating-point status flags, of open files, or of any other component of the abstract
+ machine.
+3 It is unspecified whether setjmp is a macro or an identifier declared with external
+ linkage. If a macro definition is suppressed in order to access an actual function, or a
+ program defines an external identifier with the name setjmp, the behavior is undefined.
+ 7.13.1 Save calling environment
+ 7.13.1.1 The setjmp macro
+ Synopsis
+1 #include <setjmp.h>
+ int setjmp(jmp_buf env);
+ Description
+2 The setjmp macro saves its calling environment in its jmp_buf argument for later use
+ by the longjmp function.
+ Returns
+3 If the return is from a direct invocation, the setjmp macro returns the value zero. If the
+ return is from a call to the longjmp function, the setjmp macro returns a nonzero
+ value.
+ Environmental limits
+4 An invocation of the setjmp macro shall appear only in one of the following contexts:
+ -- the entire controlling expression of a selection or iteration statement;
+ -- one operand of a relational or equality operator with the other operand an integer
+ constant expression, with the resulting expression being the entire controlling
+
+
+ 247) These functions are useful for dealing with unusual conditions encountered in a low-level function of
+ a program.
+
+[page 262]
+
+ expression of a selection or iteration statement;
+ -- the operand of a unary ! operator with the resulting expression being the entire
+ controlling expression of a selection or iteration statement; or
+ -- the entire expression of an expression statement (possibly cast to void).
+5 If the invocation appears in any other context, the behavior is undefined.
+ 7.13.2 Restore calling environment
+ 7.13.2.1 The longjmp function
+ Synopsis
+1 #include <setjmp.h>
+ _Noreturn void longjmp(jmp_buf env, int val);
+ Description
+2 The longjmp function restores the environment saved by the most recent invocation of
+ the setjmp macro in the same invocation of the program with the corresponding
+ jmp_buf argument. If there has been no such invocation, or if the invocation was from
+ another thread of execution, or if the function containing the invocation of the setjmp
+ macro has terminated execution248) in the interim, or if the invocation of the setjmp
+ macro was within the scope of an identifier with variably modified type and execution has
+ left that scope in the interim, the behavior is undefined.
+3 All accessible objects have values, and all other components of the abstract machine249)
+ have state, as of the time the longjmp function was called, except that the values of
+ objects of automatic storage duration that are local to the function containing the
+ invocation of the corresponding setjmp macro that do not have volatile-qualified type
+ and have been changed between the setjmp invocation and longjmp call are
+ indeterminate.
+ Returns
+4 After longjmp is completed, thread execution continues as if the corresponding
+ invocation of the setjmp macro had just returned the value specified by val. The
+ longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
+ the setjmp macro returns the value 1.
+5 EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
+ might cause memory associated with a variable length array object to be squandered.
+
+
+
+ 248) 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.
+ 249) This includes, but is not limited to, the floating-point status flags and the state of open files.
+
+[page 263]
+
+ #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
+ }
+
+[page 264]
+
+ 7.14 Signal handling <signal.h>
+1 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).
+2 The type defined is
+ sig_atomic_t
+ which is the (possibly volatile-qualified) integer type of an object that can be accessed as
+ an atomic entity, even in the presence of asynchronous interrupts.
+3 The macros defined are
+ SIG_DFL
+ SIG_ERR
+ SIG_IGN
+ which expand to constant expressions with distinct values that have type compatible with
+ the second argument to, and the return value of, the signal function, and whose values
+ compare unequal to the address of any declarable function; and the following, which
+ expand to positive integer constant expressions with type int and distinct values that are
+ the signal numbers, each corresponding to the specified condition:
+ SIGABRT abnormal termination, such as is initiated by the abort function
+ SIGFPE an erroneous arithmetic operation, such as zero divide or an operation
+ resulting in overflow
+ SIGILL detection of an invalid function image, such as an invalid instruction
+ SIGINT receipt of an interactive attention signal
+ SIGSEGV an invalid access to storage
+ SIGTERM a termination request sent to the program
+4 An implementation need not generate any of these signals, except as a result of explicit
+ calls to the raise function. Additional signals and pointers to undeclarable functions,
+ with macro definitions beginning, respectively, with the letters SIG and an uppercase
+ letter or with SIG_ and an uppercase letter,250) 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.
+
+
+
+
+ 250) See ''future library directions'' (7.31.7). The names of the signal numbers reflect the following terms
+ (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
+ and termination.
+
+[page 265]
+
+ 7.14.1 Specify signal handling
+ 7.14.1.1 The signal function
+ Synopsis
+1 #include <signal.h>
+ void (*signal(int sig, void (*func)(int)))(int);
+ Description
+2 The signal function chooses one of three ways in which receipt of the signal number
+ sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
+ for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
+ Otherwise, func shall point to a function to be called when that signal occurs. An
+ invocation of such a function because of a signal, or (recursively) of any further functions
+ called by that invocation (other than functions in the standard library),251) is called a
+ signal handler.
+3 When a signal occurs and func points to a function, it is implementation-defined
+ whether the equivalent of signal(sig, SIG_DFL); is executed or the
+ implementation prevents some implementation-defined set of signals (at least including
+ sig) from occurring until the current signal handling has completed; in the case of
+ SIGILL, the implementation may alternatively define that no action is taken. Then the
+ equivalent of (*func)(sig); is executed. If and when the function returns, if the
+ value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
+ value corresponding to a computational exception, the behavior is undefined; otherwise
+ the program will resume execution at the point it was interrupted.
+4 If the signal occurs as the result of calling the abort or raise function, the signal
+ handler shall not call the raise function.
+5 If the signal occurs other than as the result of calling the abort or raise function, the
+ behavior is undefined if the signal handler refers to any object with static or thread
+ storage duration that is not a lock-free atomic object other than by assigning a value to an
+ object declared as volatile sig_atomic_t, or the signal handler calls any function
+ in the standard library other than the abort function, the _Exit function, the
+ quick_exit function, or the signal function with the first argument equal to the
+ signal number corresponding to the signal that caused the invocation of the handler.
+ Furthermore, if such a call to the signal function results in a SIG_ERR return, the
+ value of errno is indeterminate.252)
+
+
+ 251) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
+ called via the abort function).
+ 252) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
+
+[page 266]
+
+6 At program startup, the equivalent of
+ signal(sig, SIG_IGN);
+ may be executed for some signals selected in an implementation-defined manner; the
+ equivalent of
+ signal(sig, SIG_DFL);
+ is executed for all other signals defined by the implementation.
+7 Use of this function in a multi-threaded program results in undefined behavior. The
+ implementation shall behave as if no library function calls the signal function.
+ Returns
+8 If the request can be honored, the signal function returns the value of func for the
+ most recent successful call to signal for the specified signal sig. Otherwise, a value of
+ SIG_ERR is returned and a positive value is stored in errno.
+ Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
+ _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).
+ 7.14.2 Send signal
+ 7.14.2.1 The raise function
+ Synopsis
+1 #include <signal.h>
+ int raise(int sig);
+ Description
+2 The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
+ signal handler is called, the raise function shall not return until after the signal handler
+ does.
+ Returns
+3 The raise function returns zero if successful, nonzero if unsuccessful.
+
+[page 267]
+
+ 7.15 Alignment <stdalign.h>
+1 The header <stdalign.h> defines four macros.
+2 The macro
+ alignas
+ expands to _Alignas; the macro
+ alignof
+ expands to _Alignof.
+3 The remaining macros are suitable for use in #if preprocessing directives. They are
+ __alignas_is_defined
+ and
+ __alignof_is_defined
+ which both expand to the integer constant 1.
+
+[page 268]
+
+ 7.16 Variable arguments <stdarg.h>
+1 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.
+2 A function may be called with a variable number of arguments of varying types. As
+ described in 6.9.1, its parameter list contains one or more parameters. The rightmost
+ parameter plays a special role in the access mechanism, and will be designated parmN in
+ this description.
+3 The type declared is
+ va_list
+ which is a complete object type suitable for holding information needed by the macros
+ va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
+ desired, the called function shall declare an object (generally referred to as ap in this
+ subclause) having type va_list. The object ap may be passed as an argument to
+ another function; if that function invokes the va_arg macro with parameter ap, the
+ value of ap in the calling function is indeterminate and shall be passed to the va_end
+ macro prior to any further reference to ap.253)
+ 7.16.1 Variable argument list access macros
+1 The va_start and va_arg macros described in this subclause shall be implemented
+ as macros, not functions. It is unspecified whether va_copy and va_end are macros or
+ identifiers declared with external linkage. If a macro definition is suppressed in order to
+ access an actual function, or a program defines an external identifier with the same name,
+ the behavior is undefined. Each invocation of the va_start and va_copy macros
+ shall be matched by a corresponding invocation of the va_end macro in the same
+ function.
+ 7.16.1.1 The va_arg macro
+ Synopsis
+1 #include <stdarg.h>
+ type va_arg(va_list ap, type);
+ Description
+2 The va_arg macro expands to an expression that has the specified type and the value of
+ the next argument in the call. The parameter ap shall have been initialized by the
+ va_start or va_copy macro (without an intervening invocation of the va_end
+
+ 253) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
+ case the original function may make further use of the original list after the other function returns.
+
+[page 269]
+
+ macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
+ values of successive arguments are returned in turn. The parameter type shall be a type
+ name specified such that the type of a pointer to an object that has the specified type can
+ be obtained simply by postfixing a * to type. If there is no actual next argument, or if
+ type is not compatible with the type of the actual next argument (as promoted according
+ to the default argument promotions), the behavior is undefined, except for the following
+ cases:
+ -- one type is a signed integer type, the other type is the corresponding unsigned integer
+ type, and the value is representable in both types;
+ -- one type is pointer to void and the other is a pointer to a character type.
+ Returns
+3 The first invocation of the va_arg macro after that of the va_start macro returns the
+ value of the argument after that specified by parmN . Successive invocations return the
+ values of the remaining arguments in succession.
+ 7.16.1.2 The va_copy macro
+ Synopsis
+1 #include <stdarg.h>
+ void va_copy(va_list dest, va_list src);
+ Description
+2 The va_copy macro initializes dest as a copy of src, as if the va_start macro had
+ been applied to dest followed by the same sequence of uses of the va_arg macro as
+ had previously been used to reach the present state of src. Neither the va_copy nor
+ va_start macro shall be invoked to reinitialize dest without an intervening
+ invocation of the va_end macro for the same dest.
+ Returns
+3 The va_copy macro returns no value.
+ 7.16.1.3 The va_end macro
+ Synopsis
+1 #include <stdarg.h>
+ void va_end(va_list ap);
+ Description
+2 The va_end macro facilitates a normal return from the function whose variable
+ argument list was referred to by the expansion of the va_start macro, or the function
+ containing the expansion of the va_copy macro, that initialized the va_list ap. The
+ va_end macro may modify ap so that it is no longer usable (without being reinitialized
+
+[page 270]
+
+ by the va_start or va_copy macro). If there is no corresponding invocation of the
+ va_start or va_copy macro, or if the va_end macro is not invoked before the
+ return, the behavior is undefined.
+ Returns
+3 The va_end macro returns no value.
+ 7.16.1.4 The va_start macro
+ Synopsis
+1 #include <stdarg.h>
+ void va_start(va_list ap, parmN);
+ Description
+2 The va_start macro shall be invoked before any access to the unnamed arguments.
+3 The va_start macro initializes ap for subsequent use by the va_arg and va_end
+ macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
+ without an intervening invocation of the va_end macro for the same ap.
+4 The parameter parmN is the identifier of the rightmost parameter in the variable
+ parameter list in the function definition (the one just before the , ...). If the parameter
+ parmN is declared with the register storage class, with a function or array type, or
+ with a type that is not compatible with the type that results after application of the default
+ argument promotions, the behavior is undefined.
+ Returns
+5 The va_start macro returns no value.
+6 EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
+ more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
+ pointers is specified by the first argument to f1.
+ #include <stdarg.h>
+ #define MAXARGS 31
+ void f1(int n_ptrs, ...)
+ {
+ va_list ap;
+ char *array[MAXARGS];
+ int ptr_no = 0;
+
+[page 271]
+
+ if (n_ptrs > MAXARGS)
+ n_ptrs = MAXARGS;
+ va_start(ap, n_ptrs);
+ while (ptr_no < n_ptrs)
+ array[ptr_no++] = va_arg(ap, char *);
+ va_end(ap);
+ f2(n_ptrs, array);
+ }
+ Each call to f1 is required to have visible the definition of the function or a declaration such as
+ void f1(int, ...);
+
+7 EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
+ indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
+ is gathered again and passed to function f4.
+ #include <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);
+ }
+
+[page 272]
+
+ 7.17 Atomics <stdatomic.h>
+ 7.17.1 Introduction
+1 The header <stdatomic.h> defines several macros and declares several types and
+ functions for performing atomic operations on data shared between threads.254)
+2 Implementations that define the macro __STDC_NO_ATOMICS__ need not provide
+ this header nor support any of its facilities.
+3 The macros defined are the atomic lock-free macros
+ ATOMIC_BOOL_LOCK_FREE
+ 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_POINTER_LOCK_FREE
+ which indicate the lock-free property of the corresponding atomic types (both signed and
+ unsigned); and
+ ATOMIC_FLAG_INIT
+ which expands to an initializer for an object of type atomic_flag.
+4 The types include
+ memory_order
+ which is an enumerated type whose enumerators identify memory ordering constraints;
+ atomic_flag
+ which is a structure type representing a lock-free, primitive atomic flag; and several *
+ atomic analogs of integer types.
+5 In the following synopses:
+ -- An A refers to one of the atomic types.
+ -- A C refers to its corresponding non-atomic type. *
+ -- An M refers to the type of the other argument for arithmetic operations. For atomic
+ integer types, M is C. For atomic pointer types, M is ptrdiff_t.
+
+ 254) See ''future library directions'' (7.31.8).
+
+[page 273]
+
+ -- The functions not ending in _explicit have the same semantics as the
+ corresponding _explicit function with memory_order_seq_cst for the
+ memory_order argument.
+6 NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not
+ changed in the standard. This qualification means that volatility is preserved when applying these
+ operations to volatile objects.
+
+ 7.17.2 Initialization
+ 7.17.2.1 The ATOMIC_VAR_INIT macro
+ Synopsis
+1 #include <stdatomic.h>
+ #define ATOMIC_VAR_INIT(C value)
+ Description
+2 The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
+ atomic object of a type that is initialization-compatible with value. An atomic object
+ with automatic storage duration that is not explicitly initialized using
+ ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
+ initialization for objects with static or thread-local storage duration is guaranteed to
+ produce a valid state.
+3 Concurrent access to the variable being initialized, even via an atomic operation,
+ constitutes a data race.
+4 EXAMPLE
+ atomic_int guide = ATOMIC_VAR_INIT(42);
+
+ 7.17.2.2 The atomic_init generic function
+ Synopsis
+1 #include <stdatomic.h>
+ void atomic_init(volatile A *obj, C value);
+ Description
+2 The atomic_init generic function initializes the atomic object pointed to by obj to
+ the value value, while also initializing any additional state that the implementation
+ might need to carry for the atomic object.
+3 Although this function initializes an atomic object, it does not avoid data races;
+ concurrent access to the variable being initialized, even via an atomic operation,
+ constitutes a data race.
+
+[page 274]
+
+ Returns
+4 The atomic_init generic function returns no value.
+5 EXAMPLE
+ atomic_int guide;
+ atomic_init(&guide, 42);
+
+ 7.17.3 Order and consistency
+1 The enumerated type memory_order specifies the detailed regular (non-atomic)
+ memory synchronization operations as defined in 5.1.2.4 and may provide for operation
+ ordering. Its enumeration constants are as follows:255)
+ memory_order_relaxed
+ memory_order_consume
+ memory_order_acquire
+ memory_order_release
+ memory_order_acq_rel
+ memory_order_seq_cst
+2 For memory_order_relaxed, no operation orders memory.
+3 For memory_order_release, memory_order_acq_rel, and
+ memory_order_seq_cst, a store operation performs a release operation on the
+ affected memory location.
+4 For memory_order_acquire, memory_order_acq_rel, and
+ memory_order_seq_cst, a load operation performs an acquire operation on the
+ affected memory location.
+5 For memory_order_consume, a load operation performs a consume operation on the
+ affected memory location.
+6 There shall be a single total order S on all memory_order_seq_cst operations,
+ consistent with the ''happens before'' order and modification orders for all affected
+ locations, such that each memory_order_seq_cst operation B that loads a value
+ from an atomic object M observes one of the following values:
+ -- the result of the last modification A of M that precedes B in S, if it exists, or
+ -- if A exists, the result of some modification of M in the visible sequence of side
+ effects with respect to B that is not memory_order_seq_cst and that does not
+ happen before A, or
+
+
+
+
+ 255) See ''future library directions'' (7.31.8).
+
+[page 275]
+
+ -- if A does not exist, the result of some modification of M in the visible sequence of
+ side effects with respect to B that is not memory_order_seq_cst.
+7 NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
+ an order that does include lock and unlock operations, since the ordering between those is already included
+ in the ''happens before'' ordering.
+
+8 NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
+ memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
+ object be indivisible with respect to all other atomic accesses to that object.
+
+9 For an atomic operation B that reads the value of an atomic object M, if there is a
+ memory_order_seq_cst fence X sequenced before B, then B observes either the
+ last memory_order_seq_cst modification of M preceding X in the total order S or
+ a later modification of M in its modification order.
+10 For atomic operations A and B on an atomic object M, where A modifies M and B takes
+ its value, if there is a memory_order_seq_cst fence X such that A is sequenced
+ before X and B follows X in S, then B observes either the effects of A or a later
+ modification of M in its modification order.
+11 For atomic operations A and B on an atomic object M, where A modifies M and B takes
+ its value, if there are memory_order_seq_cst fences X and Y such that A is
+ sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
+ either the effects of A or a later modification of M in its modification order.
+12 Atomic read-modify-write operations shall always read the last value (in the modification
+ order) stored before the write associated with the read-modify-write operation.
+13 An atomic store shall only store a value that has been computed from constants and
+ program input values by a finite sequence of program evaluations, such that each
+ evaluation observes the values of variables as computed by the last prior assignment in
+ the sequence.256) The ordering of evaluations in this sequence shall be such that
+ -- If an evaluation B observes a value computed by A in a different thread, then B does
+ not happen before A.
+ -- If an evaluation A is included in the sequence, then all evaluations that assign to the
+ same variable and happen before A are also included.
+14 NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when
+ relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
+ sequence out of thread order. For example, with x and y initially zero,
+
+
+
+
+ 256) Among other implications, atomic variables shall not decay.
+
+[page 276]
+
+ // 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
+15 The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
+ with x and y initially zero:
+ // Thread 1:
+ r1 = atomic_load_explicit(&x, memory_order_relaxed);
+ if (r1 == 42)
+ atomic_store_explicit(&y, r1, memory_order_relaxed);
+
+ // Thread 2:
+ r2 = atomic_load_explicit(&y, memory_order_relaxed);
+ if (r2 == 42)
+ atomic_store_explicit(&x, 42, memory_order_relaxed);
+ However, this is not useful behavior, and implementations should not allow it.
+16 Implementations should make atomic stores visible to atomic loads within a reasonable
+ amount of time.
+
+[page 277]
+
+ 7.17.3.1 The kill_dependency macro
+ Synopsis
+1 #include <stdatomic.h>
+ type kill_dependency(type y);
+ Description
+2 The kill_dependency macro terminates a dependency chain; the argument does not
+ carry a dependency to the return value.
+ Returns
+3 The kill_dependency macro returns the value of y.
+ 7.17.4 Fences
+1 This subclause introduces synchronization primitives called fences. Fences can have
+ acquire semantics, release semantics, or both. A fence with acquire semantics is called
+ an acquire fence; a fence with release semantics is called a release fence.
+2 A release fence A synchronizes with an acquire fence B if there exist atomic operations
+ X and Y , both operating on some atomic object M, such that A is sequenced before X, X
+ modifies M, Y is sequenced before B, and Y reads the value written by X or a value
+ written by any side effect in the hypothetical release sequence X would head if it were a
+ release operation.
+3 A release fence A synchronizes with an atomic operation B that performs an acquire
+ operation on an atomic object M if there exists an atomic operation X such that A is
+ sequenced before X, X modifies M, and B reads the value written by X or a value written
+ by any side effect in the hypothetical release sequence X would head if it were a release
+ operation.
+4 An atomic operation A that is a release operation on an atomic object M synchronizes
+ with an acquire fence B if there exists some atomic operation X on M such that X is
+ sequenced before B and reads the value written by A or a value written by any side effect
+ in the release sequence headed by A.
+ 7.17.4.1 The atomic_thread_fence function
+ Synopsis
+1 #include <stdatomic.h>
+ void atomic_thread_fence(memory_order order);
+ Description
+2 Depending on the value of order, this operation:
+ -- has no effects, if order == memory_order_relaxed;
+
+[page 278]
+
+ -- is an acquire fence, if order == memory_order_acquire or order ==
+ memory_order_consume;
+ -- is a release fence, if order == memory_order_release;
+ -- is both an acquire fence and a release fence, if order ==
+ memory_order_acq_rel;
+ -- is a sequentially consistent acquire and release fence, if order ==
+ memory_order_seq_cst.
+ Returns
+3 The atomic_thread_fence function returns no value.
+ 7.17.4.2 The atomic_signal_fence function
+ Synopsis
+1 #include <stdatomic.h>
+ void atomic_signal_fence(memory_order order);
+ Description
+2 Equivalent to atomic_thread_fence(order), except that the resulting ordering
+ constraints are established only between a thread and a signal handler executed in the
+ same thread.
+3 NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
+ performed by the thread become visible to the signal handler.
+
+4 NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
+ atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
+ have inserted are not emitted.
+
+ Returns
+5 The atomic_signal_fence function returns no value.
+ 7.17.5 Lock-free property
+1 The atomic lock-free macros indicate the lock-free property of integer and address atomic
+ types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
+ the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
+2 NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
+ memory location via two different addresses will communicate atomically. The implementation should not
+ depend on any per-process state. This restriction enables communication via memory mapped into a
+ process more than once and memory shared between two processes.
+
+[page 279]
+
+ 7.17.5.1 The atomic_is_lock_free generic function
+ Synopsis
+1 #include <stdatomic.h>
+ _Bool atomic_is_lock_free(const volatile A *obj);
+ Description
+2 The atomic_is_lock_free generic function indicates whether or not the object
+ pointed to by obj is lock-free. *
+ Returns
+3 The atomic_is_lock_free generic function returns nonzero (true) if and only if the
+ object's operations are lock-free. The result of a lock-free query on one object cannot be
+ inferred from the result of a lock-free query on another object.
+ 7.17.6 Atomic integer types
+1 For each line in the following table,257) the atomic type name is declared as a type that
+ has the same representation and alignment requirements as the corresponding direct
+ type.258)
+
+
+
+
+ 257) See ''future library directions'' (7.31.8).
+ 258) The same representation and alignment requirements are meant to imply interchangeability as
+ arguments to functions, return values from functions, and members of unions.
+
+[page 280]
+
+ Atomic type name Direct type
+ atomic_bool _Atomic _Bool
+ atomic_char _Atomic char
+ atomic_schar _Atomic signed char
+ atomic_uchar _Atomic unsigned char
+ atomic_short _Atomic short
+ atomic_ushort _Atomic unsigned short
+ atomic_int _Atomic int
+ atomic_uint _Atomic unsigned int
+ atomic_long _Atomic long
+ atomic_ulong _Atomic unsigned long
+ atomic_llong _Atomic long long
+ atomic_ullong _Atomic unsigned long long
+ atomic_char16_t _Atomic char16_t
+ atomic_char32_t _Atomic char32_t
+ atomic_wchar_t _Atomic wchar_t
+ atomic_int_least8_t _Atomic int_least8_t
+ atomic_uint_least8_t _Atomic uint_least8_t
+ atomic_int_least16_t _Atomic int_least16_t
+ atomic_uint_least16_t _Atomic uint_least16_t
+ atomic_int_least32_t _Atomic int_least32_t
+ atomic_uint_least32_t _Atomic uint_least32_t
+ atomic_int_least64_t _Atomic int_least64_t
+ atomic_uint_least64_t _Atomic uint_least64_t
+ atomic_int_fast8_t _Atomic int_fast8_t
+ atomic_uint_fast8_t _Atomic uint_fast8_t
+ atomic_int_fast16_t _Atomic int_fast16_t
+ atomic_uint_fast16_t _Atomic uint_fast16_t
+ atomic_int_fast32_t _Atomic int_fast32_t
+ atomic_uint_fast32_t _Atomic uint_fast32_t
+ atomic_int_fast64_t _Atomic int_fast64_t
+ atomic_uint_fast64_t _Atomic uint_fast64_t
+ atomic_intptr_t _Atomic intptr_t
+ atomic_uintptr_t _Atomic uintptr_t
+ atomic_size_t _Atomic size_t
+ atomic_ptrdiff_t _Atomic ptrdiff_t
+ atomic_intmax_t _Atomic intmax_t
+ atomic_uintmax_t _Atomic uintmax_t
+2 The semantics of the operations on these types are defined in 7.17.7. *
+
+[page 281]
+
+3 NOTE The representation of atomic integer types need not have the same size as their corresponding
+ regular types. They should have the same size whenever possible, as it eases effort required to port existing
+ code.
+
+ 7.17.7 Operations on atomic types
+1 There are only a few kinds of operations on atomic types, though there are many
+ instances of those kinds. This subclause specifies each general kind.
+ 7.17.7.1 The atomic_store generic functions
+ Synopsis
+1 #include <stdatomic.h>
+ void atomic_store(volatile A *object, C desired);
+ void atomic_store_explicit(volatile A *object,
+ C desired, memory_order order);
+ Description
+2 The order argument shall not be memory_order_acquire,
+ memory_order_consume, nor memory_order_acq_rel. Atomically replace the
+ value pointed to by object with the value of desired. Memory is affected according
+ to the value of order.
+ Returns
+3 The atomic_store generic functions return no value.
+ 7.17.7.2 The atomic_load generic functions
+ Synopsis
+1 #include <stdatomic.h>
+ C atomic_load(volatile A *object);
+ C atomic_load_explicit(volatile A *object,
+ memory_order order);
+ Description
+2 The order argument shall not be memory_order_release nor
+ memory_order_acq_rel. Memory is affected according to the value of order.
+ Returns
+ Atomically returns the value pointed to by object.
+
+[page 282]
+
+ 7.17.7.3 The atomic_exchange generic functions
+ Synopsis
+1 #include <stdatomic.h>
+ C atomic_exchange(volatile A *object, C desired);
+ C atomic_exchange_explicit(volatile A *object,
+ C desired, memory_order order);
+ Description
+2 Atomically replace the value pointed to by object with desired. Memory is affected
+ according to the value of order. These operations are read-modify-write operations
+ (5.1.2.4).
+ Returns
+3 Atomically returns the value pointed to by object immediately before the effects.
+ 7.17.7.4 The atomic_compare_exchange generic functions
+ Synopsis
+1 #include <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
+2 The failure argument shall not be memory_order_release nor
+ memory_order_acq_rel. The failure argument shall be no stronger than the
+ success argument. Atomically, compares the value pointed to by object for equality
+ with that in expected, and if true, replaces the value pointed to by object with
+ desired, and if false, updates the value in expected with the value pointed to by
+ object. Further, if the comparison is true, memory is affected according to the value of
+ success, and if the comparison is false, memory is affected according to the value of
+ failure. These operations are atomic read-modify-write operations (5.1.2.4).
+3 NOTE 1 For example, the effect of atomic_compare_exchange_strong is
+
+[page 283]
+
+ if (memcmp(object, expected, sizeof (*object)) == 0)
+ memcpy(object, &desired, sizeof (*object));
+ else
+ memcpy(expected, object, sizeof (*object));
+
+4 A weak compare-and-exchange operation may fail spuriously. That is, even when the
+ contents of memory referred to by expected and object are equal, it may return zero
+ and store back to expected the same memory contents that were originally there.
+5 NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
+ machines, e.g. load-locked store-conditional machines.
+
+6 EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
+ be in a loop.
+ exp = atomic_load(&cur);
+ do {
+ des = function(exp);
+ } while (!atomic_compare_exchange_weak(&cur, &exp, des));
+ When a compare-and-exchange is in a loop, the weak version will yield better performance on some
+ platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
+ strong one is preferable.
+
+ Returns
+7 The result of the comparison.
+ 7.17.7.5 The atomic_fetch and modify generic functions
+1 The following operations perform arithmetic and bitwise computations. All of these
+ operations are applicable to an object of any atomic integer type. None of these *
+ operations is applicable to atomic_bool. The key, operator, and computation
+ correspondence is:
+ key op computation
+ add + addition
+ sub - subtraction
+ or | bitwise inclusive or
+ xor ^ bitwise exclusive or
+ and & bitwise and
+ Synopsis
+2 #include <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
+3 Atomically replaces the value pointed to by object with the result of the computation
+ applied to the value pointed to by object and the given operand. Memory is affected
+
+[page 284]
+
+ 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
+4 Atomically, the value pointed to by object immediately before the effects.
+5 NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
+ operation of the corresponding op= compound assignment operators. The only differences are that the
+ compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
+ compound assignment operator is the updated value of the object, whereas the value returned by the
+ atomic_fetch and modify generic functions is the previous value of the atomic object.
+
+ 7.17.8 Atomic flag type and operations
+1 The atomic_flag type provides the classic test-and-set functionality. It has two
+ states, set and clear.
+2 Operations on an object of type atomic_flag shall be lock free.
+3 NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
+ the atomic_flag type is the minimum hardware-implemented type needed to conform to this
+ International standard. The remaining types can be emulated with atomic_flag, though with less than
+ ideal properties.
+
+4 The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
+ clear state. An atomic_flag that is not explicitly initialized with
+ ATOMIC_FLAG_INIT is initially in an indeterminate state.
+5 EXAMPLE
+ atomic_flag guard = ATOMIC_FLAG_INIT;
+
+ 7.17.8.1 The atomic_flag_test_and_set functions
+ Synopsis
+1 #include <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
+2 Atomically sets the value pointed to by object to true. Memory is affected according
+ to the value of order. These operations are atomic read-modify-write operations
+ (5.1.2.4).
+
+[page 285]
+
+ Returns
+3 Atomically, the value of the object immediately before the effects.
+ 7.17.8.2 The atomic_flag_clear functions
+ Synopsis
+1 #include <stdatomic.h>
+ void atomic_flag_clear(volatile atomic_flag *object);
+ void atomic_flag_clear_explicit(
+ volatile atomic_flag *object, memory_order order);
+ Description
+2 The order argument shall not be memory_order_acquire nor
+ memory_order_acq_rel. Atomically sets the value pointed to by object to false.
+ Memory is affected according to the value of order.
+ Returns
+3 The atomic_flag_clear functions return no value.
+
+[page 286]
+
+ 7.18 Boolean type and values <stdbool.h>
+1 The header <stdbool.h> defines four macros.
+2 The macro
+ bool
+ expands to _Bool.
+3 The remaining three macros are suitable for use in #if preprocessing directives. They
+ are
+ true
+ which expands to the integer constant 1,
+ false
+ which expands to the integer constant 0, and
+ __bool_true_false_are_defined
+ which expands to the integer constant 1.
+4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
+ redefine the macros bool, true, and false.259)
+
+
+
+
+ 259) See ''future library directions'' (7.31.9).
+
+[page 287]
+
+ 7.19 Common definitions <stddef.h>
+1 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.
+2 The types are
+ ptrdiff_t
+ which is the signed integer type of the result of subtracting two pointers;
+ size_t
+ which is the unsigned integer type of the result of the sizeof operator;
+ max_align_t
+ which is an object type whose alignment is as great as is supported by the implementation
+ in all contexts; and
+ wchar_t
+ which is an integer type whose range of values can represent distinct codes for all
+ members of the largest extended character set specified among the supported locales; the
+ null character shall have the code value zero. Each member of the basic character set
+ shall have a code value equal to its value when used as the lone character in an integer
+ character constant if an implementation does not define
+ __STDC_MB_MIGHT_NEQ_WC__.
+3 The macros are
+ NULL
+ which expands to an implementation-defined null pointer constant; and
+ offsetof(type, member-designator)
+ which expands to an integer constant expression that has type size_t, the value of
+ which is the offset in bytes, to the structure member (designated by member-designator),
+ from the beginning of its structure (designated by type). The type and member designator
+ shall be such that given
+ static type t;
+ then the expression &(t.member-designator) evaluates to an address constant. (If the
+ specified member is a bit-field, the behavior is undefined.)
+ Recommended practice
+4 The types used for size_t and ptrdiff_t should not have an integer conversion rank
+ greater than that of signed long int unless the implementation supports objects
+ large enough to make this necessary. *
+
+[page 288]
+
+ 7.20 Integer types <stdint.h>
+1 The header <stdint.h> declares sets of integer types having specified widths, and
+ defines corresponding sets of macros.260) It also defines macros that specify limits of
+ integer types corresponding to types defined in other standard headers.
+2 Types are defined in the following categories:
+ -- integer types having certain exact widths;
+ -- integer types having at least certain specified widths;
+ -- fastest integer types having at least certain specified widths;
+ -- integer types wide enough to hold pointers to objects;
+ -- integer types having greatest width.
+ (Some of these types may denote the same type.)
+3 Corresponding macros specify limits of the declared types and construct suitable
+ constants.
+4 For each type described herein that the implementation provides,261) <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'').
+ 7.20.1 Integer types
+1 When typedef names differing only in the absence or presence of the initial u are defined,
+ they shall denote corresponding signed and unsigned types as described in 6.2.5; an
+ implementation providing one of these corresponding types shall also provide the other.
+2 In the following descriptions, the symbol N represents an unsigned decimal integer with
+ no leading zeros (e.g., 8 or 24, but not 04 or 048).
+
+
+
+
+ 260) See ''future library directions'' (7.31.10).
+ 261) Some of these types may denote implementation-defined extended integer types.
+
+[page 289]
+
+ 7.20.1.1 Exact-width integer types
+1 The typedef name intN_t designates a signed integer type with width N , no padding
+ bits, and a two's complement representation. Thus, int8_t denotes such a signed
+ integer type with a width of exactly 8 bits.
+2 The typedef name uintN_t designates an unsigned integer type with width N and no
+ padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
+ exactly 24 bits.
+3 These types are optional. However, if an implementation provides integer types with
+ widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
+ two's complement representation, it shall define the corresponding typedef names.
+ 7.20.1.2 Minimum-width integer types
+1 The typedef name int_leastN_t designates a signed integer type with a width of at
+ least N , such that no signed integer type with lesser size has at least the specified width.
+ Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
+2 The typedef name uint_leastN_t designates an unsigned integer type with a width
+ of at least N , such that no unsigned integer type with lesser size has at least the specified
+ width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
+ least 16 bits.
+3 The following types are required:
+ int_least8_t uint_least8_t
+ int_least16_t uint_least16_t
+ int_least32_t uint_least32_t
+ int_least64_t uint_least64_t
+ All other types of this form are optional.
+ 7.20.1.3 Fastest minimum-width integer types
+1 Each of the following types designates an integer type that is usually fastest262) to operate
+ with among all integer types that have at least the specified width.
+2 The typedef name int_fastN_t designates the fastest signed integer type with a width
+ of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
+ type with a width of at least N .
+
+
+
+
+ 262) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
+ grounds for choosing one type over another, it will simply pick some integer type satisfying the
+ signedness and width requirements.
+
+[page 290]
+
+3 The following types are required:
+ int_fast8_t uint_fast8_t
+ int_fast16_t uint_fast16_t
+ int_fast32_t uint_fast32_t
+ int_fast64_t uint_fast64_t
+ All other types of this form are optional.
+ 7.20.1.4 Integer types capable of holding object pointers
+1 The following type designates a signed integer type with the property that any valid
+ pointer to void can be converted to this type, then converted back to pointer to void,
+ and the result will compare equal to the original pointer:
+ intptr_t
+ The following type designates an unsigned integer type with the property that any valid
+ pointer to void can be converted to this type, then converted back to pointer to void,
+ and the result will compare equal to the original pointer:
+ uintptr_t
+ These types are optional.
+ 7.20.1.5 Greatest-width integer types
+1 The following type designates a signed integer type capable of representing any value of
+ any signed integer type:
+ intmax_t
+ The following type designates an unsigned integer type capable of representing any value
+ of any unsigned integer type:
+ uintmax_t
+ These types are required.
+ 7.20.2 Limits of specified-width integer types
+1 The following object-like macros specify the minimum and maximum limits of the types
+ declared in <stdint.h>. Each macro name corresponds to a similar type name in
+ 7.20.1.
+2 Each instance of any defined macro shall be replaced by a constant expression suitable
+ for use in #if preprocessing directives, and this expression shall have the same type as
+ would an expression that is an object of the corresponding type converted according to
+ the integer promotions. Its implementation-defined value shall be equal to or greater in
+ magnitude (absolute value) than the corresponding value given below, with the same sign,
+ except where stated to be exactly the given value.
+
+[page 291]
+
+ 7.20.2.1 Limits of exact-width integer types
+1 -- minimum values of exact-width signed integer types
+ INTN_MIN exactly -(2 N -1 )
+ -- maximum values of exact-width signed integer types
+ INTN_MAX exactly 2 N -1 - 1
+ -- maximum values of exact-width unsigned integer types
+ UINTN_MAX exactly 2 N - 1
+ 7.20.2.2 Limits of minimum-width integer types
+1 -- minimum values of minimum-width signed integer types
+ INT_LEASTN_MIN -(2 N -1 - 1)
+ -- maximum values of minimum-width signed integer types
+ INT_LEASTN_MAX 2 N -1 - 1
+ -- maximum values of minimum-width unsigned integer types
+ UINT_LEASTN_MAX 2N - 1
+ 7.20.2.3 Limits of fastest minimum-width integer types
+1 -- minimum values of fastest minimum-width signed integer types
+ INT_FASTN_MIN -(2 N -1 - 1)
+ -- maximum values of fastest minimum-width signed integer types
+ INT_FASTN_MAX 2 N -1 - 1
+ -- maximum values of fastest minimum-width unsigned integer types
+ UINT_FASTN_MAX 2N - 1
+ 7.20.2.4 Limits of integer types capable of holding object pointers
+1 -- minimum value of pointer-holding signed integer type
+ INTPTR_MIN -(215 - 1)
+ -- maximum value of pointer-holding signed integer type
+ INTPTR_MAX 215 - 1
+ -- maximum value of pointer-holding unsigned integer type
+ UINTPTR_MAX 216 - 1
+
+[page 292]
+
+ 7.20.2.5 Limits of greatest-width integer types
+1 -- minimum value of greatest-width signed integer type
+ INTMAX_MIN -(263 - 1)
+ -- maximum value of greatest-width signed integer type
+ INTMAX_MAX 263 - 1
+ -- maximum value of greatest-width unsigned integer type
+ UINTMAX_MAX 264 - 1
+ 7.20.3 Limits of other integer types
+1 The following object-like macros specify the minimum and maximum limits of integer
+ types corresponding to types defined in other standard headers.
+2 Each instance of these macros shall be replaced by a constant expression suitable for use
+ in #if preprocessing directives, and this expression shall have the same type as would an
+ expression that is an object of the corresponding type converted according to the integer
+ promotions. Its implementation-defined value shall be equal to or greater in magnitude
+ (absolute value) than the corresponding value given below, with the same sign. An
+ implementation shall define only the macros corresponding to those typedef names it
+ actually provides.263)
+ -- limits of ptrdiff_t
+ PTRDIFF_MIN -65535
+ PTRDIFF_MAX +65535
+ -- limits of sig_atomic_t
+ SIG_ATOMIC_MIN see below
+ SIG_ATOMIC_MAX see below
+ -- limit of size_t
+ SIZE_MAX 65535
+ -- limits of wchar_t
+ WCHAR_MIN see below
+ WCHAR_MAX see below
+ -- limits of wint_t
+
+
+
+
+ 263) A freestanding implementation need not provide all of these types.
+
+[page 293]
+
+ WINT_MIN see below
+ WINT_MAX see below
+3 If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
+ SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
+ shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
+ type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
+ SIG_ATOMIC_MAX shall be no less than 255.
+4 If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
+ shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
+ otherwise, wchar_t is defined as an unsigned integer type, and the value of
+ WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.264)
+5 If wint_t (see 7.29) is defined as a signed integer type, the value of WINT_MIN shall
+ be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
+ otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
+ shall be 0 and the value of WINT_MAX shall be no less than 65535.
+ 7.20.4 Macros for integer constants
+1 The following function-like macros expand to integer constants suitable for initializing
+ objects that have integer types corresponding to types defined in <stdint.h>. Each
+ macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
+2 The argument in any instance of these macros shall be an unsuffixed integer constant (as
+ defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
+3 Each invocation of one of these macros shall expand to an integer constant expression
+ suitable for use in #if preprocessing directives. The type of the expression shall have
+ the same type as would an expression of the corresponding type converted according to
+ the integer promotions. The value of the expression shall be that of the argument.
+ 7.20.4.1 Macros for minimum-width integer constants
+1 The macro INTN_C(value) shall expand to an integer constant expression
+ corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
+ to an integer constant expression corresponding to the type uint_leastN_t. For
+ example, if uint_least64_t is a name for the type unsigned long long int,
+ then UINT64_C(0x123) might expand to the integer constant 0x123ULL.
+
+
+
+
+ 264) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
+ character set.
+
+[page 294]
+
+ 7.20.4.2 Macros for greatest-width integer constants
+1 The following macro expands to an integer constant expression having the value specified
+ by its argument and the type intmax_t:
+ INTMAX_C(value)
+ The following macro expands to an integer constant expression having the value specified
+ by its argument and the type uintmax_t:
+ UINTMAX_C(value)
+
+[page 295]
+
+ 7.21 Input/output <stdio.h>
+ 7.21.1 Introduction
+1 The header <stdio.h> defines several macros, and declares three types and many
+ functions for performing input and output.
+2 The types declared are size_t (described in 7.19);
+ FILE
+ which is an object type capable of recording all the information needed to control a
+ stream, including its file position indicator, a pointer to its associated buffer (if any), an
+ error indicator that records whether a read/write error has occurred, and an end-of-file
+ indicator that records whether the end of the file has been reached; and
+ fpos_t
+ which is a complete object type other than an array type capable of recording all the
+ information needed to specify uniquely every position within a file.
+3 The macros are NULL (described in 7.19);
+ _IOFBF
+ _IOLBF
+ _IONBF
+ which expand to integer constant expressions with distinct values, suitable for use as the
+ third argument to the setvbuf function;
+ BUFSIZ
+ which expands to an integer constant expression that is the size of the buffer used by the
+ setbuf function;
+ EOF
+ which expands to an integer constant expression, with type int and a negative value, that
+ is returned by several functions to indicate end-of-file, that is, no more input from a
+ stream;
+ FOPEN_MAX
+ which expands to an integer constant expression that is the minimum number of files that
+ the implementation guarantees can be open simultaneously;
+ FILENAME_MAX
+ which expands to an integer constant expression that is the size needed for an array of
+ char large enough to hold the longest file name string that the implementation
+
+[page 296]
+
+ guarantees can be opened;265)
+ L_tmpnam
+ which expands to an integer constant expression that is the size needed for an array of
+ char large enough to hold a temporary file name string generated by the tmpnam
+ function;
+ SEEK_CUR
+ SEEK_END
+ SEEK_SET
+ which expand to integer constant expressions with distinct values, suitable for use as the
+ third argument to the fseek function;
+ TMP_MAX
+ which expands to an integer constant expression that is the minimum number of unique
+ file names that can be generated by the tmpnam function;
+ stderr
+ stdin
+ stdout
+ which are expressions of type ''pointer to FILE'' that point to the FILE objects
+ associated, respectively, with the standard error, input, and output streams.
+4 The header <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.
+5 The input/output functions are given the following collective terms:
+ -- The wide character input functions -- those functions described in 7.29 that perform
+ input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
+ fwscanf, wscanf, vfwscanf, and vwscanf.
+ -- The wide character output functions -- those functions described in 7.29 that perform
+ output from wide characters and wide strings: fputwc, fputws, putwc,
+ putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.
+
+
+ 265) If the implementation imposes no practical limit on the length of file name strings, the value of
+ FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
+ string. Of course, file name string contents are subject to other system-specific constraints; therefore
+ all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.
+
+[page 297]
+
+ -- The wide character input/output functions -- the union of the ungetwc function, the
+ wide character input functions, and the wide character output functions.
+ -- The byte input/output functions -- those functions described in this subclause that
+ perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
+ fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf,
+ ungetc, vfprintf, vfscanf, vprintf, and vscanf.
+ Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
+ tmpnam function (7.21.4.4), <wchar.h> (7.29).
+ 7.21.2 Streams
+1 Input and output, whether to or from physical devices such as terminals and tape drives,
+ or whether to or from files supported on structured storage devices, are mapped into
+ logical data streams, whose properties are more uniform than their various inputs and
+ outputs. Two forms of mapping are supported, for text streams and for binary
+ streams.266)
+2 A text stream is an ordered sequence of characters composed into lines, each line
+ consisting of zero or more characters plus a terminating new-line character. Whether the
+ last line requires a terminating new-line character is implementation-defined. Characters
+ may have to be added, altered, or deleted on input and output to conform to differing
+ conventions for representing text in the host environment. Thus, there need not be a one-
+ to-one correspondence between the characters in a stream and those in the external
+ representation. Data read in from a text stream will necessarily compare equal to the data
+ that were earlier written out to that stream only if: the data consist only of printing
+ characters and the control characters horizontal tab and new-line; no new-line character is
+ immediately preceded by space characters; and the last character is a new-line character.
+ Whether space characters that are written out immediately before a new-line character
+ appear when read in is implementation-defined.
+3 A binary stream is an ordered sequence of characters that can transparently record
+ internal data. Data read in from a binary stream shall compare equal to the data that were
+ earlier written out to that stream, under the same implementation. Such a stream may,
+ however, have an implementation-defined number of null characters appended to the end
+ of the stream.
+4 Each stream has an orientation. After a stream is associated with an external file, but
+ before any operations are performed on it, the stream is without orientation. Once a wide
+ character input/output function has been applied to a stream without orientation, the
+
+
+ 266) An implementation need not distinguish between text streams and binary streams. In such an
+ implementation, there need be no new-line characters in a text stream nor any limit to the length of a
+ line.
+
+[page 298]
+
+ stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
+ been applied to a stream without orientation, the stream becomes a byte-oriented stream.
+ Only a call to the freopen function or the fwide function can otherwise alter the
+ orientation of a stream. (A successful call to freopen removes any orientation.)267)
+5 Byte input/output functions shall not be applied to a wide-oriented stream and wide
+ character input/output functions shall not be applied to a byte-oriented stream. The
+ remaining stream operations do not affect, and are not affected by, a stream's orientation,
+ except for the following additional restrictions:
+ -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
+ text and binary streams.
+ -- For wide-oriented streams, after a successful call to a file-positioning function that
+ leaves the file position indicator prior to the end-of-file, a wide character output
+ function can overwrite a partial multibyte character; any file contents beyond the
+ byte(s) written are henceforth indeterminate.
+6 Each wide-oriented stream has an associated mbstate_t object that stores the current
+ parse state of the stream. A successful call to fgetpos stores a representation of the
+ value of this mbstate_t object as part of the value of the fpos_t object. A later
+ successful call to fsetpos using the same stored fpos_t value restores the value of
+ the associated mbstate_t object as well as the position within the controlled stream.
+7 Each stream has an associated lock that is used to prevent data races when multiple
+ threads of execution access a stream, and to restrict the interleaving of stream operations
+ performed by multiple threads. Only one thread may hold this lock at a time. The lock is
+ reentrant: a single thread may hold the lock multiple times at a given time.
+8 All functions that read, write, position, or query the position of a stream lock the stream
+ before accessing it. They release the lock associated with the stream when the access is
+ complete.
+ Environmental limits
+9 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 (7.29.3.5),
+ mbstate_t (7.30.1), the fgetpos function (7.21.9.1), the fsetpos function
+ (7.21.9.3).
+
+
+
+
+ 267) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
+
+[page 299]
+
+ 7.21.3 Files
+1 A stream is associated with an external file (which may be a physical device) by opening
+ a file, which may involve creating a new file. Creating an existing file causes its former
+ contents to be discarded, if necessary. If a file can support positioning requests (such as a
+ disk file, as opposed to a terminal), then a file position indicator associated with the
+ stream is positioned at the start (character number zero) of the file, unless the file is
+ opened with append mode in which case it is implementation-defined whether the file
+ position indicator is initially positioned at the beginning or the end of the file. The file
+ position indicator is maintained by subsequent reads, writes, and positioning requests, to
+ facilitate an orderly progression through the file.
+2 Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
+ stream causes the associated file to be truncated beyond that point is implementation-
+ defined.
+3 When a stream is unbuffered, characters are intended to appear from the source or at the
+ destination as soon as possible. Otherwise characters may be accumulated and
+ transmitted to or from the host environment as a block. When a stream is fully buffered,
+ characters are intended to be transmitted to or from the host environment as a block when
+ a buffer is filled. When a stream is line buffered, characters are intended to be
+ transmitted to or from the host environment as a block when a new-line character is
+ encountered. Furthermore, characters are intended to be transmitted as a block to the host
+ environment when a buffer is filled, when input is requested on an unbuffered stream, or
+ when input is requested on a line buffered stream that requires the transmission of
+ characters from the host environment. Support for these characteristics is
+ implementation-defined, and may be affected via the setbuf and setvbuf functions.
+4 A file may be disassociated from a controlling stream by closing the file. Output streams
+ are flushed (any unwritten buffer contents are transmitted to the host environment) before
+ the stream is disassociated from the file. The value of a pointer to a FILE object is
+ indeterminate after the associated file is closed (including the standard text streams).
+ Whether a file of zero length (on which no characters have been written by an output
+ stream) actually exists is implementation-defined.
+5 The file may be subsequently reopened, by the same or another program execution, and
+ its contents reclaimed or modified (if it can be repositioned at its start). If the main
+ function returns to its original caller, or if the exit function is called, all open files are
+ closed (hence all output streams are flushed) before program termination. Other paths to
+ program termination, such as calling the abort function, need not close all files
+ properly.
+6 The address of the FILE object used to control a stream may be significant; a copy of a
+ FILE object need not serve in place of the original.
+
+[page 300]
+
+7 At program startup, three text streams are predefined and need not be opened explicitly
+ -- standard input (for reading conventional input), standard output (for writing
+ conventional output), and standard error (for writing diagnostic output). As initially
+ opened, the standard error stream is not fully buffered; the standard input and standard
+ output streams are fully buffered if and only if the stream can be determined not to refer
+ to an interactive device.
+8 Functions that open additional (nontemporary) files require a file name, which is a string.
+ The rules for composing valid file names are implementation-defined. Whether the same
+ file can be simultaneously open multiple times is also implementation-defined.
+9 Although both text and binary wide-oriented streams are conceptually sequences of wide
+ characters, the external file associated with a wide-oriented stream is a sequence of
+ multibyte characters, generalized as follows:
+ -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
+ encodings valid for use internal to the program).
+ -- A file need not begin nor end in the initial shift state.268)
+10 Moreover, the encodings used for multibyte characters may differ among files. Both the
+ nature and choice of such encodings are implementation-defined.
+11 The wide character input functions read multibyte characters from the stream and convert
+ them to wide characters as if they were read by successive calls to the fgetwc function.
+ Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
+ described by the stream's own mbstate_t object. The byte input functions read
+ characters from the stream as if by successive calls to the fgetc function.
+12 The wide character output functions convert wide characters to multibyte characters and
+ write them to the stream as if they were written by successive calls to the fputwc
+ function. Each conversion occurs as if by a call to the wcrtomb function, with the
+ conversion state described by the stream's own mbstate_t object. The byte output
+ functions write characters to the stream as if by successive calls to the fputc function.
+13 In some cases, some of the byte input/output functions also perform conversions between
+ multibyte characters and wide characters. These conversions also occur as if by calls to
+ the mbrtowc and wcrtomb functions.
+14 An encoding error occurs if the character sequence presented to the underlying
+ mbrtowc function does not form a valid (generalized) multibyte character, or if the code
+ value passed to the underlying wcrtomb does not correspond to a valid (generalized)
+
+
+ 268) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
+ undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
+ with state-dependent encoding that does not assuredly end in the initial shift state.
+
+[page 301]
+
+ multibyte character. The wide character input/output functions and the byte input/output
+ functions store the value of the macro EILSEQ in errno if and only if an encoding error
+ occurs.
+ Environmental limits
+15 The value of FOPEN_MAX shall be at least eight, including the three standard text
+ streams.
+ Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
+ fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
+ (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.29.3.1), the
+ fputwc function (7.29.3.3), conversion state (7.29.6), the mbrtowc function
+ (7.29.6.3.2), the wcrtomb function (7.29.6.3.3).
+ 7.21.4 Operations on files
+ 7.21.4.1 The remove function
+ Synopsis
+1 #include <stdio.h>
+ int remove(const char *filename);
+ Description
+2 The remove function causes the file whose name is the string pointed to by filename
+ to be no longer accessible by that name. A subsequent attempt to open that file using that
+ name will fail, unless it is created anew. If the file is open, the behavior of the remove
+ function is implementation-defined.
+ Returns
+3 The remove function returns zero if the operation succeeds, nonzero if it fails.
+ 7.21.4.2 The rename function
+ Synopsis
+1 #include <stdio.h>
+ int rename(const char *old, const char *new);
+ Description
+2 The rename function causes the file whose name is the string pointed to by old to be
+ henceforth known by the name given by the string pointed to by new. The file named
+ old is no longer accessible by that name. If a file named by the string pointed to by new
+ exists prior to the call to the rename function, the behavior is implementation-defined.
+
+[page 302]
+
+ Returns
+3 The rename function returns zero if the operation succeeds, nonzero if it fails,269) in
+ which case if the file existed previously it is still known by its original name.
+ 7.21.4.3 The tmpfile function
+ Synopsis
+1 #include <stdio.h>
+ FILE *tmpfile(void);
+ Description
+2 The tmpfile function creates a temporary binary file that is different from any other
+ existing file and that will automatically be removed when it is closed or at program
+ termination. If the program terminates abnormally, whether an open temporary file is
+ removed is implementation-defined. The file is opened for update with "wb+" mode.
+ Recommended practice
+3 It should be possible to open at least TMP_MAX temporary files during the lifetime of the
+ program (this limit may be shared with tmpnam) and there should be no limit on the
+ number simultaneously open other than this limit and any limit on the number of open
+ files (FOPEN_MAX).
+ Returns
+4 The tmpfile function returns a pointer to the stream of the file that it created. If the file
+ cannot be created, the tmpfile function returns a null pointer.
+ Forward references: the fopen function (7.21.5.3).
+ 7.21.4.4 The tmpnam function
+ Synopsis
+1 #include <stdio.h>
+ char *tmpnam(char *s);
+ Description
+2 The tmpnam function generates a string that is a valid file name and that is not the same
+ as the name of an existing file.270) The function is potentially capable of generating at
+
+
+ 269) 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.
+ 270) Files created using strings generated by the tmpnam function are temporary only in the sense that
+ their names should not collide with those generated by conventional naming rules for the
+ implementation. It is still necessary to use the remove function to remove such files when their use
+ is ended, and before program termination.
+
+[page 303]
+
+ least TMP_MAX different strings, but any or all of them may already be in use by existing
+ files and thus not be suitable return values.
+3 The tmpnam function generates a different string each time it is called.
+4 Calls to the tmpnam function with a null pointer argument may introduce data races with
+ each other. The implementation shall behave as if no library function calls the tmpnam
+ function.
+ Returns
+5 If no suitable string can be generated, the tmpnam function returns a null pointer.
+ Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
+ internal static object and returns a pointer to that object (subsequent calls to the tmpnam
+ function may modify the same object). If the argument is not a null pointer, it is assumed
+ to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
+ in that array and returns the argument as its value.
+ Environmental limits
+6 The value of the macro TMP_MAX shall be at least 25.
+ 7.21.5 File access functions
+ 7.21.5.1 The fclose function
+ Synopsis
+1 #include <stdio.h>
+ int fclose(FILE *stream);
+ Description
+2 A successful call to the fclose function causes the stream pointed to by stream to be
+ flushed and the associated file to be closed. Any unwritten buffered data for the stream
+ are delivered to the host environment to be written to the file; any unread buffered data
+ are discarded. Whether or not the call succeeds, the stream is disassociated from the file
+ and any buffer set by the setbuf or setvbuf function is disassociated from the stream
+ (and deallocated if it was automatically allocated).
+ Returns
+3 The fclose function returns zero if the stream was successfully closed, or EOF if any
+ errors were detected.
+
+[page 304]
+
+ 7.21.5.2 The fflush function
+ Synopsis
+1 #include <stdio.h>
+ int fflush(FILE *stream);
+ Description
+2 If stream points to an output stream or an update stream in which the most recent
+ operation was not input, the fflush function causes any unwritten data for that stream
+ to be delivered to the host environment to be written to the file; otherwise, the behavior is
+ undefined.
+3 If stream is a null pointer, the fflush function performs this flushing action on all
+ streams for which the behavior is defined above.
+ Returns
+4 The fflush function sets the error indicator for the stream and returns EOF if a write
+ error occurs, otherwise it returns zero.
+ Forward references: the fopen function (7.21.5.3).
+ 7.21.5.3 The fopen function
+ Synopsis
+1 #include <stdio.h>
+ FILE *fopen(const char * restrict filename,
+ const char * restrict mode);
+ Description
+2 The fopen function opens the file whose name is the string pointed to by filename,
+ and associates a stream with it.
+3 The argument mode points to a string. If the string is one of the following, the file is
+ open in the indicated mode. Otherwise, the behavior is undefined.271)
+ 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
+
+
+ 271) If the string begins with one of the above sequences, the implementation might choose to ignore the
+ remaining characters, or it might use them to select different kinds of a file (some of which might not
+ conform to the properties in 7.21.2).
+
+[page 305]
+
+ wbx create binary file for writing
+ ab append; open or create binary file for writing at end-of-file
+ r+ open text file for update (reading and writing)
+ w+ truncate to zero length or create text file for update
+ w+x create text file for update
+ a+ append; open or create text file for update, writing at end-of-file
+ r+b or rb+ open binary file for update (reading and writing)
+ w+b or wb+ truncate to zero length or create binary file for update
+ w+bx or wb+x create binary file for update
+ a+b or ab+ append; open or create binary file for update, writing at end-of-file
+4 Opening a file with read mode ('r' as the first character in the mode argument) fails if
+ the file does not exist or cannot be read.
+5 Opening a file with exclusive mode ('x' as the last character in the mode argument)
+ fails if the file already exists or cannot be created. Otherwise, the file is created with
+ exclusive (also known as non-shared) access to the extent that the underlying system
+ supports exclusive access.
+6 Opening a file with append mode ('a' as the first character in the mode argument)
+ causes all subsequent writes to the file to be forced to the then current end-of-file,
+ regardless of intervening calls to the fseek function. In some implementations, opening
+ a binary file with append mode ('b' as the second or third character in the above list of
+ mode argument values) may initially position the file position indicator for the stream
+ beyond the last data written, because of null character padding.
+7 When a file is opened with update mode ('+' as the second or third character in the
+ above list of mode argument values), both input and output may be performed on the
+ associated stream. However, output shall not be directly followed by input without an
+ intervening call to the fflush function or to a file positioning function (fseek,
+ fsetpos, or rewind), and input shall not be directly followed by output without an
+ intervening call to a file positioning function, unless the input operation encounters end-
+ of-file. Opening (or creating) a text file with update mode may instead open (or create) a
+ binary stream in some implementations.
+8 When opened, a stream is fully buffered if and only if it can be determined not to refer to
+ an interactive device. The error and end-of-file indicators for the stream are cleared.
+ Returns
+9 The fopen function returns a pointer to the object controlling the stream. If the open
+ operation fails, fopen returns a null pointer.
+ Forward references: file positioning functions (7.21.9).
+
+[page 306]
+
+ 7.21.5.4 The freopen function
+ Synopsis
+1 #include <stdio.h>
+ FILE *freopen(const char * restrict filename,
+ const char * restrict mode,
+ FILE * restrict stream);
+ Description
+2 The freopen function opens the file whose name is the string pointed to by filename
+ and associates the stream pointed to by stream with it. The mode argument is used just
+ as in the fopen function.272)
+3 If filename is a null pointer, the freopen function attempts to change the mode of
+ the stream to that specified by mode, as if the name of the file currently associated with
+ the stream had been used. It is implementation-defined which changes of mode are
+ permitted (if any), and under what circumstances.
+4 The freopen function first attempts to close any file that is associated with the specified
+ stream. Failure to close the file is ignored. The error and end-of-file indicators for the
+ stream are cleared.
+ Returns
+5 The freopen function returns a null pointer if the open operation fails. Otherwise,
+ freopen returns the value of stream.
+ 7.21.5.5 The setbuf function
+ Synopsis
+1 #include <stdio.h>
+ void setbuf(FILE * restrict stream,
+ char * restrict buf);
+ Description
+2 Except that it returns no value, the setbuf function is equivalent to the setvbuf
+ function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
+ is a null pointer), with the value _IONBF for mode.
+
+
+
+
+ 272) The primary use of the freopen function is to change the file associated with a standard text stream
+ (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
+ returned by the fopen function may be assigned.
+
+[page 307]
+
+ Returns
+3 The setbuf function returns no value.
+ Forward references: the setvbuf function (7.21.5.6).
+ 7.21.5.6 The setvbuf function
+ Synopsis
+1 #include <stdio.h>
+ int setvbuf(FILE * restrict stream,
+ char * restrict buf,
+ int mode, size_t size);
+ Description
+2 The setvbuf function may be used only after the stream pointed to by stream has
+ been associated with an open file and before any other operation (other than an
+ unsuccessful call to setvbuf) is performed on the stream. The argument mode
+ determines how stream will be buffered, as follows: _IOFBF causes input/output to be
+ fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
+ input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
+ used instead of a buffer allocated by the setvbuf function273) and the argument size
+ specifies the size of the array; otherwise, size may determine the size of a buffer
+ allocated by the setvbuf function. The contents of the array at any time are
+ indeterminate.
+ Returns
+3 The setvbuf function returns zero on success, or nonzero if an invalid value is given
+ for mode or if the request cannot be honored.
+
+
+
+
+ 273) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
+ before a buffer that has automatic storage duration is deallocated upon block exit.
+
+[page 308]
+
+ 7.21.6 Formatted input/output functions
+1 The formatted input/output functions shall behave as if there is a sequence point after the
+ actions associated with each specifier.274)
+ 7.21.6.1 The fprintf function
+ Synopsis
+1 #include <stdio.h>
+ int fprintf(FILE * restrict stream,
+ const char * restrict format, ...);
+ Description
+2 The fprintf function writes output to the stream pointed to by stream, under control
+ of the string pointed to by format that specifies how subsequent arguments are
+ converted for output. If there are insufficient arguments for the format, the behavior is
+ undefined. If the format is exhausted while arguments remain, the excess arguments are
+ evaluated (as always) but are otherwise ignored. The fprintf function returns when
+ the end of the format string is encountered.
+3 The format shall be a multibyte character sequence, beginning and ending in its initial
+ shift state. The format is composed of zero or more directives: ordinary multibyte
+ characters (not %), which are copied unchanged to the output stream; and conversion
+ specifications, each of which results in fetching zero or more subsequent arguments,
+ converting them, if applicable, according to the corresponding conversion specifier, and
+ then writing the result to the output stream.
+4 Each conversion specification is introduced by the character %. After the %, the following
+ appear in sequence:
+ -- Zero or more flags (in any order) that modify the meaning of the conversion
+ specification.
+ -- An optional minimum field width. If the converted value has fewer characters than the
+ field width, it is padded with spaces (by default) on the left (or right, if the left
+ adjustment flag, described later, has been given) to the field width. The field width
+ takes the form of an asterisk * (described later) or a nonnegative decimal integer.275)
+ -- An optional precision that gives the minimum number of digits to appear for the d, i,
+ o, u, x, and X conversions, the number of digits to appear after the decimal-point
+ character for a, A, e, E, f, and F conversions, the maximum number of significant
+ digits for the g and G conversions, or the maximum number of bytes to be written for
+
+
+ 274) The fprintf functions perform writes to memory for the %n specifier.
+ 275) Note that 0 is taken as a flag, not as the beginning of a field width.
+
+[page 309]
+
+ s conversions. The precision takes the form of a period (.) followed either by an
+ asterisk * (described later) or by an optional decimal integer; if only the period is
+ specified, the precision is taken as zero. If a precision appears with any other
+ conversion specifier, the behavior is undefined.
+ -- An optional length modifier that specifies the size of the argument.
+ -- A conversion specifier character that specifies the type of conversion to be applied.
+5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
+ this case, an int argument supplies the field width or precision. The arguments
+ specifying field width, or precision, or both, shall appear (in that order) before the
+ argument (if any) to be converted. A negative field width argument is taken as a - flag
+ followed by a positive field width. A negative precision argument is taken as if the
+ precision were omitted.
+6 The flag characters and their meanings are:
+ - The result of the conversion is left-justified within the field. (It is right-justified if
+ this flag is not specified.)
+ + The result of a signed conversion always begins with a plus or minus sign. (It
+ begins with a sign only when a negative value is converted if this flag is not
+ specified.)276)
+ 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
+
+
+ 276) The results of all floating conversions of a negative zero, and of negative values that round to zero,
+ include a minus sign.
+
+[page 310]
+
+ conversions, if a precision is specified, the 0 flag is ignored. For other
+ conversions, the behavior is undefined.
+7 The length modifiers and their meanings are:
+ hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ signed char or unsigned char argument (the argument will have
+ been promoted according to the integer promotions, but its value shall be
+ converted to signed char or unsigned char before printing); or that
+ a following n conversion specifier applies to a pointer to a signed char
+ argument.
+ h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ short int or unsigned short int argument (the argument will
+ have been promoted according to the integer promotions, but its value shall
+ be converted to short int or unsigned short int before printing);
+ or that a following n conversion specifier applies to a pointer to a short
+ int argument.
+ l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ long int or unsigned long int argument; that a following n
+ conversion specifier applies to a pointer to a long int argument; that a
+ following c conversion specifier applies to a wint_t argument; that a
+ following s conversion specifier applies to a pointer to a wchar_t
+ argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
+ specifier.
+ ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ long long int or unsigned long long int argument; or that a
+ following n conversion specifier applies to a pointer to a long long int
+ argument.
+ j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
+ an intmax_t or uintmax_t argument; or that a following n conversion
+ specifier applies to a pointer to an intmax_t argument.
+ z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ size_t or the corresponding signed integer type argument; or that a
+ following n conversion specifier applies to a pointer to a signed integer type
+ corresponding to size_t argument.
+ t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ ptrdiff_t or the corresponding unsigned integer type argument; or that a
+ following n conversion specifier applies to a pointer to a ptrdiff_t
+ argument.
+
+[page 311]
+
+ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
+ applies to a long double argument.
+ If a length modifier appears with any conversion specifier other than as specified above,
+ the behavior is undefined.
+8 The conversion specifiers and their meanings are:
+ d,i The int argument is converted to signed decimal in the style [-]dddd. The
+ precision specifies the minimum number of digits to appear; if the value
+ being converted can be represented in fewer digits, it is expanded with
+ leading zeros. The default precision is 1. The result of converting a zero
+ value with a precision of zero is no characters.
+ o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
+ decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
+ letters abcdef are used for x conversion and the letters ABCDEF for X
+ conversion. The precision specifies the minimum number of digits to appear;
+ if the value being converted can be represented in fewer digits, it is expanded
+ with leading zeros. The default precision is 1. The result of converting a
+ zero value with a precision of zero is no characters.
+ f,F A double argument representing a floating-point number is converted to
+ decimal notation in the style [-]ddd.ddd, where the number of digits after
+ the decimal-point character is equal to the precision specification. If the
+ precision is missing, it is taken as 6; if the precision is zero and the # flag is
+ not specified, no decimal-point character appears. If a decimal-point
+ character appears, at least one digit appears before it. The value is rounded to
+ the appropriate number of digits.
+ A double argument representing an infinity is converted in one of the styles
+ [-]inf or [-]infinity -- which style is implementation-defined. A
+ double argument representing a NaN is converted in one of the styles
+ [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
+ any n-char-sequence, is implementation-defined. The F conversion specifier
+ produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
+ respectively.277)
+ 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
+
+
+ 277) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
+ the # and 0 flag characters have no effect.
+
+[page 312]
+
+ 6; if the precision is zero and the # flag is not specified, no decimal-point
+ character appears. The value is rounded to the appropriate number of digits.
+ The E conversion specifier produces a number with E instead of e
+ introducing the exponent. The exponent always contains at least two digits,
+ and only as many more digits as necessary to represent the exponent. If the
+ value is zero, the exponent is zero.
+ A double argument representing an infinity or NaN is converted in the style
+ of an f or F conversion specifier.
+g,G A double argument representing a floating-point number is converted in
+ style f or e (or in style F or E in the case of a G conversion specifier),
+ depending on the value converted and the precision. Let P equal the
+ precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
+ Then, if a conversion with style E would have an exponent of X:
+ -- if P > X >= -4, the conversion is with style f (or F) and precision
+ P - (X + 1).
+ -- otherwise, the conversion is with style e (or E) and precision P - 1.
+ Finally, unless the # flag is used, any trailing zeros are removed from the
+ fractional portion of the result and the decimal-point character is removed if
+ there is no fractional portion remaining.
+ A double argument representing an infinity or NaN is converted in the style
+ of an f or F conversion specifier.
+a,A A double argument representing a floating-point number is converted in the
+ style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
+ nonzero if the argument is a normalized floating-point number and is
+ otherwise unspecified) before the decimal-point character278) 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
+
+
+
+
+278) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
+ that subsequent digits align to nibble (4-bit) boundaries.
+
+[page 313]
+
+ distinguish279) 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.280) 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
+
+279) 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.
+280) No special provisions are made for multibyte characters.
+
+[page 314]
+
+ the precision, the function would need to access a wide character one past the
+ end of the array. In no case is a partial multibyte character written.281)
+ p The argument shall be a pointer to void. The value of the pointer is
+ converted to a sequence of printing characters, in an implementation-defined
+ manner.
+ n The argument shall be a pointer to signed integer into which is written the
+ number of characters written to the output stream so far by this call to
+ fprintf. No argument is converted, but one is consumed. If the conversion
+ specification includes any flags, a field width, or a precision, the behavior is
+ undefined.
+ % A % character is written. No argument is converted. The complete
+ conversion specification shall be %%.
+9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is
+ not the correct type for the corresponding conversion specification, the behavior is
+ undefined.
+10 In no case does a nonexistent or small field width cause truncation of a field; if the result
+ of a conversion is wider than the field width, the field is expanded to contain the
+ conversion result.
+11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
+ to a hexadecimal floating number with the given precision.
+ Recommended practice
+12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
+ representable in the given precision, the result should be one of the two adjacent numbers
+ in hexadecimal floating style with the given precision, with the extra stipulation that the
+ error should have a correct sign for the current rounding direction.
+13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
+ DECIMAL_DIG, then the result should be correctly rounded.283) 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
+
+
+ 281) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
+ 282) See ''future library directions'' (7.31.11).
+ 283) For binary-to-decimal conversion, the result format's values are the numbers representable with the
+ given format specifier. The number of significant digits is determined by the format specifier, and in
+ the case of fixed-point conversion by the source value as well.
+
+[page 315]
+
+ of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
+ the error should have a correct sign for the current rounding direction.
+ Returns
+14 The fprintf function returns the number of characters transmitted, or a negative value
+ if an output or encoding error occurred.
+ Environmental limits
+15 The number of characters that can be produced by any single conversion shall be at least
+ 4095.
+16 EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
+ places:
+ #include <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));
+
+17 EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
+ members of the extended character set that consist of more than one byte each consist of exactly two bytes,
+ the first of which is denoted here by a and the second by an uppercase letter.
+18 Given the following wide string with length seven,
+ static wchar_t wstr[] = L" X Yabc Z W";
+ the seven calls
+ fprintf(stdout, "|1234567890123|\n");
+ fprintf(stdout, "|%13ls|\n", wstr);
+ fprintf(stdout, "|%-13.9ls|\n", wstr);
+ fprintf(stdout, "|%13.10ls|\n", wstr);
+ fprintf(stdout, "|%13.11ls|\n", wstr);
+ fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
+ fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
+ will print the following seven lines:
+ |1234567890123|
+ | X Yabc Z W|
+ | X Yabc Z |
+ | X Yabc Z|
+ | X Yabc Z W|
+ | abc Z W|
+ | Z|
+
+ Forward references: conversion state (7.29.6), the wcrtomb function (7.29.6.3.3).
+
+[page 316]
+
+ 7.21.6.2 The fscanf function
+ Synopsis
+1 #include <stdio.h>
+ int fscanf(FILE * restrict stream,
+ const char * restrict format, ...);
+ Description
+2 The fscanf function reads input from the stream pointed to by stream, under control
+ of the string pointed to by format that specifies the admissible input sequences and how
+ they are to be converted for assignment, using subsequent arguments as pointers to the
+ objects to receive the converted input. If there are insufficient arguments for the format,
+ the behavior is undefined. If the format is exhausted while arguments remain, the excess
+ arguments are evaluated (as always) but are otherwise ignored.
+3 The format shall be a multibyte character sequence, beginning and ending in its initial
+ shift state. The format is composed of zero or more directives: one or more white-space
+ characters, an ordinary multibyte character (neither % nor a white-space character), or a
+ conversion specification. Each conversion specification is introduced by the character %.
+ After the %, the following appear in sequence:
+ -- An optional assignment-suppressing character *.
+ -- An optional decimal integer greater than zero that specifies the maximum field width
+ (in characters).
+ -- An optional length modifier that specifies the size of the receiving object.
+ -- A conversion specifier character that specifies the type of conversion to be applied.
+4 The fscanf function executes each directive of the format in turn. When all directives
+ have been executed, or if a directive fails (as detailed below), the function returns.
+ Failures are described as input failures (due to the occurrence of an encoding error or the
+ unavailability of input characters), or matching failures (due to inappropriate input).
+5 A directive composed of white-space character(s) is executed by reading input up to the
+ first non-white-space character (which remains unread), or until no more characters can
+ be read. The directive never fails.
+6 A directive that is an ordinary multibyte character is executed by reading the next
+ characters of the stream. If any of those characters differ from the ones composing the
+ directive, the directive fails and the differing and subsequent characters remain unread.
+ Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
+ read, the directive fails.
+7 A directive that is a conversion specification defines a set of matching input sequences, as
+ described below for each specifier. A conversion specification is executed in the
+
+[page 317]
+
+ following steps:
+8 Input white-space characters (as specified by the isspace function) are skipped, unless
+ the specification includes a [, c, or n specifier.284)
+9 An input item is read from the stream, unless the specification includes an n specifier. An
+ input item is defined as the longest sequence of input characters which does not exceed
+ any specified field width and which is, or is a prefix of, a matching input sequence.285)
+ The first character, if any, after the input item remains unread. If the length of the input
+ item is zero, the execution of the directive fails; this condition is a matching failure unless
+ end-of-file, an encoding error, or a read error prevented input from the stream, in which
+ case it is an input failure.
+10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
+ count of input characters) is converted to a type appropriate to the conversion specifier. If
+ the input item is not a matching sequence, the execution of the directive fails: this
+ condition is a matching failure. Unless assignment suppression was indicated by a *, the
+ result of the conversion is placed in the object pointed to by the first argument following
+ the format argument that has not already received a conversion result. If this object
+ does not have an appropriate type, or if the result of the conversion cannot be represented
+ in the object, the behavior is undefined.
+11 The length modifiers and their meanings are:
+ hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to signed char or unsigned char.
+ h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to short int or unsigned short
+ int.
+ l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to long int or unsigned long
+ int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
+ an argument with type pointer to double; or that a following c, s, or [
+ conversion specifier applies to an argument with type pointer to wchar_t.
+ ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to long long int or unsigned
+ long long int.
+
+
+
+ 284) These white-space characters are not counted against a specified field width.
+ 285) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
+ that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
+
+[page 318]
+
+ j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to intmax_t or uintmax_t.
+ z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to size_t or the corresponding signed
+ integer type.
+ t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to ptrdiff_t or the corresponding
+ unsigned integer type.
+ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
+ applies to an argument with type pointer to long double.
+ If a length modifier appears with any conversion specifier other than as specified above,
+ the behavior is undefined.
+12 The conversion specifiers and their meanings are:
+ d Matches an optionally signed decimal integer, whose format is the same as
+ expected for the subject sequence of the strtol function with the value 10
+ for the base argument. The corresponding argument shall be a pointer to
+ signed integer.
+ i Matches an optionally signed integer, whose format is the same as expected
+ for the subject sequence of the strtol function with the value 0 for the
+ base argument. The corresponding argument shall be a pointer to signed
+ integer.
+ o Matches an optionally signed octal integer, whose format is the same as
+ expected for the subject sequence of the strtoul function with the value 8
+ for the base argument. The corresponding argument shall be a pointer to
+ unsigned integer.
+ u Matches an optionally signed decimal integer, whose format is the same as
+ expected for the subject sequence of the strtoul function with the value 10
+ for the base argument. The corresponding argument shall be a pointer to
+ unsigned integer.
+ x Matches an optionally signed hexadecimal integer, whose format is the same
+ as expected for the subject sequence of the strtoul function with the value
+ 16 for the base argument. The corresponding argument shall be a pointer to
+ unsigned integer.
+ a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
+ format is the same as expected for the subject sequence of the strtod
+ function. The corresponding argument shall be a pointer to floating.
+
+[page 319]
+
+c Matches a sequence of characters of exactly the number specified by the field
+ width (1 if no field width is present in the directive).286)
+ 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.286)
+ 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).286)
+ 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
+
+286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
+ conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
+ resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
+
+[page 320]
+
+ before the first multibyte character is converted. The corresponding argument
+ shall be a pointer to the initial element of an array of wchar_t large enough
+ to accept the sequence and the terminating null wide character, which will be
+ added automatically.
+ The conversion specifier includes all subsequent characters in the format
+ string, up to and including the matching right bracket (]). The characters
+ between the brackets (the scanlist) compose the scanset, unless the character
+ after the left bracket is a circumflex (^), in which case the scanset contains all
+ characters that do not appear in the scanlist between the circumflex and the
+ right bracket. If the conversion specifier begins with [] or [^], the right
+ bracket character is in the scanlist and the next following right bracket
+ character is the matching right bracket that ends the specification; otherwise
+ the first following right bracket character is the one that ends the
+ specification. If a - character is in the scanlist and is not the first, nor the
+ second where the first character is a ^, nor the last character, the behavior is
+ implementation-defined.
+ p Matches an implementation-defined set of sequences, which should be the
+ same as the set of sequences that may be produced by the %p conversion of
+ the fprintf function. The corresponding argument shall be a pointer to a
+ pointer to void. The input item is converted to a pointer value in an
+ implementation-defined manner. If the input item is a value converted earlier
+ during the same program execution, the pointer that results shall compare
+ equal to that value; otherwise the behavior of the %p conversion is undefined.
+ n No input is consumed. The corresponding argument shall be a pointer to
+ signed integer into which is to be written the number of characters read from
+ the input stream so far by this call to the fscanf function. Execution of a
+ %n directive does not increment the assignment count returned at the
+ completion of execution of the fscanf function. No argument is converted,
+ but one is consumed. If the conversion specification includes an assignment-
+ suppressing character or a field width, the behavior is undefined.
+ % Matches a single % character; no conversion or assignment occurs. The
+ complete conversion specification shall be %%.
+13 If a conversion specification is invalid, the behavior is undefined.287)
+14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
+ respectively, a, e, f, g, and x.
+
+
+
+ 287) See ''future library directions'' (7.31.11).
+
+[page 321]
+
+15 Trailing white space (including new-line characters) is left unread unless matched by a
+ directive. The success of literal matches and suppressed assignments is not directly
+ determinable other than via the %n directive.
+ Returns
+16 The fscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the function returns the
+ number of input items assigned, which can be fewer than provided for, or even zero, in
+ the event of an early matching failure.
+17 EXAMPLE 1 The call:
+ #include <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.
+
+18 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.
+
+19 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));
+20 If the stdin stream contains the following lines:
+ 2 quarts of oil
+ -12.8degrees Celsius
+ lots of luck
+ 10.0LBS of
+ dirt
+ 100ergs of energy
+
+[page 322]
+
+ the execution of the above example will be analogous to the following assignments:
+ quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
+ count = 3;
+ quant = -12.8; strcpy(units, "degrees");
+ count = 2; // "C" fails to match "o"
+ count = 0; // "l" fails to match "%f"
+ quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
+ count = 3;
+ count = 0; // "100e" fails to match "%f"
+ count = EOF;
+
+21 EXAMPLE 4 In:
+ #include <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.
+
+22 EXAMPLE 5 The call:
+ #include <stdio.h>
+ /* ... */
+ int n, i;
+ n = sscanf("foo % bar 42", "foo%%bar%d", &i);
+ will assign to n the value 1 and to i the value 42 because input white-space characters are skipped for both
+ the % and d conversion specifiers.
+
+23 EXAMPLE 6 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.
+24 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.
+25 In contrast, after the call:
+
+[page 323]
+
+ #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.
+26 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.
+27 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
+ (7.29.6), the wcrtomb function (7.29.6.3.3).
+ 7.21.6.3 The printf function
+ Synopsis
+1 #include <stdio.h>
+ int printf(const char * restrict format, ...);
+ Description
+2 The printf function is equivalent to fprintf with the argument stdout interposed
+ before the arguments to printf.
+ Returns
+3 The printf function returns the number of characters transmitted, or a negative value if
+ an output or encoding error occurred.
+
+[page 324]
+
+ 7.21.6.4 The scanf function
+ Synopsis
+1 #include <stdio.h>
+ int scanf(const char * restrict format, ...);
+ Description
+2 The scanf function is equivalent to fscanf with the argument stdin interposed
+ before the arguments to scanf.
+ Returns
+3 The scanf function returns the value of the macro EOF if an input failure occurs before
+ the first conversion (if any) has completed. Otherwise, the scanf function returns the
+ number of input items assigned, which can be fewer than provided for, or even zero, in
+ the event of an early matching failure.
+ 7.21.6.5 The snprintf function
+ Synopsis
+1 #include <stdio.h>
+ int snprintf(char * restrict s, size_t n,
+ const char * restrict format, ...);
+ Description
+2 The snprintf function is equivalent to fprintf, except that the output is written into
+ an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
+ and s may be a null pointer. Otherwise, output characters beyond the n-1st are
+ discarded rather than being written to the array, and a null character is written at the end
+ of the characters actually written into the array. If copying takes place between objects
+ that overlap, the behavior is undefined.
+ Returns
+3 The snprintf function returns the number of characters that would have been written
+ had n been sufficiently large, not counting the terminating null character, or a negative
+ value if an encoding error occurred. Thus, the null-terminated output has been
+ completely written if and only if the returned value is nonnegative and less than n.
+ 7.21.6.6 The sprintf function
+ Synopsis
+1 #include <stdio.h>
+ int sprintf(char * restrict s,
+ const char * restrict format, ...);
+
+[page 325]
+
+ Description
+2 The sprintf function is equivalent to fprintf, except that the output is written into
+ an array (specified by the argument s) rather than to a stream. A null character is written
+ at the end of the characters written; it is not counted as part of the returned value. If
+ copying takes place between objects that overlap, the behavior is undefined.
+ Returns
+3 The sprintf function returns the number of characters written in the array, not
+ counting the terminating null character, or a negative value if an encoding error occurred.
+ 7.21.6.7 The sscanf function
+ Synopsis
+1 #include <stdio.h>
+ int sscanf(const char * restrict s,
+ const char * restrict format, ...);
+ Description
+2 The sscanf function is equivalent to fscanf, except that input is obtained from a
+ string (specified by the argument s) rather than from a stream. Reaching the end of the
+ string is equivalent to encountering end-of-file for the fscanf function. If copying
+ takes place between objects that overlap, the behavior is undefined.
+ Returns
+3 The sscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the sscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+ 7.21.6.8 The vfprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vfprintf(FILE * restrict stream,
+ const char * restrict format,
+ va_list arg);
+ Description
+2 The vfprintf function is equivalent to fprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfprintf function does not invoke the
+
+[page 326]
+
+ va_end macro.288)
+ Returns
+3 The vfprintf function returns the number of characters transmitted, or a negative
+ value if an output or encoding error occurred.
+4 EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine.
+ #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);
+ }
+
+ 7.21.6.9 The vfscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vfscanf(FILE * restrict stream,
+ const char * restrict format,
+ va_list arg);
+ Description
+2 The vfscanf function is equivalent to fscanf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfscanf function does not invoke the
+ va_end macro.288)
+ Returns
+3 The vfscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vfscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+
+
+
+ 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
+ vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
+
+[page 327]
+
+ 7.21.6.10 The vprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vprintf(const char * restrict format,
+ va_list arg);
+ Description
+2 The vprintf function is equivalent to printf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vprintf function does not invoke the
+ va_end macro.288)
+ Returns
+3 The vprintf function returns the number of characters transmitted, or a negative value
+ if an output or encoding error occurred.
+ 7.21.6.11 The vscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vscanf(const char * restrict format,
+ va_list arg);
+ Description
+2 The vscanf function is equivalent to scanf, with the variable argument list replaced
+ by arg, which shall have been initialized by the va_start macro (and possibly
+ subsequent va_arg calls). The vscanf function does not invoke the va_end
+ macro.288)
+ Returns
+3 The vscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+
+[page 328]
+
+ 7.21.6.12 The vsnprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vsnprintf(char * restrict s, size_t n,
+ const char * restrict format,
+ va_list arg);
+ Description
+2 The vsnprintf function is equivalent to snprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vsnprintf function does not invoke the
+ va_end macro.288) If copying takes place between objects that overlap, the behavior is
+ undefined.
+ Returns
+3 The vsnprintf function returns the number of characters that would have been written
+ had n been sufficiently large, not counting the terminating null character, or a negative
+ value if an encoding error occurred. Thus, the null-terminated output has been
+ completely written if and only if the returned value is nonnegative and less than n.
+ 7.21.6.13 The vsprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vsprintf(char * restrict s,
+ const char * restrict format,
+ va_list arg);
+ Description
+2 The vsprintf function is equivalent to sprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vsprintf function does not invoke the
+ va_end macro.288) If copying takes place between objects that overlap, the behavior is
+ undefined.
+ Returns
+3 The vsprintf function returns the number of characters written in the array, not
+ counting the terminating null character, or a negative value if an encoding error occurred.
+
+[page 329]
+
+ 7.21.6.14 The vsscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ int vsscanf(const char * restrict s,
+ const char * restrict format,
+ va_list arg);
+ Description
+2 The vsscanf function is equivalent to sscanf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vsscanf function does not invoke the
+ va_end macro.288)
+ Returns
+3 The vsscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vsscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+ 7.21.7 Character input/output functions
+ 7.21.7.1 The fgetc function
+ Synopsis
+1 #include <stdio.h>
+ int fgetc(FILE *stream);
+ Description
+2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
+ next character is present, the fgetc function obtains that character as an unsigned
+ char converted to an int and advances the associated file position indicator for the
+ stream (if defined).
+ Returns
+3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
+ of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
+ fgetc function returns the next character from the input stream pointed to by stream.
+ If a read error occurs, the error indicator for the stream is set and the fgetc function
+ returns EOF.289)
+
+
+ 289) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
+
+[page 330]
+
+ 7.21.7.2 The fgets function
+ Synopsis
+1 #include <stdio.h>
+ char *fgets(char * restrict s, int n,
+ FILE * restrict stream);
+ Description
+2 The fgets function reads at most one less than the number of characters specified by n
+ from the stream pointed to by stream into the array pointed to by s. No additional
+ characters are read after a new-line character (which is retained) or after end-of-file. A
+ null character is written immediately after the last character read into the array.
+ Returns
+3 The fgets function returns s if successful. If end-of-file is encountered and no
+ characters have been read into the array, the contents of the array remain unchanged and a
+ null pointer is returned. If a read error occurs during the operation, the array contents are
+ indeterminate and a null pointer is returned.
+ 7.21.7.3 The fputc function
+ Synopsis
+1 #include <stdio.h>
+ int fputc(int c, FILE *stream);
+ Description
+2 The fputc function writes the character specified by c (converted to an unsigned
+ char) to the output stream pointed to by stream, at the position indicated by the
+ associated file position indicator for the stream (if defined), and advances the indicator
+ appropriately. If the file cannot support positioning requests, or if the stream was opened
+ with append mode, the character is appended to the output stream.
+ Returns
+3 The fputc function returns the character written. If a write error occurs, the error
+ indicator for the stream is set and fputc returns EOF.
+ 7.21.7.4 The fputs function
+ Synopsis
+1 #include <stdio.h>
+ int fputs(const char * restrict s,
+ FILE * restrict stream);
+
+[page 331]
+
+ Description
+2 The fputs function writes the string pointed to by s to the stream pointed to by
+ stream. The terminating null character is not written.
+ Returns
+3 The fputs function returns EOF if a write error occurs; otherwise it returns a
+ nonnegative value.
+ 7.21.7.5 The getc function
+ Synopsis
+1 #include <stdio.h>
+ int getc(FILE *stream);
+ Description
+2 The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
+ may evaluate stream more than once, so the argument should never be an expression
+ with side effects.
+ Returns
+3 The getc function returns the next character from the input stream pointed to by
+ stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
+ getc returns EOF. If a read error occurs, the error indicator for the stream is set and
+ getc returns EOF.
+ 7.21.7.6 The getchar function
+ Synopsis
+1 #include <stdio.h>
+ int getchar(void);
+ Description
+2 The getchar function is equivalent to getc with the argument stdin.
+ Returns
+3 The getchar function returns the next character from the input stream pointed to by
+ stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
+ getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
+ getchar returns EOF.
+
+[page 332]
+
+ 7.21.7.7 The putc function
+ Synopsis
+1 #include <stdio.h>
+ int putc(int c, FILE *stream);
+ Description
+2 The putc function is equivalent to fputc, except that if it is implemented as a macro, it
+ may evaluate stream more than once, so that argument should never be an expression
+ with side effects.
+ Returns
+3 The putc function returns the character written. If a write error occurs, the error
+ indicator for the stream is set and putc returns EOF.
+ 7.21.7.8 The putchar function
+ Synopsis
+1 #include <stdio.h>
+ int putchar(int c);
+ Description
+2 The putchar function is equivalent to putc with the second argument stdout.
+ Returns
+3 The putchar function returns the character written. If a write error occurs, the error
+ indicator for the stream is set and putchar returns EOF.
+ 7.21.7.9 The puts function
+ Synopsis
+1 #include <stdio.h>
+ int puts(const char *s);
+ Description
+2 The puts function writes the string pointed to by s to the stream pointed to by stdout,
+ and appends a new-line character to the output. The terminating null character is not
+ written.
+ Returns
+3 The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
+ value.
+
+[page 333]
+
+ 7.21.7.10 The ungetc function
+ Synopsis
+1 #include <stdio.h>
+ int ungetc(int c, FILE *stream);
+ Description
+2 The ungetc function pushes the character specified by c (converted to an unsigned
+ char) back onto the input stream pointed to by stream. Pushed-back characters will be
+ returned by subsequent reads on that stream in the reverse order of their pushing. A
+ successful intervening call (with the stream pointed to by stream) to a file positioning
+ function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
+ stream. The external storage corresponding to the stream is unchanged.
+3 One character of pushback is guaranteed. If the ungetc function is called too many
+ times on the same stream without an intervening read or file positioning operation on that
+ stream, the operation may fail.
+4 If the value of c equals that of the macro EOF, the operation fails and the input stream is
+ unchanged.
+5 A successful call to the ungetc function clears the end-of-file indicator for the stream.
+ The value of the file position indicator for the stream after reading or discarding all
+ pushed-back characters shall be the same as it was before the characters were pushed
+ back. For a text stream, the value of its file position indicator after a successful call to the
+ ungetc function is unspecified until all pushed-back characters are read or discarded.
+ 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.290)
+ Returns
+6 The ungetc function returns the character pushed back after conversion, or EOF if the
+ operation fails.
+ Forward references: file positioning functions (7.21.9).
+
+
+
+
+ 290) See ''future library directions'' (7.31.11).
+
+[page 334]
+
+ 7.21.8 Direct input/output functions
+ 7.21.8.1 The fread function
+ Synopsis
+1 #include <stdio.h>
+ size_t fread(void * restrict ptr,
+ size_t size, size_t nmemb,
+ FILE * restrict stream);
+ Description
+2 The fread function reads, into the array pointed to by ptr, up to nmemb elements
+ whose size is specified by size, from the stream pointed to by stream. For each
+ object, size calls are made to the fgetc function and the results stored, in the order
+ read, in an array of unsigned char exactly overlaying the object. The file position
+ indicator for the stream (if defined) is advanced by the number of characters successfully
+ read. If an error occurs, the resulting value of the file position indicator for the stream is
+ indeterminate. If a partial element is read, its value is indeterminate.
+ Returns
+3 The fread function returns the number of elements successfully read, which may be
+ less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
+ fread returns zero and the contents of the array and the state of the stream remain
+ unchanged.
+ 7.21.8.2 The fwrite function
+ Synopsis
+1 #include <stdio.h>
+ size_t fwrite(const void * restrict ptr,
+ size_t size, size_t nmemb,
+ FILE * restrict stream);
+ Description
+2 The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
+ whose size is specified by size, to the stream pointed to by stream. For each object,
+ size calls are made to the fputc function, taking the values (in order) from an array of
+ unsigned char exactly overlaying the object. The file position indicator for the
+ stream (if defined) is advanced by the number of characters successfully written. If an
+ error occurs, the resulting value of the file position indicator for the stream is
+ indeterminate.
+
+[page 335]
+
+ Returns
+3 The fwrite function returns the number of elements successfully written, which will be
+ less than nmemb only if a write error is encountered. If size or nmemb is zero,
+ fwrite returns zero and the state of the stream remains unchanged.
+ 7.21.9 File positioning functions
+ 7.21.9.1 The fgetpos function
+ Synopsis
+1 #include <stdio.h>
+ int fgetpos(FILE * restrict stream,
+ fpos_t * restrict pos);
+ Description
+2 The fgetpos function stores the current values of the parse state (if any) and file
+ position indicator for the stream pointed to by stream in the object pointed to by pos.
+ The values stored contain unspecified information usable by the fsetpos function for
+ repositioning the stream to its position at the time of the call to the fgetpos function.
+ Returns
+3 If successful, the fgetpos function returns zero; on failure, the fgetpos function
+ returns nonzero and stores an implementation-defined positive value in errno.
+ Forward references: the fsetpos function (7.21.9.3).
+ 7.21.9.2 The fseek function
+ Synopsis
+1 #include <stdio.h>
+ int fseek(FILE *stream, long int offset, int whence);
+ Description
+2 The fseek function sets the file position indicator for the stream pointed to by stream.
+ If a read or write error occurs, the error indicator for the stream is set and fseek fails.
+3 For a binary stream, the new position, measured in characters from the beginning of the
+ file, is obtained by adding offset to the position specified by whence. The specified
+ position is the beginning of the file if whence is SEEK_SET, the current value of the file
+ position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
+ meaningfully support fseek calls with a whence value of SEEK_END.
+4 For a text stream, either offset shall be zero, or offset shall be a value returned by
+ an earlier successful call to the ftell function on a stream associated with the same file
+ and whence shall be SEEK_SET.
+
+[page 336]
+
+5 After determining the new position, a successful call to the fseek function undoes any
+ effects of the ungetc function on the stream, clears the end-of-file indicator for the
+ stream, and then establishes the new position. After a successful fseek call, the next
+ operation on an update stream may be either input or output.
+ Returns
+6 The fseek function returns nonzero only for a request that cannot be satisfied.
+ Forward references: the ftell function (7.21.9.4).
+ 7.21.9.3 The fsetpos function
+ Synopsis
+1 #include <stdio.h>
+ int fsetpos(FILE *stream, const fpos_t *pos);
+ Description
+2 The fsetpos function sets the mbstate_t object (if any) and file position indicator
+ for the stream pointed to by stream according to the value of the object pointed to by
+ pos, which shall be a value obtained from an earlier successful call to the fgetpos
+ function on a stream associated with the same file. If a read or write error occurs, the
+ error indicator for the stream is set and fsetpos fails.
+3 A successful call to the fsetpos function undoes any effects of the ungetc function
+ on the stream, clears the end-of-file indicator for the stream, and then establishes the new
+ parse state and position. After a successful fsetpos call, the next operation on an
+ update stream may be either input or output.
+ Returns
+4 If successful, the fsetpos function returns zero; on failure, the fsetpos function
+ returns nonzero and stores an implementation-defined positive value in errno.
+ 7.21.9.4 The ftell function
+ Synopsis
+1 #include <stdio.h>
+ long int ftell(FILE *stream);
+ Description
+2 The ftell function obtains the current value of the file position indicator for the stream
+ pointed to by stream. For a binary stream, the value is the number of characters from
+ the beginning of the file. For a text stream, its file position indicator contains unspecified
+ information, usable by the fseek function for returning the file position indicator for the
+ stream to its position at the time of the ftell call; the difference between two such
+ return values is not necessarily a meaningful measure of the number of characters written
+
+[page 337]
+
+ or read.
+ Returns
+3 If successful, the ftell function returns the current value of the file position indicator
+ for the stream. On failure, the ftell function returns -1L and stores an
+ implementation-defined positive value in errno.
+ 7.21.9.5 The rewind function
+ Synopsis
+1 #include <stdio.h>
+ void rewind(FILE *stream);
+ Description
+2 The rewind function sets the file position indicator for the stream pointed to by
+ stream to the beginning of the file. It is equivalent to
+ (void)fseek(stream, 0L, SEEK_SET)
+ except that the error indicator for the stream is also cleared.
+ Returns
+3 The rewind function returns no value.
+ 7.21.10 Error-handling functions
+ 7.21.10.1 The clearerr function
+ Synopsis
+1 #include <stdio.h>
+ void clearerr(FILE *stream);
+ Description
+2 The clearerr function clears the end-of-file and error indicators for the stream pointed
+ to by stream.
+ Returns
+3 The clearerr function returns no value.
+
+[page 338]
+
+ 7.21.10.2 The feof function
+ Synopsis
+1 #include <stdio.h>
+ int feof(FILE *stream);
+ Description
+2 The feof function tests the end-of-file indicator for the stream pointed to by stream.
+ Returns
+3 The feof function returns nonzero if and only if the end-of-file indicator is set for
+ stream.
+ 7.21.10.3 The ferror function
+ Synopsis
+1 #include <stdio.h>
+ int ferror(FILE *stream);
+ Description
+2 The ferror function tests the error indicator for the stream pointed to by stream.
+ Returns
+3 The ferror function returns nonzero if and only if the error indicator is set for
+ stream.
+ 7.21.10.4 The perror function
+ Synopsis
+1 #include <stdio.h>
+ void perror(const char *s);
+ Description
+2 The perror function maps the error number in the integer expression errno to an
+ error message. It writes a sequence of characters to the standard error stream thus: first
+ (if s is not a null pointer and the character pointed to by s is not the null character), the
+ string pointed to by s followed by a colon (:) and a space; then an appropriate error
+ message string followed by a new-line character. The contents of the error message
+ strings are the same as those returned by the strerror function with argument errno.
+ Returns
+3 The perror function returns no value.
+ Forward references: the strerror function (7.24.6.2).
+
+[page 339]
+
+ 7.22 General utilities <stdlib.h>
+1 The header <stdlib.h> declares five types and several functions of general utility, and
+ defines several macros.291)
+2 The types declared are size_t and wchar_t (both described in 7.19),
+ div_t
+ which is a structure type that is the type of the value returned by the div function,
+ ldiv_t
+ which is a structure type that is the type of the value returned by the ldiv function, and
+ lldiv_t
+ which is a structure type that is the type of the value returned by the lldiv function.
+3 The macros defined are NULL (described in 7.19);
+ EXIT_FAILURE
+ and
+ EXIT_SUCCESS
+ which expand to integer constant expressions that can be used as the argument to the
+ exit function to return unsuccessful or successful termination status, respectively, to the
+ host environment;
+ RAND_MAX
+ which expands to an integer constant expression that is the maximum value returned by
+ the rand function; and
+ MB_CUR_MAX
+ which expands to a positive integer expression with type size_t that is the maximum
+ number of bytes in a multibyte character for the extended character set specified by the
+ current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.
+
+
+
+
+ 291) See ''future library directions'' (7.31.12).
+
+[page 340]
+
+ 7.22.1 Numeric conversion functions
+1 The functions atof, atoi, atol, and atoll need not affect the value of the integer
+ expression errno on an error. If the value of the result cannot be represented, the
+ behavior is undefined.
+ 7.22.1.1 The atof function
+ Synopsis
+1 #include <stdlib.h>
+ double atof(const char *nptr);
+ Description
+2 The atof function converts the initial portion of the string pointed to by nptr to
+ double representation. Except for the behavior on error, it is equivalent to
+ strtod(nptr, (char **)NULL)
+ Returns
+3 The atof function returns the converted value.
+ Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
+ 7.22.1.2 The atoi, atol, and atoll functions
+ Synopsis
+1 #include <stdlib.h>
+ int atoi(const char *nptr);
+ long int atol(const char *nptr);
+ long long int atoll(const char *nptr);
+ Description
+2 The atoi, atol, and atoll functions convert the initial portion of the string pointed
+ to by nptr to int, long int, and long long int representation, respectively.
+ Except for the behavior on error, they are equivalent to
+ atoi: (int)strtol(nptr, (char **)NULL, 10)
+ atol: strtol(nptr, (char **)NULL, 10)
+ atoll: strtoll(nptr, (char **)NULL, 10)
+ Returns
+3 The atoi, atol, and atoll functions return the converted value.
+ Forward references: the strtol, strtoll, strtoul, and strtoull functions
+ (7.22.1.4).
+
+[page 341]
+
+ 7.22.1.3 The strtod, strtof, and strtold functions
+ Synopsis
+1 #include <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
+2 The strtod, strtof, and strtold functions convert the initial portion of the string
+ pointed to by nptr to double, float, and long double representation,
+ respectively. First, they decompose the input string into three parts: an initial, possibly
+ empty, sequence of white-space characters (as specified by the isspace function), a
+ subject sequence resembling a floating-point constant or representing an infinity or NaN;
+ and a final string of one or more unrecognized characters, including the terminating null
+ character of the input string. Then, they attempt to convert the subject sequence to a
+ floating-point number, and return the result.
+3 The expected form of the subject sequence is an optional plus or minus sign, then one of
+ the following:
+ -- a nonempty sequence of decimal digits optionally containing a decimal-point
+ character, then an optional exponent part as defined in 6.4.4.2;
+ -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
+ decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
+ -- INF or INFINITY, ignoring case
+ -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
+ n-char-sequence:
+ digit
+ nondigit
+ n-char-sequence digit
+ n-char-sequence nondigit
+ The subject sequence is defined as the longest initial subsequence of the input string,
+ starting with the first non-white-space character, that is of the expected form. The subject
+ sequence contains no characters if the input string is not of the expected form.
+4 If the subject sequence has the expected form for a floating-point number, the sequence of
+ characters starting with the first digit or the decimal-point character (whichever occurs
+ first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
+
+[page 342]
+
+ decimal-point character is used in place of a period, and that if neither an exponent part
+ nor a decimal-point character appears in a decimal floating point number, or if a binary
+ exponent part does not appear in a hexadecimal floating point number, an exponent part
+ of the appropriate type with value zero is assumed to follow the last digit in the string. If
+ the subject sequence begins with a minus sign, the sequence is interpreted as negated.292)
+ 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 sequence is implementation-defined.293) A
+ pointer to the final string is stored in the object pointed to by endptr, provided that
+ endptr is not a null pointer.
+5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
+ value resulting from the conversion is correctly rounded.
+6 In other than the "C" locale, additional locale-specific subject sequence forms may be
+ accepted.
+7 If the subject sequence is empty or does not have the expected form, no conversion is
+ performed; the value of nptr is stored in the object pointed to by endptr, provided
+ that endptr is not a null pointer.
+ Recommended practice
+8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
+ the result is not exactly representable, the result should be one of the two numbers in the
+ appropriate internal format that are adjacent to the hexadecimal floating source value,
+ with the extra stipulation that the error should have a correct sign for the current rounding
+ direction.
+9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
+ <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
+
+ 292) 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.
+ 293) An implementation may use the n-char sequence to determine extra information to be represented in
+ the NaN's significand.
+
+[page 343]
+
+ stipulation that the error with respect to D should have a correct sign for the current
+ rounding direction.294)
+ Returns
+10 The functions return the converted value, if any. If no conversion could be performed,
+ zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
+ plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
+ return type and sign of the value), and the value of the macro ERANGE is stored in
+ errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
+ no greater than the smallest normalized positive number in the return type; whether
+ errno acquires the value ERANGE is implementation-defined.
+ 7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
+ Synopsis
+1 #include <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
+2 The strtol, strtoll, strtoul, and strtoull functions convert the initial
+ portion of the string pointed to by nptr to long int, long long int, unsigned
+ long int, and unsigned long long int representation, respectively. First,
+ they decompose the input string into three parts: an initial, possibly empty, sequence of
+ white-space characters (as specified by the isspace function), a subject sequence
+
+
+ 294) 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.
+
+[page 344]
+
+ resembling an integer represented in some radix determined by the value of base, and a
+ final string of one or more unrecognized characters, including the terminating null
+ character of the input string. Then, they attempt to convert the subject sequence to an
+ integer, and return the result.
+3 If the value of base is zero, the expected form of the subject sequence is that of an
+ integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
+ not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
+ expected form of the subject sequence is a sequence of letters and digits representing an
+ integer with the radix specified by base, optionally preceded by a plus or minus sign,
+ but not including an integer suffix. The letters from a (or A) through z (or Z) are
+ ascribed the values 10 through 35; only letters and digits whose ascribed values are less
+ than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
+ optionally precede the sequence of letters and digits, following the sign if present.
+4 The subject sequence is defined as the longest initial subsequence of the input string,
+ starting with the first non-white-space character, that is of the expected form. The subject
+ sequence contains no characters if the input string is empty or consists entirely of white
+ space, or if the first non-white-space character is other than a sign or a permissible letter
+ or digit.
+5 If the subject sequence has the expected form and the value of base is zero, the sequence
+ of characters starting with the first digit is interpreted as an integer constant according to
+ the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
+ is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
+ as given above. If the subject sequence begins with a minus sign, the value resulting from
+ the conversion is negated (in the return type). A pointer to the final string is stored in the
+ object pointed to by endptr, provided that endptr is not a null pointer.
+6 In other than the "C" locale, additional locale-specific subject sequence forms may be
+ accepted.
+7 If the subject sequence is empty or does not have the expected form, no conversion is
+ performed; the value of nptr is stored in the object pointed to by endptr, provided
+ that endptr is not a null pointer.
+ Returns
+8 The strtol, strtoll, strtoul, and strtoull functions return the converted
+ value, if any. If no conversion could be performed, zero is returned. If the correct value
+ is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
+ LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
+ and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
+
+[page 345]
+
+ 7.22.2 Pseudo-random sequence generation functions
+ 7.22.2.1 The rand function
+ Synopsis
+1 #include <stdlib.h>
+ int rand(void);
+ Description
+2 The rand function computes a sequence of pseudo-random integers in the range 0 to
+ RAND_MAX.295)
+3 The rand function is not required to avoid data races with other calls to pseudo-random
+ sequence generation functions. The implementation shall behave as if no library function
+ calls the rand function.
+ Returns
+4 The rand function returns a pseudo-random integer.
+ Environmental limits
+5 The value of the RAND_MAX macro shall be at least 32767.
+ 7.22.2.2 The srand function
+ Synopsis
+1 #include <stdlib.h>
+ void srand(unsigned int seed);
+ Description
+2 The srand function uses the argument as a seed for a new sequence of pseudo-random
+ numbers to be returned by subsequent calls to rand. If srand is then called with the
+ same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
+ called before any calls to srand have been made, the same sequence shall be generated
+ as when srand is first called with a seed value of 1.
+3 The srand function is not required to avoid data races with other calls to pseudo-
+ random sequence generation functions. The implementation shall behave as if no library
+ function calls the srand function.
+
+
+
+
+ 295) There are no guarantees as to the quality of the random sequence produced and some implementations
+ are known to produce sequences with distressingly non-random low-order bits. Applications with
+ particular requirements should use a generator that is known to be sufficient for their needs.
+
+[page 346]
+
+ Returns
+4 The srand function returns no value.
+5 EXAMPLE The following functions define a portable implementation of rand and srand.
+ static unsigned long int next = 1;
+ int rand(void) // RAND_MAX assumed to be 32767
+ {
+ next = next * 1103515245 + 12345;
+ return (unsigned int)(next/65536) % 32768;
+ }
+ void srand(unsigned int seed)
+ {
+ next = seed;
+ }
+
+ 7.22.3 Memory management functions
+1 The order and contiguity of storage allocated by successive calls to the
+ aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
+ pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
+ a pointer to any type of object with a fundamental alignment requirement and then used
+ to access such an object or an array of such objects in the space allocated (until the space
+ is explicitly deallocated). The lifetime of an allocated object extends from the allocation
+ until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
+ any other object. The pointer returned points to the start (lowest byte address) of the
+ allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
+ the space requested is zero, the behavior is implementation-defined: either a null pointer
+ is returned, or the behavior is as if the size were some nonzero value, except that the
+ returned pointer shall not be used to access an object.
+2 For purposes of determining the existence of a data race, memory allocation functions
+ behave as though they accessed only memory locations accessible through their
+ arguments and not other static duration storage. These functions may, however, visibly
+ modify the storage that they allocate or deallocate. A call to free or realloc that
+ deallocates a region p of memory synchronizes with any allocation call that allocates all
+ or part of the region p. This synchronization occurs after any access of p by the
+ deallocating function, and before any such access by the allocating function.
+ 7.22.3.1 The aligned_alloc function
+ Synopsis
+1 #include <stdlib.h>
+ void *aligned_alloc(size_t alignment, size_t size);
+
+[page 347]
+
+ Description
+2 The aligned_alloc function allocates space for an object whose alignment is
+ specified by alignment, whose size is specified by size, and whose value is
+ indeterminate. The value of alignment shall be a valid alignment supported by the
+ implementation and the value of size shall be an integral multiple of alignment.
+ Returns
+3 The aligned_alloc function returns either a null pointer or a pointer to the allocated
+ space.
+ 7.22.3.2 The calloc function
+ Synopsis
+1 #include <stdlib.h>
+ void *calloc(size_t nmemb, size_t size);
+ Description
+2 The calloc function allocates space for an array of nmemb objects, each of whose size
+ is size. The space is initialized to all bits zero.296)
+ Returns
+3 The calloc function returns either a null pointer or a pointer to the allocated space.
+ 7.22.3.3 The free function
+ Synopsis
+1 #include <stdlib.h>
+ void free(void *ptr);
+ Description
+2 The free function causes the space pointed to by ptr to be deallocated, that is, made
+ available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
+ the argument does not match a pointer earlier returned by a memory management
+ function, or if the space has been deallocated by a call to free or realloc, the
+ behavior is undefined.
+ Returns
+3 The free function returns no value.
+
+
+
+
+ 296) Note that this need not be the same as the representation of floating-point zero or a null pointer
+ constant.
+
+[page 348]
+
+ 7.22.3.4 The malloc function
+ Synopsis
+1 #include <stdlib.h>
+ void *malloc(size_t size);
+ Description
+2 The malloc function allocates space for an object whose size is specified by size and
+ whose value is indeterminate.
+ Returns
+3 The malloc function returns either a null pointer or a pointer to the allocated space.
+ 7.22.3.5 The realloc function
+ Synopsis
+1 #include <stdlib.h>
+ void *realloc(void *ptr, size_t size);
+ Description
+2 The realloc function deallocates the old object pointed to by ptr and returns a
+ pointer to a new object that has the size specified by size. The contents of the new
+ object shall be the same as that of the old object prior to deallocation, up to the lesser of
+ the new and old sizes. Any bytes in the new object beyond the size of the old object have
+ indeterminate values.
+3 If ptr is a null pointer, the realloc function behaves like the malloc function for the
+ specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
+ management function, or if the space has been deallocated by a call to the free or
+ realloc function, the behavior is undefined. If memory for the new object cannot be
+ allocated, the old object is not deallocated and its value is unchanged.
+ Returns
+4 The realloc function returns a pointer to the new object (which may have the same
+ value as a pointer to the old object), or a null pointer if the new object could not be
+ allocated.
+
+[page 349]
+
+ 7.22.4 Communication with the environment
+ 7.22.4.1 The abort function
+ Synopsis
+1 #include <stdlib.h>
+ _Noreturn void abort(void);
+ Description
+2 The abort function causes abnormal program termination to occur, unless the signal
+ SIGABRT is being caught and the signal handler does not return. Whether open streams
+ with unwritten buffered data are flushed, open streams are closed, or temporary files are
+ removed is implementation-defined. An implementation-defined form of the status
+ unsuccessful termination is returned to the host environment by means of the function
+ call raise(SIGABRT).
+ Returns
+3 The abort function does not return to its caller.
+ 7.22.4.2 The atexit function
+ Synopsis
+1 #include <stdlib.h>
+ int atexit(void (*func)(void));
+ Description
+2 The atexit function registers the function pointed to by func, to be called without
+ arguments at normal program termination.297) It is unspecified whether a call to the
+ atexit function that does not happen before the exit function is called will succeed.
+ Environmental limits
+3 The implementation shall support the registration of at least 32 functions.
+ Returns
+4 The atexit function returns zero if the registration succeeds, nonzero if it fails.
+ Forward references: the at_quick_exit function (7.22.4.3), the exit function
+ (7.22.4.4).
+
+
+
+
+ 297) 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.
+
+[page 350]
+
+ 7.22.4.3 The at_quick_exit function
+ Synopsis
+1 #include <stdlib.h>
+ int at_quick_exit(void (*func)(void));
+ Description
+2 The at_quick_exit function registers the function pointed to by func, to be called
+ without arguments should quick_exit be called.298) It is unspecified whether a call to
+ the at_quick_exit function that does not happen before the quick_exit function
+ is called will succeed.
+ Environmental limits
+3 The implementation shall support the registration of at least 32 functions.
+ Returns
+4 The at_quick_exit function returns zero if the registration succeeds, nonzero if it
+ fails.
+ Forward references: the quick_exit function (7.22.4.7).
+ 7.22.4.4 The exit function
+ Synopsis
+1 #include <stdlib.h>
+ _Noreturn void exit(int status);
+ Description
+2 The exit function causes normal program termination to occur. No functions registered
+ by the at_quick_exit function are called. If a program calls the exit function
+ more than once, or calls the quick_exit function in addition to the exit function, the
+ behavior is undefined.
+3 First, all functions registered by the atexit function are called, in the reverse order of
+ their registration,299) 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.
+
+
+
+ 298) 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.
+ 299) Each function is called as many times as it was registered, and in the correct order with respect to
+ other registered functions.
+
+[page 351]
+
+4 Next, all open streams with unwritten buffered data are flushed, all open streams are
+ closed, and all files created by the tmpfile function are removed.
+5 Finally, control is returned to the host environment. If the value of status is zero or
+ EXIT_SUCCESS, an implementation-defined form of the status successful termination is
+ returned. If the value of status is EXIT_FAILURE, an implementation-defined form
+ of the status unsuccessful termination is returned. Otherwise the status returned is
+ implementation-defined.
+ Returns
+6 The exit function cannot return to its caller.
+ 7.22.4.5 The _Exit function
+ Synopsis
+1 #include <stdlib.h>
+ _Noreturn void _Exit(int status);
+ Description
+2 The _Exit function causes normal program termination to occur and control to be
+ returned to the host environment. No functions registered by the atexit function, the
+ at_quick_exit function, or signal handlers registered by the signal function are
+ called. The status returned to the host environment is determined in the same way as for
+ the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
+ flushed, open streams are closed, or temporary files are removed is implementation-
+ defined.
+ Returns
+3 The _Exit function cannot return to its caller.
+ 7.22.4.6 The getenv function
+ Synopsis
+1 #include <stdlib.h>
+ char *getenv(const char *name);
+ Description
+2 The getenv function searches an environment list, provided by the host environment,
+ for a string that matches the string pointed to by name. The set of environment names
+ and the method for altering the environment list are implementation-defined. The
+ getenv function need not avoid data races with other threads of execution that modify
+ the environment list.300)
+
+ 300) Many implementations provide non-standard functions that modify the environment list.
+
+[page 352]
+
+3 The implementation shall behave as if no library function calls the getenv function.
+ Returns
+4 The getenv function returns a pointer to a string associated with the matched list
+ member. The string pointed to shall not be modified by the program, but may be
+ overwritten by a subsequent call to the getenv function. If the specified name cannot
+ be found, a null pointer is returned.
+ 7.22.4.7 The quick_exit function
+ Synopsis
+1 #include <stdlib.h>
+ _Noreturn void quick_exit(int status);
+ Description
+2 The quick_exit function causes normal program termination to occur. No functions
+ registered by the atexit function or signal handlers registered by the signal function
+ are called. If a program calls the quick_exit function more than once, or calls the
+ exit function in addition to the quick_exit function, the behavior is undefined. If a
+ signal is raised while the quick_exit function is executing, the behavior is undefined.
+3 The quick_exit function first calls all functions registered by the at_quick_exit
+ function, in the reverse order of their registration,301) except that a function is called after
+ any previously registered functions that had already been called at the time it was
+ registered. If, during the call to any such function, a call to the longjmp function is
+ made that would terminate the call to the registered function, the behavior is undefined.
+4 Then control is returned to the host environment by means of the function call
+ _Exit(status).
+ Returns
+5 The quick_exit function cannot return to its caller.
+ 7.22.4.8 The system function
+ Synopsis
+1 #include <stdlib.h>
+ int system(const char *string);
+ Description
+2 If string is a null pointer, the system function determines whether the host
+ environment has a command processor. If string is not a null pointer, the system
+
+ 301) Each function is called as many times as it was registered, and in the correct order with respect to
+ other registered functions.
+
+[page 353]
+
+ function passes the string pointed to by string to that command processor to be
+ executed in a manner which the implementation shall document; this might then cause the
+ program calling system to behave in a non-conforming manner or to terminate.
+ Returns
+3 If the argument is a null pointer, the system function returns nonzero only if a
+ command processor is available. If the argument is not a null pointer, and the system
+ function does return, it returns an implementation-defined value.
+ 7.22.5 Searching and sorting utilities
+1 These utilities make use of a comparison function to search or sort arrays of unspecified
+ type. Where an argument declared as size_t nmemb specifies the length of the array
+ for a function, nmemb can have the value zero on a call to that function; the comparison
+ function is not called, a search finds no matching element, and sorting performs no
+ rearrangement. Pointer arguments on such a call shall still have valid values, as described
+ in 7.1.4.
+2 The implementation shall ensure that the second argument of the comparison function
+ (when called from bsearch), or both arguments (when called from qsort), are
+ pointers to elements of the array.302) The first argument when called from bsearch
+ shall equal key.
+3 The comparison function shall not alter the contents of the array. The implementation
+ may reorder elements of the array between calls to the comparison function, but shall not
+ alter the contents of any individual element.
+4 When the same objects (consisting of size bytes, irrespective of their current positions
+ in the array) are passed more than once to the comparison function, the results shall be
+ consistent with one another. That is, for qsort they shall define a total ordering on the
+ array, and for bsearch the same object shall always compare the same way with the
+ key.
+5 A sequence point occurs immediately before and immediately after each call to the
+ comparison function, and also between any call to the comparison function and any
+ movement of the objects passed as arguments to that call.
+
+
+
+
+ 302) 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
+
+[page 354]
+
+ 7.22.5.1 The bsearch function
+ Synopsis
+1 #include <stdlib.h>
+ void *bsearch(const void *key, const void *base,
+ size_t nmemb, size_t size,
+ int (*compar)(const void *, const void *));
+ Description
+2 The bsearch function searches an array of nmemb objects, the initial element of which
+ is pointed to by base, for an element that matches the object pointed to by key. The
+ size of each element of the array is specified by size.
+3 The comparison function pointed to by compar is called with two arguments that point
+ to the key object and to an array element, in that order. The function shall return an
+ integer less than, equal to, or greater than zero if the key object is considered,
+ respectively, to be less than, to match, or to be greater than the array element. The array
+ shall consist of: all the elements that compare less than, all the elements that compare
+ equal to, and all the elements that compare greater than the key object, in that order.303)
+ Returns
+4 The bsearch function returns a pointer to a matching element of the array, or a null
+ pointer if no match is found. If two elements compare as equal, which element is
+ matched is unspecified.
+ 7.22.5.2 The qsort function
+ Synopsis
+1 #include <stdlib.h>
+ void qsort(void *base, size_t nmemb, size_t size,
+ int (*compar)(const void *, const void *));
+ Description
+2 The qsort function sorts an array of nmemb objects, the initial element of which is
+ pointed to by base. The size of each object is specified by size.
+3 The contents of the array are sorted into ascending order according to a comparison
+ function pointed to by compar, which is called with two arguments that point to the
+ objects being compared. The function shall return an integer less than, equal to, or
+ greater than zero if the first argument is considered to be respectively less than, equal to,
+ or greater than the second.
+
+
+ 303) In practice, the entire array is sorted according to the comparison function.
+
+[page 355]
+
+4 If two elements compare as equal, their order in the resulting sorted array is unspecified.
+ Returns
+5 The qsort function returns no value.
+ 7.22.6 Integer arithmetic functions
+ 7.22.6.1 The abs, labs and llabs functions
+ Synopsis
+1 #include <stdlib.h>
+ int abs(int j);
+ long int labs(long int j);
+ long long int llabs(long long int j);
+ Description
+2 The abs, labs, and llabs functions compute the absolute value of an integer j. If the
+ result cannot be represented, the behavior is undefined.304)
+ Returns
+3 The abs, labs, and llabs, functions return the absolute value.
+ 7.22.6.2 The div, ldiv, and lldiv functions
+ Synopsis
+1 #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
+2 The div, ldiv, and lldiv, functions compute numer / denom and numer %
+ denom in a single operation.
+ Returns
+3 The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
+ lldiv_t, respectively, comprising both the quotient and the remainder. The structures
+ shall contain (in either order) the members quot (the quotient) and rem (the remainder),
+ each of which has the same type as the arguments numer and denom. If either part of
+ the result cannot be represented, the behavior is undefined.
+
+
+
+
+ 304) The absolute value of the most negative number cannot be represented in two's complement.
+
+[page 356]
+
+ 7.22.7 Multibyte/wide character conversion functions
+1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
+ of the current locale. For a state-dependent encoding, each function is placed into its
+ initial conversion state at program startup and can be returned to that state by a call for
+ which its character pointer argument, s, is a null pointer. Subsequent calls with s as
+ other than a null pointer cause the internal conversion state of the function to be altered as
+ necessary. A call with s as a null pointer causes these functions to return a nonzero value
+ if encodings have state dependency, and zero otherwise.305) Changing the LC_CTYPE
+ category causes the conversion state of these functions to be indeterminate.
+ 7.22.7.1 The mblen function
+ Synopsis
+1 #include <stdlib.h>
+ int mblen(const char *s, size_t n);
+ Description
+2 If s is not a null pointer, the mblen function determines the number of bytes contained
+ in the multibyte character pointed to by s. Except that the conversion state of the
+ mbtowc function is not affected, it is equivalent to
+ mbtowc((wchar_t *)0, (const char *)0, 0);
+ mbtowc((wchar_t *)0, s, n);
+3 The implementation shall behave as if no library function calls the mblen function.
+ Returns
+4 If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
+ character encodings, respectively, do or do not have state-dependent encodings. If s is
+ not a null pointer, the mblen function either returns 0 (if s points to the null character),
+ or returns the number of bytes that are contained in the multibyte character (if the next n
+ or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
+ multibyte character).
+ Forward references: the mbtowc function (7.22.7.2).
+
+
+
+
+ 305) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
+ character codes, but are grouped with an adjacent multibyte character.
+
+[page 357]
+
+ 7.22.7.2 The mbtowc function
+ Synopsis
+1 #include <stdlib.h>
+ int mbtowc(wchar_t * restrict pwc,
+ const char * restrict s,
+ size_t n);
+ Description
+2 If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
+ the byte pointed to by s to determine the number of bytes needed to complete the next
+ multibyte character (including any shift sequences). If the function determines that the
+ next multibyte character is complete and valid, it determines the value of the
+ corresponding wide character and then, if pwc is not a null pointer, stores that value in
+ the object pointed to by pwc. If the corresponding wide character is the null wide
+ character, the function is left in the initial conversion state.
+3 The implementation shall behave as if no library function calls the mbtowc function.
+ Returns
+4 If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
+ character encodings, respectively, do or do not have state-dependent encodings. If s is
+ not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
+ or returns the number of bytes that are contained in the converted multibyte character (if
+ the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
+ form a valid multibyte character).
+5 In no case will the value returned be greater than n or the value of the MB_CUR_MAX
+ macro.
+ 7.22.7.3 The wctomb function
+ Synopsis
+1 #include <stdlib.h>
+ int wctomb(char *s, wchar_t wc);
+ Description
+2 The wctomb function determines the number of bytes needed to represent the multibyte
+ character corresponding to the wide character given by wc (including any shift
+ sequences), and stores the multibyte character representation in the array whose first
+ element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
+ are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
+ sequence needed to restore the initial shift state, and the function is left in the initial
+ conversion state.
+
+[page 358]
+
+3 The implementation shall behave as if no library function calls the wctomb function.
+ Returns
+4 If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
+ character encodings, respectively, do or do not have state-dependent encodings. If s is
+ not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
+ to a valid multibyte character, or returns the number of bytes that are contained in the
+ multibyte character corresponding to the value of wc.
+5 In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
+ 7.22.8 Multibyte/wide string conversion functions
+1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
+ the current locale.
+ 7.22.8.1 The mbstowcs function
+ Synopsis
+1 #include <stdlib.h>
+ size_t mbstowcs(wchar_t * restrict pwcs,
+ const char * restrict s,
+ size_t n);
+ Description
+2 The mbstowcs function converts a sequence of multibyte characters that begins in the
+ initial shift state from the array pointed to by s into a sequence of corresponding wide
+ characters and stores not more than n wide characters into the array pointed to by pwcs.
+ No multibyte characters that follow a null character (which is converted into a null wide
+ character) will be examined or converted. Each multibyte character is converted as if by
+ a call to the mbtowc function, except that the conversion state of the mbtowc function is
+ not affected.
+3 No more than n elements will be modified in the array pointed to by pwcs. If copying
+ takes place between objects that overlap, the behavior is undefined.
+ Returns
+4 If an invalid multibyte character is encountered, the mbstowcs function returns
+ (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
+ elements modified, not including a terminating null wide character, if any.306)
+
+
+
+
+ 306) The array will not be null-terminated if the value returned is n.
+
+[page 359]
+
+ 7.22.8.2 The wcstombs function
+ Synopsis
+1 #include <stdlib.h>
+ size_t wcstombs(char * restrict s,
+ const wchar_t * restrict pwcs,
+ size_t n);
+ Description
+2 The wcstombs function converts a sequence of wide characters from the array pointed
+ to by pwcs into a sequence of corresponding multibyte characters that begins in the
+ initial shift state, and stores these multibyte characters into the array pointed to by s,
+ stopping if a multibyte character would exceed the limit of n total bytes or if a null
+ character is stored. Each wide character is converted as if by a call to the wctomb
+ function, except that the conversion state of the wctomb function is not affected.
+3 No more than n bytes will be modified in the array pointed to by s. If copying takes place
+ between objects that overlap, the behavior is undefined.
+ Returns
+4 If a wide character is encountered that does not correspond to a valid multibyte character,
+ the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
+ returns the number of bytes modified, not including a terminating null character, if
+ any.306)
+
+[page 360]
+
+ 7.23 _Noreturn <stdnoreturn.h>
+1 The header <stdnoreturn.h> defines the macro
+ noreturn
+ which expands to _Noreturn.
+
+[page 361]
+
+ 7.24 String handling <string.h>
+ 7.24.1 String function conventions
+1 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.307) The type is size_t and the macro is NULL (both described in
+ 7.19). Various methods are used for determining the lengths of the arrays, but in all cases
+ a char * or void * argument points to the initial (lowest addressed) character of the
+ array. If an array is accessed beyond the end of an object, the behavior is undefined.
+2 Where an argument declared as size_t n specifies the length of the array for a
+ function, n can have the value zero on a call to that function. Unless explicitly stated
+ otherwise in the description of a particular function in this subclause, pointer arguments
+ on such a call shall still have valid values, as described in 7.1.4. On such a call, a
+ function that locates a character finds no occurrence, a function that compares two
+ character sequences returns zero, and a function that copies characters copies zero
+ characters.
+3 For all functions in this subclause, each character shall be interpreted as if it had the type
+ unsigned char (and therefore every possible object representation is valid and has a
+ different value).
+ 7.24.2 Copying functions
+ 7.24.2.1 The memcpy function
+ Synopsis
+1 #include <string.h>
+ void *memcpy(void * restrict s1,
+ const void * restrict s2,
+ size_t n);
+ Description
+2 The memcpy function copies n characters from the object pointed to by s2 into the
+ object pointed to by s1. If copying takes place between objects that overlap, the behavior
+ is undefined.
+ Returns
+3 The memcpy function returns the value of s1.
+
+
+
+
+ 307) See ''future library directions'' (7.31.13).
+
+[page 362]
+
+ 7.24.2.2 The memmove function
+ Synopsis
+1 #include <string.h>
+ void *memmove(void *s1, const void *s2, size_t n);
+ Description
+2 The memmove function copies n characters from the object pointed to by s2 into the
+ object pointed to by s1. Copying takes place as if the n characters from the object
+ pointed to by s2 are first copied into a temporary array of n characters that does not
+ overlap the objects pointed to by s1 and s2, and then the n characters from the
+ temporary array are copied into the object pointed to by s1.
+ Returns
+3 The memmove function returns the value of s1.
+ 7.24.2.3 The strcpy function
+ Synopsis
+1 #include <string.h>
+ char *strcpy(char * restrict s1,
+ const char * restrict s2);
+ Description
+2 The strcpy function copies the string pointed to by s2 (including the terminating null
+ character) into the array pointed to by s1. If copying takes place between objects that
+ overlap, the behavior is undefined.
+ Returns
+3 The strcpy function returns the value of s1.
+ 7.24.2.4 The strncpy function
+ Synopsis
+1 #include <string.h>
+ char *strncpy(char * restrict s1,
+ const char * restrict s2,
+ size_t n);
+ Description
+2 The strncpy function copies not more than n characters (characters that follow a null
+ character are not copied) from the array pointed to by s2 to the array pointed to by
+
+[page 363]
+
+ s1.308) If copying takes place between objects that overlap, the behavior is undefined.
+3 If the array pointed to by s2 is a string that is shorter than n characters, null characters
+ are appended to the copy in the array pointed to by s1, until n characters in all have been
+ written.
+ Returns
+4 The strncpy function returns the value of s1.
+ 7.24.3 Concatenation functions
+ 7.24.3.1 The strcat function
+ Synopsis
+1 #include <string.h>
+ char *strcat(char * restrict s1,
+ const char * restrict s2);
+ Description
+2 The strcat function appends a copy of the string pointed to by s2 (including the
+ terminating null character) to the end of the string pointed to by s1. The initial character
+ of s2 overwrites the null character at the end of s1. If copying takes place between
+ objects that overlap, the behavior is undefined.
+ Returns
+3 The strcat function returns the value of s1.
+ 7.24.3.2 The strncat function
+ Synopsis
+1 #include <string.h>
+ char *strncat(char * restrict s1,
+ const char * restrict s2,
+ size_t n);
+ Description
+2 The strncat function appends not more than n characters (a null character and
+ characters that follow it are not appended) from the array pointed to by s2 to the end of
+ the string pointed to by s1. The initial character of s2 overwrites the null character at the
+ end of s1. A terminating null character is always appended to the result.309) If copying
+
+ 308) 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.
+ 309) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
+ strlen(s1)+n+1.
+
+[page 364]
+
+ takes place between objects that overlap, the behavior is undefined.
+ Returns
+3 The strncat function returns the value of s1.
+ Forward references: the strlen function (7.24.6.3).
+ 7.24.4 Comparison functions
+1 The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
+ and strncmp is determined by the sign of the difference between the values of the first
+ pair of characters (both interpreted as unsigned char) that differ in the objects being
+ compared.
+ 7.24.4.1 The memcmp function
+ Synopsis
+1 #include <string.h>
+ int memcmp(const void *s1, const void *s2, size_t n);
+ Description
+2 The memcmp function compares the first n characters of the object pointed to by s1 to
+ the first n characters of the object pointed to by s2.310)
+ Returns
+3 The memcmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
+ pointed to by s2.
+ 7.24.4.2 The strcmp function
+ Synopsis
+1 #include <string.h>
+ int strcmp(const char *s1, const char *s2);
+ Description
+2 The strcmp function compares the string pointed to by s1 to the string pointed to by
+ s2.
+ Returns
+3 The strcmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
+
+ 310) The contents of ''holes'' used as padding for purposes of alignment within structure objects are
+ indeterminate. Strings shorter than their allocated space and unions may also cause problems in
+ comparison.
+
+[page 365]
+
+ pointed to by s2.
+ 7.24.4.3 The strcoll function
+ Synopsis
+1 #include <string.h>
+ int strcoll(const char *s1, const char *s2);
+ Description
+2 The strcoll function compares the string pointed to by s1 to the string pointed to by
+ s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
+ Returns
+3 The strcoll function returns an integer greater than, equal to, or less than zero,
+ accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
+ pointed to by s2 when both are interpreted as appropriate to the current locale.
+ 7.24.4.4 The strncmp function
+ Synopsis
+1 #include <string.h>
+ int strncmp(const char *s1, const char *s2, size_t n);
+ Description
+2 The strncmp function compares not more than n characters (characters that follow a
+ null character are not compared) from the array pointed to by s1 to the array pointed to
+ by s2.
+ Returns
+3 The strncmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
+ to, or less than the possibly null-terminated array pointed to by s2.
+ 7.24.4.5 The strxfrm function
+ Synopsis
+1 #include <string.h>
+ size_t strxfrm(char * restrict s1,
+ const char * restrict s2,
+ size_t n);
+ Description
+2 The strxfrm function transforms the string pointed to by s2 and places the resulting
+ string into the array pointed to by s1. The transformation is such that if the strcmp
+ function is applied to two transformed strings, it returns a value greater than, equal to, or
+
+[page 366]
+
+ less than zero, corresponding to the result of the strcoll function applied to the same
+ two original strings. No more than n characters are placed into the resulting array
+ pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
+ be a null pointer. If copying takes place between objects that overlap, the behavior is
+ undefined.
+ Returns
+3 The strxfrm function returns the length of the transformed string (not including the
+ terminating null character). If the value returned is n or more, the contents of the array
+ pointed to by s1 are indeterminate.
+4 EXAMPLE The value of the following expression is the size of the array needed to hold the
+ transformation of the string pointed to by s.
+ 1 + strxfrm(NULL, s, 0)
+
+ 7.24.5 Search functions
+ 7.24.5.1 The memchr function
+ Synopsis
+1 #include <string.h>
+ void *memchr(const void *s, int c, size_t n);
+ Description
+2 The memchr function locates the first occurrence of c (converted to an unsigned
+ char) in the initial n characters (each interpreted as unsigned char) of the object
+ pointed to by s. The implementation shall behave as if it reads the characters sequentially
+ and stops as soon as a matching character is found.
+ Returns
+3 The memchr function returns a pointer to the located character, or a null pointer if the
+ character does not occur in the object.
+ 7.24.5.2 The strchr function
+ Synopsis
+1 #include <string.h>
+ char *strchr(const char *s, int c);
+ Description
+2 The strchr function locates the first occurrence of c (converted to a char) in the
+ string pointed to by s. The terminating null character is considered to be part of the
+ string.
+
+[page 367]
+
+ Returns
+3 The strchr function returns a pointer to the located character, or a null pointer if the
+ character does not occur in the string.
+ 7.24.5.3 The strcspn function
+ Synopsis
+1 #include <string.h>
+ size_t strcspn(const char *s1, const char *s2);
+ Description
+2 The strcspn function computes the length of the maximum initial segment of the string
+ pointed to by s1 which consists entirely of characters not from the string pointed to by
+ s2.
+ Returns
+3 The strcspn function returns the length of the segment.
+ 7.24.5.4 The strpbrk function
+ Synopsis
+1 #include <string.h>
+ char *strpbrk(const char *s1, const char *s2);
+ Description
+2 The strpbrk function locates the first occurrence in the string pointed to by s1 of any
+ character from the string pointed to by s2.
+ Returns
+3 The strpbrk function returns a pointer to the character, or a null pointer if no character
+ from s2 occurs in s1.
+ 7.24.5.5 The strrchr function
+ Synopsis
+1 #include <string.h>
+ char *strrchr(const char *s, int c);
+ Description
+2 The strrchr function locates the last occurrence of c (converted to a char) in the
+ string pointed to by s. The terminating null character is considered to be part of the
+ string.
+
+[page 368]
+
+ Returns
+3 The strrchr function returns a pointer to the character, or a null pointer if c does not
+ occur in the string.
+ 7.24.5.6 The strspn function
+ Synopsis
+1 #include <string.h>
+ size_t strspn(const char *s1, const char *s2);
+ Description
+2 The strspn function computes the length of the maximum initial segment of the string
+ pointed to by s1 which consists entirely of characters from the string pointed to by s2.
+ Returns
+3 The strspn function returns the length of the segment.
+ 7.24.5.7 The strstr function
+ Synopsis
+1 #include <string.h>
+ char *strstr(const char *s1, const char *s2);
+ Description
+2 The strstr function locates the first occurrence in the string pointed to by s1 of the
+ sequence of characters (excluding the terminating null character) in the string pointed to
+ by s2.
+ Returns
+3 The strstr function returns a pointer to the located string, or a null pointer if the string
+ is not found. If s2 points to a string with zero length, the function returns s1.
+ 7.24.5.8 The strtok function
+ Synopsis
+1 #include <string.h>
+ char *strtok(char * restrict s1,
+ const char * restrict s2);
+ Description
+2 A sequence of calls to the strtok function breaks the string pointed to by s1 into a
+ sequence of tokens, each of which is delimited by a character from the string pointed to
+ by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
+ sequence have a null first argument. The separator string pointed to by s2 may be
+ different from call to call.
+
+[page 369]
+
+3 The first call in the sequence searches the string pointed to by s1 for the first character
+ that is not contained in the current separator string pointed to by s2. If no such character
+ is found, then there are no tokens in the string pointed to by s1 and the strtok function
+ returns a null pointer. If such a character is found, it is the start of the first token.
+4 The strtok function then searches from there for a character that is contained in the
+ current separator string. If no such character is found, the current token extends to the
+ end of the string pointed to by s1, and subsequent searches for a token will return a null
+ pointer. If such a character is found, it is overwritten by a null character, which
+ terminates the current token. The strtok function saves a pointer to the following
+ character, from which the next search for a token will start.
+5 Each subsequent call, with a null pointer as the value of the first argument, starts
+ searching from the saved pointer and behaves as described above.
+6 The strtok function is not required to avoid data races with other calls to the strtok
+ function.311) The implementation shall behave as if no library function calls the strtok
+ function.
+ Returns
+7 The strtok function returns a pointer to the first character of a token, or a null pointer
+ if there is no token.
+8 EXAMPLE
+ #include <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
+
+ Forward references: The strtok_s function (K.3.7.3.1).
+
+
+
+
+ 311) The strtok_s function can be used instead to avoid data races.
+
+[page 370]
+
+ 7.24.6 Miscellaneous functions
+ 7.24.6.1 The memset function
+ Synopsis
+1 #include <string.h>
+ void *memset(void *s, int c, size_t n);
+ Description
+2 The memset function copies the value of c (converted to an unsigned char) into
+ each of the first n characters of the object pointed to by s.
+ Returns
+3 The memset function returns the value of s.
+ 7.24.6.2 The strerror function
+ Synopsis
+1 #include <string.h>
+ char *strerror(int errnum);
+ Description
+2 The strerror function maps the number in errnum to a message string. Typically,
+ the values for errnum come from errno, but strerror shall map any value of type
+ int to a message.
+3 The strerror function is not required to avoid data races with other calls to the
+ strerror function.312) The implementation shall behave as if no library function calls
+ the strerror function.
+ Returns
+4 The strerror function returns a pointer to the string, the contents of which are locale-
+ specific. The array pointed to shall not be modified by the program, but may be
+ overwritten by a subsequent call to the strerror function.
+ Forward references: The strerror_s function (K.3.7.4.2).
+
+
+
+
+ 312) The strerror_s function can be used instead to avoid data races.
+
+[page 371]
+
+ 7.24.6.3 The strlen function
+ Synopsis
+1 #include <string.h>
+ size_t strlen(const char *s);
+ Description
+2 The strlen function computes the length of the string pointed to by s.
+ Returns
+3 The strlen function returns the number of characters that precede the terminating null
+ character.
+
+[page 372]
+
+ 7.25 Type-generic math <tgmath.h>
+1 The header <tgmath.h> includes the headers <math.h> and <complex.h> and
+ defines several type-generic macros.
+2 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.313) 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.314)
+3 Use of the macro invokes a function whose generic parameters have the corresponding
+ real type determined as follows:
+ -- First, if any argument for generic parameters has type long double, the type
+ determined is long double.
+ -- Otherwise, if any argument for generic parameters has type double or is of integer
+ type, the type determined is double.
+ -- Otherwise, the type determined is float.
+4 For each unsuffixed function in <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.
+
+
+
+
+ 313) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
+ make available the corresponding ordinary function.
+ 314) If the type of the argument is not compatible with the type of the parameter for the selected function,
+ the behavior is undefined.
+
+[page 373]
+
+ <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.
+5 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.
+
+[page 374]
+
+6 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.
+7 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)
+
+[page 375]
+
+ 7.26 Threads <threads.h>
+ 7.26.1 Introduction
+1 The header <threads.h> includes the header <time.h>, defines macros, and
+ declares types, enumeration constants, and functions that support multiple threads of
+ execution.315)
+2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
+ this header nor support any of its facilities.
+3 The macros are
+ thread_local
+ which expands to _Thread_local;
+ ONCE_FLAG_INIT
+ which expands to a value that can be used to initialize an object of type once_flag;
+ and
+ TSS_DTOR_ITERATIONS
+ which expands to an integer constant expression representing the maximum number of
+ times that destructors will be called when a thread terminates.
+4 The types are
+ cnd_t
+ which is a complete object type that holds an identifier for a condition variable;
+ thrd_t
+ which is a complete object type that holds an identifier for a thread;
+ tss_t
+ which is a complete object type that holds an identifier for a thread-specific storage
+ pointer;
+ mtx_t
+ which is a complete object type that holds an identifier for a mutex;
+ tss_dtor_t
+ which is the function pointer type void (*)(void*), used for a destructor for a
+ thread-specific storage pointer;
+
+
+
+ 315) See ''future library directions'' (7.31.15).
+
+[page 376]
+
+ thrd_start_t
+ which is the function pointer type int (*)(void*) that is passed to thrd_create
+ to create a new thread; and
+ once_flag
+ which is a complete object type that holds a flag for use by call_once.
+5 The enumeration constants are
+ mtx_plain
+ which is passed to mtx_init to create a mutex object that supports neither timeout nor
+ test and return;
+ mtx_recursive
+ which is passed to mtx_init to create a mutex object that supports recursive locking;
+ mtx_timed
+ which is passed to mtx_init to create a mutex object that supports timeout;
+ thrd_timedout
+ 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.
+ Forward references: date and time (7.27).
+
+[page 377]
+
+ 7.26.2 Initialization functions
+ 7.26.2.1 The call_once function
+ Synopsis
+1 #include <threads.h>
+ void call_once(once_flag *flag, void (*func)(void));
+ Description
+2 The call_once function uses the once_flag pointed to by flag to ensure that
+ func is called exactly once, the first time the call_once function is called with that
+ value of flag. Completion of an effective call to the call_once function synchronizes
+ with all subsequent calls to the call_once function with the same value of flag.
+ Returns
+3 The call_once function returns no value.
+ 7.26.3 Condition variable functions
+ 7.26.3.1 The cnd_broadcast function
+ Synopsis
+1 #include <threads.h>
+ int cnd_broadcast(cnd_t *cond);
+ Description
+2 The cnd_broadcast function unblocks all of the threads that are blocked on the
+ condition variable pointed to by cond at the time of the call. If no threads are blocked
+ on the condition variable pointed to by cond at the time of the call, the function does
+ nothing.
+ Returns
+3 The cnd_broadcast function returns thrd_success on success, or thrd_error
+ if the request could not be honored.
+ 7.26.3.2 The cnd_destroy function
+ Synopsis
+1 #include <threads.h>
+ void cnd_destroy(cnd_t *cond);
+ Description
+2 The cnd_destroy function releases all resources used by the condition variable
+ pointed to by cond. The cnd_destroy function requires that no threads be blocked
+ waiting for the condition variable pointed to by cond.
+
+[page 378]
+
+ Returns
+3 The cnd_destroy function returns no value.
+ 7.26.3.3 The cnd_init function
+ Synopsis
+1 #include <threads.h>
+ int cnd_init(cnd_t *cond);
+ Description
+2 The cnd_init function creates a condition variable. If it succeeds it sets the variable
+ pointed to by cond to a value that uniquely identifies the newly created condition
+ variable. A thread that calls cnd_wait on a newly created condition variable will
+ block.
+ Returns
+3 The cnd_init function returns thrd_success on success, or thrd_nomem if no
+ memory could be allocated for the newly created condition, or thrd_error if the
+ request could not be honored.
+ 7.26.3.4 The cnd_signal function
+ Synopsis
+1 #include <threads.h>
+ int cnd_signal(cnd_t *cond);
+ Description
+2 The cnd_signal function unblocks one of the threads that are blocked on the
+ condition variable pointed to by cond at the time of the call. If no threads are blocked
+ on the condition variable at the time of the call, the function does nothing and return
+ success.
+ Returns
+3 The cnd_signal function returns thrd_success on success or thrd_error if
+ the request could not be honored.
+ 7.26.3.5 The cnd_timedwait function
+ Synopsis
+1 #include <threads.h>
+ int cnd_timedwait(cnd_t *restrict cond,
+ mtx_t *restrict mtx,
+ const struct timespec *restrict ts);
+
+[page 379]
+
+ Description
+2 The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
+ endeavors to block until the condition variable pointed to by cond is signaled by a call to
+ cnd_signal or to cnd_broadcast, or until after the TIME_UTC-based calendar
+ time pointed to by ts. When the calling thread becomes unblocked it locks the variable
+ pointed to by mtx before it returns. The cnd_timedwait function requires that the
+ mutex pointed to by mtx be locked by the calling thread.
+ Returns
+3 The cnd_timedwait function returns thrd_success upon success, or
+ thrd_timedout if the time specified in the call was reached without acquiring the
+ requested resource, or thrd_error if the request could not be honored.
+ 7.26.3.6 The cnd_wait function
+ Synopsis
+1 #include <threads.h>
+ int cnd_wait(cnd_t *cond, mtx_t *mtx);
+ Description
+2 The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
+ to block until the condition variable pointed to by cond is signaled by a call to
+ cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
+ locks the mutex pointed to by mtx before it returns. The cnd_wait function requires
+ that the mutex pointed to by mtx be locked by the calling thread.
+ Returns
+3 The cnd_wait function returns thrd_success on success or thrd_error if the
+ request could not be honored.
+ 7.26.4 Mutex functions
+ 7.26.4.1 The mtx_destroy function
+ Synopsis
+1 #include <threads.h>
+ void mtx_destroy(mtx_t *mtx);
+ Description
+2 The mtx_destroy function releases any resources used by the mutex pointed to by
+ mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
+ Returns
+3 The mtx_destroy function returns no value.
+
+[page 380]
+
+ 7.26.4.2 The mtx_init function
+ Synopsis
+1 #include <threads.h>
+ int mtx_init(mtx_t *mtx, int type);
+ Description
+2 The mtx_init function creates a mutex object with properties indicated by type,
+ which must have one of the six values:
+ mtx_plain for a simple non-recursive mutex,
+ mtx_timed for a non-recursive mutex that supports timeout, *
+ mtx_plain | mtx_recursive for a simple recursive mutex, or
+ mtx_timed | mtx_recursive for a recursive mutex that supports timeout.
+3 If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
+ uniquely identifies the newly created mutex.
+ Returns
+4 The mtx_init function returns thrd_success on success, or thrd_error if the
+ request could not be honored.
+ 7.26.4.3 The mtx_lock function
+ Synopsis
+1 #include <threads.h>
+ int mtx_lock(mtx_t *mtx);
+ Description
+2 The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
+ is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
+ on the same mutex shall synchronize with this operation.
+ Returns
+3 The mtx_lock function returns thrd_success on success, or thrd_error if the *
+ request could not be honored.
+ 7.26.4.4 The mtx_timedlock function
+ Synopsis
+1 #include <threads.h>
+ int mtx_timedlock(mtx_t *restrict mtx,
+ const struct timespec *restrict ts);
+
+[page 381]
+
+ Description
+2 The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
+ mtx or until after the TIME_UTC-based calendar time pointed to by ts. The specified
+ mutex shall support timeout. If the operation succeeds, prior calls to mtx_unlock on
+ the same mutex shall synchronize with this operation.
+ Returns
+3 The mtx_timedlock function returns thrd_success on success, or
+ thrd_timedout if the time specified was reached without acquiring the requested
+ resource, or thrd_error if the request could not be honored.
+ 7.26.4.5 The mtx_trylock function
+ Synopsis
+1 #include <threads.h>
+ int mtx_trylock(mtx_t *mtx);
+ Description
+2 The mtx_trylock function endeavors to lock the mutex pointed to by mtx. If the *
+ mutex is already locked, the function returns without blocking. If the operation succeeds,
+ prior calls to mtx_unlock on the same mutex shall synchronize with this operation.
+ Returns
+3 The mtx_trylock function returns thrd_success on success, or thrd_busy if
+ the resource requested is already in use, or thrd_error if the request could not be
+ honored.
+ 7.26.4.6 The mtx_unlock function
+ Synopsis
+1 #include <threads.h>
+ int mtx_unlock(mtx_t *mtx);
+ Description
+2 The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
+ by mtx shall be locked by the calling thread.
+ Returns
+3 The mtx_unlock function returns thrd_success on success or thrd_error if
+ the request could not be honored.
+
+[page 382]
+
+ 7.26.5 Thread functions
+ 7.26.5.1 The thrd_create function
+ Synopsis
+1 #include <threads.h>
+ int thrd_create(thrd_t *thr, thrd_start_t func,
+ void *arg);
+ Description
+2 The thrd_create function creates a new thread executing func(arg). If the
+ thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
+ the newly created thread. (A thread's identifier may be reused for a different thread once
+ the original thread has exited and either been detached or joined to another thread.) The
+ completion of the thrd_create function synchronizes with the beginning of the
+ execution of the new thread.
+ Returns
+3 The thrd_create function returns thrd_success on success, or thrd_nomem if
+ no memory could be allocated for the thread requested, or thrd_error if the request
+ could not be honored.
+ 7.26.5.2 The thrd_current function
+ Synopsis
+1 #include <threads.h>
+ thrd_t thrd_current(void);
+ Description
+2 The thrd_current function identifies the thread that called it.
+ Returns
+3 The thrd_current function returns the identifier of the thread that called it.
+ 7.26.5.3 The thrd_detach function
+ Synopsis
+1 #include <threads.h>
+ int thrd_detach(thrd_t thr);
+ Description
+2 The thrd_detach function tells the operating system to dispose of any resources
+ allocated to the thread identified by thr when that thread terminates. The thread
+ identified by thr shall not have been previously detached or joined with another thread.
+
+[page 383]
+
+ Returns
+3 The thrd_detach function returns thrd_success on success or thrd_error if
+ the request could not be honored.
+ 7.26.5.4 The thrd_equal function
+ Synopsis
+1 #include <threads.h>
+ int thrd_equal(thrd_t thr0, thrd_t thr1);
+ Description
+2 The thrd_equal function will determine whether the thread identified by thr0 refers
+ to the thread identified by thr1.
+ Returns
+3 The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
+ different threads. Otherwise the thrd_equal function returns a nonzero value.
+ 7.26.5.5 The thrd_exit function
+ Synopsis
+1 #include <threads.h>
+ _Noreturn void thrd_exit(int res);
+ Description
+2 The thrd_exit function terminates execution of the calling thread and sets its result
+ code to res.
+3 The program shall terminate normally after the last thread has been terminated. The
+ behavior shall be as if the program called the exit function with the status
+ EXIT_SUCCESS at thread termination time.
+ Returns
+4 The thrd_exit function returns no value.
+ 7.26.5.6 The thrd_join function
+ Synopsis
+1 #include <threads.h>
+ int thrd_join(thrd_t thr, int *res);
+ Description
+2 The thrd_join function joins the thread identified by thr with the current thread by
+ blocking until the other thread has terminated. If the parameter res is not a null pointer,
+ it stores the thread's result code in the integer pointed to by res. The termination of the
+
+[page 384]
+
+ other thread synchronizes with the completion of the thrd_join function. The thread
+ identified by thr shall not have been previously detached or joined with another thread.
+ Returns
+3 The thrd_join function returns thrd_success on success or thrd_error if the
+ request could not be honored.
+ 7.26.5.7 The thrd_sleep function
+ Synopsis
+1 #include <threads.h>
+ int thrd_sleep(const struct timespec *duration,
+ struct timespec *remaining);
+ Description
+2 The thrd_sleep function suspends execution of the calling thread until either the
+ interval specified by duration has elapsed or a signal which is not being ignored is
+ received. If interrupted by a signal and the remaining argument is not null, the
+ amount of time remaining (the requested interval minus the time actually slept) is stored
+ in the interval it points to. The duration and remaining arguments may point to the
+ same object.
+3 The suspension time may be longer than requested because the interval is rounded up to
+ an integer multiple of the sleep resolution or because of the scheduling of other activity
+ by the system. But, except for the case of being interrupted by a signal, the suspension
+ time shall not be less than that specified, as measured by the system clock TIME_UTC.
+ Returns
+4 The thrd_sleep function returns zero if the requested time has elapsed, -1 if it has
+ been interrupted by a signal, or a negative value if it fails.
+ 7.26.5.8 The thrd_yield function
+ Synopsis
+1 #include <threads.h>
+ void thrd_yield(void);
+ Description
+2 The thrd_yield function endeavors to permit other threads to run, even if the current
+ thread would ordinarily continue to run.
+ Returns
+3 The thrd_yield function returns no value.
+
+[page 385]
+
+ 7.26.6 Thread-specific storage functions
+ 7.26.6.1 The tss_create function
+ Synopsis
+1 #include <threads.h>
+ int tss_create(tss_t *key, tss_dtor_t dtor);
+ Description
+2 The tss_create function creates a thread-specific storage pointer with destructor
+ dtor, which may be null.
+ Returns
+3 If the tss_create function is successful, it sets the thread-specific storage pointed to
+ by key to a value that uniquely identifies the newly created pointer and returns
+ thrd_success; otherwise, thrd_error is returned and the thread-specific storage
+ pointed to by key is set to an undefined value.
+ 7.26.6.2 The tss_delete function
+ Synopsis
+1 #include <threads.h>
+ void tss_delete(tss_t key);
+ Description
+2 The tss_delete function releases any resources used by the thread-specific storage
+ identified by key.
+ Returns
+3 The tss_delete function returns no value.
+ 7.26.6.3 The tss_get function
+ Synopsis
+1 #include <threads.h>
+ void *tss_get(tss_t key);
+ Description
+2 The tss_get function returns the value for the current thread held in the thread-specific
+ storage identified by key.
+ Returns
+3 The tss_get function returns the value for the current thread if successful, or zero if
+ unsuccessful.
+
+[page 386]
+
+ 7.26.6.4 The tss_set function
+ Synopsis
+1 #include <threads.h>
+ int tss_set(tss_t key, void *val);
+ Description
+2 The tss_set function sets the value for the current thread held in the thread-specific
+ storage identified by key to val.
+ Returns
+3 The tss_set function returns thrd_success on success or thrd_error if the
+ request could not be honored. *
+
+[page 387]
+
+ 7.27 Date and time <time.h>
+ 7.27.1 Components of time
+1 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.
+2 The macros defined are NULL (described in 7.19); *
+ 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; and
+ TIME_UTC
+ which expands to an integer constant greater than 0 that designates the UTC time
+ base.316)
+3 The types declared are size_t (described in 7.19);
+ clock_t
+ and
+ time_t
+ which are real types capable of representing times;
+ struct timespec
+ which holds an interval specified in seconds and nanoseconds (which may represent a
+ calendar time based on a particular epoch); and
+ struct tm
+ which holds the components of a calendar time, called the broken-down time.
+4 The range and precision of times representable in clock_t and time_t are
+ implementation-defined. The timespec structure shall contain at least the following
+ members, in any order.317)
+
+
+
+ 316) Implementations may define additional time bases, but are only required to support a real time clock
+ based on UTC.
+ 317) The tv_sec member is a linear count of seconds and may not have the normal semantics of a
+ time_t. The semantics of the members and their normal ranges are expressed in the comments.
+
+[page 388]
+
+ time_t tv_sec; // whole seconds -- >= 0
+ long tv_nsec; // nanoseconds -- [0, 999999999]
+ 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.318)
+ 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.
+ 7.27.2 Time manipulation functions
+ 7.27.2.1 The clock function
+ Synopsis
+1 #include <time.h>
+ clock_t clock(void);
+ Description
+2 The clock function determines the processor time used.
+ Returns
+3 The clock function returns the implementation's best approximation to the processor
+ time used by the program since the beginning of an implementation-defined era related
+ only to the program invocation. To determine the time in seconds, the value returned by
+ the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
+ the processor time used is not available or its value cannot be represented, the function
+ returns the value (clock_t)(-1).319)
+
+
+
+
+ 318) The range [0, 60] for tm_sec allows for a positive leap second.
+ 319) In order to measure the time spent in a program, the clock function should be called at the start of
+ the program and its return value subtracted from the value returned by subsequent calls.
+
+[page 389]
+
+ 7.27.2.2 The difftime function
+ Synopsis
+1 #include <time.h>
+ double difftime(time_t time1, time_t time0);
+ Description
+2 The difftime function computes the difference between two calendar times: time1 -
+ time0.
+ Returns
+3 The difftime function returns the difference expressed in seconds as a double.
+ 7.27.2.3 The mktime function
+ Synopsis
+1 #include <time.h>
+ time_t mktime(struct tm *timeptr);
+ Description
+2 The mktime function converts the broken-down time, expressed as local time, in the
+ structure pointed to by timeptr into a calendar time value with the same encoding as
+ that of the values returned by the time function. The original values of the tm_wday
+ and tm_yday components of the structure are ignored, and the original values of the
+ other components are not restricted to the ranges indicated above.320) On successful
+ completion, the values of the tm_wday and tm_yday components of the structure are
+ set appropriately, and the other components are set to represent the specified calendar
+ time, but with their values forced to the ranges indicated above; the final value of
+ tm_mday is not set until tm_mon and tm_year are determined.
+ Returns
+3 The mktime function returns the specified calendar time encoded as a value of type
+ time_t. If the calendar time cannot be represented, the function returns the value
+ (time_t)(-1).
+4 EXAMPLE What day of the week is July 4, 2001?
+
+
+
+
+ 320) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
+ Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
+ causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.
+
+[page 390]
+
+ #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]);
+
+ 7.27.2.4 The time function
+ Synopsis
+1 #include <time.h>
+ time_t time(time_t *timer);
+ Description
+2 The time function determines the current calendar time. The encoding of the value is
+ unspecified.
+ Returns
+3 The time function returns the implementation's best approximation to the current
+ calendar time. The value (time_t)(-1) is returned if the calendar time is not
+ available. If timer is not a null pointer, the return value is also assigned to the object it
+ points to.
+ 7.27.2.5 The timespec_get function
+ Synopsis
+1 #include <time.h>
+ int timespec_get(struct timespec *ts, int base);
+ Description
+2 The timespec_get function sets the interval pointed to by ts to hold the current
+ calendar time based on the specified time base.
+3 If base is TIME_UTC, the tv_sec member is set to the number of seconds since an
+ implementation defined epoch, truncated to a whole value and the tv_nsec member is
+ set to the integral number of nanoseconds, rounded to the resolution of the system
+
+[page 391]
+
+ clock.321)
+ Returns
+4 If the timespec_get function is successful it returns the nonzero value base;
+ otherwise, it returns zero.
+ 7.27.3 Time conversion functions
+1 Except for the strftime function, these functions each return a pointer to one of two
+ types of static objects: a broken-down time structure or an array of char. Execution of
+ any of the functions that return a pointer to one of these object types may overwrite the
+ information in any object of the same type pointed to by the value returned from any
+ previous call to any of them and the functions are not required to avoid data races with
+ each other.322) The implementation shall behave as if no other library functions call these
+ functions.
+ 7.27.3.1 The asctime function
+ Synopsis
+1 #include <time.h>
+ char *asctime(const struct tm *timeptr);
+ Description
+2 The asctime function converts the broken-down time in the structure pointed to by
+ timeptr into a string in the form
+ Sun Sep 16 01:03:52 1973\n\0
+ 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];
+
+
+
+ 321) Although a struct timespec object describes times with nanosecond resolution, the available
+ resolution is system dependent and may even be greater than 1 second.
+ 322) Alternative time conversion functions that do avoid data races are specified in K.3.8.2.
+
+[page 392]
+
+ sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
+ wday_name[timeptr->tm_wday],
+ mon_name[timeptr->tm_mon],
+ timeptr->tm_mday, timeptr->tm_hour,
+ timeptr->tm_min, timeptr->tm_sec,
+ 1900 + timeptr->tm_year);
+ return result;
+ }
+3 If any of the members of the broken-down time contain values that are outside their
+ normal ranges,323) the behavior of the asctime function is undefined. Likewise, if the
+ calculated year exceeds four digits or is less than the year 1000, the behavior is
+ undefined.
+ Returns
+4 The asctime function returns a pointer to the string.
+ 7.27.3.2 The ctime function
+ Synopsis
+1 #include <time.h>
+ char *ctime(const time_t *timer);
+ Description
+2 The ctime function converts the calendar time pointed to by timer to local time in the
+ form of a string. It is equivalent to
+ asctime(localtime(timer))
+ Returns
+3 The ctime function returns the pointer returned by the asctime function with that
+ broken-down time as argument.
+ Forward references: the localtime function (7.27.3.4).
+ 7.27.3.3 The gmtime function
+ Synopsis
+1 #include <time.h>
+ struct tm *gmtime(const time_t *timer);
+
+
+
+
+ 323) See 7.27.1.
+
+[page 393]
+
+ Description
+2 The gmtime function converts the calendar time pointed to by timer into a broken-
+ down time, expressed as UTC.
+ Returns
+3 The gmtime function returns a pointer to the broken-down time, or a null pointer if the
+ specified time cannot be converted to UTC.
+ 7.27.3.4 The localtime function
+ Synopsis
+1 #include <time.h>
+ struct tm *localtime(const time_t *timer);
+ Description
+2 The localtime function converts the calendar time pointed to by timer into a
+ broken-down time, expressed as local time.
+ Returns
+3 The localtime function returns a pointer to the broken-down time, or a null pointer if
+ the specified time cannot be converted to local time.
+ 7.27.3.5 The strftime function
+ Synopsis
+1 #include <time.h>
+ size_t strftime(char * restrict s,
+ size_t maxsize,
+ const char * restrict format,
+ const struct tm * restrict timeptr);
+ Description
+2 The strftime function places characters into the array pointed to by s as controlled by
+ the string pointed to by format. The format shall be a multibyte character sequence,
+ beginning and ending in its initial shift state. The format string consists of zero or
+ more conversion specifiers and ordinary multibyte characters. A conversion specifier
+ consists of a % character, possibly followed by an E or O modifier character (described
+ below), followed by a character that determines the behavior of the conversion specifier.
+ All ordinary multibyte characters (including the terminating null character) are copied
+ unchanged into the array. If copying takes place between objects that overlap, the
+ behavior is undefined. No more than maxsize characters are placed into the array.
+3 Each conversion specifier is replaced by appropriate characters as described in the
+ following list. The appropriate characters are determined using the LC_TIME category
+
+[page 394]
+
+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 7.27.1]
+%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
+
+[page 395]
+
+ (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 7.27.1]
+ %X is replaced by the locale's appropriate time representation. [all specified in 7.27.1]
+ %y is replaced by the last 2 digits of the year as a decimal number (00-99).
+ [tm_year]
+ %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year]
+ %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4
+ hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
+ zone is determinable. [tm_isdst]
+ %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no
+ time zone is determinable. [tm_isdst]
+ %% is replaced by %.
+4 Some conversion specifiers can be modified by the inclusion of an E or O modifier
+ character to indicate an alternative format or specification. If the alternative format or
+ specification does not exist for the current locale, the modifier is ignored.
+ %Ec is replaced by the locale's alternative date and time representation.
+ %EC is replaced by the name of the base year (period) in the locale's alternative
+ representation.
+ %Ex is replaced by the locale's alternative date representation.
+ %EX is replaced by the locale's alternative time representation.
+ %Ey is replaced by the offset from %EC (year only) in the locale's alternative
+ representation.
+ %EY is replaced by the locale's full alternative year representation.
+ %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
+
+[page 396]
+
+ representation, where Monday is 1.
+ %OU is replaced by the week number, using the locale's alternative numeric symbols.
+ %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
+ symbols.
+ %Ow is replaced by the weekday as a number, using the locale's alternative numeric
+ symbols.
+ %OW is replaced by the week number of the year, using the locale's alternative numeric
+ symbols.
+ %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
+ symbols.
+5 %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
+ weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
+ which is also the week that includes the first Thursday of the year, and is also the first
+ week that contains at least four days in the year. If the first Monday of January is the
+ 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
+ for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
+ December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
+ the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
+ %V is replaced by 01.
+6 If a conversion specifier is not one of the above, the behavior is undefined.
+7 In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
+ following specifiers are:
+ %a the first three characters of %A.
+ %A one of ''Sunday'', ''Monday'', ... , ''Saturday''.
+ %b the first three characters of %B.
+ %B one of ''January'', ''February'', ... , ''December''.
+ %c equivalent to ''%a %b %e %T %Y''.
+ %p one of ''AM'' or ''PM''.
+ %r equivalent to ''%I:%M:%S %p''.
+ %x equivalent to ''%m/%d/%y''.
+ %X equivalent to %T.
+ %Z implementation-defined.
+ Returns
+8 If the total number of resulting characters including the terminating null character is not
+ more than maxsize, the strftime function returns the number of characters placed
+ into the array pointed to by s not including the terminating null character. Otherwise,
+ zero is returned and the contents of the array are indeterminate.
+
+[page 397]
+
+ 7.28 Unicode utilities <uchar.h>
+1 The header <uchar.h> declares types and functions for manipulating Unicode
+ characters.
+2 The types declared are mbstate_t (described in 7.30.1) 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).
+ 7.28.1 Restartable multibyte/wide character conversion functions
+1 These functions have a parameter, ps, of type pointer to mbstate_t that points to an
+ object that can completely describe the current conversion state of the associated
+ multibyte character sequence, which the functions alter as necessary. If ps is a null
+ pointer, each function uses its own internal mbstate_t object instead, which is
+ initialized at program startup to the initial conversion state; the functions are not required
+ to avoid data races with other calls to the same function in this case. The implementation
+ behaves as if no library function calls these functions with a null pointer for ps.
+ 7.28.1.1 The mbrtoc16 function
+ Synopsis
+1 #include <uchar.h>
+ size_t mbrtoc16(char16_t * restrict pc16,
+ const char * restrict s, size_t n,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the mbrtoc16 function is equivalent to the call:
+ mbrtoc16(NULL, "", 1, ps)
+ In this case, the values of the parameters pc16 and n are ignored.
+3 If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
+ the byte pointed to by s to determine the number of bytes needed to complete the next
+ multibyte character (including any shift sequences). If the function determines that the
+ next multibyte character is complete and valid, it determines the values of the
+ corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
+ the first (or only) such character in the object pointed to by pc16. Subsequent calls will
+
+[page 398]
+
+ store successive wide characters without consuming any additional input until all the
+ characters have been stored. If the corresponding wide character is the null wide
+ character, the resulting state described is the initial conversion state.
+ Returns
+4 The mbrtoc16 function returns the first of the following that applies (given the current
+ conversion state):
+ 0 if the next n or fewer bytes complete the multibyte character that
+ corresponds to the null wide character (which is the value stored).
+ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
+ character (which is the value stored); the value returned is the number
+ of bytes that complete the multibyte character.
+ (size_t)(-3) if the next character resulting from a previous call has been stored (no
+ bytes from the input have been consumed by this call).
+ (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
+ multibyte character, and all n bytes have been processed (no value is
+ stored).324)
+ (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
+ do not contribute to a complete and valid multibyte character (no
+ value is stored); the value of the macro EILSEQ is stored in errno,
+ and the conversion state is unspecified.
+ 7.28.1.2 The c16rtomb function
+ Synopsis
+1 #include <uchar.h>
+ size_t c16rtomb(char * restrict s, char16_t c16,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the c16rtomb function is equivalent to the call
+ c16rtomb(buf, L'\0', ps)
+ where buf is an internal buffer.
+3 If s is not a null pointer, the c16rtomb function determines the number of bytes needed
+ to represent the multibyte character that corresponds to the wide character given by c16
+ (including any shift sequences), and stores the multibyte character representation in the
+
+ 324) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
+ sequence of redundant shift sequences (for implementations with state-dependent encodings).
+
+[page 399]
+
+ array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
+ c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
+ to restore the initial shift state; the resulting state described is the initial conversion state.
+ Returns
+4 The c16rtomb function returns the number of bytes stored in the array object (including
+ any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
+ the function stores the value of the macro EILSEQ in errno and returns
+ (size_t)(-1); the conversion state is unspecified.
+ 7.28.1.3 The mbrtoc32 function
+ Synopsis
+1 #include <uchar.h>
+ size_t mbrtoc32(char32_t * restrict pc32,
+ const char * restrict s, size_t n,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the mbrtoc32 function is equivalent to the call:
+ mbrtoc32(NULL, "", 1, ps)
+ In this case, the values of the parameters pc32 and n are ignored.
+3 If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
+ the byte pointed to by s to determine the number of bytes needed to complete the next
+ multibyte character (including any shift sequences). If the function determines that the
+ next multibyte character is complete and valid, it determines the values of the
+ corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
+ the first (or only) such character in the object pointed to by pc32. Subsequent calls will
+ store successive wide characters without consuming any additional input until all the
+ characters have been stored. If the corresponding wide character is the null wide
+ character, the resulting state described is the initial conversion state.
+ Returns
+4 The mbrtoc32 function returns the first of the following that applies (given the current
+ conversion state):
+ 0 if the next n or fewer bytes complete the multibyte character that
+ corresponds to the null wide character (which is the value stored).
+ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
+ character (which is the value stored); the value returned is the number
+ of bytes that complete the multibyte character.
+
+[page 400]
+
+ (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).325)
+ (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
+ do not contribute to a complete and valid multibyte character (no
+ value is stored); the value of the macro EILSEQ is stored in errno,
+ and the conversion state is unspecified.
+ 7.28.1.4 The c32rtomb function
+ Synopsis
+1 #include <uchar.h>
+ size_t c32rtomb(char * restrict s, char32_t c32,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the c32rtomb function is equivalent to the call
+ c32rtomb(buf, L'\0', ps)
+ where buf is an internal buffer.
+3 If s is not a null pointer, the c32rtomb function determines the number of bytes needed
+ to represent the multibyte character that corresponds to the wide character given by c32
+ (including any shift sequences), and stores the multibyte character representation in the
+ array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
+ c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
+ to restore the initial shift state; the resulting state described is the initial conversion state.
+ Returns
+4 The c32rtomb function returns the number of bytes stored in the array object (including
+ any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
+ the function stores the value of the macro EILSEQ in errno and returns
+ (size_t)(-1); the conversion state is unspecified.
+
+
+
+
+ 325) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
+ sequence of redundant shift sequences (for implementations with state-dependent encodings).
+
+[page 401]
+
+ 7.29 Extended multibyte and wide character utilities <wchar.h>
+ 7.29.1 Introduction
+1 The header <wchar.h> defines four macros, and declares four data types, one tag, and
+ many functions.326)
+2 The types declared are wchar_t and size_t (both described in 7.19);
+ mbstate_t
+ which is a complete object type other than an array type that can hold the conversion state
+ information necessary to convert between sequences of multibyte characters and wide
+ characters;
+ wint_t
+ which is an integer type unchanged by default argument promotions that can hold any
+ value corresponding to members of the extended character set, as well as at least one
+ value that does not correspond to any member of the extended character set (see WEOF
+ below);327) and
+ struct tm
+ which is declared as an incomplete structure type (the contents are described in 7.27.1).
+3 The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
+ (described in 7.20.3); and
+ WEOF
+ which expands to a constant expression of type wint_t whose value does not
+ correspond to any member of the extended character set.328) It is accepted (and returned)
+ by several functions in this subclause to indicate end-of-file, that is, no more input from a
+ stream. It is also used as a wide character value that does not correspond to any member
+ of the extended character set.
+4 The functions declared are grouped as follows:
+ -- Functions that perform input and output of wide characters, or multibyte characters,
+ or both;
+ -- Functions that provide wide string numeric conversion;
+ -- Functions that perform general wide string manipulation;
+
+
+ 326) See ''future library directions'' (7.31.16).
+ 327) wchar_t and wint_t can be the same integer type.
+ 328) The value of the macro WEOF may differ from that of EOF and need not be negative.
+
+[page 402]
+
+ -- Functions for wide string date and time conversion; and
+ -- Functions that provide extended capabilities for conversion between multibyte and
+ wide character sequences.
+5 Arguments to the functions in this subclause may point to arrays containing wchar_t
+ values that do not correspond to members of the extended character set. Such values
+ shall be processed according to the specified semantics, except that it is unspecified
+ whether an encoding error occurs if such a value appears in the format string for a
+ function in 7.29.2 or 7.29.5 and the specified semantics do not require that value to be
+ processed by wcrtomb.
+6 Unless explicitly stated otherwise, if the execution of a function described in this
+ subclause causes copying to take place between objects that overlap, the behavior is
+ undefined.
+ 7.29.2 Formatted wide character input/output functions
+1 The formatted wide character input/output functions shall behave as if there is a sequence
+ point after the actions associated with each specifier.329)
+ 7.29.2.1 The fwprintf function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ int fwprintf(FILE * restrict stream,
+ const wchar_t * restrict format, ...);
+ Description
+2 The fwprintf function writes output to the stream pointed to by stream, under
+ control of the wide string pointed to by format that specifies how subsequent arguments
+ are converted for output. If there are insufficient arguments for the format, the behavior
+ is undefined. If the format is exhausted while arguments remain, the excess arguments
+ are evaluated (as always) but are otherwise ignored. The fwprintf function returns
+ when the end of the format string is encountered.
+3 The format is composed of zero or more directives: ordinary wide characters (not %),
+ which are copied unchanged to the output stream; and conversion specifications, each of
+ which results in fetching zero or more subsequent arguments, converting them, if
+ applicable, according to the corresponding conversion specifier, and then writing the
+ result to the output stream.
+
+
+
+ 329) The fwprintf functions perform writes to memory for the %n specifier.
+
+[page 403]
+
+4 Each conversion specification is introduced by the wide character %. After the %, the
+ following appear in sequence:
+ -- Zero or more flags (in any order) that modify the meaning of the conversion
+ specification.
+ -- An optional minimum field width. If the converted value has fewer wide characters
+ than the field width, it is padded with spaces (by default) on the left (or right, if the
+ left adjustment flag, described later, has been given) to the field width. The field
+ width takes the form of an asterisk * (described later) or a nonnegative decimal
+ integer.330)
+ -- An optional precision that gives the minimum number of digits to appear for the d, i,
+ o, u, x, and X conversions, the number of digits to appear after the decimal-point
+ wide character for a, A, e, E, f, and F conversions, the maximum number of
+ significant digits for the g and G conversions, or the maximum number of wide
+ characters to be written for s conversions. The precision takes the form of a period
+ (.) followed either by an asterisk * (described later) or by an optional decimal
+ integer; if only the period is specified, the precision is taken as zero. If a precision
+ appears with any other conversion specifier, the behavior is undefined.
+ -- An optional length modifier that specifies the size of the argument.
+ -- A conversion specifier wide character that specifies the type of conversion to be
+ applied.
+5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
+ this case, an int argument supplies the field width or precision. The arguments
+ specifying field width, or precision, or both, shall appear (in that order) before the
+ argument (if any) to be converted. A negative field width argument is taken as a - flag
+ followed by a positive field width. A negative precision argument is taken as if the
+ precision were omitted.
+6 The flag wide characters and their meanings are:
+ - The result of the conversion is left-justified within the field. (It is right-justified if
+ this flag is not specified.)
+ + The result of a signed conversion always begins with a plus or minus sign. (It
+ begins with a sign only when a negative value is converted if this flag is not
+
+
+
+
+ 330) Note that 0 is taken as a flag, not as the beginning of a field width.
+
+[page 404]
+
+ specified.)331)
+ 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.
+7 The length modifiers and their meanings are:
+ hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ signed char or unsigned char argument (the argument will have
+ been promoted according to the integer promotions, but its value shall be
+ converted to signed char or unsigned char before printing); or that
+ a following n conversion specifier applies to a pointer to a signed char
+ argument.
+ h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ short int or unsigned short int argument (the argument will
+ have been promoted according to the integer promotions, but its value shall
+ be converted to short int or unsigned short int before printing);
+ or that a following n conversion specifier applies to a pointer to a short
+ int argument.
+ l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
+ long int or unsigned long int argument; that a following n
+ conversion specifier applies to a pointer to a long int argument; that a
+
+
+ 331) The results of all floating conversions of a negative zero, and of negative values that round to zero,
+ include a minus sign.
+
+[page 405]
+
+ 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.
+8 The conversion specifiers and their meanings are:
+ d,i The int argument is converted to signed decimal in the style [-]dddd. The
+ precision specifies the minimum number of digits to appear; if the value
+ being converted can be represented in fewer digits, it is expanded with
+ leading zeros. The default precision is 1. The result of converting a zero
+ value with a precision of zero is no wide characters.
+ o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
+ decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
+ letters abcdef are used for x conversion and the letters ABCDEF for X
+ conversion. The precision specifies the minimum number of digits to appear;
+ if the value being converted can be represented in fewer digits, it is expanded
+ with leading zeros. The default precision is 1. The result of converting a
+ zero value with a precision of zero is no wide characters.
+
+[page 406]
+
+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.332)
+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
+
+
+332) 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.
+
+[page 407]
+
+ 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 character333) 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
+ distinguish334) 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
+
+333) 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.
+334) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
+ FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
+ might suffice depending on the implementation's scheme for determining the digit to the left of the
+ decimal-point wide character.
+
+[page 408]
+
+ 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 %%.
+9 If a conversion specification is invalid, the behavior is undefined.335) If any argument is
+ not the correct type for the corresponding conversion specification, the behavior is
+ undefined.
+10 In no case does a nonexistent or small field width cause truncation of a field; if the result
+ of a conversion is wider than the field width, the field is expanded to contain the
+ conversion result.
+11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
+ to a hexadecimal floating number with the given precision.
+ Recommended practice
+12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
+ representable in the given precision, the result should be one of the two adjacent numbers
+ in hexadecimal floating style with the given precision, with the extra stipulation that the
+ error should have a correct sign for the current rounding direction.
+13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
+ DECIMAL_DIG, then the result should be correctly rounded.336) If the number of
+
+ 335) See ''future library directions'' (7.31.16).
+
+[page 409]
+
+ significant decimal digits is more than DECIMAL_DIG but the source value is exactly
+ representable with DECIMAL_DIG digits, then the result should be an exact
+ representation with trailing zeros. Otherwise, the source value is bounded by two
+ adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
+ of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
+ the error should have a correct sign for the current rounding direction.
+ Returns
+14 The fwprintf function returns the number of wide characters transmitted, or a negative
+ value if an output or encoding error occurred.
+ Environmental limits
+15 The number of wide characters that can be produced by any single conversion shall be at
+ least 4095.
+16 EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
+ places:
+ #include <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 (7.29.6.1.1), the mbrtowc function
+ (7.29.6.3.2).
+ 7.29.2.2 The fwscanf function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ int fwscanf(FILE * restrict stream,
+ const wchar_t * restrict format, ...);
+ Description
+2 The fwscanf function reads input from the stream pointed to by stream, under
+ control of the wide string pointed to by format that specifies the admissible input
+ sequences and how they are to be converted for assignment, using subsequent arguments
+
+ 336) For binary-to-decimal conversion, the result format's values are the numbers representable with the
+ given format specifier. The number of significant digits is determined by the format specifier, and in
+ the case of fixed-point conversion by the source value as well.
+
+[page 410]
+
+ as pointers to the objects to receive the converted input. If there are insufficient
+ arguments for the format, the behavior is undefined. If the format is exhausted while
+ arguments remain, the excess arguments are evaluated (as always) but are otherwise
+ ignored.
+3 The format is composed of zero or more directives: one or more white-space wide
+ characters, an ordinary wide character (neither % nor a white-space wide character), or a
+ conversion specification. Each conversion specification is introduced by the wide
+ character %. After the %, the following appear in sequence:
+ -- An optional assignment-suppressing wide character *.
+ -- An optional decimal integer greater than zero that specifies the maximum field width
+ (in wide characters).
+ -- An optional length modifier that specifies the size of the receiving object.
+ -- A conversion specifier wide character that specifies the type of conversion to be
+ applied.
+4 The fwscanf function executes each directive of the format in turn. When all directives
+ have been executed, or if a directive fails (as detailed below), the function returns.
+ Failures are described as input failures (due to the occurrence of an encoding error or the
+ unavailability of input characters), or matching failures (due to inappropriate input).
+5 A directive composed of white-space wide character(s) is executed by reading input up to
+ the first non-white-space wide character (which remains unread), or until no more wide
+ characters can be read. The directive never fails.
+6 A directive that is an ordinary wide character is executed by reading the next wide
+ character of the stream. If that wide character differs from the directive, the directive
+ fails and the differing and subsequent wide characters remain unread. Similarly, if end-
+ of-file, an encoding error, or a read error prevents a wide character from being read, the
+ directive fails.
+7 A directive that is a conversion specification defines a set of matching input sequences, as
+ described below for each specifier. A conversion specification is executed in the
+ following steps:
+8 Input white-space wide characters (as specified by the iswspace function) are skipped,
+ unless the specification includes a [, c, or n specifier.337)
+9 An input item is read from the stream, unless the specification includes an n specifier. An
+ input item is defined as the longest sequence of input wide characters which does not
+ exceed any specified field width and which is, or is a prefix of, a matching input
+
+
+ 337) These white-space wide characters are not counted against a specified field width.
+
+[page 411]
+
+ sequence.338) The first wide character, if any, after the input item remains unread. If the
+ length of the input item is zero, the execution of the directive fails; this condition is a
+ matching failure unless end-of-file, an encoding error, or a read error prevented input
+ from the stream, in which case it is an input failure.
+10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
+ count of input wide characters) is converted to a type appropriate to the conversion
+ specifier. If the input item is not a matching sequence, the execution of the directive fails:
+ this condition is a matching failure. Unless assignment suppression was indicated by a *,
+ the result of the conversion is placed in the object pointed to by the first argument
+ following the format argument that has not already received a conversion result. If this
+ object does not have an appropriate type, or if the result of the conversion cannot be
+ represented in the object, the behavior is undefined.
+11 The length modifiers and their meanings are:
+ hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to signed char or unsigned char.
+ h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to short int or unsigned short
+ int.
+ l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to long int or unsigned long
+ int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
+ an argument with type pointer to double; or that a following c, s, or [
+ conversion specifier applies to an argument with type pointer to wchar_t.
+ ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to long long int or unsigned
+ long long int.
+ j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to intmax_t or uintmax_t.
+ z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to size_t or the corresponding signed
+ integer type.
+ t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
+ to an argument with type pointer to ptrdiff_t or the corresponding
+ unsigned integer type.
+
+
+ 338) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
+ sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
+
+[page 412]
+
+ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
+ applies to an argument with type pointer to long double.
+ If a length modifier appears with any conversion specifier other than as specified above,
+ the behavior is undefined.
+12 The conversion specifiers and their meanings are:
+ d Matches an optionally signed decimal integer, whose format is the same as
+ expected for the subject sequence of the wcstol function with the value 10
+ for the base argument. The corresponding argument shall be a pointer to
+ signed integer.
+ i Matches an optionally signed integer, whose format is the same as expected
+ for the subject sequence of the wcstol function with the value 0 for the
+ base argument. The corresponding argument shall be a pointer to signed
+ 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
+
+[page 413]
+
+ 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
+
+[page 414]
+
+ 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 %%.
+13 If a conversion specification is invalid, the behavior is undefined.339)
+14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
+ respectively, a, e, f, g, and x.
+15 Trailing white space (including new-line wide characters) is left unread unless matched
+ by a directive. The success of literal matches and suppressed assignments is not directly
+ determinable other than via the %n directive.
+ Returns
+16 The fwscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the function returns the
+ number of input items assigned, which can be fewer than provided for, or even zero, in
+ the event of an early matching failure.
+17 EXAMPLE 1 The call:
+ #include <stdio.h>
+ #include <wchar.h>
+ /* ... */
+ int n, i; float x; wchar_t name[50];
+ n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
+
+
+
+ 339) See ''future library directions'' (7.31.16).
+
+[page 415]
+
+ with the input line:
+ 25 54.32E-1 thompson
+ will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
+ thompson\0.
+
+18 EXAMPLE 2 The call:
+ #include <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 (7.29.4.1.1), the
+ wcstol, wcstoll, wcstoul, and wcstoull functions (7.29.4.1.2), the wcrtomb
+ function (7.29.6.3.3).
+ 7.29.2.3 The swprintf function
+ Synopsis
+1 #include <wchar.h>
+ int swprintf(wchar_t * restrict s,
+ size_t n,
+ const wchar_t * restrict format, ...);
+ Description
+2 The swprintf function is equivalent to fwprintf, except that the argument s
+ specifies an array of wide characters into which the generated output is to be written,
+ rather than written to a stream. No more than n wide characters are written, including a
+ terminating null wide character, which is always added (unless n is zero).
+ Returns
+3 The swprintf function returns the number of wide characters written in the array, not
+ counting the terminating null wide character, or a negative value if an encoding error
+ occurred or if n or more wide characters were requested to be written.
+
+[page 416]
+
+ 7.29.2.4 The swscanf function
+ Synopsis
+1 #include <wchar.h>
+ int swscanf(const wchar_t * restrict s,
+ const wchar_t * restrict format, ...);
+ Description
+2 The swscanf function is equivalent to fwscanf, except that the argument s specifies a
+ wide string from which the input is to be obtained, rather than from a stream. Reaching
+ the end of the wide string is equivalent to encountering end-of-file for the fwscanf
+ function.
+ Returns
+3 The swscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the swscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+ 7.29.2.5 The vfwprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ #include <wchar.h>
+ int vfwprintf(FILE * restrict stream,
+ const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vfwprintf function is equivalent to fwprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfwprintf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vfwprintf function returns the number of wide characters transmitted, or a
+ negative value if an output or encoding error occurred.
+
+
+
+
+ 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
+ invoke the va_arg macro, the value of arg after the return is indeterminate.
+
+[page 417]
+
+4 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);
+ }
+
+ 7.29.2.6 The vfwscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <stdio.h>
+ #include <wchar.h>
+ int vfwscanf(FILE * restrict stream,
+ const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vfwscanf function is equivalent to fwscanf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfwscanf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vfwscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vfwscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+
+[page 418]
+
+ 7.29.2.7 The vswprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <wchar.h>
+ int vswprintf(wchar_t * restrict s,
+ size_t n,
+ const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vswprintf function is equivalent to swprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vswprintf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vswprintf function returns the number of wide characters written in the array, not
+ counting the terminating null wide character, or a negative value if an encoding error
+ occurred or if n or more wide characters were requested to be generated.
+ 7.29.2.8 The vswscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <wchar.h>
+ int vswscanf(const wchar_t * restrict s,
+ const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vswscanf function is equivalent to swscanf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vswscanf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vswscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vswscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+
+[page 419]
+
+ 7.29.2.9 The vwprintf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <wchar.h>
+ int vwprintf(const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vwprintf function is equivalent to wprintf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vwprintf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vwprintf function returns the number of wide characters transmitted, or a negative
+ value if an output or encoding error occurred.
+ 7.29.2.10 The vwscanf function
+ Synopsis
+1 #include <stdarg.h>
+ #include <wchar.h>
+ int vwscanf(const wchar_t * restrict format,
+ va_list arg);
+ Description
+2 The vwscanf function is equivalent to wscanf, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vwscanf function does not invoke the
+ va_end macro.340)
+ Returns
+3 The vwscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the vwscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+
+[page 420]
+
+ 7.29.2.11 The wprintf function
+ Synopsis
+1 #include <wchar.h>
+ int wprintf(const wchar_t * restrict format, ...);
+ Description
+2 The wprintf function is equivalent to fwprintf with the argument stdout
+ interposed before the arguments to wprintf.
+ Returns
+3 The wprintf function returns the number of wide characters transmitted, or a negative
+ value if an output or encoding error occurred.
+ 7.29.2.12 The wscanf function
+ Synopsis
+1 #include <wchar.h>
+ int wscanf(const wchar_t * restrict format, ...);
+ Description
+2 The wscanf function is equivalent to fwscanf with the argument stdin interposed
+ before the arguments to wscanf.
+ Returns
+3 The wscanf function returns the value of the macro EOF if an input failure occurs
+ before the first conversion (if any) has completed. Otherwise, the wscanf function
+ returns the number of input items assigned, which can be fewer than provided for, or even
+ zero, in the event of an early matching failure.
+ 7.29.3 Wide character input/output functions
+ 7.29.3.1 The fgetwc function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wint_t fgetwc(FILE *stream);
+ Description
+2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
+ next wide character is present, the fgetwc function obtains that wide character as a
+ wchar_t converted to a wint_t and advances the associated file position indicator for
+ the stream (if defined).
+
+[page 421]
+
+ Returns
+3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
+ of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
+ the fgetwc function returns the next wide character from the input stream pointed to by
+ stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
+ function returns WEOF. If an encoding error occurs (including too few bytes), the value of
+ the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.341)
+ 7.29.3.2 The fgetws function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wchar_t *fgetws(wchar_t * restrict s,
+ int n, FILE * restrict stream);
+ Description
+2 The fgetws function reads at most one less than the number of wide characters
+ specified by n from the stream pointed to by stream into the array pointed to by s. No
+ additional wide characters are read after a new-line wide character (which is retained) or
+ after end-of-file. A null wide character is written immediately after the last wide
+ character read into the array.
+ Returns
+3 The fgetws function returns s if successful. If end-of-file is encountered and no
+ characters have been read into the array, the contents of the array remain unchanged and a
+ null pointer is returned. If a read or encoding error occurs during the operation, the array
+ contents are indeterminate and a null pointer is returned.
+ 7.29.3.3 The fputwc function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wint_t fputwc(wchar_t c, FILE *stream);
+ Description
+2 The fputwc function writes the wide character specified by c to the output stream
+ pointed to by stream, at the position indicated by the associated file position indicator
+ for the stream (if defined), and advances the indicator appropriately. If the file cannot
+
+ 341) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
+ Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.
+
+[page 422]
+
+ support positioning requests, or if the stream was opened with append mode, the
+ character is appended to the output stream.
+ Returns
+3 The fputwc function returns the wide character written. If a write error occurs, the
+ error indicator for the stream is set and fputwc returns WEOF. If an encoding error
+ occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.
+ 7.29.3.4 The fputws function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ int fputws(const wchar_t * restrict s,
+ FILE * restrict stream);
+ Description
+2 The fputws function writes the wide string pointed to by s to the stream pointed to by
+ stream. The terminating null wide character is not written.
+ Returns
+3 The fputws function returns EOF if a write or encoding error occurs; otherwise, it
+ returns a nonnegative value.
+ 7.29.3.5 The fwide function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ int fwide(FILE *stream, int mode);
+ Description
+2 The fwide function determines the orientation of the stream pointed to by stream. If
+ mode is greater than zero, the function first attempts to make the stream wide oriented. If
+ mode is less than zero, the function first attempts to make the stream byte oriented.342)
+ Otherwise, mode is zero and the function does not alter the orientation of the stream.
+ Returns
+3 The fwide function returns a value greater than zero if, after the call, the stream has
+ wide orientation, a value less than zero if the stream has byte orientation, or zero if the
+ stream has no orientation.
+
+
+ 342) If the orientation of the stream has already been determined, fwide does not change it.
+
+[page 423]
+
+ 7.29.3.6 The getwc function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wint_t getwc(FILE *stream);
+ Description
+2 The getwc function is equivalent to fgetwc, except that if it is implemented as a
+ macro, it may evaluate stream more than once, so the argument should never be an
+ expression with side effects.
+ Returns
+3 The getwc function returns the next wide character from the input stream pointed to by
+ stream, or WEOF.
+ 7.29.3.7 The getwchar function
+ Synopsis
+1 #include <wchar.h>
+ wint_t getwchar(void);
+ Description
+2 The getwchar function is equivalent to getwc with the argument stdin.
+ Returns
+3 The getwchar function returns the next wide character from the input stream pointed to
+ by stdin, or WEOF.
+ 7.29.3.8 The putwc function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wint_t putwc(wchar_t c, FILE *stream);
+ Description
+2 The putwc function is equivalent to fputwc, except that if it is implemented as a
+ macro, it may evaluate stream more than once, so that argument should never be an
+ expression with side effects.
+ Returns
+3 The putwc function returns the wide character written, or WEOF.
+
+[page 424]
+
+ 7.29.3.9 The putwchar function
+ Synopsis
+1 #include <wchar.h>
+ wint_t putwchar(wchar_t c);
+ Description
+2 The putwchar function is equivalent to putwc with the second argument stdout.
+ Returns
+3 The putwchar function returns the character written, or WEOF.
+ 7.29.3.10 The ungetwc function
+ Synopsis
+1 #include <stdio.h>
+ #include <wchar.h>
+ wint_t ungetwc(wint_t c, FILE *stream);
+ Description
+2 The ungetwc function pushes the wide character specified by c back onto the input
+ stream pointed to by stream. Pushed-back wide characters will be returned by
+ subsequent reads on that stream in the reverse order of their pushing. A successful
+ intervening call (with the stream pointed to by stream) to a file positioning function
+ (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
+ stream. The external storage corresponding to the stream is unchanged.
+3 One wide character of pushback is guaranteed, even if the call to the ungetwc function
+ follows just after a call to a formatted wide character input function fwscanf,
+ vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
+ on the same stream without an intervening read or file positioning operation on that
+ stream, the operation may fail.
+4 If the value of c equals that of the macro WEOF, the operation fails and the input stream is
+ unchanged.
+5 A successful call to the ungetwc function clears the end-of-file indicator for the stream.
+ The value of the file position indicator for the stream after reading or discarding all
+ pushed-back wide characters is the same as it was before the wide characters were pushed
+ back. For a text or binary stream, the value of its file position indicator after a successful
+ call to the ungetwc function is unspecified until all pushed-back wide characters are
+ read or discarded.
+
+[page 425]
+
+ Returns
+6 The ungetwc function returns the wide character pushed back, or WEOF if the operation
+ fails.
+ 7.29.4 General wide string utilities
+1 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.
+2 Where an argument declared as size_t n determines the length of the array for a
+ function, n can have the value zero on a call to that function. Unless explicitly stated
+ otherwise in the description of a particular function in this subclause, pointer arguments
+ on such a call shall still have valid values, as described in 7.1.4. On such a call, a
+ function that locates a wide character finds no occurrence, a function that compares two
+ wide character sequences returns zero, and a function that copies wide characters copies
+ zero wide characters.
+ 7.29.4.1 Wide string numeric conversion functions
+ 7.29.4.1.1 The wcstod, wcstof, and wcstold functions
+ Synopsis
+1 #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
+2 The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
+ string pointed to by nptr to double, float, and long double representation,
+ respectively. First, they decompose the input string into three parts: an initial, possibly
+ empty, sequence of white-space wide characters (as specified by the iswspace
+ function), a subject sequence resembling a floating-point constant or representing an
+ infinity or NaN; and a final wide string of one or more unrecognized wide characters,
+ including the terminating null wide character of the input wide string. Then, they attempt
+ to convert the subject sequence to a floating-point number, and return the result.
+3 The expected form of the subject sequence is an optional plus or minus sign, then one of
+ the following:
+
+[page 426]
+
+ -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
+ character, then an optional exponent part as defined for the corresponding single-byte
+ characters in 6.4.4.2;
+ -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
+ decimal-point wide character, then an optional binary exponent part as defined in
+ 6.4.4.2;
+ -- INF or INFINITY, or any other wide string equivalent except for case
+ -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
+ case in the NAN part, where:
+ n-wchar-sequence:
+ digit
+ nondigit
+ n-wchar-sequence digit
+ n-wchar-sequence nondigit
+ The subject sequence is defined as the longest initial subsequence of the input wide
+ string, starting with the first non-white-space wide character, that is of the expected form.
+ The subject sequence contains no wide characters if the input wide string is not of the
+ expected form.
+4 If the subject sequence has the expected form for a floating-point number, the sequence of
+ wide characters starting with the first digit or the decimal-point wide character
+ (whichever occurs first) is interpreted as a floating constant according to the rules of
+ 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
+ if neither an exponent part nor a decimal-point wide character appears in a decimal
+ floating point number, or if a binary exponent part does not appear in a hexadecimal
+ floating point number, an exponent part of the appropriate type with value zero is
+ assumed to follow the last digit in the string. If the subject sequence begins with a minus
+ sign, the sequence is interpreted as negated.343) 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 sequence is implementation-defined.344) A pointer to the
+
+ 343) 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.
+ 344) An implementation may use the n-wchar sequence to determine extra information to be represented in
+ the NaN's significand.
+
+[page 427]
+
+ final wide string is stored in the object pointed to by endptr, provided that endptr is
+ not a null pointer.
+5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
+ value resulting from the conversion is correctly rounded.
+6 In other than the "C" locale, additional locale-specific subject sequence forms may be
+ accepted.
+7 If the subject sequence is empty or does not have the expected form, no conversion is
+ performed; the value of nptr is stored in the object pointed to by endptr, provided
+ that endptr is not a null pointer.
+ Recommended practice
+8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
+ the result is not exactly representable, the result should be one of the two numbers in the
+ appropriate internal format that are adjacent to the hexadecimal floating source value,
+ with the extra stipulation that the error should have a correct sign for the current rounding
+ direction.
+9 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.345)
+ Returns
+10 The functions return the converted value, if any. If no conversion could be performed,
+ zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
+ plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
+ return type and sign of the value), and the value of the macro ERANGE is stored in
+ errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
+ no greater than the smallest normalized positive number in the return type; whether
+ errno acquires the value ERANGE is implementation-defined.
+
+
+
+
+ 345) 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.
+
+[page 428]
+
+ 7.29.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
+ Synopsis
+1 #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
+2 The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
+ portion of the wide string pointed to by nptr to long int, long long int,
+ unsigned long int, and unsigned long long int representation,
+ respectively. First, they decompose the input string into three parts: an initial, possibly
+ empty, sequence of white-space wide characters (as specified by the iswspace
+ function), a subject sequence resembling an integer represented in some radix determined
+ by the value of base, and a final wide string of one or more unrecognized wide
+ characters, including the terminating null wide character of the input wide string. Then,
+ they attempt to convert the subject sequence to an integer, and return the result.
+3 If the value of base is zero, the expected form of the subject sequence is that of an
+ integer constant as described for the corresponding single-byte characters in 6.4.4.1,
+ optionally preceded by a plus or minus sign, but not including an integer suffix. If the
+ value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
+ is a sequence of letters and digits representing an integer with the radix specified by
+ base, optionally preceded by a plus or minus sign, but not including an integer suffix.
+ The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
+ letters and digits whose ascribed values are less than that of base are permitted. If the
+ value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
+ of letters and digits, following the sign if present.
+
+[page 429]
+
+4 The subject sequence is defined as the longest initial subsequence of the input wide
+ string, starting with the first non-white-space wide character, that is of the expected form.
+ The subject sequence contains no wide characters if the input wide string is empty or
+ consists entirely of white space, or if the first non-white-space wide character is other
+ than a sign or a permissible letter or digit.
+5 If the subject sequence has the expected form and the value of base is zero, the sequence
+ of wide characters starting with the first digit is interpreted as an integer constant
+ according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
+ value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
+ letter its value as given above. If the subject sequence begins with a minus sign, the value
+ resulting from the conversion is negated (in the return type). A pointer to the final wide
+ string is stored in the object pointed to by endptr, provided that endptr is not a null
+ pointer.
+6 In other than the "C" locale, additional locale-specific subject sequence forms may be
+ accepted.
+7 If the subject sequence is empty or does not have the expected form, no conversion is
+ performed; the value of nptr is stored in the object pointed to by endptr, provided
+ that endptr is not a null pointer.
+ Returns
+8 The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
+ value, if any. If no conversion could be performed, zero is returned. If the correct value
+ is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
+ LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
+ sign of the value, if any), and the value of the macro ERANGE is stored in errno.
+ 7.29.4.2 Wide string copying functions
+ 7.29.4.2.1 The wcscpy function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcscpy(wchar_t * restrict s1,
+ const wchar_t * restrict s2);
+ Description
+2 The wcscpy function copies the wide string pointed to by s2 (including the terminating
+ null wide character) into the array pointed to by s1.
+ Returns
+3 The wcscpy function returns the value of s1.
+
+[page 430]
+
+ 7.29.4.2.2 The wcsncpy function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcsncpy(wchar_t * restrict s1,
+ const wchar_t * restrict s2,
+ size_t n);
+ Description
+2 The wcsncpy function copies not more than n wide characters (those that follow a null
+ wide character are not copied) from the array pointed to by s2 to the array pointed to by
+ s1.346)
+3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
+ wide characters are appended to the copy in the array pointed to by s1, until n wide
+ characters in all have been written.
+ Returns
+4 The wcsncpy function returns the value of s1.
+ 7.29.4.2.3 The wmemcpy function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wmemcpy(wchar_t * restrict s1,
+ const wchar_t * restrict s2,
+ size_t n);
+ Description
+2 The wmemcpy function copies n wide characters from the object pointed to by s2 to the
+ object pointed to by s1.
+ Returns
+3 The wmemcpy function returns the value of s1.
+
+
+
+
+ 346) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
+ result will not be null-terminated.
+
+[page 431]
+
+ 7.29.4.2.4 The wmemmove function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
+ size_t n);
+ Description
+2 The wmemmove function copies n wide characters from the object pointed to by s2 to
+ the object pointed to by s1. Copying takes place as if the n wide characters from the
+ object pointed to by s2 are first copied into a temporary array of n wide characters that
+ does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
+ the temporary array are copied into the object pointed to by s1.
+ Returns
+3 The wmemmove function returns the value of s1.
+ 7.29.4.3 Wide string concatenation functions
+ 7.29.4.3.1 The wcscat function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcscat(wchar_t * restrict s1,
+ const wchar_t * restrict s2);
+ Description
+2 The wcscat function appends a copy of the wide string pointed to by s2 (including the
+ terminating null wide character) to the end of the wide string pointed to by s1. The initial
+ wide character of s2 overwrites the null wide character at the end of s1.
+ Returns
+3 The wcscat function returns the value of s1.
+ 7.29.4.3.2 The wcsncat function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcsncat(wchar_t * restrict s1,
+ const wchar_t * restrict s2,
+ size_t n);
+ Description
+2 The wcsncat function appends not more than n wide characters (a null wide character
+ and those that follow it are not appended) from the array pointed to by s2 to the end of
+
+[page 432]
+
+ 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.347)
+ Returns
+3 The wcsncat function returns the value of s1.
+ 7.29.4.4 Wide string comparison functions
+1 Unless explicitly stated otherwise, the functions described in this subclause order two
+ wide characters the same way as two integers of the underlying integer type designated
+ by wchar_t.
+ 7.29.4.4.1 The wcscmp function
+ Synopsis
+1 #include <wchar.h>
+ int wcscmp(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcscmp function compares the wide string pointed to by s1 to the wide string
+ pointed to by s2.
+ Returns
+3 The wcscmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
+ wide string pointed to by s2.
+ 7.29.4.4.2 The wcscoll function
+ Synopsis
+1 #include <wchar.h>
+ int wcscoll(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcscoll function compares the wide string pointed to by s1 to the wide string
+ pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
+ current locale.
+ Returns
+3 The wcscoll function returns an integer greater than, equal to, or less than zero,
+ accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
+
+
+ 347) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
+ wcslen(s1)+n+1.
+
+[page 433]
+
+ wide string pointed to by s2 when both are interpreted as appropriate to the current
+ locale.
+ 7.29.4.4.3 The wcsncmp function
+ Synopsis
+1 #include <wchar.h>
+ int wcsncmp(const wchar_t *s1, const wchar_t *s2,
+ size_t n);
+ Description
+2 The wcsncmp function compares not more than n wide characters (those that follow a
+ null wide character are not compared) from the array pointed to by s1 to the array
+ pointed to by s2.
+ Returns
+3 The wcsncmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
+ to, or less than the possibly null-terminated array pointed to by s2.
+ 7.29.4.4.4 The wcsxfrm function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcsxfrm(wchar_t * restrict s1,
+ const wchar_t * restrict s2,
+ size_t n);
+ Description
+2 The wcsxfrm function transforms the wide string pointed to by s2 and places the
+ resulting wide string into the array pointed to by s1. The transformation is such that if
+ the wcscmp function is applied to two transformed wide strings, it returns a value greater
+ than, equal to, or less than zero, corresponding to the result of the wcscoll function
+ applied to the same two original wide strings. No more than n wide characters are placed
+ into the resulting array pointed to by s1, including the terminating null wide character. If
+ n is zero, s1 is permitted to be a null pointer.
+ Returns
+3 The wcsxfrm function returns the length of the transformed wide string (not including
+ the terminating null wide character). If the value returned is n or greater, the contents of
+ the array pointed to by s1 are indeterminate.
+4 EXAMPLE The value of the following expression is the length of the array needed to hold the
+ transformation of the wide string pointed to by s:
+
+[page 434]
+
+ 1 + wcsxfrm(NULL, s, 0)
+
+ 7.29.4.4.5 The wmemcmp function
+ Synopsis
+1 #include <wchar.h>
+ int wmemcmp(const wchar_t *s1, const wchar_t *s2,
+ size_t n);
+ Description
+2 The wmemcmp function compares the first n wide characters of the object pointed to by
+ s1 to the first n wide characters of the object pointed to by s2.
+ Returns
+3 The wmemcmp function returns an integer greater than, equal to, or less than zero,
+ accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
+ pointed to by s2.
+ 7.29.4.5 Wide string search functions
+ 7.29.4.5.1 The wcschr function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcschr(const wchar_t *s, wchar_t c);
+ Description
+2 The wcschr function locates the first occurrence of c in the wide string pointed to by s.
+ The terminating null wide character is considered to be part of the wide string.
+ Returns
+3 The wcschr function returns a pointer to the located wide character, or a null pointer if
+ the wide character does not occur in the wide string.
+ 7.29.4.5.2 The wcscspn function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcscspn function computes the length of the maximum initial segment of the wide
+ string pointed to by s1 which consists entirely of wide characters not from the wide
+ string pointed to by s2.
+
+[page 435]
+
+ Returns
+3 The wcscspn function returns the length of the segment.
+ 7.29.4.5.3 The wcspbrk function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
+ any wide character from the wide string pointed to by s2.
+ Returns
+3 The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
+ no wide character from s2 occurs in s1.
+ 7.29.4.5.4 The wcsrchr function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
+ Description
+2 The wcsrchr function locates the last occurrence of c in the wide string pointed to by
+ s. The terminating null wide character is considered to be part of the wide string.
+ Returns
+3 The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
+ not occur in the wide string.
+ 7.29.4.5.5 The wcsspn function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcsspn function computes the length of the maximum initial segment of the wide
+ string pointed to by s1 which consists entirely of wide characters from the wide string
+ pointed to by s2.
+ Returns
+3 The wcsspn function returns the length of the segment.
+
+[page 436]
+
+ 7.29.4.5.6 The wcsstr function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
+ Description
+2 The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
+ the sequence of wide characters (excluding the terminating null wide character) in the
+ wide string pointed to by s2.
+ Returns
+3 The wcsstr function returns a pointer to the located wide string, or a null pointer if the
+ wide string is not found. If s2 points to a wide string with zero length, the function
+ returns s1.
+ 7.29.4.5.7 The wcstok function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wcstok(wchar_t * restrict s1,
+ const wchar_t * restrict s2,
+ wchar_t ** restrict ptr);
+ Description
+2 A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
+ a sequence of tokens, each of which is delimited by a wide character from the wide string
+ pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
+ which the wcstok function stores information necessary for it to continue scanning the
+ same wide string.
+3 The first call in a sequence has a non-null first argument and stores an initial value in the
+ object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
+ the object pointed to by ptr is required to have the value stored by the previous call in
+ the sequence, which is then updated. The separator wide string pointed to by s2 may be
+ different from call to call.
+4 The first call in the sequence searches the wide string pointed to by s1 for the first wide
+ character that is not contained in the current separator wide string pointed to by s2. If no
+ such wide character is found, then there are no tokens in the wide string pointed to by s1
+ and the wcstok function returns a null pointer. If such a wide character is found, it is
+ the start of the first token.
+5 The wcstok function then searches from there for a wide character that is contained in
+ the current separator wide string. If no such wide character is found, the current token
+
+[page 437]
+
+ extends to the end of the wide string pointed to by s1, and subsequent searches in the
+ same wide string for a token return a null pointer. If such a wide character is found, it is
+ overwritten by a null wide character, which terminates the current token.
+6 In all cases, the wcstok function stores sufficient information in the pointer pointed to
+ by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
+ value for ptr, shall start searching just past the element overwritten by a null wide
+ character (if any).
+ Returns
+7 The wcstok function returns a pointer to the first wide character of a token, or a null
+ pointer if there is no token.
+8 EXAMPLE
+ #include <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
+
+ 7.29.4.5.8 The wmemchr function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wmemchr(const wchar_t *s, wchar_t c,
+ size_t n);
+ Description
+2 The wmemchr function locates the first occurrence of c in the initial n wide characters of
+ the object pointed to by s.
+ Returns
+3 The wmemchr function returns a pointer to the located wide character, or a null pointer if
+ the wide character does not occur in the object.
+
+[page 438]
+
+ 7.29.4.6 Miscellaneous functions
+ 7.29.4.6.1 The wcslen function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcslen(const wchar_t *s);
+ Description
+2 The wcslen function computes the length of the wide string pointed to by s.
+ Returns
+3 The wcslen function returns the number of wide characters that precede the terminating
+ null wide character.
+ 7.29.4.6.2 The wmemset function
+ Synopsis
+1 #include <wchar.h>
+ wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
+ Description
+2 The wmemset function copies the value of c into each of the first n wide characters of
+ the object pointed to by s.
+ Returns
+3 The wmemset function returns the value of s.
+ 7.29.5 Wide character time conversion functions
+ 7.29.5.1 The wcsftime function
+ Synopsis
+1 #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
+2 The wcsftime function is equivalent to the strftime function, except that:
+ -- The argument s points to the initial element of an array of wide characters into which
+ the generated output is to be placed.
+
+[page 439]
+
+ -- The argument maxsize indicates the limiting number of wide characters.
+ -- The argument format is a wide string and the conversion specifiers are replaced by
+ corresponding sequences of wide characters.
+ -- The return value indicates the number of wide characters.
+ Returns
+3 If the total number of resulting wide characters including the terminating null wide
+ character is not more than maxsize, the wcsftime function returns the number of
+ wide characters placed into the array pointed to by s not including the terminating null
+ wide character. Otherwise, zero is returned and the contents of the array are
+ indeterminate.
+ 7.29.6 Extended multibyte/wide character conversion utilities
+1 The header <wchar.h> declares an extended set of functions useful for conversion
+ between multibyte characters and wide characters.
+2 Most of the following functions -- those that are listed as ''restartable'', 7.29.6.3 and
+ 7.29.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used
+ to describe the current conversion state from a particular multibyte character sequence to
+ a wide character sequence (or the reverse) under the rules of a particular setting for the
+ LC_CTYPE category of the current locale.
+3 The initial conversion state corresponds, for a conversion in either direction, to the
+ beginning of a new multibyte character in the initial shift state. A zero-valued
+ mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
+ valued mbstate_t object can be used to initiate conversion involving any multibyte
+ character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
+ been altered by any of the functions described in this subclause, and is then used with a
+ different multibyte character sequence, or in the other conversion direction, or with a
+ different LC_CTYPE category setting than on earlier function calls, the behavior is
+ undefined.348)
+4 On entry, each function takes the described conversion state (either internal or pointed to
+ by an argument) as current. The conversion state described by the referenced object is
+ altered as needed to track the shift state, and the position within a multibyte character, for
+ the associated multibyte character sequence.
+
+
+
+
+ 348) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
+ mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
+ character string.
+
+[page 440]
+
+ 7.29.6.1 Single-byte/wide character conversion functions
+ 7.29.6.1.1 The btowc function
+ Synopsis
+1 #include <wchar.h>
+ wint_t btowc(int c);
+ Description
+2 The btowc function determines whether c constitutes a valid single-byte character in the
+ initial shift state.
+ Returns
+3 The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
+ does not constitute a valid single-byte character in the initial shift state. Otherwise, it
+ returns the wide character representation of that character.
+ 7.29.6.1.2 The wctob function
+ Synopsis
+1 #include <wchar.h>
+ int wctob(wint_t c);
+ Description
+2 The wctob function determines whether c corresponds to a member of the extended
+ character set whose multibyte character representation is a single byte when in the initial
+ shift state.
+ Returns
+3 The wctob function returns EOF if c does not correspond to a multibyte character with
+ length one in the initial shift state. Otherwise, it returns the single-byte representation of
+ that character as an unsigned char converted to an int.
+ 7.29.6.2 Conversion state functions
+ 7.29.6.2.1 The mbsinit function
+ Synopsis
+1 #include <wchar.h>
+ int mbsinit(const mbstate_t *ps);
+ Description
+2 If ps is not a null pointer, the mbsinit function determines whether the referenced
+ mbstate_t object describes an initial conversion state.
+
+[page 441]
+
+ Returns
+3 The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
+ describes an initial conversion state; otherwise, it returns zero.
+ 7.29.6.3 Restartable multibyte/wide character conversion functions
+1 These functions differ from the corresponding multibyte character functions of 7.22.7
+ (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
+ pointer to mbstate_t that points to an object that can completely describe the current
+ conversion state of the associated multibyte character sequence. If ps is a null pointer,
+ each function uses its own internal mbstate_t object instead, which is initialized at
+ program startup to the initial conversion state; the functions are not required to avoid data
+ races with other calls to the same function in this case. The implementation behaves as if
+ no library function calls these functions with a null pointer for ps.
+2 Also unlike their corresponding functions, the return value does not represent whether the
+ encoding is state-dependent.
+ 7.29.6.3.1 The mbrlen function
+ Synopsis
+1 #include <wchar.h>
+ size_t mbrlen(const char * restrict s,
+ size_t n,
+ mbstate_t * restrict ps);
+ Description
+2 The mbrlen function is equivalent to the call:
+ mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
+ where internal is the mbstate_t object for the mbrlen function, except that the
+ expression designated by ps is evaluated only once.
+ Returns
+3 The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
+ or (size_t)(-1).
+ Forward references: the mbrtowc function (7.29.6.3.2).
+
+[page 442]
+
+ 7.29.6.3.2 The mbrtowc function
+ Synopsis
+1 #include <wchar.h>
+ size_t mbrtowc(wchar_t * restrict pwc,
+ const char * restrict s,
+ size_t n,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the mbrtowc function is equivalent to the call:
+ mbrtowc(NULL, "", 1, ps)
+ In this case, the values of the parameters pwc and n are ignored.
+3 If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
+ the byte pointed to by s to determine the number of bytes needed to complete the next
+ multibyte character (including any shift sequences). If the function determines that the
+ next multibyte character is complete and valid, it determines the value of the
+ corresponding wide character and then, if pwc is not a null pointer, stores that value in
+ the object pointed to by pwc. If the corresponding wide character is the null wide
+ character, the resulting state described is the initial conversion state.
+ Returns
+4 The mbrtowc function returns the first of the following that applies (given the current
+ conversion state):
+ 0 if the next n or fewer bytes complete the multibyte character that
+ corresponds to the null wide character (which is the value stored).
+ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
+ character (which is the value stored); the value returned is the number
+ of bytes that complete the multibyte character.
+ (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
+ multibyte character, and all n bytes have been processed (no value is
+ stored).349)
+ (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.
+
+ 349) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
+ sequence of redundant shift sequences (for implementations with state-dependent encodings).
+
+[page 443]
+
+ 7.29.6.3.3 The wcrtomb function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcrtomb(char * restrict s,
+ wchar_t wc,
+ mbstate_t * restrict ps);
+ Description
+2 If s is a null pointer, the wcrtomb function is equivalent to the call
+ wcrtomb(buf, L'\0', ps)
+ where buf is an internal buffer.
+3 If s is not a null pointer, the wcrtomb function determines the number of bytes needed
+ to represent the multibyte character that corresponds to the wide character given by wc
+ (including any shift sequences), and stores the multibyte character representation in the
+ array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
+ wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
+ to restore the initial shift state; the resulting state described is the initial conversion state.
+ Returns
+4 The wcrtomb function returns the number of bytes stored in the array object (including
+ any shift sequences). When wc is not a valid wide character, an encoding error occurs:
+ the function stores the value of the macro EILSEQ in errno and returns
+ (size_t)(-1); the conversion state is unspecified.
+ 7.29.6.4 Restartable multibyte/wide string conversion functions
+1 These functions differ from the corresponding multibyte string functions of 7.22.8
+ (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
+ mbstate_t that points to an object that can completely describe the current conversion
+ state of the associated multibyte character sequence. If ps is a null pointer, each function
+ uses its own internal mbstate_t object instead, which is initialized at program startup
+ to the initial conversion state; the functions are not required to avoid data races with other
+ calls to the same function in this case. The implementation behaves as if no library
+ function calls these functions with a null pointer for ps.
+2 Also unlike their corresponding functions, the conversion source parameter, src, has a
+ pointer-to-pointer type. When the function is storing the results of conversions (that is,
+ when dst is not a null pointer), the pointer object pointed to by this parameter is updated
+ to reflect the amount of the source processed by that invocation.
+
+[page 444]
+
+ 7.29.6.4.1 The mbsrtowcs function
+ Synopsis
+1 #include <wchar.h>
+ size_t mbsrtowcs(wchar_t * restrict dst,
+ const char ** restrict src,
+ size_t len,
+ mbstate_t * restrict ps);
+ Description
+2 The mbsrtowcs function converts a sequence of multibyte characters that begins in the
+ conversion state described by the object pointed to by ps, from the array indirectly
+ pointed to by src into a sequence of corresponding wide characters. If dst is not a null
+ pointer, the converted characters are stored into the array pointed to by dst. Conversion
+ continues up to and including a terminating null character, which is also stored.
+ Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
+ not form a valid multibyte character, or (if dst is not a null pointer) when len wide
+ characters have been stored into the array pointed to by dst.350) Each conversion takes
+ place as if by a call to the mbrtowc function.
+3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
+ pointer (if conversion stopped due to reaching a terminating null character) or the address
+ just past the last multibyte character converted (if any). If conversion stopped due to
+ reaching a terminating null character and if dst is not a null pointer, the resulting state
+ described is the initial conversion state.
+ Returns
+4 If the input conversion encounters a sequence of bytes that do not form a valid multibyte
+ character, an encoding error occurs: the mbsrtowcs function stores the value of the
+ macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
+ unspecified. Otherwise, it returns the number of multibyte characters successfully
+ converted, not including the terminating null character (if any).
+
+
+
+
+ 350) Thus, the value of len is ignored if dst is a null pointer.
+
+[page 445]
+
+ 7.29.6.4.2 The wcsrtombs function
+ Synopsis
+1 #include <wchar.h>
+ size_t wcsrtombs(char * restrict dst,
+ const wchar_t ** restrict src,
+ size_t len,
+ mbstate_t * restrict ps);
+ Description
+2 The wcsrtombs function converts a sequence of wide characters from the array
+ indirectly pointed to by src into a sequence of corresponding multibyte characters that
+ begins in the conversion state described by the object pointed to by ps. If dst is not a
+ null pointer, the converted characters are then stored into the array pointed to by dst.
+ Conversion continues up to and including a terminating null wide character, which is also
+ stored. Conversion stops earlier in two cases: when a wide character is reached that does
+ not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
+ next multibyte character would exceed the limit of len total bytes to be stored into the
+ array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
+ function.351)
+3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
+ pointer (if conversion stopped due to reaching a terminating null wide character) or the
+ address just past the last wide character converted (if any). If conversion stopped due to
+ reaching a terminating null wide character, the resulting state described is the initial
+ conversion state.
+ Returns
+4 If conversion stops because a wide character is reached that does not correspond to a
+ valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
+ value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
+ state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
+ character sequence, not including the terminating null character (if any).
+
+
+
+
+ 351) If conversion stops because a terminating null wide character has been reached, the bytes stored
+ include those necessary to reach the initial shift state immediately before the null byte.
+
+[page 446]
+
+ 7.30 Wide character classification and mapping utilities <wctype.h>
+ 7.30.1 Introduction
+1 The header <wctype.h> defines one macro, and declares three data types and many
+ functions.352)
+2 The types declared are
+ wint_t
+ described in 7.29.1;
+ wctrans_t
+ which is a scalar type that can hold values which represent locale-specific character
+ mappings; and
+ wctype_t
+ which is a scalar type that can hold values which represent locale-specific character
+ classifications.
+3 The macro defined is WEOF (described in 7.29.1).
+4 The functions declared are grouped as follows:
+ -- Functions that provide wide character classification;
+ -- Extensible functions that provide wide character classification;
+ -- Functions that provide wide character case mapping;
+ -- Extensible functions that provide wide character mapping.
+5 For all functions described in this subclause that accept an argument of type wint_t, the
+ value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
+ this argument has any other value, the behavior is undefined.
+6 The behavior of these functions is affected by the LC_CTYPE category of the current
+ locale.
+
+
+
+
+ 352) See ''future library directions'' (7.31.17).
+
+[page 447]
+
+ 7.30.2 Wide character classification utilities
+1 The header <wctype.h> declares several functions useful for classifying wide
+ characters.
+2 The term printing wide character refers to a member of a locale-specific set of wide
+ characters, each of which occupies at least one printing position on a display device. The
+ term control wide character refers to a member of a locale-specific set of wide characters
+ that are not printing wide characters.
+ 7.30.2.1 Wide character classification functions
+1 The functions in this subclause return nonzero (true) if and only if the value of the
+ argument wc conforms to that in the description of the function.
+2 Each of the following functions returns true for each wide character that corresponds (as
+ if by a call to the wctob function) to a single-byte character for which the corresponding
+ character classification function from 7.4.1 returns true, except that the iswgraph and
+ iswpunct functions may differ with respect to wide characters other than L' ' that are
+ both printing and white-space wide characters.353)
+ Forward references: the wctob function (7.29.6.1.2).
+ 7.30.2.1.1 The iswalnum function
+ Synopsis
+1 #include <wctype.h>
+ int iswalnum(wint_t wc);
+ Description
+2 The iswalnum function tests for any wide character for which iswalpha or
+ iswdigit is true.
+ 7.30.2.1.2 The iswalpha function
+ Synopsis
+1 #include <wctype.h>
+ int iswalpha(wint_t wc);
+ Description
+2 The iswalpha function tests for any wide character for which iswupper or
+ iswlower is true, or any wide character that is one of a locale-specific set of alphabetic
+
+ 353) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
+ iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
+ (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
+ && iswspace(wc) is true, but not both.
+
+[page 448]
+
+ wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
+ is true.354)
+ 7.30.2.1.3 The iswblank function
+ Synopsis
+1 #include <wctype.h>
+ int iswblank(wint_t wc);
+ Description
+2 The iswblank function tests for any wide character that is a standard blank wide
+ character or is one of a locale-specific set of wide characters for which iswspace is true
+ and that is used to separate words within a line of text. The standard blank wide
+ characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
+ locale, iswblank returns true only for the standard blank characters.
+ 7.30.2.1.4 The iswcntrl function
+ Synopsis
+1 #include <wctype.h>
+ int iswcntrl(wint_t wc);
+ Description
+2 The iswcntrl function tests for any control wide character.
+ 7.30.2.1.5 The iswdigit function
+ Synopsis
+1 #include <wctype.h>
+ int iswdigit(wint_t wc);
+ Description
+2 The iswdigit function tests for any wide character that corresponds to a decimal-digit
+ character (as defined in 5.2.1).
+ 7.30.2.1.6 The iswgraph function
+ Synopsis
+1 #include <wctype.h>
+ int iswgraph(wint_t wc);
+
+
+
+
+ 354) The functions iswlower and iswupper test true or false separately for each of these additional
+ wide characters; all four combinations are possible.
+
+[page 449]
+
+ Description
+2 The iswgraph function tests for any wide character for which iswprint is true and
+ iswspace is false.355)
+ 7.30.2.1.7 The iswlower function
+ Synopsis
+1 #include <wctype.h>
+ int iswlower(wint_t wc);
+ Description
+2 The iswlower function tests for any wide character that corresponds to a lowercase
+ letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
+ iswdigit, iswpunct, or iswspace is true.
+ 7.30.2.1.8 The iswprint function
+ Synopsis
+1 #include <wctype.h>
+ int iswprint(wint_t wc);
+ Description
+2 The iswprint function tests for any printing wide character.
+ 7.30.2.1.9 The iswpunct function
+ Synopsis
+1 #include <wctype.h>
+ int iswpunct(wint_t wc);
+ Description
+2 The iswpunct function tests for any printing wide character that is one of a locale-
+ specific set of punctuation wide characters for which neither iswspace nor iswalnum
+ is true.355)
+ 7.30.2.1.10 The iswspace function
+ Synopsis
+1 #include <wctype.h>
+ int iswspace(wint_t wc);
+
+
+
+ 355) Note that the behavior of the iswgraph and iswpunct functions may differ from their
+ corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
+ characters other than ' '.
+
+[page 450]
+
+ Description
+2 The iswspace function tests for any wide character that corresponds to a locale-specific
+ set of white-space wide characters for which none of iswalnum, iswgraph, or
+ iswpunct is true.
+ 7.30.2.1.11 The iswupper function
+ Synopsis
+1 #include <wctype.h>
+ int iswupper(wint_t wc);
+ Description
+2 The iswupper function tests for any wide character that corresponds to an uppercase
+ letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
+ iswdigit, iswpunct, or iswspace is true.
+ 7.30.2.1.12 The iswxdigit function
+ Synopsis
+1 #include <wctype.h>
+ int iswxdigit(wint_t wc);
+ Description
+2 The iswxdigit function tests for any wide character that corresponds to a
+ hexadecimal-digit character (as defined in 6.4.4.1).
+ 7.30.2.2 Extensible wide character classification functions
+1 The functions wctype and iswctype provide extensible wide character classification
+ as well as testing equivalent to that performed by the functions described in the previous
+ subclause (7.30.2.1).
+ 7.30.2.2.1 The iswctype function
+ Synopsis
+1 #include <wctype.h>
+ int iswctype(wint_t wc, wctype_t desc);
+ Description
+2 The iswctype function determines whether the wide character wc has the property
+ described by desc. The current setting of the LC_CTYPE category shall be the same as
+ during the call to wctype that returned the value desc.
+3 Each of the following expressions has a truth-value equivalent to the call to the wide
+ character classification function (7.30.2.1) in the comment that follows the expression:
+
+[page 451]
+
+ iswctype(wc, wctype("alnum")) // iswalnum(wc)
+ iswctype(wc, wctype("alpha")) // iswalpha(wc)
+ iswctype(wc, wctype("blank")) // iswblank(wc)
+ iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
+ iswctype(wc, wctype("digit")) // iswdigit(wc)
+ iswctype(wc, wctype("graph")) // iswgraph(wc)
+ iswctype(wc, wctype("lower")) // iswlower(wc)
+ iswctype(wc, wctype("print")) // iswprint(wc)
+ iswctype(wc, wctype("punct")) // iswpunct(wc)
+ iswctype(wc, wctype("space")) // iswspace(wc)
+ iswctype(wc, wctype("upper")) // iswupper(wc)
+ iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
+ Returns
+4 The iswctype function returns nonzero (true) if and only if the value of the wide
+ character wc has the property described by desc. If desc is zero, the iswctype
+ function returns zero (false).
+ Forward references: the wctype function (7.30.2.2.2).
+ 7.30.2.2.2 The wctype function
+ Synopsis
+1 #include <wctype.h>
+ wctype_t wctype(const char *property);
+ Description
+2 The wctype function constructs a value with type wctype_t that describes a class of
+ wide characters identified by the string argument property.
+3 The strings listed in the description of the iswctype function shall be valid in all
+ locales as property arguments to the wctype function.
+ Returns
+4 If property identifies a valid class of wide characters according to the LC_CTYPE
+ category of the current locale, the wctype function returns a nonzero value that is valid
+ as the second argument to the iswctype function; otherwise, it returns zero.
+
+[page 452]
+
+ 7.30.3 Wide character case mapping utilities
+1 The header <wctype.h> declares several functions useful for mapping wide characters.
+ 7.30.3.1 Wide character case mapping functions
+ 7.30.3.1.1 The towlower function
+ Synopsis
+1 #include <wctype.h>
+ wint_t towlower(wint_t wc);
+ Description
+2 The towlower function converts an uppercase letter to a corresponding lowercase letter.
+ Returns
+3 If the argument is a wide character for which iswupper is true and there are one or
+ more corresponding wide characters, as specified by the current locale, for which
+ iswlower is true, the towlower function returns one of the corresponding wide
+ characters (always the same one for any given locale); otherwise, the argument is
+ returned unchanged.
+ 7.30.3.1.2 The towupper function
+ Synopsis
+1 #include <wctype.h>
+ wint_t towupper(wint_t wc);
+ Description
+2 The towupper function converts a lowercase letter to a corresponding uppercase letter.
+ Returns
+3 If the argument is a wide character for which iswlower is true and there are one or
+ more corresponding wide characters, as specified by the current locale, for which
+ iswupper is true, the towupper function returns one of the corresponding wide
+ characters (always the same one for any given locale); otherwise, the argument is
+ returned unchanged.
+ 7.30.3.2 Extensible wide character case mapping functions
+1 The functions wctrans and towctrans provide extensible wide character mapping as
+ well as case mapping equivalent to that performed by the functions described in the
+ previous subclause (7.30.3.1).
+
+[page 453]
+
+ 7.30.3.2.1 The towctrans function
+ Synopsis
+1 #include <wctype.h>
+ wint_t towctrans(wint_t wc, wctrans_t desc);
+ Description
+2 The towctrans function maps the wide character wc using the mapping described by
+ desc. The current setting of the LC_CTYPE category shall be the same as during the call
+ to wctrans that returned the value desc.
+3 Each of the following expressions behaves the same as the call to the wide character case
+ mapping function (7.30.3.1) in the comment that follows the expression:
+ towctrans(wc, wctrans("tolower")) // towlower(wc)
+ towctrans(wc, wctrans("toupper")) // towupper(wc)
+ Returns
+4 The towctrans function returns the mapped value of wc using the mapping described
+ by desc. If desc is zero, the towctrans function returns the value of wc.
+ 7.30.3.2.2 The wctrans function
+ Synopsis
+1 #include <wctype.h>
+ wctrans_t wctrans(const char *property);
+ Description
+2 The wctrans function constructs a value with type wctrans_t that describes a
+ mapping between wide characters identified by the string argument property.
+3 The strings listed in the description of the towctrans function shall be valid in all
+ locales as property arguments to the wctrans function.
+ Returns
+4 If property identifies a valid mapping of wide characters according to the LC_CTYPE
+ category of the current locale, the wctrans function returns a nonzero value that is valid
+ as the second argument to the towctrans function; otherwise, it returns zero.
+
+[page 454]
+
+ 7.31 Future library directions
+1 The following names are grouped under individual headers for convenience. All external
+ names described below are reserved no matter what headers are included by the program.
+ 7.31.1 Complex arithmetic <complex.h>
+1 The function names
+ cerf cexpm1 clog2
+ cerfc clog10 clgamma
+ cexp2 clog1p ctgamma
+ and the same names suffixed with f or l may be added to the declarations in the
+ <complex.h> header.
+ 7.31.2 Character handling <ctype.h>
+1 Function names that begin with either is or to, and a lowercase letter may be added to
+ the declarations in the <ctype.h> header.
+ 7.31.3 Errors <errno.h>
+1 Macros that begin with E and a digit or E and an uppercase letter may be added to the
+ macros defined in the <errno.h> header.
+ 7.31.4 Floating-point environment <fenv.h>
+1 Macros that begin with FE_ and an uppercase letter may be added to the macros defined
+ in the <fenv.h> header.
+ 7.31.5 Format conversion of integer types <inttypes.h>
+1 Macros that begin with either PRI or SCN, and either a lowercase letter or X may be
+ added to the macros defined in the <inttypes.h> header.
+ 7.31.6 Localization <locale.h>
+1 Macros that begin with LC_ and an uppercase letter may be added to the macros defined
+ in the <locale.h> header.
+ 7.31.7 Signal handling <signal.h>
+1 Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
+ letter may be added to the macros defined in the <signal.h> header.
+ 7.31.8 Atomics <stdatomic.h>
+1 Macros that begin with ATOMIC_ and an uppercase letter may be added to the macros
+ defined in the <stdatomic.h> header. Typedef names that begin with either
+ atomic_ or memory_, and a lowercase letter may be added to the declarations in the
+ <stdatomic.h> header. Enumeration constants that begin with memory_order_
+
+[page 455]
+
+ and a lowercase letter may be added to the definition of the memory_order type in the
+ <stdatomic.h> header. Function names that begin with atomic_ and a lowercase
+ letter may be added to the declarations in the <stdatomic.h> header.
+ 7.31.9 Boolean type and values <stdbool.h>
+1 The ability to undefine and perhaps then redefine the macros bool, true, and false is
+ an obsolescent feature.
+ 7.31.10 Integer types <stdint.h>
+1 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.
+ 7.31.11 Input/output <stdio.h>
+1 Lowercase letters may be added to the conversion specifiers and length modifiers in
+ fprintf and fscanf. Other characters may be used in extensions.
+2 The use of ungetc on a binary stream where the file position indicator is zero prior to
+ the call is an obsolescent feature.
+ 7.31.12 General utilities <stdlib.h>
+1 Function names that begin with str and a lowercase letter may be added to the
+ declarations in the <stdlib.h> header.
+ 7.31.13 String handling <string.h>
+1 Function names that begin with str, mem, or wcs and a lowercase letter may be added
+ to the declarations in the <string.h> header.
+ 7.31.14 Date and time <time.h>
+ Macros beginning with TIME_ and an uppercase letter may be added to the macros in the
+ <time.h> header.
+ 7.31.15 Threads <threads.h>
+1 Function names, type names, and enumeration constants that begin with either cnd_,
+ mtx_, thrd_, or tss_, and a lowercase letter may be added to the declarations in the
+ <threads.h> header.
+ 7.31.16 Extended multibyte and wide character utilities <wchar.h>
+1 Function names that begin with wcs and a lowercase letter may be added to the
+ declarations in the <wchar.h> header.
+2 Lowercase letters may be added to the conversion specifiers and length modifiers in
+ fwprintf and fwscanf. Other characters may be used in extensions.
+
+[page 456]
+
+ 7.31.17 Wide character classification and mapping utilities
+ <wctype.h>
+1 Function names that begin with is or to and a lowercase letter may be added to the
+ declarations in the <wctype.h> header.
+
+[page 457]
+
+ Annex A
+ (informative)
+ Language syntax summary
+1 NOTE The notation is described in 6.1.
+
+ A.1 Lexical grammar
+ A.1.1 Lexical elements
+ (6.4) token:
+ keyword
+ identifier
+ constant
+ string-literal
+ punctuator
+ (6.4) preprocessing-token:
+ header-name
+ identifier
+ pp-number
+ character-constant
+ string-literal
+ punctuator
+ each non-white-space character that cannot be one of the above
+
+[page 458]
+
+A.1.2 Keywords
+(6.4.1) keyword: one of
+ auto * if unsigned
+ break inline void
+ case int volatile
+ char long while
+ const register _Alignas
+ continue restrict _Alignof
+ default return _Atomic
+ do short _Bool
+ double signed _Complex
+ else sizeof _Generic
+ enum static _Imaginary
+ extern struct _Noreturn
+ float switch _Static_assert
+ for typedef _Thread_local
+ goto union
+A.1.3 Identifiers
+(6.4.2.1) identifier:
+ identifier-nondigit
+ identifier identifier-nondigit
+ identifier digit
+(6.4.2.1) identifier-nondigit:
+ nondigit
+ universal-character-name
+ other implementation-defined characters
+(6.4.2.1) nondigit: one of
+ _ a b c d e f g h i j k l m
+ n o p q r s t u v w x y z
+ A B C D E F G H I J K L M
+ N O P Q R S T U V W X Y Z
+(6.4.2.1) digit: one of
+ 0 1 2 3 4 5 6 7 8 9
+
+[page 459]
+
+A.1.4 Universal character names
+(6.4.3) universal-character-name:
+ \u hex-quad
+ \U hex-quad hex-quad
+(6.4.3) hex-quad:
+ hexadecimal-digit hexadecimal-digit
+ hexadecimal-digit hexadecimal-digit
+A.1.5 Constants
+(6.4.4) constant:
+ integer-constant
+ floating-constant
+ enumeration-constant
+ character-constant
+(6.4.4.1) integer-constant:
+ decimal-constant integer-suffixopt
+ octal-constant integer-suffixopt
+ hexadecimal-constant integer-suffixopt
+(6.4.4.1) decimal-constant:
+ nonzero-digit
+ decimal-constant digit
+(6.4.4.1) octal-constant:
+ 0
+ octal-constant octal-digit
+(6.4.4.1) hexadecimal-constant:
+ hexadecimal-prefix hexadecimal-digit
+ hexadecimal-constant hexadecimal-digit
+(6.4.4.1) hexadecimal-prefix: one of
+ 0x 0X
+(6.4.4.1) nonzero-digit: one of
+ 1 2 3 4 5 6 7 8 9
+(6.4.4.1) octal-digit: one of
+ 0 1 2 3 4 5 6 7
+
+[page 460]
+
+(6.4.4.1) hexadecimal-digit: one of
+ 0 1 2 3 4 5 6 7 8 9
+ a b c d e f
+ A B C D E F
+(6.4.4.1) integer-suffix:
+ unsigned-suffix long-suffixopt
+ unsigned-suffix long-long-suffix
+ long-suffix unsigned-suffixopt
+ long-long-suffix unsigned-suffixopt
+(6.4.4.1) unsigned-suffix: one of
+ u U
+(6.4.4.1) long-suffix: one of
+ l L
+(6.4.4.1) long-long-suffix: one of
+ ll LL
+(6.4.4.2) floating-constant:
+ decimal-floating-constant
+ hexadecimal-floating-constant
+(6.4.4.2) decimal-floating-constant:
+ fractional-constant exponent-partopt floating-suffixopt
+ digit-sequence exponent-part floating-suffixopt
+(6.4.4.2) hexadecimal-floating-constant:
+ hexadecimal-prefix hexadecimal-fractional-constant
+ binary-exponent-part floating-suffixopt
+ hexadecimal-prefix hexadecimal-digit-sequence
+ binary-exponent-part floating-suffixopt
+(6.4.4.2) fractional-constant:
+ digit-sequenceopt . digit-sequence
+ digit-sequence .
+(6.4.4.2) exponent-part:
+ e signopt digit-sequence
+ E signopt digit-sequence
+(6.4.4.2) sign: one of
+ + -
+
+[page 461]
+
+(6.4.4.2) digit-sequence:
+ digit
+ digit-sequence digit
+(6.4.4.2) hexadecimal-fractional-constant:
+ hexadecimal-digit-sequenceopt .
+ hexadecimal-digit-sequence
+ hexadecimal-digit-sequence .
+(6.4.4.2) binary-exponent-part:
+ p signopt digit-sequence
+ P signopt digit-sequence
+(6.4.4.2) hexadecimal-digit-sequence:
+ hexadecimal-digit
+ hexadecimal-digit-sequence hexadecimal-digit
+(6.4.4.2) floating-suffix: one of
+ f l F L
+(6.4.4.3) enumeration-constant:
+ identifier
+(6.4.4.4) character-constant:
+ ' c-char-sequence '
+ L' c-char-sequence '
+ u' c-char-sequence '
+ U' c-char-sequence '
+(6.4.4.4) c-char-sequence:
+ c-char
+ c-char-sequence c-char
+(6.4.4.4) c-char:
+ any member of the source character set except
+ the single-quote ', backslash \, or new-line character
+ escape-sequence
+(6.4.4.4) escape-sequence:
+ simple-escape-sequence
+ octal-escape-sequence
+ hexadecimal-escape-sequence
+ universal-character-name
+
+[page 462]
+
+(6.4.4.4) simple-escape-sequence: one of
+ \' \" \? \\
+ \a \b \f \n \r \t \v
+(6.4.4.4) octal-escape-sequence:
+ \ octal-digit
+ \ octal-digit octal-digit
+ \ octal-digit octal-digit octal-digit
+(6.4.4.4) hexadecimal-escape-sequence:
+ \x hexadecimal-digit
+ hexadecimal-escape-sequence hexadecimal-digit
+A.1.6 String literals
+(6.4.5) string-literal:
+ encoding-prefixopt " s-char-sequenceopt "
+(6.4.5) encoding-prefix:
+ u8
+ u
+ U
+ L
+(6.4.5) s-char-sequence:
+ s-char
+ s-char-sequence s-char
+(6.4.5) s-char:
+ any member of the source character set except
+ the double-quote ", backslash \, or new-line character
+ escape-sequence
+A.1.7 Punctuators
+(6.4.6) punctuator: one of
+ [ ] ( ) { } . ->
+ ++ -- & * + - ~ !
+ / % << >> < > <= >= == != ^ | && ||
+ ? : ; ...
+ = *= /= %= += -= <<= >>= &= ^= |=
+ , # ##
+ <: :> <% %> %: %:%:
+
+[page 463]
+
+A.1.8 Header names
+(6.4.7) header-name:
+ < h-char-sequence >
+ " q-char-sequence "
+(6.4.7) h-char-sequence:
+ h-char
+ h-char-sequence h-char
+(6.4.7) h-char:
+ any member of the source character set except
+ the new-line character and >
+(6.4.7) q-char-sequence:
+ q-char
+ q-char-sequence q-char
+(6.4.7) q-char:
+ any member of the source character set except
+ the new-line character and "
+A.1.9 Preprocessing numbers
+(6.4.8) pp-number:
+ digit
+ . digit
+ pp-number digit
+ pp-number identifier-nondigit
+ pp-number e sign
+ pp-number E sign
+ pp-number p sign
+ pp-number P sign
+ pp-number .
+
+[page 464]
+
+A.2 Phrase structure grammar
+A.2.1 Expressions
+(6.5.1) primary-expression:
+ identifier
+ constant
+ string-literal
+ ( expression )
+ generic-selection
+(6.5.1.1) generic-selection:
+ _Generic ( assignment-expression , generic-assoc-list )
+(6.5.1.1) generic-assoc-list:
+ generic-association
+ generic-assoc-list , generic-association
+(6.5.1.1) generic-association:
+ type-name : assignment-expression
+ default : assignment-expression
+(6.5.2) postfix-expression:
+ primary-expression
+ postfix-expression [ expression ]
+ postfix-expression ( argument-expression-listopt )
+ postfix-expression . identifier
+ postfix-expression -> identifier
+ postfix-expression ++
+ postfix-expression --
+ ( type-name ) { initializer-list }
+ ( type-name ) { initializer-list , }
+(6.5.2) argument-expression-list:
+ assignment-expression
+ argument-expression-list , assignment-expression
+(6.5.3) unary-expression:
+ postfix-expression
+ ++ unary-expression
+ -- unary-expression
+ unary-operator cast-expression
+ sizeof unary-expression
+ sizeof ( type-name )
+ _Alignof ( type-name )
+
+[page 465]
+
+(6.5.3) unary-operator: one of
+ & * + - ~ !
+(6.5.4) cast-expression:
+ unary-expression
+ ( type-name ) cast-expression
+(6.5.5) multiplicative-expression:
+ cast-expression
+ multiplicative-expression * cast-expression
+ multiplicative-expression / cast-expression
+ multiplicative-expression % cast-expression
+(6.5.6) additive-expression:
+ multiplicative-expression
+ additive-expression + multiplicative-expression
+ additive-expression - multiplicative-expression
+(6.5.7) shift-expression:
+ additive-expression
+ shift-expression << additive-expression
+ shift-expression >> additive-expression
+(6.5.8) relational-expression:
+ shift-expression
+ relational-expression < shift-expression
+ relational-expression > shift-expression
+ relational-expression <= shift-expression
+ relational-expression >= shift-expression
+(6.5.9) equality-expression:
+ relational-expression
+ equality-expression == relational-expression
+ equality-expression != relational-expression
+(6.5.10) AND-expression:
+ equality-expression
+ AND-expression & equality-expression
+(6.5.11) exclusive-OR-expression:
+ AND-expression
+ exclusive-OR-expression ^ AND-expression
+
+[page 466]
+
+(6.5.12) inclusive-OR-expression:
+ exclusive-OR-expression
+ inclusive-OR-expression | exclusive-OR-expression
+(6.5.13) logical-AND-expression:
+ inclusive-OR-expression
+ logical-AND-expression && inclusive-OR-expression
+(6.5.14) logical-OR-expression:
+ logical-AND-expression
+ logical-OR-expression || logical-AND-expression
+(6.5.15) conditional-expression:
+ logical-OR-expression
+ logical-OR-expression ? expression : conditional-expression
+(6.5.16) assignment-expression:
+ conditional-expression
+ unary-expression assignment-operator assignment-expression
+(6.5.16) assignment-operator: one of
+ = *= /= %= += -= <<= >>= &= ^= |=
+(6.5.17) expression:
+ assignment-expression
+ expression , assignment-expression
+(6.6) constant-expression:
+ conditional-expression
+A.2.2 Declarations
+(6.7) declaration:
+ declaration-specifiers init-declarator-listopt ;
+ static_assert-declaration
+(6.7) declaration-specifiers:
+ storage-class-specifier declaration-specifiersopt
+ type-specifier declaration-specifiersopt
+ type-qualifier declaration-specifiersopt
+ function-specifier declaration-specifiersopt
+ alignment-specifier declaration-specifiersopt
+(6.7) init-declarator-list:
+ init-declarator
+ init-declarator-list , init-declarator
+
+[page 467]
+
+(6.7) init-declarator:
+ declarator
+ declarator = initializer
+(6.7.1) storage-class-specifier:
+ typedef
+ extern
+ static
+ _Thread_local
+ auto
+ register
+(6.7.2) type-specifier:
+ void
+ char
+ short
+ int
+ long
+ float
+ double
+ signed
+ unsigned
+ _Bool
+ _Complex
+ atomic-type-specifier
+ struct-or-union-specifier
+ enum-specifier
+ typedef-name
+(6.7.2.1) struct-or-union-specifier:
+ struct-or-union identifieropt { struct-declaration-list }
+ struct-or-union identifier
+(6.7.2.1) struct-or-union:
+ struct
+ union
+(6.7.2.1) struct-declaration-list:
+ struct-declaration
+ struct-declaration-list struct-declaration
+(6.7.2.1) struct-declaration:
+ specifier-qualifier-list struct-declarator-listopt ;
+ static_assert-declaration
+
+[page 468]
+
+(6.7.2.1) specifier-qualifier-list:
+ type-specifier specifier-qualifier-listopt
+ type-qualifier specifier-qualifier-listopt
+(6.7.2.1) struct-declarator-list:
+ struct-declarator
+ struct-declarator-list , struct-declarator
+(6.7.2.1) struct-declarator:
+ declarator
+ declaratoropt : constant-expression
+(6.7.2.2) enum-specifier:
+ enum identifieropt { enumerator-list }
+ enum identifieropt { enumerator-list , }
+ enum identifier
+(6.7.2.2) enumerator-list:
+ enumerator
+ enumerator-list , enumerator
+(6.7.2.2) enumerator:
+ enumeration-constant
+ enumeration-constant = constant-expression
+(6.7.2.4) atomic-type-specifier:
+ _Atomic ( type-name )
+(6.7.3) type-qualifier:
+ const
+ restrict
+ volatile
+ _Atomic
+(6.7.4) function-specifier:
+ inline
+ _Noreturn
+(6.7.5) alignment-specifier:
+ _Alignas ( type-name )
+ _Alignas ( constant-expression )
+(6.7.6) declarator:
+ pointeropt direct-declarator
+
+[page 469]
+
+(6.7.6) direct-declarator:
+ identifier
+ ( declarator )
+ direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
+ direct-declarator [ static type-qualifier-listopt assignment-expression ]
+ direct-declarator [ type-qualifier-list static assignment-expression ]
+ direct-declarator [ type-qualifier-listopt * ]
+ direct-declarator ( parameter-type-list )
+ direct-declarator ( identifier-listopt )
+(6.7.6) pointer:
+ * type-qualifier-listopt
+ * type-qualifier-listopt pointer
+(6.7.6) type-qualifier-list:
+ type-qualifier
+ type-qualifier-list type-qualifier
+(6.7.6) parameter-type-list:
+ parameter-list
+ parameter-list , ...
+(6.7.6) parameter-list:
+ parameter-declaration
+ parameter-list , parameter-declaration
+(6.7.6) parameter-declaration:
+ declaration-specifiers declarator
+ declaration-specifiers abstract-declaratoropt
+(6.7.6) identifier-list:
+ identifier
+ identifier-list , identifier
+(6.7.7) type-name:
+ specifier-qualifier-list abstract-declaratoropt
+(6.7.7) abstract-declarator:
+ pointer
+ pointeropt direct-abstract-declarator
+
+[page 470]
+
+(6.7.7) direct-abstract-declarator:
+ ( abstract-declarator )
+ direct-abstract-declaratoropt [ type-qualifier-listopt
+ assignment-expressionopt ]
+ direct-abstract-declaratoropt [ static type-qualifier-listopt
+ assignment-expression ]
+ direct-abstract-declaratoropt [ type-qualifier-list static
+ assignment-expression ]
+ direct-abstract-declaratoropt [ * ]
+ direct-abstract-declaratoropt ( parameter-type-listopt )
+(6.7.8) typedef-name:
+ identifier
+(6.7.9) initializer:
+ assignment-expression
+ { initializer-list }
+ { initializer-list , }
+(6.7.9) initializer-list:
+ designationopt initializer
+ initializer-list , designationopt initializer
+(6.7.9) designation:
+ designator-list =
+(6.7.9) designator-list:
+ designator
+ designator-list designator
+(6.7.9) designator:
+ [ constant-expression ]
+ . identifier
+(6.7.10) static_assert-declaration:
+ _Static_assert ( constant-expression , string-literal ) ;
+
+[page 471]
+
+A.2.3 Statements
+(6.8) statement:
+ labeled-statement
+ compound-statement
+ expression-statement
+ selection-statement
+ iteration-statement
+ jump-statement
+(6.8.1) labeled-statement:
+ identifier : statement
+ case constant-expression : statement
+ default : statement
+(6.8.2) compound-statement:
+ { block-item-listopt }
+(6.8.2) block-item-list:
+ block-item
+ block-item-list block-item
+(6.8.2) block-item:
+ declaration
+ statement
+(6.8.3) expression-statement:
+ expressionopt ;
+(6.8.4) selection-statement:
+ if ( expression ) statement
+ if ( expression ) statement else statement
+ switch ( expression ) statement
+(6.8.5) iteration-statement:
+ while ( expression ) statement
+ do statement while ( expression ) ;
+ for ( expressionopt ; expressionopt ; expressionopt ) statement
+ for ( declaration expressionopt ; expressionopt ) statement
+(6.8.6) jump-statement:
+ goto identifier ;
+ continue ;
+ break ;
+ return expressionopt ;
+
+[page 472]
+
+A.2.4 External definitions
+(6.9) translation-unit:
+ external-declaration
+ translation-unit external-declaration
+(6.9) external-declaration:
+ function-definition
+ declaration
+(6.9.1) function-definition:
+ declaration-specifiers declarator declaration-listopt compound-statement
+(6.9.1) declaration-list:
+ declaration
+ declaration-list declaration
+A.3 Preprocessing directives
+(6.10) preprocessing-file:
+ groupopt
+(6.10) group:
+ group-part
+ group group-part
+(6.10) group-part:
+ if-section
+ control-line
+ text-line
+ # non-directive
+(6.10) if-section:
+ if-group elif-groupsopt else-groupopt endif-line
+(6.10) if-group:
+ # if constant-expression new-line groupopt
+ # ifdef identifier new-line groupopt
+ # ifndef identifier new-line groupopt
+(6.10) elif-groups:
+ elif-group
+ elif-groups elif-group
+(6.10) elif-group:
+ # elif constant-expression new-line groupopt
+
+[page 473]
+
+(6.10) else-group:
+ # else new-line groupopt
+(6.10) endif-line:
+ # endif new-line
+(6.10) control-line:
+ # include pp-tokens new-line
+ # define identifier replacement-list new-line
+ # define identifier lparen identifier-listopt )
+ replacement-list new-line
+ # define identifier lparen ... ) replacement-list new-line
+ # define identifier lparen identifier-list , ... )
+ replacement-list new-line
+ # undef identifier new-line
+ # line pp-tokens new-line
+ # error pp-tokensopt new-line
+ # pragma pp-tokensopt new-line
+ # new-line
+(6.10) text-line:
+ pp-tokensopt new-line
+(6.10) non-directive:
+ pp-tokens new-line
+(6.10) lparen:
+ a ( character not immediately preceded by white-space
+(6.10) replacement-list:
+ pp-tokensopt
+(6.10) pp-tokens:
+ preprocessing-token
+ pp-tokens preprocessing-token
+(6.10) new-line:
+ the new-line character
+
+[page 474]
+
+ 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);
+
+[page 475]
+
+ double complex catanh(double complex z);
+ float complex catanhf(float complex z);
+ long double complex catanhl(long double complex z);
+ double complex ccosh(double complex z);
+ float complex ccoshf(float complex z);
+ long double complex ccoshl(long double complex z);
+ double complex csinh(double complex z);
+ float complex csinhf(float complex z);
+ long double complex csinhl(long double complex z);
+ double complex ctanh(double complex z);
+ float complex ctanhf(float complex z);
+ long double complex ctanhl(long double complex z);
+ double complex cexp(double complex z);
+ float complex cexpf(float complex z);
+ long double complex cexpl(long double complex z);
+ double complex clog(double complex z);
+ float complex clogf(float complex z);
+ long double complex clogl(long double complex z);
+ double cabs(double complex z);
+ float cabsf(float complex z);
+ long double cabsl(long double complex z);
+ double complex cpow(double complex x, double complex y);
+ float complex cpowf(float complex x, float complex y);
+ long double complex cpowl(long double complex x,
+ long double complex y);
+ double complex csqrt(double complex z);
+ float complex csqrtf(float complex z);
+ long double complex csqrtl(long double complex z);
+ double carg(double complex z);
+ float cargf(float complex z);
+ long double cargl(long double complex z);
+ double cimag(double complex z);
+ float cimagf(float complex z);
+ long double cimagl(long double complex z);
+ double complex CMPLX(double x, double y);
+ float complex CMPLXF(float x, float y);
+ long double complex CMPLXL(long double x, long double y);
+ double complex conj(double complex z);
+ float complex conjf(float complex z);
+ long double complex conjl(long double complex z);
+ double complex cproj(double complex z);
+
+[page 476]
+
+ 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);
+
+[page 477]
+
+ 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);
+
+[page 478]
+
+ 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);
+
+[page 479]
+
+ double acos(double x);
+ float acosf(float x);
+ long double acosl(long double x);
+ double asin(double x);
+ float asinf(float x);
+ long double asinl(long double x);
+ double atan(double x);
+ float atanf(float x);
+ long double atanl(long double x);
+ double atan2(double y, double x);
+ float atan2f(float y, float x);
+ long double atan2l(long double y, long double x);
+ double cos(double x);
+ float cosf(float x);
+ long double cosl(long double x);
+ double sin(double x);
+ float sinf(float x);
+ long double sinl(long double x);
+ double tan(double x);
+ float tanf(float x);
+ long double tanl(long double x);
+ double acosh(double x);
+ float acoshf(float x);
+ long double acoshl(long double x);
+ double asinh(double x);
+ float asinhf(float x);
+ long double asinhl(long double x);
+ double atanh(double x);
+ float atanhf(float x);
+ long double atanhl(long double x);
+ double cosh(double x);
+ float coshf(float x);
+ long double coshl(long double x);
+ double sinh(double x);
+ float sinhf(float x);
+ long double sinhl(long double x);
+ double tanh(double x);
+ float tanhf(float x);
+ long double tanhl(long double x);
+ double exp(double x);
+ float expf(float x);
+
+[page 480]
+
+ long double expl(long double x);
+ double exp2(double x);
+ float exp2f(float x);
+ long double exp2l(long double x);
+ double expm1(double x);
+ float expm1f(float x);
+ long double expm1l(long double x);
+ double frexp(double value, int *exp);
+ float frexpf(float value, int *exp);
+ long double frexpl(long double value, int *exp);
+ int ilogb(double x);
+ int ilogbf(float x);
+ int ilogbl(long double x);
+ double ldexp(double x, int exp);
+ float ldexpf(float x, int exp);
+ long double ldexpl(long double x, int exp);
+ double log(double x);
+ float logf(float x);
+ long double logl(long double x);
+ double log10(double x);
+ float log10f(float x);
+ long double log10l(long double x);
+ double log1p(double x);
+ float log1pf(float x);
+ long double log1pl(long double x);
+ double log2(double x);
+ float log2f(float x);
+ long double log2l(long double x);
+ double logb(double x);
+ float logbf(float x);
+ long double logbl(long double x);
+ double modf(double value, double *iptr);
+ float modff(float value, float *iptr);
+ long double modfl(long double value, long double *iptr);
+ double scalbn(double x, int n);
+ float scalbnf(float x, int n);
+ long double scalbnl(long double x, int n);
+ double scalbln(double x, long int n);
+ float scalblnf(float x, long int n);
+ long double scalblnl(long double x, long int n);
+ double cbrt(double x);
+
+[page 481]
+
+ float cbrtf(float x);
+ long double cbrtl(long double x);
+ double fabs(double x);
+ float fabsf(float x);
+ long double fabsl(long double x);
+ double hypot(double x, double y);
+ float hypotf(float x, float y);
+ long double hypotl(long double x, long double y);
+ double pow(double x, double y);
+ float powf(float x, float y);
+ long double powl(long double x, long double y);
+ double sqrt(double x);
+ float sqrtf(float x);
+ long double sqrtl(long double x);
+ double erf(double x);
+ float erff(float x);
+ long double erfl(long double x);
+ double erfc(double x);
+ float erfcf(float x);
+ long double erfcl(long double x);
+ double lgamma(double x);
+ float lgammaf(float x);
+ long double lgammal(long double x);
+ double tgamma(double x);
+ float tgammaf(float x);
+ long double tgammal(long double x);
+ double ceil(double x);
+ float ceilf(float x);
+ long double ceill(long double x);
+ double floor(double x);
+ float floorf(float x);
+ long double floorl(long double x);
+ double nearbyint(double x);
+ float nearbyintf(float x);
+ long double nearbyintl(long double x);
+ double rint(double x);
+ float rintf(float x);
+ long double rintl(long double x);
+ long int lrint(double x);
+ long int lrintf(float x);
+ long int lrintl(long double x);
+
+[page 482]
+
+ long long int llrint(double x);
+ long long int llrintf(float x);
+ long long int llrintl(long double x);
+ double round(double x);
+ float roundf(float x);
+ long double roundl(long double x);
+ long int lround(double x);
+ long int lroundf(float x);
+ long int lroundl(long double x);
+ long long int llround(double x);
+ long long int llroundf(float x);
+ long long int llroundl(long double x);
+ double trunc(double x);
+ float truncf(float x);
+ long double truncl(long double x);
+ double fmod(double x, double y);
+ float fmodf(float x, float y);
+ long double fmodl(long double x, long double y);
+ double remainder(double x, double y);
+ float remainderf(float x, float y);
+ long double remainderl(long double x, long double y);
+ double remquo(double x, double y, int *quo);
+ float remquof(float x, float y, int *quo);
+ long double remquol(long double x, long double y,
+ int *quo);
+ double copysign(double x, double y);
+ float copysignf(float x, float y);
+ long double copysignl(long double x, long double y);
+ double nan(const char *tagp);
+ float nanf(const char *tagp);
+ long double nanl(const char *tagp);
+ double nextafter(double x, double y);
+ float nextafterf(float x, float y);
+ long double nextafterl(long double x, long double y);
+ double nexttoward(double x, long double y);
+ float nexttowardf(float x, long double y);
+ long double nexttowardl(long double x, long double y);
+ double fdim(double x, double y);
+ float fdimf(float x, float y);
+ long double fdiml(long double x, long double y);
+ double fmax(double x, double y);
+
+[page 483]
+
+ 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);
+
+[page 484]
+
+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_BOOL_LOCK_FREE atomic_uint
+ ATOMIC_CHAR_LOCK_FREE atomic_long
+ ATOMIC_CHAR16_T_LOCK_FREE atomic_ulong
+ ATOMIC_CHAR32_T_LOCK_FREE atomic_llong
+ ATOMIC_WCHAR_T_LOCK_FREE atomic_ullong
+ ATOMIC_SHORT_LOCK_FREE atomic_char16_t
+ ATOMIC_INT_LOCK_FREE atomic_char32_t
+ ATOMIC_LONG_LOCK_FREE atomic_wchar_t
+ ATOMIC_LLONG_LOCK_FREE atomic_int_least8_t
+ ATOMIC_POINTER_LOCK_FREE atomic_uint_least8_t
+ ATOMIC_FLAG_INIT atomic_int_least16_t
+ memory_order atomic_uint_least16_t
+ atomic_flag atomic_int_least32_t
+ memory_order_relaxed * atomic_uint_least32_t
+ memory_order_consume atomic_int_least64_t
+ memory_order_acquire atomic_uint_least64_t
+ memory_order_release atomic_int_fast8_t
+ memory_order_acq_rel atomic_uint_fast8_t
+ memory_order_seq_cst atomic_int_fast16_t
+ atomic_bool atomic_uint_fast16_t
+ atomic_char atomic_int_fast32_t
+ atomic_schar atomic_uint_fast32_t
+ atomic_uchar atomic_int_fast64_t
+ atomic_short atomic_uint_fast64_t
+ atomic_ushort atomic_intptr_t
+ atomic_int atomic_uintptr_t
+
+[page 485]
+
+ 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(const volatile A *obj);
+ void atomic_store(volatile A *object, C desired);
+ void atomic_store_explicit(volatile A *object,
+ C desired, memory_order order);
+ C atomic_load(volatile A *object);
+ C atomic_load_explicit(volatile A *object,
+ memory_order order);
+ C atomic_exchange(volatile A *object, C desired);
+ C atomic_exchange_explicit(volatile A *object,
+ C desired, memory_order order);
+ _Bool atomic_compare_exchange_strong(volatile A *object,
+ C *expected, C desired);
+ _Bool atomic_compare_exchange_strong_explicit(
+ volatile A *object, C *expected, C desired,
+ memory_order success, memory_order failure);
+ _Bool atomic_compare_exchange_weak(volatile A *object,
+ C *expected, C desired);
+ _Bool atomic_compare_exchange_weak_explicit(
+ volatile A *object, C *expected, C desired,
+ memory_order success, memory_order failure);
+ C atomic_fetch_key(volatile A *object, M operand);
+ C atomic_fetch_key_explicit(volatile A *object,
+ M operand, memory_order order);
+ _Bool atomic_flag_test_and_set(
+ volatile atomic_flag *object);
+ _Bool atomic_flag_test_and_set_explicit(
+ volatile atomic_flag *object, memory_order order);
+ void atomic_flag_clear(volatile atomic_flag *object);
+ void atomic_flag_clear_explicit(
+ volatile atomic_flag *object, memory_order order);
+
+[page 486]
+
+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
+
+[page 487]
+
+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);
+
+[page 488]
+
+ int vsnprintf(char * restrict s, size_t n,
+ const char * restrict format, va_list arg);
+ int vsprintf(char * restrict s,
+ const char * restrict format, va_list arg);
+ int vsscanf(const char * restrict s,
+ const char * restrict format, va_list arg);
+ int fgetc(FILE *stream);
+ char *fgets(char * restrict s, int n,
+ FILE * restrict stream);
+ int fputc(int c, FILE *stream);
+ int fputs(const char * restrict s,
+ FILE * restrict stream);
+ int getc(FILE *stream);
+ int getchar(void);
+ int putc(int c, FILE *stream);
+ int putchar(int c);
+ int puts(const char *s);
+ int ungetc(int c, FILE *stream);
+ size_t fread(void * restrict ptr,
+ size_t size, size_t nmemb,
+ FILE * restrict stream);
+ size_t fwrite(const void * restrict ptr,
+ size_t size, size_t nmemb,
+ FILE * restrict stream);
+ int fgetpos(FILE * restrict stream,
+ fpos_t * restrict pos);
+ int fseek(FILE *stream, long int offset, int whence);
+ int fsetpos(FILE *stream, const fpos_t *pos);
+ long int ftell(FILE *stream);
+ void rewind(FILE *stream);
+ void clearerr(FILE *stream);
+ int feof(FILE *stream);
+ int ferror(FILE *stream);
+ void perror(const char *s);
+ __STDC_WANT_LIB_EXT1__
+ L_tmpnam_s TMP_MAX_S errno_t rsize_t
+ errno_t tmpfile_s(FILE * restrict * restrict streamptr);
+ errno_t tmpnam_s(char *s, rsize_t maxsize);
+
+[page 489]
+
+ errno_t fopen_s(FILE * restrict * restrict streamptr,
+ const char * restrict filename,
+ const char * restrict mode);
+ errno_t freopen_s(FILE * restrict * restrict newstreamptr,
+ const char * restrict filename,
+ const char * restrict mode,
+ FILE * restrict stream);
+ int fprintf_s(FILE * restrict stream,
+ const char * restrict format, ...);
+ int fscanf_s(FILE * restrict stream,
+ const char * restrict format, ...);
+ int printf_s(const char * restrict format, ...);
+ int scanf_s(const char * restrict format, ...);
+ int snprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format, ...);
+ int sprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format, ...);
+ int sscanf_s(const char * restrict s,
+ const char * restrict format, ...);
+ int vfprintf_s(FILE * restrict stream,
+ const char * restrict format,
+ va_list arg);
+ int vfscanf_s(FILE * restrict stream,
+ const char * restrict format,
+ va_list arg);
+ int vprintf_s(const char * restrict format,
+ va_list arg);
+ int vscanf_s(const char * restrict format,
+ va_list arg);
+ int vsnprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format,
+ va_list arg);
+ int vsprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format,
+ va_list arg);
+ int vsscanf_s(const char * restrict s,
+ const char * restrict format,
+ va_list arg);
+ char *gets_s(char *s, rsize_t n);
+
+[page 490]
+
+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);
+
+[page 491]
+
+ void *bsearch(const void *key, const void *base,
+ size_t nmemb, size_t size,
+ int (*compar)(const void *, const void *));
+ void qsort(void *base, size_t nmemb, size_t size,
+ int (*compar)(const void *, const void *));
+ int abs(int j);
+ long int labs(long int j);
+ long long int llabs(long long int j);
+ div_t div(int numer, int denom);
+ ldiv_t ldiv(long int numer, long int denom);
+ lldiv_t lldiv(long long int numer,
+ long long int denom);
+ int mblen(const char *s, size_t n);
+ int mbtowc(wchar_t * restrict pwc,
+ const char * restrict s, size_t n);
+ int wctomb(char *s, wchar_t wchar);
+ size_t mbstowcs(wchar_t * restrict pwcs,
+ const char * restrict s, size_t n);
+ size_t wcstombs(char * restrict s,
+ const wchar_t * restrict pwcs, size_t n);
+ __STDC_WANT_LIB_EXT1__
+ errno_t
+ rsize_t
+ constraint_handler_t
+ constraint_handler_t set_constraint_handler_s(
+ constraint_handler_t handler);
+ void abort_handler_s(
+ const char * restrict msg,
+ void * restrict ptr,
+ errno_t error);
+ void ignore_handler_s(
+ const char * restrict msg,
+ void * restrict ptr,
+ errno_t error);
+ errno_t getenv_s(size_t * restrict len,
+ char * restrict value, rsize_t maxsize,
+ const char * restrict name);
+
+[page 492]
+
+ 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 _Noreturn <stdnoreturn.h>
+ noreturn
+B.23 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);
+
+[page 493]
+
+ 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)
+
+[page 494]
+
+ 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.24 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.25 Threads <threads.h>
+ thread_local once_flag
+ ONCE_FLAG_INIT mtx_plain *
+ TSS_DTOR_ITERATIONS mtx_recursive
+ cnd_t mtx_timed
+ thrd_t thrd_timedout
+ tss_t thrd_success
+ mtx_t thrd_busy
+ tss_dtor_t thrd_error
+ thrd_start_t thrd_nomem
+ 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 *restrict cond,
+ mtx_t *restrict mtx,
+ const struct timespec *restrict ts);
+ int cnd_wait(cnd_t *cond, mtx_t *mtx);
+
+[page 495]
+
+ 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 *restrict mtx,
+ const struct timespec *restrict ts);
+ 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);
+ _Noreturn void thrd_exit(int res);
+ int thrd_join(thrd_t thr, int *res);
+ int thrd_sleep(const struct timespec *duration,
+ struct timespec *remaining);
+ 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);
+B.26 Date and time <time.h>
+ NULL size_t struct timespec
+ CLOCKS_PER_SEC clock_t struct tm
+ TIME_UTC time_t
+ clock_t clock(void);
+ double difftime(time_t time1, time_t time0);
+ time_t mktime(struct tm *timeptr);
+ time_t time(time_t *timer);
+ int timespec_get(timespec *ts, int base);
+ 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__
+
+[page 496]
+
+ 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.27 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.28 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);
+
+[page 497]
+
+ 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);
+
+[page 498]
+
+ 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);
+
+[page 499]
+
+ 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);
+
+[page 500]
+
+ 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);
+
+[page 501]
+
+ 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.29 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);
+
+[page 502]
+
+ Annex C
+ (informative)
+ Sequence points
+1 The following are the sequence points described in 5.1.2.3:
+ -- Between the evaluations of the function designator and actual arguments in a function
+ call and the actual call. (6.5.2.2).
+ -- Between the evaluations of the first and second operands of the following operators:
+ logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17).
+ -- Between the evaluations of the first operand of the conditional ? : operator and
+ whichever of the second and third operands is evaluated (6.5.15).
+ -- The end of a full declarator: declarators (6.7.6);
+ -- Between the evaluation of a full expression and the next full expression to be
+ evaluated. The following are full expressions: an initializer that is not part of a
+ compound literal (6.7.9); the expression in an expression statement (6.8.3); the
+ controlling expression of a selection statement (if or switch) (6.8.4); the
+ controlling expression of a while or do statement (6.8.5); each of the (optional)
+ expressions of a for statement (6.8.5.3); the (optional) expression in a return
+ statement (6.8.6.4).
+ -- Immediately before a library function returns (7.1.4).
+ -- After the actions associated with each formatted input/output function conversion
+ specifier (7.21.6, 7.29.2).
+ -- Immediately before and immediately after each call to a comparison function, and
+ also between any call to a comparison function and any movement of the objects
+ passed as arguments to that call (7.22.5).
+
+[page 503]
+
+ Annex D
+ (normative)
+ Universal character names for identifiers
+1 This clause lists the hexadecimal code values that are valid in universal character names
+ in identifiers.
+ D.1 Ranges of characters allowed
+1 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6,
+ 00D8-00F6, 00F8-00FF
+2 0100-167F, 1681-180D, 180F-1FFF
+3 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F
+4 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF
+5 3004-3007, 3021-302F, 3031-303F
+6 3040-D7FF
+7 F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD
+8 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD,
+ 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD,
+ B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD
+ D.2 Ranges of characters disallowed initially
+1 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F
+
+[page 504]
+
+ Annex E
+ (informative)
+ Implementation limits
+1 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
+2 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.
+3 The values given in the following list shall be replaced by implementation-defined
+ expressions:
+ #define FLT_EVAL_METHOD
+ #define FLT_ROUNDS
+4 The values given in the following list shall be replaced by implementation-defined
+ constant expressions that are greater or equal in magnitude (absolute value) to those
+ shown, with the same sign:
+
+[page 505]
+
+ #define DLB_DECIMAL_DIG 10
+ #define DBL_DIG 10
+ #define DBL_MANT_DIG
+ #define DBL_MAX_10_EXP +37
+ #define DBL_MAX_EXP
+ #define DBL_MIN_10_EXP -37
+ #define DBL_MIN_EXP
+ #define DECIMAL_DIG 10
+ #define FLT_DECIMAL_DIG 6
+ #define FLT_DIG 6
+ #define FLT_MANT_DIG
+ #define FLT_MAX_10_EXP +37
+ #define FLT_MAX_EXP
+ #define FLT_MIN_10_EXP -37
+ #define FLT_MIN_EXP
+ #define FLT_RADIX 2
+ #define LDLB_DECIMAL_DIG 10
+ #define LDBL_DIG 10
+ #define LDBL_MANT_DIG
+ #define LDBL_MAX_10_EXP +37
+ #define LDBL_MAX_EXP
+ #define LDBL_MIN_10_EXP -37
+ #define LDBL_MIN_EXP
+5 The values given in the following list shall be replaced by implementation-defined
+ constant expressions with values that are greater than or equal to those shown:
+ #define DBL_MAX 1E+37
+ #define FLT_MAX 1E+37
+ #define LDBL_MAX 1E+37
+6 The values given in the following list shall be replaced by implementation-defined
+ constant expressions with (positive) values that are less than or equal to those shown:
+ #define DBL_EPSILON 1E-9
+ #define DBL_MIN 1E-37
+ #define FLT_EPSILON 1E-5
+ #define FLT_MIN 1E-37
+ #define LDBL_EPSILON 1E-9
+ #define LDBL_MIN 1E-37
+
+[page 506]
+
+ Annex F
+ (normative)
+ IEC 60559 floating-point arithmetic
+ F.1 Introduction
+1 This annex specifies C language support for the IEC 60559 floating-point standard. The
+ IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
+ microprocessor systems, second edition (IEC 60559:1989), previously designated
+ IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic
+ (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point
+ Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove
+ dependencies on radix and word length. IEC 60559 generally refers to the floating-point
+ standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that
+ defines __STDC_IEC_559__ shall conform to the specifications in this annex.356)
+ Where a binding between the C language and IEC 60559 is indicated, the
+ IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since
+ negative and positive infinity are representable in IEC 60559 formats, all real numbers lie
+ within the range of representable values.
+ F.2 Types
+1 The C floating types match the IEC 60559 formats as follows:
+ -- The float type matches the IEC 60559 single format.
+ -- The double type matches the IEC 60559 double format.
+ -- The long double type matches an IEC 60559 extended format,357) else a
+ non-IEC 60559 extended format, else the IEC 60559 double format.
+ Any non-IEC 60559 extended format used for the long double type shall have more
+ precision than IEC 60559 double and at least the range of IEC 60559 double.358)
+
+
+
+
+ 356) Implementations that do not define __STDC_IEC_559__ are not required to conform to these
+ specifications.
+ 357) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit
+ and quadruple 128-bit IEC 60559 formats.
+ 358) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
+ all double values.
+
+[page 507]
+
+ Recommended practice
+2 The long double type should match an IEC 60559 extended format.
+ F.2.1 Infinities, signed zeros, and NaNs
+1 This specification does not define the behavior of signaling NaNs.359) 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.
+ F.3 Operators and functions
+1 C operators and functions provide IEC 60559 required and recommended facilities as
+ listed below.
+ -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and
+ divide operations.
+ -- The sqrt functions in <math.h> provide the IEC 60559 square root operation.
+ -- The remainder functions in <math.h> provide the IEC 60559 remainder
+ operation. The remquo functions in <math.h> provide the same operation but
+ with additional information.
+ -- The rint functions in <math.h> provide the IEC 60559 operation that rounds a
+ floating-point number to an integer value (in the same precision). The nearbyint
+ functions in <math.h> provide the nearbyinteger function recommended in the
+ Appendix to ANSI/IEEE 854.
+ -- The conversions for floating types provide the IEC 60559 conversions between
+ floating-point precisions.
+ -- The conversions from integer to floating types provide the IEC 60559 conversions
+ from integer to floating point.
+ -- The conversions from floating to integer types provide IEC 60559-like conversions
+ but always round toward zero.
+ -- The lrint and llrint functions in <math.h> provide the IEC 60559
+ conversions, which honor the directed rounding mode, from floating point to the
+ long int and long long int integer formats. The lrint and llrint
+ functions can be used to implement IEC 60559 conversions from floating to other
+ integer formats.
+ -- The translation time conversion of floating constants and the strtod, strtof,
+ strtold, fprintf, fscanf, and related library functions in <stdlib.h>,
+
+
+ 359) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are
+ sufficient for closure of the arithmetic.
+
+[page 508]
+
+ <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
+ strtold function in <stdlib.h> provides the conv function recommended in the
+ Appendix to ANSI/IEEE 854.
+-- The relational and equality operators provide IEC 60559 comparisons. IEC 60559
+ identifies a need for additional comparison predicates to facilitate writing code that
+ accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
+ isless, islessequal, islessgreater, and isunordered) in <math.h>
+ supplement the language operators to address this need. The islessgreater and
+ isunordered macros provide respectively a quiet version of the <> predicate and
+ the unordered predicate recommended in the Appendix to IEC 60559.
+-- The feclearexcept, feraiseexcept, and fetestexcept functions in
+ <fenv.h> provide the facility to test and alter the IEC 60559 floating-point
+ exception status flags. The fegetexceptflag and fesetexceptflag
+ functions in <fenv.h> provide the facility to save and restore all five status flags at
+ one time. These functions are used in conjunction with the type fexcept_t and the
+ floating-point exception macros (FE_INEXACT, FE_DIVBYZERO,
+ FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
+-- The fegetround and fesetround functions in <fenv.h> provide the facility
+ to select among the IEC 60559 directed rounding modes represented by the rounding
+ direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
+ FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the
+ IEC 60559 directed rounding modes.
+-- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in
+ <fenv.h> provide a facility to manage the floating-point environment, comprising
+ the IEC 60559 status flags and control modes.
+-- The copysign functions in <math.h> provide the copysign function
+ recommended in the Appendix to IEC 60559.
+-- The fabs functions in <math.h> provide the abs function recommended in the
+ Appendix to IEC 60559.
+-- The unary minus (-) operator provides the unary minus (-) operation recommended
+ in the Appendix to IEC 60559.
+-- The scalbn and scalbln functions in <math.h> provide the scalb function
+ recommended in the Appendix to IEC 60559.
+-- The logb functions in <math.h> provide the logb function recommended in the
+ Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
+-- The nextafter and nexttoward functions in <math.h> provide the nextafter
+ function recommended in the Appendix to IEC 60559 (but with a minor change to
+
+[page 509]
+
+ better handle signed zeros).
+ -- The isfinite macro in <math.h> provides the finite function recommended in
+ the Appendix to IEC 60559.
+ -- The isnan macro in <math.h> provides the isnan function recommended in the
+ Appendix to IEC 60559.
+ -- The signbit macro and the fpclassify macro in <math.h>, used in
+ conjunction with the number classification macros (FP_NAN, FP_INFINITE,
+ FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
+ function recommended in the Appendix to IEC 60559 (except that the classification
+ macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).
+ F.4 Floating to integer conversion
+1 If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised
+ (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part
+ of the floating value exceeds the range of the integer type, then the ''invalid'' floating-
+ point exception is raised and the resulting value is unspecified. Otherwise, the resulting
+ value is determined by 6.3.1.4. Conversion of an integral floating value that does not
+ exceed the range of the integer type raises no floating-point exceptions; whether
+ conversion of a non-integral floating value raises the ''inexact'' floating-point exception is
+ unspecified.360)
+ F.5 Binary-decimal conversion
+1 Conversion from the widest supported IEC 60559 format to decimal with
+ DECIMAL_DIG digits and back is the identity function.361)
+2 Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
+ particular, conversion between any supported IEC 60559 format and decimal with
+ DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
+ rounding mode), which assures that conversion from the widest supported IEC 60559
+ format to decimal with DECIMAL_DIG digits and back is the identity function.
+
+
+
+ 360) 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>.
+ 361) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
+ DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
+ IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
+ DBL_DIG are 18 and 15, respectively, for these formats.)
+
+[page 510]
+
+3 Functions such as strtod that convert character sequences to floating types honor the
+ rounding direction. Hence, if the rounding direction might be upward or downward, the
+ implementation cannot convert a minus-signed sequence by negating the converted
+ unsigned sequence.
+ F.6 The return statement
+ If the return expression is evaluated in a floating-point format different from the return
+ type, the expression is converted as if by assignment362) to the return type of the function
+ and the resulting value is returned to the caller.
+ F.7 Contracted expressions
+1 A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed
+ zeros, subnormals, and the rounding directions in a manner consistent with the basic
+ arithmetic operations covered by IEC 60559.
+ Recommended practice
+2 A contracted expression should raise floating-point exceptions in a manner generally
+ consistent with the basic arithmetic operations.
+ F.8 Floating-point environment
+1 The floating-point environment defined in <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.363)
+ F.8.1 Environment management
+1 IEC 60559 requires that floating-point operations implicitly raise floating-point exception
+ status flags, and that rounding control modes can be set explicitly to affect result values of
+ floating-point operations. When the state for the FENV_ACCESS pragma (defined in
+ <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects
+ which respect sequence points.364)
+
+
+
+
+ 362) Assignment removes any extra range and precision.
+ 363) This specification does not require dynamic rounding precision nor trap enablement modes.
+ 364) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating-
+ point control modes will be the default ones and the floating-point status flags will not be tested,
+ which allows certain optimizations (see F.9).
+
+[page 511]
+
+ F.8.2 Translation
+1 During translation the IEC 60559 default modes are in effect:
+ -- The rounding direction mode is rounding to nearest.
+ -- The rounding precision mode (if supported) is set so that results are not shortened.
+ -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
+ Recommended practice
+2 The implementation should produce a diagnostic message for each translation-time
+ floating-point exception, other than ''inexact'';365) the implementation should then
+ proceed with the translation of the program.
+ F.8.3 Execution
+1 At program startup the floating-point environment is initialized as prescribed by
+ IEC 60559:
+ -- All floating-point exception status flags are cleared.
+ -- The rounding direction mode is rounding to nearest.
+ -- The dynamic rounding precision mode (if supported) is set so that results are not
+ shortened.
+ -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
+ F.8.4 Constant expressions
+1 An arithmetic constant expression of floating type, other than one in an initializer for an
+ object that has static or thread storage duration, is evaluated (as if) during execution; thus,
+ it is affected by any operative floating-point control modes and raises floating-point
+ exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma
+ is ''on'').366)
+2 EXAMPLE
+
+
+
+ 365) 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.
+ 366) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0
+ are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
+ 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
+ efficiency of translation-time evaluation through static initialization, such as
+ const static double one_third = 1.0/3.0;
+
+[page 512]
+
+ #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
+ /* ... */
+ }
+3 For the static initialization, the division is done at translation time, raising no (execution-time) floating-
+ point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at
+ execution time.
+
+ F.8.5 Initialization
+1 All computation for automatic initialization is done (as if) at execution time; thus, it is
+ affected by any operative modes and raises floating-point exceptions as required by
+ IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation
+ for initialization of objects that have static or thread storage duration is done (as if) at
+ translation time.
+2 EXAMPLE
+ #include <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
+ /* ... */
+ }
+3 The static initialization of v raises no (execution-time) floating-point exceptions because its computation is
+ done at translation time. The automatic initialization of u and w require an execution-time conversion to
+ float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations
+ of x and y entail execution-time conversion; however, in some expression evaluation methods, the
+ conversions is not to a narrower format, in which case no floating-point exception is raised.367) 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
+
+
+
+ 367) Use of float_t and double_t variables increases the likelihood of translation-time computation.
+ For example, the automatic initialization
+ double_t x = 1.1e75;
+ could be done at translation time, regardless of the expression evaluation method.
+
+[page 513]
+
+ their internal representations occur at translation time in all cases.
+
+ F.8.6 Changing the environment
+1 Operations defined in 6.5 and functions and macros defined for the standard libraries
+ change floating-point status flags and control modes just as indicated by their
+ specifications (including conformance to IEC 60559). They do not change flags or modes
+ (so as to be detectable by the user) in any other cases.
+2 If the argument to the feraiseexcept function in <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
+1 This section identifies code transformations that might subvert IEC 60559-specified
+ behavior, and others that do not.
+ F.9.1 Global transformations
+1 Floating-point arithmetic operations and external function calls may entail side effects
+ which optimization shall honor, at least where the state of the FENV_ACCESS pragma is
+ ''on''. The flags and modes in the floating-point environment may be regarded as global
+ variables; floating-point operations (+, *, etc.) implicitly read the modes and write the
+ flags.
+2 Concern about side effects may inhibit code motion and removal of seemingly useless
+ code. For example, in
+ #include <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.)
+3 This specification does not require support for trap handlers that maintain information
+ about the order or count of floating-point exceptions. Therefore, between function calls,
+ floating-point exceptions need not be precise: the actual order and number of occurrences
+ of floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
+
+[page 514]
+
+ the preceding loop could be treated as
+ if (0 < n) x + 1;
+ F.9.2 Expression transformations
+1 x/2 <-> x x 0.5 Although similar transformations involving inexact constants
+ generally do not yield numerically equivalent expressions, if the
+ constants are exact then such transformations can be made on
+ IEC 60559 machines and others that round perfectly.
+ 1 x x and x/1 -> x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559
+ machines, among others).368)
+ 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).369)
+ 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).
+
+ 368) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and
+ other transformations that remove arithmetic operators.
+ 369) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
+ Examples include:
+ 1/(1/ (+-) (inf)) is (+-) (inf)
+ and
+ conj(csqrt(z)) is csqrt(conj(z)),
+ for complex z.
+
+[page 515]
+
+ F.9.3 Relational operators
+1 x != x -> false The expression x != x is true if x is a NaN.
+ x = x -> true The expression x = x is false if x is a NaN.
+ x < y -> isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these
+ expressions are not equivalent because of side effects when x or y is a
+ NaN and the state of the FENV_ACCESS pragma is ''on''. This
+ transformation, which would be desirable if extra code were required
+ to cause the ''invalid'' floating-point exception for unordered cases,
+ could be performed provided the state of the FENV_ACCESS pragma
+ is ''off''.
+ The sense of relational operators shall be maintained. This includes handling unordered
+ cases as expressed by the source code.
+2 EXAMPLE
+ // calls g and raises ''invalid'' if a and b are unordered
+ if (a < b)
+ f();
+ else
+ g();
+ is not equivalent to
+ // calls f and raises ''invalid'' if a and b are unordered
+ if (a >= b)
+ g();
+ else
+ f();
+ nor to
+ // calls f without raising ''invalid'' if a and b are unordered
+ if (isgreaterequal(a,b))
+ g();
+ else
+ f();
+ nor, unless the state of the FENV_ACCESS pragma is ''off'', to
+ // calls g without raising ''invalid'' if a and b are unordered
+ if (isless(a,b))
+ f();
+ else
+ g();
+ but is equivalent to
+
+[page 516]
+
+ if (!(a < b))
+ g();
+ else
+ f();
+
+ F.9.4 Constant arithmetic
+1 The implementation shall honor floating-point exceptions raised by execution-time
+ constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4
+ and F.8.5.) An operation on constants that raises no floating-point exception can be
+ folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a
+ further check is required to assure that changing the rounding direction to downward does
+ not alter the sign of the result,370) and implementations that support dynamic rounding
+ precision modes shall assure further that the result of the operation raises no floating-
+ point exception when converted to the semantic type of the operation.
+ F.10 Mathematics <math.h>
+1 This subclause contains specifications of <math.h> facilities that are particularly suited
+ for IEC 60559 implementations.
+2 The Standard C macro HUGE_VAL and its float and long double analogs,
+ HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
+ infinities.
+3 Special cases for functions in <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.
+4 The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a
+ nonzero value.
+5 The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in
+ subsequent subclauses of this annex.
+6 The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of
+ rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value
+ whose magnitude is too large.
+7 The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially
+ subnormal or zero) and suffers loss of accuracy.371)
+
+
+ 370) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward.
+ 371) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on
+ when the floating-point exception is raised.
+
+[page 517]
+
+8 Whether or when library functions raise the ''inexact'' floating-point exception is
+ unspecified, unless explicitly specified otherwise.
+9 Whether or when library functions raise an undeserved ''underflow'' floating-point
+ exception is unspecified.372) 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.
+10 Whether the functions honor the rounding direction mode is implementation-defined,
+ unless explicitly specified otherwise.
+11 Functions with a NaN argument return a NaN result and raise no floating-point exception,
+ except where stated otherwise.
+12 The specifications in the following subclauses append to the definitions in <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
+13 If a function with one or more NaN arguments returns a NaN result, the result should be
+ the same as one of the NaN arguments (after possible type conversion), except perhaps
+ for the sign.
+ F.10.1 Trigonometric functions
+ F.10.1.1 The acos functions
+1 -- acos(1) returns +0.
+ -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for
+ | x | > 1.
+ F.10.1.2 The asin functions
+1 -- asin((+-)0) returns (+-)0.
+ -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for
+ | x | > 1.
+
+
+
+
+ 372) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if
+ avoiding them would be too costly.
+
+[page 518]
+
+ F.10.1.3 The atan functions
+1 -- atan((+-)0) returns (+-)0.
+ -- atan((+-)(inf)) returns (+-)pi /2.
+ F.10.1.4 The atan2 functions
+1 -- atan2((+-)0, -0) returns (+-)pi .373)
+ -- atan2((+-)0, +0) returns (+-)0.
+ -- atan2((+-)0, x) returns (+-)pi for x < 0.
+ -- atan2((+-)0, x) returns (+-)0 for x > 0.
+ -- atan2(y, (+-)0) returns -pi /2 for y < 0.
+ -- atan2(y, (+-)0) returns pi /2 for y > 0.
+ -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0.
+ -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0.
+ -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x.
+ -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4.
+ -- atan2((+-)(inf), +(inf)) returns (+-)pi /4.
+ F.10.1.5 The cos functions
+1 -- cos((+-)0) returns 1.
+ -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
+ F.10.1.6 The sin functions
+1 -- sin((+-)0) returns (+-)0.
+ -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
+ F.10.1.7 The tan functions
+1 -- tan((+-)0) returns (+-)0.
+ -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
+
+
+
+
+ 373) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise
+ the ''divide-by-zero'' floating-point exception.
+
+[page 519]
+
+ F.10.2 Hyperbolic functions
+ F.10.2.1 The acosh functions
+1 -- acosh(1) returns +0.
+ -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1.
+ -- acosh(+(inf)) returns +(inf).
+ F.10.2.2 The asinh functions
+1 -- asinh((+-)0) returns (+-)0.
+ -- asinh((+-)(inf)) returns (+-)(inf).
+ F.10.2.3 The atanh functions
+1 -- atanh((+-)0) returns (+-)0.
+ -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for
+ | x | > 1.
+ F.10.2.4 The cosh functions
+1 -- cosh((+-)0) returns 1.
+ -- cosh((+-)(inf)) returns +(inf).
+ F.10.2.5 The sinh functions
+1 -- sinh((+-)0) returns (+-)0.
+ -- sinh((+-)(inf)) returns (+-)(inf).
+ F.10.2.6 The tanh functions
+1 -- tanh((+-)0) returns (+-)0.
+ -- tanh((+-)(inf)) returns (+-)1.
+ F.10.3 Exponential and logarithmic functions
+ F.10.3.1 The exp functions
+1 -- exp((+-)0) returns 1.
+ -- exp(-(inf)) returns +0.
+ -- exp(+(inf)) returns +(inf).
+
+[page 520]
+
+ F.10.3.2 The exp2 functions
+1 -- exp2((+-)0) returns 1.
+ -- exp2(-(inf)) returns +0.
+ -- exp2(+(inf)) returns +(inf).
+ F.10.3.3 The expm1 functions
+1 -- expm1((+-)0) returns (+-)0.
+ -- expm1(-(inf)) returns -1.
+ -- expm1(+(inf)) returns +(inf).
+ F.10.3.4 The frexp functions
+1 -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp.
+ -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object
+ pointed to by exp.
+ -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp
+ (and returns a NaN).
+2 frexp raises no floating-point exceptions.
+3 When the radix of the argument is a power of 2, the returned value is exact and is
+ independent of the current rounding direction mode.
+4 On a binary system, the body of the frexp function might be
+ {
+ *exp = (value == 0) ? 0 : (int)(1 + logb(value));
+ return scalbn(value, -(*exp));
+ }
+ F.10.3.5 The ilogb functions
+1 When the correct result is representable in the range of the return type, the returned value
+ is exact and is independent of the current rounding direction mode.
+2 If the correct result is outside the range of the return type, the numeric result is
+ unspecified and the ''invalid'' floating-point exception is raised.
+3 ilogb(x), for x zero, infinite, or NaN, raises the ''invalid'' floating-point exception and
+ returns the value specified in 7.12.6.5.
+
+[page 521]
+
+ F.10.3.6 The ldexp functions
+1 On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).
+ F.10.3.7 The log functions
+1 -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- log(1) returns +0.
+ -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
+ -- log(+(inf)) returns +(inf).
+ F.10.3.8 The log10 functions
+1 -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- log10(1) returns +0.
+ -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
+ -- log10(+(inf)) returns +(inf).
+ F.10.3.9 The log1p functions
+1 -- log1p((+-)0) returns (+-)0.
+ -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for
+ x < -1.
+ -- log1p(+(inf)) returns +(inf).
+ F.10.3.10 The log2 functions
+1 -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- log2(1) returns +0.
+ -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
+ -- log2(+(inf)) returns +(inf).
+ F.10.3.11 The logb functions
+1 -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- logb((+-)(inf)) returns +(inf).
+2 The returned value is exact and is independent of the current rounding direction mode.
+
+[page 522]
+
+ F.10.3.12 The modf functions
+1 -- modf((+-)x, iptr) returns a result with the same sign as x.
+ -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr.
+ -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
+ NaN).
+2 The returned values are exact and are independent of the current rounding direction
+ mode.
+3 modf behaves as though implemented by
+ #include <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
+1 -- scalbn((+-)0, n) returns (+-)0.
+ -- scalbn(x, 0) returns x.
+ -- scalbn((+-)(inf), n) returns (+-)(inf).
+2 If the calculation does not overflow or underflow, the returned value is exact and
+ independent of the current rounding direction mode.
+
+[page 523]
+
+ F.10.4 Power and absolute value functions
+ F.10.4.1 The cbrt functions
+1 -- cbrt((+-)0) returns (+-)0.
+ -- cbrt((+-)(inf)) returns (+-)(inf).
+ F.10.4.2 The fabs functions
+1 -- fabs((+-)0) returns +0.
+ -- fabs((+-)(inf)) returns +(inf).
+2 The returned value is exact and is independent of the current rounding direction mode.
+ F.10.4.3 The hypot functions
+1 -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent.
+ -- hypot(x, (+-)0) is equivalent to fabs(x).
+ -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN.
+ F.10.4.4 The pow functions
+1 -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception
+ for y an odd integer < 0.
+ -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception
+ for y < 0, finite, and not an odd integer.
+ -- pow((+-)0, -(inf)) returns +(inf) and may raise the ''divide-by-zero'' floating-point
+ exception.
+ -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0.
+ -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer.
+ -- pow(-1, (+-)(inf)) returns 1.
+ -- pow(+1, y) returns 1 for any y, even a NaN.
+ -- pow(x, (+-)0) returns 1 for any x, even a NaN.
+ -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for
+ finite x < 0 and finite non-integer y.
+ -- pow(x, -(inf)) returns +(inf) for | x | < 1.
+ -- pow(x, -(inf)) returns +0 for | x | > 1.
+ -- pow(x, +(inf)) returns +0 for | x | < 1.
+ -- pow(x, +(inf)) returns +(inf) for | x | > 1.
+
+[page 524]
+
+ -- pow(-(inf), y) returns -0 for y an odd integer < 0.
+ -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer.
+ -- pow(-(inf), y) returns -(inf) for y an odd integer > 0.
+ -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer.
+ -- pow(+(inf), y) returns +0 for y < 0.
+ -- pow(+(inf), y) returns +(inf) for y > 0.
+ F.10.4.5 The sqrt functions
+1 sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value
+ is dependent on the current rounding direction mode.
+ F.10.5 Error and gamma functions
+ F.10.5.1 The erf functions
+1 -- erf((+-)0) returns (+-)0.
+ -- erf((+-)(inf)) returns (+-)1.
+ F.10.5.2 The erfc functions
+1 -- erfc(-(inf)) returns 2.
+ -- erfc(+(inf)) returns +0.
+ F.10.5.3 The lgamma functions
+1 -- lgamma(1) returns +0.
+ -- lgamma(2) returns +0.
+ -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for
+ x a negative integer or zero.
+ -- lgamma(-(inf)) returns +(inf).
+ -- lgamma(+(inf)) returns +(inf).
+ F.10.5.4 The tgamma functions
+1 -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
+ -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a
+ negative integer.
+ -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
+ -- tgamma(+(inf)) returns +(inf).
+
+[page 525]
+
+ F.10.6 Nearest integer functions
+ F.10.6.1 The ceil functions
+1 -- ceil((+-)0) returns (+-)0.
+ -- ceil((+-)(inf)) returns (+-)(inf).
+2 The returned value is independent of the current rounding direction mode.
+3 The double version of ceil behaves as though implemented by
+ #include <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;
+ }
+4 The ceil functions may, but are not required to, raise the ''inexact'' floating-point
+ exception for finite non-integer arguments, as this implementation does.
+ F.10.6.2 The floor functions
+1 -- floor((+-)0) returns (+-)0.
+ -- floor((+-)(inf)) returns (+-)(inf).
+2 The returned value and is independent of the current rounding direction mode.
+3 See the sample implementation for ceil in F.10.6.1. The floor functions may, but are
+ not required to, raise the ''inexact'' floating-point exception for finite non-integer
+ arguments, as that implementation does.
+ F.10.6.3 The nearbyint functions
+1 The nearbyint functions use IEC 60559 rounding according to the current rounding
+ direction. They do not raise the ''inexact'' floating-point exception if the result differs in
+ value from the argument.
+ -- nearbyint((+-)0) returns (+-)0 (for all rounding directions).
+ -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions).
+
+[page 526]
+
+ F.10.6.4 The rint functions
+1 The rint functions differ from the nearbyint functions only in that they do raise the
+ ''inexact'' floating-point exception if the result differs in value from the argument.
+ F.10.6.5 The lrint and llrint functions
+1 The lrint and llrint functions provide floating-to-integer conversion as prescribed
+ by IEC 60559. They round according to the current rounding direction. If the rounded
+ value is outside the range of the return type, the numeric result is unspecified and the
+ ''invalid'' floating-point exception is raised. When they raise no other floating-point
+ exception and the result differs from the argument, they raise the ''inexact'' floating-point
+ exception.
+ F.10.6.6 The round functions
+1 -- round((+-)0) returns (+-)0.
+ -- round((+-)(inf)) returns (+-)(inf).
+2 The returned value is independent of the current rounding direction mode.
+3 The double version of round behaves as though implemented by
+ #include <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.
+
+[page 527]
+
+ F.10.6.7 The lround and llround functions
+1 The lround and llround functions differ from the lrint and llrint functions
+ with the default rounding direction just in that the lround and llround functions
+ round halfway cases away from zero and need not raise the ''inexact'' floating-point
+ exception for non-integer arguments that round to within the range of the return type.
+ F.10.6.8 The trunc functions
+1 The trunc functions use IEC 60559 rounding toward zero (regardless of the current
+ rounding direction). The returned value is exact.
+ -- trunc((+-)0) returns (+-)0.
+ -- trunc((+-)(inf)) returns (+-)(inf).
+2 The returned value is independent of the current rounding direction mode. The trunc
+ functions may, but are not required to, raise the ''inexact'' floating-point exception for
+ finite non-integer arguments.
+ F.10.7 Remainder functions
+ F.10.7.1 The fmod functions
+1 -- fmod((+-)0, y) returns (+-)0 for y not zero.
+ -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x
+ infinite or y zero (and neither is a NaN).
+ -- fmod(x, (+-)(inf)) returns x for x not infinite.
+2 When subnormal results are supported, the returned value is exact and is independent of
+ the current rounding direction mode.
+3 The double version of fmod behaves as though implemented by
+ #include <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);
+ }
+
+[page 528]
+
+ F.10.7.2 The remainder functions
+1 The remainder functions are fully specified as a basic arithmetic operation in
+ IEC 60559.
+2 When subnormal results are supported, the returned value is exact and is independent of
+ the current rounding direction mode.
+ F.10.7.3 The remquo functions
+1 The remquo functions follow the specifications for the remainder functions. They
+ have no further specifications special to IEC 60559 implementations.
+2 When subnormal results are supported, the returned value is exact and is independent of
+ the current rounding direction mode.
+ F.10.8 Manipulation functions
+ F.10.8.1 The copysign functions
+1 copysign is specified in the Appendix to IEC 60559.
+2 The returned value is exact and is independent of the current rounding direction mode.
+ F.10.8.2 The nan functions
+1 All IEC 60559 implementations support quiet NaNs, in all floating formats.
+2 The returned value is exact and is independent of the current rounding direction mode.
+ F.10.8.3 The nextafter functions
+1 -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions
+ for x finite and the function value infinite.
+ -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point
+ exceptions for the function value subnormal or zero and x != y.
+2 Even though underflow or overflow can occur, the returned value is independent of the
+ current rounding direction mode.
+ F.10.8.4 The nexttoward functions
+1 No additional requirements beyond those on nextafter.
+2 Even though underflow or overflow can occur, the returned value is independent of the
+ current rounding direction mode.
+
+[page 529]
+
+ F.10.9 Maximum, minimum, and positive difference functions
+ F.10.9.1 The fdim functions
+1 No additional requirements.
+ F.10.9.2 The fmax functions
+1 If just one argument is a NaN, the fmax functions return the other argument (if both
+ arguments are NaNs, the functions return a NaN).
+2 The returned value is exact and is independent of the current rounding direction mode.
+3 The body of the fmax function might be374)
+ { return (isgreaterequal(x, y) ||
+ isnan(y)) ? x : y; }
+ F.10.9.3 The fmin functions
+1 The fmin functions are analogous to the fmax functions (see F.10.9.2).
+2 The returned value is exact and is independent of the current rounding direction mode.
+ F.10.10 Floating multiply-add
+ F.10.10.1 The fma functions
+1 -- fma(x, y, z) computes xy + z, correctly rounded once.
+ -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point
+ exception if one of x and y is infinite, the other is zero, and z is a NaN.
+ -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if
+ one of x and y is infinite, the other is zero, and z is not a NaN.
+ -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x
+ times y is an exact infinity and z is also an infinity but with the opposite sign.
+
+
+
+
+ 374) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would
+ return +0; however, implementation in software might be impractical.
+
+[page 530]
+
+ F.10.11 Comparison macros
+1 Relational operators and their corresponding comparison macros (7.12.14) produce
+ equivalent result values, even if argument values are represented in wider formats. Thus,
+ comparison macro arguments represented in formats wider than their semantic types are
+ not converted to the semantic types, unless the wide evaluation method converts operands
+ of relational operators to their semantic types. The standard wide evaluation methods
+ characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert
+ operands of relational operators to their semantic types.
+
+[page 531]
+
+ Annex G
+ (normative)
+ IEC 60559-compatible complex arithmetic
+ G.1 Introduction
+1 This annex supplements annex F to specify complex arithmetic for compatibility with
+ IEC 60559 real floating-point arithmetic. An implementation that defines
+ __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.375)
+ G.2 Types
+1 There is a new keyword _Imaginary, which is used to specify imaginary types. It is
+ used as a type specifier within declaration specifiers in the same way as _Complex is
+ (thus, _Imaginary float is a valid type name).
+2 There are three imaginary types, designated as float _Imaginary, double
+ _Imaginary, and long double _Imaginary. The imaginary types (along with
+ the real floating and complex types) are floating types.
+3 For imaginary types, the corresponding real type is given by deleting the keyword
+ _Imaginary from the type name.
+4 Each imaginary type has the same representation and alignment requirements as the
+ corresponding real type. The value of an object of imaginary type is the value of the real
+ representation times the imaginary unit.
+5 The imaginary type domain comprises the imaginary types.
+ G.3 Conventions
+1 A complex or imaginary value with at least one infinite part is regarded as an infinity
+ (even if its other part is a NaN). A complex or imaginary value is a finite number if each
+ of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is
+ a zero if each of its parts is a zero.
+
+
+
+
+ 375) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform
+ to these specifications.
+
+[page 532]
+
+ G.4 Conversions
+ G.4.1 Imaginary types
+1 Conversions among imaginary types follow rules analogous to those for real floating
+ types.
+ G.4.2 Real and imaginary
+1 When a value of imaginary type is converted to a real type other than _Bool,376) the
+ result is a positive zero.
+2 When a value of real type is converted to an imaginary type, the result is a positive
+ imaginary zero.
+ G.4.3 Imaginary and complex
+1 When a value of imaginary type is converted to a complex type, the real part of the
+ complex result value is a positive zero and the imaginary part of the complex result value
+ is determined by the conversion rules for the corresponding real types.
+2 When a value of complex type is converted to an imaginary type, the real part of the
+ complex value is discarded and the value of the imaginary part is converted according to
+ the conversion rules for the corresponding real types.
+ G.5 Binary operators
+1 The following subclauses supplement 6.5 in order to specify the type of the result for an
+ operation with an imaginary operand.
+2 For most operand types, the value of the result of a binary operator with an imaginary or
+ complex operand is completely determined, with reference to real arithmetic, by the usual
+ mathematical formula. For some operand types, the usual mathematical formula is
+ problematic because of its treatment of infinities and because of undue overflow or
+ underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
+ not completely determined.
+
+
+
+
+ 376) See 6.3.1.2.
+
+[page 533]
+
+ G.5.1 Multiplicative operators
+ Semantics
+1 If one operand has real type and the other operand has imaginary type, then the result has
+ imaginary type. If both operands have imaginary type, then the result has real type. (If
+ either operand has complex type, then the result has complex type.)
+2 If the operands are not both complex, then the result and floating-point exception
+ behavior of the * operator is defined by the usual mathematical formula:
+ * u iv u + iv
+
+ x xu i(xv) (xu) + i(xv)
+
+ iy i(yu) -yv (-yv) + i(yu)
+
+ x + iy (xu) + i(yu) (-yv) + i(xv)
+3 If the second operand is not complex, then the result and floating-point exception
+ behavior of the / operator is defined by the usual mathematical formula:
+ / u iv
+
+ x x/u i(-x/v)
+
+ iy i(y/u) y/v
+
+ x + iy (x/u) + i(y/u) (y/v) + i(-x/v)
+4 The * and / operators satisfy the following infinity properties for all real, imaginary, and
+ complex operands:377)
+ -- if one operand is an infinity and the other operand is a nonzero finite number or an
+ infinity, then the result of the * operator is an infinity;
+ -- if the first operand is an infinity and the second operand is a finite number, then the
+ result of the / operator is an infinity;
+ -- if the first operand is a finite number and the second operand is an infinity, then the
+ result of the / operator is a zero;
+
+
+
+
+ 377) These properties are already implied for those cases covered in the tables, but are required for all cases
+ (at least where the state for CX_LIMITED_RANGE is ''off'').
+
+[page 534]
+
+ -- if the first operand is a nonzero finite number or an infinity and the second operand is
+ a zero, then the result of the / operator is an infinity.
+5 If both operands of the * operator are complex or if the second operand of the / operator
+ is complex, the operator raises floating-point exceptions if appropriate for the calculation
+ of the parts of the result, and may raise spurious floating-point exceptions.
+6 EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note
+ that the imaginary unit I has imaginary type (see G.6).
+ #include <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) {
+
+[page 535]
+
+ x = INFINITY * ( a * c - b * d );
+ y = INFINITY * ( a * d + b * c );
+ }
+ }
+ return x + I * y;
+ }
+7 This implementation achieves the required treatment of infinities at the cost of only one isnan test in
+ ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.
+
+8 EXAMPLE 2 Division of two double _Complex operands could be implemented as follows.
+ #include <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 (isfinite(logbw)) {
+ 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 ((logbw == INFINITY) &&
+ isfinite(a) && isfinite(b)) {
+ c = copysign(isinf(c) ? 1.0 : 0.0, c);
+ d = copysign(isinf(d) ? 1.0 : 0.0, d);
+ x = 0.0 * ( a * c + b * d );
+ y = 0.0 * ( b * c - a * d );
+
+[page 536]
+
+ }
+ }
+ return x + I * y;
+ }
+9 Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than
+ for multiplication. In the spirit of the multiplication example above, this code does not defend against
+ overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of
+ with division, provides better roundoff characteristics.
+
+ G.5.2 Additive operators
+ Semantics
+1 If both operands have imaginary type, then the result has imaginary type. (If one operand
+ has real type and the other operand has imaginary type, or if either operand has complex
+ type, then the result has complex type.)
+2 In all cases the result and floating-point exception behavior of a + or - operator is defined
+ by the usual mathematical formula:
+ + or - u iv u + iv
+
+ x x(+-)u x (+-) iv (x (+-) u) (+-) iv
+
+ iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v)
+
+ x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v)
+ G.6 Complex arithmetic <complex.h>
+1 The macros
+ imaginary
+ and
+ _Imaginary_I
+ are defined, respectively, as _Imaginary and a constant expression of type const
+ float _Imaginary with the value of the imaginary unit. The macro
+ I
+ is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
+ the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
+ imaginary.
+2 This subclause contains specifications for the <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
+
+[page 537]
+
+ shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument
+ and the result, the result has the same sign as the argument.
+3 The functions are continuous onto both sides of their branch cuts, taking into account the
+ sign of zero. For example, csqrt(-2 (+-) i0) = (+-)i(sqrt)2. -
+4 Since complex and imaginary values are composed of real values, each function may be
+ regarded as computing real values from real values. Except as noted, the functions treat
+ real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a
+ manner consistent with the specifications for real functions in F.10.378)
+5 The functions cimag, conj, cproj, and creal are fully specified for all
+ implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-
+ point exceptions.
+6 Each of the functions cabs and carg is specified by a formula in terms of a real
+ function (whose special cases are covered in annex F):
+ cabs(x + iy) = hypot(x, y)
+ carg(x + iy) = atan2(y, x)
+7 Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
+ a formula in terms of other complex functions (whose special cases are specified below):
+ casin(z) = -i casinh(iz)
+ catan(z) = -i catanh(iz)
+ ccos(z) = ccosh(iz)
+ csin(z) = -i csinh(iz)
+ ctan(z) = -i ctanh(iz)
+8 For the other functions, the following subclauses specify behavior for special cases,
+ including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For
+ families of functions, the specifications apply to all of the functions even though only the
+ principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the
+ specifications for the upper half-plane imply the specifications for the lower half-plane; if
+ the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the
+ specifications for the first quadrant imply the specifications for the other three quadrants.
+9 In the following subclauses, cis(y) is defined as cos(y) + i sin(y).
+
+
+
+
+ 378) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
+ other part is a NaN.
+
+[page 538]
+
+ G.6.1 Trigonometric functions
+ G.6.1.1 The cacos functions
+1 -- cacos(conj(z)) = conj(cacos(z)).
+ -- cacos((+-)0 + i0) returns pi /2 - i0.
+ -- cacos((+-)0 + iNaN) returns pi /2 + iNaN.
+ -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x.
+ -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for nonzero finite x.
+ -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y.
+ -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y.
+ -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf).
+ -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf).
+ -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
+ result is unspecified).
+ -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite y.
+ -- cacos(NaN + i (inf)) returns NaN - i (inf).
+ -- cacos(NaN + iNaN) returns NaN + iNaN.
+ G.6.2 Hyperbolic functions
+ G.6.2.1 The cacosh functions
+1 -- cacosh(conj(z)) = conj(cacosh(z)).
+ -- cacosh((+-)0 + i0) returns +0 + ipi /2.
+ -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x.
+ -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for finite x.
+ -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y.
+ -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y.
+ -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4.
+ -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4.
+ -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN.
+
+[page 539]
+
+ -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for finite y.
+ -- cacosh(NaN + i (inf)) returns +(inf) + iNaN.
+ -- cacosh(NaN + iNaN) returns NaN + iNaN.
+ G.6.2.2 The casinh functions
+1 -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
+ -- casinh(+0 + i0) returns 0 + i0.
+ -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x.
+ -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for finite x.
+ -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y.
+ -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4.
+ -- casinh(+(inf) + iNaN) returns +(inf) + iNaN.
+ -- casinh(NaN + i0) returns NaN + i0.
+ -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for finite nonzero y.
+ -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result
+ is unspecified).
+ -- casinh(NaN + iNaN) returns NaN + iNaN.
+ G.6.2.3 The catanh functions
+1 -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
+ -- catanh(+0 + i0) returns +0 + i0.
+ -- catanh(+0 + iNaN) returns +0 + iNaN.
+ -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point
+ exception.
+ -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x.
+ -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for nonzero finite x.
+ -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y.
+ -- catanh(+(inf) + i (inf)) returns +0 + ipi /2.
+ -- catanh(+(inf) + iNaN) returns +0 + iNaN.
+
+[page 540]
+
+ -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
+ floating-point exception, for finite y.
+ -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is
+ unspecified).
+ -- catanh(NaN + iNaN) returns NaN + iNaN.
+ G.6.2.4 The ccosh functions
+1 -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
+ -- ccosh(+0 + i0) returns 1 + i0.
+ -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the
+ result is unspecified) and raises the ''invalid'' floating-point exception.
+ -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the
+ result is unspecified).
+ -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
+ exception, for finite nonzero x.
+ -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite nonzero x.
+ -- ccosh(+(inf) + i0) returns +(inf) + i0.
+ -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
+ -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
+ unspecified) and raises the ''invalid'' floating-point exception.
+ -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN.
+ -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the
+ result is unspecified).
+ -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for all nonzero numbers y.
+ -- ccosh(NaN + iNaN) returns NaN + iNaN.
+ G.6.2.5 The csinh functions
+1 -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
+ -- csinh(+0 + i0) returns +0 + i0.
+ -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is
+ unspecified) and raises the ''invalid'' floating-point exception.
+ -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is
+ unspecified).
+
+[page 541]
+
+ -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
+ exception, for positive finite x.
+ -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite nonzero x.
+ -- csinh(+(inf) + i0) returns +(inf) + i0.
+ -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y.
+ -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
+ unspecified) and raises the ''invalid'' floating-point exception.
+ -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
+ is unspecified).
+ -- csinh(NaN + i0) returns NaN + i0.
+ -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for all nonzero numbers y.
+ -- csinh(NaN + iNaN) returns NaN + iNaN.
+ G.6.2.6 The ctanh functions
+1 -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
+ -- ctanh(+0 + i0) returns +0 + i0.
+ -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
+ exception, for finite x.
+ -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite x.
+ -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
+ -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result
+ is unspecified).
+ -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the
+ result is unspecified).
+ -- ctanh(NaN + i0) returns NaN + i0.
+ -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for all nonzero numbers y.
+ -- ctanh(NaN + iNaN) returns NaN + iNaN.
+
+[page 542]
+
+ G.6.3 Exponential and logarithmic functions
+ G.6.3.1 The cexp functions
+1 -- cexp(conj(z)) = conj(cexp(z)).
+ -- cexp((+-)0 + i0) returns 1 + i0.
+ -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
+ exception, for finite x.
+ -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite x.
+ -- cexp(+(inf) + i0) returns +(inf) + i0.
+ -- cexp(-(inf) + iy) returns +0 cis(y), for finite y.
+ -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
+ -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of
+ the result are unspecified).
+ -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point
+ exception (where the sign of the real part of the result is unspecified).
+ -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts
+ of the result are unspecified).
+ -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
+ is unspecified).
+ -- cexp(NaN + i0) returns NaN + i0.
+ -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for all nonzero numbers y.
+ -- cexp(NaN + iNaN) returns NaN + iNaN.
+ G.6.3.2 The clog functions
+1 -- clog(conj(z)) = conj(clog(z)).
+ -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point
+ exception.
+ -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point
+ exception.
+ -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x.
+ -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite x.
+
+[page 543]
+
+ -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y.
+ -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
+ -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4.
+ -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4.
+ -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN.
+ -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite y.
+ -- clog(NaN + i (inf)) returns +(inf) + iNaN.
+ -- clog(NaN + iNaN) returns NaN + iNaN.
+ G.6.4 Power and absolute-value functions
+ G.6.4.1 The cpow functions
+1 The cpow functions raise floating-point exceptions if appropriate for the calculation of
+ the parts of the result, and may also raise spurious floating-point exceptions.379)
+ G.6.4.2 The csqrt functions
+1 -- csqrt(conj(z)) = conj(csqrt(z)).
+ -- csqrt((+-)0 + i0) returns +0 + i0.
+ -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN).
+ -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite x.
+ -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y.
+ -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
+ -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
+ result is unspecified).
+ -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN.
+ -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
+ point exception, for finite y.
+ -- csqrt(NaN + iNaN) returns NaN + iNaN.
+
+
+
+
+ 379) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding
+ implementations that treat special cases more carefully.
+
+[page 544]
+
+ G.7 Type-generic math <tgmath.h>
+1 Type-generic macros that accept complex arguments also accept imaginary arguments. If
+ an argument is imaginary, the macro expands to an expression whose type is real,
+ imaginary, or complex, as appropriate for the particular function: if the argument is
+ imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the
+ types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and
+ the types of the others are complex.
+2 Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,
+ sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real
+ functions:
+ cos(iy) = cosh(y)
+ sin(iy) = i sinh(y)
+ tan(iy) = i tanh(y)
+ cosh(iy) = cos(y)
+ sinh(iy) = i sin(y)
+ tanh(iy) = i tan(y)
+ asin(iy) = i asinh(y)
+ atan(iy) = i atanh(y)
+ asinh(iy) = i asin(y)
+ atanh(iy) = i atan(y)
+
+[page 545]
+
+ Annex H
+ (informative)
+ Language independent arithmetic
+ H.1 Introduction
+1 This annex documents the extent to which the C language supports the ISO/IEC 10967-1
+ standard for language-independent arithmetic (LIA-1). LIA-1 is more general than
+ IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.
+ H.2 Types
+1 The relevant C arithmetic types meet the requirements of LIA-1 types if an
+ implementation adds notification of exceptional arithmetic operations and meets the 1
+ unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8).
+ H.2.1 Boolean type
+1 The LIA-1 data type Boolean is implemented by the C data type bool with values of
+ true and false, all from <stdbool.h>.
+ H.2.2 Integer types
+1 The signed C integer types int, long int, long long int, and the corresponding
+ unsigned types are compatible with LIA-1. If an implementation adds support for the
+ LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are
+ LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense
+ in that overflows or out-of-bounds results silently wrap. An implementation that defines
+ signed integer types as also being modulo need not detect integer overflow, in which case,
+ only integer divide-by-zero need be detected.
+2 The parameters for the integer data types can be accessed by the following:
+ maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,
+ ULLONG_MAX
+ minint INT_MIN, LONG_MIN, LLONG_MIN
+3 The parameter ''bounded'' is always true, and is not provided. The parameter ''minint''
+ is always 0 for the unsigned types, and is not provided for those types.
+
+[page 546]
+
+ H.2.2.1 Integer operations
+1 The integer operations on integer types are the following:
+ addI x + y
+ subI x - y
+ mulI x * y
+ divI, divtI x / y
+ remI, remtI x % y
+ negI -x
+ absI abs(x), labs(x), llabs(x)
+ eqI x == y
+ neqI x != y
+ lssI x < y
+ leqI x <= y
+ gtrI x > y
+ geqI x >= y
+ where x and y are expressions of the same integer type.
+ H.2.3 Floating-point types
+1 The C floating-point types float, double, and long double are compatible with
+ LIA-1. If an implementation adds support for the LIA-1 exceptional values
+ ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant
+ with LIA-1. An implementation that uses IEC 60559 floating-point formats and
+ operations (see annex F) along with IEC 60559 status flags and traps has LIA-1
+ conformant types.
+ H.2.3.1 Floating-point parameters
+1 The parameters for a floating point data type can be accessed by the following:
+ r FLT_RADIX
+ p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
+ emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
+ emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP
+2 The derived constants for the floating point types are accessed by the following:
+
+[page 547]
+
+ fmax FLT_MAX, DBL_MAX, LDBL_MAX
+ fminN FLT_MIN, DBL_MIN, LDBL_MIN
+ epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
+ rnd_style FLT_ROUNDS
+ H.2.3.2 Floating-point operations
+1 The floating-point operations on floating-point types are the following:
+ addF x + y
+ subF x - y
+ mulF x * y
+ divF x / y
+ negF -x
+ absF fabsf(x), fabs(x), fabsl(x)
+ exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
+ scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
+ scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
+ intpartF modff(x, &y), modf(x, &y), modfl(x, &y)
+ fractpartF modff(x, &y), modf(x, &y), modfl(x, &y)
+ eqF x == y
+ neqF x != y
+ lssF x < y
+ leqF x <= y
+ gtrF x > y
+ geqF x >= y
+ where x and y are expressions of the same floating point type, n is of type int, and li
+ is of type long int.
+ H.2.3.3 Rounding styles
+1 The C Standard requires all floating types to use the same radix and rounding style, so
+ that only one identifier for each is provided to map to LIA-1.
+2 The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles:
+ truncate FLT_ROUNDS == 0
+
+[page 548]
+
+ nearest FLT_ROUNDS == 1
+ other FLT_ROUNDS != 0 && FLT_ROUNDS != 1
+ provided that an implementation extends FLT_ROUNDS to cover the rounding style used
+ in all relevant LIA-1 operations, not just addition as in C.
+ H.2.4 Type conversions
+1 The LIA-1 type conversions are the following type casts:
+ cvtI' -> I (int)i, (long int)i, (long long int)i,
+ (unsigned int)i, (unsigned long int)i,
+ (unsigned long long int)i
+ cvtF -> I (int)x, (long int)x, (long long int)x,
+ (unsigned int)x, (unsigned long int)x,
+ (unsigned long long int)x
+ cvtI -> F (float)i, (double)i, (long double)i
+ cvtF' -> F (float)x, (double)x, (long double)x
+2 In the above conversions from floating to integer, the use of (cast)x can be replaced with
+ (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
+ (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer
+ conversion functions, lrint(), llrint(), lround(), and llround(), can be
+ used. They all meet LIA-1's requirements on floating to integer rounding for in-range
+ values. For out-of-range values, the conversions shall silently wrap for the modulo types.
+3 The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,
+ fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),
+ 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
+ to 65535.0 which can then be cast to unsigned short int. But, the
+ remainder() function is not useful for doing silent wrapping to signed integer types,
+ e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the
+ range -32767.0 to +32768.0 which is not, in general, in the range of signed short
+ int.
+4 C's conversions (casts) from floating-point to floating-point can meet LIA-1
+ requirements if an implementation uses round-to-nearest (IEC 60559 default).
+5 C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an
+ implementation uses round-to-nearest.
+
+[page 549]
+
+ H.3 Notification
+1 Notification is the process by which a user or program is informed that an exceptional
+ arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C
+ allows an implementation to cause a notification to occur when any arithmetic operation
+ returns an exceptional value as defined in LIA-1 clause 5.
+ H.3.1 Notification alternatives
+1 LIA-1 requires at least the following two alternatives for handling of notifications:
+ setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and-
+ resume.
+2 An implementation need only support a given notification alternative for the entire
+ program. An implementation may support the ability to switch between notification
+ alternatives during execution, but is not required to do so. An implementation can
+ provide separate selection for each kind of notification, but this is not required.
+3 C allows an implementation to provide notification. C's SIGFPE (for traps) and
+ FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
+ can provide LIA-1 notification.
+4 C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can
+ provide trap-and-terminate behavior, except for those LIA-1 operations implemented by
+ math library function calls. User-provided signal handlers for SIGFPE allow for trap-
+ and-resume behavior with the same constraint.
+ H.3.1.1 Indicators
+1 C's <fenv.h> status flags are compatible with the LIA-1 indicators.
+2 The following mapping is for floating-point types:
+ undefined FE_INVALID, FE_DIVBYZERO
+ floating_overflow FE_OVERFLOW
+ underflow FE_UNDERFLOW
+3 The floating-point indicator interrogation and manipulation operations are:
+ set_indicators feraiseexcept(i)
+ clear_indicators feclearexcept(i)
+ test_indicators fetestexcept(i)
+ current_indicators fetestexcept(FE_ALL_EXCEPT)
+ where i is an expression of type int representing a subset of the LIA-1 indicators.
+4 C allows an implementation to provide the following LIA-1 required behavior: at
+ program termination if any indicator is set the implementation shall send an unambiguous
+
+[page 550]
+
+ and ''hard to ignore'' message (see LIA-1 subclause 6.1.2)
+5 LIA-1 does not make the distinction between floating-point and integer for ''undefined''.
+ This documentation makes that distinction because <fenv.h> covers only the floating-
+ point indicators.
+ H.3.1.2 Traps
+1 C is compatible with LIA-1's trap requirements for arithmetic operations, but not for
+ math library functions (which are not permitted to invoke a user's signal handler for
+ SIGFPE). An implementation can provide an alternative of notification through
+ termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3).
+2 LIA-1 does not require that traps be precise.
+3 C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions,
+ if there is any signal raised for them.
+4 C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic
+ exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism
+ allows trap-and-terminate (either default implementation behavior or user replacement for
+ it) or trap-and-resume, at the programmer's option.
+
+[page 551]
+
+ Annex I
+ (informative)
+ Common warnings
+1 An implementation may generate warnings in many situations, none of which are
+ specified as part of this International Standard. The following are a few of the more
+ common situations.
+2 -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
+ -- A block with initialization of an object that has automatic storage duration is jumped
+ into (6.2.4).
+ -- An implicit narrowing conversion is encountered, such as the assignment of a long
+ int or a double to an int, or a pointer to void to a pointer to any type other than
+ a character type (6.3).
+ -- A hexadecimal floating constant cannot be represented exactly in its evaluation format
+ (6.4.4.2).
+ -- An integer character constant includes more than one character or a wide character
+ constant includes more than one multibyte character (6.4.4.4).
+ -- The characters /* are found in a comment (6.4.7).
+ -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an
+ lvalue in one operand, and a side effect to, or an access to the value of, the identical
+ lvalue in the other operand (6.5).
+ -- A function is called but no prototype has been supplied (6.5.2.2).
+ -- The arguments in a function call do not agree in number and type with those of the
+ parameters in a function definition that is not a prototype (6.5.2.2).
+ -- An object is defined but not used (6.7).
+ -- A value is given to an object of an enumerated type other than by assignment of an
+ enumeration constant that is a member of that type, or an enumeration object that has
+ the same type, or the value of a function that returns the same enumerated type
+ (6.7.2.2).
+ -- An aggregate has a partly bracketed initialization (6.7.8).
+ -- A statement cannot be reached (6.8).
+ -- A statement with no apparent effect is encountered (6.8).
+ -- A constant expression is used as the controlling expression of a selection statement
+ (6.8.4).
+
+[page 552]
+
+-- An incorrectly formed preprocessing group is encountered while skipping a
+ preprocessing group (6.10.1).
+-- An unrecognized #pragma directive is encountered (6.10.6).
+
+[page 553]
+
+ Annex J
+ (informative)
+ Portability issues
+1 This annex collects some information about portability that appears in this International
+ Standard.
+ J.1 Unspecified behavior
+1 The following are unspecified:
+ -- The manner and timing of static initialization (5.1.2).
+ -- The termination status returned to the hosted environment if the return type of main
+ is not compatible with int (5.1.2.2.3).
+ -- The values of objects that are neither lock-free atomic objects nor of type volatile
+ sig_atomic_t and the state of the floating-point environment, when the
+ processing of the abstract machine is interrupted by receipt of a signal (5.1.2.3).
+ -- The behavior of the display device if a printing character is written when the active
+ position is at the final position of a line (5.2.2).
+ -- The behavior of the display device if a backspace character is written when the active
+ position is at the initial position of a line (5.2.2).
+ -- The behavior of the display device if a horizontal tab character is written when the
+ active position is at or past the last defined horizontal tabulation position (5.2.2).
+ -- The behavior of the display device if a vertical tab character is written when the active
+ position is at or past the last defined vertical tabulation position (5.2.2).
+ -- How an extended source character that does not correspond to a universal character
+ name counts toward the significant initial characters in an external identifier (5.2.4.1).
+ -- Many aspects of the representations of types (6.2.6).
+ -- The value of padding bytes when storing values in structures or unions (6.2.6.1).
+ -- The values of bytes that correspond to union members other than the one last stored
+ into (6.2.6.1).
+ -- The representation used when storing a value in an object that has more than one
+ object representation for that value (6.2.6.1).
+ -- The values of any padding bits in integer representations (6.2.6.2).
+ -- Whether certain operators can generate negative zeros and whether a negative zero
+ becomes a normal zero when stored in an object (6.2.6.2).
+
+[page 554]
+
+-- Whether two string literals result in distinct arrays (6.4.5).
+-- The order in which subexpressions are evaluated and the order in which side effects
+ take place, except as specified for the function-call (), &&, ||, ? :, and comma
+ operators (6.5).
+-- The order in which the function designator, arguments, and subexpressions within the
+ arguments are evaluated in a function call (6.5.2.2).
+-- The order of side effects among compound literal initialization list expressions
+ (6.5.2.5).
+-- The order in which the operands of an assignment operator are evaluated (6.5.16).
+-- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
+-- Whether a call to an inline function uses the inline definition or the external definition
+ of the function (6.7.4).
+-- Whether or not a size expression is evaluated when it is part of the operand of a
+ sizeof operator and changing the value of the size expression would not affect the
+ result of the operator (6.7.6.2).
+-- The order in which any side effects occur among the initialization list expressions in
+ an initializer (6.7.9).
+-- The layout of storage for function parameters (6.9.1).
+-- When a fully expanded macro replacement list contains a function-like macro name
+ as its last preprocessing token and the next preprocessing token from the source file is
+ a (, and the fully expanded replacement of that macro ends with the name of the first
+ macro and the next preprocessing token from the source file is again a (, whether that
+ is considered a nested replacement (6.10.3).
+-- The order in which # and ## operations are evaluated during macro substitution
+ (6.10.3.2, 6.10.3.3).
+-- The state of the floating-point status flags when execution passes from a part of the
+ program translated with FENV_ACCESS ''off'' to a part translated with
+ FENV_ACCESS ''on'' (7.6.1).
+-- The order in which feraiseexcept raises floating-point exceptions, except as
+ stated in F.8.6 (7.6.2.3).
+-- Whether math_errhandling is a macro or an identifier with external linkage
+ (7.12).
+-- The results of the frexp functions when the specified value is not a floating-point
+ number (7.12.6.4).
+
+[page 555]
+
+-- The numeric result of the ilogb functions when the correct value is outside the
+ range of the return type (7.12.6.5, F.10.3.5).
+-- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5).
+-- The value stored by the remquo functions in the object pointed to by quo when y is
+ zero (7.12.10.3).
+-- Whether a comparison macro argument that is represented in a format wider than its
+ semantic type is converted to the semantic type (7.12.14).
+-- Whether setjmp is a macro or an identifier with external linkage (7.13).
+-- Whether va_copy and va_end are macros or identifiers with external linkage
+ (7.16.1).
+-- The hexadecimal digit before the decimal point when a non-normalized floating-point
+ number is printed with an a or A conversion specifier (7.21.6.1, 7.29.2.1).
+-- The value of the file position indicator after a successful call to the ungetc function
+ for a text stream, or the ungetwc function for any stream, until all pushed-back
+ characters are read or discarded (7.21.7.10, 7.29.3.10).
+-- The details of the value stored by the fgetpos function (7.21.9.1).
+-- The details of the value returned by the ftell function for a text stream (7.21.9.4).
+-- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold
+ functions convert a minus-signed sequence to a negative number directly or by
+ negating the value resulting from converting the corresponding unsigned sequence
+ (7.22.1.3, 7.29.4.1.1).
+-- The order and contiguity of storage allocated by successive calls to the calloc,
+ malloc, and realloc functions (7.22.3).
+-- The amount of storage allocated by a successful call to the calloc, malloc, or
+ realloc function when 0 bytes was requested (7.22.3).
+-- Whether a call to the atexit function that does not happen before the exit
+ function is called will succeed (7.22.4.2).
+-- Whether a call to the at_quick_exit function that does not happen before the
+ quick_exit function is called will succeed (7.22.4.3).
+-- Which of two elements that compare as equal is matched by the bsearch function
+ (7.22.5.1).
+-- The order of two elements that compare as equal in an array sorted by the qsort
+ function (7.22.5.2).
+
+[page 556]
+
+ -- The encoding of the calendar time returned by the time function (7.27.2.4).
+ -- The characters stored by the strftime or wcsftime function if any of the time
+ values being converted is outside the normal range (7.27.3.5, 7.29.5.1).
+ -- Whether an encoding error occurs if a wchar_t value that does not correspond to a
+ member of the extended character set appears in the format string for a function in
+ 7.29.2 or 7.29.5 and the specified semantics do not require that value to be processed
+ by wcrtomb (7.29.1).
+ -- The conversion state after an encoding error occurs (7.29.6.3.2, 7.29.6.3.3, 7.29.6.4.1,
+ 7.29.6.4.2,
+ -- The resulting value when the ''invalid'' floating-point exception is raised during
+ IEC 60559 floating to integer conversion (F.4).
+ -- Whether conversion of non-integer IEC 60559 floating values to integer raises the
+ ''inexact'' floating-point exception (F.4).
+ -- Whether or when library functions in <math.h> raise the ''inexact'' floating-point
+ exception in an IEC 60559 conformant implementation (F.10).
+ -- Whether or when library functions in <math.h> raise an undeserved ''underflow''
+ floating-point exception in an IEC 60559 conformant implementation (F.10).
+ -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4).
+ -- The numeric result returned by the lrint, llrint, lround, and llround
+ functions if the rounded value is outside the range of the return type (F.10.6.5,
+ F.10.6.7).
+ -- The sign of one part of the complex result of several math functions for certain
+ special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3,
+ G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).
+ J.2 Undefined behavior
+1 The behavior is undefined in the following circumstances:
+ -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated
+ (clause 4).
+ -- A nonempty source file does not end in a new-line character which is not immediately
+ preceded by a backslash character or ends in a partial preprocessing token or
+ comment (5.1.1.2).
+ -- Token concatenation produces a character sequence matching the syntax of a
+ universal character name (5.1.1.2).
+ -- A program in a hosted environment does not define a function named main using one
+ of the specified forms (5.1.2.2.1).
+
+[page 557]
+
+-- The execution of a program contains a data race (5.1.2.4).
+-- A character not in the basic source character set is encountered in a source file, except
+ in an identifier, a character constant, a string literal, a header name, a comment, or a
+ preprocessing token that is never converted to a token (5.2.1).
+-- An identifier, comment, string literal, character constant, or header name contains an
+ invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
+-- The same identifier has both internal and external linkage in the same translation unit
+ (6.2.2).
+-- An object is referred to outside of its lifetime (6.2.4).
+-- The value of a pointer to an object whose lifetime has ended is used (6.2.4).
+-- The value of an object with automatic storage duration is used while it is
+ indeterminate (6.2.4, 6.7.9, 6.8).
+-- A trap representation is read by an lvalue expression that does not have character type
+ (6.2.6.1).
+-- A trap representation is produced by a side effect that modifies any part of the object
+ using an lvalue expression that does not have character type (6.2.6.1).
+-- The operands to certain operators are such that they could produce a negative zero
+ result, but the implementation does not support negative zeros (6.2.6.2).
+-- Two declarations of the same object or function specify types that are not compatible
+ (6.2.7).
+-- A program requires the formation of a composite type from a variable length array
+ type whose size is specified by an expression that is not evaluated (6.2.7).
+-- Conversion to or from an integer type produces a value outside the range that can be
+ represented (6.3.1.4).
+-- Demotion of one real floating type to another produces a value outside the range that
+ can be represented (6.3.1.5).
+-- An lvalue does not designate an object when evaluated (6.3.2.1).
+-- A non-array lvalue with an incomplete type is used in a context that requires the value
+ of the designated object (6.3.2.1).
+-- An lvalue designating an object of automatic storage duration that could have been
+ declared with the register storage class is used in a context that requires the value
+ of the designated object, but the object is uninitialized. (6.3.2.1).
+-- An lvalue having array type is converted to a pointer to the initial element of the
+ array, and the array object has register storage class (6.3.2.1).
+
+[page 558]
+
+-- An attempt is made to use the value of a void expression, or an implicit or explicit
+ conversion (except to void) is applied to a void expression (6.3.2.2).
+-- Conversion of a pointer to an integer type produces a value outside the range that can
+ be represented (6.3.2.3).
+-- Conversion between two pointer types produces a result that is incorrectly aligned
+ (6.3.2.3).
+-- A pointer is used to call a function whose type is not compatible with the referenced
+ type (6.3.2.3).
+-- An unmatched ' or " character is encountered on a logical source line during
+ tokenization (6.4).
+-- A reserved keyword token is used in translation phase 7 or 8 for some purpose other
+ than as a keyword (6.4.1).
+-- A universal character name in an identifier does not designate a character whose
+ encoding falls into one of the specified ranges (6.4.2.1).
+-- The initial character of an identifier is a universal character name designating a digit
+ (6.4.2.1).
+-- Two identifiers differ only in nonsignificant characters (6.4.2.1).
+-- The identifier __func__ is explicitly declared (6.4.2.2).
+-- The program attempts to modify a string literal (6.4.5).
+-- The characters ', \, ", //, or /* occur in the sequence between the < and >
+ delimiters, or the characters ', \, //, or /* occur in the sequence between the "
+ delimiters, in a header name preprocessing token (6.4.7).
+-- A side effect on a scalar object is unsequenced relative to either a different side effect
+ on the same scalar object or a value computation using the value of the same scalar
+ object (6.5).
+-- An exceptional condition occurs during the evaluation of an expression (6.5).
+-- An object has its stored value accessed other than by an lvalue of an allowable type
+ (6.5).
+-- For a call to a function without a function prototype in scope, the number of
+ arguments does not equal the number of parameters (6.5.2.2).
+-- For call to a function without a function prototype in scope where the function is
+ defined with a function prototype, either the prototype ends with an ellipsis or the
+ types of the arguments after promotion are not compatible with the types of the
+ parameters (6.5.2.2).
+
+[page 559]
+
+-- For a call to a function without a function prototype in scope where the function is not
+ defined with a function prototype, the types of the arguments after promotion are not
+ compatible with those of the parameters after promotion (with certain exceptions)
+ (6.5.2.2).
+-- A function is defined with a type that is not compatible with the type (of the
+ expression) pointed to by the expression that denotes the called function (6.5.2.2).
+-- A member of an atomic structure or union is accessed (6.5.2.3).
+-- The operand of the unary * operator has an invalid value (6.5.3.2).
+-- A pointer is converted to other than an integer or pointer type (6.5.4).
+-- The value of the second operand of the / or % operator is zero (6.5.5).
+-- Addition or subtraction of a pointer into, or just beyond, an array object and an
+ integer type produces a result that does not point into, or just beyond, the same array
+ object (6.5.6).
+-- Addition or subtraction of a pointer into, or just beyond, an array object and an
+ integer type produces a result that points just beyond the array object and is used as
+ the operand of a unary * operator that is evaluated (6.5.6).
+-- Pointers that do not point into, or just beyond, the same array object are subtracted
+ (6.5.6).
+-- An array subscript is out of range, even if an object is apparently accessible with the
+ given subscript (as in the lvalue expression a[1][7] given the declaration int
+ a[4][5]) (6.5.6).
+-- The result of subtracting two pointers is not representable in an object of type
+ ptrdiff_t (6.5.6).
+-- An expression is shifted by a negative number or by an amount greater than or equal
+ to the width of the promoted expression (6.5.7).
+-- An expression having signed promoted type is left-shifted and either the value of the
+ expression is negative or the result of shifting would be not be representable in the
+ promoted type (6.5.7).
+-- Pointers that do not point to the same aggregate or union (nor just beyond the same
+ array object) are compared using relational operators (6.5.8).
+-- An object is assigned to an inexactly overlapping object or to an exactly overlapping
+ object with incompatible type (6.5.16.1).
+-- An expression that is required to be an integer constant expression does not have an
+ integer type; has operands that are not integer constants, enumeration constants,
+ character constants, sizeof expressions whose results are integer constants,
+
+[page 560]
+
+ _Alignof expressions, or immediately-cast floating constants; or contains casts
+ (outside operands to sizeof and _Alignof operators) other than conversions of
+ arithmetic types to integer types (6.6).
+-- A constant expression in an initializer is not, or does not evaluate to, one of the
+ following: an arithmetic constant expression, a null pointer constant, an address
+ constant, or an address constant for a complete object type plus or minus an integer
+ constant expression (6.6).
+-- An arithmetic constant expression does not have arithmetic type; has operands that
+ are not integer constants, floating constants, enumeration constants, character
+ constants, sizeof expressions whose results are integer constants, or _Alignof
+ expressions; or contains casts (outside operands to sizeof or _Alignof operators)
+ other than conversions of arithmetic types to arithmetic types (6.6).
+-- The value of an object is accessed by an array-subscript [], member-access . or ->,
+ address &, or indirection * operator or a pointer cast in creating an address constant
+ (6.6).
+-- An identifier for an object is declared with no linkage and the type of the object is
+ incomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
+-- A function is declared at block scope with an explicit storage-class specifier other
+ than extern (6.7.1).
+-- A structure or union is defined without any named members (including those
+ specified indirectly via anonymous structures and unions) (6.7.2.1).
+-- An attempt is made to access, or generate a pointer to just past, a flexible array
+ member of a structure when the referenced object provides no elements for that array
+ (6.7.2.1).
+-- When the complete type is needed, an incomplete structure or union type is not
+ completed in the same scope by another declaration of the tag that defines the content
+ (6.7.2.3).
+-- An attempt is made to modify an object defined with a const-qualified type through
+ use of an lvalue with non-const-qualified type (6.7.3).
+-- An attempt is made to refer to an object defined with a volatile-qualified type through
+ use of an lvalue with non-volatile-qualified type (6.7.3).
+-- The specification of a function type includes any type qualifiers (6.7.3).
+-- Two qualified types that are required to be compatible do not have the identically
+ qualified version of a compatible type (6.7.3).
+-- An object which has been modified is accessed through a restrict-qualified pointer to
+ a const-qualified type, or through a restrict-qualified pointer and another pointer that
+
+[page 561]
+
+ are not both based on the same object (6.7.3.1).
+-- A restrict-qualified pointer is assigned a value based on another restricted pointer
+ whose associated block neither began execution before the block associated with this
+ pointer, nor ended before the assignment (6.7.3.1).
+-- A function with external linkage is declared with an inline function specifier, but is
+ not also defined in the same translation unit (6.7.4).
+-- A function declared with a _Noreturn function specifier returns to its caller (6.7.4).
+-- The definition of an object has an alignment specifier and another declaration of that
+ object has a different alignment specifier (6.7.5).
+-- Declarations of an object in different translation units have different alignment
+ specifiers (6.7.5).
+-- Two pointer types that are required to be compatible are not identically qualified, or
+ are not pointers to compatible types (6.7.6.1).
+-- The size expression in an array declaration is not a constant expression and evaluates
+ at program execution time to a nonpositive value (6.7.6.2).
+-- In a context requiring two array types to be compatible, they do not have compatible
+ element types, or their size specifiers evaluate to unequal values (6.7.6.2).
+-- A declaration of an array parameter includes the keyword static within the [ and
+ ] and the corresponding argument does not provide access to the first element of an
+ array with at least the specified number of elements (6.7.6.3).
+-- A storage-class specifier or type qualifier modifies the keyword void as a function
+ parameter type list (6.7.6.3).
+-- In a context requiring two function types to be compatible, they do not have
+ compatible return types, or their parameters disagree in use of the ellipsis terminator
+ or the number and type of parameters (after default argument promotion, when there
+ is no parameter type list or when one type is specified by a function definition with an
+ identifier list) (6.7.6.3).
+-- The value of an unnamed member of a structure or union is used (6.7.9).
+-- The initializer for a scalar is neither a single expression nor a single expression
+ enclosed in braces (6.7.9).
+-- The initializer for a structure or union object that has automatic storage duration is
+ neither an initializer list nor a single expression that has compatible structure or union
+ type (6.7.9).
+-- The initializer for an aggregate or union, other than an array initialized by a string
+ literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9).
+
+[page 562]
+
+-- An identifier with external linkage is used, but in the program there does not exist
+ exactly one external definition for the identifier, or the identifier is not used and there
+ exist multiple external definitions for the identifier (6.9).
+-- A function definition includes an identifier list, but the types of the parameters are not
+ declared in a following declaration list (6.9.1).
+-- An adjusted parameter type in a function definition is not a complete object type
+ (6.9.1).
+-- A function that accepts a variable number of arguments is defined without a
+ parameter type list that ends with the ellipsis notation (6.9.1).
+-- The } that terminates a function is reached, and the value of the function call is used
+ by the caller (6.9.1).
+-- An identifier for an object with internal linkage and an incomplete type is declared
+ with a tentative definition (6.9.2).
+-- The token defined is generated during the expansion of a #if or #elif
+ preprocessing directive, or the use of the defined unary operator does not match
+ one of the two specified forms prior to macro replacement (6.10.1).
+-- The #include preprocessing directive that results after expansion does not match
+ one of the two header name forms (6.10.2).
+-- The character sequence in an #include preprocessing directive does not start with a
+ letter (6.10.2).
+-- There are sequences of preprocessing tokens within the list of macro arguments that
+ would otherwise act as preprocessing directives (6.10.3).
+-- The result of the preprocessing operator # is not a valid character string literal
+ (6.10.3.2).
+-- The result of the preprocessing operator ## is not a valid preprocessing token
+ (6.10.3.3).
+-- The #line preprocessing directive that results after expansion does not match one of
+ the two well-defined forms, or its digit sequence specifies zero or a number greater
+ than 2147483647 (6.10.4).
+-- A non-STDC #pragma preprocessing directive that is documented as causing
+ translation failure or some other form of undefined behavior is encountered (6.10.6).
+-- A #pragma STDC preprocessing directive does not match one of the well-defined
+ forms (6.10.6).
+-- The name of a predefined macro, or the identifier defined, is the subject of a
+ #define or #undef preprocessing directive (6.10.8).
+
+[page 563]
+
+-- An attempt is made to copy an object to an overlapping object by use of a library
+ function, other than as explicitly allowed (e.g., memmove) (clause 7).
+-- A file with the same name as one of the standard headers, not provided as part of the
+ implementation, is placed in any of the standard places that are searched for included
+ source files (7.1.2).
+-- A header is included within an external declaration or definition (7.1.2).
+-- A function, object, type, or macro that is specified as being declared or defined by
+ some standard header is used before any header that declares or defines it is included
+ (7.1.2).
+-- A standard header is included while a macro is defined with the same name as a
+ keyword (7.1.2).
+-- The program attempts to declare a library function itself, rather than via a standard
+ header, but the declaration does not have external linkage (7.1.2).
+-- The program declares or defines a reserved identifier, other than as allowed by 7.1.4
+ (7.1.3).
+-- The program removes the definition of a macro whose name begins with an
+ underscore and either an uppercase letter or another underscore (7.1.3).
+-- An argument to a library function has an invalid value or a type not expected by a
+ function with variable number of arguments (7.1.4).
+-- The pointer passed to a library function array parameter does not have a value such
+ that all address computations and object accesses are valid (7.1.4).
+-- The macro definition of assert is suppressed in order to access an actual function
+ (7.2).
+-- The argument to the assert macro does not have a scalar type (7.2).
+-- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in
+ any context other than outside all external declarations or preceding all explicit
+ declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
+-- The value of an argument to a character handling function is neither equal to the value
+ of EOF nor representable as an unsigned char (7.4).
+-- A macro definition of errno is suppressed in order to access an actual object, or the
+ program defines an identifier with the name errno (7.5).
+-- Part of the program tests floating-point status flags, sets floating-point control modes,
+ or runs under non-default mode settings, but was translated with the state for the
+ FENV_ACCESS pragma ''off'' (7.6.1).
+
+[page 564]
+
+-- The exception-mask argument for one of the functions that provide access to the
+ floating-point status flags has a nonzero value not obtained by bitwise OR of the
+ floating-point exception macros (7.6.2).
+-- The fesetexceptflag function is used to set floating-point status flags that were
+ not specified in the call to the fegetexceptflag function that provided the value
+ of the corresponding fexcept_t object (7.6.2.4).
+-- The argument to fesetenv or feupdateenv is neither an object set by a call to
+ fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
+-- The value of the result of an integer arithmetic or conversion function cannot be
+ represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1).
+-- The program modifies the string pointed to by the value returned by the setlocale
+ function (7.11.1.1).
+-- The program modifies the structure pointed to by the value returned by the
+ localeconv function (7.11.2.1).
+-- A macro definition of math_errhandling is suppressed or the program defines
+ an identifier with the name math_errhandling (7.12).
+-- An argument to a floating-point classification or comparison macro is not of real
+ floating type (7.12.3, 7.12.14).
+-- A macro definition of setjmp is suppressed in order to access an actual function, or
+ the program defines an external identifier with the name setjmp (7.13).
+-- An invocation of the setjmp macro occurs other than in an allowed context
+ (7.13.2.1).
+-- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
+-- After a longjmp, there is an attempt to access the value of an object of automatic
+ storage duration that does not have volatile-qualified type, local to the function
+ containing the invocation of the corresponding setjmp macro, that was changed
+ between the setjmp invocation and longjmp call (7.13.2.1).
+-- The program specifies an invalid pointer to a signal handler function (7.14.1.1).
+-- A signal handler returns when the signal corresponded to a computational exception
+ (7.14.1.1).
+-- A signal handler called in response to SIGFPE, SIGILL, SIGSEGV, or any other
+ implementation-defined value corresponding to a computational exception returns
+ (7.14.1.1).
+-- A signal occurs as the result of calling the abort or raise function, and the signal
+ handler calls the raise function (7.14.1.1).
+
+[page 565]
+
+-- A signal occurs other than as the result of calling the abort or raise function, and
+ the signal handler refers to an object with static or thread storage duration that is not a
+ lock-free atomic object other than by assigning a value to an object declared as
+ volatile sig_atomic_t, or calls any function in the standard library other
+ than the abort function, the _Exit function, the quick_exit function, or the
+ signal function (for the same signal number) (7.14.1.1).
+-- The value of errno is referred to after a signal occurred other than as the result of
+ calling the abort or raise function and the corresponding signal handler obtained
+ a SIG_ERR return from a call to the signal function (7.14.1.1).
+-- A signal is generated by an asynchronous signal handler (7.14.1.1).
+-- The signal function is used in a multi-threaded program (7.14.1.1).
+-- A function with a variable number of arguments attempts to access its varying
+ arguments other than through a properly declared and initialized va_list object, or
+ before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4).
+-- The macro va_arg is invoked using the parameter ap that was passed to a function
+ that invoked the macro va_arg with the same parameter (7.16).
+-- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in
+ order to access an actual function, or the program defines an external identifier with
+ the name va_copy or va_end (7.16.1).
+-- The va_start or va_copy macro is invoked without a corresponding invocation
+ of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3,
+ 7.16.1.4).
+-- The type parameter to the va_arg macro is not such that a pointer to an object of
+ that type can be obtained simply by postfixing a * (7.16.1.1).
+-- The va_arg macro is invoked when there is no actual next argument, or with a
+ specified type that is not compatible with the promoted type of the actual next
+ argument, with certain exceptions (7.16.1.1).
+-- The va_copy or va_start macro is called to initialize a va_list that was
+ previously initialized by either macro without an intervening invocation of the
+ va_end macro for the same va_list (7.16.1.2, 7.16.1.4).
+-- The parameter parmN of a va_start macro is declared with the register
+ storage class, with a function or array type, or with a type that is not compatible with
+ the type that results after application of the default argument promotions (7.16.1.4).
+-- The member designator parameter of an offsetof macro is an invalid right
+ operand of the . operator for the type parameter, or designates a bit-field (7.19).
+
+[page 566]
+
+-- The argument in an instance of one of the integer-constant macros is not a decimal,
+ octal, or hexadecimal constant, or it has a value that exceeds the limits for the
+ corresponding type (7.20.4).
+-- A byte input/output function is applied to a wide-oriented stream, or a wide character
+ input/output function is applied to a byte-oriented stream (7.21.2).
+-- Use is made of any portion of a file beyond the most recent wide character written to
+ a wide-oriented stream (7.21.2).
+-- The value of a pointer to a FILE object is used after the associated file is closed
+ (7.21.3).
+-- The stream for the fflush function points to an input stream or to an update stream
+ in which the most recent operation was input (7.21.5.2).
+-- The string pointed to by the mode argument in a call to the fopen function does not
+ exactly match one of the specified character sequences (7.21.5.3).
+-- An output operation on an update stream is followed by an input operation without an
+ intervening call to the fflush function or a file positioning function, or an input
+ operation on an update stream is followed by an output operation with an intervening
+ call to a file positioning function (7.21.5.3).
+-- An attempt is made to use the contents of the array that was supplied in a call to the
+ setvbuf function (7.21.5.6).
+-- There are insufficient arguments for the format in a call to one of the formatted
+ input/output functions, or an argument does not have an appropriate type (7.21.6.1,
+ 7.21.6.2, 7.29.2.1, 7.29.2.2).
+-- The format in a call to one of the formatted input/output functions or to the
+ strftime or wcsftime function is not a valid multibyte character sequence that
+ begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.27.3.5, 7.29.2.1, 7.29.2.2,
+ 7.29.5.1).
+-- In a call to one of the formatted output functions, a precision appears with a
+ conversion specifier other than those described (7.21.6.1, 7.29.2.1).
+-- A conversion specification for a formatted output function uses an asterisk to denote
+ an argument-supplied field width or precision, but the corresponding argument is not
+ provided (7.21.6.1, 7.29.2.1).
+-- A conversion specification for a formatted output function uses a # or 0 flag with a
+ conversion specifier other than those described (7.21.6.1, 7.29.2.1).
+-- A conversion specification for one of the formatted input/output functions uses a
+ length modifier with a conversion specifier other than those described (7.21.6.1,
+ 7.21.6.2, 7.29.2.1, 7.29.2.2).
+
+[page 567]
+
+-- An s conversion specifier is encountered by one of the formatted output functions,
+ and the argument is missing the null terminator (unless a precision is specified that
+ does not require null termination) (7.21.6.1, 7.29.2.1).
+-- An n conversion specification for one of the formatted input/output functions includes
+ any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1,
+ 7.21.6.2, 7.29.2.1, 7.29.2.2).
+-- A % conversion specifier is encountered by one of the formatted input/output
+ functions, but the complete conversion specification is not exactly %% (7.21.6.1,
+ 7.21.6.2, 7.29.2.1, 7.29.2.2).
+-- An invalid conversion specification is found in the format for one of the formatted
+ input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2,
+ 7.27.3.5, 7.29.2.1, 7.29.2.2, 7.29.5.1).
+-- The number of characters or wide characters transmitted by a formatted output
+ function (or written to an array, or that would have been written to an array) is greater
+ than INT_MAX (7.21.6.1, 7.29.2.1).
+-- The number of input items assigned by a formatted input function is greater than
+ INT_MAX (7.21.6.2, 7.29.2.2).
+-- The result of a conversion by one of the formatted input functions cannot be
+ represented in the corresponding object, or the receiving object does not have an
+ appropriate type (7.21.6.2, 7.29.2.2).
+-- A c, s, or [ conversion specifier is encountered by one of the formatted input
+ functions, and the array pointed to by the corresponding argument is not large enough
+ to accept the input sequence (and a null terminator if the conversion specifier is s or
+ [) (7.21.6.2, 7.29.2.2).
+-- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the
+ formatted input functions, but the input is not a valid multibyte character sequence
+ that begins in the initial shift state (7.21.6.2, 7.29.2.2).
+-- The input item for a %p conversion by one of the formatted input functions is not a
+ value converted earlier during the same program execution (7.21.6.2, 7.29.2.2).
+-- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
+ vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
+ vwscanf function is called with an improperly initialized va_list argument, or
+ the argument is used (other than in an invocation of va_end) after the function
+ returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
+ 7.29.2.5, 7.29.2.6, 7.29.2.7, 7.29.2.8, 7.29.2.9, 7.29.2.10).
+-- The contents of the array supplied in a call to the fgets or fgetws function are
+ used after a read error occurred (7.21.7.2, 7.29.3.2).
+
+[page 568]
+
+-- The file position indicator for a binary stream is used after a call to the ungetc
+ function where its value was zero before the call (7.21.7.10).
+-- The file position indicator for a stream is used after an error occurred during a call to
+ the fread or fwrite function (7.21.8.1, 7.21.8.2).
+-- A partial element read by a call to the fread function is used (7.21.8.1).
+-- The fseek function is called for a text stream with a nonzero offset and either the
+ offset was not returned by a previous successful call to the ftell function on a
+ stream associated with the same file or whence is not SEEK_SET (7.21.9.2).
+-- The fsetpos function is called to set a position that was not returned by a previous
+ successful call to the fgetpos function on a stream associated with the same file
+ (7.21.9.3).
+-- A non-null pointer returned by a call to the calloc, malloc, or realloc function
+ with a zero requested size is used to access an object (7.22.3).
+-- The value of a pointer that refers to space deallocated by a call to the free or
+ realloc function is used (7.22.3).
+-- The alignment requested of the aligned_alloc function is not valid or not
+ supported by the implementation, or the size requested is not an integral multiple of
+ the alignment (7.22.3.1).
+-- The pointer argument to the free or realloc function does not match a pointer
+ earlier returned by a memory management function, or the space has been deallocated
+ by a call to free or realloc (7.22.3.3, 7.22.3.5).
+-- The value of the object allocated by the malloc function is used (7.22.3.4).
+-- The value of any bytes in a new object allocated by the realloc function beyond
+ the size of the old object are used (7.22.3.5).
+-- The program calls the exit or quick_exit function more than once, or calls both
+ functions (7.22.4.4, 7.22.4.7).
+-- During the call to a function registered with the atexit or at_quick_exit
+ function, a call is made to the longjmp function that would terminate the call to the
+ registered function (7.22.4.4, 7.22.4.7).
+-- The string set up by the getenv or strerror function is modified by the program
+ (7.22.4.6, 7.24.6.2).
+-- A signal is raised while the quick_exit function is executing (7.22.4.7).
+-- A command is executed through the system function in a way that is documented as
+ causing termination or some other form of undefined behavior (7.22.4.8).
+
+[page 569]
+
+-- A searching or sorting utility function is called with an invalid pointer argument, even
+ if the number of elements is zero (7.22.5).
+-- The comparison function called by a searching or sorting utility function alters the
+ contents of the array being searched or sorted, or returns ordering values
+ inconsistently (7.22.5).
+-- The array being searched by the bsearch function does not have its elements in
+ proper order (7.22.5.1).
+-- The current conversion state is used by a multibyte/wide character conversion
+ function after changing the LC_CTYPE category (7.22.7).
+-- A string or wide string utility function is instructed to access an array beyond the end
+ of an object (7.24.1, 7.29.4).
+-- A string or wide string utility function is called with an invalid pointer argument, even
+ if the length is zero (7.24.1, 7.29.4).
+-- The contents of the destination array are used after a call to the strxfrm,
+ strftime, wcsxfrm, or wcsftime function in which the specified length was
+ too small to hold the entire null-terminated result (7.24.4.5, 7.27.3.5, 7.29.4.4.4,
+ 7.29.5.1).
+-- The first argument in the very first call to the strtok or wcstok is a null pointer
+ (7.24.5.8, 7.29.4.5.7).
+-- The type of an argument to a type-generic macro is not compatible with the type of
+ the corresponding parameter of the selected function (7.25).
+-- A complex argument is supplied for a generic parameter of a type-generic macro that
+ has no corresponding complex function (7.25).
+-- At least one member of the broken-down time passed to asctime contains a value
+ outside its normal range, or the calculated year exceeds four digits or is less than the
+ year 1000 (7.27.3.1).
+-- The argument corresponding to an s specifier without an l qualifier in a call to the
+ fwprintf function does not point to a valid multibyte character sequence that
+ begins in the initial shift state (7.29.2.11).
+-- In a call to the wcstok function, the object pointed to by ptr does not have the
+ value stored by the previous call for the same wide string (7.29.4.5.7).
+-- An mbstate_t object is used inappropriately (7.29.6).
+-- The value of an argument of type wint_t to a wide character classification or case
+ mapping function is neither equal to the value of WEOF nor representable as a
+ wchar_t (7.30.1).
+
+[page 570]
+
+ -- The iswctype function is called using a different LC_CTYPE category from the
+ one in effect for the call to the wctype function that returned the description
+ (7.30.2.2.1).
+ -- The towctrans function is called using a different LC_CTYPE category from the
+ one in effect for the call to the wctrans function that returned the description
+ (7.30.3.2.1).
+ J.3 Implementation-defined behavior
+1 A conforming implementation is required to document its choice of behavior in each of
+ the areas listed in this subclause. The following are implementation-defined:
+ J.3.1 Translation
+1 -- How a diagnostic is identified (3.10, 5.1.1.3).
+ -- Whether each nonempty sequence of white-space characters other than new-line is
+ retained or replaced by one space character in translation phase 3 (5.1.1.2).
+ J.3.2 Environment
+1 -- The mapping between physical source file multibyte characters and the source
+ character set in translation phase 1 (5.1.1.2).
+ -- The name and type of the function called at program startup in a freestanding
+ environment (5.1.2.1).
+ -- The effect of program termination in a freestanding environment (5.1.2.1).
+ -- An alternative manner in which the main function may be defined (5.1.2.2.1).
+ -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
+ -- What constitutes an interactive device (5.1.2.3).
+ -- Whether a program can have more than one thread of execution in a freestanding
+ environment (5.1.2.4).
+ -- The set of signals, their semantics, and their default handling (7.14).
+ -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a
+ computational exception (7.14.1.1).
+ -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
+ program startup (7.14.1.1).
+ -- The set of environment names and the method for altering the environment list used
+ by the getenv function (7.22.4.6).
+ -- The manner of execution of the string by the system function (7.22.4.8).
+
+[page 571]
+
+ J.3.3 Identifiers
+1 -- Which additional multibyte characters may appear in identifiers and their
+ correspondence to universal character names (6.4.2).
+ -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).
+ J.3.4 Characters
+1 -- The number of bits in a byte (3.6).
+ -- The values of the members of the execution character set (5.2.1).
+ -- The unique value of the member of the execution character set produced for each of
+ the standard alphabetic escape sequences (5.2.2).
+ -- The value of a char object into which has been stored any character other than a
+ member of the basic execution character set (6.2.5).
+ -- Which of signed char or unsigned char has the same range, representation,
+ and behavior as ''plain'' char (6.2.5, 6.3.1.1).
+ -- The mapping of members of the source character set (in character constants and string
+ literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
+ -- The value of an integer character constant containing more than one character or
+ containing a character or escape sequence that does not map to a single-byte
+ execution character (6.4.4.4).
+ -- The value of a wide character constant containing more than one multibyte character
+ or a single multibyte character that maps to multiple members of the extended
+ execution character set, or containing a multibyte character or escape sequence not
+ represented in the extended execution character set (6.4.4.4).
+ -- The current locale used to convert a wide character constant consisting of a single
+ multibyte character that maps to a member of the extended execution character set
+ into a corresponding wide character code (6.4.4.4).
+ -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so,
+ the treatment of the resulting multibyte character sequence (6.4.5).
+ -- The current locale used to convert a wide string literal into corresponding wide
+ character codes (6.4.5).
+ -- The value of a string literal containing a multibyte character or escape sequence not
+ represented in the execution character set (6.4.5).
+ -- The encoding of any of wchar_t, char16_t, and char32_t where the
+ corresponding standard encoding macro (__STDC_ISO_10646__,
+ __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2).
+
+[page 572]
+
+ J.3.5 Integers
+1 -- Any extended integer types that exist in the implementation (6.2.5).
+ -- Whether signed integer types are represented using sign and magnitude, two's
+ complement, or ones' complement, and whether the extraordinary value is a trap
+ representation or an ordinary value (6.2.6.2).
+ -- The rank of any extended integer type relative to another extended integer type with
+ the same precision (6.3.1.1).
+ -- The result of, or the signal raised by, converting an integer to a signed integer type
+ when the value cannot be represented in an object of that type (6.3.1.3).
+ -- The results of some bitwise operations on signed integers (6.5).
+ J.3.6 Floating point
+1 -- The accuracy of the floating-point operations and of the library functions in
+ <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
+ -- The accuracy of the conversions between floating-point internal representations and
+ string representations performed by the library functions in <stdio.h>,
+ <stdlib.h>, and <wchar.h> (5.2.4.2.2).
+ -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS
+ (5.2.4.2.2).
+ -- The evaluation methods characterized by non-standard negative values of
+ FLT_EVAL_METHOD (5.2.4.2.2).
+ -- The direction of rounding when an integer is converted to a floating-point number that
+ cannot exactly represent the original value (6.3.1.4).
+ -- The direction of rounding when a floating-point number is converted to a narrower
+ floating-point number (6.3.1.5).
+ -- How the nearest representable value or the larger or smaller representable value
+ immediately adjacent to the nearest representable value is chosen for certain floating
+ constants (6.4.4.2).
+ -- Whether and how floating expressions are contracted when not disallowed by the
+ FP_CONTRACT pragma (6.5).
+ -- The default state for the FENV_ACCESS pragma (7.6.1).
+ -- Additional floating-point exceptions, rounding modes, environments, and
+ classifications, and their macro names (7.6, 7.12).
+ -- The default state for the FP_CONTRACT pragma (7.12.2).
+
+[page 573]
+
+ J.3.7 Arrays and pointers
+1 -- The result of converting a pointer to an integer or vice versa (6.3.2.3).
+ -- The size of the result of subtracting two pointers to elements of the same array
+ (6.5.6).
+ J.3.8 Hints
+1 -- The extent to which suggestions made by using the register storage-class
+ specifier are effective (6.7.1).
+ -- The extent to which suggestions made by using the inline function specifier are
+ effective (6.7.4).
+ J.3.9 Structures, unions, enumerations, and bit-fields
+1 -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an
+ unsigned int bit-field (6.7.2, 6.7.2.1).
+ -- Allowable bit-field types other than _Bool, signed int, and unsigned int
+ (6.7.2.1).
+ -- Whether atomic types are permitted for bit-fields (6.7.2.1).
+ -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
+ -- The order of allocation of bit-fields within a unit (6.7.2.1).
+ -- The alignment of non-bit-field members of structures (6.7.2.1). This should present
+ no problem unless binary data written by one implementation is read by another.
+ -- The integer type compatible with each enumerated type (6.7.2.2).
+ J.3.10 Qualifiers
+1 -- What constitutes an access to an object that has volatile-qualified type (6.7.3).
+ J.3.11 Preprocessing directives
+1 -- The locations within #pragma directives where header name preprocessing tokens
+ are recognized (6.4, 6.4.7).
+ -- How sequences in both forms of header names are mapped to headers or external
+ source file names (6.4.7).
+ -- Whether the value of a character constant in a constant expression that controls
+ conditional inclusion matches the value of the same character constant in the
+ execution character set (6.10.1).
+ -- Whether the value of a single-character character constant in a constant expression
+ that controls conditional inclusion may have a negative value (6.10.1).
+
+[page 574]
+
+ -- The places that are searched for an included < > delimited header, and how the places
+ are specified or the header is identified (6.10.2).
+ -- How the named source file is searched for in an included " " delimited header
+ (6.10.2).
+ -- The method by which preprocessing tokens (possibly resulting from macro
+ expansion) in a #include directive are combined into a header name (6.10.2).
+ -- The nesting limit for #include processing (6.10.2).
+ -- Whether the # operator inserts a \ character before the \ character that begins a
+ universal character name in a character constant or string literal (6.10.3.2).
+ -- The behavior on each recognized non-STDC #pragma directive (6.10.6).
+ -- The definitions for __DATE__ and __TIME__ when respectively, the date and
+ time of translation are not available (6.10.8.1).
+ J.3.12 Library functions
+1 -- Any library facilities available to a freestanding program, other than the minimal set
+ required by clause 4 (5.1.2.1).
+ -- The format of the diagnostic printed by the assert macro (7.2.1.1).
+ -- The representation of the floating-point status flags stored by the
+ fegetexceptflag function (7.6.2.2).
+ -- Whether the feraiseexcept function raises the ''inexact'' floating-point
+ exception in addition to the ''overflow'' or ''underflow'' floating-point exception
+ (7.6.2.3).
+ -- Strings other than "C" and "" that may be passed as the second argument to the
+ setlocale function (7.11.1.1).
+ -- The types defined for float_t and double_t when the value of the
+ FLT_EVAL_METHOD macro is less than 0 (7.12).
+ -- Domain errors for the mathematics functions, other than those required by this
+ International Standard (7.12.1).
+ -- The values returned by the mathematics functions on domain errors or pole errors
+ (7.12.1).
+ -- The values returned by the mathematics functions on underflow range errors, whether
+ errno is set to the value of the macro ERANGE when the integer expression
+ math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow''
+ floating-point exception is raised when the integer expression math_errhandling
+ & MATH_ERREXCEPT is nonzero. (7.12.1).
+
+[page 575]
+
+-- Whether a domain error occurs or zero is returned when an fmod function has a
+ second argument of zero (7.12.10.1).
+-- Whether a domain error occurs or zero is returned when a remainder function has
+ a second argument of zero (7.12.10.2).
+-- The base-2 logarithm of the modulus used by the remquo functions in reducing the
+ quotient (7.12.10.3).
+-- Whether a domain error occurs or zero is returned when a remquo function has a
+ second argument of zero (7.12.10.3).
+-- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call
+ of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
+-- The null pointer constant to which the macro NULL expands (7.19).
+-- Whether the last line of a text stream requires a terminating new-line character
+ (7.21.2).
+-- Whether space characters that are written out to a text stream immediately before a
+ new-line character appear when read in (7.21.2).
+-- The number of null characters that may be appended to data written to a binary
+ stream (7.21.2).
+-- Whether the file position indicator of an append-mode stream is initially positioned at
+ the beginning or end of the file (7.21.3).
+-- Whether a write on a text stream causes the associated file to be truncated beyond that
+ point (7.21.3).
+-- The characteristics of file buffering (7.21.3).
+-- Whether a zero-length file actually exists (7.21.3).
+-- The rules for composing valid file names (7.21.3).
+-- Whether the same file can be simultaneously open multiple times (7.21.3).
+-- The nature and choice of encodings used for multibyte characters in files (7.21.3).
+-- The effect of the remove function on an open file (7.21.4.1).
+-- The effect if a file with the new name exists prior to a call to the rename function
+ (7.21.4.2).
+-- Whether an open temporary file is removed upon abnormal program termination
+ (7.21.4.3).
+-- Which changes of mode are permitted (if any), and under what circumstances
+ (7.21.5.4).
+
+[page 576]
+
+-- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
+ sequence printed for a NaN (7.21.6.1, 7.29.2.1).
+-- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1,
+ 7.29.2.1).
+-- The interpretation of a - character that is neither the first nor the last character, nor
+ the second where a ^ character is the first, in the scanlist for %[ conversion in the
+ fscanf or fwscanf function (7.21.6.2, 7.29.2.1).
+-- The set of sequences matched by a %p conversion and the interpretation of the
+ corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.29.2.2).
+-- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell
+ functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4).
+-- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is
+ converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold
+ function (7.22.1.3, 7.29.4.1.1).
+-- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold
+ function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.29.4.1.1).
+-- Whether the calloc, malloc, and realloc functions return a null pointer or a
+ pointer to an allocated object when the size requested is zero (7.22.3).
+-- Whether open streams with unwritten buffered data are flushed, open streams are
+ closed, or temporary files are removed when the abort or _Exit function is called
+ (7.22.4.1, 7.22.4.5).
+-- The termination status returned to the host environment by the abort, exit,
+ _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7).
+-- The value returned by the system function when its argument is not a null pointer
+ (7.22.4.8).
+-- The range and precision of times representable in clock_t and time_t (7.27). *
+-- The local time zone and Daylight Saving Time (7.27.1).
+-- The era for the clock function (7.27.2.1).
+-- The TIME_UTC epoch (7.27.2.5).
+-- The replacement string for the %Z specifier to the strftime, and wcsftime
+ functions in the "C" locale (7.27.3.5, 7.29.5.1).
+-- Whether the functions in <math.h> honor the rounding direction mode in an
+ IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).
+
+[page 577]
+
+ J.3.13 Architecture
+1 -- The values or expressions assigned to the macros specified in the headers
+ <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3).
+ -- The result of attempting to indirectly access an object with automatic or thread
+ storage duration from a thread other than the one with which it is associated (6.2.4).
+ -- The number, order, and encoding of bytes in any object (when not explicitly specified
+ in this International Standard) (6.2.6.1).
+ -- Whether any extended alignments are supported and the contexts in which they are
+ supported (6.2.8).
+ -- Valid alignment values other than those returned by an _Alignof expression for
+ fundamental types, if any (6.2.8).
+ -- The value of the result of the sizeof and _Alignof operators (6.5.3.4).
+ J.4 Locale-specific behavior
+1 The following characteristics of a hosted environment are locale-specific and are required
+ to be documented by the implementation:
+ -- Additional members of the source and execution character sets beyond the basic
+ character set (5.2.1).
+ -- The presence, meaning, and representation of additional multibyte characters in the
+ execution character set beyond the basic character set (5.2.1.2).
+ -- The shift states used for the encoding of multibyte characters (5.2.1.2).
+ -- The direction of writing of successive printing characters (5.2.2).
+ -- The decimal-point character (7.1.1).
+ -- The set of printing characters (7.4, 7.30.2).
+ -- The set of control characters (7.4, 7.30.2).
+ -- The sets of characters tested for by the isalpha, isblank, islower, ispunct,
+ isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,
+ iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
+ 7.4.1.11, 7.30.2.1.2, 7.30.2.1.3, 7.30.2.1.7, 7.30.2.1.9, 7.30.2.1.10, 7.30.2.1.11).
+ -- The native environment (7.11.1.1).
+ -- Additional subject sequences accepted by the numeric conversion functions (7.22.1,
+ 7.29.4.1).
+ -- The collation sequence of the execution character set (7.24.4.3, 7.29.4.4.2).
+
+[page 578]
+
+ -- The contents of the error message strings set up by the strerror function
+ (7.24.6.2).
+ -- The formats for time and date (7.27.3.5, 7.29.5.1).
+ -- Character mappings that are supported by the towctrans function (7.30.1).
+ -- Character classifications that are supported by the iswctype function (7.30.1).
+ J.5 Common extensions
+1 The following extensions are widely used in many systems, but are not portable to all
+ implementations. The inclusion of any extension that may cause a strictly conforming
+ program to become invalid renders an implementation nonconforming. Examples of such
+ extensions are new keywords, extra library functions declared in standard headers, or
+ predefined macros with names that do not begin with an underscore.
+ J.5.1 Environment arguments
+1 In a hosted environment, the main function receives a third argument, char *envp[],
+ that points to a null-terminated array of pointers to char, each of which points to a string
+ that provides information about the environment for this execution of the program
+ (5.1.2.2.1).
+ J.5.2 Specialized identifiers
+1 Characters other than the underscore _, letters, and digits, that are not part of the basic
+ source character set (such as the dollar sign $, or characters in national character sets)
+ may appear in an identifier (6.4.2).
+ J.5.3 Lengths and cases of identifiers
+1 All characters in identifiers (with or without external linkage) are significant (6.4.2).
+ J.5.4 Scopes of identifiers
+1 A function identifier, or the identifier of an object the declaration of which contains the
+ keyword extern, has file scope (6.2.1).
+ J.5.5 Writable string literals
+1 String literals are modifiable (in which case, identical string literals should denote distinct
+ objects) (6.4.5).
+
+[page 579]
+
+ J.5.6 Other arithmetic types
+1 Additional arithmetic types, such as __int128 or double double, and their
+ appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have
+ more range or precision than long double, may be used for evaluating expressions of
+ other floating types, and may be used to define float_t or double_t. Additional
+ floating types may also have less range or precision than float.
+ J.5.7 Function pointer casts
+1 A pointer to an object or to void may be cast to a pointer to a function, allowing data to
+ be invoked as a function (6.5.4).
+2 A pointer to a function may be cast to a pointer to an object or to void, allowing a
+ function to be inspected or modified (for example, by a debugger) (6.5.4).
+ J.5.8 Extended bit-field types
+1 A bit-field may be declared with a type other than _Bool, unsigned int, or
+ signed int, with an appropriate maximum width (6.7.2.1).
+ J.5.9 The fortran keyword
+1 The fortran function specifier may be used in a function declaration to indicate that
+ calls suitable for FORTRAN should be generated, or that a different representation for the
+ external name is to be generated (6.7.4).
+ J.5.10 The asm keyword
+1 The asm keyword may be used to insert assembly language directly into the translator
+ output (6.8). The most common implementation is via a statement of the form:
+ asm ( character-string-literal );
+ J.5.11 Multiple external definitions
+1 There may be more than one external definition for the identifier of an object, with or
+ without the explicit use of the keyword extern; if the definitions disagree, or more than
+ one is initialized, the behavior is undefined (6.9.2).
+
+[page 580]
+
+ J.5.12 Predefined macro names
+1 Macro names that do not begin with an underscore, describing the translation and
+ execution environments, are defined by the implementation before translation begins
+ (6.10.8).
+ J.5.13 Floating-point status flags
+1 If any floating-point status flags are set on normal termination after all calls to functions
+ registered by the atexit function have been made (see 7.22.4.4), the implementation
+ writes some diagnostics indicating the fact to the stderr stream, if it is still open,
+ J.5.14 Extra arguments for signal handlers
+1 Handlers for specific signals are called with extra arguments in addition to the signal
+ number (7.14.1.1).
+ J.5.15 Additional stream types and file-opening modes
+1 Additional mappings from files to streams are supported (7.21.2).
+2 Additional file-opening modes may be specified by characters appended to the mode
+ argument of the fopen function (7.21.5.3).
+ J.5.16 Defined file position indicator
+1 The file position indicator is decremented by each successful call to the ungetc or
+ ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10,
+ 7.29.3.10).
+ J.5.17 Math error reporting
+1 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).
+
+[page 581]
+
+ Annex K
+ (normative)
+ Bounds-checking interfaces
+ K.1 Background
+1 Traditionally, the C Library has contained many functions that trust the programmer to
+ provide output character arrays big enough to hold the result being produced. Not only
+ do these functions not check that the arrays are big enough, they frequently lack the
+ information needed to perform such checks. While it is possible to write safe, robust, and
+ error-free code using the existing library, the library tends to promote programming styles
+ that lead to mysterious failures if a result is too big for the provided array.
+2 A common programming style is to declare character arrays large enough to handle most
+ practical cases. However, if these arrays are not large enough to handle the resulting
+ strings, data can be written past the end of the array overwriting other data and program
+ structures. The program never gets any indication that a problem exists, and so never has
+ a chance to recover or to fail gracefully.
+3 Worse, this style of programming has compromised the security of computers and
+ networks. Buffer overflows can often be exploited to run arbitrary code with the
+ permissions of the vulnerable (defective) program.
+4 If the programmer writes runtime checks to verify lengths before calling library
+ functions, then those runtime checks frequently duplicate work done inside the library
+ functions, which discover string lengths as a side effect of doing their job.
+5 This annex provides alternative library functions that promote safer, more secure
+ programming. The alternative functions verify that output buffers are large enough for
+ the intended result and return a failure indicator if they are not. Data is never written past
+ the end of an array. All string results are null terminated.
+6 This annex also addresses another problem that complicates writing robust code:
+ functions that are not reentrant because they return pointers to static objects owned by the
+ function. Such functions can be troublesome since a previously returned result can
+ change if the function is called again, perhaps by another thread.
+
+[page 582]
+
+ K.2 Scope
+1 This annex specifies a series of optional extensions that can be useful in the mitigation of
+ security vulnerabilities in programs, and comprise new functions, macros, and types
+ declared or defined in existing standard headers.
+2 An implementation that defines __STDC_LIB_EXT1__ shall conform to the
+ specifications in this annex.380)
+3 Subclause K.3 should be read as if it were merged into the parallel structure of named
+ subclauses of clause 7.
+ K.3 Library
+ K.3.1 Introduction
+ K.3.1.1 Standard headers
+1 The functions, macros, and types declared or defined in K.3 and its subclauses are not
+ declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
+ defined as a macro which expands to the integer constant 0 at the point in the source file
+ where the appropriate header is first included.
+2 The functions, macros, and types declared or defined in K.3 and its subclauses are
+ declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
+ defined as a macro which expands to the integer constant 1 at the point in the source file
+ where the appropriate header is first included.381)
+3 It is implementation-defined whether the functions, macros, and types declared or defined
+ in K.3 and its subclauses are declared or defined by their respective headers if
+ __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file
+ where the appropriate header is first included.382)
+4 Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be
+ defined identically for all inclusions of any headers from subclause K.3. If
+ __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the
+ implementation shall issue a diagnostic as if a preprocessor error directive were used.
+
+
+ 380) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these
+ specifications.
+ 381) Future revisions of this International Standard may define meanings for other values of
+ __STDC_WANT_LIB_EXT1__.
+ 382) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in
+ headers. All other names are not reserved, and a conforming implementation is not permitted to use
+ them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an
+ unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the
+ implementation is not conforming.
+
+[page 583]
+
+ K.3.1.2 Reserved identifiers
+1 Each macro name in any of the following subclauses is reserved for use as specified if it
+ is defined by any of its associated headers when included; unless explicitly stated
+ otherwise (see 7.1.4).
+2 All identifiers with external linkage in any of the following subclauses are reserved for
+ use as identifiers with external linkage if any of them are used by the program. None of
+ them are reserved if none of them are used.
+3 Each identifier with file scope listed in any of the following subclauses is reserved for use
+ as a macro name and as an identifier with file scope in the same name space if it is
+ defined by any of its associated headers when included.
+ K.3.1.3 Use of errno
+1 An implementation may set errno for the functions defined in this annex, but is not
+ required to.
+ K.3.1.4 Runtime-constraint violations
+1 Most functions in this annex include as part of their specification a list of runtime-
+ constraints. These runtime-constraints are requirements on the program using the
+ library.383)
+2 Implementations shall verify that the runtime-constraints for a function are not violated
+ by the program. If a runtime-constraint is violated, the implementation shall call the
+ currently registered runtime-constraint handler (see set_constraint_handler_s
+ in <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.
+3 If the runtime-constraints section for a function states an action to be performed when a
+ runtime-constraint violation occurs, the function shall perform the action before calling
+ the runtime-constraint handler. If the runtime-constraints section lists actions that are
+ prohibited when a runtime-constraint violation occurs, then such actions are prohibited to
+ the function both before calling the handler and after the handler returns.
+4 The runtime-constraint handler might not return. If the handler does return, the library
+ function whose runtime-constraint was violated shall return some indication of failure as
+ given by the returns section in the function's specification.
+
+
+
+ 383) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still
+ exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a
+ runtime-constraint violation by calling the runtime-constraint handler. This license comes directly
+ from the definition of undefined behavior.
+
+[page 584]
+
+ K.3.2 Errors <errno.h>
+1 The header <errno.h> defines a type.
+2 The type is
+ errno_t
+ which is type int.384)
+ K.3.3 Common definitions <stddef.h>
+1 The header <stddef.h> defines a type.
+2 The type is
+ rsize_t
+ which is the type size_t.385)
+ K.3.4 Integer types <stdint.h>
+1 The header <stdint.h> defines a macro.
+2 The macro is
+ RSIZE_MAX
+ which expands to a value386) of type size_t. Functions that have parameters of type
+ rsize_t consider it a runtime-constraint violation if the values of those parameters are
+ greater than RSIZE_MAX.
+ Recommended practice
+3 Extremely large object sizes are frequently a sign that an object's size was calculated
+ incorrectly. For example, negative numbers appear as very large positive numbers when
+ converted to an unsigned type like size_t. Also, some implementations do not support
+ objects as large as the maximum value that can be represented by type size_t.
+4 For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect
+ programming errors. For implementations targeting machines with large address spaces,
+ it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest
+ object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of
+ some legitimate, but very large, objects. Implementations targeting machines with small
+ address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there
+
+ 384) 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.
+ 385) See the description of the RSIZE_MAX macro in <stdint.h>.
+ 386) The macro RSIZE_MAX need not expand to a constant expression.
+
+[page 585]
+
+ is no object size that is considered a runtime-constraint violation.
+ K.3.5 Input/output <stdio.h>
+1 The header <stdio.h> defines several macros and two types.
+2 The macros are
+ L_tmpnam_s
+ which expands to an integer constant expression that is the size needed for an array of
+ char large enough to hold a temporary file name string generated by the tmpnam_s
+ function;
+ TMP_MAX_S
+ which expands to an integer constant expression that is the maximum number of unique
+ file names that can be generated by the tmpnam_s function.
+3 The types are
+ errno_t
+ which is type int; and
+ rsize_t
+ which is the type size_t.
+ K.3.5.1 Operations on files
+ K.3.5.1.1 The tmpfile_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ errno_t tmpfile_s(FILE * restrict * restrict streamptr);
+ Runtime-constraints
+2 streamptr shall not be a null pointer.
+3 If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
+ Description
+4 The tmpfile_s function creates a temporary binary file that is different from any other
+ existing file and that will automatically be removed when it is closed or at program
+ termination. If the program terminates abnormally, whether an open temporary file is
+ removed is implementation-defined. The file is opened for update with "wb+" mode
+ with the meaning that mode has in the fopen_s function (including the mode's effect
+ on exclusive access and file permissions).
+
+[page 586]
+
+5 If the file was created successfully, then the pointer to FILE pointed to by streamptr
+ will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
+ to FILE pointed to by streamptr will be set to a null pointer.
+ Recommended practice
+ It should be possible to open at least TMP_MAX_S temporary files during the lifetime of
+ the program (this limit may be shared with tmpnam_s) and there should be no limit on
+ the number simultaneously open other than this limit and any limit on the number of open
+ files (FOPEN_MAX).
+ Returns
+6 The tmpfile_s function returns zero if it created the file. If it did not create the file or
+ there was a runtime-constraint violation, tmpfile_s returns a nonzero value.
+ K.3.5.1.2 The tmpnam_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ errno_t tmpnam_s(char *s, rsize_t maxsize);
+ Runtime-constraints
+2 s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX.
+ maxsize shall be greater than the length of the generated file name string.
+ Description
+3 The tmpnam_s function generates a string that is a valid file name and that is not the
+ same as the name of an existing file.387) The function is potentially capable of generating
+ TMP_MAX_S different strings, but any or all of them may already be in use by existing
+ files and thus not be suitable return values. The lengths of these strings shall be less than
+ the value of the L_tmpnam_s macro.
+4 The tmpnam_s function generates a different string each time it is called.
+5 It is assumed that s points to an array of at least maxsize characters. This array will be
+ set to generated string, as specified below.
+
+
+
+ 387) Files created using strings generated by the tmpnam_s function are temporary only in the sense that
+ their names should not collide with those generated by conventional naming rules for the
+ implementation. It is still necessary to use the remove function to remove such files when their use
+ is ended, and before program termination. Implementations should take care in choosing the patterns
+ used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the
+ race condition and possible conflict when multiple programs run simultaneously by the same user
+ generate the same temporary file names.
+
+[page 587]
+
+6 The implementation shall behave as if no library function except tmpnam calls the
+ tmpnam_s function.388)
+ Recommended practice
+7 After a program obtains a file name using the tmpnam_s function and before the
+ program creates a file with that name, the possibility exists that someone else may create
+ a file with that same name. To avoid this race condition, the tmpfile_s function
+ should be used instead of tmpnam_s when possible. One situation that requires the use
+ of the tmpnam_s function is when the program needs to create a temporary directory
+ rather than a temporary file.
+ Returns
+8 If no suitable string can be generated, or if there is a runtime-constraint violation, the
+ tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize
+ is greater than zero) and returns a nonzero value.
+9 Otherwise, the tmpnam_s function writes the string in the array pointed to by s and
+ returns zero.
+ Environmental limits
+10 The value of the macro TMP_MAX_S shall be at least 25.
+ K.3.5.2 File access functions
+ K.3.5.2.1 The fopen_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ errno_t fopen_s(FILE * restrict * restrict streamptr,
+ const char * restrict filename,
+ const char * restrict mode);
+ Runtime-constraints
+2 None of streamptr, filename, or mode shall be a null pointer.
+3 If there is a runtime-constraint violation, fopen_s does not attempt to open a file.
+ Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the
+ null pointer.
+
+
+
+
+ 388) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming
+ convention for temporary files), but this is not required.
+
+[page 588]
+
+ Description
+4 The fopen_s function opens the file whose name is the string pointed to by
+ filename, and associates a stream with it.
+5 The mode string shall be as described for fopen, with the addition that modes starting
+ with the character 'w' or 'a' may be preceded by the character 'u', see below:
+ uw truncate to zero length or create text file for writing, default
+ permissions
+ uwx create text file for writing, default permissions
+ ua append; open or create text file for writing at end-of-file, default
+ permissions
+ uwb truncate to zero length or create binary file for writing, default
+ permissions
+ uwbx create binary file for writing, default permissions
+ uab append; open or create binary file for writing at end-of-file, default
+ permissions
+ uw+ truncate to zero length or create text file for update, default
+ permissions
+ uw+x create text file for update, default permissions
+ ua+ append; open or create text file for update, writing at end-of-file,
+ default permissions
+ uw+b or uwb+ truncate to zero length or create binary file for update, default
+ permissions
+ uw+bx or uwb+x create binary file for update, default permissions
+ ua+b or uab+ append; open or create binary file for update, writing at end-of-file,
+ default permissions
+6 Opening a file with exclusive mode ('x' as the last character in the mode argument)
+ fails if the file already exists or cannot be created.
+7 To the extent that the underlying system supports the concepts, files opened for writing
+ shall be opened with exclusive (also known as non-shared) access. If the file is being
+ created, and the first character of the mode string is not 'u', to the extent that the
+ underlying system supports it, the file shall have a file permission that prevents other
+ users on the system from accessing the file. If the file is being created and first character
+ of the mode string is 'u', then by the time the file has been closed, it shall have the
+ system default file access permissions.389)
+8 If the file was opened successfully, then the pointer to FILE pointed to by streamptr
+ will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
+
+
+ 389) These are the same permissions that the file would have been created with by fopen.
+
+[page 589]
+
+ to FILE pointed to by streamptr will be set to a null pointer.
+ Returns
+9 The fopen_s function returns zero if it opened the file. If it did not open the file or if
+ there was a runtime-constraint violation, fopen_s returns a nonzero value.
+ K.3.5.2.2 The freopen_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ errno_t freopen_s(FILE * restrict * restrict newstreamptr,
+ const char * restrict filename,
+ const char * restrict mode,
+ FILE * restrict stream);
+ Runtime-constraints
+2 None of newstreamptr, mode, and stream shall be a null pointer.
+3 If there is a runtime-constraint violation, freopen_s neither attempts to close any file
+ associated with stream nor attempts to open a file. Furthermore, if newstreamptr is
+ not a null pointer, fopen_s sets *newstreamptr to the null pointer.
+ Description
+4 The freopen_s function opens the file whose name is the string pointed to by
+ filename and associates the stream pointed to by stream with it. The mode
+ argument has the same meaning as in the fopen_s function (including the mode's effect
+ on exclusive access and file permissions).
+5 If filename is a null pointer, the freopen_s function attempts to change the mode of
+ the stream to that specified by mode, as if the name of the file currently associated with
+ the stream had been used. It is implementation-defined which changes of mode are
+ permitted (if any), and under what circumstances.
+6 The freopen_s function first attempts to close any file that is associated with stream.
+ Failure to close the file is ignored. The error and end-of-file indicators for the stream are
+ cleared.
+7 If the file was opened successfully, then the pointer to FILE pointed to by
+ newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE
+ pointed to by newstreamptr will be set to a null pointer.
+ Returns
+8 The freopen_s function returns zero if it opened the file. If it did not open the file or
+ there was a runtime-constraint violation, freopen_s returns a nonzero value.
+
+[page 590]
+
+ K.3.5.3 Formatted input/output functions
+1 Unless explicitly stated otherwise, if the execution of a function described in this
+ subclause causes copying to take place between objects that overlap, the objects take on
+ unspecified values.
+ K.3.5.3.1 The fprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int fprintf_s(FILE * restrict stream,
+ const char * restrict format, ...);
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. The %n specifier390) (modified or
+ not by flags, field width, or precision) shall not appear in the string pointed to by
+ format. Any argument to fprintf_s corresponding to a %s specifier shall not be a
+ null pointer.
+3 If there is a runtime-constraint violation,391) the fprintf_s function does not attempt
+ to produce further output, and it is unspecified to what extent fprintf_s produced
+ output before discovering the runtime-constraint violation.
+ Description
+4 The fprintf_s function is equivalent to the fprintf function except for the explicit
+ runtime-constraints listed above.
+ Returns
+5 The fprintf_s function returns the number of characters transmitted, or a negative
+ value if an output error, encoding error, or runtime-constraint violation occurred.
+
+
+
+
+ 390) 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.
+ 391) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
+ implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
+ constraint violation.
+
+[page 591]
+
+ K.3.5.3.2 The fscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int fscanf_s(FILE * restrict stream,
+ const char * restrict format, ...);
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. Any argument indirected though in
+ order to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation,392) the fscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent fscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion
+ specifiers apply to a pair of arguments (unless assignment suppression is indicated by a
+ *). The first of these arguments is the same as for fscanf. That argument is
+ immediately followed in the argument list by the second argument, which has type
+ rsize_t and gives the number of elements in the array pointed to by the first argument
+ of the pair. If the first argument points to a scalar object, it is considered to be an array of
+ one element.393)
+5 A matching failure occurs if the number of elements in a receiving object is insufficient to
+ hold the converted input (including any trailing null character).
+ Returns
+6 The fscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+
+ 392) 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.
+ 393) If the format is known at translation time, an implementation may issue a diagnostic for any argument
+ used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
+ argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
+ the format is not known at translation time. For example, an implementation may issue a diagnostic
+ for each argument after format that has of type pointer to one of char, signed char,
+ unsigned char, or void that is not followed by an argument of a type compatible with
+ rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
+ using the hh length modifier, a length argument must follow the pointer argument. Another useful
+ diagnostic could flag any non-pointer argument following format that did not have a type
+ compatible with rsize_t.
+
+[page 592]
+
+ fscanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+7 EXAMPLE 1 The call:
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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.
+
+8 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.
+
+ K.3.5.3.3 The printf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int printf_s(const char * restrict format, ...);
+ Runtime-constraints
+2 format shall not be a null pointer. The %n specifier394) (modified or not by flags, field
+ width, or precision) shall not appear in the string pointed to by format. Any argument
+ to printf_s corresponding to a %s specifier shall not be a null pointer.
+3 If there is a runtime-constraint violation, the printf_s function does not attempt to
+ produce further output, and it is unspecified to what extent printf_s produced output
+ before discovering the runtime-constraint violation.
+
+
+ 394) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 593]
+
+ Description
+4 The printf_s function is equivalent to the printf function except for the explicit
+ runtime-constraints listed above.
+ Returns
+5 The printf_s function returns the number of characters transmitted, or a negative
+ value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.5.3.4 The scanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int scanf_s(const char * restrict format, ...);
+ Runtime-constraints
+2 format shall not be a null pointer. Any argument indirected though in order to store
+ converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the scanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent scanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The scanf_s function is equivalent to fscanf_s with the argument stdin
+ interposed before the arguments to scanf_s.
+ Returns
+5 The scanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ scanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+ K.3.5.3.5 The snprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int snprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The %n specifier395) (modified or not by flags, field width, or
+ precision) shall not appear in the string pointed to by format. Any argument to
+
+[page 594]
+
+ snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
+ error shall occur.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the
+ null character.
+ Description
+4 The snprintf_s function is equivalent to the snprintf function except for the
+ explicit runtime-constraints listed above.
+5 The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the
+ array pointed to by s.
+ Returns
+6 The snprintf_s function returns the number of characters that would have been
+ written had n been sufficiently large, not counting the terminating null character, or a
+ negative value if a runtime-constraint violation occurred. Thus, the null-terminated
+ output has been completely written if and only if the returned value is nonnegative and
+ less than n.
+ K.3.5.3.6 The sprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int sprintf_s(char * restrict s, rsize_t n,
+ const char * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The number of characters (including the trailing null) required for the
+ result to be written to the array pointed to by s shall not be greater than n. The %n
+ specifier396) (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.
+
+
+
+ 395) 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.
+ 396) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 595]
+
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the
+ null character.
+ Description
+4 The sprintf_s function is equivalent to the sprintf function except for the
+ parameter n and the explicit runtime-constraints listed above.
+5 The sprintf_s function, unlike snprintf_s, treats a result too big for the array
+ pointed to by s as a runtime-constraint violation.
+ Returns
+6 If no runtime-constraint violation occurred, the sprintf_s function returns the number
+ of characters written in the array, not counting the terminating null character. If an
+ encoding error occurred, sprintf_s returns a negative value. If any other runtime-
+ constraint violation occurred, sprintf_s returns zero.
+ K.3.5.3.7 The sscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ int sscanf_s(const char * restrict s,
+ const char * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. Any argument indirected though in order
+ to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the sscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent sscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The sscanf_s function is equivalent to fscanf_s, except that input is obtained from
+ a string (specified by the argument s) rather than from a stream. Reaching the end of the
+ string is equivalent to encountering end-of-file for the fscanf_s function. If copying
+ takes place between objects that overlap, the objects take on unspecified values.
+ Returns
+5 The sscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ sscanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+
+[page 596]
+
+ K.3.5.3.8 The vfprintf_s function
+ Synopsis
+1 #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
+2 Neither stream nor format shall be a null pointer. The %n specifier397) (modified or
+ not by flags, field width, or precision) shall not appear in the string pointed to by
+ format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a
+ null pointer.
+3 If there is a runtime-constraint violation, the vfprintf_s function does not attempt to
+ produce further output, and it is unspecified to what extent vfprintf_s produced
+ output before discovering the runtime-constraint violation.
+ Description
+4 The vfprintf_s function is equivalent to the vfprintf function except for the
+ explicit runtime-constraints listed above.
+ Returns
+5 The vfprintf_s function returns the number of characters transmitted, or a negative
+ value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.5.3.9 The vfscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <stdio.h>
+ int vfscanf_s(FILE * restrict stream,
+ const char * restrict format,
+ va_list arg);
+
+
+
+
+ 397) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 597]
+
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. Any argument indirected though in
+ order to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vfscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vfscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vfscanf_s function is equivalent to fscanf_s, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfscanf_s function does not invoke the
+ va_end macro.398)
+ Returns
+5 The vfscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vfscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+ K.3.5.3.10 The vprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <stdio.h>
+ int vprintf_s(const char * restrict format,
+ va_list arg);
+ Runtime-constraints
+2 format shall not be a null pointer. The %n specifier399) (modified or not by flags, field
+ width, or precision) shall not appear in the string pointed to by format. Any argument
+ to vprintf_s corresponding to a %s specifier shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vprintf_s function does not attempt to
+ produce further output, and it is unspecified to what extent vprintf_s produced output
+ before discovering the runtime-constraint violation.
+
+ 398) 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.
+ 399) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 598]
+
+ Description
+4 The vprintf_s function is equivalent to the vprintf function except for the explicit
+ runtime-constraints listed above.
+ Returns
+5 The vprintf_s function returns the number of characters transmitted, or a negative
+ value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.5.3.11 The vscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <stdio.h>
+ int vscanf_s(const char * restrict format,
+ va_list arg);
+ Runtime-constraints
+2 format shall not be a null pointer. Any argument indirected though in order to store
+ converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vscanf_s function is equivalent to scanf_s, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vscanf_s function does not invoke the
+ va_end macro.400)
+ Returns
+5 The vscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vscanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+
+
+
+
+ 400) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
+ vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
+ indeterminate.
+
+[page 599]
+
+ K.3.5.3.12 The vsnprintf_s function
+ Synopsis
+1 #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
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The %n specifier401) (modified or not by flags, field width, or
+ precision) shall not appear in the string pointed to by format. Any argument to
+ vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
+ error shall occur.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the
+ null character.
+ Description
+4 The vsnprintf_s function is equivalent to the vsnprintf function except for the
+ explicit runtime-constraints listed above.
+5 The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within
+ the array pointed to by s.
+ Returns
+6 The vsnprintf_s function returns the number of characters that would have been
+ written had n been sufficiently large, not counting the terminating null character, or a
+ negative value if a runtime-constraint violation occurred. Thus, the null-terminated
+ output has been completely written if and only if the returned value is nonnegative and
+ less than n.
+
+
+
+
+ 401) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 600]
+
+ K.3.5.3.13 The vsprintf_s function
+ Synopsis
+1 #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
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The number of characters (including the trailing null) required for the
+ result to be written to the array pointed to by s shall not be greater than n. The %n
+ specifier402) (modified or not by flags, field width, or precision) shall not appear in the
+ string pointed to by format. Any argument to vsprintf_s corresponding to a %s
+ specifier shall not be a null pointer. No encoding error shall occur.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the
+ null character.
+ Description
+4 The vsprintf_s function is equivalent to the vsprintf function except for the
+ parameter n and the explicit runtime-constraints listed above.
+5 The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array
+ pointed to by s as a runtime-constraint violation.
+ Returns
+6 If no runtime-constraint violation occurred, the vsprintf_s function returns the
+ number of characters written in the array, not counting the terminating null character. If
+ an encoding error occurred, vsprintf_s returns a negative value. If any other
+ runtime-constraint violation occurred, vsprintf_s returns zero.
+
+
+
+
+ 402) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
+ at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
+ format string was %%n.
+
+[page 601]
+
+ K.3.5.3.14 The vsscanf_s function
+ Synopsis
+1 #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
+2 Neither s nor format shall be a null pointer. Any argument indirected though in order
+ to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vsscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vsscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vsscanf_s function is equivalent to sscanf_s, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vsscanf_s function does not invoke the
+ va_end macro.403)
+ Returns
+5 The vsscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vscanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+ K.3.5.4 Character input/output functions
+ K.3.5.4.1 The gets_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ char *gets_s(char *s, rsize_t n);
+
+
+
+
+ 403) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
+ vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
+ indeterminate.
+
+[page 602]
+
+ Runtime-constraints
+2 s shall not be a null pointer. n shall neither be equal to zero nor be greater than
+ RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading
+ n-1 characters from stdin.404)
+3 If there is a runtime-constraint violation, s[0] is set to the null character, and characters
+ are read and discarded from stdin until a new-line character is read, or end-of-file or a
+ read error occurs.
+ Description
+4 The gets_s function reads at most one less than the number of characters specified by n
+ from the stream pointed to by stdin, into the array pointed to by s. No additional
+ characters are read after a new-line character (which is discarded) or after end-of-file.
+ The discarded new-line character does not count towards number of characters read. A
+ null character is written immediately after the last character read into the array.
+5 If end-of-file is encountered and no characters have been read into the array, or if a read
+ error occurs during the operation, then s[0] is set to the null character, and the other
+ elements of s take unspecified values.
+ Recommended practice
+6 The fgets function allows properly-written programs to safely process input lines too
+ long to store in the result array. In general this requires that callers of fgets pay
+ attention to the presence or absence of a new-line character in the result array. Consider
+ using fgets (along with any needed processing based on new-line characters) instead of
+ gets_s.
+ Returns
+7 The gets_s function returns s if successful. If there was a runtime-constraint violation,
+ or if end-of-file is encountered and no characters have been read into the array, or if a
+ read error occurs during the operation, then a null pointer is returned.
+
+
+
+
+ 404) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for
+ a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a
+ one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets
+ expect such a relationship.
+
+[page 603]
+
+ K.3.6 General utilities <stdlib.h>
+1 The header <stdlib.h> defines three types.
+2 The types are
+ errno_t
+ which is type int; and
+ rsize_t
+ which is the type size_t; and
+ constraint_handler_t
+ which has the following definition
+ typedef void (*constraint_handler_t)(
+ const char * restrict msg,
+ void * restrict ptr,
+ errno_t error);
+ K.3.6.1 Runtime-constraint handling
+ K.3.6.1.1 The set_constraint_handler_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdlib.h>
+ constraint_handler_t set_constraint_handler_s(
+ constraint_handler_t handler);
+ Description
+2 The set_constraint_handler_s function sets the runtime-constraint handler to
+ be handler. The runtime-constraint handler is the function to be called when a library
+ function detects a runtime-constraint violation. Only the most recent handler registered
+ with set_constraint_handler_s is called when a runtime-constraint violation
+ occurs.
+3 When the handler is called, it is passed the following arguments in the following order:
+ 1. A pointer to a character string describing the runtime-constraint violation.
+ 2. A null pointer or a pointer to an implementation defined object.
+ 3. If the function calling the handler has a return type declared as errno_t, the
+ return value of the function is passed. Otherwise, a positive value of type
+ errno_t is passed.
+
+[page 604]
+
+4 The implementation has a default constraint handler that is used if no calls to the
+ set_constraint_handler_s function have been made. The behavior of the
+ default handler is implementation-defined, and it may cause the program to exit or abort.
+5 If the handler argument to set_constraint_handler_s is a null pointer, the
+ implementation default handler becomes the current constraint handler.
+ Returns
+6 The set_constraint_handler_s function returns a pointer to the previously
+ registered handler.405)
+ K.3.6.1.2 The abort_handler_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdlib.h>
+ void abort_handler_s(
+ const char * restrict msg,
+ void * restrict ptr,
+ errno_t error);
+ Description
+2 A pointer to the abort_handler_s function shall be a suitable argument to the
+ set_constraint_handler_s function.
+3 The abort_handler_s function writes a message on the standard error stream in an
+ implementation-defined format. The message shall include the string pointed to by msg.
+ The abort_handler_s function then calls the abort function.406)
+ Returns
+4 The abort_handler_s function does not return to its caller.
+
+
+
+
+ 405) 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).
+ 406) Many implementations invoke a debugger when the abort function is called.
+
+[page 605]
+
+ K.3.6.1.3 The ignore_handler_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdlib.h>
+ void ignore_handler_s(
+ const char * restrict msg,
+ void * restrict ptr,
+ errno_t error);
+ Description
+2 A pointer to the ignore_handler_s function shall be a suitable argument to the
+ set_constraint_handler_s function.
+3 The ignore_handler_s function simply returns to its caller.407)
+ Returns
+4 The ignore_handler_s function returns no value.
+ K.3.6.2 Communication with the environment
+ K.3.6.2.1 The getenv_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdlib.h>
+ errno_t getenv_s(size_t * restrict len,
+ char * restrict value, rsize_t maxsize,
+ const char * restrict name);
+ Runtime-constraints
+2 name shall not be a null pointer. maxsize shall neither equal zero nor be greater than
+ RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.
+3 If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len
+ is not null), and the environment list is not searched.
+ Description
+4 The getenv_s function searches an environment list, provided by the host environment,
+ for a string that matches the string pointed to by name.
+
+
+ 407) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in
+ which a runtime-constraint violation occurs will return to its caller. The caller can determine whether
+ a runtime-constraint violation occurred based on the library function's specification (usually, the
+ library function returns a nonzero errno_t).
+
+[page 606]
+
+5 If that name is found then getenv_s performs the following actions. If len is not a
+ null pointer, the length of the string associated with the matched list member is stored in
+ the integer pointed to by len. If the length of the associated string is less than maxsize,
+ then the associated string is copied to the array pointed to by value.
+6 If that name is not found then getenv_s performs the following actions. If len is not
+ a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than
+ zero, then value[0] is set to the null character.
+7 The set of environment names and the method for altering the environment list are
+ implementation-defined. The getenv_s function need not avoid data races with other
+ threads of execution that modify the environment list.408)
+ Returns
+8 The getenv_s function returns zero if the specified name is found and the associated
+ string was successfully stored in value. Otherwise, a nonzero value is returned.
+ K.3.6.3 Searching and sorting utilities
+1 These utilities make use of a comparison function to search or sort arrays of unspecified
+ type. Where an argument declared as size_t nmemb specifies the length of the array
+ for a function, if nmemb has the value zero on a call to that function, then the comparison
+ function is not called, a search finds no matching element, sorting performs no
+ rearrangement, and the pointer to the array may be null.
+2 The implementation shall ensure that the second argument of the comparison function
+ (when called from bsearch_s), or both arguments (when called from qsort_s), are
+ pointers to elements of the array.409) The first argument when called from bsearch_s
+ shall equal key.
+3 The comparison function shall not alter the contents of either the array or search key. The
+ implementation may reorder elements of the array between calls to the comparison
+ function, but shall not otherwise alter the contents of any individual element.
+4 When the same objects (consisting of size bytes, irrespective of their current positions
+ in the array) are passed more than once to the comparison function, the results shall be
+ consistent with one another. That is, for qsort_s they shall define a total ordering on
+ the array, and for bsearch_s the same object shall always compare the same way with
+ the key.
+
+ 408) Many implementations provide non-standard functions that modify the environment list.
+ 409) That is, if the value passed is p, then the following expressions are always valid and nonzero:
+ ((char *)p - (char *)base) % size == 0
+ (char *)p >= (char *)base
+ (char *)p < (char *)base + nmemb * size
+
+[page 607]
+
+5 A sequence point occurs immediately before and immediately after each call to the
+ comparison function, and also between any call to the comparison function and any
+ movement of the objects passed as arguments to that call.
+ K.3.6.3.1 The bsearch_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
+ zero, then none of key, base, or compar shall be a null pointer.
+3 If there is a runtime-constraint violation, the bsearch_s function does not search the
+ array.
+ Description
+4 The bsearch_s function searches an array of nmemb objects, the initial element of
+ which is pointed to by base, for an element that matches the object pointed to by key.
+ The size of each element of the array is specified by size.
+5 The comparison function pointed to by compar is called with three arguments. The first
+ two point to the key object and to an array element, in that order. The function shall
+ return an integer less than, equal to, or greater than zero if the key object is considered,
+ respectively, to be less than, to match, or to be greater than the array element. The array
+ shall consist of: all the elements that compare less than, all the elements that compare
+ equal to, and all the elements that compare greater than the key object, in that order.410)
+ 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.411)
+
+
+
+
+ 410) In practice, this means that the entire array has been sorted according to the comparison function.
+ 411) The context argument is for the use of the comparison function in performing its duties. For
+ example, it might specify a collating sequence used by the comparison function.
+
+[page 608]
+
+ Returns
+6 The bsearch_s function returns a pointer to a matching element of the array, or a null
+ pointer if no match is found or there is a runtime-constraint violation. If two elements
+ compare as equal, which element is matched is unspecified.
+ K.3.6.3.2 The qsort_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
+ zero, then neither base nor compar shall be a null pointer.
+3 If there is a runtime-constraint violation, the qsort_s function does not sort the array.
+ Description
+4 The qsort_s function sorts an array of nmemb objects, the initial element of which is
+ pointed to by base. The size of each object is specified by size.
+5 The contents of the array are sorted into ascending order according to a comparison
+ function pointed to by compar, which is called with three arguments. The first two
+ point to the objects being compared. The function shall return an integer less than, equal
+ to, or greater than zero if the first argument is considered to be respectively less than,
+ equal to, or greater than the second. The third argument to the comparison function is the
+ context argument passed to qsort_s. The sole use of context by qsort_s is to
+ pass it to the comparison function.412)
+6 If two elements compare as equal, their relative order in the resulting sorted array is
+ unspecified.
+ Returns
+7 The qsort_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+
+
+
+
+ 412) The context argument is for the use of the comparison function in performing its duties. For
+ example, it might specify a collating sequence used by the comparison function.
+
+[page 609]
+
+ K.3.6.4 Multibyte/wide character conversion functions
+1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
+ of the current locale. For a state-dependent encoding, each function is placed into its
+ initial conversion state by a call for which its character pointer argument, s, is a null
+ pointer. Subsequent calls with s as other than a null pointer cause the internal conversion
+ state of the function to be altered as necessary. A call with s as a null pointer causes
+ these functions to set the int pointed to by their status argument to a nonzero value if
+ encodings have state dependency, and zero otherwise.413) Changing the LC_CTYPE
+ category causes the conversion state of these functions to be indeterminate.
+ K.3.6.4.1 The wctomb_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdlib.h>
+ errno_t wctomb_s(int * restrict status,
+ char * restrict s,
+ rsize_t smax,
+ wchar_t wc);
+ Runtime-constraints
+2 Let n denote the number of bytes needed to represent the multibyte character
+ corresponding to the wide character given by wc (including any shift sequences).
+3 If s is not a null pointer, then smax shall not be less than n, and smax shall not be
+ greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.
+4 If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to
+ by status, and if s is not a null pointer, no more than smax elements in the array
+ pointed to by s will be accessed.
+ Description
+5 The wctomb_s function determines n and stores the multibyte character representation
+ of wc in the array whose first element is pointed to by s (if s is not a null pointer). The
+ number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide
+ character, a null byte is stored, preceded by any shift sequence needed to restore the
+ initial shift state, and the function is left in the initial conversion state.
+6 The implementation shall behave as if no library function calls the wctomb_s function.
+
+
+
+ 413) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
+ character codes, but are grouped with an adjacent multibyte character.
+
+[page 610]
+
+7 If s is a null pointer, the wctomb_s function stores into the int pointed to by status a
+ nonzero or zero value, if multibyte character encodings, respectively, do or do not have
+ state-dependent encodings.
+8 If s is not a null pointer, the wctomb_s function stores into the int pointed to by
+ status either n or -1 if wc, respectively, does or does not correspond to a valid
+ multibyte character.
+9 In no case will the int pointed to by status be set to a value greater than the
+ MB_CUR_MAX macro.
+ Returns
+10 The wctomb_s function returns zero if successful, and a nonzero value if there was a
+ runtime-constraint violation or wc did not correspond to a valid multibyte character.
+ K.3.6.5 Multibyte/wide string conversion functions
+1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
+ the current locale.
+ K.3.6.5.1 The mbstowcs_s function
+ Synopsis
+1 #include <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
+2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
+ neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
+ then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
+ zero. If dst is not a null pointer and len is not less than dstmax, then a null character
+ shall occur within the first dstmax multibyte characters of the array pointed to by src.
+3 If there is a runtime-constraint violation, then mbstowcs_s does the following. If
+ retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If
+ dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
+ then mbstowcs_s sets dst[0] to the null wide character.
+ Description
+4 The mbstowcs_s function converts a sequence of multibyte characters that begins in
+ the initial shift state from the array pointed to by src into a sequence of corresponding
+ wide characters. If dst is not a null pointer, the converted characters are stored into the
+ array pointed to by dst. Conversion continues up to and including a terminating null
+ character, which is also stored. Conversion stops earlier in two cases: when a sequence of
+
+[page 611]
+
+ 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.414) If dst is not a null pointer and no null wide character was stored into the array
+ pointed to by dst, then dst[len] is set to the null wide character. Each conversion
+ takes place as if by a call to the mbrtowc function.
+5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
+ sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
+ the mbstowcs_s function stores the value (size_t)(-1) into *retval.
+ Otherwise, the mbstowcs_s function stores into *retval the number of multibyte
+ characters successfully converted, not including the terminating null character (if any).
+6 All elements following the terminating null wide character (if any) written by
+ mbstowcs_s in the array of dstmax wide characters pointed to by dst take
+ unspecified values when mbstowcs_s returns.415)
+7 If copying takes place between objects that overlap, the objects take on unspecified
+ values.
+ Returns
+8 The mbstowcs_s function returns zero if no runtime-constraint violation and no
+ encoding error occurred. Otherwise, a nonzero value is returned.
+ K.3.6.5.2 The wcstombs_s function
+ Synopsis
+1 #include <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
+2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
+ neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
+ then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
+ zero. If dst is not a null pointer and len is not less than dstmax, then the conversion
+ shall have been stopped (see below) because a terminating null wide character was
+ reached or because an encoding error occurred.
+
+
+
+
+ 414) Thus, the value of len is ignored if dst is a null pointer.
+ 415) This allows an implementation to attempt converting the multibyte string before discovering a
+ terminating null character did not occur where required.
+
+[page 612]
+
+3 If there is a runtime-constraint violation, then wcstombs_s does the following. If
+ retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If
+ dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
+ then wcstombs_s sets dst[0] to the null character.
+ Description
+4 The wcstombs_s function converts a sequence of wide characters from the array
+ pointed to by src into a sequence of corresponding multibyte characters that begins in
+ the initial shift state. If dst is not a null pointer, the converted characters are then stored
+ into the array pointed to by dst. Conversion continues up to and including a terminating
+ null wide character, which is also stored. Conversion stops earlier in two cases:
+ -- when a wide character is reached that does not correspond to a valid multibyte
+ character;
+ -- (if dst is not a null pointer) when the next multibyte character would exceed the
+ limit of n total bytes to be stored into the array pointed to by dst. If the wide
+ character being converted is the null wide character, then n is the lesser of len or
+ dstmax. Otherwise, n is the lesser of len or dstmax-1.
+ If the conversion stops without converting a null wide character and dst is not a null
+ pointer, then a null character is stored into the array pointed to by dst immediately
+ following any multibyte characters already stored. Each conversion takes place as if by a
+ call to the wcrtomb function.416)
+5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
+ wide character that does not correspond to a valid multibyte character, an encoding error
+ occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval.
+ Otherwise, the wcstombs_s function stores into *retval the number of bytes in the
+ resulting multibyte character sequence, not including the terminating null character (if
+ any).
+6 All elements following the terminating null character (if any) written by wcstombs_s
+ in the array of dstmax elements pointed to by dst take unspecified values when
+ wcstombs_s returns.417)
+7 If copying takes place between objects that overlap, the objects take on unspecified
+ values.
+
+
+ 416) 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.
+ 417) When len is not less than dstmax, the implementation might fill the array before discovering a
+ runtime-constraint violation.
+
+[page 613]
+
+ Returns
+8 The wcstombs_s function returns zero if no runtime-constraint violation and no
+ encoding error occurred. Otherwise, a nonzero value is returned.
+ K.3.7 String handling <string.h>
+1 The header <string.h> defines two types.
+2 The types are
+ errno_t
+ which is type int; and
+ rsize_t
+ which is the type size_t.
+ K.3.7.1 Copying functions
+ K.3.7.1.1 The memcpy_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ errno_t memcpy_s(void * restrict s1, rsize_t s1max,
+ const void * restrict s2, rsize_t n);
+ Runtime-constraints
+2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
+ objects that overlap.
+3 If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first
+ s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is
+ not greater than RSIZE_MAX.
+ Description
+4 The memcpy_s function copies n characters from the object pointed to by s2 into the
+ object pointed to by s1.
+ Returns
+5 The memcpy_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+
+[page 614]
+
+ K.3.7.1.2 The memmove_s function
+ Synopsis
+1 #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
+2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. n shall not be greater than s1max.
+3 If there is a runtime-constraint violation, the memmove_s function stores zeros in the
+ first s1max characters of the object pointed to by s1 if s1 is not a null pointer and
+ s1max is not greater than RSIZE_MAX.
+ Description
+4 The memmove_s function copies n characters from the object pointed to by s2 into the
+ object pointed to by s1. This copying takes place as if the n characters from the object
+ pointed to by s2 are first copied into a temporary array of n characters that does not
+ overlap the objects pointed to by s1 or s2, and then the n characters from the temporary
+ array are copied into the object pointed to by s1.
+ Returns
+5 The memmove_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.7.1.3 The strcpy_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ errno_t strcpy_s(char * restrict s1,
+ rsize_t s1max,
+ const char * restrict s2);
+ Runtime-constraints
+2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
+ s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max).
+ Copying shall not take place between objects that overlap.
+3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the
+ null character.
+
+[page 615]
+
+ Description
+4 The strcpy_s function copies the string pointed to by s2 (including the terminating
+ null character) into the array pointed to by s1.
+5 All elements following the terminating null character (if any) written by strcpy_s in
+ the array of s1max characters pointed to by s1 take unspecified values when
+ strcpy_s returns.418)
+ Returns
+6 The strcpy_s function returns zero419) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.7.1.4 The strncpy_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ errno_t strncpy_s(char * restrict s1,
+ rsize_t s1max,
+ const char * restrict s2,
+ rsize_t n);
+ Runtime-constraints
+2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
+ shall be greater than strnlen_s(s2, s1max). Copying shall not take place between
+ objects that overlap.
+3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the
+ null character.
+ Description
+4 The strncpy_s function copies not more than n successive characters (characters that
+ follow a null character are not copied) from the array pointed to by s2 to the array
+ pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null
+ character.
+
+
+ 418) 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.
+ 419) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
+ within the array pointed to by s1 and that the result in s1 is null terminated.
+
+[page 616]
+
+5 All elements following the terminating null character (if any) written by strncpy_s in
+ the array of s1max characters pointed to by s1 take unspecified values when
+ strncpy_s returns.420)
+ Returns
+6 The strncpy_s function returns zero421) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+7 EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result
+ will not be null terminated or that characters will be written past the end of the destination array.
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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.
+
+ K.3.7.2 Concatenation functions
+ K.3.7.2.1 The strcat_s function
+ Synopsis
+1 #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
+2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
+ strcat_s.
+
+
+
+
+ 420) 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.
+ 421) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
+ within the array pointed to by s1 and that the result in s1 is null terminated.
+
+[page 617]
+
+3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
+ s1max shall not equal zero. m shall not equal zero.422) m shall be greater than
+ strnlen_s(s2, m). Copying shall not take place between objects that overlap.
+4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the
+ null character.
+ Description
+5 The strcat_s function appends a copy of the string pointed to by s2 (including the
+ terminating null character) to the end of the string pointed to by s1. The initial character
+ from s2 overwrites the null character at the end of s1.
+6 All elements following the terminating null character (if any) written by strcat_s in
+ the array of s1max characters pointed to by s1 take unspecified values when
+ strcat_s returns.423)
+ Returns
+7 The strcat_s function returns zero424) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.7.2.2 The strncat_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ errno_t strncat_s(char * restrict s1,
+ rsize_t s1max,
+ const char * restrict s2,
+ rsize_t n);
+ Runtime-constraints
+2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
+ strncat_s.
+3 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.425) If n is not less
+
+
+ 422) Zero means that s1 was not null terminated upon entry to strcat_s.
+ 423) 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.
+ 424) A zero return value implies that all of the requested characters from the string pointed to by s2 were
+ appended to the string pointed to by s1 and that the result in s1 is null terminated.
+
+[page 618]
+
+ than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take
+ place between objects that overlap.
+4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the
+ null character.
+ Description
+5 The strncat_s function appends not more than n successive characters (characters
+ that follow a null character are not copied) from the array pointed to by s2 to the end of
+ the string pointed to by s1. The initial character from s2 overwrites the null character at
+ the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to
+ a null character.
+6 All elements following the terminating null character (if any) written by strncat_s in
+ the array of s1max characters pointed to by s1 take unspecified values when
+ strncat_s returns.426)
+ Returns
+7 The strncat_s function returns zero427) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+8 EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result
+ will not be null terminated or that characters will be written past the end of the destination array.
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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.
+
+
+
+ 425) Zero means that s1 was not null terminated upon entry to strncat_s.
+ 426) 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.
+ 427) A zero return value implies that all of the requested characters from the string pointed to by s2 were
+ appended to the string pointed to by s1 and that the result in s1 is null terminated.
+
+[page 619]
+
+ After the second call r2 will have the value zero and s2 will contain the sequence hello\0.
+ After the third call r3 will have a nonzero value and s3 will contain the sequence \0.
+ After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0.
+
+ K.3.7.3 Search functions
+ K.3.7.3.1 The strtok_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ char *strtok_s(char * restrict s1,
+ rsize_t * restrict s1max,
+ const char * restrict s2,
+ char ** restrict ptr);
+ Runtime-constraints
+2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
+ shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
+ The end of the token found shall occur within the first *s1max characters of s1 for the
+ first call, and shall occur within the first *s1max characters of where searching resumes
+ on subsequent calls.
+3 If there is a runtime-constraint violation, the strtok_s function does not indirect
+ through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
+ Description
+4 A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a
+ sequence of tokens, each of which is delimited by a character from the string pointed to
+ by s2. The fourth argument points to a caller-provided char pointer into which the
+ strtok_s function stores information necessary for it to continue scanning the same
+ string.
+5 The first call in a sequence has a non-null first argument and s1max points to an object
+ whose value is the number of elements in the character array pointed to by the first
+ argument. The first call stores an initial value in the object pointed to by ptr and
+ updates the value pointed to by s1max to reflect the number of elements that remain in
+ relation to ptr. Subsequent calls in the sequence have a null first argument and the
+ objects pointed to by s1max and ptr are required to have the values stored by the
+ previous call in the sequence, which are then updated. The separator string pointed to by
+ s2 may be different from call to call.
+6 The first call in the sequence searches the string pointed to by s1 for the first character
+ that is not contained in the current separator string pointed to by s2. If no such character
+ is found, then there are no tokens in the string pointed to by s1 and the strtok_s
+ function returns a null pointer. If such a character is found, it is the start of the first token.
+
+[page 620]
+
+7 The strtok_s function then searches from there for the first character in s1 that is
+ contained in the current separator string. If no such character is found, the current token
+ extends to the end of the string pointed to by s1, and subsequent searches in the same
+ string for a token return a null pointer. If such a character is found, it is overwritten by a
+ null character, which terminates the current token.
+8 In all cases, the strtok_s function stores sufficient information in the pointer pointed
+ to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
+ value for ptr, shall start searching just past the element overwritten by a null character
+ (if any).
+ Returns
+9 The strtok_s function returns a pointer to the first character of a token, or a null
+ pointer if there is no token or there is a runtime-constraint violation.
+10 EXAMPLE
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+1 #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
+2 s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n
+ shall not be greater than smax.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and smax is not
+ greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an
+ unsigned char) into each of the first smax characters of the object pointed to by s.
+
+[page 621]
+
+ Description
+4 The memset_s function copies the value of c (converted to an unsigned char) into
+ each of the first n characters of the object pointed to by s. Unlike memset, any call to
+ the memset_s function shall be evaluated strictly according to the rules of the abstract
+ machine as described in (5.1.2.3). That is, any call to the memset_s function shall
+ assume that the memory indicated by s and n may be accessible in the future and thus
+ must contain the values indicated by c.
+ Returns
+5 The memset_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.7.4.2 The strerror_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ errno_t strerror_s(char *s, rsize_t maxsize,
+ errno_t errnum);
+ Runtime-constraints
+2 s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX.
+ maxsize shall not equal zero.
+3 If there is a runtime-constraint violation, then the array (if any) pointed to by s is not
+ modified.
+ Description
+4 The strerror_s function maps the number in errnum to a locale-specific message
+ string. Typically, the values for errnum come from errno, but strerror_s shall
+ map any value of type int to a message.
+5 If the length of the desired string is less than maxsize, then the string is copied to the
+ array pointed to by s.
+6 Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied
+ from the string to the array pointed to by s and then s[maxsize-1] is set to the null
+ character. Then, if maxsize is greater than 3, then s[maxsize-2],
+ s[maxsize-3], and s[maxsize-4] are set to the character period (.).
+ Returns
+7 The strerror_s function returns zero if the length of the desired string was less than
+ maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s
+ function returns a nonzero value.
+
+[page 622]
+
+ K.3.7.4.3 The strerrorlen_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ size_t strerrorlen_s(errno_t errnum);
+ Description
+2 The strerrorlen_s function calculates the length of the (untruncated) locale-specific
+ message string that the strerror_s function maps to errnum.
+ Returns
+3 The strerrorlen_s function returns the number of characters (not including the null
+ character) in the full message string.
+ K.3.7.4.4 The strnlen_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <string.h>
+ size_t strnlen_s(const char *s, size_t maxsize);
+ Description
+2 The strnlen_s function computes the length of the string pointed to by s.
+ Returns
+3 If s is a null pointer,428) then the strnlen_s function returns zero.
+4 Otherwise, the strnlen_s function returns the number of characters that precede the
+ terminating null character. If there is no null character in the first maxsize characters of
+ s then strnlen_s returns maxsize. At most the first maxsize characters of s shall
+ be accessed by strnlen_s.
+
+
+
+
+ 428) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints
+ along with the values returned for a null pointer or an unterminated string argument make
+ strnlen_s useful in algorithms that gracefully handle such exceptional data.
+
+[page 623]
+
+ K.3.8 Date and time <time.h>
+1 The header <time.h> defines two types.
+2 The types are
+ errno_t
+ which is type int; and
+ rsize_t
+ which is the type size_t.
+ K.3.8.1 Components of time
+1 A broken-down time is normalized if the values of the members of the tm structure are in
+ their normal rages.429)
+ K.3.8.2 Time conversion functions
+1 Like the strftime function, the asctime_s and ctime_s functions do not return a
+ pointer to a static object, and other library functions are permitted to call them.
+ K.3.8.2.1 The asctime_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <time.h>
+ errno_t asctime_s(char *s, rsize_t maxsize,
+ const struct tm *timeptr);
+ Runtime-constraints
+2 Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and
+ shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr
+ shall be normalized. The calendar year represented by the broken-down time pointed to
+ by timeptr shall not be less than calendar year 0 and shall not be greater than calendar
+ year 9999.
+3 If there is a runtime-constraint violation, there is no attempt to convert the time, and
+ s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is
+ not greater than RSIZE_MAX.
+ Description
+4 The asctime_s function converts the normalized broken-down time in the structure
+ pointed to by timeptr into a 26 character (including the null character) string in the
+
+
+ 429) The normal ranges are defined in 7.27.1.
+
+[page 624]
+
+ form
+ Sun Sep 16 01:03:52 1973\n\0
+ The fields making up this string are (in order):
+ 1. The name of the day of the week represented by timeptr->tm_wday using the
+ following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat.
+ 2. The character space.
+ 3. The name of the month represented by timeptr->tm_mon using the following
+ three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
+ Nov, and Dec.
+ 4. The character space.
+ 5. The value of timeptr->tm_mday as if printed using the fprintf format
+ "%2d".
+ 6. The character space.
+ 7. The value of timeptr->tm_hour as if printed using the fprintf format
+ "%.2d".
+ 8. The character colon.
+ 9. The value of timeptr->tm_min as if printed using the fprintf format
+ "%.2d".
+ 10. The character colon.
+ 11. The value of timeptr->tm_sec as if printed using the fprintf format
+ "%.2d".
+ 12. The character space.
+ 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf
+ format "%4d".
+ 14. The character new line.
+ 15. The null character.
+ Recommended practice
+ The strftime function allows more flexible formatting and supports locale-specific
+ behavior. If you do not require the exact form of the result string produced by the
+ asctime_s function, consider using the strftime function instead.
+ Returns
+5 The asctime_s function returns zero if the time was successfully converted and stored
+ into the array pointed to by s. Otherwise, it returns a nonzero value.
+
+[page 625]
+
+ K.3.8.2.2 The ctime_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <time.h>
+ errno_t ctime_s(char *s, rsize_t maxsize,
+ const time_t *timer);
+ Runtime-constraints
+2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and
+ shall not be greater than RSIZE_MAX.
+3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null
+ pointer and maxsize is not equal zero and is not greater than RSIZE_MAX.
+ Description
+4 The ctime_s function converts the calendar time pointed to by timer to local time in
+ the form of a string. It is equivalent to
+ asctime_s(s, maxsize, localtime_s(timer))
+ Recommended practice
+ The strftime function allows more flexible formatting and supports locale-specific
+ behavior. If you do not require the exact form of the result string produced by the
+ ctime_s function, consider using the strftime function instead.
+ Returns
+5 The ctime_s function returns zero if the time was successfully converted and stored
+ into the array pointed to by s. Otherwise, it returns a nonzero value.
+ K.3.8.2.3 The gmtime_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <time.h>
+ struct tm *gmtime_s(const time_t * restrict timer,
+ struct tm * restrict result);
+ Runtime-constraints
+2 Neither timer nor result shall be a null pointer.
+3 If there is a runtime-constraint violation, there is no attempt to convert the time.
+ Description
+4 The gmtime_s function converts the calendar time pointed to by timer into a broken-
+ down time, expressed as UTC. The broken-down time is stored in the structure pointed
+
+[page 626]
+
+ to by result.
+ Returns
+5 The gmtime_s function returns result, or a null pointer if the specified time cannot
+ be converted to UTC or there is a runtime-constraint violation.
+ K.3.8.2.4 The localtime_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <time.h>
+ struct tm *localtime_s(const time_t * restrict timer,
+ struct tm * restrict result);
+ Runtime-constraints
+2 Neither timer nor result shall be a null pointer.
+3 If there is a runtime-constraint violation, there is no attempt to convert the time.
+ Description
+4 The localtime_s function converts the calendar time pointed to by timer into a
+ broken-down time, expressed as local time. The broken-down time is stored in the
+ structure pointed to by result.
+ Returns
+5 The localtime_s function returns result, or a null pointer if the specified time
+ cannot be converted to local time or there is a runtime-constraint violation.
+ K.3.9 Extended multibyte and wide character utilities <wchar.h>
+1 The header <wchar.h> defines two types.
+2 The types are
+ errno_t
+ which is type int; and
+ rsize_t
+ which is the type size_t.
+3 Unless explicitly stated otherwise, if the execution of a function described in this
+ subclause causes copying to take place between objects that overlap, the objects take on
+ unspecified values.
+
+[page 627]
+
+ K.3.9.1 Formatted wide character input/output functions
+ K.3.9.1.1 The fwprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int fwprintf_s(FILE * restrict stream,
+ const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. The %n specifier430) (modified or
+ not by flags, field width, or precision) shall not appear in the wide string pointed to by
+ format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a
+ null pointer.
+3 If there is a runtime-constraint violation, the fwprintf_s function does not attempt to
+ produce further output, and it is unspecified to what extent fwprintf_s produced
+ output before discovering the runtime-constraint violation.
+ Description
+4 The fwprintf_s function is equivalent to the fwprintf function except for the
+ explicit runtime-constraints listed above.
+ Returns
+5 The fwprintf_s function returns the number of wide characters transmitted, or a
+ negative value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.9.1.2 The fwscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdio.h>
+ #include <wchar.h>
+ int fwscanf_s(FILE * restrict stream,
+ const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. Any argument indirected though in
+ order to store converted input shall not be a null pointer.
+
+
+ 430) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 628]
+
+3 If there is a runtime-constraint violation, the fwscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent fwscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The fwscanf_s function is equivalent to fwscanf except that the c, s, and [
+ conversion specifiers apply to a pair of arguments (unless assignment suppression is
+ indicated by a *). The first of these arguments is the same as for fwscanf. That
+ argument is immediately followed in the argument list by the second argument, which has
+ type size_t and gives the number of elements in the array pointed to by the first
+ argument of the pair. If the first argument points to a scalar object, it is considered to be
+ an array of one element.431)
+5 A matching failure occurs if the number of elements in a receiving object is insufficient to
+ hold the converted input (including any trailing null character).
+ Returns
+6 The fwscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ fwscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+ K.3.9.1.3 The snwprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int snwprintf_s(wchar_t * restrict s,
+ rsize_t n,
+ const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The %n specifier432) (modified or not by flags, field width, or
+
+ 431) If the format is known at translation time, an implementation may issue a diagnostic for any argument
+ used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
+ argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
+ the format is not known at translation time. For example, an implementation may issue a diagnostic
+ for each argument after format that has of type pointer to one of char, signed char,
+ unsigned char, or void that is not followed by an argument of a type compatible with
+ rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
+ using the hh length modifier, a length argument must follow the pointer argument. Another useful
+ diagnostic could flag any non-pointer argument following format that did not have a type
+ compatible with rsize_t.
+
+[page 629]
+
+ precision) shall not appear in the wide string pointed to by format. Any argument to
+ snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
+ error shall occur.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the
+ null wide character.
+ Description
+4 The snwprintf_s function is equivalent to the swprintf function except for the
+ explicit runtime-constraints listed above.
+5 The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within
+ the array pointed to by s.
+ Returns
+6 The snwprintf_s function returns the number of wide characters that would have
+ been written had n been sufficiently large, not counting the terminating wide null
+ character, or a negative value if a runtime-constraint violation occurred. Thus, the null-
+ terminated output has been completely written if and only if the returned value is
+ nonnegative and less than n.
+ K.3.9.1.4 The swprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int swprintf_s(wchar_t * restrict s, rsize_t n,
+ const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The number of wide characters (including the trailing null) required
+ for the result to be written to the array pointed to by s shall not be greater than n. The %n
+ specifier433) (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.
+
+
+ 432) 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".
+ 433) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 630]
+
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the
+ null wide character.
+ Description
+4 The swprintf_s function is equivalent to the swprintf function except for the
+ explicit runtime-constraints listed above.
+5 The swprintf_s function, unlike snwprintf_s, treats a result too big for the array
+ pointed to by s as a runtime-constraint violation.
+ Returns
+6 If no runtime-constraint violation occurred, the swprintf_s function returns the
+ number of wide characters written in the array, not counting the terminating null wide
+ character. If an encoding error occurred or if n or more wide characters are requested to
+ be written, swprintf_s returns a negative value. If any other runtime-constraint
+ violation occurred, swprintf_s returns zero.
+ K.3.9.1.5 The swscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int swscanf_s(const wchar_t * restrict s,
+ const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. Any argument indirected though in order
+ to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the swscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent swscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The swscanf_s function is equivalent to fwscanf_s, except that the argument s
+ specifies a wide string from which the input is to be obtained, rather than from a stream.
+ Reaching the end of the wide string is equivalent to encountering end-of-file for the
+ fwscanf_s function.
+ Returns
+5 The swscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ swscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+
+[page 631]
+
+ K.3.9.1.6 The vfwprintf_s function
+ Synopsis
+1 #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
+2 Neither stream nor format shall be a null pointer. The %n specifier434) (modified or
+ not by flags, field width, or precision) shall not appear in the wide string pointed to by
+ format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be
+ a null pointer.
+3 If there is a runtime-constraint violation, the vfwprintf_s function does not attempt
+ to produce further output, and it is unspecified to what extent vfwprintf_s produced
+ output before discovering the runtime-constraint violation.
+ Description
+4 The vfwprintf_s function is equivalent to the vfwprintf function except for the
+ explicit runtime-constraints listed above.
+ Returns
+5 The vfwprintf_s function returns the number of wide characters transmitted, or a
+ negative value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.9.1.7 The vfwscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <stdio.h>
+ #include <wchar.h>
+ int vfwscanf_s(FILE * restrict stream,
+ const wchar_t * restrict format, va_list arg);
+
+
+
+ 434) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 632]
+
+ Runtime-constraints
+2 Neither stream nor format shall be a null pointer. Any argument indirected though in
+ order to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vfwscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument
+ list replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the
+ va_end macro.435)
+ Returns
+5 The vfwscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vfwscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+ K.3.9.1.8 The vsnwprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The %n specifier436) (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.
+
+ 435) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
+ value of arg after the return is indeterminate.
+ 436) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 633]
+
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to
+ the null wide character.
+ Description
+4 The vsnwprintf_s function is equivalent to the vswprintf function except for the
+ explicit runtime-constraints listed above.
+5 The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit
+ within the array pointed to by s.
+ Returns
+6 The vsnwprintf_s function returns the number of wide characters that would have
+ been written had n been sufficiently large, not counting the terminating null character, or
+ a negative value if a runtime-constraint violation occurred. Thus, the null-terminated
+ output has been completely written if and only if the returned value is nonnegative and
+ less than n.
+ K.3.9.1.9 The vswprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
+ than RSIZE_MAX. The number of wide characters (including the trailing null) required
+ for the result to be written to the array pointed to by s shall not be greater than n. The %n
+ specifier437) (modified or not by flags, field width, or precision) shall not appear in the
+ wide string pointed to by format. Any argument to vswprintf_s corresponding to a
+ %s specifier shall not be a null pointer. No encoding error shall occur.
+3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
+ than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the
+ null wide character.
+
+ 437) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 634]
+
+ Description
+4 The vswprintf_s function is equivalent to the vswprintf function except for the
+ explicit runtime-constraints listed above.
+5 The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the
+ array pointed to by s as a runtime-constraint violation.
+ Returns
+6 If no runtime-constraint violation occurred, the vswprintf_s function returns the
+ number of wide characters written in the array, not counting the terminating null wide
+ character. If an encoding error occurred or if n or more wide characters are requested to
+ be written, vswprintf_s returns a negative value. If any other runtime-constraint
+ violation occurred, vswprintf_s returns zero.
+ K.3.9.1.10 The vswscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <wchar.h>
+ int vswscanf_s(const wchar_t * restrict s,
+ const wchar_t * restrict format,
+ va_list arg);
+ Runtime-constraints
+2 Neither s nor format shall be a null pointer. Any argument indirected though in order
+ to store converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vswscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vswscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vswscanf_s function is equivalent to swscanf_s, with the variable argument
+ list replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vswscanf_s function does not invoke the
+ va_end macro.438)
+
+
+
+
+ 438) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
+ value of arg after the return is indeterminate.
+
+[page 635]
+
+ Returns
+5 The vswscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vswscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+ K.3.9.1.11 The vwprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <stdarg.h>
+ #include <wchar.h>
+ int vwprintf_s(const wchar_t * restrict format,
+ va_list arg);
+ Runtime-constraints
+2 format shall not be a null pointer. The %n specifier439) (modified or not by flags, field
+ width, or precision) shall not appear in the wide string pointed to by format. Any
+ argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vwprintf_s function does not attempt to
+ produce further output, and it is unspecified to what extent vwprintf_s produced
+ output before discovering the runtime-constraint violation.
+ Description
+4 The vwprintf_s function is equivalent to the vwprintf function except for the
+ explicit runtime-constraints listed above.
+ Returns
+5 The vwprintf_s function returns the number of wide characters transmitted, or a
+ negative value if an output error, encoding error, or runtime-constraint violation occurred.
+
+
+
+
+ 439) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 636]
+
+ K.3.9.1.12 The vwscanf_s function
+ Synopsis
+1 #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
+2 format shall not be a null pointer. Any argument indirected though in order to store
+ converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the vwscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent vwscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The vwscanf_s function is equivalent to wscanf_s, with the variable argument list
+ replaced by arg, which shall have been initialized by the va_start macro (and
+ possibly subsequent va_arg calls). The vwscanf_s function does not invoke the
+ va_end macro.440)
+ Returns
+5 The vwscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ vwscanf_s function returns the number of input items assigned, which can be fewer
+ than provided for, or even zero, in the event of an early matching failure.
+ K.3.9.1.13 The wprintf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int wprintf_s(const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 format shall not be a null pointer. The %n specifier441) (modified or not by flags, field
+
+ 440) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
+ value of arg after the return is indeterminate.
+ 441) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
+ string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
+ example, if the entire format string was L"%%n".
+
+[page 637]
+
+ width, or precision) shall not appear in the wide string pointed to by format. Any
+ argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.
+3 If there is a runtime-constraint violation, the wprintf_s function does not attempt to
+ produce further output, and it is unspecified to what extent wprintf_s produced output
+ before discovering the runtime-constraint violation.
+ Description
+4 The wprintf_s function is equivalent to the wprintf function except for the explicit
+ runtime-constraints listed above.
+ Returns
+5 The wprintf_s function returns the number of wide characters transmitted, or a
+ negative value if an output error, encoding error, or runtime-constraint violation occurred.
+ K.3.9.1.14 The wscanf_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ int wscanf_s(const wchar_t * restrict format, ...);
+ Runtime-constraints
+2 format shall not be a null pointer. Any argument indirected though in order to store
+ converted input shall not be a null pointer.
+3 If there is a runtime-constraint violation, the wscanf_s function does not attempt to
+ perform further input, and it is unspecified to what extent wscanf_s performed input
+ before discovering the runtime-constraint violation.
+ Description
+4 The wscanf_s function is equivalent to fwscanf_s with the argument stdin
+ interposed before the arguments to wscanf_s.
+ Returns
+5 The wscanf_s function returns the value of the macro EOF if an input failure occurs
+ before any conversion or if there is a runtime-constraint violation. Otherwise, the
+ wscanf_s function returns the number of input items assigned, which can be fewer than
+ provided for, or even zero, in the event of an early matching failure.
+
+[page 638]
+
+ K.3.9.2 General wide string utilities
+ K.3.9.2.1 Wide string copying functions
+ K.3.9.2.1.1 The wcscpy_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ errno_t wcscpy_s(wchar_t * restrict s1,
+ rsize_t s1max,
+ const wchar_t * restrict s2);
+ Runtime-constraints
+2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
+ s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max).
+ Copying shall not take place between objects that overlap.
+3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the
+ null wide character.
+ Description
+4 The wcscpy_s function copies the wide string pointed to by s2 (including the
+ terminating null wide character) into the array pointed to by s1.
+5 All elements following the terminating null wide character (if any) written by
+ wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified
+ values when wcscpy_s returns.442)
+ Returns
+6 The wcscpy_s function returns zero443) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+
+
+
+
+ 442) 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.
+ 443) A zero return value implies that all of the requested wide characters from the string pointed to by s2
+ fit within the array pointed to by s1 and that the result in s1 is null terminated.
+
+[page 639]
+
+ K.3.9.2.1.2 The wcsncpy_s function
+ Synopsis
+7 #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
+8 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
+ shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between
+ objects that overlap.
+9 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the
+ null wide character.
+ Description
+10 The wcsncpy_s function copies not more than n successive wide characters (wide
+ characters that follow a null wide character are not copied) from the array pointed to by
+ s2 to the array pointed to by s1. If no null wide character was copied from s2, then
+ s1[n] is set to a null wide character.
+11 All elements following the terminating null wide character (if any) written by
+ wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified
+ values when wcsncpy_s returns.444)
+ Returns
+12 The wcsncpy_s function returns zero445) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+13 EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the
+ result will not be null terminated or that wide characters will be written past the end of the destination
+ array.
+
+
+
+
+ 444) 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.
+ 445) A zero return value implies that all of the requested wide characters from the string pointed to by s2
+ fit within the array pointed to by s1 and that the result in s1 is null terminated.
+
+[page 640]
+
+ #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.
+
+ K.3.9.2.1.3 The wmemcpy_s function
+ Synopsis
+14 #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
+15 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
+ objects that overlap.
+16 If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the
+ first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
+ s1max is not greater than RSIZE_MAX.
+ Description
+17 The wmemcpy_s function copies n successive wide characters from the object pointed
+ to by s2 into the object pointed to by s1.
+ Returns
+18 The wmemcpy_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+
+[page 641]
+
+ K.3.9.2.1.4 The wmemmove_s function
+ Synopsis
+19 #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
+20 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. n shall not be greater than s1max.
+21 If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the
+ first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
+ s1max is not greater than RSIZE_MAX.
+ Description
+22 The wmemmove_s function copies n successive wide characters from the object pointed
+ to by s2 into the object pointed to by s1. This copying takes place as if the n wide
+ characters from the object pointed to by s2 are first copied into a temporary array of n
+ wide characters that does not overlap the objects pointed to by s1 or s2, and then the n
+ wide characters from the temporary array are copied into the object pointed to by s1.
+ Returns
+23 The wmemmove_s function returns zero if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.9.2.2 Wide string concatenation functions
+ K.3.9.2.2.1 The wcscat_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ errno_t wcscat_s(wchar_t * restrict s1,
+ rsize_t s1max,
+ const wchar_t * restrict s2);
+ Runtime-constraints
+2 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
+ wcscat_s.
+3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
+ s1max shall not equal zero. m shall not equal zero.446) m shall be greater than
+ wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.
+
+[page 642]
+
+4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the
+ null wide character.
+ Description
+5 The wcscat_s function appends a copy of the wide string pointed to by s2 (including
+ the terminating null wide character) to the end of the wide string pointed to by s1. The
+ initial wide character from s2 overwrites the null wide character at the end of s1.
+6 All elements following the terminating null wide character (if any) written by
+ wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified
+ values when wcscat_s returns.447)
+ Returns
+7 The wcscat_s function returns zero448) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+ K.3.9.2.2.2 The wcsncat_s function
+ Synopsis
+8 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ errno_t wcsncat_s(wchar_t * restrict s1,
+ rsize_t s1max,
+ const wchar_t * restrict s2,
+ rsize_t n);
+ Runtime-constraints
+9 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
+ wcsncat_s.
+10 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
+ RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.449) 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.
+
+
+ 446) Zero means that s1 was not null terminated upon entry to wcscat_s.
+ 447) 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.
+ 448) 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.
+ 449) Zero means that s1 was not null terminated upon entry to wcsncat_s.
+
+[page 643]
+
+11 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
+ greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the
+ null wide character.
+ Description
+12 The wcsncat_s function appends not more than n successive wide characters (wide
+ characters that follow a null wide character are not copied) from the array pointed to by
+ s2 to the end of the wide string pointed to by s1. The initial wide character from s2
+ overwrites the null wide character at the end of s1. If no null wide character was copied
+ from s2, then s1[s1max-m+n] is set to a null wide character.
+13 All elements following the terminating null wide character (if any) written by
+ wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified
+ values when wcsncat_s returns.450)
+ Returns
+14 The wcsncat_s function returns zero451) if there was no runtime-constraint violation.
+ Otherwise, a nonzero value is returned.
+15 EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the
+ result will not be null terminated or that wide characters will be written past the end of the destination
+ array.
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.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.
+
+
+
+
+ 450) 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.
+ 451) A zero return value implies that all of the requested wide characters from the wide string pointed to by
+ s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
+
+[page 644]
+
+ K.3.9.2.3 Wide string search functions
+ K.3.9.2.3.1 The wcstok_s function
+ Synopsis
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ wchar_t *wcstok_s(wchar_t * restrict s1,
+ rsize_t * restrict s1max,
+ const wchar_t * restrict s2,
+ wchar_t ** restrict ptr);
+ Runtime-constraints
+2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
+ shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
+ The end of the token found shall occur within the first *s1max wide characters of s1 for
+ the first call, and shall occur within the first *s1max wide characters of where searching
+ resumes on subsequent calls.
+3 If there is a runtime-constraint violation, the wcstok_s function does not indirect
+ through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
+ Description
+4 A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1
+ into a sequence of tokens, each of which is delimited by a wide character from the wide
+ string pointed to by s2. The fourth argument points to a caller-provided wchar_t
+ pointer into which the wcstok_s function stores information necessary for it to
+ continue scanning the same wide string.
+5 The first call in a sequence has a non-null first argument and s1max points to an object
+ whose value is the number of elements in the wide character array pointed to by the first
+ argument. The first call stores an initial value in the object pointed to by ptr and
+ updates the value pointed to by s1max to reflect the number of elements that remain in
+ relation to ptr. Subsequent calls in the sequence have a null first argument and the
+ objects pointed to by s1max and ptr are required to have the values stored by the
+ previous call in the sequence, which are then updated. The separator wide string pointed
+ to by s2 may be different from call to call.
+6 The first call in the sequence searches the wide string pointed to by s1 for the first wide
+ character that is not contained in the current separator wide string pointed to by s2. If no
+ such wide character is found, then there are no tokens in the wide string pointed to by s1
+ and the wcstok_s function returns a null pointer. If such a wide character is found, it is
+ the start of the first token.
+
+[page 645]
+
+7 The wcstok_s function then searches from there for the first wide character in s1 that
+ is contained in the current separator wide string. If no such wide character is found, the
+ current token extends to the end of the wide string pointed to by s1, and subsequent
+ searches in the same wide string for a token return a null pointer. If such a wide character
+ is found, it is overwritten by a null wide character, which terminates the current token.
+8 In all cases, the wcstok_s function stores sufficient information in the pointer pointed
+ to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
+ value for ptr, shall start searching just past the element overwritten by a null wide
+ character (if any).
+ Returns
+9 The wcstok_s function returns a pointer to the first wide character of a token, or a null
+ pointer if there is no token or there is a runtime-constraint violation.
+10 EXAMPLE
+ #define __STDC_WANT_LIB_EXT1__ 1
+ #include <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
+1 #define __STDC_WANT_LIB_EXT1__ 1
+ #include <wchar.h>
+ size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
+ Description
+2 The wcsnlen_s function computes the length of the wide string pointed to by s.
+ Returns
+3 If s is a null pointer,452) then the wcsnlen_s function returns zero.
+4 Otherwise, the wcsnlen_s function returns the number of wide characters that precede
+ the terminating null wide character. If there is no null wide character in the first
+ maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first
+
+[page 646]
+
+ maxsize wide characters of s shall be accessed by wcsnlen_s.
+ K.3.9.3 Extended multibyte/wide character conversion utilities
+ K.3.9.3.1 Restartable multibyte/wide character conversion functions
+1 Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the
+ conversion state) to be a null pointer.
+ K.3.9.3.1.1 The wcrtomb_s function
+ Synopsis
+2 #include <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
+3 Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax
+ shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer,
+ then smax shall be not be less than the number of bytes to be stored in the array pointed
+ to by s. If s is a null pointer, then smax shall equal zero.
+4 If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is
+ not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then
+ wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then
+ wcrtomb_s sets *retval to (size_t)(-1).
+ Description
+5 If s is a null pointer, the wcrtomb_s function is equivalent to the call
+ wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
+ where retval and buf are internal variables of the appropriate types, and the size of
+ buf is greater than MB_CUR_MAX.
+6 If s is not a null pointer, the wcrtomb_s function determines the number of bytes
+ needed to represent the multibyte character that corresponds to the wide character given
+ by wc (including any shift sequences), and stores the multibyte character representation
+ in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are
+ stored. If wc is a null wide character, a null byte is stored, preceded by any shift
+ sequence needed to restore the initial shift state; the resulting state described is the initial
+ conversion state.
+
+ 452) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints
+ along with the values returned for a null pointer or an unterminated wide string argument make
+ wcsnlen_s useful in algorithms that gracefully handle such exceptional data.
+
+[page 647]
+
+7 If wc does not correspond to a valid multibyte character, an encoding error occurs: the
+ wcrtomb_s function stores the value (size_t)(-1) into *retval and the
+ conversion state is unspecified. Otherwise, the wcrtomb_s function stores into
+ *retval the number of bytes (including any shift sequences) stored in the array pointed
+ to by s.
+ Returns
+8 The wcrtomb_s function returns zero if no runtime-constraint violation and no
+ encoding error occurred. Otherwise, a nonzero value is returned.
+ K.3.9.3.2 Restartable multibyte/wide string conversion functions
+1 Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not
+ permit the ps parameter (the pointer to the conversion state) to be a null pointer.
+ K.3.9.3.2.1 The mbsrtowcs_s function
+ Synopsis
+2 #include <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
+3 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
+ then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
+ pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
+ not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null
+ character shall occur within the first dstmax multibyte characters of the array pointed to
+ by *src.
+4 If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If
+ retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1).
+ If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
+ then mbsrtowcs_s sets dst[0] to the null wide character.
+ Description
+5 The mbsrtowcs_s function converts a sequence of multibyte characters that begins in
+ the conversion state described by the object pointed to by ps, from the array indirectly
+ pointed to by src into a sequence of corresponding wide characters. If dst is not a null
+ pointer, the converted characters are stored into the array pointed to by dst. Conversion
+ continues up to and including a terminating null character, which is also stored.
+ Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
+ not form a valid multibyte character, or (if dst is not a null pointer) when len wide
+
+[page 648]
+
+ characters have been stored into the array pointed to by dst.453) If dst is not a null
+ pointer and no null wide character was stored into the array pointed to by dst, then
+ dst[len] is set to the null wide character. Each conversion takes place as if by a call
+ to the mbrtowc function.
+6 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
+ pointer (if conversion stopped due to reaching a terminating null character) or the address
+ just past the last multibyte character converted (if any). If conversion stopped due to
+ reaching a terminating null character and if dst is not a null pointer, the resulting state
+ described is the initial conversion state.
+7 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
+ sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
+ the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the
+ conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into
+ *retval the number of multibyte characters successfully converted, not including the
+ terminating null character (if any).
+8 All elements following the terminating null wide character (if any) written by
+ mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take
+ unspecified values when mbsrtowcs_s returns.454)
+9 If copying takes place between objects that overlap, the objects take on unspecified
+ values.
+ Returns
+10 The mbsrtowcs_s function returns zero if no runtime-constraint violation and no
+ encoding error occurred. Otherwise, a nonzero value is returned.
+ K.3.9.3.2.2 The wcsrtombs_s function
+ Synopsis
+11 #include <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);
+
+
+
+
+ 453) Thus, the value of len is ignored if dst is a null pointer.
+ 454) This allows an implementation to attempt converting the multibyte string before discovering a
+ terminating null character did not occur where required.
+
+[page 649]
+
+ Runtime-constraints
+12 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
+ then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
+ pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
+ not equal zero. If dst is not a null pointer and len is not less than dstmax, then the
+ conversion shall have been stopped (see below) because a terminating null wide character
+ was reached or because an encoding error occurred.
+13 If there is a runtime-constraint violation, then wcsrtombs_s does the following. If
+ retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1).
+ If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
+ then wcsrtombs_s sets dst[0] to the null character.
+ Description
+14 The wcsrtombs_s function converts a sequence of wide characters from the array
+ indirectly pointed to by src into a sequence of corresponding multibyte characters that
+ begins in the conversion state described by the object pointed to by ps. If dst is not a
+ null pointer, the converted characters are then stored into the array pointed to by dst.
+ Conversion continues up to and including a terminating null wide character, which is also
+ stored. Conversion stops earlier in two cases:
+ -- when a wide character is reached that does not correspond to a valid multibyte
+ character;
+ -- (if dst is not a null pointer) when the next multibyte character would exceed the
+ limit of n total bytes to be stored into the array pointed to by dst. If the wide
+ character being converted is the null wide character, then n is the lesser of len or
+ dstmax. Otherwise, n is the lesser of len or dstmax-1.
+ If the conversion stops without converting a null wide character and dst is not a null
+ pointer, then a null character is stored into the array pointed to by dst immediately
+ following any multibyte characters already stored. Each conversion takes place as if by a
+ call to the wcrtomb function.455)
+15 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
+ pointer (if conversion stopped due to reaching a terminating null wide character) or the
+ address just past the last wide character converted (if any). If conversion stopped due to
+ reaching a terminating null wide character, the resulting state described is the initial
+ conversion state.
+
+
+ 455) If conversion stops because a terminating null wide character has been reached, the bytes stored
+ include those necessary to reach the initial shift state immediately before the null byte. However, if
+ the conversion stops before a terminating null wide character has been reached, the result will be null
+ terminated, but might not end in the initial shift state.
+
+[page 650]
+
+16 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
+ wide character that does not correspond to a valid multibyte character, an encoding error
+ occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval
+ and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores
+ into *retval the number of bytes in the resulting multibyte character sequence, not
+ including the terminating null character (if any).
+17 All elements following the terminating null character (if any) written by wcsrtombs_s
+ in the array of dstmax elements pointed to by dst take unspecified values when
+ wcsrtombs_s returns.456)
+18 If copying takes place between objects that overlap, the objects take on unspecified
+ values.
+ Returns
+19 The wcsrtombs_s function returns zero if no runtime-constraint violation and no
+ encoding error occurred. Otherwise, a nonzero value is returned.
+
+
+
+
+ 456) When len is not less than dstmax, the implementation might fill the array before discovering a
+ runtime-constraint violation.
+
+[page 651]
+
+ Annex L
+ (normative)
+ Analyzability
+ L.1 Scope
+1 This annex specifies optional behavior that can aid in the analyzability of C programs.
+2 An implementation that defines __STDC_ANALYZABLE__ shall conform to the
+ specifications in this annex.457)
+ L.2 Definitions
+ L.2.1
+1 out-of-bounds store
+ an (attempted) access (3.1) that, at run time, for a given computational state, would
+ modify (or, for an object declared volatile, fetch) one or more bytes that lie outside
+ the bounds permitted by this Standard.
+ L.2.2
+1 bounded undefined behavior
+ undefined behavior (3.4.3) that does not perform an out-of-bounds store.
+2 NOTE 1 The behavior might perform a trap.
+
+3 NOTE 2 Any values produced or stored might be indeterminate values.
+
+ L.2.3
+1 critical undefined behavior
+ undefined behavior that is not bounded undefined behavior.
+2 NOTE The behavior might perform an out-of-bounds store or perform a trap.
+
+
+
+
+ 457) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these
+ specifications.
+
+[page 652]
+
+ L.3 Requirements
+1 If the program performs a trap (3.19.5), the implementation is permitted to invoke a
+ runtime-constraint handler. Any such semantics are implementation-defined.
+2 All undefined behavior shall be limited to bounded undefined behavior, except for the
+ following which are permitted to result in critical undefined behavior:
+ -- An object is referred to outside of its lifetime (6.2.4).
+ -- A store is performed to an object that has two incompatible declarations (6.2.7),
+ -- A pointer is used to call a function whose type is not compatible with the referenced
+ type (6.2.7, 6.3.2.3, 6.5.2.2).
+ -- An lvalue does not designate an object when evaluated (6.3.2.1).
+ -- The program attempts to modify a string literal (6.4.5).
+ -- The operand of the unary * operator has an invalid value (6.5.3.2).
+ -- Addition or subtraction of a pointer into, or just beyond, an array object and an
+ integer type produces a result that points just beyond the array object and is used as
+ the operand of a unary * operator that is evaluated (6.5.6).
+ -- An attempt is made to modify an object defined with a const-qualified type through
+ use of an lvalue with non-const-qualified type (6.7.3).
+ -- An argument to a function or macro defined in the standard library has an invalid
+ value or a type not expected by a function with variable number of arguments (7.1.4).
+ -- The longjmp function is called with a jmp_buf argument where the most recent
+ invocation of the setjmp macro in the same invocation of the program with the
+ corresponding jmp_buf argument is nonexistent, or the invocation was from another
+ thread of execution, or the function containing the invocation has terminated
+ execution in the interim, or the invocation was within the scope of an identifier with
+ variably modified type and execution has left that scope in the interim (7.13.2.1).
+ -- The value of a pointer that refers to space deallocated by a call to the free or realloc
+ function is used (7.22.3).
+ -- A string or wide string utility function accesses an array beyond the end of an object
+ (7.24.1, 7.29.4).
+
+[page 653]
+
+
+ Bibliography
+ 1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was
+ published in The C Programming Language by Brian W. Kernighan and Dennis
+ M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T.
+ 2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara,
+ California, USA, November 1984.
+ 3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information
+ Processing Systems, Information Processing Systems Technical Report.
+ 4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point
+ Arithmetic.
+ 5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent
+ Floating-Point Arithmetic.
+ 6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems,
+ second edition (previously designated IEC 559:1989).
+ 7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and
+ symbols for use in the physical sciences and technology.
+ 8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for
+ information interchange.
+ 9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1:
+ Fundamental terms.
+ 10. ISO 4217:1995, Codes for the representation of currencies and funds.
+ 11. ISO 8601:1988, Data elements and interchange formats -- Information
+ interchange -- Representation of dates and times.
+ 12. ISO/IEC 9899:1990, Programming languages -- C.
+ 13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1.
+ 14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2.
+ 15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity.
+ 16. ISO/IEC 9899:1999, Programming languages -- C.
+ 17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1.
+ 18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2.
+ 19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3.
+
+[page 654]
+
+ 20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System
+ Interface (POSIX) -- Part 2: Shell and Utilities.
+ 21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the
+ preparation of programming language standards.
+ 22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet
+ Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane.
+ 23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to
+ ISO/IEC 10646-1:1993.
+ 24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to
+ ISO/IEC 10646-1:1993.
+ 25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993
+ Transformation Format for 16 planes of group 00 (UTF-16).
+ 26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS
+ Transformation Format 8 (UTF-8).
+ 27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993.
+ 28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993.
+ 29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul
+ syllables.
+ 30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993
+ Tibetan.
+ 31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33
+ additional characters.
+ 32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993.
+ 33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993
+ Identifiers for characters.
+ 34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993
+ Ethiopic.
+ 35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993
+ Unified Canadian Aboriginal Syllabics.
+ 36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993
+ Cherokee.
+ 37. ISO/IEC 10967-1:1994, Information technology -- Language independent
+ arithmetic -- Part 1: Integer and floating point arithmetic.
+
+[page 655]
+
+ 38. ISO/IEC TR 19769:2004, Information technology -- Programming languages,
+ their environments and system software interfaces -- Extensions for the
+ programming language C to support new character data types.
+ 39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages,
+ their environments and system software interfaces -- Extensions to the C library
+ -- Part 1: Bounds-checking interfaces.
+
+[page 656]
+
+
+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, 7.25, 7.31.1, G.6, J.5.17
+& (bitwise AND operator), 6.2.6.2, 6.5.10 <ctype.h> header, 7.4, 7.31.2
+&& (logical AND operator), 5.1.2.4, 6.5.13 <errno.h> header, 7.5, 7.31.3, 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,
+' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, 7.31.4, F, H
+ 7.4.1.10, 7.30.2.1.3 <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
+( ) (cast operator), 6.5.4 7.29.4.1.1
+( ) (function-call operator), 6.5.2.2 <inttypes.h> header, 7.8, 7.31.5
+( ) (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, 7.31.6
+* (indirection operator), 6.5.2.1, 6.5.3.2 <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.25, 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, 7.31.7
++ (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 7.31.8
+++ (prefix increment operator), 6.3.2.1, 6.5.3.1 <stdbool.h> header, 4, 7.18, 7.31.9, H
++= (addition assignment operator), 6.5.16.2
+
+[page 657]
+
+<stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, \u (universal character names), 6.4.3
+ 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \v (vertical-tab escape sequence), 5.2.2, 6.4.4.4,
+<stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, 7.4.1.10
+ 7.20, 7.31.10, K.3.3, K.3.4 \x hexadecimal digits (hexadecimal-character
+<stdio.h> header, 5.2.4.2.2, 7.21, 7.31.11, F, escape sequence), 6.4.4.4
+ K.3.5 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11
+<stdlib.h> header, 5.2.4.2.2, 7.22, 7.31.12, F, ^= (bitwise exclusive OR assignment operator),
+ K.3.1.4, K.3.6 6.5.16.2
+<stdnoreturn.h> header, 4, 7.23 __alignas_is_defined macro, 7.15
+<string.h> header, 7.24, 7.31.13, K.3.7 __alignof_is_defined macro, 7.15
+<tgmath.h> header, 7.25, G.7 __bool_true_false_are_defined
+<threads.h> header, 6.10.8.3, 7.1.2, 7.26, macro, 7.18
+ 7.31.15 __cplusplus macro, 6.10.8
+<time.h> header, 7.26.1, 7.27, 7.31.14, K.3.8 __DATE__ macro, 6.10.8.1
+<uchar.h> header, 6.4.4.4, 6.4.5, 7.28 __FILE__ macro, 6.10.8.1, 7.2.1.1
+<wchar.h> header, 5.2.4.2.2, 7.21.1, 7.29, __func__ identifier, 6.4.2.2, 7.2.1.1
+ 7.31.16, F, K.3.9 __LINE__ macro, 6.10.8.1, 7.2.1.1
+<wctype.h> header, 7.30, 7.31.17 __STDC_, 6.11.9
+= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC__ macro, 6.10.8.1
+= (simple assignment operator), 6.5.16.1 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1
+== (equality operator), 6.5.9 __STDC_HOSTED__ macro, 6.10.8.1
+> (greater-than operator), 6.5.8 __STDC_IEC_559__ macro, 6.10.8.3, F.1
+>= (greater-than-or-equal-to operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro,
+>> (right-shift operator), 6.2.6.2, 6.5.7 6.10.8.3, G.1
+>>= (right-shift assignment operator), 6.5.16.2 __STDC_ISO_10646__ macro, 6.10.8.2
+? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2
+?? (trigraph sequences), 5.2.1.1 __STDC_MB_MIGHT_NEQ_WC__ macro,
+[ ] (array subscript operator), 6.5.2.1, 6.5.3.2 6.10.8.2, 7.19
+[ ] (brackets punctuator), 6.7.6.2, 6.7.9 __STDC_NO_ATOMICS__ macro, 6.10.8.3,
+\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 7.17.1
+\ (escape character), 6.4.4.4 __STDC_NO_COMPLEX__ macro, 6.10.8.3,
+\" (double-quote escape sequence), 6.4.4.4, 7.3.1
+ 6.4.5, 6.10.9 __STDC_NO_THREADS__ macro, 6.10.8.3,
+\\ (backslash escape sequence), 6.4.4.4, 6.10.9 7.26.1
+\' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_NO_VLA__ macro, 6.10.8.3
+\0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_UTF_16__ macro, 6.10.8.2
+ padding of binary stream, 7.21.2 __STDC_UTF_32__ macro, 6.10.8.2
+\? (question-mark escape sequence), 6.4.4.4 __STDC_VERSION__ macro, 6.10.8.1
+\a (alert escape sequence), 5.2.2, 6.4.4.4 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1
+\b (backspace escape sequence), 5.2.2, 6.4.4.4 __TIME__ macro, 6.10.8.1
+\f (form-feed escape sequence), 5.2.2, 6.4.4.4, __VA_ARGS__ identifier, 6.10.3, 6.10.3.1
+ 7.4.1.10 _Alignas, 6.7.5
+\n (new-line escape sequence), 5.2.2, 6.4.4.4, _Alignof operator, 6.3.2.1, 6.5.3, 6.5.3.4
+ 7.4.1.10 _Atomic type qualifier, 6.7.3
+\octal digits (octal-character escape sequence), _Atomic type specifier, 6.7.2.4
+ 6.4.4.4 _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, F.4
+\r (carriage-return escape sequence), 5.2.2, _Bool type conversions, 6.3.1.2
+ 6.4.4.4, 7.4.1.10 _Complex types, 6.2.5, 6.7.2, 7.3.1, G
+\t (horizontal-tab escape sequence), 5.2.2, _Complex_I macro, 7.3.1
+ 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.30.2.1.3 _Exit function, 7.22.4.5, 7.22.4.7
+\U (universal character names), 6.4.3 _Imaginary keyword, G.2
+
+[page 658]
+
+_Imaginary types, 7.3.1, G aliasing, 6.5
+_Imaginary_I macro, 7.3.1, G.6 alignas macro, 7.15
+_IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 aligned_alloc function, 7.22.3, 7.22.3.1
+_IOLBF macro, 7.21.1, 7.21.5.6 alignment, 3.2, 6.2.8, 7.22.3.1
+_IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 pointer, 6.2.5, 6.3.2.3
+_Noreturn, 6.7.4 structure/union member, 6.7.2.1
+_Noreturn header, 7.23 alignment header, 7.15
+_Pragma operator, 5.1.1.2, 6.10.9 alignment specifier, 6.7.5
+_Static_assert, 6.7.10, 7.2 alignof macro, 7.15
+_Thread_local storage-class specifier, 6.2.4, allocated storage, order and contiguity, 7.22.3
+ 6.7.1, 7.26.1 alternative spellings header, 7.9
+{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, and macro, 7.9
+ 6.8.2 AND operators
+{ } (compound-literal operator), 6.5.2.5 bitwise (&), 6.2.6.2, 6.5.10
+| (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 bitwise assignment (&=), 6.5.16.2
+|= (bitwise inclusive OR assignment operator), logical (&&), 5.1.2.4, 6.5.13
+ 6.5.16.2 and_eq macro, 7.9
+|| (logical OR operator), 5.1.2.4, 6.5.14 anonymous structure, 6.7.2.1
+~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 anonymous union, 6.7.2.1
+ ANSI/IEEE 754, F.1
+abort function, 7.2.1.1, 7.14.1.1, 7.21.3, ANSI/IEEE 854, F.1
+ 7.22.4.1, K.3.6.1.2 argc (main function parameter), 5.1.2.2.1
+abort_handler_s function, K.3.6.1.2 argument, 3.3
+abs function, 7.22.6.1 array, 6.9.1
+absolute-value functions default promotions, 6.5.2.2
+ complex, 7.3.8, G.6.4 function, 6.5.2.2, 6.9.1
+ integer, 7.8.2.1, 7.22.6.1 macro, substitution, 6.10.3.1
+ real, 7.12.7, F.10.4 argument, complex, 7.3.9.1
+abstract declarator, 6.7.7 argv (main function parameter), 5.1.2.2.1
+abstract machine, 5.1.2.3 arithmetic constant expression, 6.6
+access, 3.1, 6.7.3, L.2.1 arithmetic conversions, usual, see usual arithmetic
+accuracy, see floating-point accuracy conversions
+acos functions, 7.12.4.1, F.10.1.1 arithmetic operators
+acos type-generic macro, 7.25 additive, 6.2.6.2, 6.5.6, G.5.2
+acosh functions, 7.12.5.1, F.10.2.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12
+acosh type-generic macro, 7.25 increment and decrement, 6.5.2.4, 6.5.3.1
+acquire fence, 7.17.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1
+acquire operation, 5.1.2.4 shift, 6.2.6.2, 6.5.7
+active position, 5.2.2 unary, 6.5.3.3
+actual argument, 3.3 arithmetic types, 6.2.5
+actual parameter (deprecated), 3.3 arithmetic, pointer, 6.5.6
+addition assignment operator (+=), 6.5.16.2 array
+addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, argument, 6.9.1
+ 6.5.6, F.3, G.5.2 declarator, 6.7.6.2
+additive expressions, 6.5.6, G.5.2 initialization, 6.7.9
+address constant, 6.6 multidimensional, 6.5.2.1
+address operator (&), 6.3.2.1, 6.5.3.2 parameter, 6.9.1
+address-free, 7.17.5 storage order, 6.5.2.1
+aggregate initialization, 6.7.9 subscript operator ([ ]), 6.5.2.1, 6.5.3.2
+aggregate types, 6.2.5 subscripting, 6.5.2.1
+alert escape sequence (\a), 5.2.2, 6.4.4.4 type, 6.2.5
+
+[page 659]
+
+ type conversion, 6.3.2.1 7.17.7.5
+ variable length, 6.7.6, 6.7.6.2, 6.10.8.3 atomic_flag type, 7.17.1, 7.17.8
+arrow operator (->), 6.5.2.3 atomic_flag_clear functions, 7.17.8.2
+as-if rule, 5.1.2.3 ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8
+ASCII code set, 5.2.1.1 atomic_flag_test_and_set functions,
+asctime function, 7.27.3.1 7.17.8.1
+asctime_s function, K.3.8.2, K.3.8.2.1 atomic_init generic function, 7.17.2.2
+asin functions, 7.12.4.2, F.10.1.2 ATOMIC_INT_LOCK_FREE macro, 7.17.1
+asin type-generic macro, 7.25, G.7 atomic_is_lock_free generic function,
+asinh functions, 7.12.5.2, F.10.2.2 7.17.5.1
+asinh type-generic macro, 7.25, G.7 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
+asm keyword, J.5.10 atomic_load generic functions, 7.17.7.2
+assert macro, 7.2.1.1 ATOMIC_LONG_LOCK_FREE macro, 7.17.1
+assert.h header, 7.2 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
+assignment ATOMIC_SHORT_LOCK_FREE macro, 7.17.1
+ compound, 6.5.16.2 atomic_signal_fence function, 7.17.4.2
+ conversion, 6.5.16.1 atomic_store generic functions, 7.17.7.1
+ expression, 6.5.16 atomic_thread_fence function, 7.17.4.1
+ operators, 6.3.2.1, 6.5.16 ATOMIC_VAR_INIT macro, 7.17.2.1
+ simple, 6.5.16.1 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1
+associativity of operators, 6.5 atomics header, 7.17, 7.31.8
+asterisk punctuator (*), 6.7.6.1, 6.7.6.2 auto storage-class specifier, 6.7.1, 6.9
+at_quick_exit function, 7.22.4.2, 7.22.4.3, automatic storage duration, 5.2.3, 6.2.4
+ 7.22.4.4, 7.22.4.5, 7.22.4.7
+atan functions, 7.12.4.3, F.10.1.3 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
+atan type-generic macro, 7.25, G.7 backslash escape sequence (\\), 6.4.4.4, 6.10.9
+atan2 functions, 7.12.4.4, F.10.1.4 backspace escape sequence (\b), 5.2.2, 6.4.4.4
+atan2 type-generic macro, 7.25 basic character set, 3.6, 3.7.2, 5.2.1
+atanh functions, 7.12.5.3, F.10.2.3 basic types, 6.2.5
+atanh type-generic macro, 7.25, G.7 behavior, 3.4
+atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, binary streams, 7.21.2, 7.21.7.10, 7.21.9.2,
+ 7.22.4.5, 7.22.4.7, J.5.13 7.21.9.4
+atof function, 7.22.1, 7.22.1.1 bit, 3.5
+atoi function, 7.22.1, 7.22.1.2 high order, 3.6
+atol function, 7.22.1, 7.22.1.2 low order, 3.6
+atoll function, 7.22.1, 7.22.1.2 bit-field, 6.7.2.1
+atomic lock-free macros, 7.17.1, 7.17.5 bitand macro, 7.9
+atomic operations, 5.1.2.4 bitor macro, 7.9
+atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, bitwise operators, 6.5
+ 6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, AND, 6.2.6.2, 6.5.10
+ 7.17.6 AND assignment (&=), 6.5.16.2
+ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3
+ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR, 6.2.6.2, 6.5.11
+ 7.17.1 exclusive OR assignment (^=), 6.5.16.2
+ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR, 6.2.6.2, 6.5.12
+ 7.17.1 inclusive OR assignment (|=), 6.5.16.2
+ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 shift, 6.2.6.2, 6.5.7
+atomic_compare_exchange generic blank character, 7.4.1.3
+ functions, 7.17.7.4 block, 6.8, 6.8.2, 6.8.4, 6.8.5
+atomic_exchange generic functions, 7.17.7.3 block scope, 6.2.1
+atomic_fetch and modify generic functions, block structure, 6.2.1
+
+[page 660]
+
+bold type convention, 6.1 type-generic macro for, 7.25
+bool macro, 7.18 cast expression, 6.5.4
+boolean type, 6.3.1.2 cast operator (( )), 6.5.4
+boolean type and values header, 7.18, 7.31.9 catan functions, 7.3.5.3, G.6
+boolean type conversion, 6.3.1.1, 6.3.1.2 type-generic macro for, 7.25
+bounded undefined behavior, L.2.2 catanh functions, 7.3.6.3, G.6.2.3
+braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9, type-generic macro for, 7.25
+ 6.8.2 cbrt functions, 7.12.7.1, F.10.4.1
+brackets operator ([ ]), 6.5.2.1, 6.5.3.2 cbrt type-generic macro, 7.25
+brackets punctuator ([ ]), 6.7.6.2, 6.7.9 ccos functions, 7.3.5.4, G.6
+branch cuts, 7.3.3 type-generic macro for, 7.25
+break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4
+broken-down time, 7.27.1, 7.27.2.3, 7.27.3, type-generic macro for, 7.25
+ 7.27.3.1, 7.27.3.3, 7.27.3.4, 7.27.3.5, 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, 7.25
+bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.31.1
+bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.31.1
+btowc function, 7.29.6.1.1 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, 7.25
+byte, 3.6, 6.5.3.4 cexp2 function, 7.31.1
+byte input/output functions, 7.21.1 cexpm1 function, 7.31.1
+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, 7.28.1.2 6.3.1.8
+c32rtomb function, 7.28.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.7.9, 6.10.8.2,
+cabs functions, 7.3.8.1, G.6 7.28
+ type-generic macro for, 7.25 char32_t type, 6.4.4.4, 6.4.5, 6.7.9, 6.10.8.2,
+cacos functions, 7.3.5.1, G.6.1.1 7.28
+ type-generic macro for, 7.25 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1
+cacosh functions, 7.3.6.1, G.6.2.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
+ type-generic macro for, 7.25 CHAR_MIN macro, 5.2.4.2.1
+calendar time, 7.27.1, 7.27.2.2, 7.27.2.3, 7.27.2.4, character, 3.7, 3.7.1
+ 7.27.3.2, 7.27.3.3, 7.27.3.4, K.3.8.2.2, character array initialization, 6.7.9
+ K.3.8.2.3, K.3.8.2.4 character case mapping functions, 7.4.2
+call by value, 6.5.2.2 wide character, 7.30.3.1
+call_once function, 7.26.1, 7.26.2.1 extensible, 7.30.3.2
+calloc function, 7.22.3, 7.22.3.2 character classification functions, 7.4.1
+carg functions, 7.3.9.1, G.6 wide character, 7.30.2.1
+carg type-generic macro, 7.25, G.7 extensible, 7.30.2.2
+carriage-return escape sequence (\r), 5.2.2, character constant, 5.1.1.2, 5.2.1, 6.4.4.4
+ 6.4.4.4, 7.4.1.10 character display semantics, 5.2.2
+carries a dependency, 5.1.2.4 character handling header, 7.4, 7.11.1.1, 7.31.2
+case label, 6.8.1, 6.8.4.2 character input/output functions, 7.21.7, K.3.5.4
+case mapping functions wide character, 7.29.3
+ character, 7.4.2 character sets, 5.2.1
+ wide character, 7.30.3.1 character string literal, see string literal
+ extensible, 7.30.3.2 character type conversion, 6.3.1.1
+casin functions, 7.3.5.2, G.6 character types, 6.2.5, 6.7.9
+ type-generic macro for, 7.25 characteristics of floating types header, 7.7
+casinh functions, 7.3.6.2, G.6.2.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6
+
+[page 661]
+
+cimag type-generic macro, 7.25, G.7 complex macro, 7.3.1
+cis function, G.6 complex numbers, 6.2.5, G
+classification functions complex type conversion, 6.3.1.6, 6.3.1.7
+ character, 7.4.1 complex type domain, 6.2.5
+ floating-point, 7.12.3 complex types, 6.2.5, 6.7.2, 6.10.8.3, G
+ wide character, 7.30.2.1 complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2,
+ extensible, 7.30.2.2 7.3, 7.25, 7.31.1, G.6, J.5.17
+clearerr function, 7.21.10.1 compliance, see conformance
+clgamma function, 7.31.1 components of time, 7.27.1, K.3.8.1
+clock function, 7.27.2.1 composite type, 6.2.7
+clock_t type, 7.27.1, 7.27.2.1 compound assignment, 6.5.16.2
+CLOCKS_PER_SEC macro, 7.27.1, 7.27.2.1 compound literals, 6.5.2.5
+clog functions, 7.3.7.2, G.6.3.2 compound statement, 6.8.2
+ type-generic macro for, 7.25 compound-literal operator (( ){ }), 6.5.2.5
+clog10 function, 7.31.1 concatenation functions
+clog1p function, 7.31.1 string, 7.24.3, K.3.7.2
+clog2 function, 7.31.1 wide string, 7.29.4.3, K.3.9.2.2
+CMPLX macros, 7.3.9.3 concatenation, preprocessing, see preprocessing
+cnd_broadcast function, 7.26.3.1, 7.26.3.5, concatenation
+ 7.26.3.6 conceptual models, 5.1
+cnd_destroy function, 7.26.3.2 conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3,
+cnd_init function, 7.26.3.3 7.1.2, F.1, G.1, K.2, L.1
+cnd_signal function, 7.26.3.4, 7.26.3.5, conditional inclusion, 6.10.1
+ 7.26.3.6 conditional operator (? :), 5.1.2.4, 6.5.15
+cnd_t type, 7.26.1 conflict, 5.1.2.4
+cnd_timedwait function, 7.26.3.5 conformance, 4
+cnd_wait function, 7.26.3.3, 7.26.3.6 conj functions, 7.3.9.4, G.6
+collating sequences, 5.2.1 conj type-generic macro, 7.25
+colon punctuator (:), 6.7.2.1 const type qualifier, 6.7.3
+comma operator (,), 5.1.2.4, 6.5.17 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
+comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, constant expression, 6.6, F.8.4
+ 6.7.2.3, 6.7.9 constants, 6.4.4
+command processor, 7.22.4.8 as primary expression, 6.5.1
+comment delimiters (/* */ and //), 6.4.9 character, 6.4.4.4
+comments, 5.1.1.2, 6.4, 6.4.9 enumeration, 6.2.1, 6.4.4.3
+common definitions header, 7.19 floating, 6.4.4.2
+common extensions, J.5 hexadecimal, 6.4.4.1
+common initial sequence, 6.5.2.3 integer, 6.4.4.1
+common real type, 6.3.1.8 octal, 6.4.4.1
+common warnings, I constraint, 3.8, 4
+comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, constraint_handler_t type, K.3.6
+ K.3.6.3, K.3.6.3.1, K.3.6.3.2 consume operation, 5.1.2.4
+ string, 7.24.4 content of structure/union/enumeration, 6.7.2.3
+ wide string, 7.29.4.4 contiguity of allocated storage, 7.22.3
+comparison macros, 7.12.14 continue statement, 6.8.6.2
+comparison, pointer, 6.5.8 contracted expression, 6.5, 7.12.2, F.7
+compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control character, 5.2.1, 7.4
+compl macro, 7.9 control wide character, 7.30.2
+complement operator (~), 6.2.6.2, 6.5.3.3 conversion, 6.3
+complete type, 6.2.5 arithmetic operands, 6.3.1
+complex arithmetic header, 7.3, 7.31.1 array argument, 6.9.1
+
+[page 662]
+
+ array parameter, 6.9.1 correctly rounded result, 3.9
+ arrays, 6.3.2.1 corresponding real type, 6.2.5
+ boolean, 6.3.1.2 cos functions, 7.12.4.5, F.10.1.5
+ boolean, characters, and integers, 6.3.1.1 cos type-generic macro, 7.25, G.7
+ by assignment, 6.5.16.1 cosh functions, 7.12.5.4, F.10.2.4
+ by return statement, 6.8.6.4 cosh type-generic macro, 7.25, G.7
+ complex types, 6.3.1.6 cpow functions, 7.3.8.2, G.6.4.1
+ explicit, 6.3 type-generic macro for, 7.25
+ function, 6.3.2.1 cproj functions, 7.3.9.5, G.6
+ function argument, 6.5.2.2, 6.9.1 cproj type-generic macro, 7.25
+ function designators, 6.3.2.1 creal functions, 7.3.9.6, G.6
+ function parameter, 6.9.1 creal type-generic macro, 7.25, G.7
+ imaginary, G.4.1 critical undefined behavior, L.2.3
+ imaginary and complex, G.4.3 csin functions, 7.3.5.5, G.6
+ implicit, 6.3 type-generic macro for, 7.25
+ 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, 7.25
+ 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, 7.25
+ 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, 7.25
+ 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, 7.25
+ conversions ctgamma function, 7.31.1
+ void type, 6.3.2.2 ctime function, 7.27.3.2
+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, 7.31.2
+ extended, 7.29.6, K.3.9.3 current object, 6.7.9
+ restartable, 7.28.1, 7.29.6.3, 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, 7.29.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.2.2, 7.22.3,
+ numeric, 7.8.2.3, 7.22.1 7.22.4.6, 7.24.5.8, 7.24.6.2, 7.27.3, 7.28.1,
+ wide string, 7.8.2.4, 7.29.4.1 7.29.6.3, 7.29.6.4, K.3.6.2.1
+ single byte/wide character, 7.29.6.1 data stream, see streams
+ time, 7.27.3, K.3.8.2 date and time header, 7.26.1, 7.27, 7.31.14, K.3.8
+ wide character, 7.29.5 Daylight Saving Time, 7.27.1
+conversion specifier, 7.21.6.1, 7.21.6.2, 7.29.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2
+ 7.29.2.2 DBL_DIG macro, 5.2.4.2.2
+conversion state, 7.22.7, 7.28.1, 7.28.1.1, DBL_EPSILON macro, 5.2.4.2.2
+ 7.28.1.2, 7.28.1.3, 7.28.1.4, 7.29.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2
+ 7.29.6.2.1, 7.29.6.3, 7.29.6.3.2, 7.29.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2
+ 7.29.6.4, 7.29.6.4.1, 7.29.6.4.2, 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, 7.29.6.2 DBL_MIN macro, 5.2.4.2.2
+copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2
+ string, 7.24.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2
+ wide string, 7.29.4.2, 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, 7.25 decimal-point character, 7.1.1, 7.11.2.1
+
+[page 663]
+
+DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1, 7.29.2.2, F.2
+ 7.22.1.3, 7.29.2.1, 7.29.4.1.1, F.5 double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
+declaration specifiers, 6.7 6.3.1.8
+declarations, 6.7 double-precision arithmetic, 5.1.2.3
+ function, 6.7.6.3 double-quote escape sequence (\"), 6.4.4.4,
+ pointer, 6.7.6.1 6.4.5, 6.10.9
+ structure/union, 6.7.2.1 double_t type, 7.12
+ typedef, 6.7.8
+declarator, 6.7.6 EDOM macro, 7.5, 7.12.1, see also domain error
+ abstract, 6.7.7 effective type, 6.5
+declarator type derivation, 6.2.5, 6.7.6 EILSEQ macro, 7.5, 7.21.3, 7.28.1.1, 7.28.1.2,
+decrement operators, see arithmetic operators, 7.28.1.3, 7.28.1.4, 7.29.3.1, 7.29.3.3,
+ increment and decrement 7.29.6.3.2, 7.29.6.3.3, 7.29.6.4.1, 7.29.6.4.2,
+default argument promotions, 6.5.2.2 see also encoding error
+default initialization, 6.7.9 element type, 6.2.5
+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, 7.21.6.1, 7.21.6.2,
+derived declarator types, 6.2.5 7.21.6.3, 7.21.6.5, 7.21.6.6, 7.21.6.8,
+derived types, 6.2.5 7.21.6.10, 7.21.6.12, 7.21.6.13, 7.28.1.1,
+designated initializer, 6.7.9 7.28.1.2, 7.28.1.3, 7.28.1.4, 7.29.1, 7.29.2.1,
+destringizing, 6.10.9 7.29.2.2, 7.29.2.3, 7.29.2.5, 7.29.2.7,
+device input/output, 5.1.2.3 7.29.2.9, 7.29.2.11, 7.29.3.1, 7.29.3.2,
+diagnostic message, 3.10, 5.1.1.3 7.29.3.3, 7.29.3.4, 7.29.6.3.2, 7.29.6.3.3,
+diagnostics, 5.1.1.3 7.29.6.4.1, 7.29.6.4.2, K.3.6.5.1, K.3.6.5.2,
+diagnostics header, 7.2 K.3.9.3.1.1, K.3.9.3.2.1, K.3.9.3.2.2
+difftime function, 7.27.2.2 end-of-file, 7.29.1
+digit, 5.2.1, 7.4 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1,
+digraphs, 6.4.6 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2,
+direct input/output functions, 7.21.8 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.29.3.1,
+display device, 5.2.2 7.29.3.10
+div function, 7.22.6.2 end-of-file macro, see EOF macro
+div_t type, 7.22 end-of-line indicator, 5.2.1
+division assignment operator (/=), 6.5.16.2 endif preprocessing directive, 6.10.1
+division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enum type, 6.2.5, 6.7.2, 6.7.2.2
+do statement, 6.8.5.2 enumerated type, 6.2.5
+documentation of implementation, 4 enumeration, 6.2.5, 6.7.2.2
+domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration constant, 6.2.1, 6.4.4.3
+ 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumeration content, 6.7.2.3
+ 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, enumeration members, 6.7.2.2
+ 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, enumeration specifiers, 6.7.2.2
+ 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 enumeration tag, 6.2.3, 6.7.2.3
+dot operator (.), 6.5.2.3 enumerator, 6.7.2.2
+double _Complex type, 6.2.5 environment, 5
+double _Complex type conversion, 6.3.1.6, environment functions, 7.22.4, K.3.6.2
+ 6.3.1.7, 6.3.1.8 environment list, 7.22.4.6, K.3.6.2.1
+double _Imaginary type, G.2 environmental considerations, 5.2
+double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, environmental limits, 5.2.4, 7.13.1.1, 7.21.2,
+
+[page 664]
+
+ 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2, evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12
+ 7.22.4.3, 7.29.2.1, K.3.5.1.2 evaluation method, 5.2.4.2.2, 6.5, F.8.5
+EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2, evaluation of expression, 5.1.2.3
+ 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11, evaluation order, see order of evaluation
+ 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4, exceptional condition, 6.5
+ 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9, excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4
+ 7.21.7.10, 7.29.1, 7.29.2.2, 7.29.2.4, excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4
+ 7.29.2.6, 7.29.2.8, 7.29.2.10, 7.29.2.12, exclusive OR operators
+ 7.29.3.4, 7.29.6.1.1, 7.29.6.1.2, K.3.5.3.7, bitwise (^), 6.2.6.2, 6.5.11
+ K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, bitwise assignment (^=), 6.5.16.2
+ K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, executable program, 5.1.1.1
+ K.3.9.1.14 execution character set, 5.2.1
+epoch, 7.27.2.5 execution environment, 5, 5.1.2, see also
+equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9 environmental limits
+equal-to operator, see equality operator execution sequence, 5.1.2.3, 6.8
+equality expressions, 6.5.9 exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4,
+equality operator (==), 6.5.9 7.22.4.5, 7.22.4.7, 7.26.5.5
+ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1, EXIT_FAILURE macro, 7.22, 7.22.4.4
+ 7.22.1.3, 7.22.1.4, 7.29.4.1.1, 7.29.4.1.2, see EXIT_SUCCESS macro, 7.22, 7.22.4.4, 7.26.5.5
+ also range error, pole error exp functions, 7.12.6.1, F.10.3.1
+erf functions, 7.12.8.1, F.10.5.1 exp type-generic macro, 7.25
+erf type-generic macro, 7.25 exp2 functions, 7.12.6.2, F.10.3.2
+erfc functions, 7.12.8.2, F.10.5.2 exp2 type-generic macro, 7.25
+erfc type-generic macro, 7.25 explicit conversion, 6.3
+errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4, expm1 functions, 7.12.6.3, F.10.3.3
+ 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, expm1 type-generic macro, 7.25
+ 7.22.1, 7.22.1.3, 7.22.1.4, 7.24.6.2, 7.28.1.1, exponent part, 6.4.4.2
+ 7.28.1.2, 7.28.1.3, 7.28.1.4, 7.29.3.1, exponential functions
+ 7.29.3.3, 7.29.4.1.1, 7.29.4.1.2, 7.29.6.3.2, complex, 7.3.7, G.6.3
+ 7.29.6.3.3, 7.29.6.4.1, 7.29.6.4.2, J.5.17, real, 7.12.6, F.10.3
+ K.3.1.3, K.3.7.4.2 expression, 6.5
+errno.h header, 7.5, 7.31.3, K.3.2 assignment, 6.5.16
+errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, cast, 6.5.4
+ K.3.7, K.3.8, K.3.9 constant, 6.6
+error evaluation, 5.1.2.3
+ domain, see domain error full, 6.8
+ encoding, see encoding error order of evaluation, see order of evaluation
+ pole, see pole error parenthesized, 6.5.1
+ range, see range error primary, 6.5.1
+error conditions, 7.12.1 unary, 6.5.3
+error functions, 7.12.8, F.10.5 expression statement, 6.8.3
+error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended alignment, 6.2.8
+ 7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7, extended character set, 3.7.2, 5.2.1, 5.2.1.2
+ 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended characters, 5.2.1
+ 7.29.3.1, 7.29.3.3 extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
+error preprocessing directive, 4, 6.10.5 7.20
+error-handling functions, 7.21.10, 7.24.6.2, extended multibyte and wide character utilities
+ K.3.7.4.2, K.3.7.4.3 header, 7.29, 7.31.16
+errors header, 7.5, 7.31.3 extended multibyte/wide character conversion
+escape character (\), 6.4.4.4 utilities, 7.29.6, K.3.9.3
+escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 extensible wide character case mapping functions,
+
+[page 665]
+
+ 7.30.3.2 7.21.7.5, 7.21.8.1
+extensible wide character classification functions, fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3
+ 7.30.2.2 fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1
+extern storage-class specifier, 6.2.2, 6.7.1 fgetwc function, 7.21.1, 7.21.3, 7.29.3.1,
+external definition, 6.9 7.29.3.6
+external identifiers, underscore, 7.1.3 fgetws function, 7.21.1, 7.29.3.2
+external linkage, 6.2.2 field width, 7.21.6.1, 7.29.2.1
+external name, 6.4.2.1 file, 7.21.3
+external object definitions, 6.9.2 access functions, 7.21.5, K.3.5.2
+ name, 7.21.3
+fabs functions, 7.12.7.2, F.3, F.10.4.2 operations, 7.21.4, K.3.5.1
+fabs type-generic macro, 7.25, G.7 position indicator, 7.21.1, 7.21.2, 7.21.3,
+false macro, 7.18 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10,
+fclose function, 7.21.5.1 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2,
+fdim functions, 7.12.12.1, F.10.9.1 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.29.3.1,
+fdim type-generic macro, 7.25 7.29.3.3, 7.29.3.10
+FE_ALL_EXCEPT macro, 7.6 positioning functions, 7.21.9
+FE_DFL_ENV macro, 7.6 file scope, 6.2.1, 6.9
+FE_DIVBYZERO macro, 7.6, 7.12, F.3 FILE type, 7.21.1, 7.21.3
+FE_DOWNWARD macro, 7.6, F.3 FILENAME_MAX macro, 7.21.1
+FE_INEXACT macro, 7.6, F.3 flags, 7.21.6.1, 7.29.2.1, see also floating-point
+FE_INVALID macro, 7.6, 7.12, F.3 status flag
+FE_OVERFLOW macro, 7.6, 7.12, F.3 flexible array member, 6.7.2.1
+FE_TONEAREST macro, 7.6, F.3 float _Complex type, 6.2.5
+FE_TOWARDZERO macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6,
+FE_UNDERFLOW macro, 7.6, F.3 6.3.1.7, 6.3.1.8
+FE_UPWARD macro, 7.6, F.3 float _Imaginary type, G.2
+feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
+fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
+fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 6.3.1.8
+fegetround function, 7.6, 7.6.3.1, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
+feholdexcept function, 7.6.4.2, 7.6.4.3, 7.29.4.1.1
+ 7.6.4.4, F.3 float_t type, 7.12
+fence, 5.1.2.4 floating constant, 6.4.4.2
+fences, 7.17.4 floating suffix, f or F, 6.4.4.2
+fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
+ 7.31.4, 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 environment header, 7.6, 7.31.4
+fesetround function, 7.6, 7.6.3.2, F.3 floating-point exception, 7.6, 7.6.2, F.10
+fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point number, 5.2.4.2.2, 6.2.5
+feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point rounding mode, 5.2.4.2.2
+fexcept_t type, 7.6, F.3 floating-point status flag, 7.6, F.8.6
+fflush function, 7.21.5.2, 7.21.5.3 floor functions, 7.12.9.2, F.10.6.2
+fgetc function, 7.21.1, 7.21.3, 7.21.7.1, floor type-generic macro, 7.25
+
+[page 666]
+
+FLT_DECIMAL_DIG macro, 5.2.4.2.2 FP_NAN macro, 7.12, F.3
+FLT_DIG macro, 5.2.4.2.2 FP_NORMAL macro, 7.12, F.3
+FLT_EPSILON macro, 5.2.4.2.2 FP_SUBNORMAL macro, 7.12, F.3
+FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12, FP_ZERO macro, 7.12, F.3
+ F.10.11 fpclassify macro, 7.12.3.1, F.3
+FLT_HAS_SUBNORM macro, 5.2.4.2.2 fpos_t type, 7.21.1, 7.21.2
+FLT_MANT_DIG macro, 5.2.4.2.2 fprintf function, 7.8.1, 7.21.1, 7.21.6.1,
+FLT_MAX macro, 5.2.4.2.2 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6,
+FLT_MAX_10_EXP macro, 5.2.4.2.2 7.21.6.8, 7.29.2.2, F.3, K.3.5.3.1
+FLT_MAX_EXP macro, 5.2.4.2.2 fprintf_s function, K.3.5.3.1
+FLT_MIN macro, 5.2.4.2.2 fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3,
+FLT_MIN_10_EXP macro, 5.2.4.2.2 7.21.7.7, 7.21.8.2
+FLT_MIN_EXP macro, 5.2.4.2.2 fputs function, 7.21.1, 7.21.7.4
+FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3, fputwc function, 7.21.1, 7.21.3, 7.29.3.3,
+ 7.29.2.1, 7.29.4.1.1 7.29.3.8
+FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3 fputws function, 7.21.1, 7.29.3.4
+FLT_TRUE_MIN macro, 5.2.4.2.2 fread function, 7.21.1, 7.21.8.1
+fma functions, 7.12, 7.12.13.1, F.10.10.1 free function, 7.22.3.3, 7.22.3.5
+fma type-generic macro, 7.25 freestanding execution environment, 4, 5.1.2,
+fmax functions, 7.12.12.2, F.10.9.2 5.1.2.1
+fmax type-generic macro, 7.25 freopen function, 7.21.2, 7.21.5.4
+fmin functions, 7.12.12.3, F.10.9.3 freopen_s function, K.3.5.2.2
+fmin type-generic macro, 7.25 frexp functions, 7.12.6.4, F.10.3.4
+fmod functions, 7.12.10.1, F.10.7.1 frexp type-generic macro, 7.25
+fmod type-generic macro, 7.25 fscanf function, 7.8.1, 7.21.1, 7.21.6.2,
+fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2
+FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fscanf_s function, K.3.5.3.2, K.3.5.3.4,
+ K.3.5.1.1 K.3.5.3.7, K.3.5.3.9
+fopen_s function, K.3.5.1.1, K.3.5.2.1, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10,
+ K.3.5.2.2 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.29.3.10
+for statement, 6.8.5, 6.8.5.3 fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10,
+form-feed character, 5.2.1, 6.4 7.21.9.1, 7.21.9.3, 7.29.3.10
+form-feed escape sequence (\f), 5.2.2, 6.4.4.4, ftell function, 7.21.9.2, 7.21.9.4
+ 7.4.1.10 full declarator, 6.7.6
+formal argument (deprecated), 3.16 full expression, 6.8
+formal parameter, 3.16 fully buffered stream, 7.21.3
+format conversion of integer types header, 7.8, function
+ 7.31.5 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, 7.29.2, 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,
+
+[page 667]
+
+ 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12 header, 5.1.1.1, 7.1.2, see also standard headers
+ prototype scope, 6.2.1, 6.7.6.2 header names, 6.4, 6.4.7, 6.10.2
+ recursive call, 6.5.2.2 hexadecimal constant, 6.4.4.1
+ return, 6.8.6.4, F.6 hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4
+ scope, 6.2.1 hexadecimal prefix, 6.4.4.1
+ type, 6.2.5 hexadecimal-character escape sequence
+ type conversion, 6.3.2.1 (\x hexadecimal digits), 6.4.4.4
+function specifiers, 6.7.4 high-order bit, 3.6
+function type, 6.2.5 horizontal-tab character, 5.2.1, 6.4
+function-call operator (( )), 6.5.2.2 horizontal-tab escape sequence (\r), 7.30.2.1.3
+function-like macro, 6.10.3 horizontal-tab escape sequence (\t), 5.2.2,
+fundamental alignment, 6.2.8 6.4.4.4, 7.4.1.3, 7.4.1.10
+future directions hosted execution environment, 4, 5.1.2, 5.1.2.2
+ language, 6.11 HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3,
+ library, 7.31 7.29.4.1.1, F.10
+fwide function, 7.21.2, 7.29.3.5 HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3,
+fwprintf function, 7.8.1, 7.21.1, 7.21.6.2, 7.29.4.1.1, F.10
+ 7.29.2.1, 7.29.2.2, 7.29.2.3, 7.29.2.5, HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3,
+ 7.29.2.11, K.3.9.1.1 7.29.4.1.1, F.10
+fwprintf_s function, K.3.9.1.1 hyperbolic functions
+fwrite function, 7.21.1, 7.21.8.2 complex, 7.3.6, G.6.2
+fwscanf function, 7.8.1, 7.21.1, 7.29.2.2, real, 7.12.5, F.10.2
+ 7.29.2.4, 7.29.2.6, 7.29.2.12, 7.29.3.10, hypot functions, 7.12.7.3, F.10.4.3
+ K.3.9.1.2 hypot type-generic macro, 7.25
+fwscanf_s function, K.3.9.1.2, K.3.9.1.5,
+ K.3.9.1.7, K.3.9.1.14 I macro, 7.3.1, 7.3.9.5, G.6
+ identifier, 6.4.2.1, 6.5.1
+gamma functions, 7.12.8, F.10.5 linkage, see linkage
+general utilities, K.3.6 maximum length, 6.4.2.1
+ wide string, 7.29.4, K.3.9.2 name spaces, 6.2.3
+general utilities header, 7.22, 7.31.12 reserved, 6.4.1, 7.1.3, K.3.1.2
+general wide string utilities, 7.29.4, K.3.9.2 scope, 6.2.1
+generic association, 6.5.1.1 type, 6.2.5
+generic parameters, 7.25 identifier list, 6.7.6
+generic selection, 6.5.1, 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, 7.29.3.6, 7.29.3.7 IEEE floating-point arithmetic standard, see
+getwchar function, 7.21.1, 7.29.3.7 IEC 60559, ANSI/IEEE 754,
+gmtime function, 7.27.3.3 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
+
+[page 668]
+
+ilogb type-generic macro, 7.25 formatted, 7.29.2, K.3.9.1
+imaginary macro, 7.3.1, G.6 input/output header, 7.21, 7.31.11, K.3.5
+imaginary numbers, G input/output, device, 5.1.2.3
+imaginary type domain, G.2 int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2
+imaginary types, G int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
+imaxabs function, 7.8.2.1 6.3.1.8
+imaxdiv function, 7.8, 7.8.2.2 INT_FASTN_MAX macros, 7.20.2.3
+imaxdiv_t type, 7.8 INT_FASTN_MIN macros, 7.20.2.3
+implementation, 3.12 int_fastN_t types, 7.20.1.3
+implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1, INT_LEASTN_MAX macros, 7.20.2.2
+ 6.7.6, 6.8.4.2, E, see also environmental INT_LEASTN_MIN macros, 7.20.2.2
+ limits int_leastN_t types, 7.20.1.2
+implementation-defined behavior, 3.4.1, 4, J.3 INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5
+implementation-defined value, 3.19.1 INT_MIN macro, 5.2.4.2.1, 7.12
+implicit conversion, 6.3 integer arithmetic functions, 7.8.2.1, 7.8.2.2,
+implicit initialization, 6.7.9 7.22.6
+include preprocessing directive, 5.1.1.2, 6.10.2 integer character constant, 6.4.4.4
+inclusive OR operators integer constant, 6.4.4.1
+ bitwise (|), 6.2.6.2, 6.5.12 integer constant expression, 6.3.2.3, 6.6, 6.7.2.1,
+ bitwise assignment (|=), 6.5.16.2 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1,
+incomplete type, 6.2.5 7.1.4
+increment operators, see arithmetic operators, integer conversion rank, 6.3.1.1
+ increment and decrement integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1,
+indeterminate value, 3.19.2 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3,
+indeterminately sequenced, 5.1.2.3, 6.5.2.2, 7.21.6.1, 7.29.2.1
+ 6.5.2.4, 6.5.16.2, see also sequenced before, integer suffix, 6.4.4.1
+ unsequenced integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
+indirection operator (*), 6.5.2.1, 6.5.3.2 F.3, F.4
+inequality operator (!=), 6.5.9 integer types, 6.2.5, 7.20
+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 integer types header, 7.20, 7.31.10
+initial position, 5.2.2 inter-thread happens before, 5.1.2.4
+initial shift state, 5.2.1.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3
+initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal linkage, 6.2.2
+ F.8.5 internal name, 6.4.2.1
+ in blocks, 6.8 interrupt, 5.2.3
+initializer, 6.7.9 INTMAX_C macro, 7.20.4.2
+ permitted form, 6.6 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
+ string literal, 6.3.2.1 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
+inline, 6.7.4 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
+inner scope, 6.2.1 7.29.2.1, 7.29.2.2
+input failure, 7.29.2.6, 7.29.2.8, 7.29.2.10, INTN_C macros, 7.20.4.1
+ K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MAX 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_MIN macros, 7.20.2.1
+ K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 intN_t types, 7.20.1.1
+input/output functions INTPTR_MAX macro, 7.20.2.4
+ character, 7.21.7, K.3.5.4 INTPTR_MIN macro, 7.20.2.4
+ direct, 7.21.8 intptr_t type, 7.20.1.4
+ formatted, 7.21.6, K.3.5.3 inttypes.h header, 7.8, 7.31.5
+ wide character, 7.29.2, K.3.9.1 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
+ wide character, 7.29.3 isalpha function, 7.4.1.1, 7.4.1.2
+
+[page 669]
+
+isblank function, 7.4.1.3 iswpunct function, 7.30.2.1, 7.30.2.1.2,
+iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7, 7.30.2.1.7, 7.30.2.1.9, 7.30.2.1.10,
+ 7.4.1.11 7.30.2.1.11, 7.30.2.2.1
+isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5, iswspace function, 7.21.6.2, 7.29.2.2,
+ 7.4.1.7, 7.4.1.11, 7.11.1.1 7.29.4.1.1, 7.29.4.1.2, 7.30.2.1.2, 7.30.2.1.6,
+isfinite macro, 7.12.3.2, F.3 7.30.2.1.7, 7.30.2.1.9, 7.30.2.1.10,
+isgraph function, 7.4.1.6 7.30.2.1.11, 7.30.2.2.1
+isgreater macro, 7.12.14.1, F.3 iswupper function, 7.30.2.1.2, 7.30.2.1.11,
+isgreaterequal macro, 7.12.14.2, F.3 7.30.2.2.1, 7.30.3.1.1, 7.30.3.1.2
+isinf macro, 7.12.3.3 iswxdigit function, 7.30.2.1.12, 7.30.2.2.1
+isless macro, 7.12.14.3, F.3 isxdigit function, 7.4.1.12, 7.11.1.1
+islessequal macro, 7.12.14.4, F.3 italic type convention, 3, 6.1
+islessgreater macro, 7.12.14.5, F.3 iteration statements, 6.8.5
+islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
+ 7.4.2.2 jmp_buf type, 7.13
+isnan macro, 7.12.3.4, F.3 jump statements, 6.8.6
+isnormal macro, 7.12.3.5
+ISO 31-11, 2, 3 keywords, 6.4.1, G.2, J.5.9, J.5.10
+ISO 4217, 2, 7.11.2.1 kill_dependency macro, 5.1.2.4, 7.17.3.1
+ISO 8601, 2, 7.27.3.5 known constant size, 6.2.5
+ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2
+ISO/IEC 10976-1, H.1 L_tmpnam macro, 7.21.1, 7.21.4.4
+ISO/IEC 2382-1, 2, 3 L_tmpnam_s macro, K.3.5, K.3.5.1.2
+ISO/IEC 646, 2, 5.2.1.1 label name, 6.2.1, 6.2.3
+ISO/IEC 9945-2, 7.11 labeled statement, 6.8.1
+iso646.h header, 4, 7.9 labs function, 7.22.6.1
+isprint function, 5.2.2, 7.4.1.8 language, 6
+ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9, future directions, 6.11
+ 7.4.1.11 syntax summary, A
+isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9, Latin alphabet, 5.2.1, 6.4.2.1
+ 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, 7.29.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.24.4.3,
+isunordered macro, 7.12.14.6, F.3 7.29.4.4.2
+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, 7.29.6, 7.30.1, 7.30.2.2.1, 7.30.2.2.2,
+iswalnum function, 7.30.2.1.1, 7.30.2.1.9, 7.30.3.2.1, 7.30.3.2.2, K.3.6.4, K.3.6.5
+ 7.30.2.1.10, 7.30.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
+iswalpha function, 7.30.2.1.1, 7.30.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
+ 7.30.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.27.3.5
+iswblank function, 7.30.2.1.3, 7.30.2.2.1 lconv structure type, 7.11
+iswcntrl function, 7.30.2.1.2, 7.30.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2
+ 7.30.2.1.7, 7.30.2.1.11, 7.30.2.2.1 LDBL_DIG macro, 5.2.4.2.2
+iswctype function, 7.30.2.2.1, 7.30.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2
+iswdigit function, 7.30.2.1.1, 7.30.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2
+ 7.30.2.1.5, 7.30.2.1.7, 7.30.2.1.11, 7.30.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2
+iswgraph function, 7.30.2.1, 7.30.2.1.6, LDBL_MAX macro, 5.2.4.2.2
+ 7.30.2.1.10, 7.30.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2
+iswlower function, 7.30.2.1.2, 7.30.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2
+ 7.30.2.2.1, 7.30.3.1.1, 7.30.3.1.2 LDBL_MIN macro, 5.2.4.2.2
+iswprint function, 7.30.2.1.6, 7.30.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2
+ 7.30.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2
+
+[page 670]
+
+LDBL_TRUE_MIN macro, 5.2.4.2.2 llround functions, 7.12.9.7, F.10.6.7
+ldexp functions, 7.12.6.6, F.10.3.6 llround type-generic macro, 7.25
+ldexp type-generic macro, 7.25 local time, 7.27.1
+ldiv function, 7.22.6.2 locale, 3.4.2
+ldiv_t type, 7.22 locale-specific behavior, 3.4.2, J.4
+leading underscore in identifiers, 7.1.3 locale.h header, 7.11, 7.31.6
+left-shift assignment operator (<<=), 6.5.16.2 localeconv function, 7.11.1.1, 7.11.2.1
+left-shift operator (<<), 6.2.6.2, 6.5.7 localization header, 7.11, 7.31.6
+length localtime function, 7.27.3.4
+ external name, 5.2.4.1, 6.4.2.1, 6.11.3 localtime_s function, K.3.8.2.4
+ function name, 5.2.4.1, 6.4.2.1, 6.11.3 log functions, 7.12.6.7, F.10.3.7
+ identifier, 6.4.2.1 log type-generic macro, 7.25
+ internal name, 5.2.4.1, 6.4.2.1 log10 functions, 7.12.6.8, F.10.3.8
+length function, 7.22.7.1, 7.24.6.3, 7.29.4.6.1, log10 type-generic macro, 7.25
+ 7.29.6.3.1, K.3.7.4.4, K.3.9.2.4.1 log1p functions, 7.12.6.9, F.10.3.9
+length modifier, 7.21.6.1, 7.21.6.2, 7.29.2.1, log1p type-generic macro, 7.25
+ 7.29.2.2 log2 functions, 7.12.6.10, F.10.3.10
+less-than operator (<), 6.5.8 log2 type-generic macro, 7.25
+less-than-or-equal-to operator (<=), 6.5.8 logarithmic functions
+letter, 5.2.1, 7.4 complex, 7.3.7, G.6.3
+lexical elements, 5.1.1.2, 6.4 real, 7.12.6, F.10.3
+lgamma functions, 7.12.8.3, F.10.5.3 logb functions, 7.12.6.11, F.3, F.10.3.11
+lgamma type-generic macro, 7.25 logb type-generic macro, 7.25
+library, 5.1.1.1, 7, K.3 logical operators
+ future directions, 7.31 AND (&&), 5.1.2.4, 6.5.13
+ summary, B negation (!), 6.5.3.3
+ terms, 7.1.1 OR (||), 5.1.2.4, 6.5.14
+ use of functions, 7.1.4 logical source lines, 5.1.1.2
+lifetime, 6.2.4 long double _Complex type, 6.2.5
+limits long double _Complex type conversion,
+ 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, 7.29.2.1, 7.29.2.2, 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, 7.29.2.1, 7.29.2.2
+ 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, 7.29.2.1, 7.29.2.2
+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
+ 7.29.4.1.2 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, 7.29.4.1.2
+ 7.29.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.29.4.1.2
+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, 7.25 7.22.4.7
+
+[page 671]
+
+loop body, 6.8.5 7.29.2.1, 7.29.2.2, 7.29.6.3.1, 7.29.6.3.2,
+low-order bit, 3.6 7.29.6.4.1, K.3.6.5.1, K.3.9.3.2.1
+lowercase letter, 5.2.1 mbsinit function, 7.29.6.2.1
+lrint functions, 7.12.9.5, F.3, F.10.6.5 mbsrtowcs function, 7.29.6.4.1, K.3.9.3.2
+lrint type-generic macro, 7.25 mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1
+lround functions, 7.12.9.7, F.10.6.7 mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1,
+lround type-generic macro, 7.25 7.21.6.2, 7.28, 7.28.1, 7.29.1, 7.29.2.1,
+lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16, 7.29.2.2, 7.29.6, 7.29.6.2.1, 7.29.6.3,
+ 6.7.2.4 7.29.6.3.1, 7.29.6.4
+lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1, mbstowcs function, 6.4.5, 7.22.8.1, 7.29.6.4
+ 6.5.16.2 mbstowcs_s function, K.3.6.5.1
+ mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2,
+macro argument substitution, 6.10.3.1 7.22.8.1, 7.29.6.3
+macro definition member access operators (. and ->), 6.5.2.3
+ library function, 7.1.4 member alignment, 6.7.2.1
+macro invocation, 6.10.3 memchr function, 7.24.5.1
+macro name, 6.10.3 memcmp function, 7.24.4, 7.24.4.1
+ length, 5.2.4.1 memcpy function, 7.24.2.1
+ predefined, 6.10.8, 6.11.9 memcpy_s function, K.3.7.1.1
+ redefinition, 6.10.3 memmove function, 7.24.2.2
+ scope, 6.10.3.5 memmove_s function, K.3.7.1.2
+macro parameter, 6.10.3 memory location, 3.14
+macro preprocessor, 6.10 memory management functions, 7.22.3
+macro replacement, 6.10.3 memory_order type, 7.17.1, 7.17.3
+magnitude, complex, 7.3.8.1 memset function, 7.24.6.1, K.3.7.4.1
+main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4, memset_s function, K.3.7.4.1
+ 7.21.3 minimum functions, 7.12.12, F.10.9
+malloc function, 7.22.3, 7.22.3.4, 7.22.3.5 minus operator, unary, 6.5.3.3
+manipulation functions miscellaneous functions
+ complex, 7.3.9 string, 7.24.6, K.3.7.4
+ real, 7.12.11, F.10.8 wide string, 7.29.4.6, K.3.9.2.4
+matching failure, 7.29.2.6, 7.29.2.8, 7.29.2.10, mktime function, 7.27.2.3
+ K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modf functions, 7.12.6.12, F.10.3.12
+math.h header, 5.2.4.2.2, 6.5, 7.12, 7.25, F, modifiable lvalue, 6.3.2.1
+ F.10, J.5.17 modification order, 5.1.2.4
+MATH_ERREXCEPT macro, 7.12, F.10 modulus functions, 7.12.6.12
+math_errhandling macro, 7.1.3, 7.12, F.10 modulus, complex, 7.3.8.1
+MATH_ERRNO macro, 7.12 mtx_destroy function, 7.26.4.1
+mathematics header, 7.12 mtx_init function, 7.26.1, 7.26.4.2
+max_align_t type, 7.19 mtx_lock function, 7.26.4.3
+maximal munch, 6.4 mtx_t type, 7.26.1
+maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.26.4.4
+MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.26.4.5
+ 7.22.7.3, 7.28.1.2, 7.28.1.4, 7.29.6.3.3, mtx_unlock function, 7.26.4.3, 7.26.4.4,
+ K.3.6.4.1, K.3.9.3.1.1 7.26.4.5, 7.26.4.6
+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, 7.29.6.3 multibyte conversion functions
+mbrlen function, 7.29.6.3.1 wide character, 7.22.7, K.3.6.4
+mbrtoc16 function, 6.4.4.4, 6.4.5, 7.28.1.1 extended, 7.29.6, K.3.9.3
+mbrtoc32 function, 6.4.4.4, 6.4.5, 7.28.1.3 restartable, 7.28.1, 7.29.6.3, 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
+
+[page 672]
+
+ restartable, 7.29.6.4, K.3.9.3.2 not macro, 7.9
+multibyte string, 7.1.1 not-equal-to operator, see inequality operator
+multibyte/wide character conversion functions, not_eq macro, 7.9
+ 7.22.7, K.3.6.4 null character (\0), 5.2.1, 6.4.4.4, 6.4.5
+ extended, 7.29.6, K.3.9.3 padding of binary stream, 7.21.2
+ restartable, 7.28.1, 7.29.6.3, K.3.9.3.1 NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.24.1,
+multibyte/wide string conversion functions, 7.27.1, 7.29.1
+ 7.22.8, K.3.6.5 null pointer, 6.3.2.3
+ restartable, 7.29.6.4, K.3.9.3.2 null pointer constant, 6.3.2.3
+multidimensional array, 6.5.2.1 null preprocessing directive, 6.10.7
+multiplication assignment operator (*=), 6.5.16.2 null statement, 6.8.3
+multiplication operator (*), 6.2.6.2, 6.5.5, F.3, null wide character, 7.1.1
+ G.5.1 number classification macros, 7.12, 7.12.3.1
+multiplicative expressions, 6.5.5, G.5.1 numeric conversion functions, 7.8.2.3, 7.22.1
+ wide string, 7.8.2.4, 7.29.4.1
+n-char sequence, 7.22.1.3 numerical limits, 5.2.4.2
+n-wchar sequence, 7.29.4.1.1
+name object, 3.15
+ external, 5.2.4.1, 6.4.2.1, 6.11.3 object representation, 6.2.6.1
+ file, 7.21.3 object type, 6.2.5
+ internal, 5.2.4.1, 6.4.2.1 object-like macro, 6.10.3
+ label, 6.2.3 observable behavior, 5.1.2.3
+ structure/union member, 6.2.3 obsolescence, 6.11, 7.31
+name spaces, 6.2.3 octal constant, 6.4.4.1
+named label, 6.8.1 octal digit, 6.4.4.1, 6.4.4.4
+NaN, 5.2.4.2.2 octal-character escape sequence (\octal digits),
+nan functions, 7.12.11.2, F.2.1, F.10.8.2 6.4.4.4
+NAN macro, 7.12, F.2.1 offsetof macro, 7.19
+NDEBUG macro, 7.2 on-off switch, 6.10.6
+nearbyint functions, 7.12.9.3, 7.12.9.4, F.3, once_flag type, 7.26.1
+ F.10.6.3 ONCE_FLAG_INIT macro, 7.26.1
+nearbyint type-generic macro, 7.25 ones' complement, 6.2.6.2
+nearest integer functions, 7.12.9, F.10.6 operand, 6.4.6, 6.5
+negation operator (!), 6.5.3.3 operating system, 5.1.2.1, 7.22.4.8
+negative zero, 6.2.6.2, 7.12.11.1 operations on files, 7.21.4, K.3.5.1
+new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operator, 6.4.6
+new-line escape sequence (\n), 5.2.2, 6.4.4.4, operators, 6.5
+ 7.4.1.10 _Alignof, 6.5.3.4
+nextafter functions, 7.12.11.3, 7.12.11.4, F.3, additive, 6.2.6.2, 6.5.6
+ F.10.8.3 assignment, 6.5.16
+nextafter type-generic macro, 7.25 associativity, 6.5
+nexttoward functions, 7.12.11.4, F.3, F.10.8.4 equality, 6.5.9
+nexttoward type-generic macro, 7.25 multiplicative, 6.2.6.2, 6.5.5, G.5.1
+no linkage, 6.2.2 postfix, 6.5.2
+no-return function, 6.7.4 precedence, 6.5
+non-stop floating-point control mode, 7.6.4.2 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
+nongraphic characters, 5.2.2, 6.4.4.4 relational, 6.5.8
+nonlocal jumps header, 7.13 shift, 6.5.7
+noreturn macro, 7.23 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
+
+[page 673]
+
+optional features, see conditional features portability, 4, J
+or macro, 7.9 position indicator, file, see file position indicator
+OR operators positive difference, 7.12.12.1
+ bitwise exclusive (^), 6.2.6.2, 6.5.11 positive difference functions, 7.12.12, F.10.9
+ bitwise exclusive assignment (^=), 6.5.16.2 postfix decrement operator (--), 6.3.2.1, 6.5.2.4
+ bitwise inclusive (|), 6.2.6.2, 6.5.12 postfix expressions, 6.5.2
+ bitwise inclusive assignment (|=), 6.5.16.2 postfix increment operator (++), 6.3.2.1, 6.5.2.4
+ logical (||), 5.1.2.4, 6.5.14 pow functions, 7.12.7.4, F.10.4.4
+or_eq macro, 7.9 pow type-generic macro, 7.25
+order of allocated storage, 7.22.3 power functions
+order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3, complex, 7.3.8, G.6.4
+ see also sequence points real, 7.12.7, F.10.4
+ordinary identifier name space, 6.2.3 pp-number, 6.4.8
+orientation of stream, 7.21.2, 7.29.3.5 pragma operator, 6.10.9
+out-of-bounds store, L.2.1 pragma preprocessing directive, 6.10.6, 6.11.8
+outer scope, 6.2.1 precedence of operators, 6.5
+over-aligned, 6.2.8 precedence of syntax rules, 5.1.1.2
+ precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.29.2.1
+padding excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4
+ binary stream, 7.21.2 predefined macro names, 6.10.8, 6.11.9
+ bits, 6.2.6.2, 7.20.1.1 prefix decrement operator (--), 6.3.2.1, 6.5.3.1
+ structure/union, 6.2.6.1, 6.7.2.1 prefix increment operator (++), 6.3.2.1, 6.5.3.1
+parameter, 3.16 preprocessing concatenation, 6.10.3.3
+ array, 6.9.1 preprocessing directives, 5.1.1.2, 6.10
+ ellipsis, 6.7.6.3, 6.10.3 preprocessing file, 5.1.1.1, 6.10
+ function, 6.5.2.2, 6.7, 6.9.1 preprocessing numbers, 6.4, 6.4.8
+ macro, 6.10.3 preprocessing operators
+ main function, 5.1.2.2.1 #, 6.10.3.2
+ program, 5.1.2.2.1 ##, 6.10.3.3
+parameter type list, 6.7.6.3 _Pragma, 5.1.1.2, 6.10.9
+parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5 defined, 6.10.1
+parenthesized expression, 6.5.1 preprocessing tokens, 5.1.1.2, 6.4, 6.10
+parse state, 7.21.2 preprocessing translation unit, 5.1.1.1
+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, 7.30.2
+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
+
+[page 674]
+
+program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1 recursion, 6.5.2.2
+program structure, 5.1.1.1 recursive function call, 6.5.2.2
+program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3, redefinition of macro, 6.10.3
+ 5.1.2.3 reentrancy, 5.1.2.3, 5.2.3
+program, conforming, 4 library functions, 7.1.4
+program, strictly conforming, 4 referenced type, 6.2.5
+promotions register storage-class specifier, 6.7.1, 6.9
+ default argument, 6.5.2.2 relational expressions, 6.5.8
+ integer, 5.1.2.3, 6.3.1.1 relaxed atomic operations, 5.1.2.4
+prototype, see function prototype release fence, 7.17.4
+pseudo-random sequence functions, 7.22.2 release operation, 5.1.2.4
+PTRDIFF_MAX macro, 7.20.3 release sequence, 5.1.2.4
+PTRDIFF_MIN macro, 7.20.3 reliability of data, interrupted, 5.1.2.3
+ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1, remainder assignment operator (%=), 6.5.16.2
+ 7.21.6.2, 7.29.2.1, 7.29.2.2 remainder functions, 7.12.10, F.10.7
+punctuators, 6.4.6 remainder functions, 7.12.10.2, 7.12.10.3, F.3,
+putc function, 7.21.1, 7.21.7.7, 7.21.7.8 F.10.7.2
+putchar function, 7.21.1, 7.21.7.8 remainder operator (%), 6.2.6.2, 6.5.5
+puts function, 7.21.1, 7.21.7.9 remainder type-generic macro, 7.25
+putwc function, 7.21.1, 7.29.3.8, 7.29.3.9 remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2
+putwchar function, 7.21.1, 7.29.3.9 remquo functions, 7.12.10.3, F.3, F.10.7.3
+ remquo type-generic macro, 7.25
+qsort function, 7.22.5, 7.22.5.2 rename function, 7.21.4.2
+qsort_s function, K.3.6.3, K.3.6.3.2 representations of types, 6.2.6
+qualified types, 6.2.5 pointer, 6.2.5
+qualified version of type, 6.2.5 rescanning and replacement, 6.10.3.4
+question-mark escape sequence (\?), 6.4.4.4 reserved identifiers, 6.4.1, 7.1.3, K.3.1.2
+quick_exit function, 7.22.4.3, 7.22.4.4, restartable multibyte/wide character conversion
+ 7.22.4.7 functions, 7.28.1, 7.29.6.3, K.3.9.3.1
+quiet NaN, 5.2.4.2.2 restartable multibyte/wide string conversion
+ functions, 7.29.6.4, K.3.9.3.2
+raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1 restore calling environment function, 7.13.2
+rand function, 7.22, 7.22.2.1, 7.22.2.2 restrict type qualifier, 6.7.3, 6.7.3.1
+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, 7.29.3.10
+ 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, 7.25
+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, 7.25
+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,
+
+[page 675]
+
+ K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2, K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3
+ K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1, setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5
+ K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1, setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1
+ K.3.9.3.2.1, K.3.9.3.2.2 setjmp.h header, 7.13
+rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2, setlocale function, 7.11.1.1, 7.11.2.1
+ K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 setvbuf function, 7.21.1, 7.21.3, 7.21.5.1,
+runtime-constraint, 3.18 7.21.5.5, 7.21.5.6
+Runtime-constraint handling functions, K.3.6.1 shall, 4
+rvalue, 6.3.2.1 shift expressions, 6.5.7
+ shift sequence, 7.1.1
+same scope, 6.2.1 shift states, 5.2.1.2
+save calling environment function, 7.13.1 short identifier, character, 5.2.4.1, 6.4.3
+scalar types, 6.2.5 short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,
+scalbln function, 7.12.6.13, F.3, F.10.3.13 7.21.6.2, 7.29.2.1, 7.29.2.2
+scalbln type-generic macro, 7.25 short int type conversion, 6.3.1.1, 6.3.1.3,
+scalbn function, 7.12.6.13, F.3, F.10.3.13 6.3.1.4, 6.3.1.8
+scalbn type-generic macro, 7.25 SHRT_MAX macro, 5.2.4.2.1
+scanf function, 7.21.1, 7.21.6.4, 7.21.6.11 SHRT_MIN macro, 5.2.4.2.1
+scanf_s function, K.3.5.3.4, K.3.5.3.11 side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4,
+scanlist, 7.21.6.2, 7.29.2.2 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5,
+scanset, 7.21.6.2, 7.29.2.2 7.21.7.7, 7.29.3.6, 7.29.3.8, F.8.1, F.9.1,
+SCHAR_MAX macro, 5.2.4.2.1 F.9.3
+SCHAR_MIN macro, 5.2.4.2.1 SIG_ATOMIC_MAX macro, 7.20.3
+SCNcFASTN macros, 7.8.1 SIG_ATOMIC_MIN macro, 7.20.3
+SCNcLEASTN macros, 7.8.1 sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1,
+SCNcMAX macros, 7.8.1 7.20.3
+SCNcN macros, 7.8.1 SIG_DFL macro, 7.14, 7.14.1.1
+SCNcPTR macros, 7.8.1 SIG_ERR macro, 7.14, 7.14.1.1
+scope of identifier, 6.2.1, 6.9.2 SIG_IGN macro, 7.14, 7.14.1.1
+search functions SIGABRT macro, 7.14, 7.22.4.1
+ string, 7.24.5, K.3.7.3 SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.2, J.5.17
+ utility, 7.22.5, K.3.6.3 SIGILL macro, 7.14, 7.14.1.1, J.2
+ wide string, 7.29.4.5, K.3.9.2.3 SIGINT macro, 7.14
+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 handling header, 7.14, 7.31.7
+ 6.8.5, 6.8.6 signal.h header, 7.14, 7.31.7
+separate compilation, 5.1.1.1 signaling NaN, 5.2.4.2.2, F.2.1
+separate translation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1
+sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signbit macro, 7.12.3.6, F.3
+ 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2,
+ 7.1.4, 7.21.6, 7.22.5, 7.29.2, C, K.3.6.3 7.29.2.1, 7.29.2.2, K.3.5.3.2, K.3.9.1.2
+sequenced after, see sequenced before signed character, 6.3.1.1
+sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
+ 6.5.16, see also indeterminately sequenced, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
+ unsequenced 6.3.1.8
+sequencing of statements, 6.8 signed types, 6.2.5, 6.7.2
+set_constraint_handler_s function, significand part, 6.4.4.2
+
+[page 676]
+
+SIGSEGV macro, 7.14, 7.14.1.1, J.2 <inttypes.h>, 7.8, 7.31.5
+SIGTERM macro, 7.14 <iso646.h>, 4, 7.9
+simple assignment operator (=), 6.5.16.1 <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10
+sin functions, 7.12.4.6, F.10.1.6 <locale.h>, 7.11, 7.31.6
+sin type-generic macro, 7.25, G.7 <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.25, F, F.10,
+single-byte character, 3.7.1, 5.2.1.2 J.5.17
+single-byte/wide character conversion functions, <setjmp.h>, 7.13
+ 7.29.6.1 <signal.h>, 7.14, 7.31.7
+single-precision arithmetic, 5.1.2.3 <stdalign.h>, 4, 7.15
+single-quote escape sequence (\'), 6.4.4.4, 6.4.5 <stdarg.h>, 4, 6.7.6.3, 7.16
+singularity, 7.12.1 <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17,
+sinh functions, 7.12.5.5, F.10.2.5 7.31.8
+sinh type-generic macro, 7.25, G.7 <stdbool.h>, 4, 7.18, 7.31.9, H
+SIZE_MAX macro, 7.20.3 <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
+size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3
+ 7.21.6.1, 7.21.6.2, 7.22, 7.24.1, 7.27.1, 7.28, <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,
+ 7.29.1, 7.29.2.1, 7.29.2.2, K.3.3, K.3.4, 7.31.10, K.3.3, K.3.4
+ K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 <stdio.h>, 5.2.4.2.2, 7.21, 7.31.11, F, K.3.5
+sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4 <stdlib.h>, 5.2.4.2.2, 7.22, 7.31.12, F,
+sizes of integer types header, 7.10 K.3.1.4, K.3.6
+snprintf function, 7.21.6.5, 7.21.6.12, <stdnoreturn.h>, 4, 7.23
+ K.3.5.3.5 <string.h>, 7.24, 7.31.13, K.3.7
+snprintf_s function, K.3.5.3.5, K.3.5.3.6 <tgmath.h>, 7.25, G.7
+snwprintf_s function, K.3.9.1.3, K.3.9.1.4 <threads.h>, 6.10.8.3, 7.1.2, 7.26, 7.31.15
+sorting utility functions, 7.22.5, K.3.6.3 <time.h>, 7.26.1, 7.27, 7.31.14, K.3.8
+source character set, 5.1.1.2, 5.2.1 <uchar.h>, 6.4.4.4, 6.4.5, 7.28
+source file, 5.1.1.1 <wchar.h>, 5.2.4.2.2, 7.21.1, 7.29, 7.31.16,
+ name, 6.10.4, 6.10.8.1 F, K.3.9
+source file inclusion, 6.10.2 <wctype.h>, 7.30, 7.31.17
+source lines, 5.1.1.2 standard input stream, 7.21.1, 7.21.3
+source text, 5.1.1.2 standard integer types, 6.2.5
+space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, standard output stream, 7.21.1, 7.21.3
+ 7.4.1.10, 7.30.2.1.3 standard signed integer types, 6.2.5
+sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6 state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4
+sprintf_s function, K.3.5.3.5, K.3.5.3.6 statements, 6.8
+sqrt functions, 7.12.7.5, F.3, F.10.4.5 break, 6.8.6.3
+sqrt type-generic macro, 7.25 compound, 6.8.2
+srand function, 7.22.2.2 continue, 6.8.6.2
+sscanf function, 7.21.6.7, 7.21.6.14 do, 6.8.5.2
+sscanf_s function, K.3.5.3.7, K.3.5.3.14 else, 6.8.4.1
+standard error stream, 7.21.1, 7.21.3, 7.21.10.4 expression, 6.8.3
+standard headers, 4, 7.1.2 for, 6.8.5.3
+ <assert.h>, 7.2 goto, 6.8.6.1
+ <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, if, 6.8.4.1
+ 7.25, 7.31.1, G.6, J.5.17 iteration, 6.8.5
+ <ctype.h>, 7.4, 7.31.2 jump, 6.8.6
+ <errno.h>, 7.5, 7.31.3, K.3.2 labeled, 6.8.1
+ <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, null, 6.8.3
+ 7.31.4, F, H return, 6.8.6.4, F.6
+ <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3, selection, 6.8.4
+ 7.29.4.1.1 sequencing, 6.8
+
+[page 677]
+
+ switch, 6.8.4.2 strerrorlen_s function, K.3.7.4.3
+ while, 6.8.5.1 strftime function, 7.11.1.1, 7.27.3, 7.27.3.5,
+static assertions, 6.7.10 7.29.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2
+static storage duration, 6.2.4 stricter, 6.2.8
+static storage-class specifier, 6.2.2, 6.2.4, 6.7.1 strictly conforming program, 4
+static, in array declarators, 6.7.6.2, 6.7.6.3 string, 7.1.1
+static_assert declaration, 6.7.10 comparison functions, 7.24.4
+static_assert macro, 7.2 concatenation functions, 7.24.3, K.3.7.2
+stdalign.h header, 4, 7.15 conversion functions, 7.11.1.1
+stdarg.h header, 4, 6.7.6.3, 7.16 copying functions, 7.24.2, K.3.7.1
+stdatomic.h header, 6.10.8.3, 7.1.2, 7.17, library function conventions, 7.24.1
+ 7.31.8 literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9
+stdbool.h header, 4, 7.18, 7.31.9, H miscellaneous functions, 7.24.6, K.3.7.4
+STDC, 6.10.6, 6.11.8 numeric conversion functions, 7.8.2.3, 7.22.1
+stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, search functions, 7.24.5, K.3.7.3
+ 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 string handling header, 7.24, 7.31.13, K.3.7
+stderr macro, 7.21.1, 7.21.2, 7.21.3 string.h header, 7.24, 7.31.13, K.3.7
+stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4, stringizing, 6.10.3.2, 6.10.9
+ 7.21.7.6, 7.29.2.12, 7.29.3.7, K.3.5.3.4, strlen function, 7.24.6.3
+ K.3.5.4.1, K.3.9.1.14 strncat function, 7.24.3.2
+stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, strncat_s function, K.3.7.2.2
+ 7.31.10, K.3.3, K.3.4 strncmp function, 7.24.4, 7.24.4.4
+stdio.h header, 5.2.4.2.2, 7.21, 7.31.11, F, strncpy function, 7.24.2.4
+ K.3.5 strncpy_s function, K.3.7.1.4
+stdlib.h header, 5.2.4.2.2, 7.22, 7.31.12, F, strnlen_s function, K.3.7.4.4
+ K.3.1.4, K.3.6 stronger, 6.2.8
+stdnoreturn.h header, 4, 7.23 strpbrk function, 7.24.5.4
+stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3, strrchr function, 7.24.5.5
+ 7.21.7.8, 7.21.7.9, 7.29.2.11, 7.29.3.9 strspn function, 7.24.5.6
+storage duration, 6.2.4 strstr function, 7.24.5.7
+storage order of array, 6.5.2.1 strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3,
+storage unit (bit-field), 6.2.6.1, 6.7.2.1 7.29.2.2, F.3
+storage-class specifiers, 6.7.1, 6.11.5 strtof function, 7.12.11.2, 7.22.1.3, F.3
+strcat function, 7.24.3.1 strtoimax function, 7.8.2.3
+strcat_s function, K.3.7.2.1 strtok function, 7.24.5.8
+strchr function, 7.24.5.2 strtok_s function, K.3.7.3.1
+strcmp function, 7.24.4, 7.24.4.2 strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2,
+strcoll function, 7.11.1.1, 7.24.4.3, 7.24.4.5 7.22.1.4, 7.29.2.2
+strcpy function, 7.24.2.3 strtold function, 7.12.11.2, 7.22.1.3, F.3
+strcpy_s function, K.3.7.1.3 strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4
+strcspn function, 7.24.5.3 strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2,
+streams, 7.21.2, 7.22.4.4 7.22.1.4, 7.29.2.2
+ 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 timespec, 7.27.1
+ standard output, 7.21.1, 7.21.3 struct tm, 7.27.1
+ unbuffered, 7.21.3 structure
+strerror function, 7.21.10.4, 7.24.6.2 arrow operator (->), 6.5.2.3
+strerror_s function, K.3.7.4.2, K.3.7.4.3 content, 6.7.2.3
+
+[page 678]
+
+ dot operator (.), 6.5.2.3 thrd_current function, 7.26.5.2
+ initialization, 6.7.9 thrd_detach function, 7.26.5.3
+ member alignment, 6.7.2.1 thrd_equal function, 7.26.5.4
+ member name space, 6.2.3 thrd_exit function, 7.26.5.5
+ member operator (.), 6.3.2.1, 6.5.2.3 thrd_join function, 7.26.5.6
+ pointer operator (->), 6.5.2.3 thrd_sleep function, 7.26.5.7
+ specifier, 6.7.2.1 thrd_start_t type, 7.26.1
+ tag, 6.2.3, 6.7.2.3 thrd_t type, 7.26.1
+ type, 6.2.5, 6.7.2.1 thrd_yield function, 7.26.5.8
+strxfrm function, 7.11.1.1, 7.24.4.5 thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6,
+subnormal floating-point numbers, 5.2.4.2.2 K.3.6.2.1
+subscripting, 6.5.2.1 thread storage duration, 6.2.4, 7.6
+subtraction assignment operator (-=), 6.5.16.2 threads header, 7.26, 7.31.15
+subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2 threads.h header, 6.10.8.3, 7.1.2, 7.26,
+suffix 7.31.15
+ floating constant, 6.4.4.2 time
+ integer constant, 6.4.4.1 broken down, 7.27.1, 7.27.2.3, 7.27.3, 7.27.3.1,
+switch body, 6.8.4.2 7.27.3.3, 7.27.3.4, 7.27.3.5, K.3.8.2.1,
+switch case label, 6.8.1, 6.8.4.2 K.3.8.2.3, K.3.8.2.4
+switch default label, 6.8.1, 6.8.4.2 calendar, 7.27.1, 7.27.2.2, 7.27.2.3, 7.27.2.4,
+switch statement, 6.8.1, 6.8.4.2 7.27.3.2, 7.27.3.3, 7.27.3.4, K.3.8.2.2,
+swprintf function, 7.29.2.3, 7.29.2.7, K.3.8.2.3, K.3.8.2.4
+ K.3.9.1.3, K.3.9.1.4 components, 7.27.1, K.3.8.1
+swprintf_s function, K.3.9.1.3, K.3.9.1.4 conversion functions, 7.27.3, K.3.8.2
+swscanf function, 7.29.2.4, 7.29.2.8 wide character, 7.29.5
+swscanf_s function, K.3.9.1.5, K.3.9.1.10 local, 7.27.1
+symbols, 3 manipulation functions, 7.27.2
+synchronization operation, 5.1.2.4 normalized broken down, K.3.8.1, K.3.8.2.1
+synchronize with, 5.1.2.4 time base, 7.27.1, 7.27.2.5
+syntactic categories, 6.1 time function, 7.27.2.4
+syntax notation, 6.1 time.h header, 7.26.1, 7.27, 7.31.14, K.3.8
+syntax rule precedence, 5.1.1.2 time_t type, 7.27.1
+syntax summary, language, A TIME_UTC macro, 7.26.3.5, 7.26.4.4, 7.26.5.7,
+system function, 7.22.4.8 7.27.1, 7.27.2.5
+ timespec structure type, 7.27.1
+tab characters, 5.2.1, 6.4 timespec_get function, 7.27.2.5
+tag compatibility, 6.2.7 tm structure type, 7.27.1, 7.29.1, K.3.8.1
+tag name space, 6.2.3 TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4
+tags, 6.7.2.3 TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2
+tan functions, 7.12.4.7, F.10.1.7 tmpfile function, 7.21.4.3, 7.22.4.4
+tan type-generic macro, 7.25, G.7 tmpfile_s function, K.3.5.1.1, K.3.5.1.2
+tanh functions, 7.12.5.6, F.10.2.6 tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4,
+tanh type-generic macro, 7.25, G.7 K.3.5.1.2
+temporary lifetime, 6.2.4 tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2
+tentative definition, 6.9.2 token, 5.1.1.2, 6.4, see also preprocessing tokens
+terms, 3 token concatenation, 6.10.3.3
+text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 token pasting, 6.10.3.3
+tgamma functions, 7.12.8.4, F.10.5.4 tolower function, 7.4.2.1
+tgamma type-generic macro, 7.25 toupper function, 7.4.2.2
+tgmath.h header, 7.25, G.7 towctrans function, 7.30.3.2.1, 7.30.3.2.2
+thrd_create function, 7.26.1, 7.26.5.1 towlower function, 7.30.3.1.1, 7.30.3.2.1
+
+[page 679]
+
+towupper function, 7.30.3.1.2, 7.30.3.2.1 UCHAR_MAX macro, 5.2.4.2.1
+translation environment, 5, 5.1.1 UINT_FASTN_MAX macros, 7.20.2.3
+translation limits, 5.2.4.1 uint_fastN_t types, 7.20.1.3
+translation phases, 5.1.1.2 uint_least16_t type, 7.28
+translation unit, 5.1.1.1, 6.9 uint_least32_t type, 7.28
+trap, see perform a trap UINT_LEASTN_MAX macros, 7.20.2.2
+trap representation, 3.19.4, 6.2.6.1, 6.2.6.2, uint_leastN_t types, 7.20.1.2
+ 6.3.2.3, 6.5.2.3 UINT_MAX macro, 5.2.4.2.1
+trigonometric functions UINTMAX_C macro, 7.20.4.2
+ complex, 7.3.5, G.6.1 UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
+ real, 7.12.4, F.10.1 uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
+trigraph sequences, 5.1.1.2, 5.2.1.1 7.29.2.1, 7.29.2.2
+true macro, 7.18 UINTN_C macros, 7.20.4.1
+trunc functions, 7.12.9.8, F.10.6.8 UINTN_MAX macros, 7.20.2.1
+trunc type-generic macro, 7.25 uintN_t types, 7.20.1.1
+truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3 UINTPTR_MAX macro, 7.20.2.4
+truncation toward zero, 6.5.5 uintptr_t type, 7.20.1.4
+tss_create function, 7.26.6.1 ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4,
+tss_delete function, 7.26.6.2 7.29.4.1.2
+TSS_DTOR_ITERATIONS macro, 7.26.1 ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4,
+tss_dtor_t type, 7.26.1 7.29.4.1.2
+tss_get function, 7.26.6.3 unary arithmetic operators, 6.5.3.3
+tss_set function, 7.26.6.4 unary expression, 6.5.3
+tss_t type, 7.26.1 unary minus operator (-), 6.5.3.3, F.3
+two's complement, 6.2.6.2, 7.20.1.1 unary operators, 6.5.3
+type category, 6.2.5 unary plus operator (+), 6.5.3.3
+type conversion, 6.3 unbuffered stream, 7.21.3
+type definitions, 6.7.8 undef preprocessing directive, 6.10.3.5, 7.1.3,
+type domain, 6.2.5, G.2 7.1.4
+type names, 6.7.7 undefined behavior, 3.4.3, 4, J.2
+type punning, 6.5.2.3 underscore character, 6.4.2.1
+type qualifiers, 6.7.3 underscore, leading, in identifier, 7.1.3
+type specifiers, 6.7.2 ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2,
+type-generic macro, 7.25, G.7 7.21.9.3
+type-generic math header, 7.25 ungetwc function, 7.21.1, 7.29.3.10
+typedef declaration, 6.7.8 Unicode, 7.28, see also char16_t type,
+typedef storage-class specifier, 6.7.1, 6.7.8 char32_t type, wchar_t type
+types, 6.2.5 Unicode required set, 6.10.8.2
+ atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3, unicode utilities header, 7.28
+ 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6 union
+ character, 6.7.9 arrow operator (->), 6.5.2.3
+ compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6 content, 6.7.2.3
+ complex, 6.2.5, G dot operator (.), 6.5.2.3
+ composite, 6.2.7 initialization, 6.7.9
+ const qualified, 6.7.3 member alignment, 6.7.2.1
+ conversions, 6.3 member name space, 6.2.3
+ imaginary, G member operator (.), 6.3.2.1, 6.5.2.3
+ restrict qualified, 6.7.3 pointer operator (->), 6.5.2.3
+ volatile qualified, 6.7.3 specifier, 6.7.2.1
+ tag, 6.2.3, 6.7.2.3
+uchar.h header, 6.4.4.4, 6.4.5, 7.28 type, 6.2.5, 6.7.2.1
+
+[page 680]
+
+universal character name, 6.4.3 value bits, 6.2.6.2
+unnormalized floating-point numbers, 5.2.4.2.2 variable arguments, 6.10.3
+unqualified type, 6.2.5 variable arguments header, 7.16
+unqualified version of type, 6.2.5 variable length array, 6.7.6, 6.7.6.2, 6.10.8.3
+unsequenced, 5.1.2.3, 6.5, 6.5.16, see also variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3
+ indeterminately sequenced, sequenced vertical-tab character, 5.2.1, 6.4
+ before vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4,
+unsigned char type, K.3.5.3.2, K.3.9.1.2 7.4.1.10
+unsigned integer suffix, u or U, 6.4.4.1 vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8
+unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1 vfprintf_s function, K.3.5.3.8, K.3.5.3.9,
+unsigned type conversion, 6.3.1.1, 6.3.1.3, K.3.5.3.11, K.3.5.3.14
+ 6.3.1.4, 6.3.1.8 vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9
+unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2, vfscanf_s function, K.3.5.3.9, K.3.5.3.11,
+ 7.29.2.1, 7.29.2.2 K.3.5.3.14
+unspecified behavior, 3.4.4, 4, J.1 vfwprintf function, 7.21.1, 7.29.2.5, K.3.9.1.6
+unspecified value, 3.19.3 vfwprintf_s function, K.3.9.1.6
+uppercase letter, 5.2.1 vfwscanf function, 7.21.1, 7.29.2.6, 7.29.3.10
+use of library functions, 7.1.4 vfwscanf_s function, K.3.9.1.7
+USHRT_MAX macro, 5.2.4.2.1 visibility of identifier, 6.2.1
+usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6, visible sequence of side effects, 5.1.2.4
+ 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15 visible side effect, 5.1.2.4
+UTF-16, 6.10.8.2 VLA, see variable length array
+UTF-32, 6.10.8.2 void expression, 6.3.2.2
+UTF-8 string literal, see string literal void function parameter, 6.7.6.3
+utilities, general, 7.22, 7.31.12, K.3.6 void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2,
+ wide string, 7.29.4, K.3.9.2 K.3.9.1.2
+utilities, unicode, 7.28 void type conversion, 6.3.2.2
+ volatile storage, 5.1.2.3
+va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2, volatile type qualifier, 6.7.3
+ 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, volatile-qualified type, 6.2.5, 6.7.3
+ 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10,
+ 7.29.2.5, 7.29.2.6, 7.29.2.7, 7.29.2.8, K.3.5.3.10
+ 7.29.2.9, 7.29.2.10, K.3.5.3.9, K.3.5.3.11, vprintf_s function, K.3.5.3.9, K.3.5.3.10,
+ K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 K.3.5.3.11, K.3.5.3.14
+va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1, vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11
+ 7.16.1.2, 7.16.1.3 vscanf_s function, K.3.5.3.9, K.3.5.3.11,
+va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3, K.3.5.3.14
+ 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, vsnprintf function, 7.21.6.8, 7.21.6.12,
+ 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, K.3.5.3.12
+ 7.29.2.5, 7.29.2.6, 7.29.2.7, 7.29.2.8, vsnprintf_s function, K.3.5.3.9, K.3.5.3.11,
+ 7.29.2.9, 7.29.2.10, K.3.5.3.9, K.3.5.3.11, K.3.5.3.12, K.3.5.3.13, K.3.5.3.14
+ K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9
+va_list type, 7.16, 7.16.1.3 vsprintf function, 7.21.6.8, 7.21.6.13,
+va_start macro, 7.16, 7.16.1, 7.16.1.1, K.3.5.3.13
+ 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8, vsprintf_s function, K.3.5.3.9, K.3.5.3.11,
+ 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, K.3.5.3.12, K.3.5.3.13, K.3.5.3.14
+ 7.21.6.13, 7.21.6.14, 7.29.2.5, 7.29.2.6, vsscanf function, 7.21.6.8, 7.21.6.14
+ 7.29.2.7, 7.29.2.8, 7.29.2.9, 7.29.2.10, vsscanf_s function, K.3.5.3.9, K.3.5.3.11,
+ K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7, K.3.5.3.14
+ K.3.9.1.10, K.3.9.1.12 vswprintf function, 7.29.2.7, K.3.9.1.8,
+value, 3.19 K.3.9.1.9
+
+[page 681]
+
+vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.29.4.1.2
+vswscanf function, 7.29.2.8 wcstombs function, 7.22.8.2, 7.29.6.4
+vswscanf_s function, K.3.9.1.10 wcstombs_s function, K.3.6.5.2
+vwprintf function, 7.21.1, 7.29.2.9, K.3.9.1.11 wcstoul function, 7.8.2.4, 7.21.6.2, 7.29.2.2,
+vwprintf_s function, K.3.9.1.11 7.29.4.1.2
+vwscanf function, 7.21.1, 7.29.2.10, 7.29.3.10 wcstoull function, 7.8.2.4, 7.29.4.1.2
+vwscanf_s function, K.3.9.1.12 wcstoumax function, 7.8.2.4
+ wcsxfrm function, 7.29.4.4.4
+warnings, I wctob function, 7.29.6.1.2, 7.30.2.1
+wchar.h header, 5.2.4.2.2, 7.21.1, 7.29, 7.31.16, wctomb function, 7.22.7.3, 7.22.8.2, 7.29.6.3
+ F, K.3.9 wctomb_s function, K.3.6.4.1
+WCHAR_MAX macro, 7.20.3, 7.29.1 wctrans function, 7.30.3.2.1, 7.30.3.2.2
+WCHAR_MIN macro, 7.20.3, 7.29.1 wctrans_t type, 7.30.1, 7.30.3.2.2
+wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19, wctype function, 7.30.2.2.1, 7.30.2.2.2
+ 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.29.1, wctype.h header, 7.30, 7.31.17
+ 7.29.2.1, 7.29.2.2 wctype_t type, 7.30.1, 7.30.2.2.2
+wcrtomb function, 7.21.3, 7.21.6.2, 7.29.1, weaker, 6.2.8
+ 7.29.2.2, 7.29.6.3.3, 7.29.6.4.2, J.1, WEOF macro, 7.29.1, 7.29.3.1, 7.29.3.3, 7.29.3.6,
+ K.3.6.5.2, K.3.9.3.1, K.3.9.3.2.2 7.29.3.7, 7.29.3.8, 7.29.3.9, 7.29.3.10,
+wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1 7.29.6.1.1, 7.30.1
+wcscat function, 7.29.4.3.1 while statement, 6.8.5.1
+wcscat_s function, K.3.9.2.2.1 white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
+wcschr function, 7.29.4.5.1 7.30.2.1.10
+wcscmp function, 7.29.4.4.1, 7.29.4.4.4 white-space characters, 6.4
+wcscoll function, 7.29.4.4.2, 7.29.4.4.4 wide character, 3.7.3
+wcscpy function, 7.29.4.2.1 case mapping functions, 7.30.3.1
+wcscpy_s function, K.3.9.2.1.1 extensible, 7.30.3.2
+wcscspn function, 7.29.4.5.2 classification functions, 7.30.2.1
+wcsftime function, 7.11.1.1, 7.29.5.1 extensible, 7.30.2.2
+wcslen function, 7.29.4.6.1 constant, 6.4.4.4
+wcsncat function, 7.29.4.3.2 formatted input/output functions, 7.29.2,
+wcsncat_s function, K.3.9.2.2.2 K.3.9.1
+wcsncmp function, 7.29.4.4.3 input functions, 7.21.1
+wcsncpy function, 7.29.4.2.2 input/output functions, 7.21.1, 7.29.3
+wcsncpy_s function, K.3.9.2.1.2 output functions, 7.21.1
+wcsnlen_s function, K.3.9.2.4.1 single-byte conversion functions, 7.29.6.1
+wcspbrk function, 7.29.4.5.3 wide character classification and mapping utilities
+wcsrchr function, 7.29.4.5.4 header, 7.30, 7.31.17
+wcsrtombs function, 7.29.6.4.2, K.3.9.3.2 wide string, 7.1.1
+wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2 wide string comparison functions, 7.29.4.4
+wcsspn function, 7.29.4.5.5 wide string concatenation functions, 7.29.4.3,
+wcsstr function, 7.29.4.5.6 K.3.9.2.2
+wcstod function, 7.21.6.2, 7.29.2.2 wide string copying functions, 7.29.4.2, K.3.9.2.1
+wcstod function, 7.29.4.1.1 wide string literal, see string literal
+wcstof function, 7.29.4.1.1 wide string miscellaneous functions, 7.29.4.6,
+wcstoimax function, 7.8.2.4 K.3.9.2.4
+wcstok function, 7.29.4.5.7 wide string numeric conversion functions, 7.8.2.4,
+wcstok_s function, K.3.9.2.3.1 7.29.4.1
+wcstol function, 7.8.2.4, 7.21.6.2, 7.29.2.2, wide string search functions, 7.29.4.5, K.3.9.2.3
+ 7.29.4.1.2 wide-oriented stream, 7.21.2
+wcstold function, 7.29.4.1.1 width, 6.2.6.2
+
+[page 682]
+
+WINT_MAX macro, 7.20.3
+WINT_MIN macro, 7.20.3
+wint_t type, 7.20.3, 7.21.6.1, 7.29.1, 7.29.2.1,
+ 7.30.1
+wmemchr function, 7.29.4.5.8
+wmemcmp function, 7.29.4.4.5
+wmemcpy function, 7.29.4.2.3
+wmemcpy_s function, K.3.9.2.1.3
+wmemmove function, 7.29.4.2.4
+wmemmove_s function, K.3.9.2.1.4
+wmemset function, 7.29.4.6.2
+wprintf function, 7.21.1, 7.29.2.9, 7.29.2.11,
+ K.3.9.1.13
+wprintf_s function, K.3.9.1.13
+wscanf function, 7.21.1, 7.29.2.10, 7.29.2.12,
+ 7.29.3.10
+wscanf_s function, K.3.9.1.12, K.3.9.1.14
+
+xor macro, 7.9
+xor_eq macro, 7.9 *
+
+[page 683]
projects / c-standard / blobdiff