1 N1516 Committee Draft -- October 4, 2010 ISO/IEC 9899:201x
6 INTERNATIONAL STANDARD (C)ISO/IEC ISO/IEC 9899:201x
11 Programming languages -- C
18 (Cover sheet to be provided by ISO Secretariat.)
20 This International Standard specifies the form and establishes the interpretation of
21 programs expressed in the programming language C. Its purpose is to promote
22 portability, reliability, maintainability, and efficient execution of C language programs on
23 a variety of computing systems.
25 Clauses are included that detail the C language itself and the contents of the C language
26 execution library. Annexes summarize aspects of both of them, and enumerate factors
27 that influence the portability of C programs.
29 Although this International Standard is intended to guide knowledgeable C language
30 programmers as well as implementors of C language translation systems, the document
31 itself is not designed to serve as a tutorial.
33 Recipients of this draft are invited to submit, with their comments, notification of any
34 relevant patent rights of which they are aware and to provide supporting documentation.
36 Changes from the previous draft (N1494) are indicated by ''diff marks'' in the right
37 margin: deleted text is marked with ''*'', new or changed text with '' ''.
49 Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
50 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
51 1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
52 2. Normative references . . . . . . . . . . . . . . . . . . . . . . . 2
53 3. Terms, definitions, and symbols . . . . . . . . . . . . . . . . . . . 3
54 4. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . 8
55 5. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 10
56 5.1 Conceptual models . . . . . . . . . . . . . . . . . . . . . 10
57 5.1.1 Translation environment . . . . . . . . . . . . . . . . 10
58 5.1.2 Execution environments . . . . . . . . . . . . . . . . 12
59 5.2 Environmental considerations . . . . . . . . . . . . . . . . . 22
60 5.2.1 Character sets . . . . . . . . . . . . . . . . . . . . 22
61 5.2.2 Character display semantics . . . . . . . . . . . . . . 24
62 5.2.3 Signals and interrupts . . . . . . . . . . . . . . . . . 25
63 5.2.4 Environmental limits . . . . . . . . . . . . . . . . . 25
64 6. Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
65 6.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 35
66 6.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 35
67 6.2.1 Scopes of identifiers . . . . . . . . . . . . . . . . . 35
68 6.2.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 36
69 6.2.3 Name spaces of identifiers . . . . . . . . . . . . . . . 37
70 6.2.4 Storage durations of objects . . . . . . . . . . . . . . 38
71 6.2.5 Types . . . . . . . . . . . . . . . . . . . . . . . 39
72 6.2.6 Representations of types . . . . . . . . . . . . . . . . 44
73 6.2.7 Compatible type and composite type . . . . . . . . . . . 47
74 6.2.8 Alignment of objects . . . . . . . . . . . . . . . . . 48
75 6.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 50
76 6.3.1 Arithmetic operands . . . . . . . . . . . . . . . . . 50
77 6.3.2 Other operands . . . . . . . . . . . . . . . . . . . 54
78 6.4 Lexical elements . . . . . . . . . . . . . . . . . . . . . . 57
79 6.4.1 Keywords . . . . . . . . . . . . . . . . . . . . . . 58
80 6.4.2 Identifiers . . . . . . . . . . . . . . . . . . . . . . 59
81 6.4.3 Universal character names . . . . . . . . . . . . . . . 61
82 6.4.4 Constants . . . . . . . . . . . . . . . . . . . . . . 62
83 6.4.5 String literals . . . . . . . . . . . . . . . . . . . . 70
84 6.4.6 Punctuators . . . . . . . . . . . . . . . . . . . . . 72
85 6.4.7 Header names . . . . . . . . . . . . . . . . . . . . 73
86 6.4.8 Preprocessing numbers . . . . . . . . . . . . . . . . 74
87 6.4.9 Comments . . . . . . . . . . . . . . . . . . . . . 75
92 6.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . 76
93 6.5.1 Primary expressions . . . . . . . . . . . . . . . . . 78
94 6.5.2 Postfix operators . . . . . . . . . . . . . . . . . . . 79
95 6.5.3 Unary operators . . . . . . . . . . . . . . . . . . . 88
96 6.5.4 Cast operators . . . . . . . . . . . . . . . . . . . . 91
97 6.5.5 Multiplicative operators . . . . . . . . . . . . . . . . 92
98 6.5.6 Additive operators . . . . . . . . . . . . . . . . . . 92
99 6.5.7 Bitwise shift operators . . . . . . . . . . . . . . . . . 94
100 6.5.8 Relational operators . . . . . . . . . . . . . . . . . . 95
101 6.5.9 Equality operators . . . . . . . . . . . . . . . . . . 96
102 6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . 97
103 6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . 98
104 6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . 98
105 6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . 99
106 6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . 99
107 6.5.15 Conditional operator . . . . . . . . . . . . . . . . . 100
108 6.5.16 Assignment operators . . . . . . . . . . . . . . . . . 101
109 6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . 104
110 6.6 Constant expressions . . . . . . . . . . . . . . . . . . . . . 105
111 6.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . 107
112 6.7.1 Storage-class specifiers . . . . . . . . . . . . . . . . 108
113 6.7.2 Type specifiers . . . . . . . . . . . . . . . . . . . . 109
114 6.7.3 Type qualifiers . . . . . . . . . . . . . . . . . . . . 119
115 6.7.4 Function specifiers . . . . . . . . . . . . . . . . . . 123
116 6.7.5 Alignment specifier . . . . . . . . . . . . . . . . . . 125
117 6.7.6 Declarators . . . . . . . . . . . . . . . . . . . . . 126
118 6.7.7 Type names . . . . . . . . . . . . . . . . . . . . . 134
119 6.7.8 Type definitions . . . . . . . . . . . . . . . . . . . 135
120 6.7.9 Initialization . . . . . . . . . . . . . . . . . . . . 137
121 6.7.10 Static assertions . . . . . . . . . . . . . . . . . . . 143
122 6.8 Statements and blocks . . . . . . . . . . . . . . . . . . . . 144
123 6.8.1 Labeled statements . . . . . . . . . . . . . . . . . . 144
124 6.8.2 Compound statement . . . . . . . . . . . . . . . . . 145
125 6.8.3 Expression and null statements . . . . . . . . . . . . . 145
126 6.8.4 Selection statements . . . . . . . . . . . . . . . . . 146
127 6.8.5 Iteration statements . . . . . . . . . . . . . . . . . . 148
128 6.8.6 Jump statements . . . . . . . . . . . . . . . . . . . 149
129 6.9 External definitions . . . . . . . . . . . . . . . . . . . . . 153
130 6.9.1 Function definitions . . . . . . . . . . . . . . . . . . 154
131 6.9.2 External object definitions . . . . . . . . . . . . . . . 156
132 6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . 158
133 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . 160
134 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . 162
135 6.10.3 Macro replacement . . . . . . . . . . . . . . . . . . 164
140 6.10.4 Line control . . . . . . . . . . . . . . . . . . . . . 171
141 6.10.5 Error directive . . . . . . . . . . . . . . . . . . . . 172
142 6.10.6 Pragma directive . . . . . . . . . . . . . . . . . . . 172
143 6.10.7 Null directive . . . . . . . . . . . . . . . . . . . . 173
144 6.10.8 Predefined macro names . . . . . . . . . . . . . . . . 173
145 6.10.9 Pragma operator . . . . . . . . . . . . . . . . . . . 175
146 6.11 Future language directions . . . . . . . . . . . . . . . . . . 177
147 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . 177
148 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 177
149 6.11.3 External names . . . . . . . . . . . . . . . . . . . 177
150 6.11.4 Character escape sequences . . . . . . . . . . . . . . 177
151 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . 177
152 6.11.6 Function declarators . . . . . . . . . . . . . . . . . 177
153 6.11.7 Function definitions . . . . . . . . . . . . . . . . . . 177
154 6.11.8 Pragma directives . . . . . . . . . . . . . . . . . . 177
155 6.11.9 Predefined macro names . . . . . . . . . . . . . . . . 177
156 7. Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
157 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 178
158 7.1.1 Definitions of terms . . . . . . . . . . . . . . . . . . 178
159 7.1.2 Standard headers . . . . . . . . . . . . . . . . . . . 179
160 7.1.3 Reserved identifiers . . . . . . . . . . . . . . . . . . 180
161 7.1.4 Use of library functions . . . . . . . . . . . . . . . . 181
162 7.2 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 184
163 7.2.1 Program diagnostics . . . . . . . . . . . . . . . . . 184
164 7.3 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 186
165 7.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 186
166 7.3.2 Conventions . . . . . . . . . . . . . . . . . . . . . 187
167 7.3.3 Branch cuts . . . . . . . . . . . . . . . . . . . . . 187
168 7.3.4 The CX_LIMITED_RANGE pragma . . . . . . . . . . . 187
169 7.3.5 Trigonometric functions . . . . . . . . . . . . . . . . 188
170 7.3.6 Hyperbolic functions . . . . . . . . . . . . . . . . . 190
171 7.3.7 Exponential and logarithmic functions . . . . . . . . . . 192
172 7.3.8 Power and absolute-value functions . . . . . . . . . . . 193
173 7.3.9 Manipulation functions . . . . . . . . . . . . . . . . 194
174 7.4 Character handling <ctype.h> . . . . . . . . . . . . . . . . 198
175 7.4.1 Character classification functions . . . . . . . . . . . . 198
176 7.4.2 Character case mapping functions . . . . . . . . . . . . 201
177 7.5 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 203
178 7.6 Floating-point environment <fenv.h> . . . . . . . . . . . . . 204
179 7.6.1 The FENV_ACCESS pragma . . . . . . . . . . . . . . 206
180 7.6.2 Floating-point exceptions . . . . . . . . . . . . . . . 207
181 7.6.3 Rounding . . . . . . . . . . . . . . . . . . . . . . 210
182 7.6.4 Environment . . . . . . . . . . . . . . . . . . . . 211
183 7.7 Characteristics of floating types <float.h> . . . . . . . . . . . 214
187 7.8 Format conversion of integer types <inttypes.h> . . . . . . . . 215
188 7.8.1 Macros for format specifiers . . . . . . . . . . . . . . 215
189 7.8.2 Functions for greatest-width integer types . . . . . . . . . 216
190 7.9 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 219
191 7.10 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 220
192 7.11 Localization <locale.h> . . . . . . . . . . . . . . . . . . 221
193 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . 222
194 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . 223
195 7.12 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 229
196 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . 231
197 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . 233
198 7.12.3 Classification macros . . . . . . . . . . . . . . . . . 233
199 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . 236
200 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . 238
201 7.12.6 Exponential and logarithmic functions . . . . . . . . . . 240
202 7.12.7 Power and absolute-value functions . . . . . . . . . . . 245
203 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . 247
204 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . 249
205 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . 252
206 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . 253
207 7.12.12 Maximum, minimum, and positive difference functions . . . 255
208 7.12.13 Floating multiply-add . . . . . . . . . . . . . . . . . 256
209 7.12.14 Comparison macros . . . . . . . . . . . . . . . . . . 257
210 7.13 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 260
211 7.13.1 Save calling environment . . . . . . . . . . . . . . . 260
212 7.13.2 Restore calling environment . . . . . . . . . . . . . . 261
213 7.14 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 263
214 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . 264
215 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . 265
216 7.15 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 266
217 7.16 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 267
218 7.16.1 Variable argument list access macros . . . . . . . . . . . 267
219 7.17 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 271
220 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . 271
221 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . 272
222 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . 273
223 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . 276
224 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . 277
225 7.17.6 Atomic integer and address types . . . . . . . . . . . . 278
226 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . 280
227 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . 283
228 7.18 Boolean type and values <stdbool.h> . . . . . . . . . . . . 285
229 7.19 Common definitions <stddef.h> . . . . . . . . . . . . . . . 286
230 7.20 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 288
235 7.20.1 Integer types . . . . . . . . . . . . . . . . . . . . 288
236 7.20.2 Limits of specified-width integer types . . . . . . . . . . 290
237 7.20.3 Limits of other integer types . . . . . . . . . . . . . . 292
238 7.20.4 Macros for integer constants . . . . . . . . . . . . . . 293
239 7.21 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 295
240 7.21.1 Introduction . . . . . . . . . . . . . . . . . . . . . 295
241 7.21.2 Streams . . . . . . . . . . . . . . . . . . . . . . 297
242 7.21.3 Files . . . . . . . . . . . . . . . . . . . . . . . . 299
243 7.21.4 Operations on files . . . . . . . . . . . . . . . . . . 301
244 7.21.5 File access functions . . . . . . . . . . . . . . . . . 303
245 7.21.6 Formatted input/output functions . . . . . . . . . . . . 308
246 7.21.7 Character input/output functions . . . . . . . . . . . . . 329
247 7.21.8 Direct input/output functions . . . . . . . . . . . . . . 333
248 7.21.9 File positioning functions . . . . . . . . . . . . . . . 334
249 7.21.10 Error-handling functions . . . . . . . . . . . . . . . . 337
250 7.22 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 339
251 7.22.1 Numeric conversion functions . . . . . . . . . . . . . . 340
252 7.22.2 Pseudo-random sequence generation functions . . . . . . . 345
253 7.22.3 Memory management functions . . . . . . . . . . . . . 346
254 7.22.4 Communication with the environment . . . . . . . . . . 348
255 7.22.5 Searching and sorting utilities . . . . . . . . . . . . . . 352
256 7.22.6 Integer arithmetic functions . . . . . . . . . . . . . . 354
257 7.22.7 Multibyte/wide character conversion functions . . . . . . . 355
258 7.22.8 Multibyte/wide string conversion functions . . . . . . . . 357
259 7.23 String handling <string.h> . . . . . . . . . . . . . . . . . 359
260 7.23.1 String function conventions . . . . . . . . . . . . . . . 359
261 7.23.2 Copying functions . . . . . . . . . . . . . . . . . . 359
262 7.23.3 Concatenation functions . . . . . . . . . . . . . . . . 361
263 7.23.4 Comparison functions . . . . . . . . . . . . . . . . . 362
264 7.23.5 Search functions . . . . . . . . . . . . . . . . . . . 364
265 7.23.6 Miscellaneous functions . . . . . . . . . . . . . . . . 367
266 7.24 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 369
267 7.25 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 372
268 7.25.1 Introduction . . . . . . . . . . . . . . . . . . . . . 372
269 7.25.2 Initialization functions . . . . . . . . . . . . . . . . . 374
270 7.25.3 Condition variable functions . . . . . . . . . . . . . . 374
271 7.25.4 Mutex functions . . . . . . . . . . . . . . . . . . . 376
272 7.25.5 Thread functions . . . . . . . . . . . . . . . . . . . 379
273 7.25.6 Thread-specific storage functions . . . . . . . . . . . . 381
274 7.25.7 Time functions . . . . . . . . . . . . . . . . . . . . 383
275 7.26 Date and time <time.h> . . . . . . . . . . . . . . . . . . 384
276 7.26.1 Components of time . . . . . . . . . . . . . . . . . 384
277 7.26.2 Time manipulation functions . . . . . . . . . . . . . . 385
278 7.26.3 Time conversion functions . . . . . . . . . . . . . . . 387
283 7.27 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 394
284 7.27.1 Restartable multibyte/wide character conversion functions . . 394
285 7.28 Extended multibyte and wide character utilities <wchar.h> . . . . . 398
286 7.28.1 Introduction . . . . . . . . . . . . . . . . . . . . . 398
287 7.28.2 Formatted wide character input/output functions . . . . . . 399
288 7.28.3 Wide character input/output functions . . . . . . . . . . 417
289 7.28.4 General wide string utilities . . . . . . . . . . . . . . 421
290 7.28.4.1 Wide string numeric conversion functions . . . . . 422
291 7.28.4.2 Wide string copying functions . . . . . . . . . . 426
292 7.28.4.3 Wide string concatenation functions . . . . . . . 428
293 7.28.4.4 Wide string comparison functions . . . . . . . . 429
294 7.28.4.5 Wide string search functions . . . . . . . . . . 431
295 7.28.4.6 Miscellaneous functions . . . . . . . . . . . . 435
296 7.28.5 Wide character time conversion functions . . . . . . . . . 435
297 7.28.6 Extended multibyte/wide character conversion utilities . . . . 436
298 7.28.6.1 Single-byte/wide character conversion functions . . . 437
299 7.28.6.2 Conversion state functions . . . . . . . . . . . 437
300 7.28.6.3 Restartable multibyte/wide character conversion
301 functions . . . . . . . . . . . . . . . . . . 438
302 7.28.6.4 Restartable multibyte/wide string conversion
303 functions . . . . . . . . . . . . . . . . . . 440
304 7.29 Wide character classification and mapping utilities <wctype.h> . . . 443
305 7.29.1 Introduction . . . . . . . . . . . . . . . . . . . . . 443
306 7.29.2 Wide character classification utilities . . . . . . . . . . . 444
307 7.29.2.1 Wide character classification functions . . . . . . 444
308 7.29.2.2 Extensible wide character classification
309 functions . . . . . . . . . . . . . . . . . . 447
310 7.29.3 Wide character case mapping utilities . . . . . . . . . . . 449
311 7.29.3.1 Wide character case mapping functions . . . . . . 449
312 7.29.3.2 Extensible wide character case mapping
313 functions . . . . . . . . . . . . . . . . . . 449
314 7.30 Future library directions . . . . . . . . . . . . . . . . . . . 451
315 7.30.1 Complex arithmetic <complex.h> . . . . . . . . . . . 451
316 7.30.2 Character handling <ctype.h> . . . . . . . . . . . . 451
317 7.30.3 Errors <errno.h> . . . . . . . . . . . . . . . . . 451
318 7.30.4 Format conversion of integer types <inttypes.h> . . . . 451
319 7.30.5 Localization <locale.h> . . . . . . . . . . . . . . 451
320 7.30.6 Signal handling <signal.h> . . . . . . . . . . . . . 451
321 7.30.7 Boolean type and values <stdbool.h> . . . . . . . . . 451
322 7.30.8 Integer types <stdint.h> . . . . . . . . . . . . . . 451
323 7.30.9 Input/output <stdio.h> . . . . . . . . . . . . . . . 452
324 7.30.10 General utilities <stdlib.h> . . . . . . . . . . . . . 452
325 7.30.11 String handling <string.h> . . . . . . . . . . . . . 452
331 7.30.12 Extended multibyte and wide character utilities
332 <wchar.h> . . . . . . . . . . . . . . . . . . . . 452
333 7.30.13 Wide character classification and mapping utilities
334 <wctype.h> . . . . . . . . . . . . . . . . . . . . 452
335 Annex A (informative) Language syntax summary . . . . . . . . . . . . 453
336 A.1 Lexical grammar . . . . . . . . . . . . . . . . . . . . . . 453
337 A.2 Phrase structure grammar . . . . . . . . . . . . . . . . . . . 460
338 A.3 Preprocessing directives . . . . . . . . . . . . . . . . . . . 468
339 Annex B (informative) Library summary . . . . . . . . . . . . . . . . 470
340 B.1 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 470
341 B.2 Complex <complex.h> . . . . . . . . . . . . . . . . . . . 470
342 B.3 Character handling <ctype.h> . . . . . . . . . . . . . . . . 472
343 B.4 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 472
344 B.5 Floating-point environment <fenv.h> . . . . . . . . . . . . . 472
345 B.6 Characteristics of floating types <float.h> . . . . . . . . . . . 473
346 B.7 Format conversion of integer types <inttypes.h> . . . . . . . . 473
347 B.8 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 474
348 B.9 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 474
349 B.10 Localization <locale.h> . . . . . . . . . . . . . . . . . . 474
350 B.11 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 474
351 B.12 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 479
352 B.13 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 479
353 B.14 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 480
354 B.15 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 480
355 B.16 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 480
356 B.17 Boolean type and values <stdbool.h> . . . . . . . . . . . . 482
357 B.18 Common definitions <stddef.h> . . . . . . . . . . . . . . . 482
358 B.19 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 482
359 B.20 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 483
360 B.21 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 486
361 B.22 String handling <string.h> . . . . . . . . . . . . . . . . . 488
362 B.23 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 490
363 B.24 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 490
364 B.25 Date and time <time.h> . . . . . . . . . . . . . . . . . . 491
365 B.26 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 492
366 B.27 Extended multibyte/wide character utilities <wchar.h> . . . . . . 492
367 B.28 Wide character classification and mapping utilities <wctype.h> . . . 497
368 Annex C (informative) Sequence points . . . . . . . . . . . . . . . . . 498
369 Annex D (normative) Universal character names for identifiers . . . . . . . 499
370 Annex E (informative) Implementation limits . . . . . . . . . . . . . . 501
371 Annex F (normative) IEC 60559 floating-point arithmetic . . . . . . . . . . 503
372 F.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 503
376 F.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
377 F.3 Operators and functions . . . . . . . . . . . . . . . . . . . 504
378 F.4 Floating to integer conversion . . . . . . . . . . . . . . . . . 506
379 F.5 Binary-decimal conversion . . . . . . . . . . . . . . . . . . 506
380 F.6 The return statement . . . . . . . . . . . . . . . . . . . . 507
381 F.7 Contracted expressions . . . . . . . . . . . . . . . . . . . . 507
382 F.8 Floating-point environment . . . . . . . . . . . . . . . . . . 507
383 F.9 Optimization . . . . . . . . . . . . . . . . . . . . . . . . 510
384 F.10 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 513
385 F.10.1 Trigonometric functions . . . . . . . . . . . . . . . . 514
386 F.10.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 516
387 F.10.3 Exponential and logarithmic functions . . . . . . . . . . 516
388 F.10.4 Power and absolute value functions . . . . . . . . . . . 519
389 F.10.5 Error and gamma functions . . . . . . . . . . . . . . . 521
390 F.10.6 Nearest integer functions . . . . . . . . . . . . . . . . 521
391 F.10.7 Remainder functions . . . . . . . . . . . . . . . . . 524
392 F.10.8 Manipulation functions . . . . . . . . . . . . . . . . 525
393 F.10.9 Maximum, minimum, and positive difference functions . . . 525
394 F.10.10 Floating multiply-add . . . . . . . . . . . . . . . . . 526
395 F.10.11 Comparison macros . . . . . . . . . . . . . . . . . . 526
396 Annex G (informative) IEC 60559-compatible complex arithmetic . . . . . . 527
397 G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 527
398 G.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
399 G.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . 527
400 G.4 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 528
401 G.4.1 Imaginary types . . . . . . . . . . . . . . . . . . . 528
402 G.4.2 Real and imaginary . . . . . . . . . . . . . . . . . . 528
403 G.4.3 Imaginary and complex . . . . . . . . . . . . . . . . 528
404 G.5 Binary operators . . . . . . . . . . . . . . . . . . . . . . 528
405 G.5.1 Multiplicative operators . . . . . . . . . . . . . . . . 529
406 G.5.2 Additive operators . . . . . . . . . . . . . . . . . . 532
407 G.6 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 532
408 G.6.1 Trigonometric functions . . . . . . . . . . . . . . . . 534
409 G.6.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 534
410 G.6.3 Exponential and logarithmic functions . . . . . . . . . . 538
411 G.6.4 Power and absolute-value functions . . . . . . . . . . . 539
412 G.7 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 540
413 Annex H (informative) Language independent arithmetic . . . . . . . . . . 541
414 H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 541
415 H.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
416 H.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 545
417 Annex I (informative) Common warnings . . . . . . . . . . . . . . . . 547
422 Annex J (informative) Portability issues . . . . . . . . . . . . . . . . . 549
423 J.1 Unspecified behavior . . . . . . . . . . . . . . . . . . . . . 549
424 J.2 Undefined behavior . . . . . . . . . . . . . . . . . . . . . 552
425 J.3 Implementation-defined behavior . . . . . . . . . . . . . . . . 566
426 J.4 Locale-specific behavior . . . . . . . . . . . . . . . . . . . 573
427 J.5 Common extensions . . . . . . . . . . . . . . . . . . . . . 574
428 Annex K (normative) Bounds-checking interfaces . . . . . . . . . . . . . 577
429 K.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 577
430 K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 578
431 K.3 Library . . . . . . . . . . . . . . . . . . . . . . . . . . 578
432 K.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 578
433 K.3.1.1 Standard headers . . . . . . . . . . . . . . . 578
434 K.3.1.2 Reserved identifiers . . . . . . . . . . . . . . 579
435 K.3.1.3 Use of errno . . . . . . . . . . . . . . . . . 579
436 K.3.1.4 Runtime-constraint violations . . . . . . . . . . 579
437 K.3.2 Errors <errno.h> . . . . . . . . . . . . . . . . . 580
438 K.3.3 Common definitions <stddef.h> . . . . . . . . . . . 580
439 K.3.4 Integer types <stdint.h> . . . . . . . . . . . . . . 580
440 K.3.5 Input/output <stdio.h> . . . . . . . . . . . . . . . 581
441 K.3.5.1 Operations on files . . . . . . . . . . . . . . 581
442 K.3.5.2 File access functions . . . . . . . . . . . . . . 583
443 K.3.5.3 Formatted input/output functions . . . . . . . . . 586
444 K.3.5.4 Character input/output functions . . . . . . . . . 597
445 K.3.6 General utilities <stdlib.h> . . . . . . . . . . . . . 599
446 K.3.6.1 Runtime-constraint handling . . . . . . . . . . 599
447 K.3.6.2 Communication with the environment . . . . . . . 601
448 K.3.6.3 Searching and sorting utilities . . . . . . . . . . 602
449 K.3.6.4 Multibyte/wide character conversion functions . . . 605
450 K.3.6.5 Multibyte/wide string conversion functions . . . . . 606
451 K.3.7 String handling <string.h> . . . . . . . . . . . . . 609
452 K.3.7.1 Copying functions . . . . . . . . . . . . . . 609
453 K.3.7.2 Concatenation functions . . . . . . . . . . . . 612
454 K.3.7.3 Search functions . . . . . . . . . . . . . . . 615
455 K.3.7.4 Miscellaneous functions . . . . . . . . . . . . 616
456 K.3.8 Date and time <time.h> . . . . . . . . . . . . . . . 619
457 K.3.8.1 Components of time . . . . . . . . . . . . . . 619
458 K.3.8.2 Time conversion functions . . . . . . . . . . . 619
459 K.3.9 Extended multibyte and wide character utilities
460 <wchar.h> . . . . . . . . . . . . . . . . . . . . 622
461 K.3.9.1 Formatted wide character input/output functions . . . 623
462 K.3.9.2 General wide string utilities . . . . . . . . . . . 634
463 K.3.9.3 Extended multibyte/wide character conversion
464 utilities . . . . . . . . . . . . . . . . . . . 642
469 Annex L (normative) Analyzability . . . . . . . . . . . . . . . . . . 647
470 L.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 647
471 L.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 647
472 L.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 648
473 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
474 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
482 1 ISO (the International Organization for Standardization) and IEC (the International
483 Electrotechnical Commission) form the specialized system for worldwide
484 standardization. National bodies that are member of ISO or IEC participate in the
485 development of International Standards through technical committees established by the
486 respective organization to deal with particular fields of technical activity. ISO and IEC
487 technical committees collaborate in fields of mutual interest. Other international
488 organizations, governmental and non-governmental, in liaison with ISO and IEC, also
489 take part in the work.
490 2 International Standards are drafted in accordance with the rules given in the ISO/IEC
491 Directives, Part 2. This International Standard was drafted in accordance with the fifth
493 3 In the field of information technology, ISO and IEC have established a joint technical
494 committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
495 committee are circulated to national bodies for voting. Publication as an International
496 Standard requires approval by at least 75% of the national bodies casting a vote.
497 4 Attention is drawn to the possibility that some of the elements of this document may be
498 the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
499 or all such patent rights.
500 5 This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
501 Information technology, Subcommittee SC 22, Programming languages, their
502 environments and system software interfaces. The Working Group responsible for this
503 standard (WG 14) maintains a site on the World Wide Web at http://www.open-
504 std.org/JTC1/SC22/WG14/ containing additional information relevant to this
505 standard such as a Rationale for many of the decisions made during its preparation and a
506 log of Defect Reports and Responses.
507 6 This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
508 corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
509 ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
510 -- conditional (optional) features (including some that were previously mandatory)
511 -- support for multiple threads of execution including an improved memory sequencing
512 model, atomic objects, and thread-local storage (<stdatomic.h> and
514 -- additional floating-point characteristic macros (<float.h>)
515 -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
516 -- Unicode characters and strings (<uchar.h>) (originally specified in
517 ISO/IEC TR 19769:2004)
518 -- type-generic expressions
524 -- anonymous structures and unions
525 -- no-return functions
526 -- macros to create complex numbers (<complex.h>)
527 -- support for opening files for exclusive access
528 -- removed the gets function (<stdio.h>)
529 -- added the aligned_alloc, at_quick_exit, and quick_exit functions
531 -- (conditional) support for bounds-checking interfaces (originally specified in
532 ISO/IEC TR 24731-1:2007)
533 -- (conditional) support for analyzability
534 7 Major changes in the second edition included:
535 -- restricted character set support via digraphs and <iso646.h> (originally specified
537 -- wide character library support in <wchar.h> and <wctype.h> (originally
539 -- more precise aliasing rules via effective type
540 -- restricted pointers
541 -- variable length arrays
542 -- flexible array members
543 -- static and type qualifiers in parameter array declarators
544 -- complex (and imaginary) support in <complex.h>
545 -- type-generic math macros in <tgmath.h>
546 -- the long long int type and library functions
547 -- increased minimum translation limits
548 -- additional floating-point characteristics in <float.h>
549 -- remove implicit int
550 -- reliable integer division
551 -- universal character names (\u and \U)
552 -- extended identifiers
553 -- hexadecimal floating-point constants and %a and %A printf/scanf conversion
561 -- designated initializers
563 -- extended integer types and library functions in <inttypes.h> and <stdint.h>
564 -- remove implicit function declaration
565 -- preprocessor arithmetic done in intmax_t/uintmax_t
566 -- mixed declarations and code
567 -- new block scopes for selection and iteration statements
568 -- integer constant type rules
569 -- integer promotion rules
570 -- macros with a variable number of arguments
571 -- the vscanf family of functions in <stdio.h> and <wchar.h>
572 -- additional math library functions in <math.h>
573 -- treatment of error conditions by math library functions (math_errhandling)
574 -- floating-point environment access in <fenv.h>
575 -- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
576 -- trailing comma allowed in enum declaration
577 -- %lf conversion specifier allowed in printf
579 -- the snprintf family of functions in <stdio.h>
580 -- boolean type in <stdbool.h>
581 -- idempotent type qualifiers
582 -- empty macro arguments
583 -- new structure type compatibility rules (tag compatibility)
584 -- additional predefined macro names
585 -- _Pragma preprocessing operator
587 -- __func__ predefined identifier
589 -- additional strftime conversion specifiers
590 -- LIA compatibility annex
595 -- deprecate ungetc at the beginning of a binary file
596 -- remove deprecation of aliased array parameters
597 -- conversion of array to pointer not limited to lvalues
598 -- relaxed constraints on aggregate and union initialization
599 -- relaxed restrictions on portable header names
600 -- return without expression not permitted in function that returns a value (and vice
602 8 Annexes D, F, K, and L form a normative part of this standard; annexes A, B, C, E, G, H,
603 I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
604 the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
605 are also for information only.
613 1 With the introduction of new devices and extended character sets, new features may be
614 added to this International Standard. Subclauses in the language and library clauses warn
615 implementors and programmers of usages which, though valid in themselves, may
616 conflict with future additions.
617 2 Certain features are obsolescent, which means that they may be considered for
618 withdrawal in future revisions of this International Standard. They are retained because
619 of their widespread use, but their use in new implementations (for implementation
620 features) or new programs (for language [6.11] or library features [7.30]) is discouraged.
621 3 This International Standard is divided into four major subdivisions:
622 -- preliminary elements (clauses 1-4);
623 -- the characteristics of environments that translate and execute C programs (clause 5);
624 -- the language syntax, constraints, and semantics (clause 6);
625 -- the library facilities (clause 7).
626 4 Examples are provided to illustrate possible forms of the constructions described.
627 Footnotes are provided to emphasize consequences of the rules described in that
628 subclause or elsewhere in this International Standard. References are used to refer to
629 other related subclauses. Recommendations are provided to give advice or guidance to
630 implementors. Annexes provide additional information and summarize the information
631 contained in this International Standard. A bibliography lists documents that were
632 referred to during the preparation of the standard.
633 5 The language clause (clause 6) is derived from ''The C Reference Manual''.
634 6 The library clause (clause 7) is based on the 1984 /usr/group Standard.
647 Programming languages -- C
652 1 This International Standard specifies the form and establishes the interpretation of
653 programs written in the C programming language.1) It specifies
654 -- the representation of C programs;
655 -- the syntax and constraints of the C language;
656 -- the semantic rules for interpreting C programs;
657 -- the representation of input data to be processed by C programs;
658 -- the representation of output data produced by C programs;
659 -- the restrictions and limits imposed by a conforming implementation of C.
660 2 This International Standard does not specify
661 -- the mechanism by which C programs are transformed for use by a data-processing
663 -- the mechanism by which C programs are invoked for use by a data-processing
665 -- the mechanism by which input data are transformed for use by a C program;
666 -- the mechanism by which output data are transformed after being produced by a C
668 -- the size or complexity of a program and its data that will exceed the capacity of any
669 specific data-processing system or the capacity of a particular processor;
670 -- all minimal requirements of a data-processing system that is capable of supporting a
671 conforming implementation.
674 1) This International Standard is designed to promote the portability of C programs among a variety of
675 data-processing systems. It is intended for use by implementors and programmers.
680 2. Normative references
681 1 The following referenced documents are indispensable for the application of this
682 document. For dated references, only the edition cited applies. For undated references,
683 the latest edition of the referenced document (including any amendments) applies.
684 2 ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for
685 use in the physical sciences and technology.
686 3 ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information
688 4 ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental
690 5 ISO 4217, Codes for the representation of currencies and funds.
691 6 ISO 8601, Data elements and interchange formats -- Information interchange --
692 Representation of dates and times.
693 7 ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded
695 8 IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
696 designated IEC 559:1989).
704 3. Terms, definitions, and symbols
705 1 For the purposes of this International Standard, the following definitions apply. Other
706 terms are defined where they appear in italic type or on the left side of a syntax rule.
707 Terms explicitly defined in this International Standard are not to be presumed to refer
708 implicitly to similar terms defined elsewhere. Terms not defined in this International
709 Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not
710 defined in this International Standard are to be interpreted according to ISO 31-11.
713 <execution-time action> to read or modify the value of an object
714 2 NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used.
716 3 NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value.
718 4 NOTE 3 Expressions that are not evaluated do not access objects.
722 requirement that objects of a particular type be located on storage boundaries with
723 addresses that are particular multiples of a byte address
727 actual parameter (deprecated)
728 expression in the comma-separated list bounded by the parentheses in a function call
729 expression, or a sequence of preprocessing tokens in the comma-separated list bounded
730 by the parentheses in a function-like macro invocation
733 external appearance or action
735 1 implementation-defined behavior
736 unspecified behavior where each implementation documents how the choice is made
737 2 EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
738 when a signed integer is shifted right.
741 1 locale-specific behavior
742 behavior that depends on local conventions of nationality, culture, and language that each
743 implementation documents
748 2 EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
749 characters other than the 26 lowercase Latin letters.
753 behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
754 for which this International Standard imposes no requirements
755 2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
756 results, to behaving during translation or program execution in a documented manner characteristic of the
757 environment (with or without the issuance of a diagnostic message), to terminating a translation or
758 execution (with the issuance of a diagnostic message).
760 3 EXAMPLE An example of undefined behavior is the behavior on integer overflow.
763 1 unspecified behavior
764 use of an unspecified value, or other behavior where this International Standard provides
765 two or more possibilities and imposes no further requirements on which is chosen in any
767 2 EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are
772 unit of data storage in the execution environment large enough to hold an object that may
773 have one of two values
774 2 NOTE It need not be possible to express the address of each individual bit of an object.
778 addressable unit of data storage large enough to hold any member of the basic character
779 set of the execution environment
780 2 NOTE 1 It is possible to express the address of each individual byte of an object uniquely.
782 3 NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
783 defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
788 <abstract> member of a set of elements used for the organization, control, or
789 representation of data
792 single-byte character
793 <C> bit representation that fits in a byte
797 1 multibyte character
798 sequence of one or more bytes representing a member of the extended character set of
799 either the source or the execution environment
800 2 NOTE The extended character set is a superset of the basic character set.
804 bit representation that fits in an object of type wchar_t, capable of representing any
805 character in the current locale
808 restriction, either syntactic or semantic, by which the exposition of language elements is
811 1 correctly rounded result
812 representation in the result format that is nearest in value, subject to the current rounding
813 mode, to what the result would be given unlimited range and precision
816 message belonging to an implementation-defined subset of the implementation's message
820 reference to a later subclause of this International Standard that contains additional
821 information relevant to this subclause
824 particular set of software, running in a particular translation environment under particular
825 control options, that performs translation of programs for, and supports execution of
826 functions in, a particular execution environment
828 1 implementation limit
829 restriction imposed upon programs by the implementation
832 either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
837 2 NOTE 1 Two threads of execution can update and access separate memory locations without interfering
840 3 NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
841 applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
842 two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
843 declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
844 members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
845 intervening bit-fields happen to be.
847 4 EXAMPLE A structure declared as
850 int b:5, c:11, :0, d:8;
851 struct { int ee:8; } e;
853 contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
854 memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
855 and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
856 modified, but b and a, for example, can be.
860 region of data storage in the execution environment, the contents of which can represent
862 2 NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.
867 formal argument (deprecated)
868 object declared as part of a function declaration or definition that acquires a value on
869 entry to the function, or an identifier from the comma-separated list bounded by the
870 parentheses immediately following the macro name in a function-like macro definition
872 1 recommended practice
873 specification that is strongly recommended as being in keeping with the intent of the
874 standard, but that may be impractical for some implementations
877 requirement on a program when calling a library function
878 2 NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
879 need not be diagnosed at translation time.
881 3 NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
882 constraints for a library function are not violated by the program; see K.3.1.4.
888 precise meaning of the contents of an object when interpreted as having a specific type
890 1 implementation-defined value
891 unspecified value where each implementation documents how the choice is made
893 1 indeterminate value
894 either an unspecified value or a trap representation
897 valid value of the relevant type where this International Standard imposes no
898 requirements on which value is chosen in any instance
899 2 NOTE An unspecified value cannot be a trap representation.
902 1 trap representation
903 an object representation that need not represent a value of the object type
906 interrupt execution of the program such that no further operations are performed
907 2 NOTE In this International Standard, when the word ''trap'' is not immediately followed by
908 ''representation'', this is the intended usage.2)
912 ceiling of x: the least integer greater than or equal to x
913 2 EXAMPLE [^2.4^] is 3, [^-2.4^] is -2.
917 floor of x: the greatest integer less than or equal to x
918 2 EXAMPLE [_2.4_] is 2, [_-2.4_] is -3.
923 2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap
924 representation might perform a trap but is not required to (see 6.2.6.1).
930 1 In this International Standard, ''shall'' is to be interpreted as a requirement on an
931 implementation or on a program; conversely, ''shall not'' is to be interpreted as a
933 2 If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime-
934 constraint is violated, the behavior is undefined. Undefined behavior is otherwise
935 indicated in this International Standard by the words ''undefined behavior'' or by the
936 omission of any explicit definition of behavior. There is no difference in emphasis among
937 these three; they all describe ''behavior that is undefined''.
938 3 A program that is correct in all other aspects, operating on correct data, containing
939 unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
940 4 The implementation shall not successfully translate a preprocessing translation unit
941 containing a #error preprocessing directive unless it is part of a group skipped by
942 conditional inclusion.
943 5 A strictly conforming program shall use only those features of the language and library
944 specified in this International Standard.3) It shall not produce output dependent on any
945 unspecified, undefined, or implementation-defined behavior, and shall not exceed any
946 minimum implementation limit.
947 6 The two forms of conforming implementation are hosted and freestanding. A conforming
948 hosted implementation shall accept any strictly conforming program. A conforming
949 freestanding implementation shall accept any strictly conforming program that does not
950 use complex types and in which the use of the features specified in the library clause
951 (clause 7) is confined to the contents of the standard headers <float.h>,
952 <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>,
953 <stddef.h>, and <stdint.h>. A conforming implementation may have extensions
954 (including additional library functions), provided they do not alter the behavior of any
955 strictly conforming program.4)
959 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
960 by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
961 #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
963 fesetround(FE_UPWARD);
967 4) This implies that a conforming implementation reserves no identifiers other than those explicitly
968 reserved in this International Standard.
972 7 A conforming program is one that is acceptable to a conforming implementation.5)
973 8 An implementation shall be accompanied by a document that defines all implementation-
974 defined and locale-specific characteristics and all extensions.
975 Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
976 characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
977 (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15),
978 variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h>
979 (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20).
984 5) Strictly conforming programs are intended to be maximally portable among conforming
985 implementations. Conforming programs may depend upon nonportable features of a conforming
992 1 An implementation translates C source files and executes C programs in two data-
993 processing-system environments, which will be called the translation environment and
994 the execution environment in this International Standard. Their characteristics define and
995 constrain the results of executing conforming C programs constructed according to the
996 syntactic and semantic rules for conforming implementations.
997 Forward references: In this clause, only a few of many possible forward references
999 5.1 Conceptual models
1000 5.1.1 Translation environment
1001 5.1.1.1 Program structure
1002 1 A C program need not all be translated at the same time. The text of the program is kept
1003 in units called source files, (or preprocessing files) in this International Standard. A
1004 source file together with all the headers and source files included via the preprocessing
1005 directive #include is known as a preprocessing translation unit. After preprocessing, a
1006 preprocessing translation unit is called a translation unit. Previously translated translation
1007 units may be preserved individually or in libraries. The separate translation units of a
1008 program communicate by (for example) calls to functions whose identifiers have external
1009 linkage, manipulation of objects whose identifiers have external linkage, or manipulation
1010 of data files. Translation units may be separately translated and then later linked to
1011 produce an executable program.
1012 Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
1013 preprocessing directives (6.10).
1014 5.1.1.2 Translation phases
1015 1 The precedence among the syntax rules of translation is specified by the following
1017 1. Physical source file multibyte characters are mapped, in an implementation-
1018 defined manner, to the source character set (introducing new-line characters for
1019 end-of-line indicators) if necessary. Trigraph sequences are replaced by
1020 corresponding single-character internal representations.
1024 6) Implementations shall behave as if these separate phases occur, even though many are typically folded
1025 together in practice. Source files, translation units, and translated translation units need not
1026 necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
1027 and any external representation. The description is conceptual only, and does not specify any
1028 particular implementation.
1032 2. Each instance of a backslash character (\) immediately followed by a new-line
1033 character is deleted, splicing physical source lines to form logical source lines.
1034 Only the last backslash on any physical source line shall be eligible for being part
1035 of such a splice. A source file that is not empty shall end in a new-line character,
1036 which shall not be immediately preceded by a backslash character before any such
1037 splicing takes place.
1038 3. The source file is decomposed into preprocessing tokens7) and sequences of
1039 white-space characters (including comments). A source file shall not end in a
1040 partial preprocessing token or in a partial comment. Each comment is replaced by
1041 one space character. New-line characters are retained. Whether each nonempty
1042 sequence of white-space characters other than new-line is retained or replaced by
1043 one space character is implementation-defined.
1044 4. Preprocessing directives are executed, macro invocations are expanded, and
1045 _Pragma unary operator expressions are executed. If a character sequence that
1046 matches the syntax of a universal character name is produced by token
1047 concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
1048 directive causes the named header or source file to be processed from phase 1
1049 through phase 4, recursively. All preprocessing directives are then deleted.
1050 5. Each source character set member and escape sequence in character constants and
1051 string literals is converted to the corresponding member of the execution character
1052 set; if there is no corresponding member, it is converted to an implementation-
1053 defined member other than the null (wide) character.8)
1054 6. Adjacent string literal tokens are concatenated.
1055 7. White-space characters separating tokens are no longer significant. Each
1056 preprocessing token is converted into a token. The resulting tokens are
1057 syntactically and semantically analyzed and translated as a translation unit.
1058 8. All external object and function references are resolved. Library components are
1059 linked to satisfy external references to functions and objects not defined in the
1060 current translation. All such translator output is collected into a program image
1061 which contains information needed for execution in its execution environment.
1062 Forward references: universal character names (6.4.3), lexical elements (6.4),
1063 preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).
1067 7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is
1068 context-dependent. For example, see the handling of < within a #include preprocessing directive.
1069 8) An implementation need not convert all non-corresponding source characters to the same execution
1075 1 A conforming implementation shall produce at least one diagnostic message (identified in
1076 an implementation-defined manner) if a preprocessing translation unit or translation unit
1077 contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
1078 specified as undefined or implementation-defined. Diagnostic messages need not be
1079 produced in other circumstances.9)
1080 2 EXAMPLE An implementation shall issue a diagnostic for the translation unit:
1083 because in those cases where wording in this International Standard describes the behavior for a construct
1084 as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.
1086 5.1.2 Execution environments
1087 1 Two execution environments are defined: freestanding and hosted. In both cases,
1088 program startup occurs when a designated C function is called by the execution
1089 environment. All objects with static storage duration shall be initialized (set to their
1090 initial values) before program startup. The manner and timing of such initialization are
1091 otherwise unspecified. Program termination returns control to the execution
1093 Forward references: storage durations of objects (6.2.4), initialization (6.7.9).
1094 5.1.2.1 Freestanding environment
1095 1 In a freestanding environment (in which C program execution may take place without any
1096 benefit of an operating system), the name and type of the function called at program
1097 startup are implementation-defined. Any library facilities available to a freestanding
1098 program, other than the minimal set required by clause 4, are implementation-defined.
1099 2 The effect of program termination in a freestanding environment is implementation-
1101 5.1.2.2 Hosted environment
1102 1 A hosted environment need not be provided, but shall conform to the following
1103 specifications if present.
1108 9) The intent is that an implementation should identify the nature of, and where possible localize, each
1109 violation. Of course, an implementation is free to produce any number of diagnostics as long as a
1110 valid program is still correctly translated. It may also successfully translate an invalid program.
1114 5.1.2.2.1 Program startup
1115 1 The function called at program startup is named main. The implementation declares no
1116 prototype for this function. It shall be defined with a return type of int and with no
1118 int main(void) { /* ... */ }
1119 or with two parameters (referred to here as argc and argv, though any names may be
1120 used, as they are local to the function in which they are declared):
1121 int main(int argc, char *argv[]) { /* ... */ }
1122 or equivalent;10) or in some other implementation-defined manner.
1123 2 If they are declared, the parameters to the main function shall obey the following
1125 -- The value of argc shall be nonnegative.
1126 -- argv[argc] shall be a null pointer.
1127 -- If the value of argc is greater than zero, the array members argv[0] through
1128 argv[argc-1] inclusive shall contain pointers to strings, which are given
1129 implementation-defined values by the host environment prior to program startup. The
1130 intent is to supply to the program information determined prior to program startup
1131 from elsewhere in the hosted environment. If the host environment is not capable of
1132 supplying strings with letters in both uppercase and lowercase, the implementation
1133 shall ensure that the strings are received in lowercase.
1134 -- If the value of argc is greater than zero, the string pointed to by argv[0]
1135 represents the program name; argv[0][0] shall be the null character if the
1136 program name is not available from the host environment. If the value of argc is
1137 greater than one, the strings pointed to by argv[1] through argv[argc-1]
1138 represent the program parameters.
1139 -- The parameters argc and argv and the strings pointed to by the argv array shall
1140 be modifiable by the program, and retain their last-stored values between program
1141 startup and program termination.
1142 5.1.2.2.2 Program execution
1143 1 In a hosted environment, a program may use all the functions, macros, type definitions,
1144 and objects described in the library clause (clause 7).
1149 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
1150 char ** argv, and so on.
1154 5.1.2.2.3 Program termination
1155 1 If the return type of the main function is a type compatible with int, a return from the
1156 initial call to the main function is equivalent to calling the exit function with the value
1157 returned by the main function as its argument;11) reaching the } that terminates the
1158 main function returns a value of 0. If the return type is not compatible with int, the
1159 termination status returned to the host environment is unspecified.
1160 Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).
1161 5.1.2.3 Program execution
1162 1 The semantic descriptions in this International Standard describe the behavior of an
1163 abstract machine in which issues of optimization are irrelevant.
1164 2 Accessing a volatile object, modifying an object, modifying a file, or calling a function
1165 that does any of those operations are all side effects,12) which are changes in the state of
1166 the execution environment. Evaluation of an expression in general includes both value
1167 computations and initiation of side effects. Value computation for an lvalue expression
1168 includes determining the identity of the designated object.
1169 3 Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
1170 executed by a single thread, which induces a partial order among those evaluations.
1171 Given any two evaluations A and B, if A is sequenced before B, then the execution of A
1172 shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
1173 sequenced after A.) If A is not sequenced before or after B, then A and B are
1174 unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced
1175 either before or after B, but it is unspecified which.13) The presence of a sequence point
1176 between the evaluation of expressions A and B implies that every value computation and
1177 side effect associated with A is sequenced before every value computation and side effect
1178 associated with B. (A summary of the sequence points is given in annex C.)
1179 4 In the abstract machine, all expressions are evaluated as specified by the semantics. An
1180 actual implementation need not evaluate part of an expression if it can deduce that its
1181 value is not used and that no needed side effects are produced (including any caused by
1183 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
1184 will have ended in the former case, even where they would not have in the latter.
1185 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
1186 flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
1187 values of floating-point operations. Implementations that support such floating-point state are
1188 required to regard changes to it as side effects -- see annex F for details. The floating-point
1189 environment library <fenv.h> provides a programming facility for indicating when these side
1190 effects matter, freeing the implementations in other cases.
1191 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations
1192 cannot interleave, but can be executed in any order.
1196 calling a function or accessing a volatile object).
1197 5 When the processing of the abstract machine is interrupted by receipt of a signal, the
1198 values of objects that are neither lock-free atomic objects nor of type volatile
1199 sig_atomic_t are unspecified, and the value of any object that is modified by the
1200 handler that is neither a lock-free atomic object nor of type volatile
1201 sig_atomic_t becomes undefined.
1202 6 The least requirements on a conforming implementation are:
1203 -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract
1205 -- At program termination, all data written into files shall be identical to the result that
1206 execution of the program according to the abstract semantics would have produced.
1207 -- The input and output dynamics of interactive devices shall take place as specified in
1208 7.21.3. The intent of these requirements is that unbuffered or line-buffered output
1209 appear as soon as possible, to ensure that prompting messages actually appear prior to
1210 a program waiting for input.
1211 This is the observable behavior of the program.
1212 7 What constitutes an interactive device is implementation-defined.
1213 8 More stringent correspondences between abstract and actual semantics may be defined by
1214 each implementation.
1215 9 EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
1216 semantics: at every sequence point, the values of the actual objects would agree with those specified by the
1217 abstract semantics. The keyword volatile would then be redundant.
1218 10 Alternatively, an implementation might perform various optimizations within each translation unit, such
1219 that the actual semantics would agree with the abstract semantics only when making function calls across
1220 translation unit boundaries. In such an implementation, at the time of each function entry and function
1221 return where the calling function and the called function are in different translation units, the values of all
1222 externally linked objects and of all objects accessible via pointers therein would agree with the abstract
1223 semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
1224 function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
1225 type of implementation, objects referred to by interrupt service routines activated by the signal function
1226 would require explicit specification of volatile storage, as well as other implementation-defined
1229 11 EXAMPLE 2 In executing the fragment
1233 the ''integer promotions'' require that the abstract machine promote the value of each variable to int size
1234 and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
1235 overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
1236 produce the same result, possibly omitting the promotions.
1240 12 EXAMPLE 3 Similarly, in the fragment
1245 the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
1246 that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
1247 were replaced by the constant 2.0, which has type double).
1249 13 EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
1250 semantics. Values are independent of whether they are represented in a register or in memory. For
1251 example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
1252 is required to round to the precision of the storage type. In particular, casts and assignments are required to
1253 perform their specified conversion. For the fragment
1256 d1 = f = expression;
1257 d2 = (float) expression;
1258 the values assigned to d1 and d2 are required to have been converted to float.
1260 14 EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
1261 precision as well as range. The implementation cannot generally apply the mathematical associative rules
1262 for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
1263 overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
1264 rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
1265 numbers are often not valid (see F.9).
1268 x = (x * y) * z; // not equivalent to x *= y * z;
1269 z = (x - y) + y ; // not equivalent to z = x;
1270 z = x + x * y; // not equivalent to z = x * (1.0 + y);
1271 y = x / 5.0; // not equivalent to y = x * 0.2;
1273 15 EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment
1276 a = a + 32760 + b + 5;
1277 the expression statement behaves exactly the same as
1278 a = (((a + 32760) + b) + 5);
1279 due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
1280 next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
1281 which overflows produce an explicit trap and in which the range of values representable by an int is
1282 [-32768, +32767], the implementation cannot rewrite this expression as
1283 a = ((a + b) + 32765);
1284 since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap
1285 while the original expression would not; nor can the expression be rewritten either as
1290 a = ((a + 32765) + b);
1292 a = (a + (b + 32765));
1293 since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine
1294 in which overflow silently generates some value and where positive and negative overflows cancel, the
1295 above expression statement can be rewritten by the implementation in any of the above ways because the
1296 same result will occur.
1298 16 EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the
1304 sum = sum * 10 - '0' + (*p++ = getchar());
1305 the expression statement is grouped as if it were written as
1306 sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
1307 but the actual increment of p can occur at any time between the previous sequence point and the next
1308 sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
1311 Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the
1312 signal function (7.14), files (7.21.3).
1313 5.1.2.4 Multi-threaded executions and data races
1314 1 Under a hosted implementation, a program can have more than one thread of execution
1315 (or thread) running concurrently. The execution of each thread proceeds as defined by
1316 the remainder of this standard. The execution of the entire program consists of an
1317 execution of all of its threads.14) Under a freestanding implementation, it is
1318 implementation-defined whether a program can have more than one thread of execution.
1319 2 The value of an object visible to a thread T at a particular point is the initial value of the
1320 object, a value stored in the object by T , or a value stored in the object by another thread,
1321 according to the rules below.
1322 3 NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
1323 the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
1324 implicitly supports a simpler view for more restricted programs.
1326 4 Two expression evaluations conflict if one of them modifies a memory location and the
1327 other one accesses or modifies the same memory location.
1332 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
1333 atomic operations, for example, allow executions inconsistent with a simple interleaving as described
1338 5 The library defines a number of atomic operations (7.17) and operations on mutexes
1339 (7.25.4) that are specially identified as synchronization operations. These operations play
1340 a special role in making assignments in one thread visible to another. A synchronization
1341 operation on one or more memory locations is either an acquire operation, a release
1342 operation, both an acquire and release operation, or a consume operation. A
1343 synchronization operation without an associated memory location is a fence and can be
1344 either an acquire fence, a release fence, or both an acquire and release fence. In addition,
1345 there are relaxed atomic operations, which are not synchronization operations, and
1346 atomic read-modify-write operations, which have special characteristics.
1347 6 NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
1348 composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
1349 operation on those same locations. Informally, performing a release operation on A forces prior side effects
1350 on other memory locations to become visible to other threads that later perform an acquire or consume
1351 operation on A. We do not include relaxed atomic operations as synchronization operations although, like
1352 synchronization operations, they cannot contribute to data races.
1354 7 All modifications to a particular atomic object M occur in some particular total order,
1355 called the modification order of M. If A and B are modifications of an atomic object M,
1356 and A happens before B, then A shall precede B in the modification order of M, which is
1358 8 NOTE 3 This states that the modification orders must respect the ''happens before'' relation.
1360 9 NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
1361 combined into a single total order for all objects. In general this will be impossible since different threads
1362 may observe modifications to different variables in inconsistent orders.
1364 10 A release sequence on an atomic object M is a maximal contiguous sub-sequence of side
1365 effects in the modification order of M, where the first operation is a release and every
1366 subsequent operation either is performed by the same thread that performed the release or
1367 is an atomic read-modify-write operation.
1368 11 Certain library calls synchronize with other library calls performed by another thread. In
1369 particular, an atomic operation A that performs a release operation on an object M
1370 synchronizes with an atomic operation B that performs an acquire operation on M and
1371 reads a value written by any side effect in the release sequence headed by A.
1372 12 NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
1373 described below. Such a requirement would sometimes interfere with efficient implementation.
1375 13 NOTE 6 The specifications of the synchronization operations define when one reads the value written by
1376 another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
1377 order. Each mutex acquisition ''reads the value written'' by the last mutex release.
1379 14 An evaluation A carries a dependency 15) to an evaluation B if:
1382 15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly
1383 strictly intra-thread.
1387 -- the value of A is used as an operand of B, unless:
1388 o B is an invocation of the kill_dependency macro,
1390 o A is the left operand of a && or || operator,
1392 o A is the left operand of a ? : operator, or
1394 o A is the left operand of a , operator;
1396 -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A
1397 is sequenced before B, or
1398 -- for some evaluation X, A carries a dependency to X and X carries a dependency to B.
1399 15 An evaluation A is dependency-ordered before16) an evaluation B if:
1400 -- A performs a release operation on an atomic object M, and B performs a consume
1401 operation on M and reads a value written by any side effect in the release sequence
1403 -- for some evaluation X, A is dependency-ordered before X and X carries a
1405 16 An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
1406 is dependency-ordered before B, or, for some evaluation X:
1407 -- A synchronizes with X and X is sequenced before B,
1408 -- A is sequenced before X and X inter-thread happens before B, or
1409 -- A inter-thread happens before X and X inter-thread happens before B.
1410 17 NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced
1411 before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The
1412 first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed
1413 by ''sequenced before''. The reason for this limitation is that a consume operation participating in a
1414 ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this
1415 consume operation actually carries a dependency. The reason that this limitation applies only to the end of
1416 such a concatenation is that any subsequent release operation will provide the required ordering for a prior
1417 consume operation. The second exception is that a concatenation is not permitted to consist entirely of
1418 ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be
1419 transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships
1420 consisting entirely of ''sequenced before''.
1422 18 An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
1423 thread happens before B.
1427 16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses
1428 release/consume in place of release/acquire.
1432 19 A visible side effect A on an object M with respect to a value computation B of M
1433 satisfies the conditions:
1434 -- A happens before B, and
1435 -- there is no other side effect X to M such that A happens before X and X happens
1437 The value of a non-atomic scalar object M, as determined by evaluation B, shall be the
1438 value stored by the visible side effect A.
1439 20 NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
1440 race and the behavior is undefined.
1442 21 NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
1443 detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
1444 restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
1447 22 The visible sequence of side effects on an atomic object M, with respect to a value
1448 computation B of M, is a maximal contiguous sub-sequence of side effects in the
1449 modification order of M, where the first side effect is visible with respect to B, and for
1450 every subsequent side effect, it is not the case that B happens before it. The value of an
1451 atomic object M, as determined by evaluation B, shall be the value stored by some
1452 operation in the visible sequence of M with respect to B. Furthermore, if a value
1453 computation A of an atomic object M happens before a value computation B of M, and
1454 the value computed by A corresponds to the value stored by side effect X, then the value
1455 computed by B shall either equal the value computed by A, or be the value stored by side
1456 effect Y , where Y follows X in the modification order of M.
1457 23 NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
1458 both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee
1459 provided by most hardware available to C atomic operations.
1461 24 NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the
1462 values observed by loads of atomics, which we are restricting here. The intended reading is that there must
1463 exist an association of atomic loads with modifications they observe that, together with suitably chosen
1464 modification orders and the ''happens before'' relation derived as described above, satisfy the resulting
1465 constraints as imposed here.
1467 25 The execution of a program contains a data race if it contains two conflicting actions in
1468 different threads, at least one of which is not atomic, and neither happens before the
1469 other. Any such data race results in undefined behavior.
1470 26 NOTE 12 It can be shown that programs that correctly use simple mutexes and
1471 memory_order_seq_cst operations to prevent all data races, and use no other synchronization
1472 operations, behave as though the operations executed by their constituent threads were simply interleaved,
1473 with each value computation of an object being the last value stored in that interleaving. This is normally
1474 referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data-
1475 race-free programs cannot observe most program transformations that do not change single-threaded
1476 program semantics. In fact, most single-threaded program transformations continue to be allowed, since
1477 any program that behaves differently as a result must contain undefined behavior.
1481 27 NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
1482 that would not be modified by the abstract machine are generally precluded by this standard, since such an
1483 assignment might overwrite another assignment by a different thread in cases in which an abstract machine
1484 execution would not have encountered a data race. This includes implementations of data member
1485 assignment that overwrite adjacent members in separate memory locations. We also generally preclude
1486 reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
1487 "visible sequence" rules.
1489 28 NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
1490 not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
1491 race. However, they are typically valid in the context of an optimizing compiler that targets a specific
1492 machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
1493 is not tolerant of races or provides hardware race detection.
1500 5.2 Environmental considerations
1501 5.2.1 Character sets
1502 1 Two sets of characters and their associated collating sequences shall be defined: the set in
1503 which source files are written (the source character set), and the set interpreted in the
1504 execution environment (the execution character set). Each set is further divided into a
1505 basic character set, whose contents are given by this subclause, and a set of zero or more
1506 locale-specific members (which are not members of the basic character set) called
1507 extended characters. The combined set is also called the extended character set. The
1508 values of the members of the execution character set are implementation-defined.
1509 2 In a character constant or string literal, members of the execution character set shall be
1510 represented by corresponding members of the source character set or by escape
1511 sequences consisting of the backslash \ followed by one or more characters. A byte with
1512 all bits set to 0, called the null character, shall exist in the basic execution character set; it
1513 is used to terminate a character string.
1514 3 Both the basic source and basic execution character sets shall have the following
1515 members: the 26 uppercase letters of the Latin alphabet
1516 A B C D E F G H I J K L M
1517 N O P Q R S T U V W X Y Z
1518 the 26 lowercase letters of the Latin alphabet
1519 a b c d e f g h i j k l m
1520 n o p q r s t u v w x y z
1521 the 10 decimal digits
1523 the following 29 graphic characters
1524 ! " # % & ' ( ) * + , - . / :
1525 ; < = > ? [ \ ] ^ _ { | } ~
1526 the space character, and control characters representing horizontal tab, vertical tab, and
1527 form feed. The representation of each member of the source and execution basic
1528 character sets shall fit in a byte. In both the source and execution basic character sets, the
1529 value of each character after 0 in the above list of decimal digits shall be one greater than
1530 the value of the previous. In source files, there shall be some way of indicating the end of
1531 each line of text; this International Standard treats such an end-of-line indicator as if it
1532 were a single new-line character. In the basic execution character set, there shall be
1533 control characters representing alert, backspace, carriage return, and new line. If any
1534 other characters are encountered in a source file (except in an identifier, a character
1535 constant, a string literal, a header name, a comment, or a preprocessing token that is never
1539 converted to a token), the behavior is undefined.
1540 4 A letter is an uppercase letter or a lowercase letter as defined above; in this International
1541 Standard the term does not include other characters that are letters in other alphabets.
1542 5 The universal character name construct provides a way to name other characters.
1543 Forward references: universal character names (6.4.3), character constants (6.4.4.4),
1544 preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
1545 5.2.1.1 Trigraph sequences
1546 1 Before any other processing takes place, each occurrence of one of the following
1547 sequences of three characters (called trigraph sequences17)) is replaced with the
1548 corresponding single character.
1552 No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
1553 above is not changed.
1555 ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
1557 #define arraycheck(a, b) a[b] || b[a]
1559 3 EXAMPLE 2 The following source line
1561 becomes (after replacement of the trigraph sequence ??/)
1564 5.2.1.2 Multibyte characters
1565 1 The source character set may contain multibyte characters, used to represent members of
1566 the extended character set. The execution character set may also contain multibyte
1567 characters, which need not have the same encoding as for the source character set. For
1568 both character sets, the following shall hold:
1569 -- The basic character set shall be present and each character shall be encoded as a
1571 -- The presence, meaning, and representation of any additional members is locale-
1574 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
1575 described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.
1579 -- A multibyte character set may have a state-dependent encoding, wherein each
1580 sequence of multibyte characters begins in an initial shift state and enters other
1581 locale-specific shift states when specific multibyte characters are encountered in the
1582 sequence. While in the initial shift state, all single-byte characters retain their usual
1583 interpretation and do not alter the shift state. The interpretation for subsequent bytes
1584 in the sequence is a function of the current shift state.
1585 -- A byte with all bits zero shall be interpreted as a null character independent of shift
1586 state. Such a byte shall not occur as part of any other multibyte character.
1587 2 For source files, the following shall hold:
1588 -- An identifier, comment, string literal, character constant, or header name shall begin
1589 and end in the initial shift state.
1590 -- An identifier, comment, string literal, character constant, or header name shall consist
1591 of a sequence of valid multibyte characters.
1592 5.2.2 Character display semantics
1593 1 The active position is that location on a display device where the next character output by
1594 the fputc function would appear. The intent of writing a printing character (as defined
1595 by the isprint function) to a display device is to display a graphic representation of
1596 that character at the active position and then advance the active position to the next
1597 position on the current line. The direction of writing is locale-specific. If the active
1598 position is at the final position of a line (if there is one), the behavior of the display device
1600 2 Alphabetic escape sequences representing nongraphic characters in the execution
1601 character set are intended to produce actions on display devices as follows:
1602 \a (alert) Produces an audible or visible alert without changing the active position.
1603 \b (backspace) Moves the active position to the previous position on the current line. If
1604 the active position is at the initial position of a line, the behavior of the display
1605 device is unspecified.
1606 \f ( form feed) Moves the active position to the initial position at the start of the next
1608 \n (new line) Moves the active position to the initial position of the next line.
1609 \r (carriage return) Moves the active position to the initial position of the current line.
1610 \t (horizontal tab) Moves the active position to the next horizontal tabulation position
1611 on the current line. If the active position is at or past the last defined horizontal
1612 tabulation position, the behavior of the display device is unspecified.
1613 \v (vertical tab) Moves the active position to the initial position of the next vertical
1614 tabulation position. If the active position is at or past the last defined vertical
1617 tabulation position, the behavior of the display device is unspecified.
1618 3 Each of these escape sequences shall produce a unique implementation-defined value
1619 which can be stored in a single char object. The external representations in a text file
1620 need not be identical to the internal representations, and are outside the scope of this
1621 International Standard.
1622 Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).
1623 5.2.3 Signals and interrupts
1624 1 Functions shall be implemented such that they may be interrupted at any time by a signal,
1625 or may be called by a signal handler, or both, with no alteration to earlier, but still active,
1626 invocations' control flow (after the interruption), function return values, or objects with
1627 automatic storage duration. All such objects shall be maintained outside the function
1628 image (the instructions that compose the executable representation of a function) on a
1629 per-invocation basis.
1630 5.2.4 Environmental limits
1631 1 Both the translation and execution environments constrain the implementation of
1632 language translators and libraries. The following summarizes the language-related
1633 environmental limits on a conforming implementation; the library-related limits are
1634 discussed in clause 7.
1635 5.2.4.1 Translation limits
1636 1 The implementation shall be able to translate and execute at least one program that
1637 contains at least one instance of every one of the following limits:18)
1638 -- 127 nesting levels of blocks
1639 -- 63 nesting levels of conditional inclusion
1640 -- 12 pointer, array, and function declarators (in any combinations) modifying an
1641 arithmetic, structure, union, or void type in a declaration
1642 -- 63 nesting levels of parenthesized declarators within a full declarator
1643 -- 63 nesting levels of parenthesized expressions within a full expression
1644 -- 63 significant initial characters in an internal identifier or a macro name (each
1645 universal character name or extended source character is considered a single
1647 -- 31 significant initial characters in an external identifier (each universal character name
1648 specifying a short identifier of 0000FFFF or less is considered 6 characters, each
1651 18) Implementations should avoid imposing fixed translation limits whenever possible.
1655 universal character name specifying a short identifier of 00010000 or more is
1656 considered 10 characters, and each extended source character is considered the same
1657 number of characters as the corresponding universal character name, if any)19)
1658 -- 4095 external identifiers in one translation unit
1659 -- 511 identifiers with block scope declared in one block
1660 -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
1661 -- 127 parameters in one function definition
1662 -- 127 arguments in one function call
1663 -- 127 parameters in one macro definition
1664 -- 127 arguments in one macro invocation
1665 -- 4095 characters in a logical source line
1666 -- 4095 characters in a string literal (after concatenation)
1667 -- 65535 bytes in an object (in a hosted environment only)
1668 -- 15 nesting levels for #included files
1669 -- 1023 case labels for a switch statement (excluding those for any nested switch
1671 -- 1023 members in a single structure or union
1672 -- 1023 enumeration constants in a single enumeration
1673 -- 63 levels of nested structure or union definitions in a single struct-declaration-list
1674 5.2.4.2 Numerical limits
1675 1 An implementation is required to document all the limits specified in this subclause,
1676 which are specified in the headers <limits.h> and <float.h>. Additional limits are
1677 specified in <stdint.h>.
1678 Forward references: integer types <stdint.h> (7.20).
1679 5.2.4.2.1 Sizes of integer types <limits.h>
1680 1 The values given below shall be replaced by constant expressions suitable for use in #if
1681 preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
1682 following shall be replaced by expressions that have the same type as would an
1683 expression that is an object of the corresponding type converted according to the integer
1684 promotions. Their implementation-defined values shall be equal or greater in magnitude
1687 19) See ''future language directions'' (6.11.3).
1691 (absolute value) to those shown, with the same sign.
1692 -- number of bits for smallest object that is not a bit-field (byte)
1694 -- minimum value for an object of type signed char
1695 SCHAR_MIN -127 // -(27 - 1)
1696 -- maximum value for an object of type signed char
1697 SCHAR_MAX +127 // 27 - 1
1698 -- maximum value for an object of type unsigned char
1699 UCHAR_MAX 255 // 28 - 1
1700 -- minimum value for an object of type char
1702 -- maximum value for an object of type char
1704 -- maximum number of bytes in a multibyte character, for any supported locale
1706 -- minimum value for an object of type short int
1707 SHRT_MIN -32767 // -(215 - 1)
1708 -- maximum value for an object of type short int
1709 SHRT_MAX +32767 // 215 - 1
1710 -- maximum value for an object of type unsigned short int
1711 USHRT_MAX 65535 // 216 - 1
1712 -- minimum value for an object of type int
1713 INT_MIN -32767 // -(215 - 1)
1714 -- maximum value for an object of type int
1715 INT_MAX +32767 // 215 - 1
1716 -- maximum value for an object of type unsigned int
1717 UINT_MAX 65535 // 216 - 1
1718 -- minimum value for an object of type long int
1719 LONG_MIN -2147483647 // -(231 - 1)
1720 -- maximum value for an object of type long int
1721 LONG_MAX +2147483647 // 231 - 1
1722 -- maximum value for an object of type unsigned long int
1723 ULONG_MAX 4294967295 // 232 - 1
1728 -- minimum value for an object of type long long int
1729 LLONG_MIN -9223372036854775807 // -(263 - 1)
1730 -- maximum value for an object of type long long int
1731 LLONG_MAX +9223372036854775807 // 263 - 1
1732 -- maximum value for an object of type unsigned long long int
1733 ULLONG_MAX 18446744073709551615 // 264 - 1
1734 2 If the value of an object of type char is treated as a signed integer when used in an
1735 expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
1736 value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
1737 CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
1738 UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1.
1739 Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).
1740 5.2.4.2.2 Characteristics of floating types <float.h>
1741 1 The characteristics of floating types are defined in terms of a model that describes a
1742 representation of floating-point numbers and values that provide information about an
1743 implementation's floating-point arithmetic.21) The following parameters are used to
1744 define the model for each floating-point type:
1746 b base or radix of exponent representation (an integer > 1)
1747 e exponent (an integer between a minimum emin and a maximum emax )
1748 p precision (the number of base-b digits in the significand)
1749 fk nonnegative integers less than b (the significand digits)
1750 2 A floating-point number (x) is defined by the following model:
1752 x = sb e (Sum) f k b-k ,
1756 3 In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be
1757 able to contain other kinds of floating-point numbers, such as subnormal floating-point
1758 numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0,
1759 e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
1760 NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
1761 through almost every arithmetic operation without raising a floating-point exception; a
1762 signaling NaN generally raises a floating-point exception when occurring as an
1766 21) The floating-point model is intended to clarify the description of each floating-point characteristic and
1767 does not require the floating-point arithmetic of the implementation to be identical.
1771 arithmetic operand.22)
1772 4 An implementation may give zero and non-numeric values (such as infinities and NaNs) a
1773 sign or may leave them unsigned. Wherever such values are unsigned, any requirement
1774 in this International Standard to retrieve the sign shall produce an unspecified sign, and
1775 any requirement to set the sign shall be ignored.
1776 5 The minimum range of representable values for a floating type is the most negative finite
1777 floating-point number representable in that type through the most positive finite floating-
1778 point number representable in that type. In addition, if negative infinity is representable
1779 in a type, the range of that type is extended to all negative real numbers; likewise, if
1780 positive infinity is representable in a type, the range of that type is extended to all positive
1782 6 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
1783 <math.h> and <complex.h> that return floating-point results is implementation-
1784 defined, as is the accuracy of the conversion between floating-point internal
1785 representations and string representations performed by the library functions in
1786 <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
1787 accuracy is unknown.
1788 7 All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
1789 expressions suitable for use in #if preprocessing directives; all floating values shall be
1790 constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
1791 and FLT_ROUNDS have separate names for all three floating-point types. The floating-
1792 point model representation is provided for all values except FLT_EVAL_METHOD and
1794 8 The rounding mode for floating-point addition is characterized by the implementation-
1795 defined value of FLT_ROUNDS:23)
1799 2 toward positive infinity
1800 3 toward negative infinity
1801 All other values for FLT_ROUNDS characterize implementation-defined rounding
1805 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
1806 IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
1808 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
1809 the function fesetround in <fenv.h>.
1813 9 Except for assignment and cast (which remove all extra range and precision), the values
1814 yielded by operators with floating operands and values subject to the usual arithmetic
1815 conversions and of floating constants are evaluated to a format whose range and precision
1816 may be greater than required by the type. The use of evaluation formats is characterized
1817 by the implementation-defined value of FLT_EVAL_METHOD:24)
1819 0 evaluate all operations and constants just to the range and precision of the
1821 1 evaluate operations and constants of type float and double to the
1822 range and precision of the double type, evaluate long double
1823 operations and constants to the range and precision of the long double
1825 2 evaluate all operations and constants to the range and precision of the
1827 All other negative values for FLT_EVAL_METHOD characterize implementation-defined
1829 10 The presence or absence of subnormal numbers is characterized by the implementation-
1830 defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and
1832 -1 indeterminable25)
1833 0 absent26) (type does not support subnormal numbers)
1834 1 present (type does support subnormal numbers)
1835 11 The values given in the following list shall be replaced by constant expressions with
1836 implementation-defined values that are greater or equal in magnitude (absolute value) to
1837 those shown, with the same sign:
1838 -- radix of exponent representation, b
1844 24) The evaluation method determines evaluation formats of expressions involving all floating types, not
1845 just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
1846 _Complex operands is represented in the double _Complex format, and its parts are evaluated to
1848 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
1849 subnormal representations as zero, nor as nonzero.
1850 26) Characterization as absent is intended if no floating-point operations produce subnormal results from
1851 non-subnormal inputs, even if the type format includes representations of subnormal numbers.
1855 -- number of base-FLT_RADIX digits in the floating-point significand, p
1859 -- number of decimal digits, n, such that any floating-point number with p radix b digits
1860 can be rounded to a floating-point number with n decimal digits and back again
1861 without change to the value,
1862 { p log10 b if b is a power of 10
1864 { [^1 + p log10 b^] otherwise
1868 -- number of decimal digits, n, such that any floating-point number in the widest
1869 supported floating type with pmax radix b digits can be rounded to a floating-point
1870 number with n decimal digits and back again without change to the value,
1871 { pmax log10 b if b is a power of 10
1873 { [^1 + pmax log10 b^] otherwise
1875 -- number of decimal digits, q, such that any floating-point number with q decimal digits
1876 can be rounded into a floating-point number with p radix b digits and back again
1877 without change to the q decimal digits,
1878 { p log10 b if b is a power of 10
1880 { [_( p - 1) log10 b_] otherwise
1884 -- minimum negative integer such that FLT_RADIX raised to one less than that power is
1885 a normalized floating-point number, emin
1895 -- minimum negative integer such that 10 raised to that power is in the range of
1896 normalized floating-point numbers, [^log10 b emin -1 ^]
1901 -- maximum integer such that FLT_RADIX raised to one less than that power is a
1902 representable finite floating-point number, emax
1906 -- maximum integer such that 10 raised to that power is in the range of representable
1907 finite floating-point numbers, [_log10 ((1 - b- p )b emax )_]
1911 12 The values given in the following list shall be replaced by constant expressions with
1912 implementation-defined values that are greater than or equal to those shown:
1913 -- maximum representable finite floating-point number, (1 - b- p )b emax
1917 13 The values given in the following list shall be replaced by constant expressions with
1918 implementation-defined (positive) values that are less than or equal to those shown:
1919 -- the difference between 1 and the least value greater than 1 that is representable in the
1920 given floating point type, b1- p
1924 -- minimum normalized positive floating-point number, b emin -1
1934 -- minimum positive floating-point number27)
1938 Recommended practice
1939 14 Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
1940 should be the identity function.
1941 15 EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
1942 requirements of this International Standard, and the appropriate values in a <float.h> header for type
1945 x = s16e (Sum) f k 16-k ,
1951 FLT_EPSILON 9.53674316E-07F
1955 FLT_MIN 2.93873588E-39F
1958 FLT_MAX 3.40282347E+38F
1961 16 EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
1962 single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a
1963 <float.h> header for types float and double:
1965 x f = s2e (Sum) f k 2-k ,
1970 x d = s2e (Sum) f k 2-k ,
1977 FLT_EPSILON 1.19209290E-07F // decimal constant
1978 FLT_EPSILON 0X1P-23F // hex constant
1982 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
1983 positive number no greater than the minimum normalized positive number for the type.
1984 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
1985 limits are one less than shown here.
1991 FLT_MIN 1.17549435E-38F // decimal constant
1992 FLT_MIN 0X1P-126F // hex constant
1993 FLT_TRUE_MIN 1.40129846E-45F // decimal constant
1994 FLT_TRUE_MIN 0X1P-149F // hex constant
1998 FLT_MAX 3.40282347E+38F // decimal constant
1999 FLT_MAX 0X1.fffffeP127F // hex constant
2002 DBL_EPSILON 2.2204460492503131E-16 // decimal constant
2003 DBL_EPSILON 0X1P-52 // hex constant
2007 DBL_MIN 2.2250738585072014E-308 // decimal constant
2008 DBL_MIN 0X1P-1022 // hex constant
2009 DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant
2010 DBL_TRUE_MIN 0X1P-1074 // hex constant
2014 DBL_MAX 1.7976931348623157E+308 // decimal constant
2015 DBL_MAX 0X1.fffffffffffffP1023 // hex constant
2017 If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
2018 example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
2019 precision), then DECIMAL_DIG would be 21.
2021 Forward references: conditional inclusion (6.10.1), complex arithmetic
2022 <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
2023 (7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
2024 (7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).
2034 1 In the syntax notation used in this clause, syntactic categories (nonterminals) are
2035 indicated by italic type, and literal words and character set members (terminals) by bold
2036 type. A colon (:) following a nonterminal introduces its definition. Alternative
2037 definitions are listed on separate lines, except when prefaced by the words ''one of''. An
2038 optional symbol is indicated by the subscript ''opt'', so that
2040 indicates an optional expression enclosed in braces.
2041 2 When syntactic categories are referred to in the main text, they are not italicized and
2042 words are separated by spaces instead of hyphens.
2043 3 A summary of the language syntax is given in annex A.
2045 6.2.1 Scopes of identifiers
2046 1 An identifier can denote an object; a function; a tag or a member of a structure, union, or
2047 enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
2048 same identifier can denote different entities at different points in the program. A member
2049 of an enumeration is called an enumeration constant. Macro names and macro
2050 parameters are not considered further here, because prior to the semantic phase of
2051 program translation any occurrences of macro names in the source file are replaced by the
2052 preprocessing token sequences that constitute their macro definitions.
2053 2 For each different entity that an identifier designates, the identifier is visible (i.e., can be
2054 used) only within a region of program text called its scope. Different entities designated
2055 by the same identifier either have different scopes, or are in different name spaces. There
2056 are four kinds of scopes: function, file, block, and function prototype. (A function
2057 prototype is a declaration of a function that declares the types of its parameters.)
2058 3 A label name is the only kind of identifier that has function scope. It can be used (in a
2059 goto statement) anywhere in the function in which it appears, and is declared implicitly
2060 by its syntactic appearance (followed by a : and a statement).
2061 4 Every other identifier has scope determined by the placement of its declaration (in a
2062 declarator or type specifier). If the declarator or type specifier that declares the identifier
2063 appears outside of any block or list of parameters, the identifier has file scope, which
2064 terminates at the end of the translation unit. If the declarator or type specifier that
2065 declares the identifier appears inside a block or within the list of parameter declarations in
2066 a function definition, the identifier has block scope, which terminates at the end of the
2067 associated block. If the declarator or type specifier that declares the identifier appears
2071 within the list of parameter declarations in a function prototype (not part of a function
2072 definition), the identifier has function prototype scope, which terminates at the end of the
2073 function declarator. If an identifier designates two different entities in the same name
2074 space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
2075 strictly before the scope of the other entity (the outer scope). Within the inner scope, the
2076 identifier designates the entity declared in the inner scope; the entity declared in the outer
2077 scope is hidden (and not visible) within the inner scope.
2078 5 Unless explicitly stated otherwise, where this International Standard uses the term
2079 ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the
2080 entity in the relevant name space whose declaration is visible at the point the identifier
2082 6 Two identifiers have the same scope if and only if their scopes terminate at the same
2084 7 Structure, union, and enumeration tags have scope that begins just after the appearance of
2085 the tag in a type specifier that declares the tag. Each enumeration constant has scope that
2086 begins just after the appearance of its defining enumerator in an enumerator list. Any
2087 other identifier has scope that begins just after the completion of its declarator.
2088 8 As a special case, a type name (which is not a declaration of an identifier) is considered to
2089 have a scope that begins just after the place within the type name where the omitted
2090 identifier would appear were it not omitted.
2091 Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
2092 (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
2093 source file inclusion (6.10.2), statements (6.8).
2094 6.2.2 Linkages of identifiers
2095 1 An identifier declared in different scopes or in the same scope more than once can be
2096 made to refer to the same object or function by a process called linkage.29) There are
2097 three kinds of linkage: external, internal, and none.
2098 2 In the set of translation units and libraries that constitutes an entire program, each
2099 declaration of a particular identifier with external linkage denotes the same object or
2100 function. Within one translation unit, each declaration of an identifier with internal
2101 linkage denotes the same object or function. Each declaration of an identifier with no
2102 linkage denotes a unique entity.
2103 3 If the declaration of a file scope identifier for an object or a function contains the storage-
2104 class specifier static, the identifier has internal linkage.30)
2108 29) There is no linkage between different identifiers.
2112 4 For an identifier declared with the storage-class specifier extern in a scope in which a
2113 prior declaration of that identifier is visible,31) if the prior declaration specifies internal or
2114 external linkage, the linkage of the identifier at the later declaration is the same as the
2115 linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
2116 declaration specifies no linkage, then the identifier has external linkage.
2117 5 If the declaration of an identifier for a function has no storage-class specifier, its linkage
2118 is determined exactly as if it were declared with the storage-class specifier extern. If
2119 the declaration of an identifier for an object has file scope and no storage-class specifier,
2120 its linkage is external.
2121 6 The following identifiers have no linkage: an identifier declared to be anything other than
2122 an object or a function; an identifier declared to be a function parameter; a block scope
2123 identifier for an object declared without the storage-class specifier extern.
2124 7 If, within a translation unit, the same identifier appears with both internal and external
2125 linkage, the behavior is undefined.
2126 Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
2128 6.2.3 Name spaces of identifiers
2129 1 If more than one declaration of a particular identifier is visible at any point in a
2130 translation unit, the syntactic context disambiguates uses that refer to different entities.
2131 Thus, there are separate name spaces for various categories of identifiers, as follows:
2132 -- label names (disambiguated by the syntax of the label declaration and use);
2133 -- the tags of structures, unions, and enumerations (disambiguated by following any32)
2134 of the keywords struct, union, or enum);
2135 -- the members of structures or unions; each structure or union has a separate name
2136 space for its members (disambiguated by the type of the expression used to access the
2137 member via the . or -> operator);
2138 -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
2139 enumeration constants).
2140 Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
2141 structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
2142 (6.7.2.3), the goto statement (6.8.6.1).
2144 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
2146 31) As specified in 6.2.1, the later declaration might hide the prior declaration.
2147 32) There is only one name space for tags even though three are possible.
2151 6.2.4 Storage durations of objects
2152 1 An object has a storage duration that determines its lifetime. There are four storage
2153 durations: static, thread, automatic, and allocated. Allocated storage is described in
2155 2 The lifetime of an object is the portion of program execution during which storage is
2156 guaranteed to be reserved for it. An object exists, has a constant address,33) and retains
2157 its last-stored value throughout its lifetime.34) If an object is referred to outside of its
2158 lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
2159 the object it points to (or just past) reaches the end of its lifetime.
2160 3 An object whose identifier is declared without the storage-class specifier
2161 _Thread_local, and either with external or internal linkage or with the storage-class
2162 specifier static, has static storage duration. Its lifetime is the entire execution of the
2163 program and its stored value is initialized only once, prior to program startup.
2164 4 An object whose identifier is declared with the storage-class specifier _Thread_local
2165 has thread storage duration. Its lifetime is the entire execution of the thread for which it
2166 is created, and its stored value is initialized when the thread is started. There is a distinct
2167 object per thread, and use of the declared name in an expression refers to the object
2168 associated with the thread evaluating the expression. The result of attempting to
2169 indirectly access an object with thread storage duration from a thread other than the one
2170 with which the object is associated is implementation-defined.
2171 5 An object whose identifier is declared with no linkage and without the storage-class
2172 specifier static has automatic storage duration, as do some compound literals. The
2173 result of attempting to indirectly access an object with automatic storage duration from a
2174 thread other than the one with which the object is associated is implementation-defined.
2175 6 For such an object that does not have a variable length array type, its lifetime extends
2176 from entry into the block with which it is associated until execution of that block ends in
2177 any way. (Entering an enclosed block or calling a function suspends, but does not end,
2178 execution of the current block.) If the block is entered recursively, a new instance of the
2179 object is created each time. The initial value of the object is indeterminate. If an
2180 initialization is specified for the object, it is performed each time the declaration or
2181 compound literal is reached in the execution of the block; otherwise, the value becomes
2182 indeterminate each time the declaration is reached.
2186 33) The term ''constant address'' means that two pointers to the object constructed at possibly different
2187 times will compare equal. The address may be different during two different executions of the same
2189 34) In the case of a volatile object, the last store need not be explicit in the program.
2193 7 For such an object that does have a variable length array type, its lifetime extends from
2194 the declaration of the object until execution of the program leaves the scope of the
2195 declaration.35) If the scope is entered recursively, a new instance of the object is created
2196 each time. The initial value of the object is indeterminate.
2197 8 A non-lvalue expression with structure or union type, where the structure or union
2198 contains a member with array type (including, recursively, members of all contained
2199 structures and unions) refers to an object with automatic storage duration and temporary
2200 lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the
2201 value of the expression. Its lifetime ends when the evaluation of the containing full
2202 expression or full declarator ends. Any attempt to modify an object with temporary
2203 lifetime results in undefined behavior.
2204 Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
2205 (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).
2207 1 The meaning of a value stored in an object or returned by a function is determined by the
2208 type of the expression used to access it. (An identifier declared to be an object is the
2209 simplest such expression; the type is specified in the declaration of the identifier.) Types
2210 are partitioned into object types (types that describe objects) and function types (types
2211 that describe functions). At various points within a translation unit an object type may be
2212 incomplete (lacking sufficient information to determine the size of objects of that type) or
2213 complete (having sufficient information).37)
2214 2 An object declared as type _Bool is large enough to store the values 0 and 1.
2215 3 An object declared as type char is large enough to store any member of the basic
2216 execution character set. If a member of the basic execution character set is stored in a
2217 char object, its value is guaranteed to be nonnegative. If any other character is stored in
2218 a char object, the resulting value is implementation-defined but shall be within the range
2219 of values that can be represented in that type.
2220 4 There are five standard signed integer types, designated as signed char, short
2221 int, int, long int, and long long int. (These and other types may be
2222 designated in several additional ways, as described in 6.7.2.) There may also be
2223 implementation-defined extended signed integer types.38) The standard and extended
2224 signed integer types are collectively called signed integer types.39)
2226 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
2227 embedded block prior to the declaration, leaves the scope of the declaration.
2228 36) The address of such an object is taken implicitly when an array member is accessed.
2229 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
2230 different points within a translation unit.
2234 5 An object declared as type signed char occupies the same amount of storage as a
2235 ''plain'' char object. A ''plain'' int object has the natural size suggested by the
2236 architecture of the execution environment (large enough to contain any value in the range
2237 INT_MIN to INT_MAX as defined in the header <limits.h>).
2238 6 For each of the signed integer types, there is a corresponding (but different) unsigned
2239 integer type (designated with the keyword unsigned) that uses the same amount of
2240 storage (including sign information) and has the same alignment requirements. The type
2241 _Bool and the unsigned integer types that correspond to the standard signed integer
2242 types are the standard unsigned integer types. The unsigned integer types that
2243 correspond to the extended signed integer types are the extended unsigned integer types.
2244 The standard and extended unsigned integer types are collectively called unsigned integer
2246 7 The standard signed integer types and standard unsigned integer types are collectively
2247 called the standard integer types, the extended signed integer types and extended
2248 unsigned integer types are collectively called the extended integer types.
2249 8 For any two integer types with the same signedness and different integer conversion rank
2250 (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
2251 subrange of the values of the other type.
2252 9 The range of nonnegative values of a signed integer type is a subrange of the
2253 corresponding unsigned integer type, and the representation of the same value in each
2254 type is the same.41) A computation involving unsigned operands can never overflow,
2255 because a result that cannot be represented by the resulting unsigned integer type is
2256 reduced modulo the number that is one greater than the largest value that can be
2257 represented by the resulting type.
2258 10 There are three real floating types, designated as float, double, and long
2259 double.42) The set of values of the type float is a subset of the set of values of the
2260 type double; the set of values of the type double is a subset of the set of values of the
2264 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
2266 39) Therefore, any statement in this Standard about signed integer types also applies to the extended
2267 signed integer types.
2268 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
2269 unsigned integer types.
2270 41) The same representation and alignment requirements are meant to imply interchangeability as
2271 arguments to functions, return values from functions, and members of unions.
2272 42) See ''future language directions'' (6.11.1).
2276 11 There are three complex types, designated as float _Complex, double
2277 _Complex, and long double _Complex.43) (Complex types are a conditional
2278 feature that implementations need not support; see 6.10.8.3.) The real floating and
2279 complex types are collectively called the floating types.
2280 12 For each floating type there is a corresponding real type, which is always a real floating
2281 type. For real floating types, it is the same type. For complex types, it is the type given
2282 by deleting the keyword _Complex from the type name.
2283 13 Each complex type has the same representation and alignment requirements as an array
2284 type containing exactly two elements of the corresponding real type; the first element is
2285 equal to the real part, and the second element to the imaginary part, of the complex
2287 14 The type char, the signed and unsigned integer types, and the floating types are
2288 collectively called the basic types. The basic types are complete object types. Even if the
2289 implementation defines two or more basic types to have the same representation, they are
2290 nevertheless different types.44)
2291 15 The three types char, signed char, and unsigned char are collectively called
2292 the character types. The implementation shall define char to have the same range,
2293 representation, and behavior as either signed char or unsigned char.45)
2294 16 An enumeration comprises a set of named integer constant values. Each distinct
2295 enumeration constitutes a different enumerated type.
2296 17 The type char, the signed and unsigned integer types, and the enumerated types are
2297 collectively called integer types. The integer and real floating types are collectively called
2299 18 Integer and floating types are collectively called arithmetic types. Each arithmetic type
2300 belongs to one type domain: the real type domain comprises the real types, the complex
2301 type domain comprises the complex types.
2302 19 The void type comprises an empty set of values; it is an incomplete object type that
2303 cannot be completed.
2307 43) A specification for imaginary types is in informative annex G.
2308 44) An implementation may define new keywords that provide alternative ways to designate a basic (or
2309 any other) type; this does not violate the requirement that all basic types be different.
2310 Implementation-defined keywords shall have the form of an identifier reserved for any use as
2312 45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be
2313 used to distinguish the two options. Irrespective of the choice made, char is a separate type from the
2314 other two and is not compatible with either.
2318 20 Any number of derived types can be constructed from the object and function types, as
2320 -- An array type describes a contiguously allocated nonempty set of objects with a
2321 particular member object type, called the element type. The element type shall be
2322 complete whenever the array type is specified. Array types are characterized by their
2323 element type and by the number of elements in the array. An array type is said to be
2324 derived from its element type, and if its element type is T , the array type is sometimes
2325 called ''array of T ''. The construction of an array type from an element type is called
2326 ''array type derivation''.
2327 -- A structure type describes a sequentially allocated nonempty set of member objects
2328 (and, in certain circumstances, an incomplete array), each of which has an optionally
2329 specified name and possibly distinct type.
2330 -- A union type describes an overlapping nonempty set of member objects, each of
2331 which has an optionally specified name and possibly distinct type.
2332 -- A function type describes a function with specified return type. A function type is
2333 characterized by its return type and the number and types of its parameters. A
2334 function type is said to be derived from its return type, and if its return type is T , the
2335 function type is sometimes called ''function returning T ''. The construction of a
2336 function type from a return type is called ''function type derivation''.
2337 -- A pointer type may be derived from a function type or an object type, called the
2338 referenced type. A pointer type describes an object whose value provides a reference
2339 to an entity of the referenced type. A pointer type derived from the referenced type T
2340 is sometimes called ''pointer to T ''. The construction of a pointer type from a
2341 referenced type is called ''pointer type derivation''. A pointer type is a complete
2343 These methods of constructing derived types can be applied recursively.
2344 21 Arithmetic types and pointer types are collectively called scalar types. Array and
2345 structure types are collectively called aggregate types.46)
2346 22 An array type of unknown size is an incomplete type. It is completed, for an identifier of
2347 that type, by specifying the size in a later declaration (with internal or external linkage).
2348 A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete
2349 type. It is completed, for all declarations of that type, by declaring the same structure or
2350 union tag with its defining content later in the same scope.
2355 46) Note that aggregate type does not include union type because an object with union type can only
2356 contain one member at a time.
2360 23 A type has known constant size if the type is not incomplete and is not a variable length
2362 24 Array, function, and pointer types are collectively called derived declarator types. A
2363 declarator type derivation from a type T is the construction of a derived declarator type
2364 from T by the application of an array-type, a function-type, or a pointer-type derivation to
2366 25 A type is characterized by its type category, which is either the outermost derivation of a
2367 derived type (as noted above in the construction of derived types), or the type itself if the
2368 type consists of no derived types.
2369 26 Any type so far mentioned is an unqualified type. Each unqualified type has several
2370 qualified versions of its type,47) corresponding to the combinations of one, two, or all
2371 three of the const, volatile, and restrict qualifiers. The qualified or unqualified
2372 versions of a type are distinct types that belong to the same type category and have the
2373 same representation and alignment requirements.48) A derived type is not qualified by the
2374 qualifiers (if any) of the type from which it is derived.
2375 27 Further, there is the _Atomic qualifier, which may combine with volatile and
2376 restrict. The size, representation, and alignment of an _Atomic-qualified type need
2377 not be the same as those of the corresponding unqualified type. (Atomic types are a
2378 conditional feature that implementations need not support; see 6.10.8.3.)
2379 28 A pointer to void shall have the same representation and alignment requirements as a
2380 pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of
2381 compatible types shall have the same representation and alignment requirements. All
2382 pointers to structure types shall have the same representation and alignment requirements
2383 as each other. All pointers to union types shall have the same representation and
2384 alignment requirements as each other. Pointers to other types need not have the same
2385 representation or alignment requirements.
2386 29 EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is
2387 pointer, not a floating type. The const-qualified version of this type is designated as ''float * const''
2388 whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const-
2389 qualified float'' and is a pointer to a qualified type.
2391 30 EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to
2392 function returning struct tag''. The array has length five and the function has a single parameter of type
2393 float. Its type category is array.
2395 Forward references: compatible type and composite type (6.2.7), declarations (6.7).
2399 47) See 6.7.3 regarding qualified array and function types.
2400 48) The same representation and alignment requirements are meant to imply interchangeability as
2401 arguments to functions, return values from functions, and members of unions.
2405 6.2.6 Representations of types
2407 1 The representations of all types are unspecified except as stated in this subclause.
2408 2 Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
2409 the number, order, and encoding of which are either explicitly specified or
2410 implementation-defined.
2411 3 Values stored in unsigned bit-fields and objects of type unsigned char shall be
2412 represented using a pure binary notation.49)
2413 4 Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT
2414 bits, where n is the size of an object of that type, in bytes. The value may be copied into
2415 an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
2416 called the object representation of the value. Values stored in bit-fields consist of m bits,
2417 where m is the size specified for the bit-field. The object representation is the set of m
2418 bits the bit-field comprises in the addressable storage unit holding it. Two values (other
2419 than NaNs) with the same object representation compare equal, but values that compare
2420 equal may have different object representations.
2421 5 Certain object representations need not represent a value of the object type. If the stored
2422 value of an object has such a representation and is read by an lvalue expression that does
2423 not have character type, the behavior is undefined. If such a representation is produced
2424 by a side effect that modifies all or any part of the object by an lvalue expression that
2425 does not have character type, the behavior is undefined.50) Such a representation is called
2426 a trap representation.
2427 6 When a value is stored in an object of structure or union type, including in a member
2428 object, the bytes of the object representation that correspond to any padding bytes take
2429 unspecified values.51) The value of a structure or union object is never a trap
2430 representation, even though the value of a member of the structure or union object may be
2431 a trap representation.
2432 7 When a value is stored in a member of an object of union type, the bytes of the object
2433 representation that do not correspond to that member but do correspond to other members
2435 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
2436 represented by successive bits are additive, begin with 1, and are multiplied by successive integral
2437 powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
2438 Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
2439 type unsigned char range from 0 to 2
2442 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
2443 behavior, but the value of the variable cannot be used until a proper value is stored in it.
2444 51) Thus, for example, structure assignment need not copy any padding bits.
2448 take unspecified values.
2449 8 Where an operator is applied to a value that has more than one object representation,
2450 which object representation is used shall not affect the value of the result.52) Where a
2451 value is stored in an object using a type that has more than one object representation for
2452 that value, it is unspecified which representation is used, but a trap representation shall
2454 9 Loads and stores of objects with _Atomic-qualified types are done with
2455 memory_order_seq_cst semantics.
2456 Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
2457 designators (6.3.2.1), order and consistency (7.17.3).
2458 6.2.6.2 Integer types
2459 1 For unsigned integer types other than unsigned char, the bits of the object
2460 representation shall be divided into two groups: value bits and padding bits (there need
2461 not be any of the latter). If there are N value bits, each bit shall represent a different
2462 power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of
2463 representing values from 0 to 2 N - 1 using a pure binary representation; this shall be
2464 known as the value representation. The values of any padding bits are unspecified.53)
2465 2 For signed integer types, the bits of the object representation shall be divided into three
2466 groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
2467 signed char shall not have any padding bits. There shall be exactly one sign bit.
2468 Each bit that is a value bit shall have the same value as the same bit in the object
2469 representation of the corresponding unsigned type (if there are M value bits in the signed
2470 type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect
2471 the resulting value. If the sign bit is one, the value shall be modified in one of the
2473 -- the corresponding value with sign bit 0 is negated (sign and magnitude);
2474 -- the sign bit has the value -(2 M ) (two's complement);
2477 52) It is possible for objects x and y with the same effective type T to have the same value when they are
2478 accessed as objects of type T, but to have different values in other contexts. In particular, if == is
2479 defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
2480 Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
2481 on values of type T may distinguish between them.
2482 53) Some combinations of padding bits might generate trap representations, for example, if one padding
2483 bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
2484 representation other than as part of an exceptional condition such as an overflow, and this cannot occur
2485 with unsigned types. All other combinations of padding bits are alternative object representations of
2486 the value specified by the value bits.
2490 -- the sign bit has the value -(2 M - 1) (ones' complement).
2491 Which of these applies is implementation-defined, as is whether the value with sign bit 1
2492 and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones'
2493 complement), is a trap representation or a normal value. In the case of sign and
2494 magnitude and ones' complement, if this representation is a normal value it is called a
2496 3 If the implementation supports negative zeros, they shall be generated only by:
2497 -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
2498 -- the +, -, *, /, and % operators where one operand is a negative zero and the result is
2500 -- compound assignment operators based on the above cases.
2501 It is unspecified whether these cases actually generate a negative zero or a normal zero,
2502 and whether a negative zero becomes a normal zero when stored in an object.
2503 4 If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
2504 and >> operators with operands that would produce such a value is undefined.
2505 5 The values of any padding bits are unspecified.54) A valid (non-trap) object representation
2506 of a signed integer type where the sign bit is zero is a valid object representation of the
2507 corresponding unsigned type, and shall represent the same value. For any integer type,
2508 the object representation where all the bits are zero shall be a representation of the value
2510 6 The precision of an integer type is the number of bits it uses to represent values,
2511 excluding any sign and padding bits. The width of an integer type is the same but
2512 including any sign bit; thus for unsigned integer types the two values are the same, while
2513 for signed integer types the width is one greater than the precision.
2518 54) Some combinations of padding bits might generate trap representations, for example, if one padding
2519 bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
2520 representation other than as part of an exceptional condition such as an overflow. All other
2521 combinations of padding bits are alternative object representations of the value specified by the value
2526 6.2.7 Compatible type and composite type
2527 1 Two types have compatible type if their types are the same. Additional rules for
2528 determining whether two types are compatible are described in 6.7.2 for type specifiers,
2529 in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure,
2530 union, or enumerated types declared in separate translation units are compatible if their
2531 tags and members satisfy the following requirements: If one is declared with a tag, the
2532 other shall be declared with the same tag. If both are completed anywhere within their
2533 respective translation units, then the following additional requirements apply: there shall
2534 be a one-to-one correspondence between their members such that each pair of
2535 corresponding members are declared with compatible types, and such that if one member
2536 of a corresponding pair is declared with a name, the other member is declared with the
2537 same name. For two structures, corresponding members shall be declared in the same
2538 order. For two structures or unions, corresponding bit-fields shall have the same widths.
2539 For two enumerations, corresponding members shall have the same values.
2540 2 All declarations that refer to the same object or function shall have compatible type;
2541 otherwise, the behavior is undefined.
2542 3 A composite type can be constructed from two types that are compatible; it is a type that
2543 is compatible with both of the two types and satisfies the following conditions:
2544 -- If both types are array types, the following rules are applied:
2545 o If one type is an array of known constant size, the composite type is an array of
2547 o Otherwise, if one type is a variable length array whose size is specified by an
2548 expression that is not evaluated, the behavior is undefined.
2549 o Otherwise, if one type is a variable length array whose size is specified, the
2550 composite type is a variable length array of that size.
2551 o Otherwise, if one type is a variable length array of unspecified size, the composite
2552 type is a variable length array of unspecified size.
2553 o Otherwise, both types are arrays of unknown size and the composite type is an
2554 array of unknown size.
2555 The element type of the composite type is the composite type of the two element
2557 -- If only one type is a function type with a parameter type list (a function prototype),
2558 the composite type is a function prototype with the parameter type list.
2562 55) Two types need not be identical to be compatible.
2566 -- If both types are function types with parameter type lists, the type of each parameter
2567 in the composite parameter type list is the composite type of the corresponding
2569 These rules apply recursively to the types from which the two types are derived.
2570 4 For an identifier with internal or external linkage declared in a scope in which a prior
2571 declaration of that identifier is visible,56) if the prior declaration specifies internal or
2572 external linkage, the type of the identifier at the later declaration becomes the composite
2574 Forward references: array declarators (6.7.6.2).
2575 5 EXAMPLE Given the following two file scope declarations:
2576 int f(int (*)(), double (*)[3]);
2577 int f(int (*)(char *), double (*)[]);
2578 The resulting composite type for the function is:
2579 int f(int (*)(char *), double (*)[3]);
2581 6.2.8 Alignment of objects
2582 1 Complete object types have alignment requirements which place restrictions on the
2583 addresses at which objects of that type may be allocated. An alignment is an
2584 implementation-defined integer value representing the number of bytes between
2585 successive addresses at which a given object can be allocated. An object type imposes an
2586 alignment requirement on every object of that type: stricter alignment can be requested
2587 using the _Alignas keyword.
2588 2 A fundamental alignment is represented by an alignment less than or equal to the greatest
2589 alignment supported by the implementation in all contexts, which is equal to
2590 alignof(max_align_t).
2591 3 An extended alignment is represented by an alignment greater than
2592 alignof(max_align_t). It is implementation-defined whether any extended
2593 alignments are supported and the contexts in which they are supported. A type having an
2594 extended alignment requirement is an over-aligned type.57)
2595 4 Alignments are represented as values of the type size_t. Valid alignments include only
2596 those values returned by an alignof expression for fundamental types, plus an
2597 additional implementation-defined set of values, which may be empty. Every valid
2598 alignment value shall be an integral power of two.
2601 56) As specified in 6.2.1, the later declaration might hide the prior declaration.
2602 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
2603 alignment has been applied.
2607 5 Alignments have an order from weaker to stronger or stricter alignments. Stricter
2608 alignments have larger alignment values. An address that satisfies an alignment
2609 requirement also satisfies any weaker valid alignment requirement.
2610 6 The alignment requirement of a complete type can be queried using an alignof
2611 expression. The types char, signed char, and unsigned char shall have the
2612 weakest alignment requirement.
2613 7 Comparing alignments is meaningful and provides the obvious results:
2614 -- Two alignments are equal when their numeric values are equal.
2615 -- Two alignments are different when their numeric values are not equal.
2616 -- When an alignment is larger than another it represents a stricter alignment.
2624 1 Several operators convert operand values from one type to another automatically. This
2625 subclause specifies the result required from such an implicit conversion, as well as those
2626 that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
2627 the conversions performed by most ordinary operators; it is supplemented as required by
2628 the discussion of each operator in 6.5.
2629 2 Conversion of an operand value to a compatible type causes no change to the value or the
2631 Forward references: cast operators (6.5.4).
2632 6.3.1 Arithmetic operands
2633 6.3.1.1 Boolean, characters, and integers
2634 1 Every integer type has an integer conversion rank defined as follows:
2635 -- No two signed integer types shall have the same rank, even if they have the same
2637 -- The rank of a signed integer type shall be greater than the rank of any signed integer
2638 type with less precision.
2639 -- The rank of long long int shall be greater than the rank of long int, which
2640 shall be greater than the rank of int, which shall be greater than the rank of short
2641 int, which shall be greater than the rank of signed char.
2642 -- The rank of any unsigned integer type shall equal the rank of the corresponding
2643 signed integer type, if any.
2644 -- The rank of any standard integer type shall be greater than the rank of any extended
2645 integer type with the same width.
2646 -- The rank of char shall equal the rank of signed char and unsigned char.
2647 -- The rank of _Bool shall be less than the rank of all other standard integer types.
2648 -- The rank of any enumerated type shall equal the rank of the compatible integer type
2650 -- The rank of any extended signed integer type relative to another extended signed
2651 integer type with the same precision is implementation-defined, but still subject to the
2652 other rules for determining the integer conversion rank.
2653 -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
2654 greater rank than T3, then T1 has greater rank than T3.
2655 2 The following may be used in an expression wherever an int or unsigned int may
2660 -- An object or expression with an integer type (other than int or unsigned int)
2661 whose integer conversion rank is less than or equal to the rank of int and
2663 -- A bit-field of type _Bool, int, signed int, or unsigned int.
2664 If an int can represent all values of the original type (as restricted by the width, for a
2665 bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
2666 int. These are called the integer promotions.58) All other types are unchanged by the
2668 3 The integer promotions preserve value including sign. As discussed earlier, whether a
2669 ''plain'' char is treated as signed is implementation-defined.
2670 Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
2672 6.3.1.2 Boolean type
2673 1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal
2674 to 0; otherwise, the result is 1.59)
2675 6.3.1.3 Signed and unsigned integers
2676 1 When a value with integer type is converted to another integer type other than _Bool, if
2677 the value can be represented by the new type, it is unchanged.
2678 2 Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
2679 subtracting one more than the maximum value that can be represented in the new type
2680 until the value is in the range of the new type.60)
2681 3 Otherwise, the new type is signed and the value cannot be represented in it; either the
2682 result is implementation-defined or an implementation-defined signal is raised.
2683 6.3.1.4 Real floating and integer
2684 1 When a finite value of real floating type is converted to an integer type other than _Bool,
2685 the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
2686 the integral part cannot be represented by the integer type, the behavior is undefined.61)
2689 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
2690 argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
2691 shift operators, as specified by their respective subclauses.
2692 59) NaNs do not compare equal to 0 and thus convert to 1.
2693 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
2694 61) The remaindering operation performed when a value of integer type is converted to unsigned type
2695 need not be performed when a value of real floating type is converted to unsigned type. Thus, the
2696 range of portable real floating values is (-1, Utype_MAX+1).
2700 2 When a value of integer type is converted to a real floating type, if the value being
2701 converted can be represented exactly in the new type, it is unchanged. If the value being
2702 converted is in the range of values that can be represented but cannot be represented
2703 exactly, the result is either the nearest higher or nearest lower representable value, chosen
2704 in an implementation-defined manner. If the value being converted is outside the range of
2705 values that can be represented, the behavior is undefined.
2706 6.3.1.5 Real floating types
2707 1 When a float is promoted to double or long double, or a double is promoted
2708 to long double, its value is unchanged (if the source value is represented in the
2709 precision and range of its type).
2710 2 When a double is demoted to float, a long double is demoted to double or
2711 float, or a value being represented in greater precision and range than required by its
2712 semantic type (see 6.3.1.8) is explicitly converted (including to its own type), if the value
2713 being converted can be represented exactly in the new type, it is unchanged. If the value
2714 being converted is in the range of values that can be represented but cannot be
2715 represented exactly, the result is either the nearest higher or nearest lower representable
2716 value, chosen in an implementation-defined manner. If the value being converted is
2717 outside the range of values that can be represented, the behavior is undefined.
2718 6.3.1.6 Complex types
2719 1 When a value of complex type is converted to another complex type, both the real and
2720 imaginary parts follow the conversion rules for the corresponding real types.
2721 6.3.1.7 Real and complex
2722 1 When a value of real type is converted to a complex type, the real part of the complex
2723 result value is determined by the rules of conversion to the corresponding real type and
2724 the imaginary part of the complex result value is a positive zero or an unsigned zero.
2725 2 When a value of complex type is converted to a real type, the imaginary part of the
2726 complex value is discarded and the value of the real part is converted according to the
2727 conversion rules for the corresponding real type.
2728 6.3.1.8 Usual arithmetic conversions
2729 1 Many operators that expect operands of arithmetic type cause conversions and yield result
2730 types in a similar way. The purpose is to determine a common real type for the operands
2731 and result. For the specified operands, each operand is converted, without change of type
2732 domain, to a type whose corresponding real type is the common real type. Unless
2733 explicitly stated otherwise, the common real type is also the corresponding real type of
2734 the result, whose type domain is the type domain of the operands if they are the same,
2735 and complex otherwise. This pattern is called the usual arithmetic conversions:
2740 First, if the corresponding real type of either operand is long double, the other
2741 operand is converted, without change of type domain, to a type whose
2742 corresponding real type is long double.
2743 Otherwise, if the corresponding real type of either operand is double, the other
2744 operand is converted, without change of type domain, to a type whose
2745 corresponding real type is double.
2746 Otherwise, if the corresponding real type of either operand is float, the other
2747 operand is converted, without change of type domain, to a type whose
2748 corresponding real type is float.62)
2749 Otherwise, the integer promotions are performed on both operands. Then the
2750 following rules are applied to the promoted operands:
2751 If both operands have the same type, then no further conversion is needed.
2752 Otherwise, if both operands have signed integer types or both have unsigned
2753 integer types, the operand with the type of lesser integer conversion rank is
2754 converted to the type of the operand with greater rank.
2755 Otherwise, if the operand that has unsigned integer type has rank greater or
2756 equal to the rank of the type of the other operand, then the operand with
2757 signed integer type is converted to the type of the operand with unsigned
2759 Otherwise, if the type of the operand with signed integer type can represent
2760 all of the values of the type of the operand with unsigned integer type, then
2761 the operand with unsigned integer type is converted to the type of the
2762 operand with signed integer type.
2763 Otherwise, both operands are converted to the unsigned integer type
2764 corresponding to the type of the operand with signed integer type.
2765 2 The values of floating operands and of the results of floating expressions may be
2766 represented in greater precision and range than that required by the type; the types are not
2772 62) For example, addition of a double _Complex and a float entails just the conversion of the
2773 float operand to double (and yields a double _Complex result).
2774 63) The cast and assignment operators are still required to perform their specified conversions as
2775 described in 6.3.1.4 and 6.3.1.5.
2779 6.3.2 Other operands
2780 6.3.2.1 Lvalues, arrays, and function designators
2781 1 An lvalue is an expression (with an object type other than void) that potentially
2782 designates an object;64) if an lvalue does not designate an object when it is evaluated, the
2783 behavior is undefined. When an object is said to have a particular type, the type is
2784 specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
2785 does not have array type, does not have an incomplete type, does not have a const-
2786 qualified type, and if it is a structure or union, does not have any member (including,
2787 recursively, any member or element of all contained aggregates or unions) with a const-
2789 2 Except when it is the operand of the sizeof operator, the unary & operator, the ++
2790 operator, the -- operator, or the left operand of the . operator or an assignment operator,
2791 an lvalue that does not have array type is converted to the value stored in the designated
2792 object (and is no longer an lvalue). If the lvalue has qualified type, the value has the
2793 unqualified version of the type of the lvalue; otherwise, the value has the type of the
2794 lvalue. If the lvalue has an incomplete type and does not have array type, the behavior is
2795 undefined. If the lvalue designates an object of automatic storage duration that could
2796 have been declared with the register storage class (never had its address taken), and
2797 that object is uninitialized (not declared with an initializer and no assignment to it has
2798 been performed prior to use), the behavior is undefined.
2799 3 Except when it is the operand of the sizeof operator or the unary & operator, or is a
2800 string literal used to initialize an array, an expression that has type ''array of type'' is
2801 converted to an expression with type ''pointer to type'' that points to the initial element of
2802 the array object and is not an lvalue. If the array object has register storage class, the
2803 behavior is undefined.
2804 4 A function designator is an expression that has function type. Except when it is the
2805 operand of the sizeof operator65) or the unary & operator, a function designator with
2806 type ''function returning type'' is converted to an expression that has type ''pointer to
2807 function returning type''.
2808 Forward references: address and indirection operators (6.5.3.2), assignment operators
2810 64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left
2811 operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
2812 object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described
2813 as the ''value of an expression''.
2814 An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
2815 expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
2816 65) Because this conversion does not occur, the operand of the sizeof operator remains a function
2817 designator and violates the constraint in 6.5.3.4.
2821 (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix
2822 increment and decrement operators (6.5.2.4), prefix increment and decrement operators
2823 (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3).
2825 1 The (nonexistent) value of a void expression (an expression that has type void) shall not
2826 be used in any way, and implicit or explicit conversions (except to void) shall not be
2827 applied to such an expression. If an expression of any other type is evaluated as a void
2828 expression, its value or designator is discarded. (A void expression is evaluated for its
2831 1 A pointer to void may be converted to or from a pointer to any object type. A pointer to
2832 any object type may be converted to a pointer to void and back again; the result shall
2833 compare equal to the original pointer.
2834 2 For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to
2835 the q-qualified version of the type; the values stored in the original and converted pointers
2836 shall compare equal.
2837 3 An integer constant expression with the value 0, or such an expression cast to type
2838 void *, is called a null pointer constant.66) If a null pointer constant is converted to a
2839 pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
2840 to a pointer to any object or function.
2841 4 Conversion of a null pointer to another pointer type yields a null pointer of that type.
2842 Any two null pointers shall compare equal.
2843 5 An integer may be converted to any pointer type. Except as previously specified, the
2844 result is implementation-defined, might not be correctly aligned, might not point to an
2845 entity of the referenced type, and might be a trap representation.67)
2846 6 Any pointer type may be converted to an integer type. Except as previously specified, the
2847 result is implementation-defined. If the result cannot be represented in the integer type,
2848 the behavior is undefined. The result need not be in the range of values of any integer
2850 7 A pointer to an object type may be converted to a pointer to a different object type. If the
2851 resulting pointer is not correctly aligned68) for the referenced type, the behavior is
2852 undefined. Otherwise, when converted back again, the result shall compare equal to the
2855 66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19.
2856 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to
2857 be consistent with the addressing structure of the execution environment.
2861 original pointer. When a pointer to an object is converted to a pointer to a character type,
2862 the result points to the lowest addressed byte of the object. Successive increments of the
2863 result, up to the size of the object, yield pointers to the remaining bytes of the object.
2864 8 A pointer to a function of one type may be converted to a pointer to a function of another
2865 type and back again; the result shall compare equal to the original pointer. If a converted
2866 pointer is used to call a function whose type is not compatible with the referenced type,
2867 the behavior is undefined.
2868 Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
2869 capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).
2874 68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a
2875 pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
2876 correctly aligned for a pointer to type C.
2880 6.4 Lexical elements
2888 preprocessing-token:
2895 each non-white-space character that cannot be one of the above
2897 2 Each preprocessing token that is converted to a token shall have the lexical form of a
2898 keyword, an identifier, a constant, a string literal, or a punctuator.
2900 3 A token is the minimal lexical element of the language in translation phases 7 and 8. The
2901 categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
2902 A preprocessing token is the minimal lexical element of the language in translation
2903 phases 3 through 6. The categories of preprocessing tokens are: header names,
2904 identifiers, preprocessing numbers, character constants, string literals, punctuators, and
2905 single non-white-space characters that do not lexically match the other preprocessing
2906 token categories.69) If a ' or a " character matches the last category, the behavior is
2907 undefined. Preprocessing tokens can be separated by white space; this consists of
2908 comments (described later), or white-space characters (space, horizontal tab, new-line,
2909 vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
2910 during translation phase 4, white space (or the absence thereof) serves as more than
2911 preprocessing token separation. White space may appear within a preprocessing token
2912 only as part of a header name or between the quotation characters in a character constant
2917 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
2918 occur in source files.
2922 4 If the input stream has been parsed into preprocessing tokens up to a given character, the
2923 next preprocessing token is the longest sequence of characters that could constitute a
2924 preprocessing token. There is one exception to this rule: header name preprocessing
2925 tokens are recognized only within #include preprocessing directives and in
2926 implementation-defined locations within #pragma directives. In such contexts, a
2927 sequence of characters that could be either a header name or a string literal is recognized
2929 5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
2930 valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
2931 might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
2932 fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
2933 not E is a macro name.
2935 6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
2936 increment operators, even though the parse x ++ + ++ y might yield a correct expression.
2938 Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
2939 floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
2940 increment and decrement operators (6.5.2.4), prefix increment and decrement operators
2941 (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
2951 const register _Alignas
2952 continue restrict _Atomic
2953 default return _Bool
2955 double signed _Generic
2956 else sizeof _Imaginary
2957 enum static _Noreturn
2958 extern struct _Static_assert
2959 float switch _Thread_local
2962 2 The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
2963 keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for
2966 specifying imaginary types.70)
2972 identifier identifier-nondigit
2974 identifier-nondigit:
2976 universal-character-name
2977 other implementation-defined characters
2979 _ a b c d e f g h i j k l m
2980 n o p q r s t u v w x y z
2981 A B C D E F G H I J K L M
2982 N O P Q R S T U V W X Y Z
2986 2 An identifier is a sequence of nondigit characters (including the underscore _, the
2987 lowercase and uppercase Latin letters, and other characters) and digits, which designates
2988 one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
2989 There is no specific limit on the maximum length of an identifier.
2990 3 Each universal character name in an identifier shall designate a character whose encoding
2991 in ISO/IEC 10646 falls into one of the ranges specified in annex D.71) The initial
2992 character shall not be a universal character name designating a digit. An implementation
2993 may allow multibyte characters that are not part of the basic source character set to
2994 appear in identifiers; which characters and their correspondence to universal character
2995 names is implementation-defined.
2999 70) One possible specification for imaginary types appears in annex G.
3000 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
3001 name may be used in forming valid external identifiers. For example, some otherwise unused
3002 character or sequence of characters may be used to encode the \u in a universal character name.
3003 Extended characters may produce a long external identifier.
3007 4 When preprocessing tokens are converted to tokens during translation phase 7, if a
3008 preprocessing token could be converted to either a keyword or an identifier, it is converted
3010 Implementation limits
3011 5 As discussed in 5.2.4.1, an implementation may limit the number of significant initial
3012 characters in an identifier; the limit for an external name (an identifier that has external
3013 linkage) may be more restrictive than that for an internal name (a macro name or an
3014 identifier that does not have external linkage). The number of significant characters in an
3015 identifier is implementation-defined.
3016 6 Any identifiers that differ in a significant character are different identifiers. If two
3017 identifiers differ only in nonsignificant characters, the behavior is undefined.
3018 Forward references: universal character names (6.4.3), macro replacement (6.10.3).
3019 6.4.2.2 Predefined identifiers
3021 1 The identifier __func__ shall be implicitly declared by the translator as if,
3022 immediately following the opening brace of each function definition, the declaration
3023 static const char __func__[] = "function-name";
3024 appeared, where function-name is the name of the lexically-enclosing function.72)
3025 2 This name is encoded as if the implicit declaration had been written in the source
3026 character set and then translated into the execution character set as indicated in translation
3028 3 EXAMPLE Consider the code fragment:
3032 printf("%s\n", __func__);
3035 Each time the function is called, it will print to the standard output stream:
3038 Forward references: function definitions (6.9.1).
3043 72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other
3044 identifier is explicitly declared using the name __func__, the behavior is undefined.
3048 6.4.3 Universal character names
3050 1 universal-character-name:
3052 \U hex-quad hex-quad
3054 hexadecimal-digit hexadecimal-digit
3055 hexadecimal-digit hexadecimal-digit
3057 2 A universal character name shall not specify a character whose short identifier is less than
3058 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through
3061 3 Universal character names may be used in identifiers, character constants, and string
3062 literals to designate characters that are not in the basic character set.
3064 4 The universal character name \Unnnnnnnn designates the character whose eight-digit
3065 short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal
3066 character name \unnnn designates the character whose four-digit short identifier is nnnn
3067 (and whose eight-digit short identifier is 0000nnnn).
3072 73) The disallowed characters are the characters in the basic character set and the code positions reserved
3073 by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
3076 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997.
3085 enumeration-constant
3088 2 Each constant shall have a type and the value of a constant shall be in the range of
3089 representable values for its type.
3091 3 Each constant has a type, determined by its form and value, as detailed later.
3092 6.4.4.1 Integer constants
3095 decimal-constant integer-suffixopt
3096 octal-constant integer-suffixopt
3097 hexadecimal-constant integer-suffixopt
3100 decimal-constant digit
3103 octal-constant octal-digit
3104 hexadecimal-constant:
3105 hexadecimal-prefix hexadecimal-digit
3106 hexadecimal-constant hexadecimal-digit
3107 hexadecimal-prefix: one of
3109 nonzero-digit: one of
3119 hexadecimal-digit: one of
3124 unsigned-suffix long-suffixopt
3125 unsigned-suffix long-long-suffix
3126 long-suffix unsigned-suffixopt
3127 long-long-suffix unsigned-suffixopt
3128 unsigned-suffix: one of
3132 long-long-suffix: one of
3135 2 An integer constant begins with a digit, but has no period or exponent part. It may have a
3136 prefix that specifies its base and a suffix that specifies its type.
3137 3 A decimal constant begins with a nonzero digit and consists of a sequence of decimal
3138 digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
3139 digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
3140 by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
3141 10 through 15 respectively.
3143 4 The value of a decimal constant is computed base 10; that of an octal constant, base 8;
3144 that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
3145 5 The type of an integer constant is the first of the corresponding list in which its value can
3153 Octal or Hexadecimal
3154 Suffix Decimal Constant Constant
3157 long int unsigned int
3158 long long int long int
3161 unsigned long long int
3163 u or U unsigned int unsigned int
3164 unsigned long int unsigned long int
3165 unsigned long long int unsigned long long int
3167 l or L long int long int
3168 long long int unsigned long int
3170 unsigned long long int
3172 Both u or U unsigned long int unsigned long int
3173 and l or L unsigned long long int unsigned long long int
3175 ll or LL long long int long long int
3176 unsigned long long int
3178 Both u or U unsigned long long int unsigned long long int
3180 6 If an integer constant cannot be represented by any type in its list, it may have an
3181 extended integer type, if the extended integer type can represent its value. If all of the
3182 types in the list for the constant are signed, the extended integer type shall be signed. If
3183 all of the types in the list for the constant are unsigned, the extended integer type shall be
3184 unsigned. If the list contains both signed and unsigned types, the extended integer type
3185 may be signed or unsigned. If an integer constant cannot be represented by any type in
3186 its list and has no extended integer type, then the integer constant has no type.
3193 6.4.4.2 Floating constants
3195 1 floating-constant:
3196 decimal-floating-constant
3197 hexadecimal-floating-constant
3198 decimal-floating-constant:
3199 fractional-constant exponent-partopt floating-suffixopt
3200 digit-sequence exponent-part floating-suffixopt
3201 hexadecimal-floating-constant:
3202 hexadecimal-prefix hexadecimal-fractional-constant
3203 binary-exponent-part floating-suffixopt
3204 hexadecimal-prefix hexadecimal-digit-sequence
3205 binary-exponent-part floating-suffixopt
3206 fractional-constant:
3207 digit-sequenceopt . digit-sequence
3210 e signopt digit-sequence
3211 E signopt digit-sequence
3216 digit-sequence digit
3217 hexadecimal-fractional-constant:
3218 hexadecimal-digit-sequenceopt .
3219 hexadecimal-digit-sequence
3220 hexadecimal-digit-sequence .
3221 binary-exponent-part:
3222 p signopt digit-sequence
3223 P signopt digit-sequence
3224 hexadecimal-digit-sequence:
3226 hexadecimal-digit-sequence hexadecimal-digit
3227 floating-suffix: one of
3233 2 A floating constant has a significand part that may be followed by an exponent part and a
3234 suffix that specifies its type. The components of the significand part may include a digit
3235 sequence representing the whole-number part, followed by a period (.), followed by a
3236 digit sequence representing the fraction part. The components of the exponent part are an
3237 e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
3238 Either the whole-number part or the fraction part has to be present; for decimal floating
3239 constants, either the period or the exponent part has to be present.
3241 3 The significand part is interpreted as a (decimal or hexadecimal) rational number; the
3242 digit sequence in the exponent part is interpreted as a decimal integer. For decimal
3243 floating constants, the exponent indicates the power of 10 by which the significand part is
3244 to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
3245 by which the significand part is to be scaled. For decimal floating constants, and also for
3246 hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
3247 the nearest representable value, or the larger or smaller representable value immediately
3248 adjacent to the nearest representable value, chosen in an implementation-defined manner.
3249 For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
3251 4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
3252 type float. If suffixed by the letter l or L, it has type long double.
3253 5 Floating constants are converted to internal format as if at translation-time. The
3254 conversion of a floating constant shall not raise an exceptional condition or a floating-
3255 point exception at execution time.
3256 Recommended practice
3257 6 The implementation should produce a diagnostic message if a hexadecimal constant
3258 cannot be represented exactly in its evaluation format; the implementation should then
3259 proceed with the translation of the program.
3260 7 The translation-time conversion of floating constants should match the execution-time
3261 conversion of character strings by library functions, such as strtod, given matching
3262 inputs suitable for both conversions, the same result format, and default execution-time
3268 75) The specification for the library functions recommends more accurate conversion than required for
3269 floating constants (see 7.22.1.3).
3273 6.4.4.3 Enumeration constants
3275 1 enumeration-constant:
3278 2 An identifier declared as an enumeration constant has type int.
3279 Forward references: enumeration specifiers (6.7.2.2).
3280 6.4.4.4 Character constants
3282 1 character-constant:
3284 L' c-char-sequence '
3285 u' c-char-sequence '
3286 U' c-char-sequence '
3289 c-char-sequence c-char
3291 any member of the source character set except
3292 the single-quote ', backslash \, or new-line character
3295 simple-escape-sequence
3296 octal-escape-sequence
3297 hexadecimal-escape-sequence
3298 universal-character-name
3299 simple-escape-sequence: one of
3301 \a \b \f \n \r \t \v
3302 octal-escape-sequence:
3304 \ octal-digit octal-digit
3305 \ octal-digit octal-digit octal-digit
3312 hexadecimal-escape-sequence:
3313 \x hexadecimal-digit
3314 hexadecimal-escape-sequence hexadecimal-digit
3316 2 An integer character constant is a sequence of one or more multibyte characters enclosed
3317 in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
3318 letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
3319 any members of the source character set; they are mapped in an implementation-defined
3320 manner to members of the execution character set.
3321 3 The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
3322 arbitrary integer values are representable according to the following table of escape
3328 octal character \octal digits
3329 hexadecimal character \x hexadecimal digits
3330 4 The double-quote " and question-mark ? are representable either by themselves or by the
3331 escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
3332 shall be represented, respectively, by the escape sequences \' and \\.
3333 5 The octal digits that follow the backslash in an octal escape sequence are taken to be part
3334 of the construction of a single character for an integer character constant or of a single
3335 wide character for a wide character constant. The numerical value of the octal integer so
3336 formed specifies the value of the desired character or wide character.
3337 6 The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
3338 sequence are taken to be part of the construction of a single character for an integer
3339 character constant or of a single wide character for a wide character constant. The
3340 numerical value of the hexadecimal integer so formed specifies the value of the desired
3341 character or wide character.
3342 7 Each octal or hexadecimal escape sequence is the longest sequence of characters that can
3343 constitute the escape sequence.
3344 8 In addition, characters not in the basic character set are representable by universal
3345 character names and certain nongraphic characters are representable by escape sequences
3346 consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
3354 9 The value of an octal or hexadecimal escape sequence shall be in the range of
3355 representable values for the corresponding type:
3356 Prefix Corresponding Type
3358 L the unsigned type corresponding to wchar_t
3362 10 An integer character constant has type int. The value of an integer character constant
3363 containing a single character that maps to a single-byte execution character is the
3364 numerical value of the representation of the mapped character interpreted as an integer.
3365 The value of an integer character constant containing more than one character (e.g.,
3366 'ab'), or containing a character or escape sequence that does not map to a single-byte
3367 execution character, is implementation-defined. If an integer character constant contains
3368 a single character or escape sequence, its value is the one that results when an object with
3369 type char whose value is that of the single character or escape sequence is converted to
3371 11 A wide character constant prefixed by the letter L has type wchar_t, an integer type
3372 defined in the <stddef.h> header; a wide character constant prefixed by the letter u or
3373 U has type char16_t or char32_t, respectively, unsigned integer types defined in the
3374 <uchar.h> header. The value of a wide character constant containing a single
3375 multibyte character that maps to a single member of the extended execution character set
3376 is the wide character corresponding to that multibyte character, as defined by the
3377 mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an
3378 implementation-defined current locale. The value of a wide character constant containing
3379 more than one multibyte character or a single multibyte character that maps to multiple
3380 members of the extended execution character set, or containing a multibyte character or
3381 escape sequence not represented in the extended execution character set, is
3382 implementation-defined.
3383 12 EXAMPLE 1 The construction '\0' is commonly used to represent the null character.
3385 13 EXAMPLE 2 Consider implementations that use two's-complement representation for integers and eight
3386 bits for objects that have type char. In an implementation in which type char has the same range of
3387 values as signed char, the integer character constant '\xFF' has the value -1; if type char has the
3388 same range of values as unsigned char, the character constant '\xFF' has the value +255.
3393 76) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
3394 the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4).
3398 14 EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
3399 specifies an integer character constant containing only one character, since a hexadecimal escape sequence
3400 is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
3401 two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
3402 escape sequence is terminated after three octal digits. (The value of this two-character integer character
3403 constant is implementation-defined.)
3405 15 EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
3406 L'\1234' specifies the implementation-defined value that results from the combination of the values
3409 Forward references: common definitions <stddef.h> (7.19), the mbtowc function
3410 (7.22.7.2), Unicode utilities <uchar.h> (7.27).
3411 6.4.5 String literals
3414 encoding-prefixopt " s-char-sequenceopt "
3422 s-char-sequence s-char
3424 any member of the source character set except
3425 the double-quote ", backslash \, or new-line character
3428 2 A sequence of adjacent string literal tokens shall not include both a wide string literal and
3429 a UTF-8 string literal.
3431 3 A character string literal is a sequence of zero or more multibyte characters enclosed in
3432 double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8.
3433 A wide string literal is the same, except prefixed by the letter L, u, or U.
3434 4 The same considerations apply to each element of the sequence in a string literal as if it
3435 were in an integer character constant (for a character or UTF-8 string literal) or a wide
3436 character constant (for a wide string literal), except that the single-quote ' is
3437 representable either by itself or by the escape sequence \', but the double-quote " shall
3440 be represented by the escape sequence \".
3442 5 In translation phase 6, the multibyte character sequences specified by any sequence of
3443 adjacent character and identically-prefixed string literal tokens are concatenated into a
3444 single multibyte character sequence. If any of the tokens has an encoding prefix, the
3445 resulting multibyte character sequence is treated as having the same prefix; otherwise, it
3446 is treated as a character string literal. Whether differently-prefixed wide string literal
3447 tokens can be concatenated and, if so, the treatment of the resulting multibyte character
3448 sequence are implementation-defined.
3449 6 In translation phase 7, a byte or code of value zero is appended to each multibyte
3450 character sequence that results from a string literal or literals.77) The multibyte character
3451 sequence is then used to initialize an array of static storage duration and length just
3452 sufficient to contain the sequence. For character string literals, the array elements have
3453 type char, and are initialized with the individual bytes of the multibyte character
3454 sequence. For UTF-8 string literals, the array elements have type char, and are
3455 initialized with the characters of the multibyte character sequence, as encoded in UTF-8.
3456 For wide string literals prefixed by the letter L, the array elements have type wchar_t
3457 and are initialized with the sequence of wide characters corresponding to the multibyte
3458 character sequence, as defined by the mbstowcs function with an implementation-
3459 defined current locale. For wide string literals prefixed by the letter u or U, the array
3460 elements have type char16_t or char32_t, respectively, and are initialized with the
3461 sequence of wide characters corresponding to the multibyte character sequence, as
3462 defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
3463 its type, with an implementation-defined current locale. The value of a string literal
3464 containing a multibyte character or escape sequence not represented in the execution
3465 character set is implementation-defined.
3466 7 It is unspecified whether these arrays are distinct provided their elements have the
3467 appropriate values. If the program attempts to modify such an array, the behavior is
3469 8 EXAMPLE 1 This pair of adjacent character string literals
3471 produces a single character string literal containing the two characters whose values are '\x12' and '3',
3472 because escape sequences are converted into single members of the execution character set just prior to
3473 adjacent string literal concatenation.
3475 9 EXAMPLE 2 Each of the sequences of adjacent string literal tokens
3479 77) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
3488 is equivalent to the string literal
3490 Likewise, each of the sequences
3498 Forward references: common definitions <stddef.h> (7.19), the mbstowcs
3499 function (7.22.8.1), Unicode utilities <uchar.h> (7.27).
3502 1 punctuator: one of
3505 / % << >> < > <= >= == != ^ | && ||
3507 = *= /= %= += -= <<= >>= &= ^= |=
3511 2 A punctuator is a symbol that has independent syntactic and semantic significance.
3512 Depending on context, it may specify an operation to be performed (which in turn may
3513 yield a value or a function designator, produce a side effect, or some combination thereof)
3514 in which case it is known as an operator (other forms of operator also exist in some
3515 contexts). An operand is an entity on which an operator acts.
3522 3 In all aspects of the language, the six tokens78)
3524 behave, respectively, the same as the six tokens
3526 except for their spelling.79)
3527 Forward references: expressions (6.5), declarations (6.7), preprocessing directives
3528 (6.10), statements (6.8).
3536 h-char-sequence h-char
3538 any member of the source character set except
3539 the new-line character and >
3542 q-char-sequence q-char
3544 any member of the source character set except
3545 the new-line character and "
3547 2 The sequences in both forms of header names are mapped in an implementation-defined
3548 manner to headers or external source file names as specified in 6.10.2.
3549 3 If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
3550 the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the
3555 78) These tokens are sometimes called ''digraphs''.
3556 79) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely
3561 sequence between the " delimiters, the behavior is undefined.80) Header name
3562 preprocessing tokens are recognized only within #include preprocessing directives and
3563 in implementation-defined locations within #pragma directives.81)
3564 4 EXAMPLE The following sequence of characters:
3567 #define const.member@$
3568 forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
3569 by a { on the left and a } on the right).
3570 {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
3571 {#}{include} {<1/a.h>}
3572 {#}{define} {const}{.}{member}{@}{$}
3574 Forward references: source file inclusion (6.10.2).
3575 6.4.8 Preprocessing numbers
3581 pp-number identifier-nondigit
3588 2 A preprocessing number begins with a digit optionally preceded by a period (.) and may
3589 be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
3591 3 Preprocessing number tokens lexically include all floating and integer constant tokens.
3593 4 A preprocessing number does not have type or a value; it acquires both after a successful
3594 conversion (as part of translation phase 7) to a floating constant token or an integer
3598 80) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
3599 81) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.
3604 1 Except within a character constant, a string literal, or a comment, the characters /*
3605 introduce a comment. The contents of such a comment are examined only to identify
3606 multibyte characters and to find the characters */ that terminate it.82)
3607 2 Except within a character constant, a string literal, or a comment, the characters //
3608 introduce a comment that includes all multibyte characters up to, but not including, the
3609 next new-line character. The contents of such a comment are examined only to identify
3610 multibyte characters and to find the terminating new-line character.
3612 "a//b" // four-character string literal
3613 #include "//e" // undefined behavior
3614 // */ // comment, not syntax error
3615 f = g/**//h; // equivalent to f = g / h;
3617 i(); // part of a two-line comment
3619 / j(); // part of a two-line comment
3620 #define glue(x,y) x##y
3621 glue(/,/) k(); // syntax error, not comment
3622 /*//*/ l(); // equivalent to l();
3624 + p; // equivalent to m = n + p;
3629 82) Thus, /* ... */ comments do not nest.
3634 1 An expression is a sequence of operators and operands that specifies computation of a
3635 value, or that designates an object or a function, or that generates side effects, or that
3636 performs a combination thereof. The value computations of the operands of an operator
3637 are sequenced before the value computation of the result of the operator.
3638 2 If a side effect on a scalar object is unsequenced relative to either a different side effect
3639 on the same scalar object or a value computation using the value of the same scalar
3640 object, the behavior is undefined. If there are multiple allowable orderings of the
3641 subexpressions of an expression, the behavior is undefined if such an unsequenced side
3642 effect occurs in any of the orderings.83)
3643 3 The grouping of operators and operands is indicated by the syntax.84) Except as specified
3644 later, side effects and value computations of subexpressions are unsequenced.85)
3645 4 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
3646 collectively described as bitwise operators) are required to have operands that have
3647 integer type. These operators yield values that depend on the internal representations of
3648 integers, and have implementation-defined and undefined aspects for signed types.
3649 5 If an exceptional condition occurs during the evaluation of an expression (that is, if the
3650 result is not mathematically defined or not in the range of representable values for its
3651 type), the behavior is undefined.
3655 83) This paragraph renders undefined statement expressions such as
3662 84) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
3663 as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
3664 expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
3665 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
3666 (6.5.3), and an operand contained between any of the following pairs of operators: grouping
3667 parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
3668 the conditional operator ? : (6.5.15).
3669 Within each major subclause, the operators have the same precedence. Left- or right-associativity is
3670 indicated in each subclause by the syntax for the expressions discussed therein.
3671 85) In an expression that is evaluated more than once during the execution of a program, unsequenced and
3672 indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
3673 different evaluations.
3677 6 The effective type of an object for an access to its stored value is the declared type of the
3678 object, if any.86) If a value is stored into an object having no declared type through an
3679 lvalue having a type that is not a character type, then the type of the lvalue becomes the
3680 effective type of the object for that access and for subsequent accesses that do not modify
3681 the stored value. If a value is copied into an object having no declared type using
3682 memcpy or memmove, or is copied as an array of character type, then the effective type
3683 of the modified object for that access and for subsequent accesses that do not modify the
3684 value is the effective type of the object from which the value is copied, if it has one. For
3685 all other accesses to an object having no declared type, the effective type of the object is
3686 simply the type of the lvalue used for the access.
3687 7 An object shall have its stored value accessed only by an lvalue expression that has one of
3688 the following types:87)
3689 -- a type compatible with the effective type of the object,
3690 -- a qualified version of a type compatible with the effective type of the object,
3691 -- a type that is the signed or unsigned type corresponding to the effective type of the
3693 -- a type that is the signed or unsigned type corresponding to a qualified version of the
3694 effective type of the object,
3695 -- an aggregate or union type that includes one of the aforementioned types among its
3696 members (including, recursively, a member of a subaggregate or contained union), or
3697 -- a character type.
3698 8 A floating expression may be contracted, that is, evaluated as though it were a single
3699 operation, thereby omitting rounding errors implied by the source code and the
3700 expression evaluation method.88) The FP_CONTRACT pragma in <math.h> provides a
3701 way to disallow contracted expressions. Otherwise, whether and how expressions are
3702 contracted is implementation-defined.89)
3703 Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2).
3706 86) Allocated objects have no declared type.
3707 87) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
3708 88) The intermediate operations in the contracted expression are evaluated as if to infinite precision and
3709 range, while the final operation is rounded to the format determined by the expression evaluation
3710 method. A contracted expression might also omit the raising of floating-point exceptions.
3711 89) This license is specifically intended to allow implementations to exploit fast machine instructions that
3712 combine multiple C operators. As contractions potentially undermine predictability, and can even
3713 decrease accuracy for containing expressions, their use needs to be well-defined and clearly
3718 6.5.1 Primary expressions
3720 1 primary-expression:
3727 2 An identifier is a primary expression, provided it has been declared as designating an
3728 object (in which case it is an lvalue) or a function (in which case it is a function
3730 3 A constant is a primary expression. Its type depends on its form and value, as detailed in
3732 4 A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
3733 5 A parenthesized expression is a primary expression. Its type and value are identical to
3734 those of the unparenthesized expression. It is an lvalue, a function designator, or a void
3735 expression if the unparenthesized expression is, respectively, an lvalue, a function
3736 designator, or a void expression.
3737 Forward references: declarations (6.7).
3738 6.5.1.1 Generic selection
3740 1 generic-selection:
3741 _Generic ( assignment-expression , generic-assoc-list )
3744 generic-assoc-list , generic-association
3745 generic-association:
3746 type-name : assignment-expression
3747 default : assignment-expression
3749 2 A generic selection shall have no more than one default generic association. The type
3750 name in a generic association shall specify a complete object type other than a variably
3752 90) Thus, an undeclared identifier is a violation of the syntax.
3756 modified type. No two generic associations in the same generic selection shall specify
3757 compatible types. The controlling expression of a generic selection shall have type
3758 compatible with at most one of the types named in its generic association list. If a
3759 generic selection has no default generic association, its controlling expression shall
3760 have type compatible with exactly one of the types named in its generic association list.
3762 3 The controlling expression of a generic selection is not evaluated. If a generic selection
3763 has a generic association with a type name that is compatible with the type of the
3764 controlling expression, then the result expression of the generic selection is the
3765 expression in that generic association. Otherwise, the result expression of the generic
3766 selection is the expression in the default generic association. None of the expressions
3767 from any other generic association of the generic selection is evaluated.
3768 4 The type and value of a generic selection are identical to those of its result expression. It
3769 is an lvalue, a function designator, or a void expression if its result expression is,
3770 respectively, an lvalue, a function designator, or a void expression.
3771 5 EXAMPLE The cbrt type-generic macro could be implemented as follows:
3772 #define cbrt(X) _Generic((X), \
3773 long double: cbrtl, \
3778 6.5.2 Postfix operators
3780 1 postfix-expression:
3782 postfix-expression [ expression ]
3783 postfix-expression ( argument-expression-listopt )
3784 postfix-expression . identifier
3785 postfix-expression -> identifier
3786 postfix-expression ++
3787 postfix-expression --
3788 ( type-name ) { initializer-list }
3789 ( type-name ) { initializer-list , }
3790 argument-expression-list:
3791 assignment-expression
3792 argument-expression-list , assignment-expression
3799 6.5.2.1 Array subscripting
3801 1 One of the expressions shall have type ''pointer to complete object type'', the other
3802 expression shall have integer type, and the result has type ''type''.
3804 2 A postfix expression followed by an expression in square brackets [] is a subscripted
3805 designation of an element of an array object. The definition of the subscript operator []
3806 is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
3807 apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
3808 initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
3809 element of E1 (counting from zero).
3810 3 Successive subscript operators designate an element of a multidimensional array object.
3811 If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as
3812 other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with
3813 dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or
3814 implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional
3815 array, which itself is converted into a pointer if used as other than an lvalue. It follows
3816 from this that arrays are stored in row-major order (last subscript varies fastest).
3817 4 EXAMPLE Consider the array object defined by the declaration
3819 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
3820 array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
3821 a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
3822 entails multiplying i by the size of the object to which the pointer points, namely an array of five int
3823 objects. The results are added and indirection is applied to yield an array of five ints. When used in the
3824 expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
3827 Forward references: additive operators (6.5.6), address and indirection operators
3828 (6.5.3.2), array declarators (6.7.6.2).
3829 6.5.2.2 Function calls
3831 1 The expression that denotes the called function91) shall have type pointer to function
3832 returning void or returning a complete object type other than an array type.
3833 2 If the expression that denotes the called function has a type that includes a prototype, the
3834 number of arguments shall agree with the number of parameters. Each argument shall
3837 91) Most often, this is the result of converting an identifier that is a function designator.
3841 have a type such that its value may be assigned to an object with the unqualified version
3842 of the type of its corresponding parameter.
3844 3 A postfix expression followed by parentheses () containing a possibly empty, comma-
3845 separated list of expressions is a function call. The postfix expression denotes the called
3846 function. The list of expressions specifies the arguments to the function.
3847 4 An argument may be an expression of any complete object type. In preparing for the call
3848 to a function, the arguments are evaluated, and each parameter is assigned the value of the
3849 corresponding argument.92)
3850 5 If the expression that denotes the called function has type pointer to function returning an
3851 object type, the function call expression has the same type as that object type, and has the
3852 value determined as specified in 6.8.6.4. Otherwise, the function call has type void.
3853 6 If the expression that denotes the called function has a type that does not include a
3854 prototype, the integer promotions are performed on each argument, and arguments that
3855 have type float are promoted to double. These are called the default argument
3856 promotions. If the number of arguments does not equal the number of parameters, the
3857 behavior is undefined. If the function is defined with a type that includes a prototype, and
3858 either the prototype ends with an ellipsis (, ...) or the types of the arguments after
3859 promotion are not compatible with the types of the parameters, the behavior is undefined.
3860 If the function is defined with a type that does not include a prototype, and the types of
3861 the arguments after promotion are not compatible with those of the parameters after
3862 promotion, the behavior is undefined, except for the following cases:
3863 -- one promoted type is a signed integer type, the other promoted type is the
3864 corresponding unsigned integer type, and the value is representable in both types;
3865 -- both types are pointers to qualified or unqualified versions of a character type or
3867 7 If the expression that denotes the called function has a type that does include a prototype,
3868 the arguments are implicitly converted, as if by assignment, to the types of the
3869 corresponding parameters, taking the type of each parameter to be the unqualified version
3870 of its declared type. The ellipsis notation in a function prototype declarator causes
3871 argument type conversion to stop after the last declared parameter. The default argument
3872 promotions are performed on trailing arguments.
3876 92) A function may change the values of its parameters, but these changes cannot affect the values of the
3877 arguments. On the other hand, it is possible to pass a pointer to an object, and the function may
3878 change the value of the object pointed to. A parameter declared to have array or function type is
3879 adjusted to have a pointer type as described in 6.9.1.
3883 8 No other conversions are performed implicitly; in particular, the number and types of
3884 arguments are not compared with those of the parameters in a function definition that
3885 does not include a function prototype declarator.
3886 9 If the function is defined with a type that is not compatible with the type (of the
3887 expression) pointed to by the expression that denotes the called function, the behavior is
3889 10 There is a sequence point after the evaluations of the function designator and the actual
3890 arguments but before the actual call. Every evaluation in the calling function (including
3891 other function calls) that is not otherwise specifically sequenced before or after the
3892 execution of the body of the called function is indeterminately sequenced with respect to
3893 the execution of the called function.93)
3894 11 Recursive function calls shall be permitted, both directly and indirectly through any chain
3896 12 EXAMPLE In the function call
3897 (*pf[f1()]) (f2(), f3() + f4())
3898 the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
3899 the function pointed to by pf[f1()] is called.
3901 Forward references: function declarators (including prototypes) (6.7.6.3), function
3902 definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
3903 6.5.2.3 Structure and union members
3905 1 The first operand of the . operator shall have a qualified or unqualified structure or union
3906 type, and the second operand shall name a member of that type.
3907 2 The first operand of the -> operator shall have type ''pointer to qualified or unqualified
3908 structure'' or ''pointer to qualified or unqualified union'', and the second operand shall
3909 name a member of the type pointed to.
3911 3 A postfix expression followed by the . operator and an identifier designates a member of
3912 a structure or union object. The value is that of the named member,94) and is an lvalue if
3913 the first expression is an lvalue. If the first expression has qualified type, the result has
3914 the so-qualified version of the type of the designated member.
3916 93) In other words, function executions do not ''interleave'' with each other.
3917 94) If the member used to access the contents of a union object is not the same as the member last used to
3918 store a value in the object, the appropriate part of the object representation of the value is reinterpreted
3919 as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type
3920 punning''). This might be a trap representation.
3924 4 A postfix expression followed by the -> operator and an identifier designates a member
3925 of a structure or union object. The value is that of the named member of the object to
3926 which the first expression points, and is an lvalue.95) If the first expression is a pointer to
3927 a qualified type, the result has the so-qualified version of the type of the designated
3929 5 Accessing a member of an _Atomic-qualified structure or union object results in
3930 undefined behavior.96)
3931 6 One special guarantee is made in order to simplify the use of unions: if a union contains
3932 several structures that share a common initial sequence (see below), and if the union
3933 object currently contains one of these structures, it is permitted to inspect the common
3934 initial part of any of them anywhere that a declaration of the completed type of the union
3935 is visible. Two structures share a common initial sequence if corresponding members
3936 have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
3938 7 EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
3939 union, f().x is a valid postfix expression but is not an lvalue.
3942 struct s { int i; const int ci; };
3945 volatile struct s vs;
3946 the various members have the types:
3952 vs.ci volatile const int
3957 95) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to
3958 its operand), the expression (&E)->MOS is the same as E.MOS.
3959 96) A data race would occur if access to the entire structure or union in one thread conflicts with access to
3960 a member from another thread, where at least one access is a modification. Such a data race results in
3965 9 EXAMPLE 3 The following is a valid fragment:
3980 u.nf.doublenode = 3.14;
3982 if (u.n.alltypes == 1)
3983 if (sin(u.nf.doublenode) == 0.0)
3985 The following is not a valid fragment (because the union type is not visible within function f):
3986 struct t1 { int m; };
3987 struct t2 { int m; };
3988 int f(struct t1 *p1, struct t2 *p2)
4001 return f(&u.s1, &u.s2);
4004 Forward references: address and indirection operators (6.5.3.2), structure and union
4005 specifiers (6.7.2.1).
4012 6.5.2.4 Postfix increment and decrement operators
4014 1 The operand of the postfix increment or decrement operator shall have qualified or
4015 unqualified real or pointer type and shall be a modifiable lvalue.
4017 2 The result of the postfix ++ operator is the value of the operand. As a side effect, the
4018 value of the operand object is incremented (that is, the value 1 of the appropriate type is
4019 added to it). See the discussions of additive operators and compound assignment for
4020 information on constraints, types, and conversions and the effects of operations on
4021 pointers. The value computation of the result is sequenced before the side effect of
4022 updating the stored value of the operand. With respect to an indeterminately-sequenced
4023 function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
4024 with _Atomic-qualified type is a read-modify-write operation with
4026 memory_order_seq_cst memory order semantics.
4027 3 The postfix -- operator is analogous to the postfix ++ operator, except that the value of
4028 the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
4030 Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
4031 6.5.2.5 Compound literals
4033 1 The type name shall specify a complete object type or an array of unknown size, but not a
4034 variable length array type.
4035 2 All the constraints for initializer lists in 6.7.9 also apply to compound literals.
4037 3 A postfix expression that consists of a parenthesized type name followed by a brace-
4038 enclosed list of initializers is a compound literal. It provides an unnamed object whose
4039 value is given by the initializer list.98)
4042 97) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
4043 where T is the type of E:
4048 } while (!atomic_compare_exchange_strong(&E, &result, tmp));
4049 with result being the result of the operation.
4053 4 If the type name specifies an array of unknown size, the size is determined by the
4054 initializer list as specified in 6.7.9, and the type of the compound literal is that of the
4055 completed array type. Otherwise (when the type name specifies an object type), the type
4056 of the compound literal is that specified by the type name. In either case, the result is an
4058 5 The value of the compound literal is that of an unnamed object initialized by the
4059 initializer list. If the compound literal occurs outside the body of a function, the object
4060 has static storage duration; otherwise, it has automatic storage duration associated with
4061 the enclosing block.
4062 6 All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.99)
4063 7 String literals, and compound literals with const-qualified types, need not designate
4064 distinct objects.100)
4065 8 EXAMPLE 1 The file scope definition
4066 int *p = (int []){2, 4};
4067 initializes p to point to the first element of an array of two ints, the first having the value two and the
4068 second, four. The expressions in this compound literal are required to be constant. The unnamed object
4069 has static storage duration.
4071 9 EXAMPLE 2 In contrast, in
4079 p is assigned the address of the first element of an array of two ints, the first having the value previously
4080 pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
4081 unnamed object has automatic storage duration.
4083 10 EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
4084 created using compound literals can be passed to functions without depending on member order:
4085 drawline((struct point){.x=1, .y=1},
4086 (struct point){.x=3, .y=4});
4087 Or, if drawline instead expected pointers to struct point:
4091 98) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
4092 or void only, and the result of a cast expression is not an lvalue.
4093 99) For example, subobjects without explicit initializers are initialized to zero.
4094 100) This allows implementations to share storage for string literals and constant compound literals with
4095 the same or overlapping representations.
4099 drawline(&(struct point){.x=1, .y=1},
4100 &(struct point){.x=3, .y=4});
4102 11 EXAMPLE 4 A read-only compound literal can be specified through constructions like:
4103 (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
4105 12 EXAMPLE 5 The following three expressions have different meanings:
4107 (char []){"/tmp/fileXXXXXX"}
4108 (const char []){"/tmp/fileXXXXXX"}
4109 The first always has static storage duration and has type array of char, but need not be modifiable; the last
4110 two have automatic storage duration when they occur within the body of a function, and the first of these
4113 13 EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
4114 and can even be shared. For example,
4115 (const char []){"abc"} == "abc"
4116 might yield 1 if the literals' storage is shared.
4118 14 EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
4119 linked object. For example, there is no way to write a self-referential compound literal that could be used
4120 as the function argument in place of the named object endless_zeros below:
4121 struct int_list { int car; struct int_list *cdr; };
4122 struct int_list endless_zeros = {0, &endless_zeros};
4123 eval(endless_zeros);
4125 15 EXAMPLE 8 Each compound literal creates only a single object in a given scope:
4126 struct s { int i; };
4129 struct s *p = 0, *q;
4132 q = p, p = &((struct s){ j++ });
4133 if (j < 2) goto again;
4134 return p == q && q->i == 1;
4136 The function f() always returns the value 1.
4137 16 Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
4138 lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
4139 have an indeterminate value, which would result in undefined behavior.
4141 Forward references: type names (6.7.7), initialization (6.7.9).
4148 6.5.3 Unary operators
4154 unary-operator cast-expression
4155 sizeof unary-expression
4156 sizeof ( type-name )
4157 alignof ( type-name )
4158 unary-operator: one of
4160 6.5.3.1 Prefix increment and decrement operators
4162 1 The operand of the prefix increment or decrement operator shall have qualified or
4163 unqualified real or pointer type and shall be a modifiable lvalue.
4165 2 The value of the operand of the prefix ++ operator is incremented. The result is the new
4166 value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
4167 See the discussions of additive operators and compound assignment for information on
4168 constraints, types, side effects, and conversions and the effects of operations on pointers.
4169 3 The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
4170 operand is decremented.
4171 Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
4172 6.5.3.2 Address and indirection operators
4174 1 The operand of the unary & operator shall be either a function designator, the result of a
4175 [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
4176 not declared with the register storage-class specifier.
4177 2 The operand of the unary * operator shall have pointer type.
4179 3 The unary & operator yields the address of its operand. If the operand has type ''type'',
4180 the result has type ''pointer to type''. If the operand is the result of a unary * operator,
4181 neither that operator nor the & operator is evaluated and the result is as if both were
4182 omitted, except that the constraints on the operators still apply and the result is not an
4186 lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
4187 the unary * that is implied by the [] is evaluated and the result is as if the & operator
4188 were removed and the [] operator were changed to a + operator. Otherwise, the result is
4189 a pointer to the object or function designated by its operand.
4190 4 The unary * operator denotes indirection. If the operand points to a function, the result is
4191 a function designator; if it points to an object, the result is an lvalue designating the
4192 object. If the operand has type ''pointer to type'', the result has type ''type''. If an
4193 invalid value has been assigned to the pointer, the behavior of the unary * operator is
4195 Forward references: storage-class specifiers (6.7.1), structure and union specifiers
4197 6.5.3.3 Unary arithmetic operators
4199 1 The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
4200 integer type; of the ! operator, scalar type.
4202 2 The result of the unary + operator is the value of its (promoted) operand. The integer
4203 promotions are performed on the operand, and the result has the promoted type.
4204 3 The result of the unary - operator is the negative of its (promoted) operand. The integer
4205 promotions are performed on the operand, and the result has the promoted type.
4206 4 The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
4207 each bit in the result is set if and only if the corresponding bit in the converted operand is
4208 not set). The integer promotions are performed on the operand, and the result has the
4209 promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
4210 to the maximum value representable in that type minus E.
4211 5 The result of the logical negation operator ! is 0 if the value of its operand compares
4212 unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
4213 The expression !E is equivalent to (0==E).
4217 101) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
4218 always true that if E is a function designator or an lvalue that is a valid operand of the unary &
4219 operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
4220 an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
4221 Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
4222 address inappropriately aligned for the type of object pointed to, and the address of an object after the
4223 end of its lifetime.
4227 6.5.3.4 The sizeof and alignof operators
4229 1 The sizeof operator shall not be applied to an expression that has function type or an
4230 incomplete type, to the parenthesized name of such a type, or to an expression that
4231 designates a bit-field member. The alignof operator shall not be applied to a function
4232 type or an incomplete type.
4234 2 The sizeof operator yields the size (in bytes) of its operand, which may be an
4235 expression or the parenthesized name of a type. The size is determined from the type of
4236 the operand. The result is an integer. If the type of the operand is a variable length array
4237 type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
4239 3 The alignof operator yields the alignment requirement of its operand type. The result
4240 is an integer constant. When applied to an array type, the result is the alignment
4241 requirement of the element type.
4242 4 When sizeof is applied to an operand that has type char, unsigned char, or
4243 signed char, (or a qualified version thereof) the result is 1. When applied to an
4244 operand that has array type, the result is the total number of bytes in the array.102) When
4245 applied to an operand that has structure or union type, the result is the total number of
4246 bytes in such an object, including internal and trailing padding.
4247 5 The value of the result of both operators is implementation-defined, and its type (an
4248 unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
4249 6 EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
4250 allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
4251 allocate and return a pointer to void. For example:
4252 extern void *alloc(size_t);
4253 double *dp = alloc(sizeof *dp);
4254 The implementation of the alloc function should ensure that its return value is aligned suitably for
4255 conversion to a pointer to double.
4257 7 EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array:
4258 sizeof array / sizeof array[0]
4260 8 EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a
4266 102) When applied to a parameter declared to have array or function type, the sizeof operator yields the
4267 size of the adjusted (pointer) type (see 6.9.1).
4271 size_t fsize3(int n)
4273 char b[n+3]; // variable length array
4274 return sizeof b; // execution time sizeof
4279 size = fsize3(10); // fsize3 returns 13
4283 Forward references: common definitions <stddef.h> (7.19), declarations (6.7),
4284 structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).
4285 6.5.4 Cast operators
4289 ( type-name ) cast-expression
4291 2 Unless the type name specifies a void type, the type name shall specify qualified or
4292 unqualified scalar type and the operand shall have scalar type.
4293 3 Conversions that involve pointers, other than where permitted by the constraints of
4294 6.5.16.1, shall be specified by means of an explicit cast.
4295 4 A pointer type shall not be converted to any floating type. A floating type shall not be
4296 converted to any pointer type.
4298 5 Preceding an expression by a parenthesized type name converts the value of the
4299 expression to the named type. This construction is called a cast.103) A cast that specifies
4300 no conversion has no effect on the type or value of an expression.
4301 6 If the value of the expression is represented with greater precision or range than required
4302 by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
4303 type of the expression is the same as the named type.
4304 Forward references: equality operators (6.5.9), function declarators (including
4305 prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).
4309 103) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
4310 unqualified version of the type.
4314 6.5.5 Multiplicative operators
4316 1 multiplicative-expression:
4318 multiplicative-expression * cast-expression
4319 multiplicative-expression / cast-expression
4320 multiplicative-expression % cast-expression
4322 2 Each of the operands shall have arithmetic type. The operands of the % operator shall
4325 3 The usual arithmetic conversions are performed on the operands.
4326 4 The result of the binary * operator is the product of the operands.
4327 5 The result of the / operator is the quotient from the division of the first operand by the
4328 second; the result of the % operator is the remainder. In both operations, if the value of
4329 the second operand is zero, the behavior is undefined.
4330 6 When integers are divided, the result of the / operator is the algebraic quotient with any
4331 fractional part discarded.104) If the quotient a/b is representable, the expression
4332 (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
4334 6.5.6 Additive operators
4336 1 additive-expression:
4337 multiplicative-expression
4338 additive-expression + multiplicative-expression
4339 additive-expression - multiplicative-expression
4341 2 For addition, either both operands shall have arithmetic type, or one operand shall be a
4342 pointer to a complete object type and the other shall have integer type. (Incrementing is
4343 equivalent to adding 1.)
4344 3 For subtraction, one of the following shall hold:
4349 104) This is often called ''truncation toward zero''.
4353 -- both operands have arithmetic type;
4354 -- both operands are pointers to qualified or unqualified versions of compatible complete
4356 -- the left operand is a pointer to a complete object type and the right operand has
4358 (Decrementing is equivalent to subtracting 1.)
4360 4 If both operands have arithmetic type, the usual arithmetic conversions are performed on
4362 5 The result of the binary + operator is the sum of the operands.
4363 6 The result of the binary - operator is the difference resulting from the subtraction of the
4364 second operand from the first.
4365 7 For the purposes of these operators, a pointer to an object that is not an element of an
4366 array behaves the same as a pointer to the first element of an array of length one with the
4367 type of the object as its element type.
4368 8 When an expression that has integer type is added to or subtracted from a pointer, the
4369 result has the type of the pointer operand. If the pointer operand points to an element of
4370 an array object, and the array is large enough, the result points to an element offset from
4371 the original element such that the difference of the subscripts of the resulting and original
4372 array elements equals the integer expression. In other words, if the expression P points to
4373 the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
4374 (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
4375 the array object, provided they exist. Moreover, if the expression P points to the last
4376 element of an array object, the expression (P)+1 points one past the last element of the
4377 array object, and if the expression Q points one past the last element of an array object,
4378 the expression (Q)-1 points to the last element of the array object. If both the pointer
4379 operand and the result point to elements of the same array object, or one past the last
4380 element of the array object, the evaluation shall not produce an overflow; otherwise, the
4381 behavior is undefined. If the result points one past the last element of the array object, it
4382 shall not be used as the operand of a unary * operator that is evaluated.
4383 9 When two pointers are subtracted, both shall point to elements of the same array object,
4384 or one past the last element of the array object; the result is the difference of the
4385 subscripts of the two array elements. The size of the result is implementation-defined,
4386 and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
4387 If the result is not representable in an object of that type, the behavior is undefined. In
4388 other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of
4389 an array object, the expression (P)-(Q) has the value i-j provided the value fits in an
4393 object of type ptrdiff_t. Moreover, if the expression P points either to an element of
4394 an array object or one past the last element of an array object, and the expression Q points
4395 to the last element of the same array object, the expression ((Q)+1)-(P) has the same
4396 value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
4397 expression P points one past the last element of the array object, even though the
4398 expression (Q)+1 does not point to an element of the array object.105)
4399 10 EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types.
4403 int (*p)[m] = a; // p == &a[0]
4404 p += 1; // p == &a[1]
4405 (*p)[2] = 99; // a[1][2] == 99
4406 n = p - a; // n == 1
4408 11 If array a in the above example were declared to be an array of known constant size, and pointer p were
4409 declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
4412 Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
4414 6.5.7 Bitwise shift operators
4418 shift-expression << additive-expression
4419 shift-expression >> additive-expression
4421 2 Each of the operands shall have integer type.
4423 3 The integer promotions are performed on each of the operands. The type of the result is
4424 that of the promoted left operand. If the value of the right operand is negative or is
4426 105) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
4427 this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
4428 by the size of the object originally pointed to, and the resulting pointer is converted back to the
4429 original type. For pointer subtraction, the result of the difference between the character pointers is
4430 similarly divided by the size of the object originally pointed to.
4431 When viewed in this way, an implementation need only provide one extra byte (which may overlap
4432 another object in the program) just after the end of the object in order to satisfy the ''one past the last
4433 element'' requirements.
4437 greater than or equal to the width of the promoted left operand, the behavior is undefined.
4438 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
4439 zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo
4440 one more than the maximum value representable in the result type. If E1 has a signed
4441 type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is
4442 the resulting value; otherwise, the behavior is undefined.
4443 5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
4444 or if E1 has a signed type and a nonnegative value, the value of the result is the integral
4445 part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
4446 resulting value is implementation-defined.
4447 6.5.8 Relational operators
4449 1 relational-expression:
4451 relational-expression < shift-expression
4452 relational-expression > shift-expression
4453 relational-expression <= shift-expression
4454 relational-expression >= shift-expression
4456 2 One of the following shall hold:
4457 -- both operands have real type; or
4458 -- both operands are pointers to qualified or unqualified versions of compatible object
4461 3 If both of the operands have arithmetic type, the usual arithmetic conversions are
4463 4 For the purposes of these operators, a pointer to an object that is not an element of an
4464 array behaves the same as a pointer to the first element of an array of length one with the
4465 type of the object as its element type.
4466 5 When two pointers are compared, the result depends on the relative locations in the
4467 address space of the objects pointed to. If two pointers to object types both point to the
4468 same object, or both point one past the last element of the same array object, they
4469 compare equal. If the objects pointed to are members of the same aggregate object,
4470 pointers to structure members declared later compare greater than pointers to members
4471 declared earlier in the structure, and pointers to array elements with larger subscript
4472 values compare greater than pointers to elements of the same array with lower subscript
4476 values. All pointers to members of the same union object compare equal. If the
4477 expression P points to an element of an array object and the expression Q points to the
4478 last element of the same array object, the pointer expression Q+1 compares greater than
4479 P. In all other cases, the behavior is undefined.
4480 6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
4481 (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
4482 false.106) The result has type int.
4483 6.5.9 Equality operators
4485 1 equality-expression:
4486 relational-expression
4487 equality-expression == relational-expression
4488 equality-expression != relational-expression
4490 2 One of the following shall hold:
4491 -- both operands have arithmetic type;
4492 -- both operands are pointers to qualified or unqualified versions of compatible types;
4493 -- one operand is a pointer to an object type and the other is a pointer to a qualified or
4494 unqualified version of void; or
4495 -- one operand is a pointer and the other is a null pointer constant.
4497 3 The == (equal to) and != (not equal to) operators are analogous to the relational
4498 operators except for their lower precedence.107) Each of the operators yields 1 if the
4499 specified relation is true and 0 if it is false. The result has type int. For any pair of
4500 operands, exactly one of the relations is true.
4501 4 If both of the operands have arithmetic type, the usual arithmetic conversions are
4502 performed. Values of complex types are equal if and only if both their real parts are equal
4503 and also their imaginary parts are equal. Any two values of arithmetic types from
4504 different type domains are equal if and only if the results of their conversions to the
4505 (complex) result type determined by the usual arithmetic conversions are equal.
4509 106) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it
4510 means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''.
4511 107) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.
4515 5 Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a
4516 null pointer constant, the null pointer constant is converted to the type of the pointer. If
4517 one operand is a pointer to an object type and the other is a pointer to a qualified or
4518 unqualified version of void, the former is converted to the type of the latter.
4519 6 Two pointers compare equal if and only if both are null pointers, both are pointers to the
4520 same object (including a pointer to an object and a subobject at its beginning) or function,
4521 both are pointers to one past the last element of the same array object, or one is a pointer
4522 to one past the end of one array object and the other is a pointer to the start of a different
4523 array object that happens to immediately follow the first array object in the address
4525 7 For the purposes of these operators, a pointer to an object that is not an element of an
4526 array behaves the same as a pointer to the first element of an array of length one with the
4527 type of the object as its element type.
4528 6.5.10 Bitwise AND operator
4532 AND-expression & equality-expression
4534 2 Each of the operands shall have integer type.
4536 3 The usual arithmetic conversions are performed on the operands.
4537 4 The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
4538 the result is set if and only if each of the corresponding bits in the converted operands is
4544 108) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
4545 adjacent members of a structure with no padding between them, or because the implementation chose
4546 to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
4547 outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
4552 6.5.11 Bitwise exclusive OR operator
4554 1 exclusive-OR-expression:
4556 exclusive-OR-expression ^ AND-expression
4558 2 Each of the operands shall have integer type.
4560 3 The usual arithmetic conversions are performed on the operands.
4561 4 The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
4562 in the result is set if and only if exactly one of the corresponding bits in the converted
4564 6.5.12 Bitwise inclusive OR operator
4566 1 inclusive-OR-expression:
4567 exclusive-OR-expression
4568 inclusive-OR-expression | exclusive-OR-expression
4570 2 Each of the operands shall have integer type.
4572 3 The usual arithmetic conversions are performed on the operands.
4573 4 The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
4574 the result is set if and only if at least one of the corresponding bits in the converted
4582 6.5.13 Logical AND operator
4584 1 logical-AND-expression:
4585 inclusive-OR-expression
4586 logical-AND-expression && inclusive-OR-expression
4588 2 Each of the operands shall have scalar type.
4590 3 The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
4591 yields 0. The result has type int.
4592 4 Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
4593 if the second operand is evaluated, there is a sequence point between the evaluations of
4594 the first and second operands. If the first operand compares equal to 0, the second
4595 operand is not evaluated.
4596 6.5.14 Logical OR operator
4598 1 logical-OR-expression:
4599 logical-AND-expression
4600 logical-OR-expression || logical-AND-expression
4602 2 Each of the operands shall have scalar type.
4604 3 The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
4605 yields 0. The result has type int.
4606 4 Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the
4607 second operand is evaluated, there is a sequence point between the evaluations of the first
4608 and second operands. If the first operand compares unequal to 0, the second operand is
4616 6.5.15 Conditional operator
4618 1 conditional-expression:
4619 logical-OR-expression
4620 logical-OR-expression ? expression : conditional-expression
4622 2 The first operand shall have scalar type.
4623 3 One of the following shall hold for the second and third operands:
4624 -- both operands have arithmetic type;
4625 -- both operands have the same structure or union type;
4626 -- both operands have void type;
4627 -- both operands are pointers to qualified or unqualified versions of compatible types;
4628 -- one operand is a pointer and the other is a null pointer constant; or
4629 -- one operand is a pointer to an object type and the other is a pointer to a qualified or
4630 unqualified version of void.
4632 4 The first operand is evaluated; there is a sequence point between its evaluation and the
4633 evaluation of the second or third operand (whichever is evaluated). The second operand
4634 is evaluated only if the first compares unequal to 0; the third operand is evaluated only if
4635 the first compares equal to 0; the result is the value of the second or third operand
4636 (whichever is evaluated), converted to the type described below.109)
4637 5 If both the second and third operands have arithmetic type, the result type that would be
4638 determined by the usual arithmetic conversions, were they applied to those two operands,
4639 is the type of the result. If both the operands have structure or union type, the result has
4640 that type. If both operands have void type, the result has void type.
4641 6 If both the second and third operands are pointers or one is a null pointer constant and the
4642 other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers
4643 of the types referenced by both operands. Furthermore, if both operands are pointers to
4644 compatible types or to differently qualified versions of compatible types, the result type is
4645 a pointer to an appropriately qualified version of the composite type; if one operand is a
4646 null pointer constant, the result has the type of the other operand; otherwise, one operand
4647 is a pointer to void or a qualified version of void, in which case the result type is a
4648 pointer to an appropriately qualified version of void.
4650 109) A conditional expression does not yield an lvalue.
4654 7 EXAMPLE The common type that results when the second and third operands are pointers is determined
4655 in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two
4656 pointers have compatible types.
4657 8 Given the declarations
4664 the third column in the following table is the common type that is the result of a conditional expression in
4665 which the first two columns are the second and third operands (in either order):
4666 c_vp c_ip const void *
4667 v_ip 0 volatile int *
4668 c_ip v_ip const volatile int *
4669 vp c_cp const void *
4673 6.5.16 Assignment operators
4675 1 assignment-expression:
4676 conditional-expression
4677 unary-expression assignment-operator assignment-expression
4678 assignment-operator: one of
4679 = *= /= %= += -= <<= >>= &= ^= |=
4681 2 An assignment operator shall have a modifiable lvalue as its left operand.
4683 3 An assignment operator stores a value in the object designated by the left operand. An
4684 assignment expression has the value of the left operand after the assignment,110) but is not
4685 an lvalue. The type of an assignment expression is the type of the left operand unless the
4686 left operand has qualified type, in which case it is the unqualified version of the type of
4687 the left operand. The side effect of updating the stored value of the left operand is
4688 sequenced after the value computations of the left and right operands. The evaluations of
4689 the operands are unsequenced.
4694 110) The implementation is permitted to read the object to determine the value but is not required to, even
4695 when the object has volatile-qualified type.
4699 6.5.16.1 Simple assignment
4701 1 One of the following shall hold:111)
4702 -- the left operand has qualified or unqualified arithmetic type and the right has
4704 -- the left operand has a qualified or unqualified version of a structure or union type
4705 compatible with the type of the right;
4706 -- both operands are pointers to qualified or unqualified versions of compatible types,
4707 and the type pointed to by the left has all the qualifiers of the type pointed to by the
4709 -- one operand is a pointer to an object type and the other is a pointer to a qualified or
4710 unqualified version of void, and the type pointed to by the left has all the qualifiers
4711 of the type pointed to by the right;
4712 -- the left operand is a pointer and the right is a null pointer constant; or
4713 -- the left operand has type _Bool and the right is a pointer.
4715 2 In simple assignment (=), the value of the right operand is converted to the type of the
4716 assignment expression and replaces the value stored in the object designated by the left
4718 3 If the value being stored in an object is read from another object that overlaps in any way
4719 the storage of the first object, then the overlap shall be exact and the two objects shall
4720 have qualified or unqualified versions of a compatible type; otherwise, the behavior is
4722 4 EXAMPLE 1 In the program fragment
4726 if ((c = f()) == -1)
4728 the int value returned by the function may be truncated when stored in the char, and then converted back
4729 to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
4730 values as unsigned char (and char is narrower than int), the result of the conversion cannot be
4734 111) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
4735 (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type
4736 qualifiers that were applied to the type category of the expression (for example, it removes const but
4737 not volatile from the type int volatile * const).
4741 negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
4742 variable c should be declared as int.
4744 5 EXAMPLE 2 In the fragment:
4749 the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
4750 of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
4751 that is, long int type.
4753 6 EXAMPLE 3 Consider the fragment:
4757 cpp = &p; // constraint violation
4760 The first assignment is unsafe because it would allow the following valid code to attempt to change the
4761 value of the const object c.
4763 6.5.16.2 Compound assignment
4765 1 For the operators += and -= only, either the left operand shall be a pointer to a complete
4766 object type and the right shall have integer type, or the left operand shall have qualified or
4767 unqualified arithmetic type and the right shall have arithmetic type.
4768 2 For the other operators, each operand shall have arithmetic type consistent with those
4769 allowed by the corresponding binary operator.
4771 3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
4772 expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
4773 respect to an indeterminately-sequenced function call, the operation of a compound
4774 assignment is a single evaluation. If E1 has an _Atomic-qualified type, compound
4775 assignment is a read-modify-write operation with memory_order_seq_cst memory
4776 order semantics.112)
4783 6.5.17 Comma operator
4786 assignment-expression
4787 expression , assignment-expression
4789 2 The left operand of a comma operator is evaluated as a void expression; there is a
4790 sequence point between its evaluation and that of the right operand. Then the right
4791 operand is evaluated; the result has its type and value.113)
4792 3 EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
4793 appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
4794 of initializers). On the other hand, it can be used within a parenthesized expression or within the second
4795 expression of a conditional operator in such contexts. In the function call
4797 the function has three arguments, the second of which has the value 5.
4799 Forward references: initialization (6.7.9).
4804 112) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
4805 where T is the type of E1:
4809 result = tmp op (E2);
4810 } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
4811 with result being the result of the operation.
4812 113) A comma operator does not yield an lvalue.
4816 6.6 Constant expressions
4818 1 constant-expression:
4819 conditional-expression
4821 2 A constant expression can be evaluated during translation rather than runtime, and
4822 accordingly may be used in any place that a constant may be.
4824 3 Constant expressions shall not contain assignment, increment, decrement, function-call,
4825 or comma operators, except when they are contained within a subexpression that is not
4827 4 Each constant expression shall evaluate to a constant that is in the range of representable
4828 values for its type.
4830 5 An expression that evaluates to a constant is required in several contexts. If a floating
4831 expression is evaluated in the translation environment, the arithmetic precision and range
4832 shall be at least as great as if the expression were being evaluated in the execution
4834 6 An integer constant expression116) shall have integer type and shall only have operands
4835 that are integer constants, enumeration constants, character constants, sizeof
4836 expressions whose results are integer constants, and floating constants that are the
4837 immediate operands of casts. Cast operators in an integer constant expression shall only
4838 convert arithmetic types to integer types, except as part of an operand to the sizeof
4840 7 More latitude is permitted for constant expressions in initializers. Such a constant
4841 expression shall be, or evaluate to, one of the following:
4842 -- an arithmetic constant expression,
4846 114) The operand of a sizeof operator is usually not evaluated (6.5.3.4).
4847 115) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
4848 the translation environment.
4849 116) An integer constant expression is required in a number of contexts such as the size of a bit-field
4850 member of a structure, the value of an enumeration constant, and the size of a non-variable length
4851 array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
4852 preprocessing directives are discussed in 6.10.1.
4856 -- a null pointer constant,
4857 -- an address constant, or
4858 -- an address constant for a complete object type plus or minus an integer constant
4860 8 An arithmetic constant expression shall have arithmetic type and shall only have
4861 operands that are integer constants, floating constants, enumeration constants, character
4862 constants, and sizeof expressions. Cast operators in an arithmetic constant expression
4863 shall only convert arithmetic types to arithmetic types, except as part of an operand to a
4864 sizeof operator whose result is an integer constant.
4865 9 An address constant is a null pointer, a pointer to an lvalue designating an object of static
4866 storage duration, or a pointer to a function designator; it shall be created explicitly using
4867 the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
4868 an expression of array or function type. The array-subscript [] and member-access .
4869 and -> operators, the address & and indirection * unary operators, and pointer casts may
4870 be used in the creation of an address constant, but the value of an object shall not be
4871 accessed by use of these operators.
4872 10 An implementation may accept other forms of constant expressions.
4873 11 The semantic rules for the evaluation of a constant expression are the same as for
4874 nonconstant expressions.117)
4875 Forward references: array declarators (6.7.6.2), initialization (6.7.9).
4880 117) Thus, in the following initialization,
4881 static int i = 2 || 1 / 0;
4882 the expression is a valid integer constant expression with value one.
4889 declaration-specifiers init-declarator-listopt ;
4890 static_assert-declaration *
4891 declaration-specifiers:
4892 storage-class-specifier declaration-specifiersopt
4893 type-specifier declaration-specifiersopt
4894 type-qualifier declaration-specifiersopt
4895 function-specifier declaration-specifiersopt
4896 alignment-specifier declaration-specifiersopt
4897 init-declarator-list:
4899 init-declarator-list , init-declarator
4902 declarator = initializer
4904 2 A declaration other than a static_assert declaration shall declare at least a declarator
4905 (other than the parameters of a function or the members of a structure or union), a tag, or
4906 the members of an enumeration.
4907 3 If an identifier has no linkage, there shall be no more than one declaration of the identifier
4908 (in a declarator or type specifier) with the same scope and in the same name space, except
4909 that a typedef name can be redefined to denote the same type as it currently does and tags
4910 may be redeclared as specified in 6.7.2.3.
4911 4 All declarations in the same scope that refer to the same object or function shall specify
4914 5 A declaration specifies the interpretation and attributes of a set of identifiers. A definition
4915 of an identifier is a declaration for that identifier that:
4916 -- for an object, causes storage to be reserved for that object;
4917 -- for a function, includes the function body;118)
4921 118) Function definitions have a different syntax, described in 6.9.1.
4925 -- for an enumeration constant or typedef name, is the (only) declaration of the
4927 6 The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
4928 storage duration, and part of the type of the entities that the declarators denote. The init-
4929 declarator-list is a comma-separated sequence of declarators, each of which may have
4930 additional type information, or an initializer, or both. The declarators contain the
4931 identifiers (if any) being declared.
4932 7 If an identifier for an object is declared with no linkage, the type for the object shall be *
4933 complete by the end of its declarator, or by the end of its init-declarator if it has an
4934 initializer; in the case of function parameters (including in prototypes), it is the adjusted
4935 type (see 6.7.6.3) that is required to be complete.
4936 Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
4937 (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
4938 6.7.1 Storage-class specifiers
4940 1 storage-class-specifier:
4948 2 At most, one storage-class specifier may be given in the declaration specifiers in a
4949 declaration, except that _Thread_local may appear with static or extern.119)
4950 3 In the declaration of an object with block scope, if the declaration specifiers include
4951 _Thread_local, they shall also include either static or extern. If
4952 _Thread_local appears in any declaration of an object, it shall be present in every
4953 declaration of that object.
4955 4 The typedef specifier is called a ''storage-class specifier'' for syntactic convenience
4956 only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
4957 were discussed in 6.2.2 and 6.2.4.
4961 119) See ''future language directions'' (6.11.5).
4965 5 A declaration of an identifier for an object with storage-class specifier register
4966 suggests that access to the object be as fast as possible. The extent to which such
4967 suggestions are effective is implementation-defined.120)
4968 6 The declaration of an identifier for a function that has block scope shall have no explicit
4969 storage-class specifier other than extern.
4970 7 If an aggregate or union object is declared with a storage-class specifier other than
4971 typedef, the properties resulting from the storage-class specifier, except with respect to
4972 linkage, also apply to the members of the object, and so on recursively for any aggregate
4973 or union member objects.
4974 Forward references: type definitions (6.7.8).
4975 6.7.2 Type specifiers
4989 _Atomic ( type-name )
4990 struct-or-union-specifier
4994 2 At least one type specifier shall be given in the declaration specifiers in each declaration,
4995 and in the specifier-qualifier list in each struct declaration and type name. Each list of
4998 120) The implementation may treat any register declaration simply as an auto declaration. However,
4999 whether or not addressable storage is actually used, the address of any part of an object declared with
5000 storage-class specifier register cannot be computed, either explicitly (by use of the unary &
5001 operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
5002 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier
5007 type specifiers shall be one of the following multisets (delimited by commas, when there
5008 is more than one multiset per item); the type specifiers may occur in any order, possibly
5009 intermixed with the other declaration specifiers.
5014 -- short, signed short, short int, or signed short int
5015 -- unsigned short, or unsigned short int
5016 -- int, signed, or signed int
5017 -- unsigned, or unsigned int
5018 -- long, signed long, long int, or signed long int
5019 -- unsigned long, or unsigned long int
5020 -- long long, signed long long, long long int, or
5021 signed long long int
5022 -- unsigned long long, or unsigned long long int
5029 -- long double _Complex
5030 -- _Atomic ( type-name )
5031 -- struct or union specifier
5034 3 The type specifier _Complex shall not be used if the implementation does not support
5035 complex types; likewise, _Atomic shall not be used if the implementation does not
5036 support atomic types (see 6.10.8.3).
5043 4 The _Atomic form of type specifier designates the _Atomic-qualified version of the
5045 5 Specifiers for structures, unions, and enumerations are discussed in 6.7.2.1 through
5046 6.7.2.3. Declarations of typedef names are discussed in 6.7.8. The characteristics of the
5047 other types are discussed in 6.2.5.
5048 6 Each of the comma-separated multisets designates the same type, except that for bit-
5049 fields, it is implementation-defined whether the specifier int designates the same type as
5050 signed int or the same type as unsigned int.
5051 Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
5052 (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
5053 6.7.2.1 Structure and union specifiers
5055 1 struct-or-union-specifier:
5056 struct-or-union identifieropt { struct-declaration-list }
5057 struct-or-union identifier
5061 struct-declaration-list:
5063 struct-declaration-list struct-declaration
5065 specifier-qualifier-list struct-declarator-listopt ;
5066 static_assert-declaration
5067 specifier-qualifier-list:
5068 type-specifier specifier-qualifier-listopt
5069 type-qualifier specifier-qualifier-listopt
5070 struct-declarator-list:
5072 struct-declarator-list , struct-declarator
5075 declaratoropt : constant-expression
5082 2 A struct-declaration that does not declare an anonymous structure or anonymous union
5083 shall contain a struct-declarator-list.
5084 3 A structure or union shall not contain a member with incomplete or function type (hence,
5085 a structure shall not contain an instance of itself, but may contain a pointer to an instance
5086 of itself), except that the last member of a structure with more than one named member
5087 may have incomplete array type; such a structure (and any union containing, possibly
5088 recursively, a member that is such a structure) shall not be a member of a structure or an
5089 element of an array.
5090 4 The expression that specifies the width of a bit-field shall be an integer constant
5091 expression with a nonnegative value that does not exceed the width of an object of the
5092 type that would be specified were the colon and expression omitted.121) If the value is
5093 zero, the declaration shall have no declarator.
5094 5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
5095 int, unsigned int, or some other implementation-defined type.
5097 6 As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
5098 storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
5099 of members whose storage overlap.
5100 7 Structure and union specifiers have the same form. The keywords struct and union
5101 indicate that the type being specified is, respectively, a structure type or a union type.
5102 8 The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
5103 within a translation unit. The struct-declaration-list is a sequence of declarations for the
5104 members of the structure or union. If the struct-declaration-list contains no named
5105 members, no anonymous structures, and no anonymous unions, the behavior is undefined.
5106 The type is incomplete until immediately after the } that terminates the list, and complete
5108 9 A member of a structure or union may have any complete object type other than a
5109 variably modified type.122) In addition, a member may be declared to consist of a
5110 specified number of bits (including a sign bit, if any). Such a member is called a
5111 bit-field;123) its width is preceded by a colon.
5115 121) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
5116 value bits) of a _Bool may be just 1 bit.
5117 122) A structure or union cannot contain a member with a variably modified type because member names
5118 are not ordinary identifiers as defined in 6.2.3.
5122 10 A bit-field is interpreted as a signed or unsigned integer type consisting of the specified
5123 number of bits.124) If the value 0 or 1 is stored into a nonzero-width bit-field of type
5124 _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool bit-
5125 field has the semantics of a _Bool.
5126 11 An implementation may allocate any addressable storage unit large enough to hold a bit-
5127 field. If enough space remains, a bit-field that immediately follows another bit-field in a
5128 structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
5129 whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
5130 implementation-defined. The order of allocation of bit-fields within a unit (high-order to
5131 low-order or low-order to high-order) is implementation-defined. The alignment of the
5132 addressable storage unit is unspecified.
5133 12 A bit-field declaration with no declarator, but only a colon and a width, indicates an
5134 unnamed bit-field.125) As a special case, a bit-field structure member with a width of 0
5135 indicates that no further bit-field is to be packed into the unit in which the previous bit-
5136 field, if any, was placed.
5137 13 An unnamed member of structure type with no tag is called an anonymous structure; an
5138 unnamed member of union type with no tag is called an anonymous union. The members
5139 of an anonymous structure or union are considered to be members of the containing
5140 structure or union. This applies recursively if the containing structure or union is also
5142 14 Each non-bit-field member of a structure or union object is aligned in an implementation-
5143 defined manner appropriate to its type.
5144 15 Within a structure object, the non-bit-field members and the units in which bit-fields
5145 reside have addresses that increase in the order in which they are declared. A pointer to a
5146 structure object, suitably converted, points to its initial member (or if that member is a
5147 bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
5148 padding within a structure object, but not at its beginning.
5149 16 The size of a union is sufficient to contain the largest of its members. The value of at
5150 most one of the members can be stored in a union object at any time. A pointer to a
5151 union object, suitably converted, points to each of its members (or if a member is a bit-
5152 field, then to the unit in which it resides), and vice versa.
5155 123) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
5156 or arrays of bit-field objects.
5157 124) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
5158 then it is implementation-defined whether the bit-field is signed or unsigned.
5159 125) An unnamed bit-field structure member is useful for padding to conform to externally imposed
5164 17 There may be unnamed padding at the end of a structure or union.
5165 18 As a special case, the last element of a structure with more than one named member may
5166 have an incomplete array type; this is called a flexible array member. In most situations,
5167 the flexible array member is ignored. In particular, the size of the structure is as if the
5168 flexible array member were omitted except that it may have more trailing padding than
5169 the omission would imply. However, when a . (or ->) operator has a left operand that is
5170 (a pointer to) a structure with a flexible array member and the right operand names that
5171 member, it behaves as if that member were replaced with the longest array (with the same
5172 element type) that would not make the structure larger than the object being accessed; the
5173 offset of the array shall remain that of the flexible array member, even if this would differ
5174 from that of the replacement array. If this array would have no elements, it behaves as if
5175 it had one element but the behavior is undefined if any attempt is made to access that
5176 element or to generate a pointer one past it.
5177 19 EXAMPLE 1 The following illustrates anonymous structures and unions:
5179 union { // anonymous union
5180 struct { int i, j; }; // anonymous structure
5181 struct { long k, l; } w;
5186 v1.k = 3; // invalid: inner structure is not anonymous
5187 v1.w.k = 5; // valid
5189 20 EXAMPLE 2 After the declaration:
5190 struct s { int n; double d[]; };
5191 the structure struct s has a flexible array member d. A typical way to use this is:
5192 int m = /* some value */;
5193 struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
5194 and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
5195 p had been declared as:
5196 struct { int n; double d[m]; } *p;
5197 (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
5199 21 Following the above declaration:
5200 struct s t1 = { 0 }; // valid
5201 struct s t2 = { 1, { 4.2 }}; // invalid
5203 t1.d[0] = 4.2; // might be undefined behavior
5204 The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
5205 contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
5209 sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
5210 in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
5212 22 After the further declaration:
5213 struct ss { int n; };
5215 sizeof (struct s) >= sizeof (struct ss)
5216 sizeof (struct s) >= offsetof(struct s, d)
5217 are always equal to 1.
5218 23 If sizeof (double) is 8, then after the following code is executed:
5221 s1 = malloc(sizeof (struct s) + 64);
5222 s2 = malloc(sizeof (struct s) + 46);
5223 and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
5224 purposes, as if the identifiers had been declared as:
5225 struct { int n; double d[8]; } *s1;
5226 struct { int n; double d[5]; } *s2;
5227 24 Following the further successful assignments:
5228 s1 = malloc(sizeof (struct s) + 10);
5229 s2 = malloc(sizeof (struct s) + 6);
5230 they then behave as if the declarations were:
5231 struct { int n; double d[1]; } *s1, *s2;
5234 dp = &(s1->d[0]); // valid
5236 dp = &(s2->d[0]); // valid
5237 *dp = 42; // undefined behavior
5240 only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
5241 of the structure, they might be copied or simply overwritten with indeterminate values.
5243 Forward references: declarators (6.7.6), tags (6.7.2.3).
5250 6.7.2.2 Enumeration specifiers
5253 enum identifieropt { enumerator-list }
5254 enum identifieropt { enumerator-list , }
5258 enumerator-list , enumerator
5260 enumeration-constant
5261 enumeration-constant = constant-expression
5263 2 The expression that defines the value of an enumeration constant shall be an integer
5264 constant expression that has a value representable as an int.
5266 3 The identifiers in an enumerator list are declared as constants that have type int and
5267 may appear wherever such are permitted.126) An enumerator with = defines its
5268 enumeration constant as the value of the constant expression. If the first enumerator has
5269 no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
5270 defines its enumeration constant as the value of the constant expression obtained by
5271 adding 1 to the value of the previous enumeration constant. (The use of enumerators with
5272 = may produce enumeration constants with values that duplicate other values in the same
5273 enumeration.) The enumerators of an enumeration are also known as its members.
5274 4 Each enumerated type shall be compatible with char, a signed integer type, or an
5275 unsigned integer type. The choice of type is implementation-defined,127) but shall be
5276 capable of representing the values of all the members of the enumeration. The
5277 enumerated type is incomplete until immediately after the } that terminates the list of
5278 enumerator declarations, and complete thereafter.
5283 126) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
5284 each other and from other identifiers declared in ordinary declarators.
5285 127) An implementation may delay the choice of which integer type until all enumeration constants have
5290 5 EXAMPLE The following fragment:
5291 enum hue { chartreuse, burgundy, claret=20, winedark };
5295 if (*cp != burgundy)
5297 makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
5298 pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.
5300 Forward references: tags (6.7.2.3).
5303 1 A specific type shall have its content defined at most once.
5304 2 Where two declarations that use the same tag declare the same type, they shall both use
5305 the same choice of struct, union, or enum.
5306 3 A type specifier of the form
5308 without an enumerator list shall only appear after the type it specifies is complete.
5310 4 All declarations of structure, union, or enumerated types that have the same scope and
5311 use the same tag declare the same type. Irrespective of whether there is a tag or what
5312 other declarations of the type are in the same translation unit, the type is incomplete128)
5313 until immediately after the closing brace of the list defining the content, and complete
5315 5 Two declarations of structure, union, or enumerated types which are in different scopes or
5316 use different tags declare distinct types. Each declaration of a structure, union, or
5317 enumerated type which does not include a tag declares a distinct type.
5318 6 A type specifier of the form
5323 128) An incomplete type may only by used when the size of an object of that type is not needed. It is not
5324 needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
5325 when a pointer to or a function returning a structure or union is being declared. (See incomplete types
5326 in 6.2.5.) The specification has to be complete before such a function is called or defined.
5330 struct-or-union identifieropt { struct-declaration-list }
5332 enum identifieropt { enumerator-list }
5334 enum identifieropt { enumerator-list , }
5335 declares a structure, union, or enumerated type. The list defines the structure content,
5336 union content, or enumeration content. If an identifier is provided,129) the type specifier
5337 also declares the identifier to be the tag of that type.
5338 7 A declaration of the form
5339 struct-or-union identifier ;
5340 specifies a structure or union type and declares the identifier as a tag of that type.130)
5341 8 If a type specifier of the form
5342 struct-or-union identifier
5343 occurs other than as part of one of the above forms, and no other declaration of the
5344 identifier as a tag is visible, then it declares an incomplete structure or union type, and
5345 declares the identifier as the tag of that type.130)
5346 9 If a type specifier of the form
5347 struct-or-union identifier
5350 occurs other than as part of one of the above forms, and a declaration of the identifier as a
5351 tag is visible, then it specifies the same type as that other declaration, and does not
5353 10 EXAMPLE 1 This mechanism allows declaration of a self-referential structure.
5356 struct tnode *left, *right;
5358 specifies a structure that contains an integer and two pointers to objects of the same type. Once this
5359 declaration has been given, the declaration
5364 129) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
5365 of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
5366 can make use of that typedef name to declare objects having the specified structure, union, or
5368 130) A similar construction with enum does not exist.
5372 struct tnode s, *sp;
5373 declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
5374 these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
5375 which sp points; the expression s.right->count designates the count member of the right struct
5376 tnode pointed to from s.
5377 11 The following alternative formulation uses the typedef mechanism:
5378 typedef struct tnode TNODE;
5381 TNODE *left, *right;
5385 12 EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
5386 structures, the declarations
5387 struct s1 { struct s2 *s2p; /* ... */ }; // D1
5388 struct s2 { struct s1 *s1p; /* ... */ }; // D2
5389 specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
5390 declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
5391 D2. To eliminate this context sensitivity, the declaration
5393 may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
5394 completes the specification of the new type.
5396 Forward references: declarators (6.7.6), type definitions (6.7.8).
5397 6.7.3 Type qualifiers
5405 2 Types other than pointer types whose referenced type is an object type shall not be
5408 3 The properties associated with qualified types are meaningful only for expressions that
5410 4 If the same qualifier appears more than once in the same specifier-qualifier-list, either
5411 directly or via one or more typedefs, the behavior is the same as if it appeared only
5415 5 If an attempt is made to modify an object defined with a const-qualified type through use
5416 of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
5417 made to refer to an object defined with a volatile-qualified type through use of an lvalue
5418 with non-volatile-qualified type, the behavior is undefined.132) If an attempt is made to
5419 refer to an object defined with an _Atomic-qualified type through use of an lvalue with
5420 non-_Atomic-qualified type, the behavior is undefined.
5421 6 An object that has volatile-qualified type may be modified in ways unknown to the
5422 implementation or have other unknown side effects. Therefore any expression referring
5423 to such an object shall be evaluated strictly according to the rules of the abstract machine,
5424 as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
5425 object shall agree with that prescribed by the abstract machine, except as modified by the
5426 unknown factors mentioned previously.133) What constitutes an access to an object that
5427 has volatile-qualified type is implementation-defined.
5428 7 An object that is accessed through a restrict-qualified pointer has a special association
5429 with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
5430 that object use, directly or indirectly, the value of that particular pointer.134) The intended
5431 use of the restrict qualifier (like the register storage class) is to promote
5432 optimization, and deleting all instances of the qualifier from all preprocessing translation
5433 units composing a conforming program does not change its meaning (i.e., observable
5435 8 If the specification of an array type includes any type qualifiers, the element type is so-
5436 qualified, not the array type. If the specification of a function type includes any type
5437 qualifiers, the behavior is undefined.135)
5438 9 For two qualified types to be compatible, both shall have the identically qualified version
5439 of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
5440 does not affect the specified type.
5442 131) The implementation may place a const object that is not volatile in a read-only region of
5443 storage. Moreover, the implementation need not allocate storage for such an object if its address is
5445 132) This applies to those objects that behave as if they were defined with qualified types, even if they are
5446 never actually defined as objects in the program (such as an object at a memory-mapped input/output
5448 133) A volatile declaration may be used to describe an object corresponding to a memory-mapped
5449 input/output port or an object accessed by an asynchronously interrupting function. Actions on
5450 objects so declared shall not be ''optimized out'' by an implementation or reordered except as
5451 permitted by the rules for evaluating expressions.
5452 134) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
5453 association between the allocated object and the pointer.
5454 135) Both of these can occur through the use of typedefs.
5458 10 EXAMPLE 1 An object declared
5459 extern const volatile int real_time_clock;
5460 may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
5462 11 EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
5463 modify an aggregate type:
5464 const struct s { int mem; } cs = { 1 };
5465 struct s ncs; // the object ncs is modifiable
5466 typedef int A[2][3];
5467 const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
5471 cs = ncs; // violates modifiable lvalue constraint for =
5472 pi = &ncs.mem; // valid
5473 pi = &cs.mem; // violates type constraints for =
5474 pci = &cs.mem; // valid
5475 pi = a[0]; // invalid: a[0] has type ''const int *''
5477 6.7.3.1 Formal definition of restrict
5478 1 Let D be a declaration of an ordinary identifier that provides a means of designating an
5479 object P as a restrict-qualified pointer to type T.
5480 2 If D appears inside a block and does not have storage class extern, let B denote the
5481 block. If D appears in the list of parameter declarations of a function definition, let B
5482 denote the associated block. Otherwise, let B denote the block of main (or the block of
5483 whatever function is called at program startup in a freestanding environment).
5484 3 In what follows, a pointer expression E is said to be based on object P if (at some
5485 sequence point in the execution of B prior to the evaluation of E) modifying P to point to
5486 a copy of the array object into which it formerly pointed would change the value of E.136)
5487 Note that ''based'' is defined only for expressions with pointer types.
5488 4 During each execution of B, let L be any lvalue that has &L based on P. If L is used to
5489 access the value of the object X that it designates, and X is also modified (by any means),
5490 then the following requirements apply: T shall not be const-qualified. Every other lvalue
5491 used to access the value of X shall also have its address based on P. Every access that
5492 modifies X shall be considered also to modify P, for the purposes of this subclause. If P
5493 is assigned the value of a pointer expression E that is based on another restricted pointer
5494 object P2, associated with block B2, then either the execution of B2 shall begin before
5497 136) In other words, E depends on the value of P itself rather than on the value of an object referenced
5498 indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
5499 expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
5500 expressions *p and p[1] are not.
5504 the execution of B, or the execution of B2 shall end prior to the assignment. If these
5505 requirements are not met, then the behavior is undefined.
5506 5 Here an execution of B means that portion of the execution of the program that would
5507 correspond to the lifetime of an object with scalar type and automatic storage duration
5509 6 A translator is free to ignore any or all aliasing implications of uses of restrict.
5510 7 EXAMPLE 1 The file scope declarations
5514 assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
5515 program, then it is never accessed using either of the other two.
5517 8 EXAMPLE 2 The function parameter declarations in the following example
5518 void f(int n, int * restrict p, int * restrict q)
5523 assert that, during each execution of the function, if an object is accessed through one of the pointer
5524 parameters, then it is not also accessed through the other.
5525 9 The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
5526 analysis of function f without examining any of the calls of f in the program. The cost is that the
5527 programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
5528 second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
5533 f(50, d + 50, d); // valid
5534 f(50, d + 1, d); // undefined behavior
5537 10 EXAMPLE 3 The function parameter declarations
5538 void h(int n, int * restrict p, int * restrict q, int * restrict r)
5541 for (i = 0; i < n; i++)
5544 illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
5545 are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
5546 modified within function h.
5548 11 EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
5549 function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments
5553 between restricted pointers declared in nested blocks have defined behavior.
5557 p1 = q1; // undefined behavior
5559 int * restrict p2 = p1; // valid
5560 int * restrict q2 = q1; // valid
5561 p1 = q2; // undefined behavior
5562 p2 = q2; // undefined behavior
5565 12 The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
5566 precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
5567 example, this permits new_vector to return a vector.
5568 typedef struct { int n; float * restrict v; } vector;
5569 vector new_vector(int n)
5573 t.v = malloc(n * sizeof (float));
5577 6.7.4 Function specifiers
5579 1 function-specifier:
5583 2 Function specifiers shall be used only in the declaration of an identifier for a function.
5584 3 An inline definition of a function with external linkage shall not contain a definition of a
5585 modifiable object with static or thread storage duration, and shall not contain a reference
5586 to an identifier with internal linkage.
5587 4 In a hosted environment, no function specifier(s) shall appear in a declaration of main.
5589 5 A function specifier may appear more than once; the behavior is the same as if it
5591 6 A function declared with an inline function specifier is an inline function. Making a
5592 function an inline function suggests that calls to the function be as fast as possible.137)
5593 The extent to which such suggestions are effective is implementation-defined.138)
5597 7 Any function with internal linkage can be an inline function. For a function with external
5598 linkage, the following restrictions apply: If a function is declared with an inline
5599 function specifier, then it shall also be defined in the same translation unit. If all of the
5600 file scope declarations for a function in a translation unit include the inline function
5601 specifier without extern, then the definition in that translation unit is an inline
5602 definition. An inline definition does not provide an external definition for the function,
5603 and does not forbid an external definition in another translation unit. An inline definition
5604 provides an alternative to an external definition, which a translator may use to implement
5605 any call to the function in the same translation unit. It is unspecified whether a call to the
5606 function uses the inline definition or the external definition.139)
5607 8 A function declared with a _Noreturn function specifier shall not return to its caller.
5608 Recommended practice
5609 9 The implementation should produce a diagnostic message for a function declared with a
5610 _Noreturn function specifier that appears to be capable of returning to its caller.
5611 10 EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
5612 definition, or a definition available for use only within the translation unit. A file scope declaration with
5613 extern creates an external definition. The following example shows an entire translation unit.
5614 inline double fahr(double t)
5616 return (9.0 * t) / 5.0 + 32.0;
5618 inline double cels(double t)
5620 return (5.0 * (t - 32.0)) / 9.0;
5622 extern double fahr(double); // creates an external definition
5627 137) By using, for example, an alternative to the usual function call mechanism, such as ''inline
5628 substitution''. Inline substitution is not textual substitution, nor does it create a new function.
5629 Therefore, for example, the expansion of a macro used within the body of the function uses the
5630 definition it had at the point the function body appears, and not where the function is called; and
5631 identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
5632 single address, regardless of the number of inline definitions that occur in addition to the external
5634 138) For example, an implementation might never perform inline substitution, or might only perform inline
5635 substitutions to calls in the scope of an inline declaration.
5636 139) Since an inline definition is distinct from the corresponding external definition and from any other
5637 corresponding inline definitions in other translation units, all corresponding objects with static storage
5638 duration are also distinct in each of the definitions.
5642 double convert(int is_fahr, double temp)
5644 /* A translator may perform inline substitutions */
5645 return is_fahr ? cels(temp) : fahr(temp);
5647 11 Note that the definition of fahr is an external definition because fahr is also declared with extern, but
5648 the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
5649 external definition has to appear in another translation unit (see 6.9); the inline definition and the external
5650 definition are distinct and either may be used for the call.
5653 _Noreturn void f () {
5656 _Noreturn void g (int i) { // causes undefined behavior if i <= 0
5660 Forward references: function definitions (6.9.1).
5661 6.7.5 Alignment specifier
5663 1 alignment-specifier:
5664 _Alignas ( type-name )
5665 _Alignas ( constant-expression )
5667 2 An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
5668 a function, or a parameter, or an object declared with the register storage-class
5670 3 The constant expression shall be an integer constant expression. It shall evaluate to a
5671 valid fundamental alignment, or to a valid extended alignment supported by the
5672 implementation in the context in which it appears, or to zero.
5673 4 The combined effect of all alignment attributes in a declaration shall not specify an
5674 alignment that is less strict than the alignment that would otherwise be required for the
5675 type of the object or field being declared.
5677 5 The first form is equivalent to _Alignas(alignof(type-name)).
5678 6 The alignment requirement of the declared object or field is taken to be the specified
5679 alignment. An alignment specification of zero has no effect.140) When multiple
5680 alignment specifiers occur in a declaration, the effective alignment requirement is the
5681 strictest specified alignment.
5685 7 If the definition of an object has an alignment specifier, any other declaration of that
5686 object shall either specify equivalent alignment or have no alignment specifier. If the
5687 definition of an object does not have an alignment specifier, any other declaration of that
5688 object shall also have no alignment specifier. If declarations of an object in different
5689 translation units have different alignment specifiers, the behavior is undefined.
5693 pointeropt direct-declarator
5697 direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
5698 direct-declarator [ static type-qualifier-listopt assignment-expression ]
5699 direct-declarator [ type-qualifier-list static assignment-expression ]
5700 direct-declarator [ type-qualifier-listopt * ]
5701 direct-declarator ( parameter-type-list )
5702 direct-declarator ( identifier-listopt )
5704 * type-qualifier-listopt
5705 * type-qualifier-listopt pointer
5706 type-qualifier-list:
5708 type-qualifier-list type-qualifier
5709 parameter-type-list:
5711 parameter-list , ...
5713 parameter-declaration
5714 parameter-list , parameter-declaration
5715 parameter-declaration:
5716 declaration-specifiers declarator
5717 declaration-specifiers abstract-declaratoropt
5721 140) An alignment specification of zero also does not affect other alignment specifications in the same
5728 identifier-list , identifier
5730 2 Each declarator declares one identifier, and asserts that when an operand of the same
5731 form as the declarator appears in an expression, it designates a function or object with the
5732 scope, storage duration, and type indicated by the declaration specifiers.
5733 3 A full declarator is a declarator that is not part of another declarator. The end of a full
5734 declarator is a sequence point. If, in the nested sequence of declarators in a full
5735 declarator, there is a declarator specifying a variable length array type, the type specified
5736 by the full declarator is said to be variably modified. Furthermore, any type derived by
5737 declarator type derivation from a variably modified type is itself variably modified.
5738 4 In the following subclauses, consider a declaration
5740 where T contains the declaration specifiers that specify a type T (such as int) and D1 is
5741 a declarator that contains an identifier ident. The type specified for the identifier ident in
5742 the various forms of declarator is described inductively using this notation.
5743 5 If, in the declaration ''T D1'', D1 has the form
5745 then the type specified for ident is T .
5746 6 If, in the declaration ''T D1'', D1 has the form
5748 then ident has the type specified by the declaration ''T D''. Thus, a declarator in
5749 parentheses is identical to the unparenthesized declarator, but the binding of complicated
5750 declarators may be altered by parentheses.
5751 Implementation limits
5752 7 As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
5753 function declarators that modify an arithmetic, structure, union, or void type, either
5754 directly or via one or more typedefs.
5755 Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
5762 6.7.6.1 Pointer declarators
5764 1 If, in the declaration ''T D1'', D1 has the form
5765 * type-qualifier-listopt D
5766 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5767 T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list
5768 pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
5769 2 For two pointer types to be compatible, both shall be identically qualified and both shall
5770 be pointers to compatible types.
5771 3 EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer
5772 to a constant value'' and a ''constant pointer to a variable value''.
5773 const int *ptr_to_constant;
5774 int *const constant_ptr;
5775 The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
5776 but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
5777 int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
5779 4 The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
5780 type ''pointer to int''.
5781 typedef int *int_ptr;
5782 const int_ptr constant_ptr;
5783 declares constant_ptr as an object that has type ''const-qualified pointer to int''.
5785 6.7.6.2 Array declarators
5787 1 In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
5788 an expression or *. If they delimit an expression (which specifies the size of an array), the
5789 expression shall have an integer type. If the expression is a constant expression, it shall
5790 have a value greater than zero. The element type shall not be an incomplete or function
5791 type. The optional type qualifiers and the keyword static shall appear only in a
5792 declaration of a function parameter with an array type, and then only in the outermost
5793 array type derivation.
5794 2 An ordinary identifier (as defined in 6.2.3) that has a variably modified type shall have
5795 either block scope and no linkage or function prototype scope. If an identifier is declared
5796 to be an object with static or thread storage duration, it shall not have a variable length
5805 3 If, in the declaration ''T D1'', D1 has one of the forms:
5806 D[ type-qualifier-listopt assignment-expressionopt ]
5807 D[ static type-qualifier-listopt assignment-expression ]
5808 D[ type-qualifier-list static assignment-expression ]
5809 D[ type-qualifier-listopt * ]
5810 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5811 T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.141)
5812 (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
5813 4 If the size is not present, the array type is an incomplete type. If the size is * instead of
5814 being an expression, the array type is a variable length array type of unspecified size,
5815 which can only be used in declarations or type names with function prototype scope;142)
5816 such arrays are nonetheless complete types. If the size is an integer constant expression
5817 and the element type has a known constant size, the array type is not a variable length
5818 array type; otherwise, the array type is a variable length array type. (Variable length
5819 arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
5820 5 If the size is an expression that is not an integer constant expression: if it occurs in a
5821 declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
5822 each time it is evaluated it shall have a value greater than zero. The size of each instance
5823 of a variable length array type does not change during its lifetime. Where a size
5824 expression is part of the operand of a sizeof operator and changing the value of the
5825 size expression would not affect the result of the operator, it is unspecified whether or not
5826 the size expression is evaluated.
5827 6 For two array types to be compatible, both shall have compatible element types, and if
5828 both size specifiers are present, and are integer constant expressions, then both size
5829 specifiers shall have the same constant value. If the two array types are used in a context
5830 which requires them to be compatible, it is undefined behavior if the two size specifiers
5831 evaluate to unequal values.
5833 float fa[11], *afp[17];
5834 declares an array of float numbers and an array of pointers to float numbers.
5836 8 EXAMPLE 2 Note the distinction between the declarations
5841 141) When several ''array of'' specifications are adjacent, a multidimensional array is declared.
5842 142) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).
5848 The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
5849 (an incomplete type), the storage for which is defined elsewhere.
5851 9 EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types.
5859 int (*r)[n][n][n+1];
5860 p = a; // invalid: not compatible because 4 != 6
5861 r = c; // compatible, but defined behavior only if
5862 // n == 6 and m == n+1
5865 10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
5866 function prototype scope. Array objects declared with the _Thread_local, static, or extern
5867 storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
5868 the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
5869 identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
5870 structures or unions.
5872 int A[n]; // invalid: file scope VLA
5873 extern int (*p2)[n]; // invalid: file scope VM
5874 int B[100]; // valid: file scope but not VM
5875 void fvla(int m, int C[m][m]); // valid: VLA with prototype scope
5876 void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA
5878 typedef int VLA[m][m]; // valid: block scope typedef VLA
5880 int (*y)[n]; // invalid: y not ordinary identifier
5881 int z[n]; // invalid: z not ordinary identifier
5883 int D[m]; // valid: auto VLA
5884 static int E[m]; // invalid: static block scope VLA
5885 extern int F[m]; // invalid: F has linkage and is VLA
5886 int (*s)[m]; // valid: auto pointer to VLA
5887 extern int (*r)[m]; // invalid: r has linkage and points to VLA
5888 static int (*q)[m] = &B; // valid: q is a static block pointer to VLA
5891 Forward references: function declarators (6.7.6.3), function definitions (6.9.1),
5892 initialization (6.7.9).
5898 6.7.6.3 Function declarators (including prototypes)
5900 1 A function declarator shall not specify a return type that is a function type or an array
5902 2 The only storage-class specifier that shall occur in a parameter declaration is register.
5903 3 An identifier list in a function declarator that is not part of a definition of that function
5905 4 After adjustment, the parameters in a parameter type list in a function declarator that is
5906 part of a definition of that function shall not have incomplete type.
5908 5 If, in the declaration ''T D1'', D1 has the form
5909 D( parameter-type-list )
5911 D( identifier-listopt )
5912 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5913 T '', then the type specified for ident is ''derived-declarator-type-list function returning
5915 6 A parameter type list specifies the types of, and may declare identifiers for, the
5916 parameters of the function.
5917 7 A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to
5918 type'', where the type qualifiers (if any) are those specified within the [ and ] of the
5919 array type derivation. If the keyword static also appears within the [ and ] of the
5920 array type derivation, then for each call to the function, the value of the corresponding
5921 actual argument shall provide access to the first element of an array with at least as many
5922 elements as specified by the size expression.
5923 8 A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to
5924 function returning type'', as in 6.3.2.1.
5925 9 If the list terminates with an ellipsis (, ...), no information about the number or types
5926 of the parameters after the comma is supplied.143)
5927 10 The special case of an unnamed parameter of type void as the only item in the list
5928 specifies that the function has no parameters.
5932 143) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
5933 correspond to the ellipsis.
5937 11 If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
5938 parameter name, it shall be taken as a typedef name.
5939 12 If the function declarator is not part of a definition of that function, parameters may have
5940 incomplete type and may use the [*] notation in their sequences of declarator specifiers
5941 to specify variable length array types.
5942 13 The storage-class specifier in the declaration specifiers for a parameter declaration, if
5943 present, is ignored unless the declared parameter is one of the members of the parameter
5944 type list for a function definition.
5945 14 An identifier list declares only the identifiers of the parameters of the function. An empty
5946 list in a function declarator that is part of a definition of that function specifies that the
5947 function has no parameters. The empty list in a function declarator that is not part of a
5948 definition of that function specifies that no information about the number or types of the
5949 parameters is supplied.144)
5950 15 For two function types to be compatible, both shall specify compatible return types.145)
5951 Moreover, the parameter type lists, if both are present, shall agree in the number of
5952 parameters and in use of the ellipsis terminator; corresponding parameters shall have
5953 compatible types. If one type has a parameter type list and the other type is specified by a
5954 function declarator that is not part of a function definition and that contains an empty
5955 identifier list, the parameter list shall not have an ellipsis terminator and the type of each
5956 parameter shall be compatible with the type that results from the application of the
5957 default argument promotions. If one type has a parameter type list and the other type is
5958 specified by a function definition that contains a (possibly empty) identifier list, both shall
5959 agree in the number of parameters, and the type of each prototype parameter shall be
5960 compatible with the type that results from the application of the default argument
5961 promotions to the type of the corresponding identifier. (In the determination of type
5962 compatibility and of a composite type, each parameter declared with function or array
5963 type is taken as having the adjusted type and each parameter declared with qualified type
5964 is taken as having the unqualified version of its declared type.)
5965 16 EXAMPLE 1 The declaration
5966 int f(void), *fip(), (*pfi)();
5967 declares a function f with no parameters returning an int, a function fip with no parameter specification
5968 returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
5969 int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
5970 declaration suggests, and the same construction in an expression requires, the calling of a function fip,
5971 and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
5972 extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
5975 144) See ''future language directions'' (6.11.6).
5976 145) If both function types are ''old style'', parameter types are not compared.
5980 designator, which is then used to call the function; it returns an int.
5981 17 If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
5982 declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
5983 internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
5984 the identifier of the pointer pfi has block scope and no linkage.
5986 18 EXAMPLE 2 The declaration
5987 int (*apfi[3])(int *x, int *y);
5988 declares an array apfi of three pointers to functions returning int. Each of these functions has two
5989 parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
5990 go out of scope at the end of the declaration of apfi.
5992 19 EXAMPLE 3 The declaration
5993 int (*fpfi(int (*)(long), int))(int, ...);
5994 declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
5995 parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
5996 The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
5997 additional arguments of any type.
5999 20 EXAMPLE 4 The following prototype has a variably modified parameter.
6000 void addscalar(int n, int m,
6001 double a[n][n*m+300], double x);
6005 addscalar(4, 2, b, 2.17);
6008 void addscalar(int n, int m,
6009 double a[n][n*m+300], double x)
6011 for (int i = 0; i < n; i++)
6012 for (int j = 0, k = n*m+300; j < k; j++)
6013 // a is a pointer to a VLA with n*m+300 elements
6017 21 EXAMPLE 5 The following are all compatible function prototype declarators.
6018 double maximum(int n, int m, double a[n][m]);
6019 double maximum(int n, int m, double a[*][*]);
6020 double maximum(int n, int m, double a[ ][*]);
6021 double maximum(int n, int m, double a[ ][m]);
6023 void f(double (* restrict a)[5]);
6024 void f(double a[restrict][5]);
6025 void f(double a[restrict 3][5]);
6026 void f(double a[restrict static 3][5]);
6031 (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
6032 non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)
6034 Forward references: function definitions (6.9.1), type names (6.7.7).
6038 specifier-qualifier-list abstract-declaratoropt
6039 abstract-declarator:
6041 pointeropt direct-abstract-declarator
6042 direct-abstract-declarator:
6043 ( abstract-declarator )
6044 direct-abstract-declaratoropt [ type-qualifier-listopt
6045 assignment-expressionopt ]
6046 direct-abstract-declaratoropt [ static type-qualifier-listopt
6047 assignment-expression ]
6048 direct-abstract-declaratoropt [ type-qualifier-list static
6049 assignment-expression ]
6050 direct-abstract-declaratoropt [ * ]
6051 direct-abstract-declaratoropt ( parameter-type-listopt )
6053 2 In several contexts, it is necessary to specify a type. This is accomplished using a type
6054 name, which is syntactically a declaration for a function or an object of that type that
6055 omits the identifier.146)
6056 3 EXAMPLE The constructions
6064 (h) int (*const [])(unsigned int, ...)
6065 name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
6066 array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
6067 with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
6070 146) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no
6071 parameter specification'', rather than redundant parentheses around the omitted identifier.
6075 returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
6076 parameter that has type unsigned int and an unspecified number of other parameters, returning an
6079 6.7.8 Type definitions
6084 2 If a typedef name specifies a variably modified type then it shall have block scope.
6086 3 In a declaration whose storage-class specifier is typedef, each declarator defines an
6087 identifier to be a typedef name that denotes the type specified for the identifier in the way
6088 described in 6.7.6. Any array size expressions associated with variable length array
6089 declarators are evaluated each time the declaration of the typedef name is reached in the
6090 order of execution. A typedef declaration does not introduce a new type, only a
6091 synonym for the type so specified. That is, in the following declarations:
6092 typedef T type_ident;
6094 type_ident is defined as a typedef name with the type specified by the declaration
6095 specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator-
6096 type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
6097 typedef name shares the same name space as other identifiers declared in ordinary
6100 typedef int MILES, KLICKSP();
6101 typedef struct { double hi, lo; } range;
6104 extern KLICKSP *metricp;
6107 are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no
6108 parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
6109 such a structure. The object distance has a type compatible with any other int object.
6111 5 EXAMPLE 2 After the declarations
6112 typedef struct s1 { int x; } t1, *tp1;
6113 typedef struct s2 { int x; } t2, *tp2;
6114 type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
6118 s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.
6120 6 EXAMPLE 3 The following obscure constructions
6121 typedef signed int t;
6128 declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
6129 with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
6130 qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
6131 [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
6132 (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
6133 unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
6134 type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
6135 in an inner scope by
6138 then a function f is declared with type ''function returning signed int with one unnamed parameter
6139 with type pointer to function returning signed int with one unnamed parameter with type signed
6140 int'', and an identifier t with type long int.
6142 7 EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
6143 following declarations of the signal function specify exactly the same type, the first without making use
6144 of any typedef names.
6145 typedef void fv(int), (*pfv)(int);
6146 void (*signal(int, void (*)(int)))(int);
6147 fv *signal(int, fv *);
6148 pfv signal(int, pfv);
6150 8 EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
6151 time the typedef name is defined, not each time it is used:
6154 typedef int B[n]; // B is n ints, n evaluated now
6156 B a; // a is n ints, n without += 1
6157 int b[n]; // a and b are different sizes
6158 for (int i = 1; i < n; i++)
6167 6.7.9 Initialization
6170 assignment-expression
6171 { initializer-list }
6172 { initializer-list , }
6174 designationopt initializer
6175 initializer-list , designationopt initializer
6180 designator-list designator
6182 [ constant-expression ]
6185 2 No initializer shall attempt to provide a value for an object not contained within the entity
6187 3 The type of the entity to be initialized shall be an array of unknown size or a complete
6188 object type that is not a variable length array type.
6189 4 All the expressions in an initializer for an object that has static or thread storage duration
6190 shall be constant expressions or string literals.
6191 5 If the declaration of an identifier has block scope, and the identifier has external or
6192 internal linkage, the declaration shall have no initializer for the identifier.
6193 6 If a designator has the form
6194 [ constant-expression ]
6195 then the current object (defined below) shall have array type and the expression shall be
6196 an integer constant expression. If the array is of unknown size, any nonnegative value is
6198 7 If a designator has the form
6200 then the current object (defined below) shall have structure or union type and the
6201 identifier shall be the name of a member of that type.
6205 8 An initializer specifies the initial value stored in an object.
6206 9 Except where explicitly stated otherwise, for the purposes of this subclause unnamed
6207 members of objects of structure and union type do not participate in initialization.
6208 Unnamed members of structure objects have indeterminate value even after initialization.
6209 10 If an object that has automatic storage duration is not initialized explicitly, its value is
6210 indeterminate. If an object that has static or thread storage duration is not initialized
6212 -- if it has pointer type, it is initialized to a null pointer;
6213 -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
6214 -- if it is an aggregate, every member is initialized (recursively) according to these rules,
6215 and any padding is initialized to zero bits;
6216 -- if it is a union, the first named member is initialized (recursively) according to these
6217 rules, and any padding is initialized to zero bits;
6218 11 The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
6219 initial value of the object is that of the expression (after conversion); the same type
6220 constraints and conversions as for simple assignment apply, taking the type of the scalar
6221 to be the unqualified version of its declared type.
6222 12 The rest of this subclause deals with initializers for objects that have aggregate or union
6224 13 The initializer for a structure or union object that has automatic storage duration shall be
6225 either an initializer list as described below, or a single expression that has compatible
6226 structure or union type. In the latter case, the initial value of the object, including
6227 unnamed members, is that of the expression.
6228 14 An array of character type may be initialized by a character string literal or UTF-8 string
6229 literal, optionally enclosed in braces. Successive bytes of the string literal (including the
6230 terminating null character if there is room or if the array is of unknown size) initialize the
6231 elements of the array.
6232 15 An array with element type compatible with a qualified or unqualified version of
6233 wchar_t may be initialized by a wide string literal, optionally enclosed in braces.
6234 Successive wide characters of the wide string literal (including the terminating null wide
6235 character if there is room or if the array is of unknown size) initialize the elements of the
6237 16 Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
6238 enclosed list of initializers for the elements or named members.
6243 17 Each brace-enclosed initializer list has an associated current object. When no
6244 designations are present, subobjects of the current object are initialized in order according
6245 to the type of the current object: array elements in increasing subscript order, structure
6246 members in declaration order, and the first named member of a union.147) In contrast, a
6247 designation causes the following initializer to begin initialization of the subobject
6248 described by the designator. Initialization then continues forward in order, beginning
6249 with the next subobject after that described by the designator.148)
6250 18 Each designator list begins its description with the current object associated with the
6251 closest surrounding brace pair. Each item in the designator list (in order) specifies a
6252 particular member of its current object and changes the current object for the next
6253 designator (if any) to be that member.149) The current object that results at the end of the
6254 designator list is the subobject to be initialized by the following initializer.
6255 19 The initialization shall occur in initializer list order, each initializer provided for a
6256 particular subobject overriding any previously listed initializer for the same subobject;150)
6257 all subobjects that are not initialized explicitly shall be initialized implicitly the same as
6258 objects that have static storage duration.
6259 20 If the aggregate or union contains elements or members that are aggregates or unions,
6260 these rules apply recursively to the subaggregates or contained unions. If the initializer of
6261 a subaggregate or contained union begins with a left brace, the initializers enclosed by
6262 that brace and its matching right brace initialize the elements or members of the
6263 subaggregate or the contained union. Otherwise, only enough initializers from the list are
6264 taken to account for the elements or members of the subaggregate or the first member of
6265 the contained union; any remaining initializers are left to initialize the next element or
6266 member of the aggregate of which the current subaggregate or contained union is a part.
6267 21 If there are fewer initializers in a brace-enclosed list than there are elements or members
6268 of an aggregate, or fewer characters in a string literal used to initialize an array of known
6269 size than there are elements in the array, the remainder of the aggregate shall be
6270 initialized implicitly the same as objects that have static storage duration.
6274 147) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
6275 subobjects are initialized as usual, but the subaggregate or contained union does not become the
6276 current object: current objects are associated only with brace-enclosed initializer lists.
6277 148) After a union member is initialized, the next object is not the next member of the union; instead, it is
6278 the next subobject of an object containing the union.
6279 149) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
6280 the surrounding brace pair. Note, too, that each separate designator list is independent.
6281 150) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
6282 not be evaluated at all.
6286 22 If an array of unknown size is initialized, its size is determined by the largest indexed
6287 element with an explicit initializer. The array type is completed at the end of its
6289 23 The order in which any side effects occur among the initialization list expressions is
6291 24 EXAMPLE 1 Provided that <complex.h> has been #included, the declarations
6293 double complex c = 5 + 3 * I;
6294 define and initialize i with the value 3 and c with the value 5.0 + i3.0.
6296 25 EXAMPLE 2 The declaration
6297 int x[] = { 1, 3, 5 };
6298 defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
6299 and there are three initializers.
6301 26 EXAMPLE 3 The declaration
6307 is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
6308 y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
6309 y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
6312 1, 3, 5, 2, 4, 6, 3, 5, 7
6314 The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
6315 next three are taken successively for y[1] and y[2].
6317 27 EXAMPLE 4 The declaration
6319 { 1 }, { 2 }, { 3 }, { 4 }
6321 initializes the first column of z as specified and initializes the rest with zeros.
6323 28 EXAMPLE 5 The declaration
6324 struct { int a[3], b; } w[] = { { 1 }, 2 };
6325 is a definition with an inconsistently bracketed initialization. It defines an array with two element
6326 structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
6330 151) In particular, the evaluation order need not be the same as the order of subobject initialization.
6334 29 EXAMPLE 6 The declaration
6335 short q[4][3][2] = {
6340 contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
6341 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
6342 q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
6343 q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
6344 only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
6345 for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
6346 respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
6347 diagnostic message would have been issued. The same initialization result could have been achieved by:
6348 short q[4][3][2] = {
6354 short q[4][3][2] = {
6366 in a fully bracketed form.
6367 30 Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
6370 31 EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the
6372 typedef int A[]; // OK - declared with block scope
6374 A a = { 1, 2 }, b = { 3, 4, 5 };
6376 int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
6377 due to the rules for incomplete types.
6383 32 EXAMPLE 8 The declaration
6384 char s[] = "abc", t[3] = "abc";
6385 defines ''plain'' char array objects s and t whose elements are initialized with character string literals.
6386 This declaration is identical to
6387 char s[] = { 'a', 'b', 'c', '\0' },
6388 t[] = { 'a', 'b', 'c' };
6389 The contents of the arrays are modifiable. On the other hand, the declaration
6391 defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char''
6392 with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
6393 modify the contents of the array, the behavior is undefined.
6395 33 EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using
6397 enum { member_one, member_two };
6398 const char *nm[] = {
6399 [member_two] = "member two",
6400 [member_one] = "member one",
6403 34 EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order:
6404 div_t answer = { .quot = 2, .rem = -1 };
6406 35 EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
6407 might be misunderstood:
6408 struct { int a[3], b; } w[] =
6409 { [0].a = {1}, [1].a[0] = 2 };
6411 36 EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator:
6413 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
6415 37 In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
6416 than ten, some of the values provided by the first five initializers will be overridden by the second five.
6418 38 EXAMPLE 13 Any member of a union can be initialized:
6419 union { /* ... */ } u = { .any_member = 42 };
6421 Forward references: common definitions <stddef.h> (7.19).
6428 6.7.10 Static assertions
6430 1 static_assert-declaration:
6431 _Static_assert ( constant-expression , string-literal ) ;
6433 2 The constant expression shall compare unequal to 0.
6435 3 The constant expression shall be an integer constant expression. If the value of the
6436 constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
6437 constraint is violated and the implementation shall produce a diagnostic message that
6438 includes the text of the string literal, except that characters not in the basic source
6439 character set are not required to appear in the message.
6440 Forward references: diagnostics (7.2).
6447 6.8 Statements and blocks
6452 expression-statement
6457 2 A statement specifies an action to be performed. Except as indicated, statements are
6458 executed in sequence.
6459 3 A block allows a set of declarations and statements to be grouped into one syntactic unit.
6460 The initializers of objects that have automatic storage duration, and the variable length
6461 array declarators of ordinary identifiers with block scope, are evaluated and the values are
6462 stored in the objects (including storing an indeterminate value in objects without an
6463 initializer) each time the declaration is reached in the order of execution, as if it were a
6464 statement, and within each declaration in the order that declarators appear.
6465 4 A full expression is an expression that is not part of another expression or of a declarator.
6466 Each of the following is a full expression: an initializer that is not part of a compound
6467 literal; the expression in an expression statement; the controlling expression of a selection
6468 statement (if or switch); the controlling expression of a while or do statement; each
6469 of the (optional) expressions of a for statement; the (optional) expression in a return
6470 statement. There is a sequence point between the evaluation of a full expression and the
6471 evaluation of the next full expression to be evaluated.
6472 Forward references: expression and null statements (6.8.3), selection statements
6473 (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
6474 6.8.1 Labeled statements
6476 1 labeled-statement:
6477 identifier : statement
6478 case constant-expression : statement
6481 2 A case or default label shall appear only in a switch statement. Further
6482 constraints on such labels are discussed under the switch statement.
6486 3 Label names shall be unique within a function.
6488 4 Any statement may be preceded by a prefix that declares an identifier as a label name.
6489 Labels in themselves do not alter the flow of control, which continues unimpeded across
6491 Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).
6492 6.8.2 Compound statement
6494 1 compound-statement:
6495 { block-item-listopt }
6498 block-item-list block-item
6503 2 A compound statement is a block.
6504 6.8.3 Expression and null statements
6506 1 expression-statement:
6509 2 The expression in an expression statement is evaluated as a void expression for its side
6511 3 A null statement (consisting of just a semicolon) performs no operations.
6512 4 EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
6513 discarding of its value may be made explicit by converting the expression to a void expression by means of
6521 152) Such as assignments, and function calls which have side effects.
6525 5 EXAMPLE 2 In the program fragment
6528 while (*s++ != '\0')
6530 a null statement is used to supply an empty loop body to the iteration statement.
6532 6 EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound
6546 Forward references: iteration statements (6.8.5).
6547 6.8.4 Selection statements
6549 1 selection-statement:
6550 if ( expression ) statement
6551 if ( expression ) statement else statement
6552 switch ( expression ) statement
6554 2 A selection statement selects among a set of statements depending on the value of a
6555 controlling expression.
6556 3 A selection statement is a block whose scope is a strict subset of the scope of its
6557 enclosing block. Each associated substatement is also a block whose scope is a strict
6558 subset of the scope of the selection statement.
6559 6.8.4.1 The if statement
6561 1 The controlling expression of an if statement shall have scalar type.
6563 2 In both forms, the first substatement is executed if the expression compares unequal to 0.
6564 In the else form, the second substatement is executed if the expression compares equal
6569 to 0. If the first substatement is reached via a label, the second substatement is not
6571 3 An else is associated with the lexically nearest preceding if that is allowed by the
6573 6.8.4.2 The switch statement
6575 1 The controlling expression of a switch statement shall have integer type.
6576 2 If a switch statement has an associated case or default label within the scope of an
6577 identifier with a variably modified type, the entire switch statement shall be within the
6578 scope of that identifier.153)
6579 3 The expression of each case label shall be an integer constant expression and no two of
6580 the case constant expressions in the same switch statement shall have the same value
6581 after conversion. There may be at most one default label in a switch statement.
6582 (Any enclosed switch statement may have a default label or case constant
6583 expressions with values that duplicate case constant expressions in the enclosing
6586 4 A switch statement causes control to jump to, into, or past the statement that is the
6587 switch body, depending on the value of a controlling expression, and on the presence of a
6588 default label and the values of any case labels on or in the switch body. A case or
6589 default label is accessible only within the closest enclosing switch statement.
6590 5 The integer promotions are performed on the controlling expression. The constant
6591 expression in each case label is converted to the promoted type of the controlling
6592 expression. If a converted value matches that of the promoted controlling expression,
6593 control jumps to the statement following the matched case label. Otherwise, if there is
6594 a default label, control jumps to the labeled statement. If no converted case constant
6595 expression matches and there is no default label, no part of the switch body is
6597 Implementation limits
6598 6 As discussed in 5.2.4.1, the implementation may limit the number of case values in a
6604 153) That is, the declaration either precedes the switch statement, or it follows the last case or
6605 default label associated with the switch that is in the block containing the declaration.
6609 7 EXAMPLE In the artificial program fragment
6616 /* falls through into default code */
6620 the object whose identifier is i exists with automatic storage duration (within the block) but is never
6621 initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
6622 access an indeterminate value. Similarly, the call to the function f cannot be reached.
6624 6.8.5 Iteration statements
6626 1 iteration-statement:
6627 while ( expression ) statement
6628 do statement while ( expression ) ;
6629 for ( expressionopt ; expressionopt ; expressionopt ) statement
6630 for ( declaration expressionopt ; expressionopt ) statement
6632 2 The controlling expression of an iteration statement shall have scalar type.
6633 3 The declaration part of a for statement shall only declare identifiers for objects having
6634 storage class auto or register.
6636 4 An iteration statement causes a statement called the loop body to be executed repeatedly
6637 until the controlling expression compares equal to 0. The repetition occurs regardless of
6638 whether the loop body is entered from the iteration statement or by a jump.154)
6639 5 An iteration statement is a block whose scope is a strict subset of the scope of its
6640 enclosing block. The loop body is also a block whose scope is a strict subset of the scope
6641 of the iteration statement.
6642 6 An iteration statement that performs no input/output operations, does not access volatile
6643 objects, and performs no synchronization or atomic operations in its body, controlling
6644 expression, or (in the case of a for statement) its expression-3, may be assumed by the
6645 implementation to terminate.155)
6647 154) Code jumped over is not executed. In particular, the controlling expression of a for or while
6648 statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
6652 6.8.5.1 The while statement
6653 1 The evaluation of the controlling expression takes place before each execution of the loop
6655 6.8.5.2 The do statement
6656 1 The evaluation of the controlling expression takes place after each execution of the loop
6658 6.8.5.3 The for statement
6660 for ( clause-1 ; expression-2 ; expression-3 ) statement
6661 behaves as follows: The expression expression-2 is the controlling expression that is
6662 evaluated before each execution of the loop body. The expression expression-3 is
6663 evaluated as a void expression after each execution of the loop body. If clause-1 is a
6664 declaration, the scope of any identifiers it declares is the remainder of the declaration and
6665 the entire loop, including the other two expressions; it is reached in the order of execution
6666 before the first evaluation of the controlling expression. If clause-1 is an expression, it is
6667 evaluated as a void expression before the first evaluation of the controlling expression.156)
6668 2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
6670 6.8.6 Jump statements
6676 return expressionopt ;
6678 2 A jump statement causes an unconditional jump to another place.
6683 155) This is intended to allow compiler transformations such as removal of empty loops even when
6684 termination cannot be proven.
6685 156) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
6686 the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
6687 such that execution of the loop continues until the expression compares equal to 0; and expression-3
6688 specifies an operation (such as incrementing) that is performed after each iteration.
6692 6.8.6.1 The goto statement
6694 1 The identifier in a goto statement shall name a label located somewhere in the enclosing
6695 function. A goto statement shall not jump from outside the scope of an identifier having
6696 a variably modified type to inside the scope of that identifier.
6698 2 A goto statement causes an unconditional jump to the statement prefixed by the named
6699 label in the enclosing function.
6700 3 EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
6701 following outline presents one possible approach to a problem based on these three assumptions:
6702 1. The general initialization code accesses objects only visible to the current function.
6703 2. The general initialization code is too large to warrant duplication.
6704 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
6705 continue statements, for example.)
6709 // determine next operation
6711 if (need to reinitialize) {
6712 // reinitialize-only code
6715 // general initialization code
6719 // handle other operations
6728 4 EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
6729 modified types. A jump within the scope, however, is permitted.
6730 goto lab3; // invalid: going INTO scope of VLA.
6736 goto lab4; // valid: going WITHIN scope of VLA.
6741 goto lab4; // invalid: going INTO scope of VLA.
6743 6.8.6.2 The continue statement
6745 1 A continue statement shall appear only in or as a loop body.
6747 2 A continue statement causes a jump to the loop-continuation portion of the smallest
6748 enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
6750 while (/* ... */) { do { for (/* ... */) {
6751 /* ... */ /* ... */ /* ... */
6752 continue; continue; continue;
6753 /* ... */ /* ... */ /* ... */
6754 contin: ; contin: ; contin: ;
6755 } } while (/* ... */); }
6756 unless the continue statement shown is in an enclosed iteration statement (in which
6757 case it is interpreted within that statement), it is equivalent to goto contin;.157)
6758 6.8.6.3 The break statement
6760 1 A break statement shall appear only in or as a switch body or loop body.
6762 2 A break statement terminates execution of the smallest enclosing switch or iteration
6767 157) Following the contin: label is a null statement.
6771 6.8.6.4 The return statement
6773 1 A return statement with an expression shall not appear in a function whose return type
6774 is void. A return statement without an expression shall only appear in a function
6775 whose return type is void.
6777 2 A return statement terminates execution of the current function and returns control to
6778 its caller. A function may have any number of return statements.
6779 3 If a return statement with an expression is executed, the value of the expression is
6780 returned to the caller as the value of the function call expression. If the expression has a
6781 type different from the return type of the function in which it appears, the value is
6782 converted as if by assignment to an object having the return type of the function.158)
6784 struct s { double i; } f(void);
6801 there is no undefined behavior, although there would be if the assignment were done directly (without using
6802 a function call to fetch the value).
6807 158) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
6808 apply to the case of function return. The representation of floating-point values may have wider range
6809 or precision than implied by the type; a cast may be used to remove this extra range and precision.
6813 6.9 External definitions
6816 external-declaration
6817 translation-unit external-declaration
6818 external-declaration:
6822 2 The storage-class specifiers auto and register shall not appear in the declaration
6823 specifiers in an external declaration.
6824 3 There shall be no more than one external definition for each identifier declared with
6825 internal linkage in a translation unit. Moreover, if an identifier declared with internal
6826 linkage is used in an expression (other than as a part of the operand of a sizeof
6827 operator whose result is an integer constant), there shall be exactly one external definition
6828 for the identifier in the translation unit.
6830 4 As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
6831 which consists of a sequence of external declarations. These are described as ''external''
6832 because they appear outside any function (and hence have file scope). As discussed in
6833 6.7, a declaration that also causes storage to be reserved for an object or a function named
6834 by the identifier is a definition.
6835 5 An external definition is an external declaration that is also a definition of a function
6836 (other than an inline definition) or an object. If an identifier declared with external
6837 linkage is used in an expression (other than as part of the operand of a sizeof operator
6838 whose result is an integer constant), somewhere in the entire program there shall be
6839 exactly one external definition for the identifier; otherwise, there shall be no more than
6845 159) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
6846 external definition for it.
6850 6.9.1 Function definitions
6852 1 function-definition:
6853 declaration-specifiers declarator declaration-listopt compound-statement
6856 declaration-list declaration
6858 2 The identifier declared in a function definition (which is the name of the function) shall
6859 have a function type, as specified by the declarator portion of the function definition.160)
6860 3 The return type of a function shall be void or a complete object type other than array
6862 4 The storage-class specifier, if any, in the declaration specifiers shall be either extern or
6864 5 If the declarator includes a parameter type list, the declaration of each parameter shall
6865 include an identifier, except for the special case of a parameter list consisting of a single
6866 parameter of type void, in which case there shall not be an identifier. No declaration list
6868 6 If the declarator includes an identifier list, each declaration in the declaration list shall
6869 have at least one declarator, those declarators shall declare only identifiers from the
6870 identifier list, and every identifier in the identifier list shall be declared. An identifier
6871 declared as a typedef name shall not be redeclared as a parameter. The declarations in the
6872 declaration list shall contain no storage-class specifier other than register and no
6877 160) The intent is that the type category in a function definition cannot be inherited from a typedef:
6878 typedef int F(void); // type F is ''function with no parameters
6880 F f, g; // f and g both have type compatible with F
6881 F f { /* ... */ } // WRONG: syntax/constraint error
6882 F g() { /* ... */ } // WRONG: declares that g returns a function
6883 int f(void) { /* ... */ } // RIGHT: f has type compatible with F
6884 int g() { /* ... */ } // RIGHT: g has type compatible with F
6885 F *e(void) { /* ... */ } // e returns a pointer to a function
6886 F *((e))(void) { /* ... */ } // same: parentheses irrelevant
6887 int (*fp)(void); // fp points to a function that has type F
6888 F *Fp; // Fp points to a function that has type F
6894 7 The declarator in a function definition specifies the name of the function being defined
6895 and the identifiers of its parameters. If the declarator includes a parameter type list, the
6896 list also specifies the types of all the parameters; such a declarator also serves as a
6897 function prototype for later calls to the same function in the same translation unit. If the
6898 declarator includes an identifier list,161) the types of the parameters shall be declared in a
6899 following declaration list. In either case, the type of each parameter is adjusted as
6900 described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
6902 8 If a function that accepts a variable number of arguments is defined without a parameter
6903 type list that ends with the ellipsis notation, the behavior is undefined.
6904 9 Each parameter has automatic storage duration; its identifier is an lvalue.162) The layout
6905 of the storage for parameters is unspecified.
6906 10 On entry to the function, the size expressions of each variably modified parameter are
6907 evaluated and the value of each argument expression is converted to the type of the
6908 corresponding parameter as if by assignment. (Array expressions and function
6909 designators as arguments were converted to pointers before the call.)
6910 11 After all parameters have been assigned, the compound statement that constitutes the
6911 body of the function definition is executed.
6912 12 If the } that terminates a function is reached, and the value of the function call is used by
6913 the caller, the behavior is undefined.
6914 13 EXAMPLE 1 In the following:
6915 extern int max(int a, int b)
6917 return a > b ? a : b;
6919 extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
6920 function declarator; and
6921 { return a > b ? a : b; }
6922 is the function body. The following similar definition uses the identifier-list form for the parameter
6928 161) See ''future language directions'' (6.11.7).
6929 162) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
6933 extern int max(a, b)
6936 return a > b ? a : b;
6938 Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
6939 that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
6940 to the function, whereas the second form does not.
6942 14 EXAMPLE 2 To pass one function to another, one might say
6946 Then the definition of g might read
6947 void g(int (*funcp)(void))
6950 (*funcp)(); /* or funcp(); ... */
6953 void g(int func(void))
6956 func(); /* or (*func)(); ... */
6959 6.9.2 External object definitions
6961 1 If the declaration of an identifier for an object has file scope and an initializer, the
6962 declaration is an external definition for the identifier.
6963 2 A declaration of an identifier for an object that has file scope without an initializer, and
6964 without a storage-class specifier or with the storage-class specifier static, constitutes a
6965 tentative definition. If a translation unit contains one or more tentative definitions for an
6966 identifier, and the translation unit contains no external definition for that identifier, then
6967 the behavior is exactly as if the translation unit contains a file scope declaration of that
6968 identifier, with the composite type as of the end of the translation unit, with an initializer
6970 3 If the declaration of an identifier for an object is a tentative definition and has internal
6971 linkage, the declared type shall not be an incomplete type.
6979 int i1 = 1; // definition, external linkage
6980 static int i2 = 2; // definition, internal linkage
6981 extern int i3 = 3; // definition, external linkage
6982 int i4; // tentative definition, external linkage
6983 static int i5; // tentative definition, internal linkage
6984 int i1; // valid tentative definition, refers to previous
6985 int i2; // 6.2.2 renders undefined, linkage disagreement
6986 int i3; // valid tentative definition, refers to previous
6987 int i4; // valid tentative definition, refers to previous
6988 int i5; // 6.2.2 renders undefined, linkage disagreement
6989 extern int i1; // refers to previous, whose linkage is external
6990 extern int i2; // refers to previous, whose linkage is internal
6991 extern int i3; // refers to previous, whose linkage is external
6992 extern int i4; // refers to previous, whose linkage is external
6993 extern int i5; // refers to previous, whose linkage is internal
6995 5 EXAMPLE 2 If at the end of the translation unit containing
6997 the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
6998 zero on program startup.
7005 6.10 Preprocessing directives
7007 1 preprocessing-file:
7018 if-group elif-groupsopt else-groupopt endif-line
7020 # if constant-expression new-line groupopt
7021 # ifdef identifier new-line groupopt
7022 # ifndef identifier new-line groupopt
7025 elif-groups elif-group
7027 # elif constant-expression new-line groupopt
7029 # else new-line groupopt
7039 # include pp-tokens new-line
7040 # define identifier replacement-list new-line
7041 # define identifier lparen identifier-listopt )
7042 replacement-list new-line
7043 # define identifier lparen ... ) replacement-list new-line
7044 # define identifier lparen identifier-list , ... )
7045 replacement-list new-line
7046 # undef identifier new-line
7047 # line pp-tokens new-line
7048 # error pp-tokensopt new-line
7049 # pragma pp-tokensopt new-line
7052 pp-tokensopt new-line
7056 a ( character not immediately preceded by white-space
7061 pp-tokens preprocessing-token
7063 the new-line character
7065 2 A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
7066 following constraints: The first token in the sequence is a # preprocessing token that (at
7067 the start of translation phase 4) is either the first character in the source file (optionally
7068 after white space containing no new-line characters) or that follows white space
7069 containing at least one new-line character. The last token in the sequence is the first new-
7070 line character that follows the first token in the sequence.163) A new-line character ends
7071 the preprocessing directive even if it occurs within what would otherwise be an
7073 163) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic
7074 significance, as all white space is equivalent except in certain situations during preprocessing (see the
7075 # character string literal creation operator in 6.10.3.2, for example).
7079 invocation of a function-like macro.
7080 3 A text line shall not begin with a # preprocessing token. A non-directive shall not begin
7081 with any of the directive names appearing in the syntax.
7082 4 When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
7083 sequence of preprocessing tokens to occur between the directive name and the following
7086 5 The only white-space characters that shall appear between preprocessing tokens within a
7087 preprocessing directive (from just after the introducing # preprocessing token through
7088 just before the terminating new-line character) are space and horizontal-tab (including
7089 spaces that have replaced comments or possibly other white-space characters in
7090 translation phase 3).
7092 6 The implementation can process and skip sections of source files conditionally, include
7093 other source files, and replace macros. These capabilities are called preprocessing,
7094 because conceptually they occur before translation of the resulting translation unit.
7095 7 The preprocessing tokens within a preprocessing directive are not subject to macro
7096 expansion unless otherwise stated.
7099 EMPTY # include <file.h>
7100 the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
7101 begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
7104 6.10.1 Conditional inclusion
7106 1 The expression that controls conditional inclusion shall be an integer constant expression
7107 except that: identifiers (including those lexically identical to keywords) are interpreted as
7108 described below;164) and it may contain unary operator expressions of the form
7111 defined ( identifier )
7112 which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is
7115 164) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
7116 either are or are not macro names -- there simply are no keywords, enumeration constants, etc.
7120 predefined or if it has been the subject of a #define preprocessing directive without an
7121 intervening #undef directive with the same subject identifier), 0 if it is not.
7122 2 Each preprocessing token that remains (in the list of preprocessing tokens that will
7123 become the controlling expression) after all macro replacements have occurred shall be in
7124 the lexical form of a token (6.4).
7126 3 Preprocessing directives of the forms
7127 # if constant-expression new-line groupopt
7128 # elif constant-expression new-line groupopt
7129 check whether the controlling constant expression evaluates to nonzero.
7130 4 Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
7131 the controlling constant expression are replaced (except for those macro names modified
7132 by the defined unary operator), just as in normal text. If the token defined is
7133 generated as a result of this replacement process or use of the defined unary operator
7134 does not match one of the two specified forms prior to macro replacement, the behavior is
7135 undefined. After all replacements due to macro expansion and the defined unary
7136 operator have been performed, all remaining identifiers (including those lexically
7137 identical to keywords) are replaced with the pp-number 0, and then each preprocessing
7138 token is converted into a token. The resulting tokens compose the controlling constant
7139 expression which is evaluated according to the rules of 6.6. For the purposes of this
7140 token conversion and evaluation, all signed integer types and all unsigned integer types
7141 act as if they have the same representation as, respectively, the types intmax_t and
7142 uintmax_t defined in the header <stdint.h>.165) This includes interpreting
7143 character constants, which may involve converting escape sequences into execution
7144 character set members. Whether the numeric value for these character constants matches
7145 the value obtained when an identical character constant occurs in an expression (other
7146 than within a #if or #elif directive) is implementation-defined.166) Also, whether a
7147 single-character character constant may have a negative value is implementation-defined.
7152 165) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
7153 0x8000 is signed and positive within a #if expression even though it would be unsigned in
7154 translation phase 7.
7155 166) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
7156 evaluate to the same value in these two contexts.
7158 if ('z' - 'a' == 25)
7163 5 Preprocessing directives of the forms
7164 # ifdef identifier new-line groupopt
7165 # ifndef identifier new-line groupopt
7166 check whether the identifier is or is not currently defined as a macro name. Their
7167 conditions are equivalent to #if defined identifier and #if !defined identifier
7169 6 Each directive's condition is checked in order. If it evaluates to false (zero), the group
7170 that it controls is skipped: directives are processed only through the name that determines
7171 the directive in order to keep track of the level of nested conditionals; the rest of the
7172 directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
7173 group. Only the first group whose control condition evaluates to true (nonzero) is
7174 processed. If none of the conditions evaluates to true, and there is a #else directive, the
7175 group controlled by the #else is processed; lacking a #else directive, all the groups
7176 until the #endif are skipped.167)
7177 Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
7178 integer types (7.20.1.5).
7179 6.10.2 Source file inclusion
7181 1 A #include directive shall identify a header or source file that can be processed by the
7184 2 A preprocessing directive of the form
7185 # include <h-char-sequence> new-line
7186 searches a sequence of implementation-defined places for a header identified uniquely by
7187 the specified sequence between the < and > delimiters, and causes the replacement of that
7188 directive by the entire contents of the header. How the places are specified or the header
7189 identified is implementation-defined.
7190 3 A preprocessing directive of the form
7191 # include "q-char-sequence" new-line
7192 causes the replacement of that directive by the entire contents of the source file identified
7193 by the specified sequence between the " delimiters. The named source file is searched
7196 167) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
7197 before the terminating new-line character. However, comments may appear anywhere in a source file,
7198 including within a preprocessing directive.
7202 for in an implementation-defined manner. If this search is not supported, or if the search
7203 fails, the directive is reprocessed as if it read
7204 # include <h-char-sequence> new-line
7205 with the identical contained sequence (including > characters, if any) from the original
7207 4 A preprocessing directive of the form
7208 # include pp-tokens new-line
7209 (that does not match one of the two previous forms) is permitted. The preprocessing
7210 tokens after include in the directive are processed just as in normal text. (Each
7211 identifier currently defined as a macro name is replaced by its replacement list of
7212 preprocessing tokens.) The directive resulting after all replacements shall match one of
7213 the two previous forms.168) The method by which a sequence of preprocessing tokens
7214 between a < and a > preprocessing token pair or a pair of " characters is combined into a
7215 single header name preprocessing token is implementation-defined.
7216 5 The implementation shall provide unique mappings for sequences consisting of one or
7217 more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
7218 first character shall not be a digit. The implementation may ignore distinctions of
7219 alphabetical case and restrict the mapping to eight significant characters before the
7221 6 A #include preprocessing directive may appear in a source file that has been read
7222 because of a #include directive in another file, up to an implementation-defined
7223 nesting limit (see 5.2.4.1).
7224 7 EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following:
7231 168) Note that adjacent string literals are not concatenated into a single string literal (see the translation
7232 phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
7236 8 EXAMPLE 2 This illustrates macro-replaced #include directives:
7238 #define INCFILE "vers1.h"
7240 #define INCFILE "vers2.h" // and so on
7242 #define INCFILE "versN.h"
7246 Forward references: macro replacement (6.10.3).
7247 6.10.3 Macro replacement
7249 1 Two replacement lists are identical if and only if the preprocessing tokens in both have
7250 the same number, ordering, spelling, and white-space separation, where all white-space
7251 separations are considered identical.
7252 2 An identifier currently defined as an object-like macro shall not be redefined by another
7253 #define preprocessing directive unless the second definition is an object-like macro
7254 definition and the two replacement lists are identical. Likewise, an identifier currently
7255 defined as a function-like macro shall not be redefined by another #define
7256 preprocessing directive unless the second definition is a function-like macro definition
7257 that has the same number and spelling of parameters, and the two replacement lists are
7259 3 There shall be white-space between the identifier and the replacement list in the definition
7260 of an object-like macro.
7261 4 If the identifier-list in the macro definition does not end with an ellipsis, the number of
7262 arguments (including those arguments consisting of no preprocessing tokens) in an
7263 invocation of a function-like macro shall equal the number of parameters in the macro
7264 definition. Otherwise, there shall be more arguments in the invocation than there are
7265 parameters in the macro definition (excluding the ...). There shall exist a )
7266 preprocessing token that terminates the invocation.
7267 5 The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like
7268 macro that uses the ellipsis notation in the parameters.
7269 6 A parameter identifier in a function-like macro shall be uniquely declared within its
7272 7 The identifier immediately following the define is called the macro name. There is one
7273 name space for macro names. Any white-space characters preceding or following the
7274 replacement list of preprocessing tokens are not considered part of the replacement list
7278 for either form of macro.
7279 8 If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
7280 a preprocessing directive could begin, the identifier is not subject to macro replacement.
7281 9 A preprocessing directive of the form
7282 # define identifier replacement-list new-line
7283 defines an object-like macro that causes each subsequent instance of the macro name169)
7284 to be replaced by the replacement list of preprocessing tokens that constitute the
7285 remainder of the directive. The replacement list is then rescanned for more macro names
7287 10 A preprocessing directive of the form
7288 # define identifier lparen identifier-listopt ) replacement-list new-line
7289 # define identifier lparen ... ) replacement-list new-line
7290 # define identifier lparen identifier-list , ... ) replacement-list new-line
7291 defines a function-like macro with parameters, whose use is similar syntactically to a
7292 function call. The parameters are specified by the optional list of identifiers, whose scope
7293 extends from their declaration in the identifier list until the new-line character that
7294 terminates the #define preprocessing directive. Each subsequent instance of the
7295 function-like macro name followed by a ( as the next preprocessing token introduces the
7296 sequence of preprocessing tokens that is replaced by the replacement list in the definition
7297 (an invocation of the macro). The replaced sequence of preprocessing tokens is
7298 terminated by the matching ) preprocessing token, skipping intervening matched pairs of
7299 left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
7300 tokens making up an invocation of a function-like macro, new-line is considered a normal
7301 white-space character.
7302 11 The sequence of preprocessing tokens bounded by the outside-most matching parentheses
7303 forms the list of arguments for the function-like macro. The individual arguments within
7304 the list are separated by comma preprocessing tokens, but comma preprocessing tokens
7305 between matching inner parentheses do not separate arguments. If there are sequences of
7306 preprocessing tokens within the list of arguments that would otherwise act as
7307 preprocessing directives,170) the behavior is undefined.
7308 12 If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
7309 including any separating comma preprocessing tokens, are merged to form a single item:
7312 169) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
7313 not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
7314 are never scanned for macro names or parameters.
7315 170) Despite the name, a non-directive is a preprocessing directive.
7319 the variable arguments. The number of arguments so combined is such that, following
7320 merger, the number of arguments is one more than the number of parameters in the macro
7321 definition (excluding the ...).
7322 6.10.3.1 Argument substitution
7323 1 After the arguments for the invocation of a function-like macro have been identified,
7324 argument substitution takes place. A parameter in the replacement list, unless preceded
7325 by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
7326 replaced by the corresponding argument after all macros contained therein have been
7327 expanded. Before being substituted, each argument's preprocessing tokens are
7328 completely macro replaced as if they formed the rest of the preprocessing file; no other
7329 preprocessing tokens are available.
7330 2 An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it
7331 were a parameter, and the variable arguments shall form the preprocessing tokens used to
7333 6.10.3.2 The # operator
7335 1 Each # preprocessing token in the replacement list for a function-like macro shall be
7336 followed by a parameter as the next preprocessing token in the replacement list.
7338 2 If, in the replacement list, a parameter is immediately preceded by a # preprocessing
7339 token, both are replaced by a single character string literal preprocessing token that
7340 contains the spelling of the preprocessing token sequence for the corresponding
7341 argument. Each occurrence of white space between the argument's preprocessing tokens
7342 becomes a single space character in the character string literal. White space before the
7343 first preprocessing token and after the last preprocessing token composing the argument
7344 is deleted. Otherwise, the original spelling of each preprocessing token in the argument
7345 is retained in the character string literal, except for special handling for producing the
7346 spelling of string literals and character constants: a \ character is inserted before each "
7347 and \ character of a character constant or string literal (including the delimiting "
7348 characters), except that it is implementation-defined whether a \ character is inserted
7349 before the \ character beginning a universal character name. If the replacement that
7350 results is not a valid character string literal, the behavior is undefined. The character
7351 string literal corresponding to an empty argument is "". The order of evaluation of # and
7352 ## operators is unspecified.
7359 6.10.3.3 The ## operator
7361 1 A ## preprocessing token shall not occur at the beginning or at the end of a replacement
7362 list for either form of macro definition.
7364 2 If, in the replacement list of a function-like macro, a parameter is immediately preceded
7365 or followed by a ## preprocessing token, the parameter is replaced by the corresponding
7366 argument's preprocessing token sequence; however, if an argument consists of no
7367 preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
7369 3 For both object-like and function-like macro invocations, before the replacement list is
7370 reexamined for more macro names to replace, each instance of a ## preprocessing token
7371 in the replacement list (not from an argument) is deleted and the preceding preprocessing
7372 token is concatenated with the following preprocessing token. Placemarker
7373 preprocessing tokens are handled specially: concatenation of two placemarkers results in
7374 a single placemarker preprocessing token, and concatenation of a placemarker with a
7375 non-placemarker preprocessing token results in the non-placemarker preprocessing token.
7376 If the result is not a valid preprocessing token, the behavior is undefined. The resulting
7377 token is available for further macro replacement. The order of evaluation of ## operators
7379 4 EXAMPLE In the following fragment:
7380 #define hash_hash # ## #
7381 #define mkstr(a) # a
7382 #define in_between(a) mkstr(a)
7383 #define join(c, d) in_between(c hash_hash d)
7384 char p[] = join(x, y); // equivalent to
7385 // char p[] = "x ## y";
7386 The expansion produces, at various stages:
7388 in_between(x hash_hash y)
7392 In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
7393 this new token is not the ## operator.
7396 171) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
7397 exist only within translation phase 4.
7401 6.10.3.4 Rescanning and further replacement
7402 1 After all parameters in the replacement list have been substituted and # and ##
7403 processing has taken place, all placemarker preprocessing tokens are removed. The
7404 resulting preprocessing token sequence is then rescanned, along with all subsequent
7405 preprocessing tokens of the source file, for more macro names to replace.
7406 2 If the name of the macro being replaced is found during this scan of the replacement list
7407 (not including the rest of the source file's preprocessing tokens), it is not replaced.
7408 Furthermore, if any nested replacements encounter the name of the macro being replaced,
7409 it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
7410 available for further replacement even if they are later (re)examined in contexts in which
7411 that macro name preprocessing token would otherwise have been replaced.
7412 3 The resulting completely macro-replaced preprocessing token sequence is not processed
7413 as a preprocessing directive even if it resembles one, but all pragma unary operator
7414 expressions within it are then processed as specified in 6.10.9 below.
7415 6.10.3.5 Scope of macro definitions
7416 1 A macro definition lasts (independent of block structure) until a corresponding #undef
7417 directive is encountered or (if none is encountered) until the end of the preprocessing
7418 translation unit. Macro definitions have no significance after translation phase 4.
7419 2 A preprocessing directive of the form
7420 # undef identifier new-line
7421 causes the specified identifier no longer to be defined as a macro name. It is ignored if
7422 the specified identifier is not currently defined as a macro name.
7423 3 EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in
7427 4 EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
7428 It has the advantages of working for any compatible types of the arguments and of generating in-line code
7429 without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
7430 arguments a second time (including side effects) and generating more code than a function if invoked
7431 several times. It also cannot have its address taken, as it has none.
7432 #define max(a, b) ((a) > (b) ? (a) : (b))
7433 The parentheses ensure that the arguments and the resulting expression are bound properly.
7440 5 EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence
7442 #define f(a) f(x * (a))
7453 #define r(x,y) x ## y
7455 f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
7456 g(x+(3,4)-w) | h 5) & m
7458 p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
7459 char c[2][6] = { str(hello), str() };
7461 f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
7462 f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
7463 int i[] = { 1, 23, 4, 5, };
7464 char c[2][6] = { "hello", "" };
7466 6 EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the
7469 #define xstr(s) str(s)
7470 #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
7472 #define INCFILE(n) vers ## n
7473 #define glue(a, b) a ## b
7474 #define xglue(a, b) glue(a, b)
7475 #define HIGHLOW "hello"
7476 #define LOW LOW ", world"
7478 fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
7479 == 0) str(: @\n), s);
7480 #include xstr(INCFILE(2).h)
7490 printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
7492 "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
7494 #include "vers2.h" (after macro replacement, before file access)
7497 or, after concatenation of the character string literals,
7498 printf("x1= %d, x2= %s", x1, x2);
7500 "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
7502 #include "vers2.h" (after macro replacement, before file access)
7505 Space around the # and ## tokens in the macro definition is optional.
7507 7 EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence
7508 #define t(x,y,z) x ## y ## z
7509 int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
7510 t(10,,), t(,11,), t(,,12), t(,,) };
7512 int j[] = { 123, 45, 67, 89,
7515 8 EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid.
7516 #define OBJ_LIKE (1-1)
7517 #define OBJ_LIKE /* white space */ (1-1) /* other */
7518 #define FUNC_LIKE(a) ( a )
7519 #define FUNC_LIKE( a )( /* note the white space */ \
7520 a /* other stuff on this line
7522 But the following redefinitions are invalid:
7523 #define OBJ_LIKE (0) // different token sequence
7524 #define OBJ_LIKE (1 - 1) // different white space
7525 #define FUNC_LIKE(b) ( a ) // different parameter usage
7526 #define FUNC_LIKE(b) ( b ) // different parameter spelling
7528 9 EXAMPLE 7 Finally, to show the variable argument list macro facilities:
7529 #define debug(...) fprintf(stderr, __VA_ARGS__)
7530 #define showlist(...) puts(#__VA_ARGS__)
7531 #define report(test, ...) ((test)?puts(#test):\
7532 printf(__VA_ARGS__))
7534 debug("X = %d\n", x);
7535 showlist(The first, second, and third items.);
7536 report(x>y, "x is %d but y is %d", x, y);
7542 fprintf(stderr, "Flag" );
7543 fprintf(stderr, "X = %d\n", x );
7544 puts( "The first, second, and third items." );
7546 printf("x is %d but y is %d", x, y));
7550 1 The string literal of a #line directive, if present, shall be a character string literal.
7552 2 The line number of the current source line is one greater than the number of new-line
7553 characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
7554 file to the current token.
7555 3 A preprocessing directive of the form
7556 # line digit-sequence new-line
7557 causes the implementation to behave as if the following sequence of source lines begins
7558 with a source line that has a line number as specified by the digit sequence (interpreted as
7559 a decimal integer). The digit sequence shall not specify zero, nor a number greater than
7561 4 A preprocessing directive of the form
7562 # line digit-sequence "s-char-sequenceopt" new-line
7563 sets the presumed line number similarly and changes the presumed name of the source
7564 file to be the contents of the character string literal.
7565 5 A preprocessing directive of the form
7566 # line pp-tokens new-line
7567 (that does not match one of the two previous forms) is permitted. The preprocessing
7568 tokens after line on the directive are processed just as in normal text (each identifier
7569 currently defined as a macro name is replaced by its replacement list of preprocessing
7570 tokens). The directive resulting after all replacements shall match one of the two
7571 previous forms and is then processed as appropriate.
7578 6.10.5 Error directive
7580 1 A preprocessing directive of the form
7581 # error pp-tokensopt new-line
7582 causes the implementation to produce a diagnostic message that includes the specified
7583 sequence of preprocessing tokens.
7584 6.10.6 Pragma directive
7586 1 A preprocessing directive of the form
7587 # pragma pp-tokensopt new-line
7588 where the preprocessing token STDC does not immediately follow pragma in the
7589 directive (prior to any macro replacement)172) causes the implementation to behave in an
7590 implementation-defined manner. The behavior might cause translation to fail or cause the
7591 translator or the resulting program to behave in a non-conforming manner. Any such
7592 pragma that is not recognized by the implementation is ignored.
7593 2 If the preprocessing token STDC does immediately follow pragma in the directive (prior
7594 to any macro replacement), then no macro replacement is performed on the directive, and
7595 the directive shall have one of the following forms173) whose meanings are described
7597 #pragma STDC FP_CONTRACT on-off-switch
7598 #pragma STDC FENV_ACCESS on-off-switch
7599 #pragma STDC CX_LIMITED_RANGE on-off-switch
7600 on-off-switch: one of
7602 Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
7603 (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).
7608 172) An implementation is not required to perform macro replacement in pragmas, but it is permitted
7609 except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
7610 replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
7611 implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
7612 but is not required to.
7613 173) See ''future language directions'' (6.11.8).
7617 6.10.7 Null directive
7619 1 A preprocessing directive of the form
7622 6.10.8 Predefined macro names
7623 1 The values of the predefined macros listed in the following subclauses174) (except for
7624 __FILE__ and __LINE__) remain constant throughout the translation unit.
7625 2 None of these macro names, nor the identifier defined, shall be the subject of a
7626 #define or a #undef preprocessing directive. Any other predefined macro names
7627 shall begin with a leading underscore followed by an uppercase letter or a second
7629 3 The implementation shall not predefine the macro __cplusplus, nor shall it define it
7630 in any standard header.
7631 Forward references: standard headers (7.1.2).
7632 6.10.8.1 Mandatory macros
7633 1 The following macro names shall be defined by the implementation:
7634 __DATE__ The date of translation of the preprocessing translation unit: a character
7635 string literal of the form "Mmm dd yyyy", where the names of the
7636 months are the same as those generated by the asctime function, and the
7637 first character of dd is a space character if the value is less than 10. If the
7638 date of translation is not available, an implementation-defined valid date
7640 __FILE__ The presumed name of the current source file (a character string literal).175)
7641 __LINE__ The presumed line number (within the current source file) of the current
7642 source line (an integer constant).175)
7643 __STDC__ The integer constant 1, intended to indicate a conforming implementation.
7644 __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted
7645 implementation or the integer constant 0 if it is not.
7650 174) See ''future language directions'' (6.11.9).
7651 175) The presumed source file name and line number can be changed by the #line directive.
7655 __STDC_VERSION__ The integer constant 201ymmL.176)
7656 __TIME__ The time of translation of the preprocessing translation unit: a character
7657 string literal of the form "hh:mm:ss" as in the time generated by the
7658 asctime function. If the time of translation is not available, an
7659 implementation-defined valid time shall be supplied.
7660 Forward references: the asctime function (7.26.3.1).
7661 6.10.8.2 Environment macros
7662 1 The following macro names are conditionally defined by the implementation:
7663 __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example,
7664 199712L). If this symbol is defined, then every character in the Unicode
7665 required set, when stored in an object of type wchar_t, has the same
7666 value as the short identifier of that character. The Unicode required set
7667 consists of all the characters that are defined by ISO/IEC 10646, along with
7668 all amendments and technical corrigenda, as of the specified year and
7669 month. If some other encoding is used, the macro shall not be defined and
7670 the actual encoding used is implementation-defined.
7671 __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in
7672 the encoding for wchar_t, a member of the basic character set need not
7673 have a code value equal to its value when used as the lone character in an
7674 integer character constant.
7675 __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type
7676 char16_t are UTF-16 encoded. If some other encoding is used, the
7677 macro shall not be defined and the actual encoding used is implementation-
7679 __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type
7680 char32_t are UTF-32 encoded. If some other encoding is used, the
7681 macro shall not be defined and the actual encoding used is implementation-
7683 Forward references: common definitions (7.19), unicode utilities (7.27).
7688 176) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
7689 ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
7690 remain an integer constant of type long int that is increased with each revision of this International
7695 6.10.8.3 Conditional feature macros
7696 1 The following macro names are conditionally defined by the implementation:
7697 __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to
7698 the specifications in annex L (Analyzability).
7699 __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the
7700 specifications in annex F (IEC 60559 floating-point arithmetic).
7701 __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate
7702 adherence to the specifications in informative annex G (IEC 60559
7703 compatible complex arithmetic).
7704 __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support
7705 for the extensions defined in annex K (Bounds-checking interfaces).177)
7706 __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the
7707 implementation does not support complex types or the <complex.h>
7709 __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the
7710 implementation does not support atomic types (including the _Atomic
7711 type qualifier and the <stdatomic.h> header) or the <threads.h>
7713 __STDC_NO_VLA__ The integer constant 1, intended to indicate that the
7714 implementation does not support variable length arrays or variably
7716 6.10.9 Pragma operator
7718 1 A unary operator expression of the form:
7719 _Pragma ( string-literal )
7720 is processed as follows: The string literal is destringized by deleting the L prefix, if
7721 present, deleting the leading and trailing double-quotes, replacing each escape sequence
7722 \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The
7723 resulting sequence of characters is processed through translation phase 3 to produce
7724 preprocessing tokens that are executed as if they were the pp-tokens in a pragma
7725 directive. The original four preprocessing tokens in the unary operator expression are
7729 177) The intention is that this will remain an integer constant of type long int that is increased with
7730 each revision of this International Standard.
7734 2 EXAMPLE A directive of the form:
7735 #pragma listing on "..\listing.dir"
7736 can also be expressed as:
7737 _Pragma ( "listing on \"..\\listing.dir\"" )
7738 The latter form is processed in the same way whether it appears literally as shown, or results from macro
7740 #define LISTING(x) PRAGMA(listing on #x)
7741 #define PRAGMA(x) _Pragma(#x)
7742 LISTING ( ..\listing.dir )
7749 6.11 Future language directions
7750 6.11.1 Floating types
7751 1 Future standardization may include additional floating-point types, including those with
7752 greater range, precision, or both than long double.
7753 6.11.2 Linkages of identifiers
7754 1 Declaring an identifier with internal linkage at file scope without the static storage-
7755 class specifier is an obsolescent feature.
7756 6.11.3 External names
7757 1 Restriction of the significance of an external name to fewer than 255 characters
7758 (considering each universal character name or extended source character as a single
7759 character) is an obsolescent feature that is a concession to existing implementations.
7760 6.11.4 Character escape sequences
7761 1 Lowercase letters as escape sequences are reserved for future standardization. Other
7762 characters may be used in extensions.
7763 6.11.5 Storage-class specifiers
7764 1 The placement of a storage-class specifier other than at the beginning of the declaration
7765 specifiers in a declaration is an obsolescent feature.
7766 6.11.6 Function declarators
7767 1 The use of function declarators with empty parentheses (not prototype-format parameter
7768 type declarators) is an obsolescent feature.
7769 6.11.7 Function definitions
7770 1 The use of function definitions with separate parameter identifier and declaration lists
7771 (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
7772 6.11.8 Pragma directives
7773 1 Pragmas whose first preprocessing token is STDC are reserved for future standardization.
7774 6.11.9 Predefined macro names
7775 1 Macro names beginning with __STDC_ are reserved for future standardization.
7785 7.1.1 Definitions of terms
7786 1 A string is a contiguous sequence of characters terminated by and including the first null
7787 character. The term multibyte string is sometimes used instead to emphasize special
7788 processing given to multibyte characters contained in the string or to avoid confusion
7789 with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
7790 character. The length of a string is the number of bytes preceding the null character and
7791 the value of a string is the sequence of the values of the contained characters, in order.
7792 2 The decimal-point character is the character used by functions that convert floating-point
7793 numbers to or from character sequences to denote the beginning of the fractional part of
7794 such character sequences.178) It is represented in the text and examples by a period, but
7795 may be changed by the setlocale function.
7796 3 A null wide character is a wide character with code value zero.
7797 4 A wide string is a contiguous sequence of wide characters terminated by and including
7798 the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
7799 addressed) wide character. The length of a wide string is the number of wide characters
7800 preceding the null wide character and the value of a wide string is the sequence of code
7801 values of the contained wide characters, in order.
7802 5 A shift sequence is a contiguous sequence of bytes within a multibyte string that
7803 (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
7804 corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
7806 Forward references: character handling (7.4), the setlocale function (7.11.1.1).
7811 178) The functions that make use of the decimal-point character are the numeric conversion functions
7812 (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2).
7813 179) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
7814 enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
7815 sequence of maximum length. Whether these counts provide for more than one shift sequence is the
7816 implementation's choice.
7820 7.1.2 Standard headers
7821 1 Each library function is declared, with a type that includes a prototype, in a header,180)
7822 whose contents are made available by the #include preprocessing directive. The
7823 header declares a set of related functions, plus any necessary types and additional macros
7824 needed to facilitate their use. Declarations of types described in this clause shall not
7825 include type qualifiers, unless explicitly stated otherwise.
7826 2 The standard headers are181)
7827 <assert.h> <iso646.h> <stdarg.h> <string.h>
7828 <complex.h> <limits.h> <stdatomic.h> <tgmath.h>
7829 <ctype.h> <locale.h> <stdbool.h> <threads.h>
7830 <errno.h> <math.h> <stddef.h> <time.h>
7831 <fenv.h> <setjmp.h> <stdint.h> <uchar.h>
7832 <float.h> <signal.h> <stdio.h> <wchar.h>
7833 <inttypes.h> <stdalign.h> <stdlib.h> <wctype.h>
7834 3 If a file with the same name as one of the above < and > delimited sequences, not
7835 provided as part of the implementation, is placed in any of the standard places that are
7836 searched for included source files, the behavior is undefined.
7837 4 Standard headers may be included in any order; each may be included more than once in
7838 a given scope, with no effect different from being included only once, except that the
7839 effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
7840 used, a header shall be included outside of any external declaration or definition, and it
7841 shall first be included before the first reference to any of the functions or objects it
7842 declares, or to any of the types or macros it defines. However, if an identifier is declared
7843 or defined in more than one header, the second and subsequent associated headers may be
7844 included after the initial reference to the identifier. The program shall not have any
7845 macros with names lexically identical to keywords currently defined prior to the
7847 5 Any definition of an object-like macro described in this clause shall expand to code that is
7848 fully protected by parentheses where necessary, so that it groups in an arbitrary
7849 expression as if it were a single identifier.
7850 6 Any declaration of a library function shall have external linkage.
7855 180) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
7856 necessarily valid source file names.
7857 181) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
7858 implementations need not support; see 6.10.8.3.
7862 7 A summary of the contents of the standard headers is given in annex B.
7863 Forward references: diagnostics (7.2).
7864 7.1.3 Reserved identifiers
7865 1 Each header declares or defines all identifiers listed in its associated subclause, and
7866 optionally declares or defines identifiers listed in its associated future library directions
7867 subclause and identifiers which are always reserved either for any use or for use as file
7869 -- All identifiers that begin with an underscore and either an uppercase letter or another
7870 underscore are always reserved for any use.
7871 -- All identifiers that begin with an underscore are always reserved for use as identifiers
7872 with file scope in both the ordinary and tag name spaces.
7873 -- Each macro name in any of the following subclauses (including the future library
7874 directions) is reserved for use as specified if any of its associated headers is included;
7875 unless explicitly stated otherwise (see 7.1.4).
7876 -- All identifiers with external linkage in any of the following subclauses (including the
7877 future library directions) and errno are always reserved for use as identifiers with
7878 external linkage.182)
7879 -- Each identifier with file scope listed in any of the following subclauses (including the
7880 future library directions) is reserved for use as a macro name and as an identifier with
7881 file scope in the same name space if any of its associated headers is included.
7882 2 No other identifiers are reserved. If the program declares or defines an identifier in a
7883 context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
7884 identifier as a macro name, the behavior is undefined.
7885 3 If the program removes (with #undef) any macro definition of an identifier in the first
7886 group listed above, the behavior is undefined.
7891 182) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
7892 va_copy, and va_end.
7896 7.1.4 Use of library functions
7897 1 Each of the following statements applies unless explicitly stated otherwise in the detailed
7898 descriptions that follow: If an argument to a function has an invalid value (such as a value
7899 outside the domain of the function, or a pointer outside the address space of the program,
7900 or a null pointer, or a pointer to non-modifiable storage when the corresponding
7901 parameter is not const-qualified) or a type (after promotion) not expected by a function
7902 with variable number of arguments, the behavior is undefined. If a function argument is
7903 described as being an array, the pointer actually passed to the function shall have a value
7904 such that all address computations and accesses to objects (that would be valid if the
7905 pointer did point to the first element of such an array) are in fact valid. Any function
7906 declared in a header may be additionally implemented as a function-like macro defined in
7907 the header, so if a library function is declared explicitly when its header is included, one
7908 of the techniques shown below can be used to ensure the declaration is not affected by
7909 such a macro. Any macro definition of a function can be suppressed locally by enclosing
7910 the name of the function in parentheses, because the name is then not followed by the left
7911 parenthesis that indicates expansion of a macro function name. For the same syntactic
7912 reason, it is permitted to take the address of a library function even if it is also defined as
7913 a macro.183) The use of #undef to remove any macro definition will also ensure that an
7914 actual function is referred to. Any invocation of a library function that is implemented as
7915 a macro shall expand to code that evaluates each of its arguments exactly once, fully
7916 protected by parentheses where necessary, so it is generally safe to use arbitrary
7917 expressions as arguments.184) Likewise, those function-like macros described in the
7918 following subclauses may be invoked in an expression anywhere a function with a
7919 compatible return type could be called.185) All object-like macros listed as expanding to
7922 183) This means that an implementation shall provide an actual function for each library function, even if it
7923 also provides a macro for that function.
7924 184) Such macros might not contain the sequence points that the corresponding function calls do.
7925 185) Because external identifiers and some macro names beginning with an underscore are reserved,
7926 implementations may provide special semantics for such names. For example, the identifier
7927 _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
7928 appropriate header could specify
7929 #define abs(x) _BUILTIN_abs(x)
7930 for a compiler whose code generator will accept it.
7931 In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
7934 whether the implementation's header provides a macro implementation of abs or a built-in
7935 implementation. The prototype for the function, which precedes and is hidden by any macro
7936 definition, is thereby revealed also.
7940 integer constant expressions shall additionally be suitable for use in #if preprocessing
7942 2 Provided that a library function can be declared without reference to any type defined in a
7943 header, it is also permissible to declare the function and use it without including its
7945 3 There is a sequence point immediately before a library function returns.
7946 4 The functions in the standard library are not guaranteed to be reentrant and may modify
7947 objects with static or thread storage duration.186)
7948 5 Unless explicitly stated otherwise in the detailed descriptions that follow, library
7949 functions shall prevent data races as follows: A library function shall not directly or
7950 indirectly access objects accessible by threads other than the current thread unless the
7951 objects are accessed directly or indirectly via the function's arguments. A library
7952 function shall not directly or indirectly modify objects accessible by threads other than
7953 the current thread unless the objects are accessed directly or indirectly via the function's
7954 non-const arguments.187) Implementations may share their own internal objects between
7955 threads if the objects are not visible to users and are protected against data races.
7956 6 Unless otherwise specified, library functions shall perform all operations solely within the
7957 current thread if those operations have effects that are visible to users.188)
7958 7 EXAMPLE The function atoi may be used in any of several ways:
7959 -- by use of its associated header (possibly generating a macro expansion)
7964 -- by use of its associated header (assuredly generating a true function reference)
7969 186) Thus, a signal handler cannot, in general, call standard library functions.
7970 187) This means, for example, that an implementation is not permitted to use a static object for internal
7971 purposes without synchronization because it could cause a data race even in programs that do not
7972 explicitly share objects between threads.
7973 188) This allows implementations to parallelize operations if there are no visible side effects.
7987 -- by explicit declaration
7988 extern int atoi(const char *);
7998 7.2 Diagnostics <assert.h>
7999 1 The header <assert.h> defines the assert and static_assert macros and
8000 refers to another macro,
8002 which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
8003 point in the source file where <assert.h> is included, the assert macro is defined
8005 #define assert(ignore) ((void)0)
8006 The assert macro is redefined according to the current state of NDEBUG each time that
8007 <assert.h> is included.
8008 2 The assert macro shall be implemented as a macro, not as an actual function. If the
8009 macro definition is suppressed in order to access an actual function, the behavior is
8013 expands to _Static_assert.
8014 7.2.1 Program diagnostics
8015 7.2.1.1 The assert macro
8017 1 #include <assert.h>
8018 void assert(scalar expression);
8020 2 The assert macro puts diagnostic tests into programs; it expands to a void expression.
8021 When it is executed, if expression (which shall have a scalar type) is false (that is,
8022 compares equal to 0), the assert macro writes information about the particular call that
8023 failed (including the text of the argument, the name of the source file, the source line
8024 number, and the name of the enclosing function -- the latter are respectively the values of
8025 the preprocessing macros __FILE__ and __LINE__ and of the identifier
8026 __func__) on the standard error stream in an implementation-defined format.189) It
8027 then calls the abort function.
8031 189) The message written might be of the form:
8032 Assertion failed: expression, function abc, file xyz, line nnn.
8038 3 The assert macro returns no value.
8039 Forward references: the abort function (7.22.4.1).
8046 7.3 Complex arithmetic <complex.h>
8048 1 The header <complex.h> defines macros and declares functions that support complex
8050 2 Implementations that define the macro __STDC_NO_COMPLEX__ need not provide
8051 this header nor support any of its facilities.
8052 3 Each synopsis specifies a family of functions consisting of a principal function with one
8053 or more double complex parameters and a double complex or double return
8054 value; and other functions with the same name but with f and l suffixes which are
8055 corresponding functions with float and long double parameters and return values.
8058 expands to _Complex; the macro
8060 expands to a constant expression of type const float _Complex, with the value of
8061 the imaginary unit.191)
8066 are defined if and only if the implementation supports imaginary types;192) if defined,
8067 they expand to _Imaginary and a constant expression of type const float
8068 _Imaginary with the value of the imaginary unit.
8071 expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
8072 defined, I shall expand to _Complex_I.
8073 7 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
8074 redefine the macros complex, imaginary, and I.
8076 190) See ''future library directions'' (7.30.1).
8077 191) The imaginary unit is a number i such that i 2 = -1.
8078 192) A specification for imaginary types is in informative annex G.
8082 Forward references: IEC 60559-compatible complex arithmetic (annex G).
8084 1 Values are interpreted as radians, not degrees. An implementation may set errno but is
8087 1 Some of the functions below have branch cuts, across which the function is
8088 discontinuous. For implementations with a signed zero (including all IEC 60559
8089 implementations) that follow the specifications of annex G, the sign of zero distinguishes
8090 one side of a cut from another so the function is continuous (except for format
8091 limitations) as the cut is approached from either side. For example, for the square root
8092 function, which has a branch cut along the negative real axis, the top of the cut, with
8093 imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
8094 imaginary part -0, maps to the negative imaginary axis.
8095 2 Implementations that do not support a signed zero (see annex F) cannot distinguish the
8096 sides of branch cuts. These implementations shall map a cut so the function is continuous
8097 as the cut is approached coming around the finite endpoint of the cut in a counter
8098 clockwise direction. (Branch cuts for the functions specified here have just one finite
8099 endpoint.) For example, for the square root function, coming counter clockwise around
8100 the finite endpoint of the cut along the negative real axis approaches the cut from above,
8101 so the cut maps to the positive imaginary axis.
8102 7.3.4 The CX_LIMITED_RANGE pragma
8104 1 #include <complex.h>
8105 #pragma STDC CX_LIMITED_RANGE on-off-switch
8107 2 The usual mathematical formulas for complex multiply, divide, and absolute value are
8108 problematic because of their treatment of infinities and because of undue overflow and
8109 underflow. The CX_LIMITED_RANGE pragma can be used to inform the
8110 implementation that (where the state is ''on'') the usual mathematical formulas are
8111 acceptable.193) The pragma can occur either outside external declarations or preceding all
8112 explicit declarations and statements inside a compound statement. When outside external
8113 declarations, the pragma takes effect from its occurrence until another
8114 CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
8115 When inside a compound statement, the pragma takes effect from its occurrence until
8116 another CX_LIMITED_RANGE pragma is encountered (including within a nested
8117 compound statement), or until the end of the compound statement; at the end of a
8118 compound statement the state for the pragma is restored to its condition just before the
8122 compound statement. If this pragma is used in any other context, the behavior is
8123 undefined. The default state for the pragma is ''off''.
8124 7.3.5 Trigonometric functions
8125 7.3.5.1 The cacos functions
8127 1 #include <complex.h>
8128 double complex cacos(double complex z);
8129 float complex cacosf(float complex z);
8130 long double complex cacosl(long double complex z);
8132 2 The cacos functions compute the complex arc cosine of z, with branch cuts outside the
8133 interval [-1, +1] along the real axis.
8135 3 The cacos functions return the complex arc cosine value, in the range of a strip
8136 mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the
8138 7.3.5.2 The casin functions
8140 1 #include <complex.h>
8141 double complex casin(double complex z);
8142 float complex casinf(float complex z);
8143 long double complex casinl(long double complex z);
8145 2 The casin functions compute the complex arc sine of z, with branch cuts outside the
8146 interval [-1, +1] along the real axis.
8148 3 The casin functions return the complex arc sine value, in the range of a strip
8149 mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
8151 193) The purpose of the pragma is to allow the implementation to use the formulas:
8152 (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
8153 (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
8154 | x + iy | = sqrt: x 2 + y 2
8156 where the programmer can determine they are safe.
8160 along the real axis.
8161 7.3.5.3 The catan functions
8163 1 #include <complex.h>
8164 double complex catan(double complex z);
8165 float complex catanf(float complex z);
8166 long double complex catanl(long double complex z);
8168 2 The catan functions compute the complex arc tangent of z, with branch cuts outside the
8169 interval [-i, +i] along the imaginary axis.
8171 3 The catan functions return the complex arc tangent value, in the range of a strip
8172 mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
8173 along the real axis.
8174 7.3.5.4 The ccos functions
8176 1 #include <complex.h>
8177 double complex ccos(double complex z);
8178 float complex ccosf(float complex z);
8179 long double complex ccosl(long double complex z);
8181 2 The ccos functions compute the complex cosine of z.
8183 3 The ccos functions return the complex cosine value.
8184 7.3.5.5 The csin functions
8186 1 #include <complex.h>
8187 double complex csin(double complex z);
8188 float complex csinf(float complex z);
8189 long double complex csinl(long double complex z);
8191 2 The csin functions compute the complex sine of z.
8198 3 The csin functions return the complex sine value.
8199 7.3.5.6 The ctan functions
8201 1 #include <complex.h>
8202 double complex ctan(double complex z);
8203 float complex ctanf(float complex z);
8204 long double complex ctanl(long double complex z);
8206 2 The ctan functions compute the complex tangent of z.
8208 3 The ctan functions return the complex tangent value.
8209 7.3.6 Hyperbolic functions
8210 7.3.6.1 The cacosh functions
8212 1 #include <complex.h>
8213 double complex cacosh(double complex z);
8214 float complex cacoshf(float complex z);
8215 long double complex cacoshl(long double complex z);
8217 2 The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
8218 cut at values less than 1 along the real axis.
8220 3 The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
8221 half-strip of non-negative values along the real axis and in the interval [-ipi , +ipi ] along
8223 7.3.6.2 The casinh functions
8225 1 #include <complex.h>
8226 double complex casinh(double complex z);
8227 float complex casinhf(float complex z);
8228 long double complex casinhl(long double complex z);
8235 2 The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
8236 outside the interval [-i, +i] along the imaginary axis.
8238 3 The casinh functions return the complex arc hyperbolic sine value, in the range of a
8239 strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
8240 along the imaginary axis.
8241 7.3.6.3 The catanh functions
8243 1 #include <complex.h>
8244 double complex catanh(double complex z);
8245 float complex catanhf(float complex z);
8246 long double complex catanhl(long double complex z);
8248 2 The catanh functions compute the complex arc hyperbolic tangent of z, with branch
8249 cuts outside the interval [-1, +1] along the real axis.
8251 3 The catanh functions return the complex arc hyperbolic tangent value, in the range of a
8252 strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
8253 along the imaginary axis.
8254 7.3.6.4 The ccosh functions
8256 1 #include <complex.h>
8257 double complex ccosh(double complex z);
8258 float complex ccoshf(float complex z);
8259 long double complex ccoshl(long double complex z);
8261 2 The ccosh functions compute the complex hyperbolic cosine of z.
8263 3 The ccosh functions return the complex hyperbolic cosine value.
8270 7.3.6.5 The csinh functions
8272 1 #include <complex.h>
8273 double complex csinh(double complex z);
8274 float complex csinhf(float complex z);
8275 long double complex csinhl(long double complex z);
8277 2 The csinh functions compute the complex hyperbolic sine of z.
8279 3 The csinh functions return the complex hyperbolic sine value.
8280 7.3.6.6 The ctanh functions
8282 1 #include <complex.h>
8283 double complex ctanh(double complex z);
8284 float complex ctanhf(float complex z);
8285 long double complex ctanhl(long double complex z);
8287 2 The ctanh functions compute the complex hyperbolic tangent of z.
8289 3 The ctanh functions return the complex hyperbolic tangent value.
8290 7.3.7 Exponential and logarithmic functions
8291 7.3.7.1 The cexp functions
8293 1 #include <complex.h>
8294 double complex cexp(double complex z);
8295 float complex cexpf(float complex z);
8296 long double complex cexpl(long double complex z);
8298 2 The cexp functions compute the complex base-e exponential of z.
8300 3 The cexp functions return the complex base-e exponential value.
8306 7.3.7.2 The clog functions
8308 1 #include <complex.h>
8309 double complex clog(double complex z);
8310 float complex clogf(float complex z);
8311 long double complex clogl(long double complex z);
8313 2 The clog functions compute the complex natural (base-e) logarithm of z, with a branch
8314 cut along the negative real axis.
8316 3 The clog functions return the complex natural logarithm value, in the range of a strip
8317 mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the
8319 7.3.8 Power and absolute-value functions
8320 7.3.8.1 The cabs functions
8322 1 #include <complex.h>
8323 double cabs(double complex z);
8324 float cabsf(float complex z);
8325 long double cabsl(long double complex z);
8327 2 The cabs functions compute the complex absolute value (also called norm, modulus, or
8330 3 The cabs functions return the complex absolute value.
8331 7.3.8.2 The cpow functions
8333 1 #include <complex.h>
8334 double complex cpow(double complex x, double complex y);
8335 float complex cpowf(float complex x, float complex y);
8336 long double complex cpowl(long double complex x,
8337 long double complex y);
8345 2 The cpow functions compute the complex power function xy , with a branch cut for the
8346 first parameter along the negative real axis.
8348 3 The cpow functions return the complex power function value.
8349 7.3.8.3 The csqrt functions
8351 1 #include <complex.h>
8352 double complex csqrt(double complex z);
8353 float complex csqrtf(float complex z);
8354 long double complex csqrtl(long double complex z);
8356 2 The csqrt functions compute the complex square root of z, with a branch cut along the
8359 3 The csqrt functions return the complex square root value, in the range of the right half-
8360 plane (including the imaginary axis).
8361 7.3.9 Manipulation functions
8362 7.3.9.1 The carg functions
8364 1 #include <complex.h>
8365 double carg(double complex z);
8366 float cargf(float complex z);
8367 long double cargl(long double complex z);
8369 2 The carg functions compute the argument (also called phase angle) of z, with a branch
8370 cut along the negative real axis.
8372 3 The carg functions return the value of the argument in the interval [-pi , +pi ].
8379 7.3.9.2 The cimag functions
8381 1 #include <complex.h>
8382 double cimag(double complex z);
8383 float cimagf(float complex z);
8384 long double cimagl(long double complex z);
8386 2 The cimag functions compute the imaginary part of z.194)
8388 3 The cimag functions return the imaginary part value (as a real).
8389 7.3.9.3 The CMPLX macros
8391 1 #include <complex.h>
8392 double complex CMPLX(double x, double y);
8393 float complex CMPLXF(float x, float y);
8394 long double complex CMPLXL(long double x, long double y);
8396 2 The CMPLX macros expand to an expression of the specified complex type, with the real
8397 part having the (converted) value of x and the imaginary part having the (converted)
8399 Recommended practice
8400 3 The resulting expression should be suitable for use as an initializer for an object with
8401 static or thread storage duration, provided both arguments are likewise suitable.
8403 4 The CMPLX macros return the complex value x + i y.
8404 5 NOTE These macros act as if the implementation supported imaginary types and the definitions were:
8405 #define CMPLX(x, y) ((double complex)((double)(x) + \
8406 _Imaginary_I * (double)(y)))
8407 #define CMPLXF(x, y) ((float complex)((float)(x) + \
8408 _Imaginary_I * (float)(y)))
8409 #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
8410 _Imaginary_I * (long double)(y)))
8415 194) For a variable z of complex type, z == creal(z) + cimag(z)*I.
8419 7.3.9.4 The conj functions
8421 1 #include <complex.h>
8422 double complex conj(double complex z);
8423 float complex conjf(float complex z);
8424 long double complex conjl(long double complex z);
8426 2 The conj functions compute the complex conjugate of z, by reversing the sign of its
8429 3 The conj functions return the complex conjugate value.
8430 7.3.9.5 The cproj functions
8432 1 #include <complex.h>
8433 double complex cproj(double complex z);
8434 float complex cprojf(float complex z);
8435 long double complex cprojl(long double complex z);
8437 2 The cproj functions compute a projection of z onto the Riemann sphere: z projects to
8438 z except that all complex infinities (even those with one infinite part and one NaN part)
8439 project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
8441 INFINITY + I * copysign(0.0, cimag(z))
8443 3 The cproj functions return the value of the projection onto the Riemann sphere.
8444 7.3.9.6 The creal functions
8446 1 #include <complex.h>
8447 double creal(double complex z);
8448 float crealf(float complex z);
8449 long double creall(long double complex z);
8451 2 The creal functions compute the real part of z.195)
8457 3 The creal functions return the real part value.
8462 195) For a variable z of complex type, z == creal(z) + cimag(z)*I.
8466 7.4 Character handling <ctype.h>
8467 1 The header <ctype.h> declares several functions useful for classifying and mapping
8468 characters.196) In all cases the argument is an int, the value of which shall be
8469 representable as an unsigned char or shall equal the value of the macro EOF. If the
8470 argument has any other value, the behavior is undefined.
8471 2 The behavior of these functions is affected by the current locale. Those functions that
8472 have locale-specific aspects only when not in the "C" locale are noted below.
8473 3 The term printing character refers to a member of a locale-specific set of characters, each
8474 of which occupies one printing position on a display device; the term control character
8475 refers to a member of a locale-specific set of characters that are not printing
8476 characters.197) All letters and digits are printing characters.
8477 Forward references: EOF (7.21.1), localization (7.11).
8478 7.4.1 Character classification functions
8479 1 The functions in this subclause return nonzero (true) if and only if the value of the
8480 argument c conforms to that in the description of the function.
8481 7.4.1.1 The isalnum function
8483 1 #include <ctype.h>
8486 2 The isalnum function tests for any character for which isalpha or isdigit is true.
8487 7.4.1.2 The isalpha function
8489 1 #include <ctype.h>
8492 2 The isalpha function tests for any character for which isupper or islower is true,
8493 or any character that is one of a locale-specific set of alphabetic characters for which
8497 196) See ''future library directions'' (7.30.2).
8498 197) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
8499 whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
8500 values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
8504 none of iscntrl, isdigit, ispunct, or isspace is true.198) In the "C" locale,
8505 isalpha returns true only for the characters for which isupper or islower is true.
8506 7.4.1.3 The isblank function
8508 1 #include <ctype.h>
8511 2 The isblank function tests for any character that is a standard blank character or is one
8512 of a locale-specific set of characters for which isspace is true and that is used to
8513 separate words within a line of text. The standard blank characters are the following:
8514 space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
8515 for the standard blank characters.
8516 7.4.1.4 The iscntrl function
8518 1 #include <ctype.h>
8521 2 The iscntrl function tests for any control character.
8522 7.4.1.5 The isdigit function
8524 1 #include <ctype.h>
8527 2 The isdigit function tests for any decimal-digit character (as defined in 5.2.1).
8528 7.4.1.6 The isgraph function
8530 1 #include <ctype.h>
8536 198) The functions islower and isupper test true or false separately for each of these additional
8537 characters; all four combinations are possible.
8542 2 The isgraph function tests for any printing character except space (' ').
8543 7.4.1.7 The islower function
8545 1 #include <ctype.h>
8548 2 The islower function tests for any character that is a lowercase letter or is one of a
8549 locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
8550 isspace is true. In the "C" locale, islower returns true only for the lowercase
8551 letters (as defined in 5.2.1).
8552 7.4.1.8 The isprint function
8554 1 #include <ctype.h>
8557 2 The isprint function tests for any printing character including space (' ').
8558 7.4.1.9 The ispunct function
8560 1 #include <ctype.h>
8563 2 The ispunct function tests for any printing character that is one of a locale-specific set
8564 of punctuation characters for which neither isspace nor isalnum is true. In the "C"
8565 locale, ispunct returns true for every printing character for which neither isspace
8566 nor isalnum is true.
8567 7.4.1.10 The isspace function
8569 1 #include <ctype.h>
8572 2 The isspace function tests for any character that is a standard white-space character or
8573 is one of a locale-specific set of characters for which isalnum is false. The standard
8577 white-space characters are the following: space (' '), form feed ('\f'), new-line
8578 ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
8579 "C" locale, isspace returns true only for the standard white-space characters.
8580 7.4.1.11 The isupper function
8582 1 #include <ctype.h>
8585 2 The isupper function tests for any character that is an uppercase letter or is one of a
8586 locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
8587 isspace is true. In the "C" locale, isupper returns true only for the uppercase
8588 letters (as defined in 5.2.1).
8589 7.4.1.12 The isxdigit function
8591 1 #include <ctype.h>
8592 int isxdigit(int c);
8594 2 The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
8595 7.4.2 Character case mapping functions
8596 7.4.2.1 The tolower function
8598 1 #include <ctype.h>
8601 2 The tolower function converts an uppercase letter to a corresponding lowercase letter.
8603 3 If the argument is a character for which isupper is true and there are one or more
8604 corresponding characters, as specified by the current locale, for which islower is true,
8605 the tolower function returns one of the corresponding characters (always the same one
8606 for any given locale); otherwise, the argument is returned unchanged.
8613 7.4.2.2 The toupper function
8615 1 #include <ctype.h>
8618 2 The toupper function converts a lowercase letter to a corresponding uppercase letter.
8620 3 If the argument is a character for which islower is true and there are one or more
8621 corresponding characters, as specified by the current locale, for which isupper is true,
8622 the toupper function returns one of the corresponding characters (always the same one
8623 for any given locale); otherwise, the argument is returned unchanged.
8630 7.5 Errors <errno.h>
8631 1 The header <errno.h> defines several macros, all relating to the reporting of error
8637 which expand to integer constant expressions with type int, distinct positive values, and
8638 which are suitable for use in #if preprocessing directives; and
8640 which expands to a modifiable lvalue199) that has type int and thread local storage
8641 duration, the value of which is set to a positive error number by several library functions.
8642 If a macro definition is suppressed in order to access an actual object, or a program
8643 defines an identifier with the name errno, the behavior is undefined.
8644 3 The value of errno in the initial thread is zero at program startup (the initial value of
8645 errno in other threads is an indeterminate value), but is never set to zero by any library
8646 function.200) The value of errno may be set to nonzero by a library function call
8647 whether or not there is an error, provided the use of errno is not documented in the
8648 description of the function in this International Standard.
8649 4 Additional macro definitions, beginning with E and a digit or E and an uppercase
8650 letter,201) may also be specified by the implementation.
8655 199) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
8656 resulting from a function call (for example, *errno()).
8657 200) Thus, a program that uses errno for error checking should set it to zero before a library function call,
8658 then inspect it before a subsequent library function call. Of course, a library function can save the
8659 value of errno on entry and then set it to zero, as long as the original value is restored if errno's
8660 value is still zero just before the return.
8661 201) See ''future library directions'' (7.30.3).
8665 7.6 Floating-point environment <fenv.h>
8666 1 The header <fenv.h> defines several macros, and declares types and functions that
8667 provide access to the floating-point environment. The floating-point environment refers
8668 collectively to any floating-point status flags and control modes supported by the
8669 implementation.202) A floating-point status flag is a system variable whose value is set
8670 (but never cleared) when a floating-point exception is raised, which occurs as a side effect
8671 of exceptional floating-point arithmetic to provide auxiliary information.203) A floating-
8672 point control mode is a system variable whose value may be set by the user to affect the
8673 subsequent behavior of floating-point arithmetic.
8674 2 The floating-point environment has thread storage duration. The initial state for a
8675 thread's floating-point environment is the current state of the floating-point environment
8676 of the thread that creates it at the time of creation.
8677 3 Certain programming conventions support the intended model of use for the floating-
8678 point environment:204)
8679 -- a function call does not alter its caller's floating-point control modes, clear its caller's
8680 floating-point status flags, nor depend on the state of its caller's floating-point status
8681 flags unless the function is so documented;
8682 -- a function call is assumed to require default floating-point control modes, unless its
8683 documentation promises otherwise;
8684 -- a function call is assumed to have the potential for raising floating-point exceptions,
8685 unless its documentation promises otherwise.
8688 represents the entire floating-point environment.
8691 represents the floating-point status flags collectively, including any status the
8692 implementation associates with the flags.
8695 202) This header is designed to support the floating-point exception status flags and directed-rounding
8696 control modes required by IEC 60559, and other similar floating-point state information. Also it is
8697 designed to facilitate code portability among all systems.
8698 203) A floating-point status flag is not an object and can be set more than once within an expression.
8699 204) With these conventions, a programmer can safely assume default floating-point control modes (or be
8700 unaware of them). The responsibilities associated with accessing the floating-point environment fall
8701 on the programmer or program that does so explicitly.
8705 6 Each of the macros
8711 is defined if and only if the implementation supports the floating-point exception by
8712 means of the functions in 7.6.2.205) Additional implementation-defined floating-point
8713 exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also
8714 be specified by the implementation. The defined macros expand to integer constant
8715 expressions with values such that bitwise ORs of all combinations of the macros result in
8716 distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
8720 is simply the bitwise OR of all floating-point exception macros defined by the
8721 implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
8722 8 Each of the macros
8727 is defined if and only if the implementation supports getting and setting the represented
8728 rounding direction by means of the fegetround and fesetround functions.
8729 Additional implementation-defined rounding directions, with macro definitions beginning
8730 with FE_ and an uppercase letter, may also be specified by the implementation. The
8731 defined macros expand to integer constant expressions whose values are distinct
8732 nonnegative values.207)
8737 205) The implementation supports an exception if there are circumstances where a call to at least one of the
8738 functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not necessary for
8739 all the functions to succeed all the time.
8740 206) The macros should be distinct powers of two.
8741 207) Even though the rounding direction macros may expand to constants corresponding to the values of
8742 FLT_ROUNDS, they are not required to do so.
8747 represents the default floating-point environment -- the one installed at program startup
8748 -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to
8749 <fenv.h> functions that manage the floating-point environment.
8750 10 Additional implementation-defined environments, with macro definitions beginning with
8751 FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may
8752 also be specified by the implementation.
8753 7.6.1 The FENV_ACCESS pragma
8756 #pragma STDC FENV_ACCESS on-off-switch
8758 2 The FENV_ACCESS pragma provides a means to inform the implementation when a
8759 program might access the floating-point environment to test floating-point status flags or
8760 run under non-default floating-point control modes.208) The pragma shall occur either
8761 outside external declarations or preceding all explicit declarations and statements inside a
8762 compound statement. When outside external declarations, the pragma takes effect from
8763 its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
8764 the translation unit. When inside a compound statement, the pragma takes effect from its
8765 occurrence until another FENV_ACCESS pragma is encountered (including within a
8766 nested compound statement), or until the end of the compound statement; at the end of a
8767 compound statement the state for the pragma is restored to its condition just before the
8768 compound statement. If this pragma is used in any other context, the behavior is
8769 undefined. If part of a program tests floating-point status flags, sets floating-point control
8770 modes, or runs under non-default mode settings, but was translated with the state for the
8771 FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or
8772 ''off'') for the pragma is implementation-defined. (When execution passes from a part of
8773 the program translated with FENV_ACCESS ''off'' to a part translated with
8774 FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the
8775 floating-point control modes have their default settings.)
8780 208) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
8781 tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
8782 folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default
8783 modes are in effect and the flags are not tested.
8791 #pragma STDC FENV_ACCESS ON
8799 4 If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
8800 x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
8801 contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.209)
8803 7.6.2 Floating-point exceptions
8804 1 The following functions provide access to the floating-point status flags.210) The int
8805 input argument for the functions represents a subset of floating-point exceptions, and can
8806 be zero or the bitwise OR of one or more floating-point exception macros, for example
8807 FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
8808 functions is undefined.
8809 7.6.2.1 The feclearexcept function
8812 int feclearexcept(int excepts);
8814 2 The feclearexcept function attempts to clear the supported floating-point exceptions
8815 represented by its argument.
8817 3 The feclearexcept function returns zero if the excepts argument is zero or if all
8818 the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.
8821 209) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
8822 hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
8823 ''off'', just one evaluation of x + 1 would suffice.
8824 210) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
8825 abstraction of flags that are either set or clear. An implementation may endow floating-point status
8826 flags with more information -- for example, the address of the code which first raised the floating-
8827 point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
8832 7.6.2.2 The fegetexceptflag function
8835 int fegetexceptflag(fexcept_t *flagp,
8838 2 The fegetexceptflag function attempts to store an implementation-defined
8839 representation of the states of the floating-point status flags indicated by the argument
8840 excepts in the object pointed to by the argument flagp.
8842 3 The fegetexceptflag function returns zero if the representation was successfully
8843 stored. Otherwise, it returns a nonzero value.
8844 7.6.2.3 The feraiseexcept function
8847 int feraiseexcept(int excepts);
8849 2 The feraiseexcept function attempts to raise the supported floating-point exceptions
8850 represented by its argument.211) The order in which these floating-point exceptions are
8851 raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
8852 additionally raises the ''inexact'' floating-point exception whenever it raises the
8853 ''overflow'' or ''underflow'' floating-point exception is implementation-defined.
8855 3 The feraiseexcept function returns zero if the excepts argument is zero or if all
8856 the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.
8861 211) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
8862 Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
8863 in F.8.6 is in the same spirit.
8867 7.6.2.4 The fesetexceptflag function
8870 int fesetexceptflag(const fexcept_t *flagp,
8873 2 The fesetexceptflag function attempts to set the floating-point status flags
8874 indicated by the argument excepts to the states stored in the object pointed to by
8875 flagp. The value of *flagp shall have been set by a previous call to
8876 fegetexceptflag whose second argument represented at least those floating-point
8877 exceptions represented by the argument excepts. This function does not raise floating-
8878 point exceptions, but only sets the state of the flags.
8880 3 The fesetexceptflag function returns zero if the excepts argument is zero or if
8881 all the specified flags were successfully set to the appropriate state. Otherwise, it returns
8883 7.6.2.5 The fetestexcept function
8886 int fetestexcept(int excepts);
8888 2 The fetestexcept function determines which of a specified subset of the floating-
8889 point exception flags are currently set. The excepts argument specifies the floating-
8890 point status flags to be queried.212)
8892 3 The fetestexcept function returns the value of the bitwise OR of the floating-point
8893 exception macros corresponding to the currently set floating-point exceptions included in
8895 4 EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set:
8900 212) This mechanism allows testing several floating-point exceptions with just one function call.
8907 #pragma STDC FENV_ACCESS ON
8909 feclearexcept(FE_INVALID | FE_OVERFLOW);
8910 // maybe raise exceptions
8911 set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
8912 if (set_excepts & FE_INVALID) f();
8913 if (set_excepts & FE_OVERFLOW) g();
8918 1 The fegetround and fesetround functions provide control of rounding direction
8920 7.6.3.1 The fegetround function
8923 int fegetround(void);
8925 2 The fegetround function gets the current rounding direction.
8927 3 The fegetround function returns the value of the rounding direction macro
8928 representing the current rounding direction or a negative value if there is no such
8929 rounding direction macro or the current rounding direction is not determinable.
8930 7.6.3.2 The fesetround function
8933 int fesetround(int round);
8935 2 The fesetround function establishes the rounding direction represented by its
8936 argument round. If the argument is not equal to the value of a rounding direction macro,
8937 the rounding direction is not changed.
8939 3 The fesetround function returns zero if and only if the requested rounding direction
8945 4 EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
8946 rounding direction fails.
8949 void f(int round_dir)
8951 #pragma STDC FENV_ACCESS ON
8954 save_round = fegetround();
8955 setround_ok = fesetround(round_dir);
8956 assert(setround_ok == 0);
8958 fesetround(save_round);
8963 1 The functions in this section manage the floating-point environment -- status flags and
8964 control modes -- as one entity.
8965 7.6.4.1 The fegetenv function
8968 int fegetenv(fenv_t *envp);
8970 2 The fegetenv function attempts to store the current floating-point environment in the
8971 object pointed to by envp.
8973 3 The fegetenv function returns zero if the environment was successfully stored.
8974 Otherwise, it returns a nonzero value.
8975 7.6.4.2 The feholdexcept function
8978 int feholdexcept(fenv_t *envp);
8980 2 The feholdexcept function saves the current floating-point environment in the object
8981 pointed to by envp, clears the floating-point status flags, and then installs a non-stop
8982 (continue on floating-point exceptions) mode, if available, for all floating-point
8988 3 The feholdexcept function returns zero if and only if non-stop floating-point
8989 exception handling was successfully installed.
8990 7.6.4.3 The fesetenv function
8993 int fesetenv(const fenv_t *envp);
8995 2 The fesetenv function attempts to establish the floating-point environment represented
8996 by the object pointed to by envp. The argument envp shall point to an object set by a
8997 call to fegetenv or feholdexcept, or equal a floating-point environment macro.
8998 Note that fesetenv merely installs the state of the floating-point status flags
8999 represented through its argument, and does not raise these floating-point exceptions.
9001 3 The fesetenv function returns zero if the environment was successfully established.
9002 Otherwise, it returns a nonzero value.
9003 7.6.4.4 The feupdateenv function
9006 int feupdateenv(const fenv_t *envp);
9008 2 The feupdateenv function attempts to save the currently raised floating-point
9009 exceptions in its automatic storage, install the floating-point environment represented by
9010 the object pointed to by envp, and then raise the saved floating-point exceptions. The
9011 argument envp shall point to an object set by a call to feholdexcept or fegetenv,
9012 or equal a floating-point environment macro.
9014 3 The feupdateenv function returns zero if all the actions were successfully carried out.
9015 Otherwise, it returns a nonzero value.
9020 213) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
9021 handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
9022 such systems, the feholdexcept function can be used in conjunction with the feupdateenv
9023 function to write routines that hide spurious floating-point exceptions from their callers.
9027 4 EXAMPLE Hide spurious underflow floating-point exceptions:
9031 #pragma STDC FENV_ACCESS ON
9034 if (feholdexcept(&save_env))
9035 return /* indication of an environmental problem */;
9037 if (/* test spurious underflow */)
9038 if (feclearexcept(FE_UNDERFLOW))
9039 return /* indication of an environmental problem */;
9040 if (feupdateenv(&save_env))
9041 return /* indication of an environmental problem */;
9050 7.7 Characteristics of floating types <float.h>
9051 1 The header <float.h> defines several macros that expand to various limits and
9052 parameters of the standard floating-point types.
9053 2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
9061 7.8 Format conversion of integer types <inttypes.h>
9062 1 The header <inttypes.h> includes the header <stdint.h> and extends it with
9063 additional facilities provided by hosted implementations.
9064 2 It declares functions for manipulating greatest-width integers and converting numeric
9065 character strings to greatest-width integers, and it declares the type
9067 which is a structure type that is the type of the value returned by the imaxdiv function.
9068 For each type declared in <stdint.h>, it defines corresponding macros for conversion
9069 specifiers for use with the formatted input/output functions.214)
9070 Forward references: integer types <stdint.h> (7.20), formatted input/output
9071 functions (7.21.6), formatted wide character input/output functions (7.28.2).
9072 7.8.1 Macros for format specifiers
9073 1 Each of the following object-like macros expands to a character string literal containing a
9074 conversion specifier, possibly modified by a length modifier, suitable for use within the
9075 format argument of a formatted input/output function when converting the corresponding
9076 integer type. These macro names have the general form of PRI (character string literals
9077 for the fprintf and fwprintf family) or SCN (character string literals for the
9078 fscanf and fwscanf family),215) followed by the conversion specifier, followed by a
9079 name corresponding to a similar type name in 7.20.1. In these names, N represents the
9080 width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
9081 format string to print the value of an integer of type int_fast32_t.
9082 2 The fprintf macros for signed integers are:
9083 PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
9084 PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
9085 3 The fprintf macros for unsigned integers are:
9086 PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
9087 PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
9088 PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
9089 PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
9090 4 The fscanf macros for signed integers are:
9094 214) See ''future library directions'' (7.30.4).
9095 215) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
9096 different format specifiers may be required for fprintf and fscanf, even when the type is the
9101 SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
9102 SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
9103 5 The fscanf macros for unsigned integers are:
9104 SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
9105 SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
9106 SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
9107 6 For each type that the implementation provides in <stdint.h>, the corresponding
9108 fprintf macros shall be defined and the corresponding fscanf macros shall be
9109 defined unless the implementation does not have a suitable fscanf length modifier for
9112 #include <inttypes.h>
9116 uintmax_t i = UINTMAX_MAX; // this type always exists
9117 wprintf(L"The largest integer value is %020"
9122 7.8.2 Functions for greatest-width integer types
9123 7.8.2.1 The imaxabs function
9125 1 #include <inttypes.h>
9126 intmax_t imaxabs(intmax_t j);
9128 2 The imaxabs function computes the absolute value of an integer j. If the result cannot
9129 be represented, the behavior is undefined.216)
9131 3 The imaxabs function returns the absolute value.
9136 216) The absolute value of the most negative number cannot be represented in two's complement.
9140 7.8.2.2 The imaxdiv function
9142 1 #include <inttypes.h>
9143 imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
9145 2 The imaxdiv function computes numer / denom and numer % denom in a single
9148 3 The imaxdiv function returns a structure of type imaxdiv_t comprising both the
9149 quotient and the remainder. The structure shall contain (in either order) the members
9150 quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
9151 either part of the result cannot be represented, the behavior is undefined.
9152 7.8.2.3 The strtoimax and strtoumax functions
9154 1 #include <inttypes.h>
9155 intmax_t strtoimax(const char * restrict nptr,
9156 char ** restrict endptr, int base);
9157 uintmax_t strtoumax(const char * restrict nptr,
9158 char ** restrict endptr, int base);
9160 2 The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
9161 strtoul, and strtoull functions, except that the initial portion of the string is
9162 converted to intmax_t and uintmax_t representation, respectively.
9164 3 The strtoimax and strtoumax functions return the converted value, if any. If no
9165 conversion could be performed, zero is returned. If the correct value is outside the range
9166 of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
9167 (according to the return type and sign of the value, if any), and the value of the macro
9168 ERANGE is stored in errno.
9169 Forward references: the strtol, strtoll, strtoul, and strtoull functions
9177 7.8.2.4 The wcstoimax and wcstoumax functions
9179 1 #include <stddef.h> // for wchar_t
9180 #include <inttypes.h>
9181 intmax_t wcstoimax(const wchar_t * restrict nptr,
9182 wchar_t ** restrict endptr, int base);
9183 uintmax_t wcstoumax(const wchar_t * restrict nptr,
9184 wchar_t ** restrict endptr, int base);
9186 2 The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
9187 wcstoul, and wcstoull functions except that the initial portion of the wide string is
9188 converted to intmax_t and uintmax_t representation, respectively.
9190 3 The wcstoimax function returns the converted value, if any. If no conversion could be
9191 performed, zero is returned. If the correct value is outside the range of representable
9192 values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
9193 return type and sign of the value, if any), and the value of the macro ERANGE is stored in
9195 Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
9203 7.9 Alternative spellings <iso646.h>
9204 1 The header <iso646.h> defines the following eleven macros (on the left) that expand
9205 to the corresponding tokens (on the right):
9223 7.10 Sizes of integer types <limits.h>
9224 1 The header <limits.h> defines several macros that expand to various limits and
9225 parameters of the standard integer types.
9226 2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
9234 7.11 Localization <locale.h>
9235 1 The header <locale.h> declares two functions, one type, and defines several macros.
9238 which contains members related to the formatting of numeric values. The structure shall
9239 contain at least the following members, in any order. The semantics of the members and
9240 their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
9241 the values specified in the comments.
9242 char *decimal_point; // "."
9243 char *thousands_sep; // ""
9244 char *grouping; // ""
9245 char *mon_decimal_point; // ""
9246 char *mon_thousands_sep; // ""
9247 char *mon_grouping; // ""
9248 char *positive_sign; // ""
9249 char *negative_sign; // ""
9250 char *currency_symbol; // ""
9251 char frac_digits; // CHAR_MAX
9252 char p_cs_precedes; // CHAR_MAX
9253 char n_cs_precedes; // CHAR_MAX
9254 char p_sep_by_space; // CHAR_MAX
9255 char n_sep_by_space; // CHAR_MAX
9256 char p_sign_posn; // CHAR_MAX
9257 char n_sign_posn; // CHAR_MAX
9258 char *int_curr_symbol; // ""
9259 char int_frac_digits; // CHAR_MAX
9260 char int_p_cs_precedes; // CHAR_MAX
9261 char int_n_cs_precedes; // CHAR_MAX
9262 char int_p_sep_by_space; // CHAR_MAX
9263 char int_n_sep_by_space; // CHAR_MAX
9264 char int_p_sign_posn; // CHAR_MAX
9265 char int_n_sign_posn; // CHAR_MAX
9272 3 The macros defined are NULL (described in 7.19); and
9279 which expand to integer constant expressions with distinct values, suitable for use as the
9280 first argument to the setlocale function.217) Additional macro definitions, beginning
9281 with the characters LC_ and an uppercase letter,218) may also be specified by the
9283 7.11.1 Locale control
9284 7.11.1.1 The setlocale function
9286 1 #include <locale.h>
9287 char *setlocale(int category, const char *locale);
9289 2 The setlocale function selects the appropriate portion of the program's locale as
9290 specified by the category and locale arguments. The setlocale function may be
9291 used to change or query the program's entire current locale or portions thereof. The value
9292 LC_ALL for category names the program's entire locale; the other values for
9293 category name only a portion of the program's locale. LC_COLLATE affects the
9294 behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
9295 the character handling functions219) and the multibyte and wide character functions.
9296 LC_MONETARY affects the monetary formatting information returned by the
9297 localeconv function. LC_NUMERIC affects the decimal-point character for the
9298 formatted input/output functions and the string conversion functions, as well as the
9299 nonmonetary formatting information returned by the localeconv function. LC_TIME
9300 affects the behavior of the strftime and wcsftime functions.
9301 3 A value of "C" for locale specifies the minimal environment for C translation; a value
9302 of "" for locale specifies the locale-specific native environment. Other
9303 implementation-defined strings may be passed as the second argument to setlocale.
9305 217) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
9306 218) See ''future library directions'' (7.30.5).
9307 219) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
9312 4 At program startup, the equivalent of
9313 setlocale(LC_ALL, "C");
9315 5 A call to the setlocale function may introduce a data race with other calls to the
9316 setlocale function or with calls to functions that are affected by the current locale.
9317 The implementation shall behave as if no library function calls the setlocale function.
9319 6 If a pointer to a string is given for locale and the selection can be honored, the
9320 setlocale function returns a pointer to the string associated with the specified
9321 category for the new locale. If the selection cannot be honored, the setlocale
9322 function returns a null pointer and the program's locale is not changed.
9323 7 A null pointer for locale causes the setlocale function to return a pointer to the
9324 string associated with the category for the program's current locale; the program's
9325 locale is not changed.220)
9326 8 The pointer to string returned by the setlocale function is such that a subsequent call
9327 with that string value and its associated category will restore that part of the program's
9328 locale. The string pointed to shall not be modified by the program, but may be
9329 overwritten by a subsequent call to the setlocale function.
9330 Forward references: formatted input/output functions (7.21.6), multibyte/wide
9331 character conversion functions (7.22.7), multibyte/wide string conversion functions
9332 (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the
9333 strftime function (7.26.3.5), the strxfrm function (7.23.4.5).
9334 7.11.2 Numeric formatting convention inquiry
9335 7.11.2.1 The localeconv function
9337 1 #include <locale.h>
9338 struct lconv *localeconv(void);
9340 2 The localeconv function sets the components of an object with type struct lconv
9341 with values appropriate for the formatting of numeric quantities (monetary and otherwise)
9342 according to the rules of the current locale.
9346 220) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
9347 locale when category has the value LC_ALL.
9351 3 The members of the structure with type char * are pointers to strings, any of which
9352 (except decimal_point) can point to "", to indicate that the value is not available in
9353 the current locale or is of zero length. Apart from grouping and mon_grouping, the
9354 strings shall start and end in the initial shift state. The members with type char are
9355 nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
9356 available in the current locale. The members include the following:
9358 The decimal-point character used to format nonmonetary quantities.
9360 The character used to separate groups of digits before the decimal-point
9361 character in formatted nonmonetary quantities.
9363 A string whose elements indicate the size of each group of digits in
9364 formatted nonmonetary quantities.
9365 char *mon_decimal_point
9366 The decimal-point used to format monetary quantities.
9367 char *mon_thousands_sep
9368 The separator for groups of digits before the decimal-point in formatted
9369 monetary quantities.
9371 A string whose elements indicate the size of each group of digits in
9372 formatted monetary quantities.
9374 The string used to indicate a nonnegative-valued formatted monetary
9377 The string used to indicate a negative-valued formatted monetary quantity.
9378 char *currency_symbol
9379 The local currency symbol applicable to the current locale.
9381 The number of fractional digits (those after the decimal-point) to be
9382 displayed in a locally formatted monetary quantity.
9384 Set to 1 or 0 if the currency_symbol respectively precedes or
9385 succeeds the value for a nonnegative locally formatted monetary quantity.
9392 Set to 1 or 0 if the currency_symbol respectively precedes or
9393 succeeds the value for a negative locally formatted monetary quantity.
9395 Set to a value indicating the separation of the currency_symbol, the
9396 sign string, and the value for a nonnegative locally formatted monetary
9399 Set to a value indicating the separation of the currency_symbol, the
9400 sign string, and the value for a negative locally formatted monetary
9403 Set to a value indicating the positioning of the positive_sign for a
9404 nonnegative locally formatted monetary quantity.
9406 Set to a value indicating the positioning of the negative_sign for a
9407 negative locally formatted monetary quantity.
9408 char *int_curr_symbol
9409 The international currency symbol applicable to the current locale. The
9410 first three characters contain the alphabetic international currency symbol
9411 in accordance with those specified in ISO 4217. The fourth character
9412 (immediately preceding the null character) is the character used to separate
9413 the international currency symbol from the monetary quantity.
9414 char int_frac_digits
9415 The number of fractional digits (those after the decimal-point) to be
9416 displayed in an internationally formatted monetary quantity.
9417 char int_p_cs_precedes
9418 Set to 1 or 0 if the int_curr_symbol respectively precedes or
9419 succeeds the value for a nonnegative internationally formatted monetary
9421 char int_n_cs_precedes
9422 Set to 1 or 0 if the int_curr_symbol respectively precedes or
9423 succeeds the value for a negative internationally formatted monetary
9425 char int_p_sep_by_space
9426 Set to a value indicating the separation of the int_curr_symbol, the
9427 sign string, and the value for a nonnegative internationally formatted
9431 char int_n_sep_by_space
9432 Set to a value indicating the separation of the int_curr_symbol, the
9433 sign string, and the value for a negative internationally formatted monetary
9435 char int_p_sign_posn
9436 Set to a value indicating the positioning of the positive_sign for a
9437 nonnegative internationally formatted monetary quantity.
9438 char int_n_sign_posn
9439 Set to a value indicating the positioning of the negative_sign for a
9440 negative internationally formatted monetary quantity.
9441 4 The elements of grouping and mon_grouping are interpreted according to the
9443 CHAR_MAX No further grouping is to be performed.
9444 0 The previous element is to be repeatedly used for the remainder of the
9446 other The integer value is the number of digits that compose the current group.
9447 The next element is examined to determine the size of the next group of
9448 digits before the current group.
9449 5 The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
9450 and int_n_sep_by_space are interpreted according to the following:
9451 0 No space separates the currency symbol and value.
9452 1 If the currency symbol and sign string are adjacent, a space separates them from the
9453 value; otherwise, a space separates the currency symbol from the value.
9454 2 If the currency symbol and sign string are adjacent, a space separates them;
9455 otherwise, a space separates the sign string from the value.
9456 For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
9457 int_curr_symbol is used instead of a space.
9458 6 The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and
9459 int_n_sign_posn are interpreted according to the following:
9460 0 Parentheses surround the quantity and currency symbol.
9461 1 The sign string precedes the quantity and currency symbol.
9462 2 The sign string succeeds the quantity and currency symbol.
9463 3 The sign string immediately precedes the currency symbol.
9464 4 The sign string immediately succeeds the currency symbol.
9469 7 The implementation shall behave as if no library function calls the localeconv
9472 8 The localeconv function returns a pointer to the filled-in object. The structure
9473 pointed to by the return value shall not be modified by the program, but may be
9474 overwritten by a subsequent call to the localeconv function. In addition, calls to the
9475 setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
9476 overwrite the contents of the structure.
9477 9 EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
9478 monetary quantities.
9479 Local format International format
9481 Country Positive Negative Positive Negative
9483 Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56
9484 Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234
9485 Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56
9486 Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C
9487 10 For these four countries, the respective values for the monetary members of the structure returned by
9488 localeconv could be:
9489 Country1 Country2 Country3 Country4
9491 mon_decimal_point "," "" "," "."
9492 mon_thousands_sep "." "." "." ","
9493 mon_grouping "\3" "\3" "\3" "\3"
9494 positive_sign "" "" "" ""
9495 negative_sign "-" "-" "-" "C"
9496 currency_symbol "mk" "L." "\u0192" "SFrs."
9498 p_cs_precedes 0 1 1 1
9499 n_cs_precedes 0 1 1 1
9500 p_sep_by_space 1 0 1 0
9501 n_sep_by_space 1 0 2 0
9504 int_curr_symbol "FIM " "ITL " "NLG " "CHF "
9505 int_frac_digits 2 0 2 2
9506 int_p_cs_precedes 1 1 1 1
9507 int_n_cs_precedes 1 1 1 1
9508 int_p_sep_by_space 1 1 1 1
9509 int_n_sep_by_space 2 1 2 1
9510 int_p_sign_posn 1 1 1 1
9511 int_n_sign_posn 4 1 4 2
9518 11 EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
9519 affect the formatted value.
9522 p_cs_precedes p_sign_posn 0 1 2
9524 0 0 (1.25$) (1.25 $) (1.25$)
9525 1 +1.25$ +1.25 $ + 1.25$
9526 2 1.25$+ 1.25 $+ 1.25$ +
9527 3 1.25+$ 1.25 +$ 1.25+ $
9528 4 1.25$+ 1.25 $+ 1.25$ +
9530 1 0 ($1.25) ($ 1.25) ($1.25)
9531 1 +$1.25 +$ 1.25 + $1.25
9532 2 $1.25+ $ 1.25+ $1.25 +
9533 3 +$1.25 +$ 1.25 + $1.25
9534 4 $+1.25 $+ 1.25 $ +1.25
9541 7.12 Mathematics <math.h>
9542 1 The header <math.h> declares two types and many mathematical functions and defines
9543 several macros. Most synopses specify a family of functions consisting of a principal
9544 function with one or more double parameters, a double return value, or both; and
9545 other functions with the same name but with f and l suffixes, which are corresponding
9546 functions with float and long double parameters, return values, or both.221)
9547 Integer arithmetic functions and conversion functions are discussed later.
9551 are floating types at least as wide as float and double, respectively, and such that
9552 double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
9553 float_t and double_t are float and double, respectively; if
9554 FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
9555 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
9556 otherwise implementation-defined.222)
9559 expands to a positive double constant expression, not necessarily representable as a
9563 are respectively float and long double analogs of HUGE_VAL.223)
9566 expands to a constant expression of type float representing positive or unsigned
9567 infinity, if available; else to a positive constant of type float that overflows at
9571 221) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
9572 and return values in wider format than the synopsis prototype indicates.
9573 222) The types float_t and double_t are intended to be the implementation's most efficient types at
9574 least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
9575 type float_t is the narrowest type used by the implementation to evaluate floating expressions.
9576 223) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
9577 supports infinities.
9581 translation time.224)
9584 is defined if and only if the implementation supports quiet NaNs for the float type. It
9585 expands to a constant expression of type float representing a quiet NaN.
9586 6 The number classification macros
9592 represent the mutually exclusive kinds of floating-point values. They expand to integer
9593 constant expressions with distinct values. Additional implementation-defined floating-
9594 point classifications, with macro definitions beginning with FP_ and an uppercase letter,
9595 may also be specified by the implementation.
9598 is optionally defined. If defined, it indicates that the fma function generally executes
9599 about as fast as, or faster than, a multiply and an add of double operands.225) The
9603 are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
9604 these macros expand to the integer constant 1.
9608 expand to integer constant expressions whose values are returned by ilogb(x) if x is
9609 zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
9610 -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
9613 224) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
9614 225) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
9615 directly with a hardware multiply-add instruction. Software implementations are expected to be
9616 substantially slower.
9623 expand to the integer constants 1 and 2, respectively; the macro
9625 expands to an expression that has type int and the value MATH_ERRNO,
9626 MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
9627 constant for the duration of the program. It is unspecified whether
9628 math_errhandling is a macro or an identifier with external linkage. If a macro
9629 definition is suppressed or a program defines an identifier with the name
9630 math_errhandling, the behavior is undefined. If the expression
9631 math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
9632 shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
9634 7.12.1 Treatment of error conditions
9635 1 The behavior of each of the functions in <math.h> is specified for all representable
9636 values of its input arguments, except where stated otherwise. Each function shall execute
9637 as if it were a single operation without raising SIGFPE and without generating any of the
9638 exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect the result of the
9640 2 For all functions, a domain error occurs if an input argument is outside the domain over
9641 which the mathematical function is defined. The description of each function lists any
9642 required domain errors; an implementation may define additional domain errors, provided
9643 that such errors are consistent with the mathematical definition of the function.226) On a
9644 domain error, the function returns an implementation-defined value; if the integer
9645 expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
9646 errno acquires the value EDOM; if the integer expression math_errhandling &
9647 MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised.
9648 3 Similarly, a pole error (also known as a singularity or infinitary) occurs if the
9649 mathematical function has an exact infinite result as the finite input argument(s) are
9650 approached in the limit (for example, log(0.0)). The description of each function lists
9651 any required pole errors; an implementation may define additional pole errors, provided
9652 that such errors are consistent with the mathematical definition of the function. On a pole
9653 error, the function returns an implementation-defined value; if the integer expression
9656 226) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
9657 error if the mathematical domain of the function does not include the infinity.
9661 math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
9662 acquires the value ERANGE; if the integer expression math_errhandling &
9663 MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised.
9664 4 Likewise, a range error occurs if the mathematical result of the function cannot be
9665 represented in an object of the specified type, due to extreme magnitude.
9666 5 A floating result overflows if the magnitude of the mathematical result is finite but so
9667 large that the mathematical result cannot be represented without extraordinary roundoff
9668 error in an object of the specified type. If a floating result overflows and default rounding
9669 is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or
9670 HUGE_VALL according to the return type, with the same sign as the correct value of the
9671 function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
9672 the integer expression errno acquires the value ERANGE; if the integer expression
9673 math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating-
9674 point exception is raised.
9675 6 The result underflows if the magnitude of the mathematical result is so small that the
9676 mathematical result cannot be represented, without extraordinary roundoff error, in an
9677 object of the specified type.227) If the result underflows, the function returns an
9678 implementation-defined value whose magnitude is no greater than the smallest
9679 normalized positive number in the specified type; if the integer expression
9680 math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
9681 value ERANGE is implementation-defined; if the integer expression
9682 math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow''
9683 floating-point exception is raised is implementation-defined.
9684 7 If a domain, pole, or range error occurs and the integer expression
9685 math_errhandling & MATH_ERRNO is zero,228) then errno shall either be set to
9686 the value corresponding to the error or left unmodified. If no such error occurs, errno
9687 shall be left unmodified regardless of the setting of math_errhandling.
9692 227) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and
9693 also ''flush-to-zero'' underflow.
9694 228) Math errors are being indicated by the floating-point exception flags rather than by errno.
9698 7.12.2 The FP_CONTRACT pragma
9701 #pragma STDC FP_CONTRACT on-off-switch
9703 2 The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the
9704 state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur
9705 either outside external declarations or preceding all explicit declarations and statements
9706 inside a compound statement. When outside external declarations, the pragma takes
9707 effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
9708 the end of the translation unit. When inside a compound statement, the pragma takes
9709 effect from its occurrence until another FP_CONTRACT pragma is encountered
9710 (including within a nested compound statement), or until the end of the compound
9711 statement; at the end of a compound statement the state for the pragma is restored to its
9712 condition just before the compound statement. If this pragma is used in any other
9713 context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is
9714 implementation-defined.
9715 7.12.3 Classification macros
9716 1 In the synopses in this subclause, real-floating indicates that the argument shall be an
9717 expression of real floating type.
9718 7.12.3.1 The fpclassify macro
9721 int fpclassify(real-floating x);
9723 2 The fpclassify macro classifies its argument value as NaN, infinite, normal,
9724 subnormal, zero, or into another implementation-defined category. First, an argument
9725 represented in a format wider than its semantic type is converted to its semantic type.
9726 Then classification is based on the type of the argument.229)
9728 3 The fpclassify macro returns the value of the number classification macro
9729 appropriate to the value of its argument.
9732 229) Since an expression can be evaluated with more range and precision than its type has, it is important to
9733 know the type that classification is based on. For example, a normal long double value might
9734 become subnormal when converted to double, and zero when converted to float.
9738 7.12.3.2 The isfinite macro
9741 int isfinite(real-floating x);
9743 2 The isfinite macro determines whether its argument has a finite value (zero,
9744 subnormal, or normal, and not infinite or NaN). First, an argument represented in a
9745 format wider than its semantic type is converted to its semantic type. Then determination
9746 is based on the type of the argument.
9748 3 The isfinite macro returns a nonzero value if and only if its argument has a finite
9750 7.12.3.3 The isinf macro
9753 int isinf(real-floating x);
9755 2 The isinf macro determines whether its argument value is an infinity (positive or
9756 negative). First, an argument represented in a format wider than its semantic type is
9757 converted to its semantic type. Then determination is based on the type of the argument.
9759 3 The isinf macro returns a nonzero value if and only if its argument has an infinite
9761 7.12.3.4 The isnan macro
9764 int isnan(real-floating x);
9766 2 The isnan macro determines whether its argument value is a NaN. First, an argument
9767 represented in a format wider than its semantic type is converted to its semantic type.
9768 Then determination is based on the type of the argument.230)
9771 230) For the isnan macro, the type for determination does not matter unless the implementation supports
9772 NaNs in the evaluation type but not in the semantic type.
9777 3 The isnan macro returns a nonzero value if and only if its argument has a NaN value.
9778 7.12.3.5 The isnormal macro
9781 int isnormal(real-floating x);
9783 2 The isnormal macro determines whether its argument value is normal (neither zero,
9784 subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
9785 semantic type is converted to its semantic type. Then determination is based on the type
9788 3 The isnormal macro returns a nonzero value if and only if its argument has a normal
9790 7.12.3.6 The signbit macro
9793 int signbit(real-floating x);
9795 2 The signbit macro determines whether the sign of its argument value is negative.231)
9797 3 The signbit macro returns a nonzero value if and only if the sign of its argument value
9803 231) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
9804 unsigned, it is treated as positive.
9808 7.12.4 Trigonometric functions
9809 7.12.4.1 The acos functions
9812 double acos(double x);
9813 float acosf(float x);
9814 long double acosl(long double x);
9816 2 The acos functions compute the principal value of the arc cosine of x. A domain error
9817 occurs for arguments not in the interval [-1, +1].
9819 3 The acos functions return arccos x in the interval [0, pi ] radians.
9820 7.12.4.2 The asin functions
9823 double asin(double x);
9824 float asinf(float x);
9825 long double asinl(long double x);
9827 2 The asin functions compute the principal value of the arc sine of x. A domain error
9828 occurs for arguments not in the interval [-1, +1].
9830 3 The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians.
9831 7.12.4.3 The atan functions
9834 double atan(double x);
9835 float atanf(float x);
9836 long double atanl(long double x);
9838 2 The atan functions compute the principal value of the arc tangent of x.
9846 3 The atan functions return arctan x in the interval [-pi /2, +pi /2] radians.
9847 7.12.4.4 The atan2 functions
9850 double atan2(double y, double x);
9851 float atan2f(float y, float x);
9852 long double atan2l(long double y, long double x);
9854 2 The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
9855 arguments to determine the quadrant of the return value. A domain error may occur if
9856 both arguments are zero.
9858 3 The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians.
9859 7.12.4.5 The cos functions
9862 double cos(double x);
9863 float cosf(float x);
9864 long double cosl(long double x);
9866 2 The cos functions compute the cosine of x (measured in radians).
9868 3 The cos functions return cos x.
9869 7.12.4.6 The sin functions
9872 double sin(double x);
9873 float sinf(float x);
9874 long double sinl(long double x);
9876 2 The sin functions compute the sine of x (measured in radians).
9883 3 The sin functions return sin x.
9884 7.12.4.7 The tan functions
9887 double tan(double x);
9888 float tanf(float x);
9889 long double tanl(long double x);
9891 2 The tan functions return the tangent of x (measured in radians).
9893 3 The tan functions return tan x.
9894 7.12.5 Hyperbolic functions
9895 7.12.5.1 The acosh functions
9898 double acosh(double x);
9899 float acoshf(float x);
9900 long double acoshl(long double x);
9902 2 The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
9903 error occurs for arguments less than 1.
9905 3 The acosh functions return arcosh x in the interval [0, +(inf)].
9906 7.12.5.2 The asinh functions
9909 double asinh(double x);
9910 float asinhf(float x);
9911 long double asinhl(long double x);
9913 2 The asinh functions compute the arc hyperbolic sine of x.
9919 3 The asinh functions return arsinh x.
9920 7.12.5.3 The atanh functions
9923 double atanh(double x);
9924 float atanhf(float x);
9925 long double atanhl(long double x);
9927 2 The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
9928 for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
9931 3 The atanh functions return artanh x.
9932 7.12.5.4 The cosh functions
9935 double cosh(double x);
9936 float coshf(float x);
9937 long double coshl(long double x);
9939 2 The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
9940 magnitude of x is too large.
9942 3 The cosh functions return cosh x.
9943 7.12.5.5 The sinh functions
9946 double sinh(double x);
9947 float sinhf(float x);
9948 long double sinhl(long double x);
9950 2 The sinh functions compute the hyperbolic sine of x. A range error occurs if the
9951 magnitude of x is too large.
9955 3 The sinh functions return sinh x.
9956 7.12.5.6 The tanh functions
9959 double tanh(double x);
9960 float tanhf(float x);
9961 long double tanhl(long double x);
9963 2 The tanh functions compute the hyperbolic tangent of x.
9965 3 The tanh functions return tanh x.
9966 7.12.6 Exponential and logarithmic functions
9967 7.12.6.1 The exp functions
9970 double exp(double x);
9971 float expf(float x);
9972 long double expl(long double x);
9974 2 The exp functions compute the base-e exponential of x. A range error occurs if the
9975 magnitude of x is too large.
9977 3 The exp functions return ex .
9978 7.12.6.2 The exp2 functions
9981 double exp2(double x);
9982 float exp2f(float x);
9983 long double exp2l(long double x);
9985 2 The exp2 functions compute the base-2 exponential of x. A range error occurs if the
9986 magnitude of x is too large.
9991 3 The exp2 functions return 2x .
9992 7.12.6.3 The expm1 functions
9995 double expm1(double x);
9996 float expm1f(float x);
9997 long double expm1l(long double x);
9999 2 The expm1 functions compute the base-e exponential of the argument, minus 1. A range
10000 error occurs if x is too large.232)
10002 3 The expm1 functions return ex - 1.
10003 7.12.6.4 The frexp functions
10005 1 #include <math.h>
10006 double frexp(double value, int *exp);
10007 float frexpf(float value, int *exp);
10008 long double frexpl(long double value, int *exp);
10010 2 The frexp functions break a floating-point number into a normalized fraction and an
10011 integral power of 2. They store the integer in the int object pointed to by exp.
10013 3 If value is not a floating-point number or if the integral power of 2 is outside the range
10014 of int, the results are unspecified. Otherwise, the frexp functions return the value x,
10015 such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp .
10016 If value is zero, both parts of the result are zero.
10021 232) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.
10025 7.12.6.5 The ilogb functions
10027 1 #include <math.h>
10028 int ilogb(double x);
10029 int ilogbf(float x);
10030 int ilogbl(long double x);
10032 2 The ilogb functions extract the exponent of x as a signed int value. If x is zero they
10033 compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
10034 a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
10035 the corresponding logb function and casting the returned value to type int. A domain
10036 error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
10037 the range of the return type, the numeric result is unspecified.
10039 3 The ilogb functions return the exponent of x as a signed int value.
10040 Forward references: the logb functions (7.12.6.11).
10041 7.12.6.6 The ldexp functions
10043 1 #include <math.h>
10044 double ldexp(double x, int exp);
10045 float ldexpf(float x, int exp);
10046 long double ldexpl(long double x, int exp);
10048 2 The ldexp functions multiply a floating-point number by an integral power of 2. A
10049 range error may occur.
10051 3 The ldexp functions return x x 2exp .
10052 7.12.6.7 The log functions
10054 1 #include <math.h>
10055 double log(double x);
10056 float logf(float x);
10057 long double logl(long double x);
10064 2 The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
10065 the argument is negative. A pole error may occur if the argument is zero.
10067 3 The log functions return loge x.
10068 7.12.6.8 The log10 functions
10070 1 #include <math.h>
10071 double log10(double x);
10072 float log10f(float x);
10073 long double log10l(long double x);
10075 2 The log10 functions compute the base-10 (common) logarithm of x. A domain error
10076 occurs if the argument is negative. A pole error may occur if the argument is zero.
10078 3 The log10 functions return log10 x.
10079 7.12.6.9 The log1p functions
10081 1 #include <math.h>
10082 double log1p(double x);
10083 float log1pf(float x);
10084 long double log1pl(long double x);
10086 2 The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.233)
10087 A domain error occurs if the argument is less than -1. A pole error may occur if the
10088 argument equals -1.
10090 3 The log1p functions return loge (1 + x).
10095 233) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).
10099 7.12.6.10 The log2 functions
10101 1 #include <math.h>
10102 double log2(double x);
10103 float log2f(float x);
10104 long double log2l(long double x);
10106 2 The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
10107 argument is less than zero. A pole error may occur if the argument is zero.
10109 3 The log2 functions return log2 x.
10110 7.12.6.11 The logb functions
10112 1 #include <math.h>
10113 double logb(double x);
10114 float logbf(float x);
10115 long double logbl(long double x);
10117 2 The logb functions extract the exponent of x, as a signed integer value in floating-point
10118 format. If x is subnormal it is treated as though it were normalized; thus, for positive
10120 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
10121 A domain error or pole error may occur if the argument is zero.
10123 3 The logb functions return the signed exponent of x.
10124 7.12.6.12 The modf functions
10126 1 #include <math.h>
10127 double modf(double value, double *iptr);
10128 float modff(float value, float *iptr);
10129 long double modfl(long double value, long double *iptr);
10131 2 The modf functions break the argument value into integral and fractional parts, each of
10132 which has the same type and sign as the argument. They store the integral part (in
10135 floating-point format) in the object pointed to by iptr.
10137 3 The modf functions return the signed fractional part of value.
10138 7.12.6.13 The scalbn and scalbln functions
10140 1 #include <math.h>
10141 double scalbn(double x, int n);
10142 float scalbnf(float x, int n);
10143 long double scalbnl(long double x, int n);
10144 double scalbln(double x, long int n);
10145 float scalblnf(float x, long int n);
10146 long double scalblnl(long double x, long int n);
10148 2 The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not
10149 normally by computing FLT_RADIXn explicitly. A range error may occur.
10151 3 The scalbn and scalbln functions return x x FLT_RADIXn .
10152 7.12.7 Power and absolute-value functions
10153 7.12.7.1 The cbrt functions
10155 1 #include <math.h>
10156 double cbrt(double x);
10157 float cbrtf(float x);
10158 long double cbrtl(long double x);
10160 2 The cbrt functions compute the real cube root of x.
10162 3 The cbrt functions return x1/3 .
10169 7.12.7.2 The fabs functions
10171 1 #include <math.h>
10172 double fabs(double x);
10173 float fabsf(float x);
10174 long double fabsl(long double x);
10176 2 The fabs functions compute the absolute value of a floating-point number x.
10178 3 The fabs functions return | x |.
10179 7.12.7.3 The hypot functions
10181 1 #include <math.h>
10182 double hypot(double x, double y);
10183 float hypotf(float x, float y);
10184 long double hypotl(long double x, long double y);
10186 2 The hypot functions compute the square root of the sum of the squares of x and y,
10187 without undue overflow or underflow. A range error may occur.
10189 4 The hypot functions return sqrt:x2 + y2 .
10192 7.12.7.4 The pow functions
10194 1 #include <math.h>
10195 double pow(double x, double y);
10196 float powf(float x, float y);
10197 long double powl(long double x, long double y);
10199 2 The pow functions compute x raised to the power y. A domain error occurs if x is finite
10200 and negative and y is finite and not an integer value. A range error may occur. A domain
10201 error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
10202 zero and y is less than zero.
10210 3 The pow functions return xy .
10211 7.12.7.5 The sqrt functions
10213 1 #include <math.h>
10214 double sqrt(double x);
10215 float sqrtf(float x);
10216 long double sqrtl(long double x);
10218 2 The sqrt functions compute the nonnegative square root of x. A domain error occurs if
10219 the argument is less than zero.
10221 3 The sqrt functions return sqrt:x.
10224 7.12.8 Error and gamma functions
10225 7.12.8.1 The erf functions
10227 1 #include <math.h>
10228 double erf(double x);
10229 float erff(float x);
10230 long double erfl(long double x);
10232 2 The erf functions compute the error function of x.
10237 The erf functions return erf x =
10242 7.12.8.2 The erfc functions
10244 1 #include <math.h>
10245 double erfc(double x);
10246 float erfcf(float x);
10247 long double erfcl(long double x);
10249 2 The erfc functions compute the complementary error function of x. A range error
10250 occurs if x is too large.
10257 The erfc functions return erfc x = 1 - erf x =
10262 7.12.8.3 The lgamma functions
10264 1 #include <math.h>
10265 double lgamma(double x);
10266 float lgammaf(float x);
10267 long double lgammal(long double x);
10269 2 The lgamma functions compute the natural logarithm of the absolute value of gamma of
10270 x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
10273 3 The lgamma functions return loge | (Gamma)(x) |.
10274 7.12.8.4 The tgamma functions
10276 1 #include <math.h>
10277 double tgamma(double x);
10278 float tgammaf(float x);
10279 long double tgammal(long double x);
10281 2 The tgamma functions compute the gamma function of x. A domain error or pole error
10282 may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
10283 too large and may occur if the magnitude of x is too small.
10285 3 The tgamma functions return (Gamma)(x).
10292 7.12.9 Nearest integer functions
10293 7.12.9.1 The ceil functions
10295 1 #include <math.h>
10296 double ceil(double x);
10297 float ceilf(float x);
10298 long double ceill(long double x);
10300 2 The ceil functions compute the smallest integer value not less than x.
10302 3 The ceil functions return [^x^], expressed as a floating-point number.
10303 7.12.9.2 The floor functions
10305 1 #include <math.h>
10306 double floor(double x);
10307 float floorf(float x);
10308 long double floorl(long double x);
10310 2 The floor functions compute the largest integer value not greater than x.
10312 3 The floor functions return [_x_], expressed as a floating-point number.
10313 7.12.9.3 The nearbyint functions
10315 1 #include <math.h>
10316 double nearbyint(double x);
10317 float nearbyintf(float x);
10318 long double nearbyintl(long double x);
10320 2 The nearbyint functions round their argument to an integer value in floating-point
10321 format, using the current rounding direction and without raising the ''inexact'' floating-
10330 3 The nearbyint functions return the rounded integer value.
10331 7.12.9.4 The rint functions
10333 1 #include <math.h>
10334 double rint(double x);
10335 float rintf(float x);
10336 long double rintl(long double x);
10338 2 The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
10339 rint functions may raise the ''inexact'' floating-point exception if the result differs in
10340 value from the argument.
10342 3 The rint functions return the rounded integer value.
10343 7.12.9.5 The lrint and llrint functions
10345 1 #include <math.h>
10346 long int lrint(double x);
10347 long int lrintf(float x);
10348 long int lrintl(long double x);
10349 long long int llrint(double x);
10350 long long int llrintf(float x);
10351 long long int llrintl(long double x);
10353 2 The lrint and llrint functions round their argument to the nearest integer value,
10354 rounding according to the current rounding direction. If the rounded value is outside the
10355 range of the return type, the numeric result is unspecified and a domain error or range
10358 3 The lrint and llrint functions return the rounded integer value.
10365 7.12.9.6 The round functions
10367 1 #include <math.h>
10368 double round(double x);
10369 float roundf(float x);
10370 long double roundl(long double x);
10372 2 The round functions round their argument to the nearest integer value in floating-point
10373 format, rounding halfway cases away from zero, regardless of the current rounding
10376 3 The round functions return the rounded integer value.
10377 7.12.9.7 The lround and llround functions
10379 1 #include <math.h>
10380 long int lround(double x);
10381 long int lroundf(float x);
10382 long int lroundl(long double x);
10383 long long int llround(double x);
10384 long long int llroundf(float x);
10385 long long int llroundl(long double x);
10387 2 The lround and llround functions round their argument to the nearest integer value,
10388 rounding halfway cases away from zero, regardless of the current rounding direction. If
10389 the rounded value is outside the range of the return type, the numeric result is unspecified
10390 and a domain error or range error may occur.
10392 3 The lround and llround functions return the rounded integer value.
10393 7.12.9.8 The trunc functions
10395 1 #include <math.h>
10396 double trunc(double x);
10397 float truncf(float x);
10398 long double truncl(long double x);
10404 2 The trunc functions round their argument to the integer value, in floating format,
10405 nearest to but no larger in magnitude than the argument.
10407 3 The trunc functions return the truncated integer value.
10408 7.12.10 Remainder functions
10409 7.12.10.1 The fmod functions
10411 1 #include <math.h>
10412 double fmod(double x, double y);
10413 float fmodf(float x, float y);
10414 long double fmodl(long double x, long double y);
10416 2 The fmod functions compute the floating-point remainder of x/y.
10418 3 The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
10419 the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
10420 whether a domain error occurs or the fmod functions return zero is implementation-
10422 7.12.10.2 The remainder functions
10424 1 #include <math.h>
10425 double remainder(double x, double y);
10426 float remainderf(float x, float y);
10427 long double remainderl(long double x, long double y);
10429 2 The remainder functions compute the remainder x REM y required by IEC 60559.234)
10434 234) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the
10435 mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever
10436 | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for
10437 all implementations.
10442 3 The remainder functions return x REM y. If y is zero, whether a domain error occurs
10443 or the functions return zero is implementation defined.
10444 7.12.10.3 The remquo functions
10446 1 #include <math.h>
10447 double remquo(double x, double y, int *quo);
10448 float remquof(float x, float y, int *quo);
10449 long double remquol(long double x, long double y,
10452 2 The remquo functions compute the same remainder as the remainder functions. In
10453 the object pointed to by quo they store a value whose sign is the sign of x/y and whose
10454 magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
10455 n is an implementation-defined integer greater than or equal to 3.
10457 3 The remquo functions return x REM y. If y is zero, the value stored in the object
10458 pointed to by quo is unspecified and whether a domain error occurs or the functions
10459 return zero is implementation defined.
10460 7.12.11 Manipulation functions
10461 7.12.11.1 The copysign functions
10463 1 #include <math.h>
10464 double copysign(double x, double y);
10465 float copysignf(float x, float y);
10466 long double copysignl(long double x, long double y);
10468 2 The copysign functions produce a value with the magnitude of x and the sign of y.
10469 They produce a NaN (with the sign of y) if x is a NaN. On implementations that
10470 represent a signed zero but do not treat negative zero consistently in arithmetic
10471 operations, the copysign functions regard the sign of zero as positive.
10473 3 The copysign functions return a value with the magnitude of x and the sign of y.
10479 7.12.11.2 The nan functions
10481 1 #include <math.h>
10482 double nan(const char *tagp);
10483 float nanf(const char *tagp);
10484 long double nanl(const char *tagp);
10486 2 The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
10487 sequence)", (char**) NULL); the call nan("") is equivalent to
10488 strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
10489 sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
10490 NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
10493 3 The nan functions return a quiet NaN, if available, with content indicated through tagp.
10494 If the implementation does not support quiet NaNs, the functions return zero.
10495 Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
10496 7.12.11.3 The nextafter functions
10498 1 #include <math.h>
10499 double nextafter(double x, double y);
10500 float nextafterf(float x, float y);
10501 long double nextafterl(long double x, long double y);
10503 2 The nextafter functions determine the next representable value, in the type of the
10504 function, after x in the direction of y, where x and y are first converted to the type of the
10505 function.235) The nextafter functions return y if x equals y. A range error may occur
10506 if the magnitude of x is the largest finite value representable in the type and the result is
10507 infinite or not representable in the type.
10509 3 The nextafter functions return the next representable value in the specified format
10510 after x in the direction of y.
10513 235) The argument values are converted to the type of the function, even by a macro implementation of the
10518 7.12.11.4 The nexttoward functions
10520 1 #include <math.h>
10521 double nexttoward(double x, long double y);
10522 float nexttowardf(float x, long double y);
10523 long double nexttowardl(long double x, long double y);
10525 2 The nexttoward functions are equivalent to the nextafter functions except that the
10526 second parameter has type long double and the functions return y converted to the
10527 type of the function if x equals y.236)
10528 7.12.12 Maximum, minimum, and positive difference functions
10529 7.12.12.1 The fdim functions
10531 1 #include <math.h>
10532 double fdim(double x, double y);
10533 float fdimf(float x, float y);
10534 long double fdiml(long double x, long double y);
10536 2 The fdim functions determine the positive difference between their arguments:
10540 A range error may occur.
10542 3 The fdim functions return the positive difference value.
10543 7.12.12.2 The fmax functions
10545 1 #include <math.h>
10546 double fmax(double x, double y);
10547 float fmaxf(float x, float y);
10548 long double fmaxl(long double x, long double y);
10552 236) The result of the nexttoward functions is determined in the type of the function, without loss of
10553 range or precision in a floating second argument.
10558 2 The fmax functions determine the maximum numeric value of their arguments.237)
10560 3 The fmax functions return the maximum numeric value of their arguments.
10561 7.12.12.3 The fmin functions
10563 1 #include <math.h>
10564 double fmin(double x, double y);
10565 float fminf(float x, float y);
10566 long double fminl(long double x, long double y);
10568 2 The fmin functions determine the minimum numeric value of their arguments.238)
10570 3 The fmin functions return the minimum numeric value of their arguments.
10571 7.12.13 Floating multiply-add
10572 7.12.13.1 The fma functions
10574 1 #include <math.h>
10575 double fma(double x, double y, double z);
10576 float fmaf(float x, float y, float z);
10577 long double fmal(long double x, long double y,
10580 2 The fma functions compute (x x y) + z, rounded as one ternary operation: they compute
10581 the value (as if) to infinite precision and round once to the result format, according to the
10582 current rounding mode. A range error may occur.
10584 3 The fma functions return (x x y) + z, rounded as one ternary operation.
10589 237) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
10590 fmax functions choose the numeric value. See F.10.9.2.
10591 238) The fmin functions are analogous to the fmax functions in their treatment of NaNs.
10595 7.12.14 Comparison macros
10596 1 The relational and equality operators support the usual mathematical relationships
10597 between numeric values. For any ordered pair of numeric values exactly one of the
10598 relationships -- less, greater, and equal -- is true. Relational operators may raise the
10599 ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a
10600 numeric value, or for two NaNs, just the unordered relationship is true.239) The following
10601 subclauses provide macros that are quiet (non floating-point exception raising) versions
10602 of the relational operators, and other comparison macros that facilitate writing efficient
10603 code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In
10604 the synopses in this subclause, real-floating indicates that the argument shall be an
10605 expression of real floating type (both arguments need not have the same type).240)
10606 7.12.14.1 The isgreater macro
10608 1 #include <math.h>
10609 int isgreater(real-floating x, real-floating y);
10611 2 The isgreater macro determines whether its first argument is greater than its second
10612 argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
10613 unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point
10614 exception when x and y are unordered.
10616 3 The isgreater macro returns the value of (x) > (y).
10617 7.12.14.2 The isgreaterequal macro
10619 1 #include <math.h>
10620 int isgreaterequal(real-floating x, real-floating y);
10622 2 The isgreaterequal macro determines whether its first argument is greater than or
10623 equal to its second argument. The value of isgreaterequal(x, y) is always equal
10624 to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
10627 239) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if
10628 the operands compare unordered, as an error indicator for programs written without consideration of
10629 NaNs; the result in these cases is false.
10630 240) Whether an argument represented in a format wider than its semantic type is converted to the semantic
10631 type is unspecified.
10635 not raise the ''invalid'' floating-point exception when x and y are unordered.
10637 3 The isgreaterequal macro returns the value of (x) >= (y).
10638 7.12.14.3 The isless macro
10640 1 #include <math.h>
10641 int isless(real-floating x, real-floating y);
10643 2 The isless macro determines whether its first argument is less than its second
10644 argument. The value of isless(x, y) is always equal to (x) < (y); however,
10645 unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point
10646 exception when x and y are unordered.
10648 3 The isless macro returns the value of (x) < (y).
10649 7.12.14.4 The islessequal macro
10651 1 #include <math.h>
10652 int islessequal(real-floating x, real-floating y);
10654 2 The islessequal macro determines whether its first argument is less than or equal to
10655 its second argument. The value of islessequal(x, y) is always equal to
10656 (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
10657 the ''invalid'' floating-point exception when x and y are unordered.
10659 3 The islessequal macro returns the value of (x) <= (y).
10660 7.12.14.5 The islessgreater macro
10662 1 #include <math.h>
10663 int islessgreater(real-floating x, real-floating y);
10665 2 The islessgreater macro determines whether its first argument is less than or
10666 greater than its second argument. The islessgreater(x, y) macro is similar to
10667 (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
10671 the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
10674 3 The islessgreater macro returns the value of (x) < (y) || (x) > (y).
10675 7.12.14.6 The isunordered macro
10677 1 #include <math.h>
10678 int isunordered(real-floating x, real-floating y);
10680 2 The isunordered macro determines whether its arguments are unordered.
10682 3 The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.
10689 7.13 Nonlocal jumps <setjmp.h>
10690 1 The header <setjmp.h> defines the macro setjmp, and declares one function and
10691 one type, for bypassing the normal function call and return discipline.241)
10692 2 The type declared is
10694 which is an array type suitable for holding the information needed to restore a calling
10695 environment. The environment of a call to the setjmp macro consists of information
10696 sufficient for a call to the longjmp function to return execution to the correct block and
10697 invocation of that block, were it called recursively. It does not include the state of the
10698 floating-point status flags, of open files, or of any other component of the abstract
10700 3 It is unspecified whether setjmp is a macro or an identifier declared with external
10701 linkage. If a macro definition is suppressed in order to access an actual function, or a
10702 program defines an external identifier with the name setjmp, the behavior is undefined.
10703 7.13.1 Save calling environment
10704 7.13.1.1 The setjmp macro
10706 1 #include <setjmp.h>
10707 int setjmp(jmp_buf env);
10709 2 The setjmp macro saves its calling environment in its jmp_buf argument for later use
10710 by the longjmp function.
10712 3 If the return is from a direct invocation, the setjmp macro returns the value zero. If the
10713 return is from a call to the longjmp function, the setjmp macro returns a nonzero
10715 Environmental limits
10716 4 An invocation of the setjmp macro shall appear only in one of the following contexts:
10717 -- the entire controlling expression of a selection or iteration statement;
10718 -- one operand of a relational or equality operator with the other operand an integer
10719 constant expression, with the resulting expression being the entire controlling
10722 241) These functions are useful for dealing with unusual conditions encountered in a low-level function of
10727 expression of a selection or iteration statement;
10728 -- the operand of a unary ! operator with the resulting expression being the entire
10729 controlling expression of a selection or iteration statement; or
10730 -- the entire expression of an expression statement (possibly cast to void).
10731 5 If the invocation appears in any other context, the behavior is undefined.
10732 7.13.2 Restore calling environment
10733 7.13.2.1 The longjmp function
10735 1 #include <setjmp.h>
10736 _Noreturn void longjmp(jmp_buf env, int val);
10738 2 The longjmp function restores the environment saved by the most recent invocation of
10739 the setjmp macro in the same invocation of the program with the corresponding
10740 jmp_buf argument. If there has been no such invocation, or if the function containing
10741 the invocation of the setjmp macro has terminated execution242) in the interim, or if the
10742 invocation of the setjmp macro was within the scope of an identifier with variably
10743 modified type and execution has left that scope in the interim, the behavior is undefined.
10744 3 All accessible objects have values, and all other components of the abstract machine243)
10745 have state, as of the time the longjmp function was called, except that the values of
10746 objects of automatic storage duration that are local to the function containing the
10747 invocation of the corresponding setjmp macro that do not have volatile-qualified type
10748 and have been changed between the setjmp invocation and longjmp call are
10751 4 After longjmp is completed, program execution continues as if the corresponding
10752 invocation of the setjmp macro had just returned the value specified by val. The
10753 longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
10754 the setjmp macro returns the value 1.
10755 5 EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
10756 might cause memory associated with a variable length array object to be squandered.
10761 242) For example, by executing a return statement or because another longjmp call has caused a
10762 transfer to a setjmp invocation in a function earlier in the set of nested calls.
10763 243) This includes, but is not limited to, the floating-point status flags and the state of open files.
10767 #include <setjmp.h>
10774 int x[n]; // valid: f is not terminated
10780 int a[n]; // a may remain allocated
10785 int b[n]; // b may remain allocated
10786 longjmp(buf, 2); // might cause memory loss
10794 7.14 Signal handling <signal.h>
10795 1 The header <signal.h> declares a type and two functions and defines several macros,
10796 for handling various signals (conditions that may be reported during program execution).
10797 2 The type defined is
10799 which is the (possibly volatile-qualified) integer type of an object that can be accessed as
10800 an atomic entity, even in the presence of asynchronous interrupts.
10801 3 The macros defined are
10805 which expand to constant expressions with distinct values that have type compatible with
10806 the second argument to, and the return value of, the signal function, and whose values
10807 compare unequal to the address of any declarable function; and the following, which
10808 expand to positive integer constant expressions with type int and distinct values that are
10809 the signal numbers, each corresponding to the specified condition:
10810 SIGABRT abnormal termination, such as is initiated by the abort function
10811 SIGFPE an erroneous arithmetic operation, such as zero divide or an operation
10812 resulting in overflow
10813 SIGILL detection of an invalid function image, such as an invalid instruction
10814 SIGINT receipt of an interactive attention signal
10815 SIGSEGV an invalid access to storage
10816 SIGTERM a termination request sent to the program
10817 4 An implementation need not generate any of these signals, except as a result of explicit
10818 calls to the raise function. Additional signals and pointers to undeclarable functions,
10819 with macro definitions beginning, respectively, with the letters SIG and an uppercase
10820 letter or with SIG_ and an uppercase letter,244) may also be specified by the
10821 implementation. The complete set of signals, their semantics, and their default handling
10822 is implementation-defined; all signal numbers shall be positive.
10827 244) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms
10828 (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
10833 7.14.1 Specify signal handling
10834 7.14.1.1 The signal function
10836 1 #include <signal.h>
10837 void (*signal(int sig, void (*func)(int)))(int);
10839 2 The signal function chooses one of three ways in which receipt of the signal number
10840 sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
10841 for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
10842 Otherwise, func shall point to a function to be called when that signal occurs. An
10843 invocation of such a function because of a signal, or (recursively) of any further functions
10844 called by that invocation (other than functions in the standard library), is called a signal
10846 3 When a signal occurs and func points to a function, it is implementation-defined
10847 whether the equivalent of signal(sig, SIG_DFL); is executed or the
10848 implementation prevents some implementation-defined set of signals (at least including
10849 sig) from occurring until the current signal handling has completed; in the case of
10850 SIGILL, the implementation may alternatively define that no action is taken. Then the
10851 equivalent of (*func)(sig); is executed. If and when the function returns, if the
10852 value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
10853 value corresponding to a computational exception, the behavior is undefined; otherwise
10854 the program will resume execution at the point it was interrupted.
10855 4 If the signal occurs as the result of calling the abort or raise function, the signal
10856 handler shall not call the raise function.
10857 5 If the signal occurs other than as the result of calling the abort or raise function, the
10858 behavior is undefined if the signal handler refers to any object with static or thread
10859 storage duration other than by assigning a value to an object declared as volatile
10860 sig_atomic_t, or the signal handler calls any function in the standard library other
10861 than the abort function, the _Exit function, the quick_exit function, or the
10862 signal function with the first argument equal to the signal number corresponding to the
10863 signal that caused the invocation of the handler. Furthermore, if such a call to the
10864 signal function results in a SIG_ERR return, the value of errno is indeterminate.245)
10865 6 At program startup, the equivalent of
10866 signal(sig, SIG_IGN);
10869 245) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
10873 may be executed for some signals selected in an implementation-defined manner; the
10875 signal(sig, SIG_DFL);
10876 is executed for all other signals defined by the implementation.
10877 7 The implementation shall behave as if no library function calls the signal function.
10879 8 If the request can be honored, the signal function returns the value of func for the
10880 most recent successful call to signal for the specified signal sig. Otherwise, a value of
10881 SIG_ERR is returned and a positive value is stored in errno.
10882 Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
10883 _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).
10885 7.14.2.1 The raise function
10887 1 #include <signal.h>
10888 int raise(int sig);
10890 2 The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
10891 signal handler is called, the raise function shall not return until after the signal handler
10894 3 The raise function returns zero if successful, nonzero if unsuccessful.
10901 7.15 Alignment <stdalign.h>
10902 1 The header <stdalign.h> defines two macros.
10905 expands to _Alignas.
10906 3 The remaining macro is suitable for use in #if preprocessing directives. It is
10907 __alignas_is_defined
10908 which expands to the integer constant 1.
10915 7.16 Variable arguments <stdarg.h>
10916 1 The header <stdarg.h> declares a type and defines four macros, for advancing
10917 through a list of arguments whose number and types are not known to the called function
10918 when it is translated.
10919 2 A function may be called with a variable number of arguments of varying types. As
10920 described in 6.9.1, its parameter list contains one or more parameters. The rightmost
10921 parameter plays a special role in the access mechanism, and will be designated parmN in
10923 3 The type declared is
10925 which is a complete object type suitable for holding information needed by the macros
10926 va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
10927 desired, the called function shall declare an object (generally referred to as ap in this
10928 subclause) having type va_list. The object ap may be passed as an argument to
10929 another function; if that function invokes the va_arg macro with parameter ap, the
10930 value of ap in the calling function is indeterminate and shall be passed to the va_end
10931 macro prior to any further reference to ap.246)
10932 7.16.1 Variable argument list access macros
10933 1 The va_start and va_arg macros described in this subclause shall be implemented
10934 as macros, not functions. It is unspecified whether va_copy and va_end are macros or
10935 identifiers declared with external linkage. If a macro definition is suppressed in order to
10936 access an actual function, or a program defines an external identifier with the same name,
10937 the behavior is undefined. Each invocation of the va_start and va_copy macros
10938 shall be matched by a corresponding invocation of the va_end macro in the same
10940 7.16.1.1 The va_arg macro
10942 1 #include <stdarg.h>
10943 type va_arg(va_list ap, type);
10945 2 The va_arg macro expands to an expression that has the specified type and the value of
10946 the next argument in the call. The parameter ap shall have been initialized by the
10947 va_start or va_copy macro (without an intervening invocation of the va_end
10949 246) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
10950 case the original function may make further use of the original list after the other function returns.
10954 macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
10955 values of successive arguments are returned in turn. The parameter type shall be a type
10956 name specified such that the type of a pointer to an object that has the specified type can
10957 be obtained simply by postfixing a * to type. If there is no actual next argument, or if
10958 type is not compatible with the type of the actual next argument (as promoted according
10959 to the default argument promotions), the behavior is undefined, except for the following
10961 -- one type is a signed integer type, the other type is the corresponding unsigned integer
10962 type, and the value is representable in both types;
10963 -- one type is pointer to void and the other is a pointer to a character type.
10965 3 The first invocation of the va_arg macro after that of the va_start macro returns the
10966 value of the argument after that specified by parmN . Successive invocations return the
10967 values of the remaining arguments in succession.
10968 7.16.1.2 The va_copy macro
10970 1 #include <stdarg.h>
10971 void va_copy(va_list dest, va_list src);
10973 2 The va_copy macro initializes dest as a copy of src, as if the va_start macro had
10974 been applied to dest followed by the same sequence of uses of the va_arg macro as
10975 had previously been used to reach the present state of src. Neither the va_copy nor
10976 va_start macro shall be invoked to reinitialize dest without an intervening
10977 invocation of the va_end macro for the same dest.
10979 3 The va_copy macro returns no value.
10980 7.16.1.3 The va_end macro
10982 1 #include <stdarg.h>
10983 void va_end(va_list ap);
10985 2 The va_end macro facilitates a normal return from the function whose variable
10986 argument list was referred to by the expansion of the va_start macro, or the function
10987 containing the expansion of the va_copy macro, that initialized the va_list ap. The
10988 va_end macro may modify ap so that it is no longer usable (without being reinitialized
10992 by the va_start or va_copy macro). If there is no corresponding invocation of the
10993 va_start or va_copy macro, or if the va_end macro is not invoked before the
10994 return, the behavior is undefined.
10996 3 The va_end macro returns no value.
10997 7.16.1.4 The va_start macro
10999 1 #include <stdarg.h>
11000 void va_start(va_list ap, parmN);
11002 2 The va_start macro shall be invoked before any access to the unnamed arguments.
11003 3 The va_start macro initializes ap for subsequent use by the va_arg and va_end
11004 macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
11005 without an intervening invocation of the va_end macro for the same ap.
11006 4 The parameter parmN is the identifier of the rightmost parameter in the variable
11007 parameter list in the function definition (the one just before the , ...). If the parameter
11008 parmN is declared with the register storage class, with a function or array type, or
11009 with a type that is not compatible with the type that results after application of the default
11010 argument promotions, the behavior is undefined.
11012 5 The va_start macro returns no value.
11013 6 EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
11014 more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
11015 pointers is specified by the first argument to f1.
11016 #include <stdarg.h>
11018 void f1(int n_ptrs, ...)
11021 char *array[MAXARGS];
11029 if (n_ptrs > MAXARGS)
11031 va_start(ap, n_ptrs);
11032 while (ptr_no < n_ptrs)
11033 array[ptr_no++] = va_arg(ap, char *);
11037 Each call to f1 is required to have visible the definition of the function or a declaration such as
11040 7 EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
11041 indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
11042 is gathered again and passed to function f4.
11043 #include <stdarg.h>
11045 void f3(int n_ptrs, int f4_after, ...)
11047 va_list ap, ap_save;
11048 char *array[MAXARGS];
11050 if (n_ptrs > MAXARGS)
11052 va_start(ap, f4_after);
11053 while (ptr_no < n_ptrs) {
11054 array[ptr_no++] = va_arg(ap, char *);
11055 if (ptr_no == f4_after)
11056 va_copy(ap_save, ap);
11060 // Now process the saved copy.
11061 n_ptrs -= f4_after;
11063 while (ptr_no < n_ptrs)
11064 array[ptr_no++] = va_arg(ap_save, char *);
11074 7.17 Atomics <stdatomic.h>
11075 7.17.1 Introduction
11076 1 The header <stdatomic.h> defines several macros and declares several types and
11077 functions for performing atomic operations on data shared between threads.
11078 2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
11079 this header nor support any of its facilities.
11080 3 The macros defined are the atomic lock-free macros
11081 ATOMIC_CHAR_LOCK_FREE
11082 ATOMIC_CHAR16_T_LOCK_FREE
11083 ATOMIC_CHAR32_T_LOCK_FREE
11084 ATOMIC_WCHAR_T_LOCK_FREE
11085 ATOMIC_SHORT_LOCK_FREE
11086 ATOMIC_INT_LOCK_FREE
11087 ATOMIC_LONG_LOCK_FREE
11088 ATOMIC_LLONG_LOCK_FREE
11089 ATOMIC_ADDRESS_LOCK_FREE
11090 which indicate the lock-free property of the corresponding atomic types (both signed and
11093 which expands to an initializer for an object of type atomic_flag.
11094 4 The types include
11096 which is an enumerated type whose enumerators identify memory ordering constraints;
11098 which is a structure type representing a lock-free, primitive atomic flag;
11100 which is a structure type representing the atomic analog of the type _Bool;
11102 which is a structure type representing the atomic analog of a pointer type; and several
11103 atomic analogs of integer types.
11104 5 In the following operation definitions:
11105 -- An A refers to one of the atomic types.
11110 -- A C refers to its corresponding non-atomic type. The atomic_address atomic
11111 type corresponds to the void * non-atomic type.
11112 -- An M refers to the type of the other argument for arithmetic operations. For atomic
11113 integer types, M is C. For atomic address types, M is ptrdiff_t.
11114 -- The functions not ending in _explicit have the same semantics as the
11115 corresponding _explicit function with memory_order_seq_cst for the
11116 memory_order argument.
11117 6 NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not
11118 changed in the standard. This qualification means that volatility is preserved when applying these
11119 operations to volatile objects.
11121 7.17.2 Initialization
11122 7.17.2.1 The ATOMIC_VAR_INIT macro
11124 1 #include <stdatomic.h>
11125 #define ATOMIC_VAR_INIT(C value)
11127 2 The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
11128 atomic object of a type that is initialization-compatible with value. An atomic object
11129 with automatic storage duration that is not explicitly initialized using
11130 ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
11131 initialization for objects with static or thread-local storage duration is guaranteed to
11132 produce a valid state.
11133 3 Concurrent access to the variable being initialized, even via an atomic operation,
11134 constitutes a data race.
11136 atomic_int guide = ATOMIC_VAR_INIT(42);
11138 7.17.2.2 The atomic_init generic function
11140 1 #include <stdatomic.h>
11141 void atomic_init(volatile A *obj, C value);
11143 2 The atomic_init generic function initializes the atomic object pointed to by obj to
11144 the value value, while also initializing any additional state that the implementation
11145 might need to carry for the atomic object.
11151 3 Although this function initializes an atomic object, it does not avoid data races;
11152 concurrent access to the variable being initialized, even via an atomic operation,
11153 constitutes a data race.
11155 4 The atomic_init generic function returns no value.
11158 atomic_init(&guide, 42);
11160 7.17.3 Order and consistency
11161 1 The enumerated type memory_order specifies the detailed regular (non-atomic)
11162 memory synchronization operations as defined in 5.1.2.4 and may provide for operation
11163 ordering. Its enumeration constants are as follows:
11164 memory_order_relaxed
11165 memory_order_consume
11166 memory_order_acquire
11167 memory_order_release
11168 memory_order_acq_rel
11169 memory_order_seq_cst
11170 2 For memory_order_relaxed, no operation orders memory.
11171 3 For memory_order_release, memory_order_acq_rel, and
11172 memory_order_seq_cst, a store operation performs a release operation on the
11173 affected memory location.
11174 4 For memory_order_acquire, memory_order_acq_rel, and
11175 memory_order_seq_cst, a load operation performs an acquire operation on the
11176 affected memory location.
11177 5 For memory_order_consume, a load operation performs a consume operation on the
11178 affected memory location.
11179 6 For memory_order_seq_cst, there shall be a single total order S on all operations,
11180 consistent with the ''happens before'' order and modification orders for all affected
11181 locations, such that each memory_order_seq_cst operation that loads a value
11182 observes either the last preceding modification according to this order S, or the result of
11183 an operation that is not memory_order_seq_cst.
11184 7 NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
11185 an order that does include lock and unlock operations, since the ordering between those is already included
11186 in the ''happens before'' ordering.
11188 8 NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
11189 memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
11193 object be indivisible with respect to all other atomic accesses to that object.
11195 9 For an atomic operation B that reads the value of an atomic object M, if there is a
11196 memory_order_seq_cst fence X sequenced before B, then B observes either the
11197 last memory_order_seq_cst modification of M preceding X in the total order S or
11198 a later modification of M in its modification order.
11199 10 For atomic operations A and B on an atomic object M, where A modifies M and B takes
11200 its value, if there is a memory_order_seq_cst fence X such that A is sequenced
11201 before X and B follows X in S, then B observes either the effects of A or a later
11202 modification of M in its modification order.
11203 11 For atomic operations A and B on an atomic object M, where A modifies M and B takes
11204 its value, if there are memory_order_seq_cst fences X and Y such that A is
11205 sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
11206 either the effects of A or a later modification of M in its modification order.
11207 12 Atomic read-modify-write operations shall always read the last value (in the modification
11208 order) stored before the write associated with the read-modify-write operation.
11209 13 An atomic store shall only store a value that has been computed from constants and
11210 program input values by a finite sequence of program evaluations, such that each
11211 evaluation observes the values of variables as computed by the last prior assignment in
11212 the sequence.247) The ordering of evaluations in this sequence shall be such that
11213 -- If an evaluation B observes a value computed by A in a different thread, then B does
11214 not happen before A.
11215 -- If an evaluation A is included in the sequence, then all evaluations that assign to the
11216 same variable and happen before A are also included.
11217 14 NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when
11218 relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
11219 sequence out of thread order. For example, with x and y initially zero,
11221 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11222 atomic_store_explicit(&x, r1, memory_order_relaxed);
11225 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11226 atomic_store_explicit(&y, 42, memory_order_relaxed);
11227 is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
11232 247) Among other implications, atomic variables shall not decay.
11236 atomic_store_explicit(&y, 42, memory_order_relaxed);
11237 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11238 atomic_store_explicit(&x, r1, memory_order_relaxed);
11239 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11242 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11243 atomic_store_explicit(&x, r1, memory_order_relaxed);
11246 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11247 atomic_store_explicit(&y, r2, memory_order_relaxed);
11248 is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
11249 in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with
11250 weaker than memory_order_acq_rel ordering, the second requirement has no impact.
11252 Recommended practice
11253 15 The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
11254 with x and y initially zero:
11256 r1 = atomic_load_explicit(&x, memory_order_relaxed);
11258 atomic_store_explicit(&y, r1, memory_order_relaxed);
11261 r2 = atomic_load_explicit(&y, memory_order_relaxed);
11263 atomic_store_explicit(&x, 42, memory_order_relaxed);
11264 However, this is not useful behavior, and implementations should not allow it.
11265 16 Implementations should make atomic stores visible to atomic loads within a reasonable
11267 7.17.3.1 The kill_dependency macro
11269 1 #include <stdatomic.h>
11270 type kill_dependency(type y);
11272 2 The kill_dependency macro terminates a dependency chain; the argument does not
11273 carry a dependency to the return value.
11280 3 The kill_dependency macro returns the value of y.
11282 1 This subclause introduces synchronization primitives called fences. Fences can have
11283 acquire semantics, release semantics, or both. A fence with acquire semantics is called
11284 an acquire fence; a fence with release semantics is called a release fence.
11285 2 A release fence A synchronizes with an acquire fence B if there exist atomic operations
11286 X and Y , both operating on some atomic object M, such that A is sequenced before X, X
11287 modifies M, Y is sequenced before B, and Y reads the value written by X or a value
11288 written by any side effect in the hypothetical release sequence X would head if it were a
11290 3 A release fence A synchronizes with an atomic operation B that performs an acquire
11291 operation on an atomic object M if there exists an atomic operation X such that A is
11292 sequenced before X, X modifies M, and B reads the value written by X or a value written
11293 by any side effect in the hypothetical release sequence X would head if it were a release
11295 4 An atomic operation A that is a release operation on an atomic object M synchronizes
11296 with an acquire fence B if there exists some atomic operation X on M such that X is
11297 sequenced before B and reads the value written by A or a value written by any side effect
11298 in the release sequence headed by A.
11299 7.17.4.1 The atomic_thread_fence function
11301 1 #include <stdatomic.h>
11302 void atomic_thread_fence(memory_order order);
11304 2 Depending on the value of order, this operation:
11305 -- has no effects, if order == memory_order_relaxed;
11306 -- is an acquire fence, if order == memory_order_acquire or order ==
11307 memory_order_consume;
11308 -- is a release fence, if order == memory_order_release;
11309 -- is both an acquire fence and a release fence, if order ==
11310 memory_order_acq_rel;
11311 -- is a sequentially consistent acquire and release fence, if order ==
11312 memory_order_seq_cst.
11318 3 The atomic_thread_fence function returns no value.
11319 7.17.4.2 The atomic_signal_fence function
11321 1 #include <stdatomic.h>
11322 void atomic_signal_fence(memory_order order);
11324 2 Equivalent to atomic_thread_fence(order), except that ''synchronizes with''
11325 relationships are established only between a thread and a signal handler executed in the
11327 3 NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
11328 performed by the thread become visible to the signal handler.
11330 4 NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
11331 atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
11332 have inserted are not emitted.
11335 5 The atomic_signal_fence function returns no value.
11336 7.17.5 Lock-free property
11337 1 The atomic lock-free macros indicate the lock-free property of integer and address atomic
11338 types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
11339 the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
11340 2 NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
11341 memory location via two different addresses will communicate atomically. The implementation should not
11342 depend on any per-process state. This restriction enables communication via memory mapped into a
11343 process more than once and memory shared between two processes.
11345 7.17.5.1 The atomic_is_lock_free generic function
11347 1 #include <stdatomic.h>
11348 _Bool atomic_is_lock_free(atomic_type const volatile *obj);
11350 2 The atomic_is_lock_free generic function indicates whether or not the object
11351 pointed to by obj is lock-free. atomic_type can be any atomic type.
11353 3 The atomic_is_lock_free generic function returns nonzero (true) if and only if the
11354 object's operations are lock-free. The result of a lock-free query on one object cannot be
11358 inferred from the result of a lock-free query on another object.
11359 7.17.6 Atomic integer and address types
11360 1 For each line in the following table, the atomic type name is declared as the
11361 corresponding direct type.
11370 Atomic type name Direct type
11371 atomic_char _Atomic char
11372 atomic_schar _Atomic signed char
11373 atomic_uchar _Atomic unsigned char
11374 atomic_short _Atomic short
11375 atomic_ushort _Atomic unsigned short
11376 atomic_int _Atomic int
11377 atomic_uint _Atomic unsigned int
11378 atomic_long _Atomic long
11379 atomic_ulong _Atomic unsigned long
11380 atomic_llong _Atomic long long
11381 atomic_ullong _Atomic unsigned long long
11382 atomic_char16_t _Atomic char16_t
11383 atomic_char32_t _Atomic char32_t
11384 atomic_wchar_t _Atomic wchar_t
11385 atomic_int_least8_t _Atomic int_least8_t
11386 atomic_uint_least8_t _Atomic uint_least8_t
11387 atomic_int_least16_t _Atomic int_least16_t
11388 atomic_uint_least16_t _Atomic uint_least16_t
11389 atomic_int_least32_t _Atomic int_least32_t
11390 atomic_uint_least32_t _Atomic uint_least32_t
11391 atomic_int_least64_t _Atomic int_least64_t
11392 atomic_uint_least64_t _Atomic uint_least64_t
11393 atomic_int_fast8_t _Atomic int_fast8_t
11394 atomic_uint_fast8_t _Atomic uint_fast8_t
11395 atomic_int_fast16_t _Atomic int_fast16_t
11396 atomic_uint_fast16_t _Atomic uint_fast16_t
11397 atomic_int_fast32_t _Atomic int_fast32_t
11398 atomic_uint_fast32_t _Atomic uint_fast32_t
11399 atomic_int_fast64_t _Atomic int_fast64_t
11400 atomic_uint_fast64_t _Atomic uint_fast64_t
11401 atomic_intptr_t _Atomic intptr_t
11402 atomic_uintptr_t _Atomic uintptr_t
11403 atomic_size_t _Atomic size_t
11404 atomic_ptrdiff_t _Atomic ptrdiff_t
11405 atomic_intmax_t _Atomic intmax_t
11406 atomic_uintmax_t _Atomic uintmax_t
11407 2 The semantics of the operations on these types are defined in 7.17.7.
11413 3 The atomic_bool type provides an atomic boolean.
11414 4 The atomic_address type provides atomic void * operations. The unit of
11415 addition/subtraction shall be one byte.
11416 5 NOTE The representation of atomic integer and address types need not have the same size as their
11417 corresponding regular types. They should have the same size whenever possible, as it eases effort required
11418 to port existing code.
11420 7.17.7 Operations on atomic types
11421 1 There are only a few kinds of operations on atomic types, though there are many
11422 instances of those kinds. This subclause specifies each general kind.
11423 7.17.7.1 The atomic_store generic functions
11425 1 #include <stdatomic.h>
11426 void atomic_store(volatile A *object, C desired);
11427 void atomic_store_explicit(volatile A *object,
11428 C desired, memory_order order);
11430 2 The order argument shall not be memory_order_acquire,
11431 memory_order_consume, nor memory_order_acq_rel. Atomically replace the
11432 value pointed to by object with the value of desired. Memory is affected according
11433 to the value of order.
11435 3 The atomic_store generic functions return no value.
11436 7.17.7.2 The atomic_load generic functions
11438 1 #include <stdatomic.h>
11439 C atomic_load(volatile A *object);
11440 C atomic_load_explicit(volatile A *object,
11441 memory_order order);
11443 2 The order argument shall not be memory_order_release nor
11444 memory_order_acq_rel. Memory is affected according to the value of order.
11446 Atomically returns the value pointed to by object.
11452 7.17.7.3 The atomic_exchange generic functions
11454 1 #include <stdatomic.h>
11455 C atomic_exchange(volatile A *object, C desired);
11456 C atomic_exchange_explicit(volatile A *object,
11457 C desired, memory_order order);
11459 2 Atomically replace the value pointed to by object with desired. Memory is affected
11460 according to the value of order. These operations are read-modify-write operations
11463 3 Atomically returns the value pointed to by object immediately before the effects.
11464 7.17.7.4 The atomic_compare_exchange generic functions
11466 1 #include <stdatomic.h>
11467 _Bool atomic_compare_exchange_strong(volatile A *object,
11468 C *expected, C desired);
11469 _Bool atomic_compare_exchange_strong_explicit(
11470 volatile A *object, C *expected, C desired,
11471 memory_order success, memory_order failure);
11472 _Bool atomic_compare_exchange_weak(volatile A *object,
11473 C *expected, C desired);
11474 _Bool atomic_compare_exchange_weak_explicit(
11475 volatile A *object, C *expected, C desired,
11476 memory_order success, memory_order failure);
11478 2 The failure argument shall not be memory_order_release nor
11479 memory_order_acq_rel. The failure argument shall be no stronger than the
11480 success argument. Atomically, compares the value pointed to by object for equality
11481 with that in expected, and if true, replaces the value pointed to by object with
11482 desired, and if false, updates the value in expected with the value pointed to by
11483 object. Further, if the comparison is true, memory is affected according to the value of
11484 success, and if the comparison is false, memory is affected according to the value of
11485 failure. These operations are atomic read-modify-write operations (5.1.2.4).
11486 3 NOTE 1 The effect of the compare-and-exchange operations is
11493 if (*object == *expected)
11496 *expected = *object;
11498 4 The weak compare-and-exchange operations may fail spuriously, that is, return zero
11499 while leaving the value pointed to by expected unchanged.
11500 5 NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
11501 machines, e.g. load-locked store-conditional machines.
11503 6 EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
11505 exp = atomic_load(&cur);
11507 des = function(exp);
11508 } while (!atomic_compare_exchange_weak(&cur, &exp, des));
11509 When a compare-and-exchange is in a loop, the weak version will yield better performance on some
11510 platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
11511 strong one is preferable.
11514 7 The result of the comparison.
11515 7.17.7.5 The atomic_fetch and modify generic functions
11516 1 The following operations perform arithmetic and bitwise computations. All of these
11517 operations are applicable to an object of any atomic integer type. Only addition and
11518 subtraction are applicable to atomic_address. None of these operations is applicable
11519 to atomic_bool. The key, operator, and computation correspondence is:
11525 or | bitwise inclusive or
11526 xor ^ bitwise exclusive or
11529 2 #include <stdatomic.h>
11530 C atomic_fetch_key(volatile A *object, M operand);
11531 C atomic_fetch_key_explicit(volatile A *object,
11532 M operand, memory_order order);
11534 3 Atomically replaces the value pointed to by object with the result of the computation
11535 applied to the value pointed to by object and the given operand. Memory is affected
11538 according to the value of order. These operations are atomic read-modify-write
11539 operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's-
11540 complement representation. There are no undefined results. For address types, the result
11541 may be an undefined address, but the operations otherwise have no undefined behavior.
11543 4 Atomically, the value pointed to by object immediately before the effects.
11544 5 NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
11545 operation of the corresponding op= compound assignment operators. The only differences are that the
11546 compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
11547 compound assignment operator is the updated value of the object, whereas the value returned by the
11548 atomic_fetch and modify generic functions is the previous value of the atomic object.
11550 7.17.8 Atomic flag type and operations
11551 1 The atomic_flag type provides the classic test-and-set functionality. It has two
11552 states, set and clear.
11553 2 Operations on an object of type atomic_flag shall be lock free.
11554 3 NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
11555 the atomic_flag type is the minimum hardware-implemented type needed to conform to this
11556 International standard. The remaining types can be emulated with atomic_flag, though with less than
11559 4 The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
11560 clear state. An atomic_flag that is not explicitly initialized with
11561 ATOMIC_FLAG_INIT is initially in an indeterminate state.
11563 atomic_flag guard = ATOMIC_FLAG_INIT;
11565 7.17.8.1 The atomic_flag_test_and_set functions
11567 1 #include <stdatomic.h>
11568 bool atomic_flag_test_and_set(
11569 volatile atomic_flag *object);
11570 bool atomic_flag_test_and_set_explicit(
11571 volatile atomic_flag *object, memory_order order);
11573 2 Atomically sets the value pointed to by object to true. Memory is affected according
11574 to the value of order. These operations are atomic read-modify-write operations
11583 3 Atomically, the value of the object immediately before the effects.
11584 7.17.8.2 The atomic_flag_clear functions
11586 1 #include <stdatomic.h>
11587 void atomic_flag_clear(volatile atomic_flag *object);
11588 void atomic_flag_clear_explicit(
11589 volatile atomic_flag *object, memory_order order);
11591 2 The order argument shall not be memory_order_acquire nor
11592 memory_order_acq_rel. Atomically sets the value pointed to by object to false.
11593 Memory is affected according to the value of order.
11595 3 The atomic_flag_clear functions return no value.
11602 7.18 Boolean type and values <stdbool.h>
11603 1 The header <stdbool.h> defines four macros.
11607 3 The remaining three macros are suitable for use in #if preprocessing directives. They
11610 which expands to the integer constant 1,
11612 which expands to the integer constant 0, and
11613 __bool_true_false_are_defined
11614 which expands to the integer constant 1.
11615 4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
11616 redefine the macros bool, true, and false.248)
11621 248) See ''future library directions'' (7.30.7).
11625 7.19 Common definitions <stddef.h>
11626 1 The header <stddef.h> defines the following macros and declares the following types.
11627 Some are also defined in other headers, as noted in their respective subclauses.
11630 which is the signed integer type of the result of subtracting two pointers;
11632 which is the unsigned integer type of the result of the sizeof operator;
11634 which is an object type whose alignment is as great as is supported by the implementation
11635 in all contexts; and
11637 which is an integer type whose range of values can represent distinct codes for all
11638 members of the largest extended character set specified among the supported locales; the
11639 null character shall have the code value zero. Each member of the basic character set
11640 shall have a code value equal to its value when used as the lone character in an integer
11641 character constant if an implementation does not define
11642 __STDC_MB_MIGHT_NEQ_WC__.
11645 which expands to an implementation-defined null pointer constant; and
11646 offsetof(type, member-designator)
11647 which expands to an integer constant expression that has type size_t, the value of
11648 which is the offset in bytes, to the structure member (designated by member-designator),
11649 from the beginning of its structure (designated by type). The type and member designator
11650 shall be such that given
11652 then the expression &(t.member-designator) evaluates to an address constant. (If the
11653 specified member is a bit-field, the behavior is undefined.)
11654 Recommended practice
11655 4 The types used for size_t and ptrdiff_t should not have an integer conversion rank
11656 greater than that of signed long int unless the implementation supports objects
11657 large enough to make this necessary.
11661 Forward references: localization (7.11).
11668 7.20 Integer types <stdint.h>
11669 1 The header <stdint.h> declares sets of integer types having specified widths, and
11670 defines corresponding sets of macros.249) It also defines macros that specify limits of
11671 integer types corresponding to types defined in other standard headers.
11672 2 Types are defined in the following categories:
11673 -- integer types having certain exact widths;
11674 -- integer types having at least certain specified widths;
11675 -- fastest integer types having at least certain specified widths;
11676 -- integer types wide enough to hold pointers to objects;
11677 -- integer types having greatest width.
11678 (Some of these types may denote the same type.)
11679 3 Corresponding macros specify limits of the declared types and construct suitable
11681 4 For each type described herein that the implementation provides,250) <stdint.h> shall
11682 declare that typedef name and define the associated macros. Conversely, for each type
11683 described herein that the implementation does not provide, <stdint.h> shall not
11684 declare that typedef name nor shall it define the associated macros. An implementation
11685 shall provide those types described as ''required'', but need not provide any of the others
11686 (described as ''optional'').
11687 7.20.1 Integer types
11688 1 When typedef names differing only in the absence or presence of the initial u are defined,
11689 they shall denote corresponding signed and unsigned types as described in 6.2.5; an
11690 implementation providing one of these corresponding types shall also provide the other.
11691 2 In the following descriptions, the symbol N represents an unsigned decimal integer with
11692 no leading zeros (e.g., 8 or 24, but not 04 or 048).
11697 249) See ''future library directions'' (7.30.8).
11698 250) Some of these types may denote implementation-defined extended integer types.
11702 7.20.1.1 Exact-width integer types
11703 1 The typedef name intN_t designates a signed integer type with width N , no padding
11704 bits, and a two's complement representation. Thus, int8_t denotes such a signed
11705 integer type with a width of exactly 8 bits.
11706 2 The typedef name uintN_t designates an unsigned integer type with width N and no
11707 padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
11709 3 These types are optional. However, if an implementation provides integer types with
11710 widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
11711 two's complement representation, it shall define the corresponding typedef names.
11712 7.20.1.2 Minimum-width integer types
11713 1 The typedef name int_leastN_t designates a signed integer type with a width of at
11714 least N , such that no signed integer type with lesser size has at least the specified width.
11715 Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
11716 2 The typedef name uint_leastN_t designates an unsigned integer type with a width
11717 of at least N , such that no unsigned integer type with lesser size has at least the specified
11718 width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
11720 3 The following types are required:
11721 int_least8_t uint_least8_t
11722 int_least16_t uint_least16_t
11723 int_least32_t uint_least32_t
11724 int_least64_t uint_least64_t
11725 All other types of this form are optional.
11726 7.20.1.3 Fastest minimum-width integer types
11727 1 Each of the following types designates an integer type that is usually fastest251) to operate
11728 with among all integer types that have at least the specified width.
11729 2 The typedef name int_fastN_t designates the fastest signed integer type with a width
11730 of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
11731 type with a width of at least N .
11736 251) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
11737 grounds for choosing one type over another, it will simply pick some integer type satisfying the
11738 signedness and width requirements.
11742 3 The following types are required:
11743 int_fast8_t uint_fast8_t
11744 int_fast16_t uint_fast16_t
11745 int_fast32_t uint_fast32_t
11746 int_fast64_t uint_fast64_t
11747 All other types of this form are optional.
11748 7.20.1.4 Integer types capable of holding object pointers
11749 1 The following type designates a signed integer type with the property that any valid
11750 pointer to void can be converted to this type, then converted back to pointer to void,
11751 and the result will compare equal to the original pointer:
11753 The following type designates an unsigned integer type with the property that any valid
11754 pointer to void can be converted to this type, then converted back to pointer to void,
11755 and the result will compare equal to the original pointer:
11757 These types are optional.
11758 7.20.1.5 Greatest-width integer types
11759 1 The following type designates a signed integer type capable of representing any value of
11760 any signed integer type:
11762 The following type designates an unsigned integer type capable of representing any value
11763 of any unsigned integer type:
11765 These types are required.
11766 7.20.2 Limits of specified-width integer types
11767 1 The following object-like macros specify the minimum and maximum limits of the types
11768 declared in <stdint.h>. Each macro name corresponds to a similar type name in
11770 2 Each instance of any defined macro shall be replaced by a constant expression suitable
11771 for use in #if preprocessing directives, and this expression shall have the same type as
11772 would an expression that is an object of the corresponding type converted according to
11773 the integer promotions. Its implementation-defined value shall be equal to or greater in
11774 magnitude (absolute value) than the corresponding value given below, with the same sign,
11775 except where stated to be exactly the given value.
11779 7.20.2.1 Limits of exact-width integer types
11780 1 -- minimum values of exact-width signed integer types
11781 INTN_MIN exactly -(2 N -1 )
11782 -- maximum values of exact-width signed integer types
11783 INTN_MAX exactly 2 N -1 - 1
11784 -- maximum values of exact-width unsigned integer types
11785 UINTN_MAX exactly 2 N - 1
11786 7.20.2.2 Limits of minimum-width integer types
11787 1 -- minimum values of minimum-width signed integer types
11788 INT_LEASTN_MIN -(2 N -1 - 1)
11789 -- maximum values of minimum-width signed integer types
11790 INT_LEASTN_MAX 2 N -1 - 1
11791 -- maximum values of minimum-width unsigned integer types
11792 UINT_LEASTN_MAX 2N - 1
11793 7.20.2.3 Limits of fastest minimum-width integer types
11794 1 -- minimum values of fastest minimum-width signed integer types
11795 INT_FASTN_MIN -(2 N -1 - 1)
11796 -- maximum values of fastest minimum-width signed integer types
11797 INT_FASTN_MAX 2 N -1 - 1
11798 -- maximum values of fastest minimum-width unsigned integer types
11799 UINT_FASTN_MAX 2N - 1
11800 7.20.2.4 Limits of integer types capable of holding object pointers
11801 1 -- minimum value of pointer-holding signed integer type
11802 INTPTR_MIN -(215 - 1)
11803 -- maximum value of pointer-holding signed integer type
11805 -- maximum value of pointer-holding unsigned integer type
11806 UINTPTR_MAX 216 - 1
11812 7.20.2.5 Limits of greatest-width integer types
11813 1 -- minimum value of greatest-width signed integer type
11814 INTMAX_MIN -(263 - 1)
11815 -- maximum value of greatest-width signed integer type
11817 -- maximum value of greatest-width unsigned integer type
11818 UINTMAX_MAX 264 - 1
11819 7.20.3 Limits of other integer types
11820 1 The following object-like macros specify the minimum and maximum limits of integer
11821 types corresponding to types defined in other standard headers.
11822 2 Each instance of these macros shall be replaced by a constant expression suitable for use
11823 in #if preprocessing directives, and this expression shall have the same type as would an
11824 expression that is an object of the corresponding type converted according to the integer
11825 promotions. Its implementation-defined value shall be equal to or greater in magnitude
11826 (absolute value) than the corresponding value given below, with the same sign. An
11827 implementation shall define only the macros corresponding to those typedef names it
11828 actually provides.252)
11829 -- limits of ptrdiff_t
11832 -- limits of sig_atomic_t
11833 SIG_ATOMIC_MIN see below
11834 SIG_ATOMIC_MAX see below
11837 -- limits of wchar_t
11838 WCHAR_MIN see below
11839 WCHAR_MAX see below
11840 -- limits of wint_t
11845 252) A freestanding implementation need not provide all of these types.
11851 3 If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
11852 SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
11853 shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
11854 type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
11855 SIG_ATOMIC_MAX shall be no less than 255.
11856 4 If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
11857 shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
11858 otherwise, wchar_t is defined as an unsigned integer type, and the value of
11859 WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.253)
11860 5 If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall
11861 be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
11862 otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
11863 shall be 0 and the value of WINT_MAX shall be no less than 65535.
11864 7.20.4 Macros for integer constants
11865 1 The following function-like macros expand to integer constants suitable for initializing
11866 objects that have integer types corresponding to types defined in <stdint.h>. Each
11867 macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
11868 2 The argument in any instance of these macros shall be an unsuffixed integer constant (as
11869 defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
11870 3 Each invocation of one of these macros shall expand to an integer constant expression
11871 suitable for use in #if preprocessing directives. The type of the expression shall have
11872 the same type as would an expression of the corresponding type converted according to
11873 the integer promotions. The value of the expression shall be that of the argument.
11874 7.20.4.1 Macros for minimum-width integer constants
11875 1 The macro INTN_C(value) shall expand to an integer constant expression
11876 corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
11877 to an integer constant expression corresponding to the type uint_leastN_t. For
11878 example, if uint_least64_t is a name for the type unsigned long long int,
11879 then UINT64_C(0x123) might expand to the integer constant 0x123ULL.
11884 253) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
11889 7.20.4.2 Macros for greatest-width integer constants
11890 1 The following macro expands to an integer constant expression having the value specified
11891 by its argument and the type intmax_t:
11893 The following macro expands to an integer constant expression having the value specified
11894 by its argument and the type uintmax_t:
11902 7.21 Input/output <stdio.h>
11903 7.21.1 Introduction
11904 1 The header <stdio.h> defines several macros, and declares three types and many
11905 functions for performing input and output.
11906 2 The types declared are size_t (described in 7.19);
11908 which is an object type capable of recording all the information needed to control a
11909 stream, including its file position indicator, a pointer to its associated buffer (if any), an
11910 error indicator that records whether a read/write error has occurred, and an end-of-file
11911 indicator that records whether the end of the file has been reached; and
11913 which is a complete object type other than an array type capable of recording all the
11914 information needed to specify uniquely every position within a file.
11915 3 The macros are NULL (described in 7.19);
11919 which expand to integer constant expressions with distinct values, suitable for use as the
11920 third argument to the setvbuf function;
11922 which expands to an integer constant expression that is the size of the buffer used by the
11925 which expands to an integer constant expression, with type int and a negative value, that
11926 is returned by several functions to indicate end-of-file, that is, no more input from a
11929 which expands to an integer constant expression that is the minimum number of files that
11930 the implementation guarantees can be open simultaneously;
11932 which expands to an integer constant expression that is the size needed for an array of
11933 char large enough to hold the longest file name string that the implementation
11939 guarantees can be opened;254)
11941 which expands to an integer constant expression that is the size needed for an array of
11942 char large enough to hold a temporary file name string generated by the tmpnam
11947 which expand to integer constant expressions with distinct values, suitable for use as the
11948 third argument to the fseek function;
11950 which expands to an integer constant expression that is the minimum number of unique
11951 file names that can be generated by the tmpnam function;
11955 which are expressions of type ''pointer to FILE'' that point to the FILE objects
11956 associated, respectively, with the standard error, input, and output streams.
11957 4 The header <wchar.h> declares a number of functions useful for wide character input
11958 and output. The wide character input/output functions described in that subclause
11959 provide operations analogous to most of those described here, except that the
11960 fundamental units internal to the program are wide characters. The external
11961 representation (in the file) is a sequence of ''generalized'' multibyte characters, as
11962 described further in 7.21.3.
11963 5 The input/output functions are given the following collective terms:
11964 -- The wide character input functions -- those functions described in 7.28 that perform
11965 input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
11966 fwscanf, wscanf, vfwscanf, and vwscanf.
11967 -- The wide character output functions -- those functions described in 7.28 that perform
11968 output from wide characters and wide strings: fputwc, fputws, putwc,
11969 putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.
11972 254) If the implementation imposes no practical limit on the length of file name strings, the value of
11973 FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
11974 string. Of course, file name string contents are subject to other system-specific constraints; therefore
11975 all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.
11979 -- The wide character input/output functions -- the union of the ungetwc function, the
11980 wide character input functions, and the wide character output functions.
11981 -- The byte input/output functions -- those functions described in this subclause that
11982 perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
11983 fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf,
11984 ungetc, vfprintf, vfscanf, vprintf, and vscanf.
11985 Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
11986 tmpnam function (7.21.4.4), <wchar.h> (7.28).
11988 1 Input and output, whether to or from physical devices such as terminals and tape drives,
11989 or whether to or from files supported on structured storage devices, are mapped into
11990 logical data streams, whose properties are more uniform than their various inputs and
11991 outputs. Two forms of mapping are supported, for text streams and for binary
11993 2 A text stream is an ordered sequence of characters composed into lines, each line
11994 consisting of zero or more characters plus a terminating new-line character. Whether the
11995 last line requires a terminating new-line character is implementation-defined. Characters
11996 may have to be added, altered, or deleted on input and output to conform to differing
11997 conventions for representing text in the host environment. Thus, there need not be a one-
11998 to-one correspondence between the characters in a stream and those in the external
11999 representation. Data read in from a text stream will necessarily compare equal to the data
12000 that were earlier written out to that stream only if: the data consist only of printing
12001 characters and the control characters horizontal tab and new-line; no new-line character is
12002 immediately preceded by space characters; and the last character is a new-line character.
12003 Whether space characters that are written out immediately before a new-line character
12004 appear when read in is implementation-defined.
12005 3 A binary stream is an ordered sequence of characters that can transparently record
12006 internal data. Data read in from a binary stream shall compare equal to the data that were
12007 earlier written out to that stream, under the same implementation. Such a stream may,
12008 however, have an implementation-defined number of null characters appended to the end
12010 4 Each stream has an orientation. After a stream is associated with an external file, but
12011 before any operations are performed on it, the stream is without orientation. Once a wide
12012 character input/output function has been applied to a stream without orientation, the
12015 255) An implementation need not distinguish between text streams and binary streams. In such an
12016 implementation, there need be no new-line characters in a text stream nor any limit to the length of a
12021 stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
12022 been applied to a stream without orientation, the stream becomes a byte-oriented stream.
12023 Only a call to the freopen function or the fwide function can otherwise alter the
12024 orientation of a stream. (A successful call to freopen removes any orientation.)256)
12025 5 Byte input/output functions shall not be applied to a wide-oriented stream and wide
12026 character input/output functions shall not be applied to a byte-oriented stream. The
12027 remaining stream operations do not affect, and are not affected by, a stream's orientation,
12028 except for the following additional restrictions:
12029 -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
12030 text and binary streams.
12031 -- For wide-oriented streams, after a successful call to a file-positioning function that
12032 leaves the file position indicator prior to the end-of-file, a wide character output
12033 function can overwrite a partial multibyte character; any file contents beyond the
12034 byte(s) written are henceforth indeterminate.
12035 6 Each wide-oriented stream has an associated mbstate_t object that stores the current
12036 parse state of the stream. A successful call to fgetpos stores a representation of the
12037 value of this mbstate_t object as part of the value of the fpos_t object. A later
12038 successful call to fsetpos using the same stored fpos_t value restores the value of
12039 the associated mbstate_t object as well as the position within the controlled stream.
12040 Environmental limits
12041 7 An implementation shall support text files with lines containing at least 254 characters,
12042 including the terminating new-line character. The value of the macro BUFSIZ shall be at
12044 Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5),
12045 mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function
12051 256) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
12056 1 A stream is associated with an external file (which may be a physical device) by opening
12057 a file, which may involve creating a new file. Creating an existing file causes its former
12058 contents to be discarded, if necessary. If a file can support positioning requests (such as a
12059 disk file, as opposed to a terminal), then a file position indicator associated with the
12060 stream is positioned at the start (character number zero) of the file, unless the file is
12061 opened with append mode in which case it is implementation-defined whether the file
12062 position indicator is initially positioned at the beginning or the end of the file. The file
12063 position indicator is maintained by subsequent reads, writes, and positioning requests, to
12064 facilitate an orderly progression through the file.
12065 2 Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
12066 stream causes the associated file to be truncated beyond that point is implementation-
12068 3 When a stream is unbuffered, characters are intended to appear from the source or at the
12069 destination as soon as possible. Otherwise characters may be accumulated and
12070 transmitted to or from the host environment as a block. When a stream is fully buffered,
12071 characters are intended to be transmitted to or from the host environment as a block when
12072 a buffer is filled. When a stream is line buffered, characters are intended to be
12073 transmitted to or from the host environment as a block when a new-line character is
12074 encountered. Furthermore, characters are intended to be transmitted as a block to the host
12075 environment when a buffer is filled, when input is requested on an unbuffered stream, or
12076 when input is requested on a line buffered stream that requires the transmission of
12077 characters from the host environment. Support for these characteristics is
12078 implementation-defined, and may be affected via the setbuf and setvbuf functions.
12079 4 A file may be disassociated from a controlling stream by closing the file. Output streams
12080 are flushed (any unwritten buffer contents are transmitted to the host environment) before
12081 the stream is disassociated from the file. The value of a pointer to a FILE object is
12082 indeterminate after the associated file is closed (including the standard text streams).
12083 Whether a file of zero length (on which no characters have been written by an output
12084 stream) actually exists is implementation-defined.
12085 5 The file may be subsequently reopened, by the same or another program execution, and
12086 its contents reclaimed or modified (if it can be repositioned at its start). If the main
12087 function returns to its original caller, or if the exit function is called, all open files are
12088 closed (hence all output streams are flushed) before program termination. Other paths to
12089 program termination, such as calling the abort function, need not close all files
12091 6 The address of the FILE object used to control a stream may be significant; a copy of a
12092 FILE object need not serve in place of the original.
12096 7 At program startup, three text streams are predefined and need not be opened explicitly
12097 -- standard input (for reading conventional input), standard output (for writing
12098 conventional output), and standard error (for writing diagnostic output). As initially
12099 opened, the standard error stream is not fully buffered; the standard input and standard
12100 output streams are fully buffered if and only if the stream can be determined not to refer
12101 to an interactive device.
12102 8 Functions that open additional (nontemporary) files require a file name, which is a string.
12103 The rules for composing valid file names are implementation-defined. Whether the same
12104 file can be simultaneously open multiple times is also implementation-defined.
12105 9 Although both text and binary wide-oriented streams are conceptually sequences of wide
12106 characters, the external file associated with a wide-oriented stream is a sequence of
12107 multibyte characters, generalized as follows:
12108 -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
12109 encodings valid for use internal to the program).
12110 -- A file need not begin nor end in the initial shift state.257)
12111 10 Moreover, the encodings used for multibyte characters may differ among files. Both the
12112 nature and choice of such encodings are implementation-defined.
12113 11 The wide character input functions read multibyte characters from the stream and convert
12114 them to wide characters as if they were read by successive calls to the fgetwc function.
12115 Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
12116 described by the stream's own mbstate_t object. The byte input functions read
12117 characters from the stream as if by successive calls to the fgetc function.
12118 12 The wide character output functions convert wide characters to multibyte characters and
12119 write them to the stream as if they were written by successive calls to the fputwc
12120 function. Each conversion occurs as if by a call to the wcrtomb function, with the
12121 conversion state described by the stream's own mbstate_t object. The byte output
12122 functions write characters to the stream as if by successive calls to the fputc function.
12123 13 In some cases, some of the byte input/output functions also perform conversions between
12124 multibyte characters and wide characters. These conversions also occur as if by calls to
12125 the mbrtowc and wcrtomb functions.
12126 14 An encoding error occurs if the character sequence presented to the underlying
12127 mbrtowc function does not form a valid (generalized) multibyte character, or if the code
12128 value passed to the underlying wcrtomb does not correspond to a valid (generalized)
12131 257) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
12132 undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
12133 with state-dependent encoding that does not assuredly end in the initial shift state.
12137 multibyte character. The wide character input/output functions and the byte input/output
12138 functions store the value of the macro EILSEQ in errno if and only if an encoding error
12140 Environmental limits
12141 15 The value of FOPEN_MAX shall be at least eight, including the three standard text
12143 Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
12144 fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
12145 (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the
12146 fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function
12147 (7.28.6.3.2), the wcrtomb function (7.28.6.3.3).
12148 7.21.4 Operations on files
12149 7.21.4.1 The remove function
12151 1 #include <stdio.h>
12152 int remove(const char *filename);
12154 2 The remove function causes the file whose name is the string pointed to by filename
12155 to be no longer accessible by that name. A subsequent attempt to open that file using that
12156 name will fail, unless it is created anew. If the file is open, the behavior of the remove
12157 function is implementation-defined.
12159 3 The remove function returns zero if the operation succeeds, nonzero if it fails.
12160 7.21.4.2 The rename function
12162 1 #include <stdio.h>
12163 int rename(const char *old, const char *new);
12165 2 The rename function causes the file whose name is the string pointed to by old to be
12166 henceforth known by the name given by the string pointed to by new. The file named
12167 old is no longer accessible by that name. If a file named by the string pointed to by new
12168 exists prior to the call to the rename function, the behavior is implementation-defined.
12176 3 The rename function returns zero if the operation succeeds, nonzero if it fails,258) in
12177 which case if the file existed previously it is still known by its original name.
12178 7.21.4.3 The tmpfile function
12180 1 #include <stdio.h>
12181 FILE *tmpfile(void);
12183 2 The tmpfile function creates a temporary binary file that is different from any other
12184 existing file and that will automatically be removed when it is closed or at program
12185 termination. If the program terminates abnormally, whether an open temporary file is
12186 removed is implementation-defined. The file is opened for update with "wb+" mode.
12187 Recommended practice
12188 3 It should be possible to open at least TMP_MAX temporary files during the lifetime of the
12189 program (this limit may be shared with tmpnam) and there should be no limit on the
12190 number simultaneously open other than this limit and any limit on the number of open
12193 4 The tmpfile function returns a pointer to the stream of the file that it created. If the file
12194 cannot be created, the tmpfile function returns a null pointer.
12195 Forward references: the fopen function (7.21.5.3).
12196 7.21.4.4 The tmpnam function
12198 1 #include <stdio.h>
12199 char *tmpnam(char *s);
12201 2 The tmpnam function generates a string that is a valid file name and that is not the same
12202 as the name of an existing file.259) The function is potentially capable of generating at
12205 258) Among the reasons the implementation may cause the rename function to fail are that the file is open
12206 or that it is necessary to copy its contents to effectuate its renaming.
12207 259) Files created using strings generated by the tmpnam function are temporary only in the sense that
12208 their names should not collide with those generated by conventional naming rules for the
12209 implementation. It is still necessary to use the remove function to remove such files when their use
12210 is ended, and before program termination.
12214 least TMP_MAX different strings, but any or all of them may already be in use by existing
12215 files and thus not be suitable return values.
12216 3 The tmpnam function generates a different string each time it is called.
12217 4 Calls to the tmpnam function with a null pointer argument may introduce data races with
12218 each other. The implementation shall behave as if no library function calls the tmpnam
12221 5 If no suitable string can be generated, the tmpnam function returns a null pointer.
12222 Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
12223 internal static object and returns a pointer to that object (subsequent calls to the tmpnam
12224 function may modify the same object). If the argument is not a null pointer, it is assumed
12225 to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
12226 in that array and returns the argument as its value.
12227 Environmental limits
12228 6 The value of the macro TMP_MAX shall be at least 25.
12229 7.21.5 File access functions
12230 7.21.5.1 The fclose function
12232 1 #include <stdio.h>
12233 int fclose(FILE *stream);
12235 2 A successful call to the fclose function causes the stream pointed to by stream to be
12236 flushed and the associated file to be closed. Any unwritten buffered data for the stream
12237 are delivered to the host environment to be written to the file; any unread buffered data
12238 are discarded. Whether or not the call succeeds, the stream is disassociated from the file
12239 and any buffer set by the setbuf or setvbuf function is disassociated from the stream
12240 (and deallocated if it was automatically allocated).
12242 3 The fclose function returns zero if the stream was successfully closed, or EOF if any
12243 errors were detected.
12250 7.21.5.2 The fflush function
12252 1 #include <stdio.h>
12253 int fflush(FILE *stream);
12255 2 If stream points to an output stream or an update stream in which the most recent
12256 operation was not input, the fflush function causes any unwritten data for that stream
12257 to be delivered to the host environment to be written to the file; otherwise, the behavior is
12259 3 If stream is a null pointer, the fflush function performs this flushing action on all
12260 streams for which the behavior is defined above.
12262 4 The fflush function sets the error indicator for the stream and returns EOF if a write
12263 error occurs, otherwise it returns zero.
12264 Forward references: the fopen function (7.21.5.3).
12265 7.21.5.3 The fopen function
12267 1 #include <stdio.h>
12268 FILE *fopen(const char * restrict filename,
12269 const char * restrict mode);
12271 2 The fopen function opens the file whose name is the string pointed to by filename,
12272 and associates a stream with it.
12273 3 The argument mode points to a string. If the string is one of the following, the file is
12274 open in the indicated mode. Otherwise, the behavior is undefined.260)
12275 r open text file for reading
12276 w truncate to zero length or create text file for writing
12277 wx create text file for writing
12278 a append; open or create text file for writing at end-of-file
12279 rb open binary file for reading
12280 wb truncate to zero length or create binary file for writing
12283 260) If the string begins with one of the above sequences, the implementation might choose to ignore the
12284 remaining characters, or it might use them to select different kinds of a file (some of which might not
12285 conform to the properties in 7.21.2).
12289 wbx create binary file for writing
12290 ab append; open or create binary file for writing at end-of-file
12291 r+ open text file for update (reading and writing)
12292 w+ truncate to zero length or create text file for update
12293 w+x create text file for update
12294 a+ append; open or create text file for update, writing at end-of-file
12295 r+b or rb+ open binary file for update (reading and writing)
12296 w+b or wb+ truncate to zero length or create binary file for update
12297 w+bx or wb+x create binary file for update
12298 a+b or ab+ append; open or create binary file for update, writing at end-of-file
12299 4 Opening a file with read mode ('r' as the first character in the mode argument) fails if
12300 the file does not exist or cannot be read.
12301 5 Opening a file with exclusive mode ('x' as the last character in the mode argument)
12302 fails if the file already exists or cannot be created. Otherwise, the file is created with
12303 exclusive (also known as non-shared) access to the extent that the underlying system
12304 supports exclusive access.
12305 6 Opening a file with append mode ('a' as the first character in the mode argument)
12306 causes all subsequent writes to the file to be forced to the then current end-of-file,
12307 regardless of intervening calls to the fseek function. In some implementations, opening
12308 a binary file with append mode ('b' as the second or third character in the above list of
12309 mode argument values) may initially position the file position indicator for the stream
12310 beyond the last data written, because of null character padding.
12311 7 When a file is opened with update mode ('+' as the second or third character in the
12312 above list of mode argument values), both input and output may be performed on the
12313 associated stream. However, output shall not be directly followed by input without an
12314 intervening call to the fflush function or to a file positioning function (fseek,
12315 fsetpos, or rewind), and input shall not be directly followed by output without an
12316 intervening call to a file positioning function, unless the input operation encounters end-
12317 of-file. Opening (or creating) a text file with update mode may instead open (or create) a
12318 binary stream in some implementations.
12319 8 When opened, a stream is fully buffered if and only if it can be determined not to refer to
12320 an interactive device. The error and end-of-file indicators for the stream are cleared.
12322 9 The fopen function returns a pointer to the object controlling the stream. If the open
12323 operation fails, fopen returns a null pointer.
12324 Forward references: file positioning functions (7.21.9).
12330 7.21.5.4 The freopen function
12332 1 #include <stdio.h>
12333 FILE *freopen(const char * restrict filename,
12334 const char * restrict mode,
12335 FILE * restrict stream);
12337 2 The freopen function opens the file whose name is the string pointed to by filename
12338 and associates the stream pointed to by stream with it. The mode argument is used just
12339 as in the fopen function.261)
12340 3 If filename is a null pointer, the freopen function attempts to change the mode of
12341 the stream to that specified by mode, as if the name of the file currently associated with
12342 the stream had been used. It is implementation-defined which changes of mode are
12343 permitted (if any), and under what circumstances.
12344 4 The freopen function first attempts to close any file that is associated with the specified
12345 stream. Failure to close the file is ignored. The error and end-of-file indicators for the
12346 stream are cleared.
12348 5 The freopen function returns a null pointer if the open operation fails. Otherwise,
12349 freopen returns the value of stream.
12350 7.21.5.5 The setbuf function
12352 1 #include <stdio.h>
12353 void setbuf(FILE * restrict stream,
12354 char * restrict buf);
12356 2 Except that it returns no value, the setbuf function is equivalent to the setvbuf
12357 function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
12358 is a null pointer), with the value _IONBF for mode.
12363 261) The primary use of the freopen function is to change the file associated with a standard text stream
12364 (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
12365 returned by the fopen function may be assigned.
12370 3 The setbuf function returns no value.
12371 Forward references: the setvbuf function (7.21.5.6).
12372 7.21.5.6 The setvbuf function
12374 1 #include <stdio.h>
12375 int setvbuf(FILE * restrict stream,
12376 char * restrict buf,
12377 int mode, size_t size);
12379 2 The setvbuf function may be used only after the stream pointed to by stream has
12380 been associated with an open file and before any other operation (other than an
12381 unsuccessful call to setvbuf) is performed on the stream. The argument mode
12382 determines how stream will be buffered, as follows: _IOFBF causes input/output to be
12383 fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
12384 input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
12385 used instead of a buffer allocated by the setvbuf function262) and the argument size
12386 specifies the size of the array; otherwise, size may determine the size of a buffer
12387 allocated by the setvbuf function. The contents of the array at any time are
12390 3 The setvbuf function returns zero on success, or nonzero if an invalid value is given
12391 for mode or if the request cannot be honored.
12396 262) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
12397 before a buffer that has automatic storage duration is deallocated upon block exit.
12401 7.21.6 Formatted input/output functions
12402 1 The formatted input/output functions shall behave as if there is a sequence point after the
12403 actions associated with each specifier.263)
12404 7.21.6.1 The fprintf function
12406 1 #include <stdio.h>
12407 int fprintf(FILE * restrict stream,
12408 const char * restrict format, ...);
12410 2 The fprintf function writes output to the stream pointed to by stream, under control
12411 of the string pointed to by format that specifies how subsequent arguments are
12412 converted for output. If there are insufficient arguments for the format, the behavior is
12413 undefined. If the format is exhausted while arguments remain, the excess arguments are
12414 evaluated (as always) but are otherwise ignored. The fprintf function returns when
12415 the end of the format string is encountered.
12416 3 The format shall be a multibyte character sequence, beginning and ending in its initial
12417 shift state. The format is composed of zero or more directives: ordinary multibyte
12418 characters (not %), which are copied unchanged to the output stream; and conversion
12419 specifications, each of which results in fetching zero or more subsequent arguments,
12420 converting them, if applicable, according to the corresponding conversion specifier, and
12421 then writing the result to the output stream.
12422 4 Each conversion specification is introduced by the character %. After the %, the following
12423 appear in sequence:
12424 -- Zero or more flags (in any order) that modify the meaning of the conversion
12426 -- An optional minimum field width. If the converted value has fewer characters than the
12427 field width, it is padded with spaces (by default) on the left (or right, if the left
12428 adjustment flag, described later, has been given) to the field width. The field width
12429 takes the form of an asterisk * (described later) or a nonnegative decimal integer.264)
12430 -- An optional precision that gives the minimum number of digits to appear for the d, i,
12431 o, u, x, and X conversions, the number of digits to appear after the decimal-point
12432 character for a, A, e, E, f, and F conversions, the maximum number of significant
12433 digits for the g and G conversions, or the maximum number of bytes to be written for
12436 263) The fprintf functions perform writes to memory for the %n specifier.
12437 264) Note that 0 is taken as a flag, not as the beginning of a field width.
12441 s conversions. The precision takes the form of a period (.) followed either by an
12442 asterisk * (described later) or by an optional decimal integer; if only the period is
12443 specified, the precision is taken as zero. If a precision appears with any other
12444 conversion specifier, the behavior is undefined.
12445 -- An optional length modifier that specifies the size of the argument.
12446 -- A conversion specifier character that specifies the type of conversion to be applied.
12447 5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
12448 this case, an int argument supplies the field width or precision. The arguments
12449 specifying field width, or precision, or both, shall appear (in that order) before the
12450 argument (if any) to be converted. A negative field width argument is taken as a - flag
12451 followed by a positive field width. A negative precision argument is taken as if the
12452 precision were omitted.
12453 6 The flag characters and their meanings are:
12454 - The result of the conversion is left-justified within the field. (It is right-justified if
12455 this flag is not specified.)
12456 + The result of a signed conversion always begins with a plus or minus sign. (It
12457 begins with a sign only when a negative value is converted if this flag is not
12459 space If the first character of a signed conversion is not a sign, or if a signed conversion
12460 results in no characters, a space is prefixed to the result. If the space and + flags
12461 both appear, the space flag is ignored.
12462 # The result is converted to an ''alternative form''. For o conversion, it increases
12463 the precision, if and only if necessary, to force the first digit of the result to be a
12464 zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
12465 conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
12466 and G conversions, the result of converting a floating-point number always
12467 contains a decimal-point character, even if no digits follow it. (Normally, a
12468 decimal-point character appears in the result of these conversions only if a digit
12469 follows it.) For g and G conversions, trailing zeros are not removed from the
12470 result. For other conversions, the behavior is undefined.
12471 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
12472 (following any indication of sign or base) are used to pad to the field width rather
12473 than performing space padding, except when converting an infinity or NaN. If the
12474 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
12477 265) The results of all floating conversions of a negative zero, and of negative values that round to zero,
12478 include a minus sign.
12482 conversions, if a precision is specified, the 0 flag is ignored. For other
12483 conversions, the behavior is undefined.
12484 7 The length modifiers and their meanings are:
12485 hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12486 signed char or unsigned char argument (the argument will have
12487 been promoted according to the integer promotions, but its value shall be
12488 converted to signed char or unsigned char before printing); or that
12489 a following n conversion specifier applies to a pointer to a signed char
12491 h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12492 short int or unsigned short int argument (the argument will
12493 have been promoted according to the integer promotions, but its value shall
12494 be converted to short int or unsigned short int before printing);
12495 or that a following n conversion specifier applies to a pointer to a short
12497 l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12498 long int or unsigned long int argument; that a following n
12499 conversion specifier applies to a pointer to a long int argument; that a
12500 following c conversion specifier applies to a wint_t argument; that a
12501 following s conversion specifier applies to a pointer to a wchar_t
12502 argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
12504 ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12505 long long int or unsigned long long int argument; or that a
12506 following n conversion specifier applies to a pointer to a long long int
12508 j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
12509 an intmax_t or uintmax_t argument; or that a following n conversion
12510 specifier applies to a pointer to an intmax_t argument.
12511 z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12512 size_t or the corresponding signed integer type argument; or that a
12513 following n conversion specifier applies to a pointer to a signed integer type
12514 corresponding to size_t argument.
12515 t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12516 ptrdiff_t or the corresponding unsigned integer type argument; or that a
12517 following n conversion specifier applies to a pointer to a ptrdiff_t
12523 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
12524 applies to a long double argument.
12525 If a length modifier appears with any conversion specifier other than as specified above,
12526 the behavior is undefined.
12527 8 The conversion specifiers and their meanings are:
12528 d,i The int argument is converted to signed decimal in the style [-]dddd. The
12529 precision specifies the minimum number of digits to appear; if the value
12530 being converted can be represented in fewer digits, it is expanded with
12531 leading zeros. The default precision is 1. The result of converting a zero
12532 value with a precision of zero is no characters.
12533 o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
12534 decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
12535 letters abcdef are used for x conversion and the letters ABCDEF for X
12536 conversion. The precision specifies the minimum number of digits to appear;
12537 if the value being converted can be represented in fewer digits, it is expanded
12538 with leading zeros. The default precision is 1. The result of converting a
12539 zero value with a precision of zero is no characters.
12540 f,F A double argument representing a floating-point number is converted to
12541 decimal notation in the style [-]ddd.ddd, where the number of digits after
12542 the decimal-point character is equal to the precision specification. If the
12543 precision is missing, it is taken as 6; if the precision is zero and the # flag is
12544 not specified, no decimal-point character appears. If a decimal-point
12545 character appears, at least one digit appears before it. The value is rounded to
12546 the appropriate number of digits.
12547 A double argument representing an infinity is converted in one of the styles
12548 [-]inf or [-]infinity -- which style is implementation-defined. A
12549 double argument representing a NaN is converted in one of the styles
12550 [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
12551 any n-char-sequence, is implementation-defined. The F conversion specifier
12552 produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
12554 e,E A double argument representing a floating-point number is converted in the
12555 style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
12556 argument is nonzero) before the decimal-point character and the number of
12557 digits after it is equal to the precision; if the precision is missing, it is taken as
12560 266) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
12561 the # and 0 flag characters have no effect.
12565 6; if the precision is zero and the # flag is not specified, no decimal-point
12566 character appears. The value is rounded to the appropriate number of digits.
12567 The E conversion specifier produces a number with E instead of e
12568 introducing the exponent. The exponent always contains at least two digits,
12569 and only as many more digits as necessary to represent the exponent. If the
12570 value is zero, the exponent is zero.
12571 A double argument representing an infinity or NaN is converted in the style
12572 of an f or F conversion specifier.
12573 g,G A double argument representing a floating-point number is converted in
12574 style f or e (or in style F or E in the case of a G conversion specifier),
12575 depending on the value converted and the precision. Let P equal the
12576 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
12577 Then, if a conversion with style E would have an exponent of X:
12578 -- if P > X >= -4, the conversion is with style f (or F) and precision
12580 -- otherwise, the conversion is with style e (or E) and precision P - 1.
12581 Finally, unless the # flag is used, any trailing zeros are removed from the
12582 fractional portion of the result and the decimal-point character is removed if
12583 there is no fractional portion remaining.
12584 A double argument representing an infinity or NaN is converted in the style
12585 of an f or F conversion specifier.
12586 a,A A double argument representing a floating-point number is converted in the
12587 style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
12588 nonzero if the argument is a normalized floating-point number and is
12589 otherwise unspecified) before the decimal-point character267) and the number
12590 of hexadecimal digits after it is equal to the precision; if the precision is
12591 missing and FLT_RADIX is a power of 2, then the precision is sufficient for
12592 an exact representation of the value; if the precision is missing and
12593 FLT_RADIX is not a power of 2, then the precision is sufficient to
12598 267) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
12599 that subsequent digits align to nibble (4-bit) boundaries.
12603 distinguish268) values of type double, except that trailing zeros may be
12604 omitted; if the precision is zero and the # flag is not specified, no decimal-
12605 point character appears. The letters abcdef are used for a conversion and
12606 the letters ABCDEF for A conversion. The A conversion specifier produces a
12607 number with X and P instead of x and p. The exponent always contains at
12608 least one digit, and only as many more digits as necessary to represent the
12609 decimal exponent of 2. If the value is zero, the exponent is zero.
12610 A double argument representing an infinity or NaN is converted in the style
12611 of an f or F conversion specifier.
12612 c If no l length modifier is present, the int argument is converted to an
12613 unsigned char, and the resulting character is written.
12614 If an l length modifier is present, the wint_t argument is converted as if by
12615 an ls conversion specification with no precision and an argument that points
12616 to the initial element of a two-element array of wchar_t, the first element
12617 containing the wint_t argument to the lc conversion specification and the
12618 second a null wide character.
12619 s If no l length modifier is present, the argument shall be a pointer to the initial
12620 element of an array of character type.269) Characters from the array are
12621 written up to (but not including) the terminating null character. If the
12622 precision is specified, no more than that many bytes are written. If the
12623 precision is not specified or is greater than the size of the array, the array shall
12624 contain a null character.
12625 If an l length modifier is present, the argument shall be a pointer to the initial
12626 element of an array of wchar_t type. Wide characters from the array are
12627 converted to multibyte characters (each as if by a call to the wcrtomb
12628 function, with the conversion state described by an mbstate_t object
12629 initialized to zero before the first wide character is converted) up to and
12630 including a terminating null wide character. The resulting multibyte
12631 characters are written up to (but not including) the terminating null character
12632 (byte). If no precision is specified, the array shall contain a null wide
12633 character. If a precision is specified, no more than that many bytes are
12634 written (including shift sequences, if any), and the array shall contain a null
12635 wide character if, to equal the multibyte character sequence length given by
12637 268) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
12638 FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
12639 might suffice depending on the implementation's scheme for determining the digit to the left of the
12640 decimal-point character.
12641 269) No special provisions are made for multibyte characters.
12645 the precision, the function would need to access a wide character one past the
12646 end of the array. In no case is a partial multibyte character written.270)
12647 p The argument shall be a pointer to void. The value of the pointer is
12648 converted to a sequence of printing characters, in an implementation-defined
12650 n The argument shall be a pointer to signed integer into which is written the
12651 number of characters written to the output stream so far by this call to
12652 fprintf. No argument is converted, but one is consumed. If the conversion
12653 specification includes any flags, a field width, or a precision, the behavior is
12655 % A % character is written. No argument is converted. The complete
12656 conversion specification shall be %%.
12657 9 If a conversion specification is invalid, the behavior is undefined.271) If any argument is
12658 not the correct type for the corresponding conversion specification, the behavior is
12660 10 In no case does a nonexistent or small field width cause truncation of a field; if the result
12661 of a conversion is wider than the field width, the field is expanded to contain the
12663 11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
12664 to a hexadecimal floating number with the given precision.
12665 Recommended practice
12666 12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
12667 representable in the given precision, the result should be one of the two adjacent numbers
12668 in hexadecimal floating style with the given precision, with the extra stipulation that the
12669 error should have a correct sign for the current rounding direction.
12670 13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
12671 DECIMAL_DIG, then the result should be correctly rounded.272) If the number of
12672 significant decimal digits is more than DECIMAL_DIG but the source value is exactly
12673 representable with DECIMAL_DIG digits, then the result should be an exact
12674 representation with trailing zeros. Otherwise, the source value is bounded by two
12675 adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
12678 270) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
12679 271) See ''future library directions'' (7.30.9).
12680 272) For binary-to-decimal conversion, the result format's values are the numbers representable with the
12681 given format specifier. The number of significant digits is determined by the format specifier, and in
12682 the case of fixed-point conversion by the source value as well.
12686 of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
12687 the error should have a correct sign for the current rounding direction.
12689 14 The fprintf function returns the number of characters transmitted, or a negative value
12690 if an output or encoding error occurred.
12691 Environmental limits
12692 15 The number of characters that can be produced by any single conversion shall be at least
12694 16 EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
12699 char *weekday, *month; // pointers to strings
12700 int day, hour, min;
12701 fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
12702 weekday, month, day, hour, min);
12703 fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
12705 17 EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
12706 members of the extended character set that consist of more than one byte each consist of exactly two bytes,
12707 the first of which is denoted here by a and the second by an uppercase letter.
12708 18 Given the following wide string with length seven,
12709 static wchar_t wstr[] = L" X Yabc Z W";
12711 fprintf(stdout, "|1234567890123|\n");
12712 fprintf(stdout, "|%13ls|\n", wstr);
12713 fprintf(stdout, "|%-13.9ls|\n", wstr);
12714 fprintf(stdout, "|%13.10ls|\n", wstr);
12715 fprintf(stdout, "|%13.11ls|\n", wstr);
12716 fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
12717 fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
12718 will print the following seven lines:
12727 Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3).
12733 7.21.6.2 The fscanf function
12735 1 #include <stdio.h>
12736 int fscanf(FILE * restrict stream,
12737 const char * restrict format, ...);
12739 2 The fscanf function reads input from the stream pointed to by stream, under control
12740 of the string pointed to by format that specifies the admissible input sequences and how
12741 they are to be converted for assignment, using subsequent arguments as pointers to the
12742 objects to receive the converted input. If there are insufficient arguments for the format,
12743 the behavior is undefined. If the format is exhausted while arguments remain, the excess
12744 arguments are evaluated (as always) but are otherwise ignored.
12745 3 The format shall be a multibyte character sequence, beginning and ending in its initial
12746 shift state. The format is composed of zero or more directives: one or more white-space
12747 characters, an ordinary multibyte character (neither % nor a white-space character), or a
12748 conversion specification. Each conversion specification is introduced by the character %.
12749 After the %, the following appear in sequence:
12750 -- An optional assignment-suppressing character *.
12751 -- An optional decimal integer greater than zero that specifies the maximum field width
12753 -- An optional length modifier that specifies the size of the receiving object.
12754 -- A conversion specifier character that specifies the type of conversion to be applied.
12755 4 The fscanf function executes each directive of the format in turn. When all directives
12756 have been executed, or if a directive fails (as detailed below), the function returns.
12757 Failures are described as input failures (due to the occurrence of an encoding error or the
12758 unavailability of input characters), or matching failures (due to inappropriate input).
12759 5 A directive composed of white-space character(s) is executed by reading input up to the
12760 first non-white-space character (which remains unread), or until no more characters can
12762 6 A directive that is an ordinary multibyte character is executed by reading the next
12763 characters of the stream. If any of those characters differ from the ones composing the
12764 directive, the directive fails and the differing and subsequent characters remain unread.
12765 Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
12766 read, the directive fails.
12767 7 A directive that is a conversion specification defines a set of matching input sequences, as
12768 described below for each specifier. A conversion specification is executed in the
12773 8 Input white-space characters (as specified by the isspace function) are skipped, unless
12774 the specification includes a [, c, or n specifier.273)
12775 9 An input item is read from the stream, unless the specification includes an n specifier. An
12776 input item is defined as the longest sequence of input characters which does not exceed
12777 any specified field width and which is, or is a prefix of, a matching input sequence.274)
12778 The first character, if any, after the input item remains unread. If the length of the input
12779 item is zero, the execution of the directive fails; this condition is a matching failure unless
12780 end-of-file, an encoding error, or a read error prevented input from the stream, in which
12781 case it is an input failure.
12782 10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
12783 count of input characters) is converted to a type appropriate to the conversion specifier. If
12784 the input item is not a matching sequence, the execution of the directive fails: this
12785 condition is a matching failure. Unless assignment suppression was indicated by a *, the
12786 result of the conversion is placed in the object pointed to by the first argument following
12787 the format argument that has not already received a conversion result. If this object
12788 does not have an appropriate type, or if the result of the conversion cannot be represented
12789 in the object, the behavior is undefined.
12790 11 The length modifiers and their meanings are:
12791 hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12792 to an argument with type pointer to signed char or unsigned char.
12793 h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12794 to an argument with type pointer to short int or unsigned short
12796 l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12797 to an argument with type pointer to long int or unsigned long
12798 int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
12799 an argument with type pointer to double; or that a following c, s, or [
12800 conversion specifier applies to an argument with type pointer to wchar_t.
12801 ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12802 to an argument with type pointer to long long int or unsigned
12807 273) These white-space characters are not counted against a specified field width.
12808 274) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
12809 that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
12813 j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12814 to an argument with type pointer to intmax_t or uintmax_t.
12815 z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12816 to an argument with type pointer to size_t or the corresponding signed
12818 t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12819 to an argument with type pointer to ptrdiff_t or the corresponding
12820 unsigned integer type.
12821 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
12822 applies to an argument with type pointer to long double.
12823 If a length modifier appears with any conversion specifier other than as specified above,
12824 the behavior is undefined.
12825 12 The conversion specifiers and their meanings are:
12826 d Matches an optionally signed decimal integer, whose format is the same as
12827 expected for the subject sequence of the strtol function with the value 10
12828 for the base argument. The corresponding argument shall be a pointer to
12830 i Matches an optionally signed integer, whose format is the same as expected
12831 for the subject sequence of the strtol function with the value 0 for the
12832 base argument. The corresponding argument shall be a pointer to signed
12834 o Matches an optionally signed octal integer, whose format is the same as
12835 expected for the subject sequence of the strtoul function with the value 8
12836 for the base argument. The corresponding argument shall be a pointer to
12838 u Matches an optionally signed decimal integer, whose format is the same as
12839 expected for the subject sequence of the strtoul function with the value 10
12840 for the base argument. The corresponding argument shall be a pointer to
12842 x Matches an optionally signed hexadecimal integer, whose format is the same
12843 as expected for the subject sequence of the strtoul function with the value
12844 16 for the base argument. The corresponding argument shall be a pointer to
12846 a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
12847 format is the same as expected for the subject sequence of the strtod
12848 function. The corresponding argument shall be a pointer to floating.
12853 c Matches a sequence of characters of exactly the number specified by the field
12854 width (1 if no field width is present in the directive).275)
12855 If no l length modifier is present, the corresponding argument shall be a
12856 pointer to the initial element of a character array large enough to accept the
12857 sequence. No null character is added.
12858 If an l length modifier is present, the input shall be a sequence of multibyte
12859 characters that begins in the initial shift state. Each multibyte character in the
12860 sequence is converted to a wide character as if by a call to the mbrtowc
12861 function, with the conversion state described by an mbstate_t object
12862 initialized to zero before the first multibyte character is converted. The
12863 corresponding argument shall be a pointer to the initial element of an array of
12864 wchar_t large enough to accept the resulting sequence of wide characters.
12865 No null wide character is added.
12866 s Matches a sequence of non-white-space characters.275)
12867 If no l length modifier is present, the corresponding argument shall be a
12868 pointer to the initial element of a character array large enough to accept the
12869 sequence and a terminating null character, which will be added automatically.
12870 If an l length modifier is present, the input shall be a sequence of multibyte
12871 characters that begins in the initial shift state. Each multibyte character is
12872 converted to a wide character as if by a call to the mbrtowc function, with
12873 the conversion state described by an mbstate_t object initialized to zero
12874 before the first multibyte character is converted. The corresponding argument
12875 shall be a pointer to the initial element of an array of wchar_t large enough
12876 to accept the sequence and the terminating null wide character, which will be
12877 added automatically.
12878 [ Matches a nonempty sequence of characters from a set of expected characters
12880 If no l length modifier is present, the corresponding argument shall be a
12881 pointer to the initial element of a character array large enough to accept the
12882 sequence and a terminating null character, which will be added automatically.
12883 If an l length modifier is present, the input shall be a sequence of multibyte
12884 characters that begins in the initial shift state. Each multibyte character is
12885 converted to a wide character as if by a call to the mbrtowc function, with
12886 the conversion state described by an mbstate_t object initialized to zero
12888 275) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
12889 conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
12890 resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
12894 before the first multibyte character is converted. The corresponding argument
12895 shall be a pointer to the initial element of an array of wchar_t large enough
12896 to accept the sequence and the terminating null wide character, which will be
12897 added automatically.
12898 The conversion specifier includes all subsequent characters in the format
12899 string, up to and including the matching right bracket (]). The characters
12900 between the brackets (the scanlist) compose the scanset, unless the character
12901 after the left bracket is a circumflex (^), in which case the scanset contains all
12902 characters that do not appear in the scanlist between the circumflex and the
12903 right bracket. If the conversion specifier begins with [] or [^], the right
12904 bracket character is in the scanlist and the next following right bracket
12905 character is the matching right bracket that ends the specification; otherwise
12906 the first following right bracket character is the one that ends the
12907 specification. If a - character is in the scanlist and is not the first, nor the
12908 second where the first character is a ^, nor the last character, the behavior is
12909 implementation-defined.
12910 p Matches an implementation-defined set of sequences, which should be the
12911 same as the set of sequences that may be produced by the %p conversion of
12912 the fprintf function. The corresponding argument shall be a pointer to a
12913 pointer to void. The input item is converted to a pointer value in an
12914 implementation-defined manner. If the input item is a value converted earlier
12915 during the same program execution, the pointer that results shall compare
12916 equal to that value; otherwise the behavior of the %p conversion is undefined.
12917 n No input is consumed. The corresponding argument shall be a pointer to
12918 signed integer into which is to be written the number of characters read from
12919 the input stream so far by this call to the fscanf function. Execution of a
12920 %n directive does not increment the assignment count returned at the
12921 completion of execution of the fscanf function. No argument is converted,
12922 but one is consumed. If the conversion specification includes an assignment-
12923 suppressing character or a field width, the behavior is undefined.
12924 % Matches a single % character; no conversion or assignment occurs. The
12925 complete conversion specification shall be %%.
12926 13 If a conversion specification is invalid, the behavior is undefined.276)
12927 14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
12928 respectively, a, e, f, g, and x.
12932 276) See ''future library directions'' (7.30.9).
12936 15 Trailing white space (including new-line characters) is left unread unless matched by a
12937 directive. The success of literal matches and suppressed assignments is not directly
12938 determinable other than via the %n directive.
12940 16 The fscanf function returns the value of the macro EOF if an input failure occurs
12941 before the first conversion (if any) has completed. Otherwise, the function returns the
12942 number of input items assigned, which can be fewer than provided for, or even zero, in
12943 the event of an early matching failure.
12944 17 EXAMPLE 1 The call:
12947 int n, i; float x; char name[50];
12948 n = fscanf(stdin, "%d%f%s", &i, &x, name);
12949 with the input line:
12950 25 54.32E-1 thompson
12951 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
12954 18 EXAMPLE 2 The call:
12957 int i; float x; char name[50];
12958 fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
12961 will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
12962 sequence 56\0. The next character read from the input stream will be a.
12964 19 EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
12967 int count; float quant; char units[21], item[21];
12969 count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
12970 fscanf(stdin,"%*[^\n]");
12971 } while (!feof(stdin) && !ferror(stdin));
12972 20 If the stdin stream contains the following lines:
12974 -12.8degrees Celsius
12982 the execution of the above example will be analogous to the following assignments:
12983 quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
12985 quant = -12.8; strcpy(units, "degrees");
12986 count = 2; // "C" fails to match "o"
12987 count = 0; // "l" fails to match "%f"
12988 quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
12990 count = 0; // "100e" fails to match "%f"
12996 int d1, d2, n1, n2, i;
12997 i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
12998 the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value
12999 of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.
13001 22 EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the
13002 members of the extended character set that consist of more than one byte each consist of exactly two bytes,
13003 the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
13004 such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes
13005 entry into the alternate shift state.
13010 fscanf(stdin, "a%s", str);
13011 with the input line:
13012 a(uparrow) X Y(downarrow) bc
13013 str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte
13014 characters, in the more general case) appears to be a single-byte white-space character.
13015 24 In contrast, after the call:
13017 #include <stddef.h>
13020 fscanf(stdin, "a%ls", wstr);
13021 with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
13022 terminating null wide character.
13023 25 However, the call:
13031 #include <stddef.h>
13034 fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr);
13035 with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format
13037 26 Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
13038 character Y, after the call:
13040 #include <stddef.h>
13043 fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr);
13044 with the same input line, zero will again be returned, but stdin will be left with a partially consumed
13045 multibyte character.
13047 Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
13048 strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
13049 (7.28.6), the wcrtomb function (7.28.6.3.3).
13050 7.21.6.3 The printf function
13052 1 #include <stdio.h>
13053 int printf(const char * restrict format, ...);
13055 2 The printf function is equivalent to fprintf with the argument stdout interposed
13056 before the arguments to printf.
13058 3 The printf function returns the number of characters transmitted, or a negative value if
13059 an output or encoding error occurred.
13060 7.21.6.4 The scanf function
13062 1 #include <stdio.h>
13063 int scanf(const char * restrict format, ...);
13065 2 The scanf function is equivalent to fscanf with the argument stdin interposed
13066 before the arguments to scanf.
13073 3 The scanf function returns the value of the macro EOF if an input failure occurs before
13074 the first conversion (if any) has completed. Otherwise, the scanf function returns the
13075 number of input items assigned, which can be fewer than provided for, or even zero, in
13076 the event of an early matching failure.
13077 7.21.6.5 The snprintf function
13079 1 #include <stdio.h>
13080 int snprintf(char * restrict s, size_t n,
13081 const char * restrict format, ...);
13083 2 The snprintf function is equivalent to fprintf, except that the output is written into
13084 an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
13085 and s may be a null pointer. Otherwise, output characters beyond the n-1st are
13086 discarded rather than being written to the array, and a null character is written at the end
13087 of the characters actually written into the array. If copying takes place between objects
13088 that overlap, the behavior is undefined.
13090 3 The snprintf function returns the number of characters that would have been written
13091 had n been sufficiently large, not counting the terminating null character, or a negative
13092 value if an encoding error occurred. Thus, the null-terminated output has been
13093 completely written if and only if the returned value is nonnegative and less than n.
13094 7.21.6.6 The sprintf function
13096 1 #include <stdio.h>
13097 int sprintf(char * restrict s,
13098 const char * restrict format, ...);
13100 2 The sprintf function is equivalent to fprintf, except that the output is written into
13101 an array (specified by the argument s) rather than to a stream. A null character is written
13102 at the end of the characters written; it is not counted as part of the returned value. If
13103 copying takes place between objects that overlap, the behavior is undefined.
13105 3 The sprintf function returns the number of characters written in the array, not
13106 counting the terminating null character, or a negative value if an encoding error occurred.
13110 7.21.6.7 The sscanf function
13112 1 #include <stdio.h>
13113 int sscanf(const char * restrict s,
13114 const char * restrict format, ...);
13116 2 The sscanf function is equivalent to fscanf, except that input is obtained from a
13117 string (specified by the argument s) rather than from a stream. Reaching the end of the
13118 string is equivalent to encountering end-of-file for the fscanf function. If copying
13119 takes place between objects that overlap, the behavior is undefined.
13121 3 The sscanf function returns the value of the macro EOF if an input failure occurs
13122 before the first conversion (if any) has completed. Otherwise, the sscanf function
13123 returns the number of input items assigned, which can be fewer than provided for, or even
13124 zero, in the event of an early matching failure.
13125 7.21.6.8 The vfprintf function
13127 1 #include <stdarg.h>
13129 int vfprintf(FILE * restrict stream,
13130 const char * restrict format,
13133 2 The vfprintf function is equivalent to fprintf, with the variable argument list
13134 replaced by arg, which shall have been initialized by the va_start macro (and
13135 possibly subsequent va_arg calls). The vfprintf function does not invoke the
13138 3 The vfprintf function returns the number of characters transmitted, or a negative
13139 value if an output or encoding error occurred.
13140 4 EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine.
13145 277) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
13146 vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
13150 #include <stdarg.h>
13152 void error(char *function_name, char *format, ...)
13155 va_start(args, format);
13156 // print out name of function causing error
13157 fprintf(stderr, "ERROR in %s: ", function_name);
13158 // print out remainder of message
13159 vfprintf(stderr, format, args);
13163 7.21.6.9 The vfscanf function
13165 1 #include <stdarg.h>
13167 int vfscanf(FILE * restrict stream,
13168 const char * restrict format,
13171 2 The vfscanf function is equivalent to fscanf, with the variable argument list
13172 replaced by arg, which shall have been initialized by the va_start macro (and
13173 possibly subsequent va_arg calls). The vfscanf function does not invoke the
13176 3 The vfscanf function returns the value of the macro EOF if an input failure occurs
13177 before the first conversion (if any) has completed. Otherwise, the vfscanf function
13178 returns the number of input items assigned, which can be fewer than provided for, or even
13179 zero, in the event of an early matching failure.
13180 7.21.6.10 The vprintf function
13182 1 #include <stdarg.h>
13184 int vprintf(const char * restrict format,
13187 2 The vprintf function is equivalent to printf, with the variable argument list
13188 replaced by arg, which shall have been initialized by the va_start macro (and
13192 possibly subsequent va_arg calls). The vprintf function does not invoke the
13195 3 The vprintf function returns the number of characters transmitted, or a negative value
13196 if an output or encoding error occurred.
13197 7.21.6.11 The vscanf function
13199 1 #include <stdarg.h>
13201 int vscanf(const char * restrict format,
13204 2 The vscanf function is equivalent to scanf, with the variable argument list replaced
13205 by arg, which shall have been initialized by the va_start macro (and possibly
13206 subsequent va_arg calls). The vscanf function does not invoke the va_end
13209 3 The vscanf function returns the value of the macro EOF if an input failure occurs
13210 before the first conversion (if any) has completed. Otherwise, the vscanf function
13211 returns the number of input items assigned, which can be fewer than provided for, or even
13212 zero, in the event of an early matching failure.
13213 7.21.6.12 The vsnprintf function
13215 1 #include <stdarg.h>
13217 int vsnprintf(char * restrict s, size_t n,
13218 const char * restrict format,
13221 2 The vsnprintf function is equivalent to snprintf, with the variable argument list
13222 replaced by arg, which shall have been initialized by the va_start macro (and
13223 possibly subsequent va_arg calls). The vsnprintf function does not invoke the
13224 va_end macro.277) If copying takes place between objects that overlap, the behavior is
13232 3 The vsnprintf function returns the number of characters that would have been written
13233 had n been sufficiently large, not counting the terminating null character, or a negative
13234 value if an encoding error occurred. Thus, the null-terminated output has been
13235 completely written if and only if the returned value is nonnegative and less than n.
13236 7.21.6.13 The vsprintf function
13238 1 #include <stdarg.h>
13240 int vsprintf(char * restrict s,
13241 const char * restrict format,
13244 2 The vsprintf function is equivalent to sprintf, with the variable argument list
13245 replaced by arg, which shall have been initialized by the va_start macro (and
13246 possibly subsequent va_arg calls). The vsprintf function does not invoke the
13247 va_end macro.277) If copying takes place between objects that overlap, the behavior is
13250 3 The vsprintf function returns the number of characters written in the array, not
13251 counting the terminating null character, or a negative value if an encoding error occurred.
13252 7.21.6.14 The vsscanf function
13254 1 #include <stdarg.h>
13256 int vsscanf(const char * restrict s,
13257 const char * restrict format,
13260 2 The vsscanf function is equivalent to sscanf, with the variable argument list
13261 replaced by arg, which shall have been initialized by the va_start macro (and
13262 possibly subsequent va_arg calls). The vsscanf function does not invoke the
13265 3 The vsscanf function returns the value of the macro EOF if an input failure occurs
13266 before the first conversion (if any) has completed. Otherwise, the vsscanf function
13269 returns the number of input items assigned, which can be fewer than provided for, or even
13270 zero, in the event of an early matching failure.
13271 7.21.7 Character input/output functions
13272 7.21.7.1 The fgetc function
13274 1 #include <stdio.h>
13275 int fgetc(FILE *stream);
13277 2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
13278 next character is present, the fgetc function obtains that character as an unsigned
13279 char converted to an int and advances the associated file position indicator for the
13280 stream (if defined).
13282 3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
13283 of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
13284 fgetc function returns the next character from the input stream pointed to by stream.
13285 If a read error occurs, the error indicator for the stream is set and the fgetc function
13287 7.21.7.2 The fgets function
13289 1 #include <stdio.h>
13290 char *fgets(char * restrict s, int n,
13291 FILE * restrict stream);
13293 2 The fgets function reads at most one less than the number of characters specified by n
13294 from the stream pointed to by stream into the array pointed to by s. No additional
13295 characters are read after a new-line character (which is retained) or after end-of-file. A
13296 null character is written immediately after the last character read into the array.
13298 3 The fgets function returns s if successful. If end-of-file is encountered and no
13299 characters have been read into the array, the contents of the array remain unchanged and a
13300 null pointer is returned. If a read error occurs during the operation, the array contents are
13301 indeterminate and a null pointer is returned.
13303 278) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
13307 7.21.7.3 The fputc function
13309 1 #include <stdio.h>
13310 int fputc(int c, FILE *stream);
13312 2 The fputc function writes the character specified by c (converted to an unsigned
13313 char) to the output stream pointed to by stream, at the position indicated by the
13314 associated file position indicator for the stream (if defined), and advances the indicator
13315 appropriately. If the file cannot support positioning requests, or if the stream was opened
13316 with append mode, the character is appended to the output stream.
13318 3 The fputc function returns the character written. If a write error occurs, the error
13319 indicator for the stream is set and fputc returns EOF.
13320 7.21.7.4 The fputs function
13322 1 #include <stdio.h>
13323 int fputs(const char * restrict s,
13324 FILE * restrict stream);
13326 2 The fputs function writes the string pointed to by s to the stream pointed to by
13327 stream. The terminating null character is not written.
13329 3 The fputs function returns EOF if a write error occurs; otherwise it returns a
13331 7.21.7.5 The getc function
13333 1 #include <stdio.h>
13334 int getc(FILE *stream);
13336 2 The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
13337 may evaluate stream more than once, so the argument should never be an expression
13346 3 The getc function returns the next character from the input stream pointed to by
13347 stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
13348 getc returns EOF. If a read error occurs, the error indicator for the stream is set and
13350 7.21.7.6 The getchar function
13352 1 #include <stdio.h>
13355 2 The getchar function is equivalent to getc with the argument stdin.
13357 3 The getchar function returns the next character from the input stream pointed to by
13358 stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
13359 getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
13360 getchar returns EOF.
13361 7.21.7.7 The putc function
13363 1 #include <stdio.h>
13364 int putc(int c, FILE *stream);
13366 2 The putc function is equivalent to fputc, except that if it is implemented as a macro, it
13367 may evaluate stream more than once, so that argument should never be an expression
13370 3 The putc function returns the character written. If a write error occurs, the error
13371 indicator for the stream is set and putc returns EOF.
13372 7.21.7.8 The putchar function
13374 1 #include <stdio.h>
13375 int putchar(int c);
13377 2 The putchar function is equivalent to putc with the second argument stdout.
13383 3 The putchar function returns the character written. If a write error occurs, the error
13384 indicator for the stream is set and putchar returns EOF.
13385 7.21.7.9 The puts function
13387 1 #include <stdio.h>
13388 int puts(const char *s);
13390 2 The puts function writes the string pointed to by s to the stream pointed to by stdout,
13391 and appends a new-line character to the output. The terminating null character is not
13394 3 The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
13396 7.21.7.10 The ungetc function
13398 1 #include <stdio.h>
13399 int ungetc(int c, FILE *stream);
13401 2 The ungetc function pushes the character specified by c (converted to an unsigned
13402 char) back onto the input stream pointed to by stream. Pushed-back characters will be
13403 returned by subsequent reads on that stream in the reverse order of their pushing. A
13404 successful intervening call (with the stream pointed to by stream) to a file positioning
13405 function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
13406 stream. The external storage corresponding to the stream is unchanged.
13407 3 One character of pushback is guaranteed. If the ungetc function is called too many
13408 times on the same stream without an intervening read or file positioning operation on that
13409 stream, the operation may fail.
13410 4 If the value of c equals that of the macro EOF, the operation fails and the input stream is
13412 5 A successful call to the ungetc function clears the end-of-file indicator for the stream.
13413 The value of the file position indicator for the stream after reading or discarding all
13414 pushed-back characters shall be the same as it was before the characters were pushed
13415 back. For a text stream, the value of its file position indicator after a successful call to the
13416 ungetc function is unspecified until all pushed-back characters are read or discarded.
13420 For a binary stream, its file position indicator is decremented by each successful call to
13421 the ungetc function; if its value was zero before a call, it is indeterminate after the
13424 6 The ungetc function returns the character pushed back after conversion, or EOF if the
13426 Forward references: file positioning functions (7.21.9).
13427 7.21.8 Direct input/output functions
13428 7.21.8.1 The fread function
13430 1 #include <stdio.h>
13431 size_t fread(void * restrict ptr,
13432 size_t size, size_t nmemb,
13433 FILE * restrict stream);
13435 2 The fread function reads, into the array pointed to by ptr, up to nmemb elements
13436 whose size is specified by size, from the stream pointed to by stream. For each
13437 object, size calls are made to the fgetc function and the results stored, in the order
13438 read, in an array of unsigned char exactly overlaying the object. The file position
13439 indicator for the stream (if defined) is advanced by the number of characters successfully
13440 read. If an error occurs, the resulting value of the file position indicator for the stream is
13441 indeterminate. If a partial element is read, its value is indeterminate.
13443 3 The fread function returns the number of elements successfully read, which may be
13444 less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
13445 fread returns zero and the contents of the array and the state of the stream remain
13451 279) See ''future library directions'' (7.30.9).
13455 7.21.8.2 The fwrite function
13457 1 #include <stdio.h>
13458 size_t fwrite(const void * restrict ptr,
13459 size_t size, size_t nmemb,
13460 FILE * restrict stream);
13462 2 The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
13463 whose size is specified by size, to the stream pointed to by stream. For each object,
13464 size calls are made to the fputc function, taking the values (in order) from an array of
13465 unsigned char exactly overlaying the object. The file position indicator for the
13466 stream (if defined) is advanced by the number of characters successfully written. If an
13467 error occurs, the resulting value of the file position indicator for the stream is
13470 3 The fwrite function returns the number of elements successfully written, which will be
13471 less than nmemb only if a write error is encountered. If size or nmemb is zero,
13472 fwrite returns zero and the state of the stream remains unchanged.
13473 7.21.9 File positioning functions
13474 7.21.9.1 The fgetpos function
13476 1 #include <stdio.h>
13477 int fgetpos(FILE * restrict stream,
13478 fpos_t * restrict pos);
13480 2 The fgetpos function stores the current values of the parse state (if any) and file
13481 position indicator for the stream pointed to by stream in the object pointed to by pos.
13482 The values stored contain unspecified information usable by the fsetpos function for
13483 repositioning the stream to its position at the time of the call to the fgetpos function.
13485 3 If successful, the fgetpos function returns zero; on failure, the fgetpos function
13486 returns nonzero and stores an implementation-defined positive value in errno.
13487 Forward references: the fsetpos function (7.21.9.3).
13494 7.21.9.2 The fseek function
13496 1 #include <stdio.h>
13497 int fseek(FILE *stream, long int offset, int whence);
13499 2 The fseek function sets the file position indicator for the stream pointed to by stream.
13500 If a read or write error occurs, the error indicator for the stream is set and fseek fails.
13501 3 For a binary stream, the new position, measured in characters from the beginning of the
13502 file, is obtained by adding offset to the position specified by whence. The specified
13503 position is the beginning of the file if whence is SEEK_SET, the current value of the file
13504 position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
13505 meaningfully support fseek calls with a whence value of SEEK_END.
13506 4 For a text stream, either offset shall be zero, or offset shall be a value returned by
13507 an earlier successful call to the ftell function on a stream associated with the same file
13508 and whence shall be SEEK_SET.
13509 5 After determining the new position, a successful call to the fseek function undoes any
13510 effects of the ungetc function on the stream, clears the end-of-file indicator for the
13511 stream, and then establishes the new position. After a successful fseek call, the next
13512 operation on an update stream may be either input or output.
13514 6 The fseek function returns nonzero only for a request that cannot be satisfied.
13515 Forward references: the ftell function (7.21.9.4).
13516 7.21.9.3 The fsetpos function
13518 1 #include <stdio.h>
13519 int fsetpos(FILE *stream, const fpos_t *pos);
13521 2 The fsetpos function sets the mbstate_t object (if any) and file position indicator
13522 for the stream pointed to by stream according to the value of the object pointed to by
13523 pos, which shall be a value obtained from an earlier successful call to the fgetpos
13524 function on a stream associated with the same file. If a read or write error occurs, the
13525 error indicator for the stream is set and fsetpos fails.
13526 3 A successful call to the fsetpos function undoes any effects of the ungetc function
13527 on the stream, clears the end-of-file indicator for the stream, and then establishes the new
13528 parse state and position. After a successful fsetpos call, the next operation on an
13532 update stream may be either input or output.
13534 4 If successful, the fsetpos function returns zero; on failure, the fsetpos function
13535 returns nonzero and stores an implementation-defined positive value in errno.
13536 7.21.9.4 The ftell function
13538 1 #include <stdio.h>
13539 long int ftell(FILE *stream);
13541 2 The ftell function obtains the current value of the file position indicator for the stream
13542 pointed to by stream. For a binary stream, the value is the number of characters from
13543 the beginning of the file. For a text stream, its file position indicator contains unspecified
13544 information, usable by the fseek function for returning the file position indicator for the
13545 stream to its position at the time of the ftell call; the difference between two such
13546 return values is not necessarily a meaningful measure of the number of characters written
13549 3 If successful, the ftell function returns the current value of the file position indicator
13550 for the stream. On failure, the ftell function returns -1L and stores an
13551 implementation-defined positive value in errno.
13552 7.21.9.5 The rewind function
13554 1 #include <stdio.h>
13555 void rewind(FILE *stream);
13557 2 The rewind function sets the file position indicator for the stream pointed to by
13558 stream to the beginning of the file. It is equivalent to
13559 (void)fseek(stream, 0L, SEEK_SET)
13560 except that the error indicator for the stream is also cleared.
13562 3 The rewind function returns no value.
13569 7.21.10 Error-handling functions
13570 7.21.10.1 The clearerr function
13572 1 #include <stdio.h>
13573 void clearerr(FILE *stream);
13575 2 The clearerr function clears the end-of-file and error indicators for the stream pointed
13578 3 The clearerr function returns no value.
13579 7.21.10.2 The feof function
13581 1 #include <stdio.h>
13582 int feof(FILE *stream);
13584 2 The feof function tests the end-of-file indicator for the stream pointed to by stream.
13586 3 The feof function returns nonzero if and only if the end-of-file indicator is set for
13588 7.21.10.3 The ferror function
13590 1 #include <stdio.h>
13591 int ferror(FILE *stream);
13593 2 The ferror function tests the error indicator for the stream pointed to by stream.
13595 3 The ferror function returns nonzero if and only if the error indicator is set for
13603 7.21.10.4 The perror function
13605 1 #include <stdio.h>
13606 void perror(const char *s);
13608 2 The perror function maps the error number in the integer expression errno to an
13609 error message. It writes a sequence of characters to the standard error stream thus: first
13610 (if s is not a null pointer and the character pointed to by s is not the null character), the
13611 string pointed to by s followed by a colon (:) and a space; then an appropriate error
13612 message string followed by a new-line character. The contents of the error message
13613 strings are the same as those returned by the strerror function with argument errno.
13615 3 The perror function returns no value.
13616 Forward references: the strerror function (7.23.6.2).
13623 7.22 General utilities <stdlib.h>
13624 1 The header <stdlib.h> declares five types and several functions of general utility, and
13625 defines several macros.280)
13626 2 The types declared are size_t and wchar_t (both described in 7.19),
13628 which is a structure type that is the type of the value returned by the div function,
13630 which is a structure type that is the type of the value returned by the ldiv function, and
13632 which is a structure type that is the type of the value returned by the lldiv function.
13633 3 The macros defined are NULL (described in 7.19);
13637 which expand to integer constant expressions that can be used as the argument to the
13638 exit function to return unsuccessful or successful termination status, respectively, to the
13641 which expands to an integer constant expression that is the maximum value returned by
13642 the rand function; and
13644 which expands to a positive integer expression with type size_t that is the maximum
13645 number of bytes in a multibyte character for the extended character set specified by the
13646 current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.
13651 280) See ''future library directions'' (7.30.10).
13655 7.22.1 Numeric conversion functions
13656 1 The functions atof, atoi, atol, and atoll need not affect the value of the integer
13657 expression errno on an error. If the value of the result cannot be represented, the
13658 behavior is undefined.
13659 7.22.1.1 The atof function
13661 1 #include <stdlib.h>
13662 double atof(const char *nptr);
13664 2 The atof function converts the initial portion of the string pointed to by nptr to
13665 double representation. Except for the behavior on error, it is equivalent to
13666 strtod(nptr, (char **)NULL)
13668 3 The atof function returns the converted value.
13669 Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
13670 7.22.1.2 The atoi, atol, and atoll functions
13672 1 #include <stdlib.h>
13673 int atoi(const char *nptr);
13674 long int atol(const char *nptr);
13675 long long int atoll(const char *nptr);
13677 2 The atoi, atol, and atoll functions convert the initial portion of the string pointed
13678 to by nptr to int, long int, and long long int representation, respectively.
13679 Except for the behavior on error, they are equivalent to
13680 atoi: (int)strtol(nptr, (char **)NULL, 10)
13681 atol: strtol(nptr, (char **)NULL, 10)
13682 atoll: strtoll(nptr, (char **)NULL, 10)
13684 3 The atoi, atol, and atoll functions return the converted value.
13685 Forward references: the strtol, strtoll, strtoul, and strtoull functions
13692 7.22.1.3 The strtod, strtof, and strtold functions
13694 1 #include <stdlib.h>
13695 double strtod(const char * restrict nptr,
13696 char ** restrict endptr);
13697 float strtof(const char * restrict nptr,
13698 char ** restrict endptr);
13699 long double strtold(const char * restrict nptr,
13700 char ** restrict endptr);
13702 2 The strtod, strtof, and strtold functions convert the initial portion of the string
13703 pointed to by nptr to double, float, and long double representation,
13704 respectively. First, they decompose the input string into three parts: an initial, possibly
13705 empty, sequence of white-space characters (as specified by the isspace function), a
13706 subject sequence resembling a floating-point constant or representing an infinity or NaN;
13707 and a final string of one or more unrecognized characters, including the terminating null
13708 character of the input string. Then, they attempt to convert the subject sequence to a
13709 floating-point number, and return the result.
13710 3 The expected form of the subject sequence is an optional plus or minus sign, then one of
13712 -- a nonempty sequence of decimal digits optionally containing a decimal-point
13713 character, then an optional exponent part as defined in 6.4.4.2;
13714 -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
13715 decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
13716 -- INF or INFINITY, ignoring case
13717 -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
13721 n-char-sequence digit
13722 n-char-sequence nondigit
13723 The subject sequence is defined as the longest initial subsequence of the input string,
13724 starting with the first non-white-space character, that is of the expected form. The subject
13725 sequence contains no characters if the input string is not of the expected form.
13726 4 If the subject sequence has the expected form for a floating-point number, the sequence of
13727 characters starting with the first digit or the decimal-point character (whichever occurs
13728 first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
13731 decimal-point character is used in place of a period, and that if neither an exponent part
13732 nor a decimal-point character appears in a decimal floating point number, or if a binary
13733 exponent part does not appear in a hexadecimal floating point number, an exponent part
13734 of the appropriate type with value zero is assumed to follow the last digit in the string. If
13735 the subject sequence begins with a minus sign, the sequence is interpreted as negated.281)
13736 A character sequence INF or INFINITY is interpreted as an infinity, if representable in
13737 the return type, else like a floating constant that is too large for the range of the return
13738 type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet
13739 NaN, if supported in the return type, else like a subject sequence part that does not have
13740 the expected form; the meaning of the n-char sequences is implementation-defined.282) A
13741 pointer to the final string is stored in the object pointed to by endptr, provided that
13742 endptr is not a null pointer.
13743 5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
13744 value resulting from the conversion is correctly rounded.
13745 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
13747 7 If the subject sequence is empty or does not have the expected form, no conversion is
13748 performed; the value of nptr is stored in the object pointed to by endptr, provided
13749 that endptr is not a null pointer.
13750 Recommended practice
13751 8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
13752 the result is not exactly representable, the result should be one of the two numbers in the
13753 appropriate internal format that are adjacent to the hexadecimal floating source value,
13754 with the extra stipulation that the error should have a correct sign for the current rounding
13756 9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
13757 <float.h>) significant digits, the result should be correctly rounded. If the subject
13758 sequence D has the decimal form and more than DECIMAL_DIG significant digits,
13759 consider the two bounding, adjacent decimal strings L and U, both having
13760 DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
13761 The result should be one of the (equal or adjacent) values that would be obtained by
13762 correctly rounding L and U according to the current rounding direction, with the extra
13764 281) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
13765 negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
13766 methods may yield different results if rounding is toward positive or negative infinity. In either case,
13767 the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
13768 282) An implementation may use the n-char sequence to determine extra information to be represented in
13769 the NaN's significand.
13773 stipulation that the error with respect to D should have a correct sign for the current
13774 rounding direction.283)
13776 10 The functions return the converted value, if any. If no conversion could be performed,
13777 zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
13778 plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
13779 return type and sign of the value), and the value of the macro ERANGE is stored in
13780 errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
13781 no greater than the smallest normalized positive number in the return type; whether
13782 errno acquires the value ERANGE is implementation-defined.
13783 7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
13785 1 #include <stdlib.h>
13787 const char * restrict nptr,
13788 char ** restrict endptr,
13790 long long int strtoll(
13791 const char * restrict nptr,
13792 char ** restrict endptr,
13794 unsigned long int strtoul(
13795 const char * restrict nptr,
13796 char ** restrict endptr,
13798 unsigned long long int strtoull(
13799 const char * restrict nptr,
13800 char ** restrict endptr,
13803 2 The strtol, strtoll, strtoul, and strtoull functions convert the initial
13804 portion of the string pointed to by nptr to long int, long long int, unsigned
13805 long int, and unsigned long long int representation, respectively. First,
13806 they decompose the input string into three parts: an initial, possibly empty, sequence of
13807 white-space characters (as specified by the isspace function), a subject sequence
13810 283) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
13811 to the same internal floating value, but if not will round to adjacent values.
13815 resembling an integer represented in some radix determined by the value of base, and a
13816 final string of one or more unrecognized characters, including the terminating null
13817 character of the input string. Then, they attempt to convert the subject sequence to an
13818 integer, and return the result.
13819 3 If the value of base is zero, the expected form of the subject sequence is that of an
13820 integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
13821 not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
13822 expected form of the subject sequence is a sequence of letters and digits representing an
13823 integer with the radix specified by base, optionally preceded by a plus or minus sign,
13824 but not including an integer suffix. The letters from a (or A) through z (or Z) are
13825 ascribed the values 10 through 35; only letters and digits whose ascribed values are less
13826 than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
13827 optionally precede the sequence of letters and digits, following the sign if present.
13828 4 The subject sequence is defined as the longest initial subsequence of the input string,
13829 starting with the first non-white-space character, that is of the expected form. The subject
13830 sequence contains no characters if the input string is empty or consists entirely of white
13831 space, or if the first non-white-space character is other than a sign or a permissible letter
13833 5 If the subject sequence has the expected form and the value of base is zero, the sequence
13834 of characters starting with the first digit is interpreted as an integer constant according to
13835 the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
13836 is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
13837 as given above. If the subject sequence begins with a minus sign, the value resulting from
13838 the conversion is negated (in the return type). A pointer to the final string is stored in the
13839 object pointed to by endptr, provided that endptr is not a null pointer.
13840 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
13842 7 If the subject sequence is empty or does not have the expected form, no conversion is
13843 performed; the value of nptr is stored in the object pointed to by endptr, provided
13844 that endptr is not a null pointer.
13846 8 The strtol, strtoll, strtoul, and strtoull functions return the converted
13847 value, if any. If no conversion could be performed, zero is returned. If the correct value
13848 is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
13849 LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
13850 and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
13857 7.22.2 Pseudo-random sequence generation functions
13858 7.22.2.1 The rand function
13860 1 #include <stdlib.h>
13863 2 The rand function computes a sequence of pseudo-random integers in the range 0 to
13865 3 The rand function is not required to avoid data races. The implementation shall behave
13866 as if no library function calls the rand function.
13868 4 The rand function returns a pseudo-random integer.
13869 Environmental limits
13870 5 The value of the RAND_MAX macro shall be at least 32767.
13871 7.22.2.2 The srand function
13873 1 #include <stdlib.h>
13874 void srand(unsigned int seed);
13876 2 The srand function uses the argument as a seed for a new sequence of pseudo-random
13877 numbers to be returned by subsequent calls to rand. If srand is then called with the
13878 same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
13879 called before any calls to srand have been made, the same sequence shall be generated
13880 as when srand is first called with a seed value of 1.
13881 3 The implementation shall behave as if no library function calls the srand function.
13883 4 The srand function returns no value.
13888 284) There are no guarantees as to the quality of the random sequence produced and some implementations
13889 are known to produce sequences with distressingly non-random low-order bits. Applications with
13890 particular requirements should use a generator that is known to be sufficient for their needs.
13894 5 EXAMPLE The following functions define a portable implementation of rand and srand.
13895 static unsigned long int next = 1;
13896 int rand(void) // RAND_MAX assumed to be 32767
13898 next = next * 1103515245 + 12345;
13899 return (unsigned int)(next/65536) % 32768;
13901 void srand(unsigned int seed)
13906 7.22.3 Memory management functions
13907 1 The order and contiguity of storage allocated by successive calls to the
13908 aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
13909 pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
13910 a pointer to any type of object with a fundamental alignment requirement and then used
13911 to access such an object or an array of such objects in the space allocated (until the space
13912 is explicitly deallocated). The lifetime of an allocated object extends from the allocation
13913 until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
13914 any other object. The pointer returned points to the start (lowest byte address) of the
13915 allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
13916 the space requested is zero, the behavior is implementation-defined: either a null pointer
13917 is returned, or the behavior is as if the size were some nonzero value, except that the
13918 returned pointer shall not be used to access an object.
13919 7.22.3.1 The aligned_alloc function
13921 1 #include <stdlib.h>
13922 void *aligned_alloc(size_t alignment, size_t size);
13924 2 The aligned_alloc function allocates space for an object whose alignment is
13925 specified by alignment, whose size is specified by size, and whose value is
13926 indeterminate. The value of alignment shall be a valid alignment supported by the
13927 implementation and the value of size shall be an integral multiple of alignment.
13929 3 The aligned_alloc function returns either a null pointer or a pointer to the allocated
13937 7.22.3.2 The calloc function
13939 1 #include <stdlib.h>
13940 void *calloc(size_t nmemb, size_t size);
13942 2 The calloc function allocates space for an array of nmemb objects, each of whose size
13943 is size. The space is initialized to all bits zero.285)
13945 3 The calloc function returns either a null pointer or a pointer to the allocated space.
13946 7.22.3.3 The free function
13948 1 #include <stdlib.h>
13949 void free(void *ptr);
13951 2 The free function causes the space pointed to by ptr to be deallocated, that is, made
13952 available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
13953 the argument does not match a pointer earlier returned by a memory management
13954 function, or if the space has been deallocated by a call to free or realloc, the
13955 behavior is undefined.
13957 3 The free function returns no value.
13958 7.22.3.4 The malloc function
13960 1 #include <stdlib.h>
13961 void *malloc(size_t size);
13963 2 The malloc function allocates space for an object whose size is specified by size and
13964 whose value is indeterminate.
13969 285) Note that this need not be the same as the representation of floating-point zero or a null pointer
13975 3 The malloc function returns either a null pointer or a pointer to the allocated space.
13976 7.22.3.5 The realloc function
13978 1 #include <stdlib.h>
13979 void *realloc(void *ptr, size_t size);
13981 2 The realloc function deallocates the old object pointed to by ptr and returns a
13982 pointer to a new object that has the size specified by size. The contents of the new
13983 object shall be the same as that of the old object prior to deallocation, up to the lesser of
13984 the new and old sizes. Any bytes in the new object beyond the size of the old object have
13985 indeterminate values.
13986 3 If ptr is a null pointer, the realloc function behaves like the malloc function for the
13987 specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
13988 management function, or if the space has been deallocated by a call to the free or
13989 realloc function, the behavior is undefined. If memory for the new object cannot be
13990 allocated, the old object is not deallocated and its value is unchanged.
13992 4 The realloc function returns a pointer to the new object (which may have the same
13993 value as a pointer to the old object), or a null pointer if the new object could not be
13995 7.22.4 Communication with the environment
13996 7.22.4.1 The abort function
13998 1 #include <stdlib.h>
13999 _Noreturn void abort(void);
14001 2 The abort function causes abnormal program termination to occur, unless the signal
14002 SIGABRT is being caught and the signal handler does not return. Whether open streams
14003 with unwritten buffered data are flushed, open streams are closed, or temporary files are
14004 removed is implementation-defined. An implementation-defined form of the status
14005 unsuccessful termination is returned to the host environment by means of the function
14006 call raise(SIGABRT).
14014 3 The abort function does not return to its caller.
14015 7.22.4.2 The atexit function
14017 1 #include <stdlib.h>
14018 int atexit(void (*func)(void));
14020 2 The atexit function registers the function pointed to by func, to be called without
14021 arguments at normal program termination.286)
14022 Environmental limits
14023 3 The implementation shall support the registration of at least 32 functions.
14025 4 The atexit function returns zero if the registration succeeds, nonzero if it fails.
14026 Forward references: the at_quick_exit function (7.22.4.3), the exit function
14028 7.22.4.3 The at_quick_exit function
14030 1 #include <stdlib.h>
14031 int at_quick_exit(void (*func)(void));
14033 2 The at_quick_exit function registers the function pointed to by func, to be called
14034 without arguments should quick_exit be called.287)
14035 Environmental limits
14036 3 The implementation shall support the registration of at least 32 functions.
14038 4 The at_quick_exit function returns zero if the registration succeeds, nonzero if it
14040 Forward references: the quick_exit function (7.22.4.7).
14042 286) The atexit function registrations are distinct from the at_quick_exit registrations, so
14043 applications may need to call both registration functions with the same argument.
14044 287) The at_quick_exit function registrations are distinct from the atexit registrations, so
14045 applications may need to call both registration functions with the same argument.
14049 7.22.4.4 The exit function
14051 1 #include <stdlib.h>
14052 _Noreturn void exit(int status);
14054 2 The exit function causes normal program termination to occur. No functions registered
14055 by the at_quick_exit function are called. If a program calls the exit function
14056 more than once, or calls the quick_exit function in addition to the exit function, the
14057 behavior is undefined.
14058 3 First, all functions registered by the atexit function are called, in the reverse order of
14059 their registration,288) except that a function is called after any previously registered
14060 functions that had already been called at the time it was registered. If, during the call to
14061 any such function, a call to the longjmp function is made that would terminate the call
14062 to the registered function, the behavior is undefined.
14063 4 Next, all open streams with unwritten buffered data are flushed, all open streams are
14064 closed, and all files created by the tmpfile function are removed.
14065 5 Finally, control is returned to the host environment. If the value of status is zero or
14066 EXIT_SUCCESS, an implementation-defined form of the status successful termination is
14067 returned. If the value of status is EXIT_FAILURE, an implementation-defined form
14068 of the status unsuccessful termination is returned. Otherwise the status returned is
14069 implementation-defined.
14071 6 The exit function cannot return to its caller.
14072 7.22.4.5 The _Exit function
14074 1 #include <stdlib.h>
14075 _Noreturn void _Exit(int status);
14077 2 The _Exit function causes normal program termination to occur and control to be
14078 returned to the host environment. No functions registered by the atexit function, the
14079 at_quick_exit function, or signal handlers registered by the signal function are
14080 called. The status returned to the host environment is determined in the same way as for
14083 288) Each function is called as many times as it was registered, and in the correct order with respect to
14084 other registered functions.
14088 the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
14089 flushed, open streams are closed, or temporary files are removed is implementation-
14092 3 The _Exit function cannot return to its caller.
14093 7.22.4.6 The getenv function
14095 1 #include <stdlib.h>
14096 char *getenv(const char *name);
14098 2 The getenv function searches an environment list, provided by the host environment,
14099 for a string that matches the string pointed to by name. The set of environment names
14100 and the method for altering the environment list are implementation-defined. The
14101 getenv function need not avoid data races with other threads of execution that modify
14102 the environment list.289)
14103 3 The implementation shall behave as if no library function calls the getenv function.
14105 4 The getenv function returns a pointer to a string associated with the matched list
14106 member. The string pointed to shall not be modified by the program, but may be
14107 overwritten by a subsequent call to the getenv function. If the specified name cannot
14108 be found, a null pointer is returned.
14109 7.22.4.7 The quick_exit function
14111 1 #include <stdlib.h>
14112 _Noreturn void quick_exit(int status);
14114 2 The quick_exit function causes normal program termination to occur. No functions
14115 registered by the atexit function or signal handlers registered by the signal function
14116 are called. If a program calls the quick_exit function more than once, or calls the
14117 exit function in addition to the quick_exit function, the behavior is undefined.
14118 3 The quick_exit function first calls all functions registered by the at_quick_exit
14119 function, in the reverse order of their registration,290) except that a function is called after
14122 289) Many implementations provide non-standard functions that modify the environment list.
14126 any previously registered functions that had already been called at the time it was
14127 registered. If, during the call to any such function, a call to the longjmp function is
14128 made that would terminate the call to the registered function, the behavior is undefined.
14129 4 Then control is returned to the host environment by means of the function call
14132 5 The quick_exit function cannot return to its caller.
14133 7.22.4.8 The system function
14135 1 #include <stdlib.h>
14136 int system(const char *string);
14138 2 If string is a null pointer, the system function determines whether the host
14139 environment has a command processor. If string is not a null pointer, the system
14140 function passes the string pointed to by string to that command processor to be
14141 executed in a manner which the implementation shall document; this might then cause the
14142 program calling system to behave in a non-conforming manner or to terminate.
14144 3 If the argument is a null pointer, the system function returns nonzero only if a
14145 command processor is available. If the argument is not a null pointer, and the system
14146 function does return, it returns an implementation-defined value.
14147 7.22.5 Searching and sorting utilities
14148 1 These utilities make use of a comparison function to search or sort arrays of unspecified
14149 type. Where an argument declared as size_t nmemb specifies the length of the array
14150 for a function, nmemb can have the value zero on a call to that function; the comparison
14151 function is not called, a search finds no matching element, and sorting performs no
14152 rearrangement. Pointer arguments on such a call shall still have valid values, as described
14154 2 The implementation shall ensure that the second argument of the comparison function
14155 (when called from bsearch), or both arguments (when called from qsort), are
14156 pointers to elements of the array.291) The first argument when called from bsearch
14161 290) Each function is called as many times as it was registered, and in the correct order with respect to
14162 other registered functions.
14166 3 The comparison function shall not alter the contents of the array. The implementation
14167 may reorder elements of the array between calls to the comparison function, but shall not
14168 alter the contents of any individual element.
14169 4 When the same objects (consisting of size bytes, irrespective of their current positions
14170 in the array) are passed more than once to the comparison function, the results shall be
14171 consistent with one another. That is, for qsort they shall define a total ordering on the
14172 array, and for bsearch the same object shall always compare the same way with the
14174 5 A sequence point occurs immediately before and immediately after each call to the
14175 comparison function, and also between any call to the comparison function and any
14176 movement of the objects passed as arguments to that call.
14177 7.22.5.1 The bsearch function
14179 1 #include <stdlib.h>
14180 void *bsearch(const void *key, const void *base,
14181 size_t nmemb, size_t size,
14182 int (*compar)(const void *, const void *));
14184 2 The bsearch function searches an array of nmemb objects, the initial element of which
14185 is pointed to by base, for an element that matches the object pointed to by key. The
14186 size of each element of the array is specified by size.
14187 3 The comparison function pointed to by compar is called with two arguments that point
14188 to the key object and to an array element, in that order. The function shall return an
14189 integer less than, equal to, or greater than zero if the key object is considered,
14190 respectively, to be less than, to match, or to be greater than the array element. The array
14191 shall consist of: all the elements that compare less than, all the elements that compare
14192 equal to, and all the elements that compare greater than the key object, in that order.292)
14194 4 The bsearch function returns a pointer to a matching element of the array, or a null
14195 pointer if no match is found. If two elements compare as equal, which element is
14198 291) That is, if the value passed is p, then the following expressions are always nonzero:
14199 ((char *)p - (char *)base) % size == 0
14200 (char *)p >= (char *)base
14201 (char *)p < (char *)base + nmemb * size
14203 292) In practice, the entire array is sorted according to the comparison function.
14207 matched is unspecified.
14208 7.22.5.2 The qsort function
14210 1 #include <stdlib.h>
14211 void qsort(void *base, size_t nmemb, size_t size,
14212 int (*compar)(const void *, const void *));
14214 2 The qsort function sorts an array of nmemb objects, the initial element of which is
14215 pointed to by base. The size of each object is specified by size.
14216 3 The contents of the array are sorted into ascending order according to a comparison
14217 function pointed to by compar, which is called with two arguments that point to the
14218 objects being compared. The function shall return an integer less than, equal to, or
14219 greater than zero if the first argument is considered to be respectively less than, equal to,
14220 or greater than the second.
14221 4 If two elements compare as equal, their order in the resulting sorted array is unspecified.
14223 5 The qsort function returns no value.
14224 7.22.6 Integer arithmetic functions
14225 7.22.6.1 The abs, labs and llabs functions
14227 1 #include <stdlib.h>
14229 long int labs(long int j);
14230 long long int llabs(long long int j);
14232 2 The abs, labs, and llabs functions compute the absolute value of an integer j. If the
14233 result cannot be represented, the behavior is undefined.293)
14235 3 The abs, labs, and llabs, functions return the absolute value.
14240 293) The absolute value of the most negative number cannot be represented in two's complement.
14244 7.22.6.2 The div, ldiv, and lldiv functions
14246 1 #include <stdlib.h>
14247 div_t div(int numer, int denom);
14248 ldiv_t ldiv(long int numer, long int denom);
14249 lldiv_t lldiv(long long int numer, long long int denom);
14251 2 The div, ldiv, and lldiv, functions compute numer / denom and numer %
14252 denom in a single operation.
14254 3 The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
14255 lldiv_t, respectively, comprising both the quotient and the remainder. The structures
14256 shall contain (in either order) the members quot (the quotient) and rem (the remainder),
14257 each of which has the same type as the arguments numer and denom. If either part of
14258 the result cannot be represented, the behavior is undefined.
14259 7.22.7 Multibyte/wide character conversion functions
14260 1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
14261 of the current locale. For a state-dependent encoding, each function is placed into its
14262 initial conversion state at program startup and can be returned to that state by a call for
14263 which its character pointer argument, s, is a null pointer. Subsequent calls with s as
14264 other than a null pointer cause the internal conversion state of the function to be altered as
14265 necessary. A call with s as a null pointer causes these functions to return a nonzero value
14266 if encodings have state dependency, and zero otherwise.294) Changing the LC_CTYPE
14267 category causes the conversion state of these functions to be indeterminate.
14268 7.22.7.1 The mblen function
14270 1 #include <stdlib.h>
14271 int mblen(const char *s, size_t n);
14273 2 If s is not a null pointer, the mblen function determines the number of bytes contained
14274 in the multibyte character pointed to by s. Except that the conversion state of the
14275 mbtowc function is not affected, it is equivalent to
14279 294) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
14280 character codes, but are grouped with an adjacent multibyte character.
14284 mbtowc((wchar_t *)0, (const char *)0, 0);
14285 mbtowc((wchar_t *)0, s, n);
14286 3 The implementation shall behave as if no library function calls the mblen function.
14288 4 If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
14289 character encodings, respectively, do or do not have state-dependent encodings. If s is
14290 not a null pointer, the mblen function either returns 0 (if s points to the null character),
14291 or returns the number of bytes that are contained in the multibyte character (if the next n
14292 or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
14293 multibyte character).
14294 Forward references: the mbtowc function (7.22.7.2).
14295 7.22.7.2 The mbtowc function
14297 1 #include <stdlib.h>
14298 int mbtowc(wchar_t * restrict pwc,
14299 const char * restrict s,
14302 2 If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
14303 the byte pointed to by s to determine the number of bytes needed to complete the next
14304 multibyte character (including any shift sequences). If the function determines that the
14305 next multibyte character is complete and valid, it determines the value of the
14306 corresponding wide character and then, if pwc is not a null pointer, stores that value in
14307 the object pointed to by pwc. If the corresponding wide character is the null wide
14308 character, the function is left in the initial conversion state.
14309 3 The implementation shall behave as if no library function calls the mbtowc function.
14311 4 If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
14312 character encodings, respectively, do or do not have state-dependent encodings. If s is
14313 not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
14314 or returns the number of bytes that are contained in the converted multibyte character (if
14315 the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
14316 form a valid multibyte character).
14317 5 In no case will the value returned be greater than n or the value of the MB_CUR_MAX
14323 7.22.7.3 The wctomb function
14325 1 #include <stdlib.h>
14326 int wctomb(char *s, wchar_t wc);
14328 2 The wctomb function determines the number of bytes needed to represent the multibyte
14329 character corresponding to the wide character given by wc (including any shift
14330 sequences), and stores the multibyte character representation in the array whose first
14331 element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
14332 are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
14333 sequence needed to restore the initial shift state, and the function is left in the initial
14335 3 The implementation shall behave as if no library function calls the wctomb function.
14337 4 If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
14338 character encodings, respectively, do or do not have state-dependent encodings. If s is
14339 not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
14340 to a valid multibyte character, or returns the number of bytes that are contained in the
14341 multibyte character corresponding to the value of wc.
14342 5 In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
14343 7.22.8 Multibyte/wide string conversion functions
14344 1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
14345 the current locale.
14346 7.22.8.1 The mbstowcs function
14348 1 #include <stdlib.h>
14349 size_t mbstowcs(wchar_t * restrict pwcs,
14350 const char * restrict s,
14353 2 The mbstowcs function converts a sequence of multibyte characters that begins in the
14354 initial shift state from the array pointed to by s into a sequence of corresponding wide
14355 characters and stores not more than n wide characters into the array pointed to by pwcs.
14356 No multibyte characters that follow a null character (which is converted into a null wide
14357 character) will be examined or converted. Each multibyte character is converted as if by
14358 a call to the mbtowc function, except that the conversion state of the mbtowc function is
14362 3 No more than n elements will be modified in the array pointed to by pwcs. If copying
14363 takes place between objects that overlap, the behavior is undefined.
14365 4 If an invalid multibyte character is encountered, the mbstowcs function returns
14366 (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
14367 elements modified, not including a terminating null wide character, if any.295)
14368 7.22.8.2 The wcstombs function
14370 1 #include <stdlib.h>
14371 size_t wcstombs(char * restrict s,
14372 const wchar_t * restrict pwcs,
14375 2 The wcstombs function converts a sequence of wide characters from the array pointed
14376 to by pwcs into a sequence of corresponding multibyte characters that begins in the
14377 initial shift state, and stores these multibyte characters into the array pointed to by s,
14378 stopping if a multibyte character would exceed the limit of n total bytes or if a null
14379 character is stored. Each wide character is converted as if by a call to the wctomb
14380 function, except that the conversion state of the wctomb function is not affected.
14381 3 No more than n bytes will be modified in the array pointed to by s. If copying takes place
14382 between objects that overlap, the behavior is undefined.
14384 4 If a wide character is encountered that does not correspond to a valid multibyte character,
14385 the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
14386 returns the number of bytes modified, not including a terminating null character, if
14392 295) The array will not be null-terminated if the value returned is n.
14396 7.23 String handling <string.h>
14397 7.23.1 String function conventions
14398 1 The header <string.h> declares one type and several functions, and defines one
14399 macro useful for manipulating arrays of character type and other objects treated as arrays
14400 of character type.296) The type is size_t and the macro is NULL (both described in
14401 7.19). Various methods are used for determining the lengths of the arrays, but in all cases
14402 a char * or void * argument points to the initial (lowest addressed) character of the
14403 array. If an array is accessed beyond the end of an object, the behavior is undefined.
14404 2 Where an argument declared as size_t n specifies the length of the array for a
14405 function, n can have the value zero on a call to that function. Unless explicitly stated
14406 otherwise in the description of a particular function in this subclause, pointer arguments
14407 on such a call shall still have valid values, as described in 7.1.4. On such a call, a
14408 function that locates a character finds no occurrence, a function that compares two
14409 character sequences returns zero, and a function that copies characters copies zero
14411 3 For all functions in this subclause, each character shall be interpreted as if it had the type
14412 unsigned char (and therefore every possible object representation is valid and has a
14414 7.23.2 Copying functions
14415 7.23.2.1 The memcpy function
14417 1 #include <string.h>
14418 void *memcpy(void * restrict s1,
14419 const void * restrict s2,
14422 2 The memcpy function copies n characters from the object pointed to by s2 into the
14423 object pointed to by s1. If copying takes place between objects that overlap, the behavior
14426 3 The memcpy function returns the value of s1.
14431 296) See ''future library directions'' (7.30.11).
14435 7.23.2.2 The memmove function
14437 1 #include <string.h>
14438 void *memmove(void *s1, const void *s2, size_t n);
14440 2 The memmove function copies n characters from the object pointed to by s2 into the
14441 object pointed to by s1. Copying takes place as if the n characters from the object
14442 pointed to by s2 are first copied into a temporary array of n characters that does not
14443 overlap the objects pointed to by s1 and s2, and then the n characters from the
14444 temporary array are copied into the object pointed to by s1.
14446 3 The memmove function returns the value of s1.
14447 7.23.2.3 The strcpy function
14449 1 #include <string.h>
14450 char *strcpy(char * restrict s1,
14451 const char * restrict s2);
14453 2 The strcpy function copies the string pointed to by s2 (including the terminating null
14454 character) into the array pointed to by s1. If copying takes place between objects that
14455 overlap, the behavior is undefined.
14457 3 The strcpy function returns the value of s1.
14458 7.23.2.4 The strncpy function
14460 1 #include <string.h>
14461 char *strncpy(char * restrict s1,
14462 const char * restrict s2,
14465 2 The strncpy function copies not more than n characters (characters that follow a null
14466 character are not copied) from the array pointed to by s2 to the array pointed to by
14473 s1.297) If copying takes place between objects that overlap, the behavior is undefined.
14474 3 If the array pointed to by s2 is a string that is shorter than n characters, null characters
14475 are appended to the copy in the array pointed to by s1, until n characters in all have been
14478 4 The strncpy function returns the value of s1.
14479 7.23.3 Concatenation functions
14480 7.23.3.1 The strcat function
14482 1 #include <string.h>
14483 char *strcat(char * restrict s1,
14484 const char * restrict s2);
14486 2 The strcat function appends a copy of the string pointed to by s2 (including the
14487 terminating null character) to the end of the string pointed to by s1. The initial character
14488 of s2 overwrites the null character at the end of s1. If copying takes place between
14489 objects that overlap, the behavior is undefined.
14491 3 The strcat function returns the value of s1.
14492 7.23.3.2 The strncat function
14494 1 #include <string.h>
14495 char *strncat(char * restrict s1,
14496 const char * restrict s2,
14499 2 The strncat function appends not more than n characters (a null character and
14500 characters that follow it are not appended) from the array pointed to by s2 to the end of
14501 the string pointed to by s1. The initial character of s2 overwrites the null character at the
14502 end of s1. A terminating null character is always appended to the result.298) If copying
14504 297) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
14505 not be null-terminated.
14506 298) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
14511 takes place between objects that overlap, the behavior is undefined.
14513 3 The strncat function returns the value of s1.
14514 Forward references: the strlen function (7.23.6.3).
14515 7.23.4 Comparison functions
14516 1 The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
14517 and strncmp is determined by the sign of the difference between the values of the first
14518 pair of characters (both interpreted as unsigned char) that differ in the objects being
14520 7.23.4.1 The memcmp function
14522 1 #include <string.h>
14523 int memcmp(const void *s1, const void *s2, size_t n);
14525 2 The memcmp function compares the first n characters of the object pointed to by s1 to
14526 the first n characters of the object pointed to by s2.299)
14528 3 The memcmp function returns an integer greater than, equal to, or less than zero,
14529 accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
14531 7.23.4.2 The strcmp function
14533 1 #include <string.h>
14534 int strcmp(const char *s1, const char *s2);
14536 2 The strcmp function compares the string pointed to by s1 to the string pointed to by
14539 3 The strcmp function returns an integer greater than, equal to, or less than zero,
14540 accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
14542 299) The contents of ''holes'' used as padding for purposes of alignment within structure objects are
14543 indeterminate. Strings shorter than their allocated space and unions may also cause problems in
14549 7.23.4.3 The strcoll function
14551 1 #include <string.h>
14552 int strcoll(const char *s1, const char *s2);
14554 2 The strcoll function compares the string pointed to by s1 to the string pointed to by
14555 s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
14557 3 The strcoll function returns an integer greater than, equal to, or less than zero,
14558 accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
14559 pointed to by s2 when both are interpreted as appropriate to the current locale.
14560 7.23.4.4 The strncmp function
14562 1 #include <string.h>
14563 int strncmp(const char *s1, const char *s2, size_t n);
14565 2 The strncmp function compares not more than n characters (characters that follow a
14566 null character are not compared) from the array pointed to by s1 to the array pointed to
14569 3 The strncmp function returns an integer greater than, equal to, or less than zero,
14570 accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
14571 to, or less than the possibly null-terminated array pointed to by s2.
14572 7.23.4.5 The strxfrm function
14574 1 #include <string.h>
14575 size_t strxfrm(char * restrict s1,
14576 const char * restrict s2,
14579 2 The strxfrm function transforms the string pointed to by s2 and places the resulting
14580 string into the array pointed to by s1. The transformation is such that if the strcmp
14581 function is applied to two transformed strings, it returns a value greater than, equal to, or
14585 less than zero, corresponding to the result of the strcoll function applied to the same
14586 two original strings. No more than n characters are placed into the resulting array
14587 pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
14588 be a null pointer. If copying takes place between objects that overlap, the behavior is
14591 3 The strxfrm function returns the length of the transformed string (not including the
14592 terminating null character). If the value returned is n or more, the contents of the array
14593 pointed to by s1 are indeterminate.
14594 4 EXAMPLE The value of the following expression is the size of the array needed to hold the
14595 transformation of the string pointed to by s.
14596 1 + strxfrm(NULL, s, 0)
14598 7.23.5 Search functions
14599 7.23.5.1 The memchr function
14601 1 #include <string.h>
14602 void *memchr(const void *s, int c, size_t n);
14604 2 The memchr function locates the first occurrence of c (converted to an unsigned
14605 char) in the initial n characters (each interpreted as unsigned char) of the object
14608 3 The memchr function returns a pointer to the located character, or a null pointer if the
14609 character does not occur in the object.
14610 7.23.5.2 The strchr function
14612 1 #include <string.h>
14613 char *strchr(const char *s, int c);
14615 2 The strchr function locates the first occurrence of c (converted to a char) in the
14616 string pointed to by s. The terminating null character is considered to be part of the
14619 3 The strchr function returns a pointer to the located character, or a null pointer if the
14620 character does not occur in the string.
14623 7.23.5.3 The strcspn function
14625 1 #include <string.h>
14626 size_t strcspn(const char *s1, const char *s2);
14628 2 The strcspn function computes the length of the maximum initial segment of the string
14629 pointed to by s1 which consists entirely of characters not from the string pointed to by
14632 3 The strcspn function returns the length of the segment.
14633 7.23.5.4 The strpbrk function
14635 1 #include <string.h>
14636 char *strpbrk(const char *s1, const char *s2);
14638 2 The strpbrk function locates the first occurrence in the string pointed to by s1 of any
14639 character from the string pointed to by s2.
14641 3 The strpbrk function returns a pointer to the character, or a null pointer if no character
14642 from s2 occurs in s1.
14643 7.23.5.5 The strrchr function
14645 1 #include <string.h>
14646 char *strrchr(const char *s, int c);
14648 2 The strrchr function locates the last occurrence of c (converted to a char) in the
14649 string pointed to by s. The terminating null character is considered to be part of the
14652 3 The strrchr function returns a pointer to the character, or a null pointer if c does not
14653 occur in the string.
14660 7.23.5.6 The strspn function
14662 1 #include <string.h>
14663 size_t strspn(const char *s1, const char *s2);
14665 2 The strspn function computes the length of the maximum initial segment of the string
14666 pointed to by s1 which consists entirely of characters from the string pointed to by s2.
14668 3 The strspn function returns the length of the segment.
14669 7.23.5.7 The strstr function
14671 1 #include <string.h>
14672 char *strstr(const char *s1, const char *s2);
14674 2 The strstr function locates the first occurrence in the string pointed to by s1 of the
14675 sequence of characters (excluding the terminating null character) in the string pointed to
14678 3 The strstr function returns a pointer to the located string, or a null pointer if the string
14679 is not found. If s2 points to a string with zero length, the function returns s1.
14680 7.23.5.8 The strtok function
14682 1 #include <string.h>
14683 char *strtok(char * restrict s1,
14684 const char * restrict s2);
14686 2 A sequence of calls to the strtok function breaks the string pointed to by s1 into a
14687 sequence of tokens, each of which is delimited by a character from the string pointed to
14688 by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
14689 sequence have a null first argument. The separator string pointed to by s2 may be
14690 different from call to call.
14691 3 The first call in the sequence searches the string pointed to by s1 for the first character
14692 that is not contained in the current separator string pointed to by s2. If no such character
14693 is found, then there are no tokens in the string pointed to by s1 and the strtok function
14697 returns a null pointer. If such a character is found, it is the start of the first token.
14698 4 The strtok function then searches from there for a character that is contained in the
14699 current separator string. If no such character is found, the current token extends to the
14700 end of the string pointed to by s1, and subsequent searches for a token will return a null
14701 pointer. If such a character is found, it is overwritten by a null character, which
14702 terminates the current token. The strtok function saves a pointer to the following
14703 character, from which the next search for a token will start.
14704 5 Each subsequent call, with a null pointer as the value of the first argument, starts
14705 searching from the saved pointer and behaves as described above.
14706 6 The strtok function is not required to avoid data races. The implementation shall
14707 behave as if no library function calls the strtok function.
14709 7 The strtok function returns a pointer to the first character of a token, or a null pointer
14710 if there is no token.
14712 #include <string.h>
14713 static char str[] = "?a???b,,,#c";
14715 t = strtok(str, "?"); // t points to the token "a"
14716 t = strtok(NULL, ","); // t points to the token "??b"
14717 t = strtok(NULL, "#,"); // t points to the token "c"
14718 t = strtok(NULL, "?"); // t is a null pointer
14720 7.23.6 Miscellaneous functions
14721 7.23.6.1 The memset function
14723 1 #include <string.h>
14724 void *memset(void *s, int c, size_t n);
14726 2 The memset function copies the value of c (converted to an unsigned char) into
14727 each of the first n characters of the object pointed to by s.
14729 3 The memset function returns the value of s.
14736 7.23.6.2 The strerror function
14738 1 #include <string.h>
14739 char *strerror(int errnum);
14741 2 The strerror function maps the number in errnum to a message string. Typically,
14742 the values for errnum come from errno, but strerror shall map any value of type
14744 3 The strerror function is not required to avoid data races. The implementation shall
14745 behave as if no library function calls the strerror function.
14747 4 The strerror function returns a pointer to the string, the contents of which are locale-
14748 specific. The array pointed to shall not be modified by the program, but may be
14749 overwritten by a subsequent call to the strerror function.
14750 7.23.6.3 The strlen function
14752 1 #include <string.h>
14753 size_t strlen(const char *s);
14755 2 The strlen function computes the length of the string pointed to by s.
14757 3 The strlen function returns the number of characters that precede the terminating null
14765 7.24 Type-generic math <tgmath.h>
14766 1 The header <tgmath.h> includes the headers <math.h> and <complex.h> and
14767 defines several type-generic macros.
14768 2 Of the <math.h> and <complex.h> functions without an f (float) or l (long
14769 double) suffix, several have one or more parameters whose corresponding real type is
14770 double. For each such function, except modf, there is a corresponding type-generic
14771 macro.300) The parameters whose corresponding real type is double in the function
14772 synopsis are generic parameters. Use of the macro invokes a function whose
14773 corresponding real type and type domain are determined by the arguments for the generic
14775 3 Use of the macro invokes a function whose generic parameters have the corresponding
14776 real type determined as follows:
14777 -- First, if any argument for generic parameters has type long double, the type
14778 determined is long double.
14779 -- Otherwise, if any argument for generic parameters has type double or is of integer
14780 type, the type determined is double.
14781 -- Otherwise, the type determined is float.
14782 4 For each unsuffixed function in <math.h> for which there is a function in
14783 <complex.h> with the same name except for a c prefix, the corresponding type-
14784 generic macro (for both functions) has the same name as the function in <math.h>. The
14785 corresponding type-generic macro for fabs and cabs is fabs.
14790 300) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
14791 make available the corresponding ordinary function.
14792 301) If the type of the argument is not compatible with the type of the parameter for the selected function,
14793 the behavior is undefined.
14797 <math.h> <complex.h> type-generic
14798 function function macro
14816 If at least one argument for a generic parameter is complex, then use of the macro invokes
14817 a complex function; otherwise, use of the macro invokes a real function.
14818 5 For each unsuffixed function in <math.h> without a c-prefixed counterpart in
14819 <complex.h> (except modf), the corresponding type-generic macro has the same
14820 name as the function. These type-generic macros are:
14821 atan2 fma llround remainder
14822 cbrt fmax log10 remquo
14823 ceil fmin log1p rint
14824 copysign fmod log2 round
14825 erf frexp logb scalbn
14826 erfc hypot lrint scalbln
14827 exp2 ilogb lround tgamma
14828 expm1 ldexp nearbyint trunc
14829 fdim lgamma nextafter
14830 floor llrint nexttoward
14831 If all arguments for generic parameters are real, then use of the macro invokes a real
14832 function; otherwise, use of the macro results in undefined behavior.
14839 6 For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
14840 function in <math.h>, the corresponding type-generic macro has the same name as the
14841 function. These type-generic macros are:
14844 Use of the macro with any real or complex argument invokes a complex function.
14845 7 EXAMPLE With the declarations
14846 #include <tgmath.h>
14853 long double complex ldc;
14854 functions invoked by use of type-generic macros are shown in the following table:
14856 exp(n) exp(n), the function
14858 sin(d) sin(d), the function
14862 pow(ldc, f) cpowl(ldc, f)
14863 remainder(n, n) remainder(n, n), the function
14864 nextafter(d, f) nextafter(d, f), the function
14865 nexttoward(f, ld) nexttowardf(f, ld)
14866 copysign(n, ld) copysignl(n, ld)
14867 ceil(fc) undefined behavior
14868 rint(dc) undefined behavior
14869 fmax(ldc, ld) undefined behavior
14870 carg(n) carg(n), the function
14872 creal(d) creal(d), the function
14873 cimag(ld) cimagl(ld)
14875 carg(dc) carg(dc), the function
14876 cproj(ldc) cprojl(ldc)
14883 7.25 Threads <threads.h>
14884 7.25.1 Introduction
14885 1 The header <threads.h> defines macros, and declares types, enumeration constants,
14886 and functions that support multiple threads of execution.
14887 2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
14888 this header nor support any of its facilities.
14891 which expands to a value that can be used to initialize an object of type once_flag;
14893 TSS_DTOR_ITERATIONS
14894 which expands to an integer constant expression representing the maximum number of
14895 times that destructors will be called when a thread terminates.
14898 which is a complete object type that holds an identifier for a condition variable;
14900 which is a complete object type that holds an identifier for a thread;
14902 which is a complete object type that holds an identifier for a thread-specific storage
14905 which is a complete object type that holds an identifier for a mutex;
14907 which is the function pointer type void (*)(void*), used for a destructor for a
14908 thread-specific storage pointer;
14910 which is the function pointer type int (*)(void*) that is passed to thrd_create
14911 to create a new thread;
14913 which is a complete object type that holds a flag for use by call_once; and
14919 which is a structure type that holds a time specified in seconds and nanoseconds. The
14920 structure shall contain at least the following members, in any order.
14923 5 The enumeration constants are
14925 which is passed to mtx_init to create a mutex object that supports neither timeout nor
14928 which is passed to mtx_init to create a mutex object that supports recursive locking;
14930 which is passed to mtx_init to create a mutex object that supports timeout;
14932 which is passed to mtx_init to create a mutex object that supports test and return;
14934 which is returned by a timed wait function to indicate that the time specified in the call
14935 was reached without acquiring the requested resource;
14937 which is returned by a function to indicate that the requested operation succeeded;
14939 which is returned by a function to indicate that the requested operation failed because a
14940 resource requested by a test and return function is already in use;
14942 which is returned by a function to indicate that the requested operation failed; and
14944 which is returned by a function to indicate that the requested operation failed because it
14945 was unable to allocate memory.
14952 7.25.2 Initialization functions
14953 7.25.2.1 The call_once function
14955 1 #include <threads.h>
14956 void call_once(once_flag *flag, void (*func)(void));
14958 2 The call_once function uses the once_flag pointed to by flag to ensure that
14959 func is called exactly once, the first time the call_once function is called with that
14960 value of flag. Completion of an effective call to the call_once function synchronizes
14961 with all subsequent calls to the call_once function with the same value of flag.
14963 3 The call_once function returns no value.
14964 7.25.3 Condition variable functions
14965 7.25.3.1 The cnd_broadcast function
14967 1 #include <threads.h>
14968 int cnd_broadcast(cnd_t *cond);
14970 2 The cnd_broadcast function unblocks all of the threads that are blocked on the
14971 condition variable pointed to by cond at the time of the call. If no threads are blocked
14972 on the condition variable pointed to by cond at the time of the call, the function does
14975 3 The cnd_broadcast function returns thrd_success on success, or thrd_error
14976 if the request could not be honored.
14977 7.25.3.2 The cnd_destroy function
14979 1 #include <threads.h>
14980 void cnd_destroy(cnd_t *cond);
14982 2 The cnd_destroy function releases all resources used by the condition variable
14983 pointed to by cond. The cnd_destroy function requires that no threads be blocked
14984 waiting for the condition variable pointed to by cond.
14989 3 The cnd_destroy function returns no value.
14990 7.25.3.3 The cnd_init function
14992 1 #include <threads.h>
14993 int cnd_init(cnd_t *cond);
14995 2 The cnd_init function creates a condition variable. If it succeeds it sets the variable
14996 pointed to by cond to a value that uniquely identifies the newly created condition
14997 variable. A thread that calls cnd_wait on a newly created condition variable will
15000 3 The cnd_init function returns thrd_success on success, or thrd_nomem if no
15001 memory could be allocated for the newly created condition, or thrd_error if the
15002 request could not be honored.
15003 7.25.3.4 The cnd_signal function
15005 1 #include <threads.h>
15006 int cnd_signal(cnd_t *cond);
15008 2 The cnd_signal function unblocks one of the threads that are blocked on the
15009 condition variable pointed to by cond at the time of the call. If no threads are blocked
15010 on the condition variable at the time of the call, the function does nothing and return
15013 3 The cnd_signal function returns thrd_success on success or thrd_error if
15014 the request could not be honored.
15015 7.25.3.5 The cnd_timedwait function
15017 1 #include <threads.h>
15018 int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
15027 2 The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
15028 endeavors to block until the condition variable pointed to by cond is signaled by a call to
15029 cnd_signal or to cnd_broadcast, or until after the time specified by the xtime
15030 object pointed to by xt. When the calling thread becomes unblocked it locks the variable
15031 pointed to by mtx before it returns. The cnd_timedwait function requires that the
15032 mutex pointed to by mtx be locked by the calling thread.
15034 3 The cnd_timedwait function returns thrd_success upon success, or
15035 thrd_timeout if the time specified in the call was reached without acquiring the
15036 requested resource, or thrd_error if the request could not be honored.
15037 7.25.3.6 The cnd_wait function
15039 1 #include <threads.h>
15040 int cnd_wait(cnd_t *cond, mtx_t *mtx);
15042 2 The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
15043 to block until the condition variable pointed to by cond is signaled by a call to
15044 cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
15045 locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is
15046 not locked by the calling thread, the cnd_wait function will act as if the abort
15047 function is called.
15049 3 The cnd_wait function returns thrd_success on success or thrd_error if the
15050 request could not be honored.
15051 7.25.4 Mutex functions
15052 7.25.4.1 The mtx_destroy function
15054 1 #include <threads.h>
15055 void mtx_destroy(mtx_t *mtx);
15057 2 The mtx_destroy function releases any resources used by the mutex pointed to by
15058 mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
15065 3 The mtx_destroy function returns no value.
15066 7.25.4.2 The mtx_init function
15068 1 #include <threads.h>
15069 int mtx_init(mtx_t *mtx, int type);
15071 2 The mtx_init function creates a mutex object with properties indicated by type,
15072 which must have one of the six values:
15073 mtx_plain for a simple non-recursive mutex,
15074 mtx_timed for a non-recursive mutex that supports timeout,
15075 mtx_try for a non-recursive mutex that supports test and return,
15076 mtx_plain | mtx_recursive for a simple recursive mutex,
15077 mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or
15078 mtx_try | mtx_recursive for a recursive mutex that supports test and return.
15079 3 If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
15080 uniquely identifies the newly created mutex.
15082 4 The mtx_init function returns thrd_success on success, or thrd_error if the
15083 request could not be honored.
15084 7.25.4.3 The mtx_lock function
15086 1 #include <threads.h>
15087 int mtx_lock(mtx_t *mtx);
15089 2 The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
15090 is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
15091 on the same mutex shall synchronize with this operation.
15093 3 The mtx_lock function returns thrd_success on success, or thrd_busy if the
15094 resource requested is already in use, or thrd_error if the request could not be
15102 7.25.4.4 The mtx_timedlock function
15104 1 #include <threads.h>
15105 int mtx_timedlock(mtx_t *mtx, const xtime *xt);
15107 2 The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
15108 mtx or until the time specified by the xtime object xt has passed. The specified mutex
15109 shall support timeout. Prior calls to mtx_unlock on the same mutex shall synchronize
15110 with this operation. *
15112 3 The mtx_timedlock function returns thrd_success on success, or thrd_busy
15113 if the resource requested is already in use, or thrd_timeout if the time specified was
15114 reached without acquiring the requested resource, or thrd_error if the request could
15116 7.25.4.5 The mtx_trylock function
15118 1 #include <threads.h>
15119 int mtx_trylock(mtx_t *mtx);
15121 2 The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The
15122 specified mutex shall support either test and return or timeout. If the mutex is already
15123 locked, the function returns without blocking. Prior calls to mtx_unlock on the same
15124 mutex shall synchronize with this operation. *
15126 3 The mtx_trylock function returns thrd_success on success, or thrd_busy if
15127 the resource requested is already in use, or thrd_error if the request could not be
15129 7.25.4.6 The mtx_unlock function
15131 1 #include <threads.h>
15132 int mtx_unlock(mtx_t *mtx);
15134 2 The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
15135 by mtx shall be locked by the calling thread.
15140 3 The mtx_unlock function returns thrd_success on success or thrd_error if
15141 the request could not be honored.
15142 7.25.5 Thread functions
15143 7.25.5.1 The thrd_create function
15145 1 #include <threads.h>
15146 int thrd_create(thrd_t *thr, thrd_start_t func,
15149 2 The thrd_create function creates a new thread executing func(arg). If the
15150 thrd_create function succeeds, it sets the thread thr to a value that uniquely
15151 identifies the newly created thread.
15153 3 The thrd_create function returns thrd_success on success, or thrd_nomem if
15154 no memory could be allocated for the thread requested, or thrd_error if the request
15155 could not be honored.
15156 7.25.5.2 The thrd_current function
15158 1 #include <threads.h>
15159 thrd_t thrd_current(void);
15161 2 The thrd_current function identifies the thread that called it.
15163 3 The thrd_current function returns a value that uniquely identifies the thread that
15165 7.25.5.3 The thrd_detach function
15167 1 #include <threads.h>
15168 int thrd_detach(thrd_t thr);
15170 2 The thrd_detach function tells the operating system to dispose of any resources
15171 allocated to the thread identified by thr when that thread terminates. The value of the
15175 thread identified by thr value shall not have been set by a call to thrd_join or
15178 3 The thrd_detach function returns thrd_success on success or thrd_error if
15179 the request could not be honored.
15180 7.25.5.4 The thrd_equal function
15182 1 #include <threads.h>
15183 int thrd_equal(thrd_t thr0, thrd_t thr1);
15185 2 The thrd_equal function will determine whether the thread identified by thr0 refers
15186 to the thread identified by thr1.
15188 3 The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
15189 different threads. Otherwise the thrd_equal function returns a nonzero value.
15190 7.25.5.5 The thrd_exit function
15192 1 #include <threads.h>
15193 void thrd_exit(int res);
15195 2 The thrd_exit function terminates execution of the calling thread and sets its result
15198 3 The thrd_exit function returns no value.
15199 7.25.5.6 The thrd_join function
15201 1 #include <threads.h>
15202 int thrd_join(thrd_t thr, int *res);
15204 2 The thrd_join function blocks until the thread identified by thr has terminated. If
15205 the parameter res is not a null pointer, it stores the thread's result code in the integer
15206 pointed to by res. The value of the thread identified by thr shall not have been set by a
15207 call to thrd_join or thrd_detach.
15212 3 The thrd_join function returns thrd_success on success or thrd_error if the
15213 request could not be honored.
15214 7.25.5.7 The thrd_sleep function
15216 1 #include <threads.h>
15217 void thrd_sleep(const xtime *xt);
15219 2 The thrd_sleep function suspends execution of the calling thread until after the time
15220 specified by the xtime object pointed to by xt.
15222 3 The thrd_sleep function returns no value.
15223 7.25.5.8 The thrd_yield function
15225 1 #include <threads.h>
15226 void thrd_yield(void);
15228 2 The thrd_yield function endeavors to permit other threads to run, even if the current
15229 thread would ordinarily continue to run.
15231 3 The thrd_yield function returns no value.
15232 7.25.6 Thread-specific storage functions
15233 7.25.6.1 The tss_create function
15235 1 #include <threads.h>
15236 int tss_create(tss_t *key, tss_dtor_t dtor);
15238 2 The tss_create function creates a thread-specific storage pointer with destructor
15239 dtor, which may be null.
15241 3 If the tss_create function is successful, it sets the thread-specific storage pointed to
15242 by key to a value that uniquely identifies the newly created pointer and returns
15243 thrd_success; otherwise, thrd_error is returned and the thread-specific storage
15246 pointed to by key is set to an undefined value.
15247 7.25.6.2 The tss_delete function
15249 1 #include <threads.h>
15250 void tss_delete(tss_t key);
15252 2 The tss_delete function releases any resources used by the thread-specific storage
15255 3 The tss_delete function returns no value.
15256 7.25.6.3 The tss_get function
15258 1 #include <threads.h>
15259 void *tss_get(tss_t key);
15261 2 The tss_get function returns the value for the current thread held in the thread-specific
15262 storage identified by key.
15264 3 The tss_get function returns the value for the current thread if successful, or zero if
15266 7.25.6.4 The tss_set function
15268 1 #include <threads.h>
15269 int tss_set(tss_t key, void *val);
15271 2 The tss_set function sets the value for the current thread held in the thread-specific
15272 storage identified by key to val.
15274 3 The tss_set function returns thrd_success on success or thrd_error if the
15275 request could not be honored.
15282 7.25.7 Time functions
15283 7.25.7.1 The xtime_get function
15285 1 #include <threads.h>
15286 int xtime_get(xtime *xt, int base);
15288 2 The xtime_get function sets the xtime object pointed to by xt to hold the current
15289 time based on the time base base.
15291 3 If the xtime_get function is successful it returns the nonzero value base, which must
15292 be TIME_UTC; otherwise, it returns zero.302)
15297 302) Although an xtime object describes times with nanosecond resolution, the actual resolution in an
15298 xtime object is system dependent.
15302 7.26 Date and time <time.h>
15303 7.26.1 Components of time
15304 1 The header <time.h> defines two macros, and declares several types and functions for
15305 manipulating time. Many functions deal with a calendar time that represents the current
15306 date (according to the Gregorian calendar) and time. Some functions deal with local
15307 time, which is the calendar time expressed for some specific time zone, and with Daylight
15308 Saving Time, which is a temporary change in the algorithm for determining local time.
15309 The local time zone and Daylight Saving Time are implementation-defined.
15310 2 The macros defined are NULL (described in 7.19); and
15312 which expands to an expression with type clock_t (described below) that is the
15313 number per second of the value returned by the clock function.
15314 3 The types declared are size_t (described in 7.19);
15318 which are arithmetic types capable of representing times; and
15320 which holds the components of a calendar time, called the broken-down time.
15321 4 The range and precision of times representable in clock_t and time_t are
15322 implementation-defined. The tm structure shall contain at least the following members,
15323 in any order. The semantics of the members and their normal ranges are expressed in the
15325 int tm_sec; // seconds after the minute -- [0, 60]
15326 int tm_min; // minutes after the hour -- [0, 59]
15327 int tm_hour; // hours since midnight -- [0, 23]
15328 int tm_mday; // day of the month -- [1, 31]
15329 int tm_mon; // months since January -- [0, 11]
15330 int tm_year; // years since 1900
15331 int tm_wday; // days since Sunday -- [0, 6]
15332 int tm_yday; // days since January 1 -- [0, 365]
15333 int tm_isdst; // Daylight Saving Time flag
15337 303) The range [0, 60] for tm_sec allows for a positive leap second.
15341 The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
15342 Saving Time is not in effect, and negative if the information is not available.
15343 7.26.2 Time manipulation functions
15344 7.26.2.1 The clock function
15346 1 #include <time.h>
15347 clock_t clock(void);
15349 2 The clock function determines the processor time used.
15351 3 The clock function returns the implementation's best approximation to the processor
15352 time used by the program since the beginning of an implementation-defined era related
15353 only to the program invocation. To determine the time in seconds, the value returned by
15354 the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
15355 the processor time used is not available or its value cannot be represented, the function
15356 returns the value (clock_t)(-1).304)
15357 7.26.2.2 The difftime function
15359 1 #include <time.h>
15360 double difftime(time_t time1, time_t time0);
15362 2 The difftime function computes the difference between two calendar times: time1 -
15365 3 The difftime function returns the difference expressed in seconds as a double.
15370 304) In order to measure the time spent in a program, the clock function should be called at the start of
15371 the program and its return value subtracted from the value returned by subsequent calls.
15375 7.26.2.3 The mktime function
15377 1 #include <time.h>
15378 time_t mktime(struct tm *timeptr);
15380 2 The mktime function converts the broken-down time, expressed as local time, in the
15381 structure pointed to by timeptr into a calendar time value with the same encoding as
15382 that of the values returned by the time function. The original values of the tm_wday
15383 and tm_yday components of the structure are ignored, and the original values of the
15384 other components are not restricted to the ranges indicated above.305) On successful
15385 completion, the values of the tm_wday and tm_yday components of the structure are
15386 set appropriately, and the other components are set to represent the specified calendar
15387 time, but with their values forced to the ranges indicated above; the final value of
15388 tm_mday is not set until tm_mon and tm_year are determined.
15390 3 The mktime function returns the specified calendar time encoded as a value of type
15391 time_t. If the calendar time cannot be represented, the function returns the value
15393 4 EXAMPLE What day of the week is July 4, 2001?
15396 static const char *const wday[] = {
15397 "Sunday", "Monday", "Tuesday", "Wednesday",
15398 "Thursday", "Friday", "Saturday", "-unknown-"
15400 struct tm time_str;
15406 305) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
15407 Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
15408 causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.
15412 time_str.tm_year = 2001 - 1900;
15413 time_str.tm_mon = 7 - 1;
15414 time_str.tm_mday = 4;
15415 time_str.tm_hour = 0;
15416 time_str.tm_min = 0;
15417 time_str.tm_sec = 1;
15418 time_str.tm_isdst = -1;
15419 if (mktime(&time_str) == (time_t)(-1))
15420 time_str.tm_wday = 7;
15421 printf("%s\n", wday[time_str.tm_wday]);
15423 7.26.2.4 The time function
15425 1 #include <time.h>
15426 time_t time(time_t *timer);
15428 2 The time function determines the current calendar time. The encoding of the value is
15431 3 The time function returns the implementation's best approximation to the current
15432 calendar time. The value (time_t)(-1) is returned if the calendar time is not
15433 available. If timer is not a null pointer, the return value is also assigned to the object it
15435 7.26.3 Time conversion functions
15436 1 Except for the strftime function, these functions each return a pointer to one of two
15437 types of static objects: a broken-down time structure or an array of char. Execution of
15438 any of the functions that return a pointer to one of these object types may overwrite the
15439 information in any object of the same type pointed to by the value returned from any
15440 previous call to any of them and the functions are not required to avoid data races. The
15441 implementation shall behave as if no other library functions call these functions.
15442 7.26.3.1 The asctime function
15444 1 #include <time.h>
15445 char *asctime(const struct tm *timeptr);
15447 2 The asctime function converts the broken-down time in the structure pointed to by
15448 timeptr into a string in the form
15449 Sun Sep 16 01:03:52 1973\n\0
15453 using the equivalent of the following algorithm.
15454 char *asctime(const struct tm *timeptr)
15456 static const char wday_name[7][3] = {
15457 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
15459 static const char mon_name[12][3] = {
15460 "Jan", "Feb", "Mar", "Apr", "May", "Jun",
15461 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
15463 static char result[26];
15464 sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
15465 wday_name[timeptr->tm_wday],
15466 mon_name[timeptr->tm_mon],
15467 timeptr->tm_mday, timeptr->tm_hour,
15468 timeptr->tm_min, timeptr->tm_sec,
15469 1900 + timeptr->tm_year);
15472 3 If any of the fields of the broken-down time contain values that are outside their normal
15473 ranges,306) the behavior of the asctime function is undefined. Likewise, if the
15474 calculated year exceeds four digits or is less than the year 1000, the behavior is
15477 4 The asctime function returns a pointer to the string.
15478 7.26.3.2 The ctime function
15480 1 #include <time.h>
15481 char *ctime(const time_t *timer);
15483 2 The ctime function converts the calendar time pointed to by timer to local time in the
15484 form of a string. It is equivalent to
15485 asctime(localtime(timer))
15494 3 The ctime function returns the pointer returned by the asctime function with that
15495 broken-down time as argument.
15496 Forward references: the localtime function (7.26.3.4).
15497 7.26.3.3 The gmtime function
15499 1 #include <time.h>
15500 struct tm *gmtime(const time_t *timer);
15502 2 The gmtime function converts the calendar time pointed to by timer into a broken-
15503 down time, expressed as UTC.
15505 3 The gmtime function returns a pointer to the broken-down time, or a null pointer if the
15506 specified time cannot be converted to UTC.
15507 7.26.3.4 The localtime function
15509 1 #include <time.h>
15510 struct tm *localtime(const time_t *timer);
15512 2 The localtime function converts the calendar time pointed to by timer into a
15513 broken-down time, expressed as local time.
15515 3 The localtime function returns a pointer to the broken-down time, or a null pointer if
15516 the specified time cannot be converted to local time.
15517 7.26.3.5 The strftime function
15519 1 #include <time.h>
15520 size_t strftime(char * restrict s,
15522 const char * restrict format,
15523 const struct tm * restrict timeptr);
15531 2 The strftime function places characters into the array pointed to by s as controlled by
15532 the string pointed to by format. The format shall be a multibyte character sequence,
15533 beginning and ending in its initial shift state. The format string consists of zero or
15534 more conversion specifiers and ordinary multibyte characters. A conversion specifier
15535 consists of a % character, possibly followed by an E or O modifier character (described
15536 below), followed by a character that determines the behavior of the conversion specifier.
15537 All ordinary multibyte characters (including the terminating null character) are copied
15538 unchanged into the array. If copying takes place between objects that overlap, the
15539 behavior is undefined. No more than maxsize characters are placed into the array.
15540 3 Each conversion specifier is replaced by appropriate characters as described in the
15541 following list. The appropriate characters are determined using the LC_TIME category
15542 of the current locale and by the values of zero or more members of the broken-down time
15543 structure pointed to by timeptr, as specified in brackets in the description. If any of
15544 the specified values is outside the normal range, the characters stored are unspecified.
15545 %a is replaced by the locale's abbreviated weekday name. [tm_wday]
15546 %A is replaced by the locale's full weekday name. [tm_wday]
15547 %b is replaced by the locale's abbreviated month name. [tm_mon]
15548 %B is replaced by the locale's full month name. [tm_mon]
15549 %c is replaced by the locale's appropriate date and time representation. [all specified
15551 %C is replaced by the year divided by 100 and truncated to an integer, as a decimal
15552 number (00-99). [tm_year]
15553 %d is replaced by the day of the month as a decimal number (01-31). [tm_mday]
15554 %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year]
15555 %e is replaced by the day of the month as a decimal number (1-31); a single digit is
15556 preceded by a space. [tm_mday]
15557 %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon,
15559 %g is replaced by the last 2 digits of the week-based year (see below) as a decimal
15560 number (00-99). [tm_year, tm_wday, tm_yday]
15561 %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
15562 [tm_year, tm_wday, tm_yday]
15563 %h is equivalent to ''%b''. [tm_mon]
15564 %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour]
15565 %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour]
15566 %j is replaced by the day of the year as a decimal number (001-366). [tm_yday]
15567 %m is replaced by the month as a decimal number (01-12). [tm_mon]
15568 %M is replaced by the minute as a decimal number (00-59). [tm_min]
15569 %n is replaced by a new-line character.
15573 %p is replaced by the locale's equivalent of the AM/PM designations associated with a
15574 12-hour clock. [tm_hour]
15575 %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec]
15576 %R is equivalent to ''%H:%M''. [tm_hour, tm_min]
15577 %S is replaced by the second as a decimal number (00-60). [tm_sec]
15578 %t is replaced by a horizontal-tab character.
15579 %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min,
15581 %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday
15583 %U is replaced by the week number of the year (the first Sunday as the first day of week
15584 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
15585 %V is replaced by the ISO 8601 week number (see below) as a decimal number
15586 (01-53). [tm_year, tm_wday, tm_yday]
15587 %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0.
15589 %W is replaced by the week number of the year (the first Monday as the first day of
15590 week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
15591 %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1]
15592 %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1]
15593 %y is replaced by the last 2 digits of the year as a decimal number (00-99).
15595 %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year]
15596 %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4
15597 hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
15598 zone is determinable. [tm_isdst]
15599 %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no
15600 time zone is determinable. [tm_isdst]
15601 %% is replaced by %.
15602 4 Some conversion specifiers can be modified by the inclusion of an E or O modifier
15603 character to indicate an alternative format or specification. If the alternative format or
15604 specification does not exist for the current locale, the modifier is ignored.
15605 %Ec is replaced by the locale's alternative date and time representation.
15606 %EC is replaced by the name of the base year (period) in the locale's alternative
15608 %Ex is replaced by the locale's alternative date representation.
15609 %EX is replaced by the locale's alternative time representation.
15610 %Ey is replaced by the offset from %EC (year only) in the locale's alternative
15612 %EY is replaced by the locale's full alternative year representation.
15616 %Od is replaced by the day of the month, using the locale's alternative numeric symbols
15617 (filled as needed with leading zeros, or with leading spaces if there is no alternative
15619 %Oe is replaced by the day of the month, using the locale's alternative numeric symbols
15620 (filled as needed with leading spaces).
15621 %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric
15623 %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric
15625 %Om is replaced by the month, using the locale's alternative numeric symbols.
15626 %OM is replaced by the minutes, using the locale's alternative numeric symbols.
15627 %OS is replaced by the seconds, using the locale's alternative numeric symbols.
15628 %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative
15629 representation, where Monday is 1.
15630 %OU is replaced by the week number, using the locale's alternative numeric symbols.
15631 %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
15633 %Ow is replaced by the weekday as a number, using the locale's alternative numeric
15635 %OW is replaced by the week number of the year, using the locale's alternative numeric
15637 %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
15639 5 %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
15640 weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
15641 which is also the week that includes the first Thursday of the year, and is also the first
15642 week that contains at least four days in the year. If the first Monday of January is the
15643 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
15644 for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
15645 December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
15646 the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
15647 %V is replaced by 01.
15648 6 If a conversion specifier is not one of the above, the behavior is undefined.
15649 7 In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
15650 following specifiers are:
15651 %a the first three characters of %A.
15652 %A one of ''Sunday'', ''Monday'', ... , ''Saturday''.
15653 %b the first three characters of %B.
15654 %B one of ''January'', ''February'', ... , ''December''.
15655 %c equivalent to ''%a %b %e %T %Y''.
15658 %p one of ''AM'' or ''PM''.
15659 %r equivalent to ''%I:%M:%S %p''.
15660 %x equivalent to ''%m/%d/%y''.
15661 %X equivalent to %T.
15662 %Z implementation-defined.
15664 8 If the total number of resulting characters including the terminating null character is not
15665 more than maxsize, the strftime function returns the number of characters placed
15666 into the array pointed to by s not including the terminating null character. Otherwise,
15667 zero is returned and the contents of the array are indeterminate.
15674 7.27 Unicode utilities <uchar.h>
15675 1 The header <uchar.h> declares types and functions for manipulating Unicode
15677 2 The types declared are mbstate_t (described in 7.29.1) and size_t (described in
15680 which is an unsigned integer type used for 16-bit characters and is the same type as
15681 uint_least16_t (described in 7.20.1.2); and
15683 which is an unsigned integer type used for 32-bit characters and is the same type as
15684 uint_least32_t (also described in 7.20.1.2).
15685 7.27.1 Restartable multibyte/wide character conversion functions
15686 1 These functions have a parameter, ps, of type pointer to mbstate_t that points to an
15687 object that can completely describe the current conversion state of the associated
15688 multibyte character sequence, which the functions alter as necessary. If ps is a null
15689 pointer, each function uses its own internal mbstate_t object instead, which is
15690 initialized at program startup to the initial conversion state; the functions are not required
15691 to avoid data races in this case. The implementation behaves as if no library function
15692 calls these functions with a null pointer for ps.
15693 7.27.1.1 The mbrtoc16 function
15695 1 #include <uchar.h>
15696 size_t mbrtoc16(char16_t * restrict pc16,
15697 const char * restrict s, size_t n,
15698 mbstate_t * restrict ps);
15700 2 If s is a null pointer, the mbrtoc16 function is equivalent to the call:
15701 mbrtoc16(NULL, "", 1, ps)
15702 In this case, the values of the parameters pc16 and n are ignored.
15703 3 If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
15704 the byte pointed to by s to determine the number of bytes needed to complete the next
15705 multibyte character (including any shift sequences). If the function determines that the
15706 next multibyte character is complete and valid, it determines the values of the
15707 corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
15708 the first (or only) such character in the object pointed to by pc16. Subsequent calls will
15711 store successive wide characters without consuming any additional input until all the
15712 characters have been stored. If the corresponding wide character is the null wide
15713 character, the resulting state described is the initial conversion state.
15715 4 The mbrtoc16 function returns the first of the following that applies (given the current
15717 0 if the next n or fewer bytes complete the multibyte character that
15718 corresponds to the null wide character (which is the value stored).
15719 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
15720 character (which is the value stored); the value returned is the number
15721 of bytes that complete the multibyte character.
15722 (size_t)(-3) if the next character resulting from a previous call has been stored (no
15723 bytes from the input have been consumed by this call).
15724 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
15725 multibyte character, and all n bytes have been processed (no value is
15727 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
15728 do not contribute to a complete and valid multibyte character (no
15729 value is stored); the value of the macro EILSEQ is stored in errno,
15730 and the conversion state is unspecified.
15731 7.27.1.2 The c16rtomb function
15733 1 #include <uchar.h>
15734 size_t c16rtomb(char * restrict s, char16_t c16,
15735 mbstate_t * restrict ps);
15737 2 If s is a null pointer, the c16rtomb function is equivalent to the call
15738 c16rtomb(buf, L'\0', ps)
15739 where buf is an internal buffer.
15740 3 If s is not a null pointer, the c16rtomb function determines the number of bytes needed
15741 to represent the multibyte character that corresponds to the wide character given by c16
15742 (including any shift sequences), and stores the multibyte character representation in the
15744 307) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
15745 sequence of redundant shift sequences (for implementations with state-dependent encodings).
15749 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
15750 c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
15751 to restore the initial shift state; the resulting state described is the initial conversion state.
15753 4 The c16rtomb function returns the number of bytes stored in the array object (including
15754 any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
15755 the function stores the value of the macro EILSEQ in errno and returns
15756 (size_t)(-1); the conversion state is unspecified.
15757 7.27.1.3 The mbrtoc32 function
15759 1 #include <uchar.h>
15760 size_t mbrtoc32(char32_t * restrict pc32,
15761 const char * restrict s, size_t n,
15762 mbstate_t * restrict ps);
15764 2 If s is a null pointer, the mbrtoc32 function is equivalent to the call:
15765 mbrtoc32(NULL, "", 1, ps)
15766 In this case, the values of the parameters pc32 and n are ignored.
15767 3 If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
15768 the byte pointed to by s to determine the number of bytes needed to complete the next
15769 multibyte character (including any shift sequences). If the function determines that the
15770 next multibyte character is complete and valid, it determines the values of the
15771 corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
15772 the first (or only) such character in the object pointed to by pc32. Subsequent calls will
15773 store successive wide characters without consuming any additional input until all the
15774 characters have been stored. If the corresponding wide character is the null wide
15775 character, the resulting state described is the initial conversion state.
15777 4 The mbrtoc32 function returns the first of the following that applies (given the current
15779 0 if the next n or fewer bytes complete the multibyte character that
15780 corresponds to the null wide character (which is the value stored).
15781 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
15782 character (which is the value stored); the value returned is the number
15783 of bytes that complete the multibyte character.
15788 (size_t)(-3) if the next character resulting from a previous call has been stored (no
15789 bytes from the input have been consumed by this call).
15790 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
15791 multibyte character, and all n bytes have been processed (no value is
15793 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
15794 do not contribute to a complete and valid multibyte character (no
15795 value is stored); the value of the macro EILSEQ is stored in errno,
15796 and the conversion state is unspecified.
15797 7.27.1.4 The c32rtomb function
15799 1 #include <uchar.h>
15800 size_t c32rtomb(char * restrict s, char32_t c32,
15801 mbstate_t * restrict ps);
15803 2 If s is a null pointer, the c32rtomb function is equivalent to the call
15804 c32rtomb(buf, L'\0', ps)
15805 where buf is an internal buffer.
15806 3 If s is not a null pointer, the c32rtomb function determines the number of bytes needed
15807 to represent the multibyte character that corresponds to the wide character given by c32
15808 (including any shift sequences), and stores the multibyte character representation in the
15809 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
15810 c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
15811 to restore the initial shift state; the resulting state described is the initial conversion state.
15813 4 The c32rtomb function returns the number of bytes stored in the array object (including
15814 any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
15815 the function stores the value of the macro EILSEQ in errno and returns
15816 (size_t)(-1); the conversion state is unspecified.
15821 308) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
15822 sequence of redundant shift sequences (for implementations with state-dependent encodings).
15826 7.28 Extended multibyte and wide character utilities <wchar.h>
15827 7.28.1 Introduction
15828 1 The header <wchar.h> defines four macros, and declares four data types, one tag, and
15829 many functions.309)
15830 2 The types declared are wchar_t and size_t (both described in 7.19);
15832 which is a complete object type other than an array type that can hold the conversion state
15833 information necessary to convert between sequences of multibyte characters and wide
15836 which is an integer type unchanged by default argument promotions that can hold any
15837 value corresponding to members of the extended character set, as well as at least one
15838 value that does not correspond to any member of the extended character set (see WEOF
15841 which is declared as an incomplete structure type (the contents are described in 7.26.1).
15842 3 The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
15843 (described in 7.20.3); and
15845 which expands to a constant expression of type wint_t whose value does not
15846 correspond to any member of the extended character set.311) It is accepted (and returned)
15847 by several functions in this subclause to indicate end-of-file, that is, no more input from a
15848 stream. It is also used as a wide character value that does not correspond to any member
15849 of the extended character set.
15850 4 The functions declared are grouped as follows:
15851 -- Functions that perform input and output of wide characters, or multibyte characters,
15853 -- Functions that provide wide string numeric conversion;
15854 -- Functions that perform general wide string manipulation;
15857 309) See ''future library directions'' (7.30.12).
15858 310) wchar_t and wint_t can be the same integer type.
15859 311) The value of the macro WEOF may differ from that of EOF and need not be negative.
15863 -- Functions for wide string date and time conversion; and
15864 -- Functions that provide extended capabilities for conversion between multibyte and
15865 wide character sequences.
15866 5 Unless explicitly stated otherwise, if the execution of a function described in this
15867 subclause causes copying to take place between objects that overlap, the behavior is
15869 7.28.2 Formatted wide character input/output functions
15870 1 The formatted wide character input/output functions shall behave as if there is a sequence
15871 point after the actions associated with each specifier.312)
15872 7.28.2.1 The fwprintf function
15874 1 #include <stdio.h>
15876 int fwprintf(FILE * restrict stream,
15877 const wchar_t * restrict format, ...);
15879 2 The fwprintf function writes output to the stream pointed to by stream, under
15880 control of the wide string pointed to by format that specifies how subsequent arguments
15881 are converted for output. If there are insufficient arguments for the format, the behavior
15882 is undefined. If the format is exhausted while arguments remain, the excess arguments
15883 are evaluated (as always) but are otherwise ignored. The fwprintf function returns
15884 when the end of the format string is encountered.
15885 3 The format is composed of zero or more directives: ordinary wide characters (not %),
15886 which are copied unchanged to the output stream; and conversion specifications, each of
15887 which results in fetching zero or more subsequent arguments, converting them, if
15888 applicable, according to the corresponding conversion specifier, and then writing the
15889 result to the output stream.
15890 4 Each conversion specification is introduced by the wide character %. After the %, the
15891 following appear in sequence:
15892 -- Zero or more flags (in any order) that modify the meaning of the conversion
15894 -- An optional minimum field width. If the converted value has fewer wide characters
15895 than the field width, it is padded with spaces (by default) on the left (or right, if the
15898 312) The fwprintf functions perform writes to memory for the %n specifier.
15902 left adjustment flag, described later, has been given) to the field width. The field
15903 width takes the form of an asterisk * (described later) or a nonnegative decimal
15905 -- An optional precision that gives the minimum number of digits to appear for the d, i,
15906 o, u, x, and X conversions, the number of digits to appear after the decimal-point
15907 wide character for a, A, e, E, f, and F conversions, the maximum number of
15908 significant digits for the g and G conversions, or the maximum number of wide
15909 characters to be written for s conversions. The precision takes the form of a period
15910 (.) followed either by an asterisk * (described later) or by an optional decimal
15911 integer; if only the period is specified, the precision is taken as zero. If a precision
15912 appears with any other conversion specifier, the behavior is undefined.
15913 -- An optional length modifier that specifies the size of the argument.
15914 -- A conversion specifier wide character that specifies the type of conversion to be
15916 5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
15917 this case, an int argument supplies the field width or precision. The arguments
15918 specifying field width, or precision, or both, shall appear (in that order) before the
15919 argument (if any) to be converted. A negative field width argument is taken as a - flag
15920 followed by a positive field width. A negative precision argument is taken as if the
15921 precision were omitted.
15922 6 The flag wide characters and their meanings are:
15923 - The result of the conversion is left-justified within the field. (It is right-justified if
15924 this flag is not specified.)
15925 + The result of a signed conversion always begins with a plus or minus sign. (It
15926 begins with a sign only when a negative value is converted if this flag is not
15928 space If the first wide character of a signed conversion is not a sign, or if a signed
15929 conversion results in no wide characters, a space is prefixed to the result. If the
15930 space and + flags both appear, the space flag is ignored.
15931 # The result is converted to an ''alternative form''. For o conversion, it increases
15932 the precision, if and only if necessary, to force the first digit of the result to be a
15933 zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
15934 conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
15937 313) Note that 0 is taken as a flag, not as the beginning of a field width.
15938 314) The results of all floating conversions of a negative zero, and of negative values that round to zero,
15939 include a minus sign.
15943 and G conversions, the result of converting a floating-point number always
15944 contains a decimal-point wide character, even if no digits follow it. (Normally, a
15945 decimal-point wide character appears in the result of these conversions only if a
15946 digit follows it.) For g and G conversions, trailing zeros are not removed from the
15947 result. For other conversions, the behavior is undefined.
15948 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
15949 (following any indication of sign or base) are used to pad to the field width rather
15950 than performing space padding, except when converting an infinity or NaN. If the
15951 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
15952 conversions, if a precision is specified, the 0 flag is ignored. For other
15953 conversions, the behavior is undefined.
15954 7 The length modifiers and their meanings are:
15955 hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15956 signed char or unsigned char argument (the argument will have
15957 been promoted according to the integer promotions, but its value shall be
15958 converted to signed char or unsigned char before printing); or that
15959 a following n conversion specifier applies to a pointer to a signed char
15961 h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15962 short int or unsigned short int argument (the argument will
15963 have been promoted according to the integer promotions, but its value shall
15964 be converted to short int or unsigned short int before printing);
15965 or that a following n conversion specifier applies to a pointer to a short
15967 l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15968 long int or unsigned long int argument; that a following n
15969 conversion specifier applies to a pointer to a long int argument; that a
15970 following c conversion specifier applies to a wint_t argument; that a
15971 following s conversion specifier applies to a pointer to a wchar_t
15972 argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
15974 ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15975 long long int or unsigned long long int argument; or that a
15976 following n conversion specifier applies to a pointer to a long long int
15978 j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
15979 an intmax_t or uintmax_t argument; or that a following n conversion
15980 specifier applies to a pointer to an intmax_t argument.
15984 z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15985 size_t or the corresponding signed integer type argument; or that a
15986 following n conversion specifier applies to a pointer to a signed integer type
15987 corresponding to size_t argument.
15988 t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
15989 ptrdiff_t or the corresponding unsigned integer type argument; or that a
15990 following n conversion specifier applies to a pointer to a ptrdiff_t
15992 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
15993 applies to a long double argument.
15994 If a length modifier appears with any conversion specifier other than as specified above,
15995 the behavior is undefined.
15996 8 The conversion specifiers and their meanings are:
15997 d,i The int argument is converted to signed decimal in the style [-]dddd. The
15998 precision specifies the minimum number of digits to appear; if the value
15999 being converted can be represented in fewer digits, it is expanded with
16000 leading zeros. The default precision is 1. The result of converting a zero
16001 value with a precision of zero is no wide characters.
16002 o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
16003 decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
16004 letters abcdef are used for x conversion and the letters ABCDEF for X
16005 conversion. The precision specifies the minimum number of digits to appear;
16006 if the value being converted can be represented in fewer digits, it is expanded
16007 with leading zeros. The default precision is 1. The result of converting a
16008 zero value with a precision of zero is no wide characters.
16009 f,F A double argument representing a floating-point number is converted to
16010 decimal notation in the style [-]ddd.ddd, where the number of digits after
16011 the decimal-point wide character is equal to the precision specification. If the
16012 precision is missing, it is taken as 6; if the precision is zero and the # flag is
16013 not specified, no decimal-point wide character appears. If a decimal-point
16014 wide character appears, at least one digit appears before it. The value is
16015 rounded to the appropriate number of digits.
16016 A double argument representing an infinity is converted in one of the styles
16017 [-]inf or [-]infinity -- which style is implementation-defined. A
16018 double argument representing a NaN is converted in one of the styles
16019 [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
16020 any n-wchar-sequence, is implementation-defined. The F conversion
16021 specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
16025 nan, respectively.315)
16026 e,E A double argument representing a floating-point number is converted in the
16027 style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
16028 argument is nonzero) before the decimal-point wide character and the number
16029 of digits after it is equal to the precision; if the precision is missing, it is taken
16030 as 6; if the precision is zero and the # flag is not specified, no decimal-point
16031 wide character appears. The value is rounded to the appropriate number of
16032 digits. The E conversion specifier produces a number with E instead of e
16033 introducing the exponent. The exponent always contains at least two digits,
16034 and only as many more digits as necessary to represent the exponent. If the
16035 value is zero, the exponent is zero.
16036 A double argument representing an infinity or NaN is converted in the style
16037 of an f or F conversion specifier.
16038 g,G A double argument representing a floating-point number is converted in
16039 style f or e (or in style F or E in the case of a G conversion specifier),
16040 depending on the value converted and the precision. Let P equal the
16041 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
16042 Then, if a conversion with style E would have an exponent of X:
16043 -- if P > X >= -4, the conversion is with style f (or F) and precision
16045 -- otherwise, the conversion is with style e (or E) and precision P - 1.
16046 Finally, unless the # flag is used, any trailing zeros are removed from the
16047 fractional portion of the result and the decimal-point wide character is
16048 removed if there is no fractional portion remaining.
16049 A double argument representing an infinity or NaN is converted in the style
16050 of an f or F conversion specifier.
16051 a,A A double argument representing a floating-point number is converted in the
16052 style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
16053 nonzero if the argument is a normalized floating-point number and is
16054 otherwise unspecified) before the decimal-point wide character316) and the
16055 number of hexadecimal digits after it is equal to the precision; if the precision
16056 is missing and FLT_RADIX is a power of 2, then the precision is sufficient
16059 315) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
16060 meaning; the # and 0 flag wide characters have no effect.
16061 316) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
16062 character so that subsequent digits align to nibble (4-bit) boundaries.
16066 for an exact representation of the value; if the precision is missing and
16067 FLT_RADIX is not a power of 2, then the precision is sufficient to
16068 distinguish317) values of type double, except that trailing zeros may be
16069 omitted; if the precision is zero and the # flag is not specified, no decimal-
16070 point wide character appears. The letters abcdef are used for a conversion
16071 and the letters ABCDEF for A conversion. The A conversion specifier
16072 produces a number with X and P instead of x and p. The exponent always
16073 contains at least one digit, and only as many more digits as necessary to
16074 represent the decimal exponent of 2. If the value is zero, the exponent is
16076 A double argument representing an infinity or NaN is converted in the style
16077 of an f or F conversion specifier.
16078 c If no l length modifier is present, the int argument is converted to a wide
16079 character as if by calling btowc and the resulting wide character is written.
16080 If an l length modifier is present, the wint_t argument is converted to
16081 wchar_t and written.
16082 s If no l length modifier is present, the argument shall be a pointer to the initial
16083 element of a character array containing a multibyte character sequence
16084 beginning in the initial shift state. Characters from the array are converted as
16085 if by repeated calls to the mbrtowc function, with the conversion state
16086 described by an mbstate_t object initialized to zero before the first
16087 multibyte character is converted, and written up to (but not including) the
16088 terminating null wide character. If the precision is specified, no more than
16089 that many wide characters are written. If the precision is not specified or is
16090 greater than the size of the converted array, the converted array shall contain a
16091 null wide character.
16092 If an l length modifier is present, the argument shall be a pointer to the initial
16093 element of an array of wchar_t type. Wide characters from the array are
16094 written up to (but not including) a terminating null wide character. If the
16095 precision is specified, no more than that many wide characters are written. If
16096 the precision is not specified or is greater than the size of the array, the array
16097 shall contain a null wide character.
16098 p The argument shall be a pointer to void. The value of the pointer is
16099 converted to a sequence of printing wide characters, in an implementation-
16101 317) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
16102 FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
16103 might suffice depending on the implementation's scheme for determining the digit to the left of the
16104 decimal-point wide character.
16109 n The argument shall be a pointer to signed integer into which is written the
16110 number of wide characters written to the output stream so far by this call to
16111 fwprintf. No argument is converted, but one is consumed. If the
16112 conversion specification includes any flags, a field width, or a precision, the
16113 behavior is undefined.
16114 % A % wide character is written. No argument is converted. The complete
16115 conversion specification shall be %%.
16116 9 If a conversion specification is invalid, the behavior is undefined.318) If any argument is
16117 not the correct type for the corresponding conversion specification, the behavior is
16119 10 In no case does a nonexistent or small field width cause truncation of a field; if the result
16120 of a conversion is wider than the field width, the field is expanded to contain the
16122 11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
16123 to a hexadecimal floating number with the given precision.
16124 Recommended practice
16125 12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
16126 representable in the given precision, the result should be one of the two adjacent numbers
16127 in hexadecimal floating style with the given precision, with the extra stipulation that the
16128 error should have a correct sign for the current rounding direction.
16129 13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
16130 DECIMAL_DIG, then the result should be correctly rounded.319) If the number of
16131 significant decimal digits is more than DECIMAL_DIG but the source value is exactly
16132 representable with DECIMAL_DIG digits, then the result should be an exact
16133 representation with trailing zeros. Otherwise, the source value is bounded by two
16134 adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
16135 of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
16136 the error should have a correct sign for the current rounding direction.
16138 14 The fwprintf function returns the number of wide characters transmitted, or a negative
16139 value if an output or encoding error occurred.
16141 318) See ''future library directions'' (7.30.12).
16142 319) For binary-to-decimal conversion, the result format's values are the numbers representable with the
16143 given format specifier. The number of significant digits is determined by the format specifier, and in
16144 the case of fixed-point conversion by the source value as well.
16148 Environmental limits
16149 15 The number of wide characters that can be produced by any single conversion shall be at
16151 16 EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
16157 wchar_t *weekday, *month; // pointers to wide strings
16158 int day, hour, min;
16159 fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
16160 weekday, month, day, hour, min);
16161 fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
16163 Forward references: the btowc function (7.28.6.1.1), the mbrtowc function
16165 7.28.2.2 The fwscanf function
16167 1 #include <stdio.h>
16169 int fwscanf(FILE * restrict stream,
16170 const wchar_t * restrict format, ...);
16172 2 The fwscanf function reads input from the stream pointed to by stream, under
16173 control of the wide string pointed to by format that specifies the admissible input
16174 sequences and how they are to be converted for assignment, using subsequent arguments
16175 as pointers to the objects to receive the converted input. If there are insufficient
16176 arguments for the format, the behavior is undefined. If the format is exhausted while
16177 arguments remain, the excess arguments are evaluated (as always) but are otherwise
16179 3 The format is composed of zero or more directives: one or more white-space wide
16180 characters, an ordinary wide character (neither % nor a white-space wide character), or a
16181 conversion specification. Each conversion specification is introduced by the wide
16182 character %. After the %, the following appear in sequence:
16183 -- An optional assignment-suppressing wide character *.
16184 -- An optional decimal integer greater than zero that specifies the maximum field width
16185 (in wide characters).
16191 -- An optional length modifier that specifies the size of the receiving object.
16192 -- A conversion specifier wide character that specifies the type of conversion to be
16194 4 The fwscanf function executes each directive of the format in turn. When all directives
16195 have been executed, or if a directive fails (as detailed below), the function returns.
16196 Failures are described as input failures (due to the occurrence of an encoding error or the
16197 unavailability of input characters), or matching failures (due to inappropriate input).
16198 5 A directive composed of white-space wide character(s) is executed by reading input up to
16199 the first non-white-space wide character (which remains unread), or until no more wide
16200 characters can be read.
16201 6 A directive that is an ordinary wide character is executed by reading the next wide
16202 character of the stream. If that wide character differs from the directive, the directive
16203 fails and the differing and subsequent wide characters remain unread. Similarly, if end-
16204 of-file, an encoding error, or a read error prevents a wide character from being read, the
16206 7 A directive that is a conversion specification defines a set of matching input sequences, as
16207 described below for each specifier. A conversion specification is executed in the
16209 8 Input white-space wide characters (as specified by the iswspace function) are skipped,
16210 unless the specification includes a [, c, or n specifier.320)
16211 9 An input item is read from the stream, unless the specification includes an n specifier. An
16212 input item is defined as the longest sequence of input wide characters which does not
16213 exceed any specified field width and which is, or is a prefix of, a matching input
16214 sequence.321) The first wide character, if any, after the input item remains unread. If the
16215 length of the input item is zero, the execution of the directive fails; this condition is a
16216 matching failure unless end-of-file, an encoding error, or a read error prevented input
16217 from the stream, in which case it is an input failure.
16218 10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
16219 count of input wide characters) is converted to a type appropriate to the conversion
16220 specifier. If the input item is not a matching sequence, the execution of the directive fails:
16221 this condition is a matching failure. Unless assignment suppression was indicated by a *,
16222 the result of the conversion is placed in the object pointed to by the first argument
16223 following the format argument that has not already received a conversion result. If this
16226 320) These white-space wide characters are not counted against a specified field width.
16227 321) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
16228 sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
16232 object does not have an appropriate type, or if the result of the conversion cannot be
16233 represented in the object, the behavior is undefined.
16234 11 The length modifiers and their meanings are:
16235 hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16236 to an argument with type pointer to signed char or unsigned char.
16237 h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16238 to an argument with type pointer to short int or unsigned short
16240 l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16241 to an argument with type pointer to long int or unsigned long
16242 int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
16243 an argument with type pointer to double; or that a following c, s, or [
16244 conversion specifier applies to an argument with type pointer to wchar_t.
16245 ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16246 to an argument with type pointer to long long int or unsigned
16248 j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16249 to an argument with type pointer to intmax_t or uintmax_t.
16250 z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16251 to an argument with type pointer to size_t or the corresponding signed
16253 t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16254 to an argument with type pointer to ptrdiff_t or the corresponding
16255 unsigned integer type.
16256 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
16257 applies to an argument with type pointer to long double.
16258 If a length modifier appears with any conversion specifier other than as specified above,
16259 the behavior is undefined.
16260 12 The conversion specifiers and their meanings are:
16261 d Matches an optionally signed decimal integer, whose format is the same as
16262 expected for the subject sequence of the wcstol function with the value 10
16263 for the base argument. The corresponding argument shall be a pointer to
16265 i Matches an optionally signed integer, whose format is the same as expected
16266 for the subject sequence of the wcstol function with the value 0 for the
16267 base argument. The corresponding argument shall be a pointer to signed
16272 o Matches an optionally signed octal integer, whose format is the same as
16273 expected for the subject sequence of the wcstoul function with the value 8
16274 for the base argument. The corresponding argument shall be a pointer to
16276 u Matches an optionally signed decimal integer, whose format is the same as
16277 expected for the subject sequence of the wcstoul function with the value 10
16278 for the base argument. The corresponding argument shall be a pointer to
16280 x Matches an optionally signed hexadecimal integer, whose format is the same
16281 as expected for the subject sequence of the wcstoul function with the value
16282 16 for the base argument. The corresponding argument shall be a pointer to
16284 a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
16285 format is the same as expected for the subject sequence of the wcstod
16286 function. The corresponding argument shall be a pointer to floating.
16287 c Matches a sequence of wide characters of exactly the number specified by the
16288 field width (1 if no field width is present in the directive).
16289 If no l length modifier is present, characters from the input field are
16290 converted as if by repeated calls to the wcrtomb function, with the
16291 conversion state described by an mbstate_t object initialized to zero
16292 before the first wide character is converted. The corresponding argument
16293 shall be a pointer to the initial element of a character array large enough to
16294 accept the sequence. No null character is added.
16295 If an l length modifier is present, the corresponding argument shall be a
16296 pointer to the initial element of an array of wchar_t large enough to accept
16297 the sequence. No null wide character is added.
16298 s Matches a sequence of non-white-space wide characters.
16299 If no l length modifier is present, characters from the input field are
16300 converted as if by repeated calls to the wcrtomb function, with the
16301 conversion state described by an mbstate_t object initialized to zero
16302 before the first wide character is converted. The corresponding argument
16303 shall be a pointer to the initial element of a character array large enough to
16304 accept the sequence and a terminating null character, which will be added
16306 If an l length modifier is present, the corresponding argument shall be a
16307 pointer to the initial element of an array of wchar_t large enough to accept
16311 the sequence and the terminating null wide character, which will be added
16313 [ Matches a nonempty sequence of wide characters from a set of expected
16314 characters (the scanset).
16315 If no l length modifier is present, characters from the input field are
16316 converted as if by repeated calls to the wcrtomb function, with the
16317 conversion state described by an mbstate_t object initialized to zero
16318 before the first wide character is converted. The corresponding argument
16319 shall be a pointer to the initial element of a character array large enough to
16320 accept the sequence and a terminating null character, which will be added
16322 If an l length modifier is present, the corresponding argument shall be a
16323 pointer to the initial element of an array of wchar_t large enough to accept
16324 the sequence and the terminating null wide character, which will be added
16326 The conversion specifier includes all subsequent wide characters in the
16327 format string, up to and including the matching right bracket (]). The wide
16328 characters between the brackets (the scanlist) compose the scanset, unless the
16329 wide character after the left bracket is a circumflex (^), in which case the
16330 scanset contains all wide characters that do not appear in the scanlist between
16331 the circumflex and the right bracket. If the conversion specifier begins with
16332 [] or [^], the right bracket wide character is in the scanlist and the next
16333 following right bracket wide character is the matching right bracket that ends
16334 the specification; otherwise the first following right bracket wide character is
16335 the one that ends the specification. If a - wide character is in the scanlist and
16336 is not the first, nor the second where the first wide character is a ^, nor the
16337 last character, the behavior is implementation-defined.
16338 p Matches an implementation-defined set of sequences, which should be the
16339 same as the set of sequences that may be produced by the %p conversion of
16340 the fwprintf function. The corresponding argument shall be a pointer to a
16341 pointer to void. The input item is converted to a pointer value in an
16342 implementation-defined manner. If the input item is a value converted earlier
16343 during the same program execution, the pointer that results shall compare
16344 equal to that value; otherwise the behavior of the %p conversion is undefined.
16345 n No input is consumed. The corresponding argument shall be a pointer to
16346 signed integer into which is to be written the number of wide characters read
16347 from the input stream so far by this call to the fwscanf function. Execution
16348 of a %n directive does not increment the assignment count returned at the
16349 completion of execution of the fwscanf function. No argument is
16352 converted, but one is consumed. If the conversion specification includes an
16353 assignment-suppressing wide character or a field width, the behavior is
16355 % Matches a single % wide character; no conversion or assignment occurs. The
16356 complete conversion specification shall be %%.
16357 13 If a conversion specification is invalid, the behavior is undefined.322)
16358 14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
16359 respectively, a, e, f, g, and x.
16360 15 Trailing white space (including new-line wide characters) is left unread unless matched
16361 by a directive. The success of literal matches and suppressed assignments is not directly
16362 determinable other than via the %n directive.
16364 16 The fwscanf function returns the value of the macro EOF if an input failure occurs
16365 before the first conversion (if any) has completed. Otherwise, the function returns the
16366 number of input items assigned, which can be fewer than provided for, or even zero, in
16367 the event of an early matching failure.
16368 17 EXAMPLE 1 The call:
16372 int n, i; float x; wchar_t name[50];
16373 n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
16374 with the input line:
16375 25 54.32E-1 thompson
16376 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
16379 18 EXAMPLE 2 The call:
16383 int i; float x; double y;
16384 fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
16387 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
16388 56.0. The next wide character read from the input stream will be a.
16391 322) See ''future library directions'' (7.30.12).
16395 Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the
16396 wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb
16397 function (7.28.6.3.3).
16398 7.28.2.3 The swprintf function
16400 1 #include <wchar.h>
16401 int swprintf(wchar_t * restrict s,
16403 const wchar_t * restrict format, ...);
16405 2 The swprintf function is equivalent to fwprintf, except that the argument s
16406 specifies an array of wide characters into which the generated output is to be written,
16407 rather than written to a stream. No more than n wide characters are written, including a
16408 terminating null wide character, which is always added (unless n is zero).
16410 3 The swprintf function returns the number of wide characters written in the array, not
16411 counting the terminating null wide character, or a negative value if an encoding error
16412 occurred or if n or more wide characters were requested to be written.
16413 7.28.2.4 The swscanf function
16415 1 #include <wchar.h>
16416 int swscanf(const wchar_t * restrict s,
16417 const wchar_t * restrict format, ...);
16419 2 The swscanf function is equivalent to fwscanf, except that the argument s specifies a
16420 wide string from which the input is to be obtained, rather than from a stream. Reaching
16421 the end of the wide string is equivalent to encountering end-of-file for the fwscanf
16424 3 The swscanf function returns the value of the macro EOF if an input failure occurs
16425 before the first conversion (if any) has completed. Otherwise, the swscanf function
16426 returns the number of input items assigned, which can be fewer than provided for, or even
16427 zero, in the event of an early matching failure.
16434 7.28.2.5 The vfwprintf function
16436 1 #include <stdarg.h>
16439 int vfwprintf(FILE * restrict stream,
16440 const wchar_t * restrict format,
16443 2 The vfwprintf function is equivalent to fwprintf, with the variable argument list
16444 replaced by arg, which shall have been initialized by the va_start macro (and
16445 possibly subsequent va_arg calls). The vfwprintf function does not invoke the
16448 3 The vfwprintf function returns the number of wide characters transmitted, or a
16449 negative value if an output or encoding error occurred.
16450 4 EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting
16452 #include <stdarg.h>
16455 void error(char *function_name, wchar_t *format, ...)
16458 va_start(args, format);
16459 // print out name of function causing error
16460 fwprintf(stderr, L"ERROR in %s: ", function_name);
16461 // print out remainder of message
16462 vfwprintf(stderr, format, args);
16469 323) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
16470 invoke the va_arg macro, the value of arg after the return is indeterminate.
16474 7.28.2.6 The vfwscanf function
16476 1 #include <stdarg.h>
16479 int vfwscanf(FILE * restrict stream,
16480 const wchar_t * restrict format,
16483 2 The vfwscanf function is equivalent to fwscanf, with the variable argument list
16484 replaced by arg, which shall have been initialized by the va_start macro (and
16485 possibly subsequent va_arg calls). The vfwscanf function does not invoke the
16488 3 The vfwscanf function returns the value of the macro EOF if an input failure occurs
16489 before the first conversion (if any) has completed. Otherwise, the vfwscanf function
16490 returns the number of input items assigned, which can be fewer than provided for, or even
16491 zero, in the event of an early matching failure.
16492 7.28.2.7 The vswprintf function
16494 1 #include <stdarg.h>
16496 int vswprintf(wchar_t * restrict s,
16498 const wchar_t * restrict format,
16501 2 The vswprintf function is equivalent to swprintf, with the variable argument list
16502 replaced by arg, which shall have been initialized by the va_start macro (and
16503 possibly subsequent va_arg calls). The vswprintf function does not invoke the
16506 3 The vswprintf function returns the number of wide characters written in the array, not
16507 counting the terminating null wide character, or a negative value if an encoding error
16508 occurred or if n or more wide characters were requested to be generated.
16513 7.28.2.8 The vswscanf function
16515 1 #include <stdarg.h>
16517 int vswscanf(const wchar_t * restrict s,
16518 const wchar_t * restrict format,
16521 2 The vswscanf function is equivalent to swscanf, with the variable argument list
16522 replaced by arg, which shall have been initialized by the va_start macro (and
16523 possibly subsequent va_arg calls). The vswscanf function does not invoke the
16526 3 The vswscanf function returns the value of the macro EOF if an input failure occurs
16527 before the first conversion (if any) has completed. Otherwise, the vswscanf function
16528 returns the number of input items assigned, which can be fewer than provided for, or even
16529 zero, in the event of an early matching failure.
16530 7.28.2.9 The vwprintf function
16532 1 #include <stdarg.h>
16534 int vwprintf(const wchar_t * restrict format,
16537 2 The vwprintf function is equivalent to wprintf, with the variable argument list
16538 replaced by arg, which shall have been initialized by the va_start macro (and
16539 possibly subsequent va_arg calls). The vwprintf function does not invoke the
16542 3 The vwprintf function returns the number of wide characters transmitted, or a negative
16543 value if an output or encoding error occurred.
16550 7.28.2.10 The vwscanf function
16552 1 #include <stdarg.h>
16554 int vwscanf(const wchar_t * restrict format,
16557 2 The vwscanf function is equivalent to wscanf, with the variable argument list
16558 replaced by arg, which shall have been initialized by the va_start macro (and
16559 possibly subsequent va_arg calls). The vwscanf function does not invoke the
16562 3 The vwscanf function returns the value of the macro EOF if an input failure occurs
16563 before the first conversion (if any) has completed. Otherwise, the vwscanf function
16564 returns the number of input items assigned, which can be fewer than provided for, or even
16565 zero, in the event of an early matching failure.
16566 7.28.2.11 The wprintf function
16568 1 #include <wchar.h>
16569 int wprintf(const wchar_t * restrict format, ...);
16571 2 The wprintf function is equivalent to fwprintf with the argument stdout
16572 interposed before the arguments to wprintf.
16574 3 The wprintf function returns the number of wide characters transmitted, or a negative
16575 value if an output or encoding error occurred.
16576 7.28.2.12 The wscanf function
16578 1 #include <wchar.h>
16579 int wscanf(const wchar_t * restrict format, ...);
16581 2 The wscanf function is equivalent to fwscanf with the argument stdin interposed
16582 before the arguments to wscanf.
16588 3 The wscanf function returns the value of the macro EOF if an input failure occurs
16589 before the first conversion (if any) has completed. Otherwise, the wscanf function
16590 returns the number of input items assigned, which can be fewer than provided for, or even
16591 zero, in the event of an early matching failure.
16592 7.28.3 Wide character input/output functions
16593 7.28.3.1 The fgetwc function
16595 1 #include <stdio.h>
16597 wint_t fgetwc(FILE *stream);
16599 2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
16600 next wide character is present, the fgetwc function obtains that wide character as a
16601 wchar_t converted to a wint_t and advances the associated file position indicator for
16602 the stream (if defined).
16604 3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
16605 of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
16606 the fgetwc function returns the next wide character from the input stream pointed to by
16607 stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
16608 function returns WEOF. If an encoding error occurs (including too few bytes), the value of
16609 the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.324)
16610 7.28.3.2 The fgetws function
16612 1 #include <stdio.h>
16614 wchar_t *fgetws(wchar_t * restrict s,
16615 int n, FILE * restrict stream);
16617 2 The fgetws function reads at most one less than the number of wide characters
16618 specified by n from the stream pointed to by stream into the array pointed to by s. No
16621 324) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
16622 Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.
16626 additional wide characters are read after a new-line wide character (which is retained) or
16627 after end-of-file. A null wide character is written immediately after the last wide
16628 character read into the array.
16630 3 The fgetws function returns s if successful. If end-of-file is encountered and no
16631 characters have been read into the array, the contents of the array remain unchanged and a
16632 null pointer is returned. If a read or encoding error occurs during the operation, the array
16633 contents are indeterminate and a null pointer is returned.
16634 7.28.3.3 The fputwc function
16636 1 #include <stdio.h>
16638 wint_t fputwc(wchar_t c, FILE *stream);
16640 2 The fputwc function writes the wide character specified by c to the output stream
16641 pointed to by stream, at the position indicated by the associated file position indicator
16642 for the stream (if defined), and advances the indicator appropriately. If the file cannot
16643 support positioning requests, or if the stream was opened with append mode, the
16644 character is appended to the output stream.
16646 3 The fputwc function returns the wide character written. If a write error occurs, the
16647 error indicator for the stream is set and fputwc returns WEOF. If an encoding error
16648 occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.
16649 7.28.3.4 The fputws function
16651 1 #include <stdio.h>
16653 int fputws(const wchar_t * restrict s,
16654 FILE * restrict stream);
16656 2 The fputws function writes the wide string pointed to by s to the stream pointed to by
16657 stream. The terminating null wide character is not written.
16659 3 The fputws function returns EOF if a write or encoding error occurs; otherwise, it
16660 returns a nonnegative value.
16664 7.28.3.5 The fwide function
16666 1 #include <stdio.h>
16668 int fwide(FILE *stream, int mode);
16670 2 The fwide function determines the orientation of the stream pointed to by stream. If
16671 mode is greater than zero, the function first attempts to make the stream wide oriented. If
16672 mode is less than zero, the function first attempts to make the stream byte oriented.325)
16673 Otherwise, mode is zero and the function does not alter the orientation of the stream.
16675 3 The fwide function returns a value greater than zero if, after the call, the stream has
16676 wide orientation, a value less than zero if the stream has byte orientation, or zero if the
16677 stream has no orientation.
16678 7.28.3.6 The getwc function
16680 1 #include <stdio.h>
16682 wint_t getwc(FILE *stream);
16684 2 The getwc function is equivalent to fgetwc, except that if it is implemented as a
16685 macro, it may evaluate stream more than once, so the argument should never be an
16686 expression with side effects.
16688 3 The getwc function returns the next wide character from the input stream pointed to by
16690 7.28.3.7 The getwchar function
16692 1 #include <wchar.h>
16693 wint_t getwchar(void);
16698 325) If the orientation of the stream has already been determined, fwide does not change it.
16703 2 The getwchar function is equivalent to getwc with the argument stdin.
16705 3 The getwchar function returns the next wide character from the input stream pointed to
16707 7.28.3.8 The putwc function
16709 1 #include <stdio.h>
16711 wint_t putwc(wchar_t c, FILE *stream);
16713 2 The putwc function is equivalent to fputwc, except that if it is implemented as a
16714 macro, it may evaluate stream more than once, so that argument should never be an
16715 expression with side effects.
16717 3 The putwc function returns the wide character written, or WEOF.
16718 7.28.3.9 The putwchar function
16720 1 #include <wchar.h>
16721 wint_t putwchar(wchar_t c);
16723 2 The putwchar function is equivalent to putwc with the second argument stdout.
16725 3 The putwchar function returns the character written, or WEOF.
16726 7.28.3.10 The ungetwc function
16728 1 #include <stdio.h>
16730 wint_t ungetwc(wint_t c, FILE *stream);
16732 2 The ungetwc function pushes the wide character specified by c back onto the input
16733 stream pointed to by stream. Pushed-back wide characters will be returned by
16734 subsequent reads on that stream in the reverse order of their pushing. A successful
16738 intervening call (with the stream pointed to by stream) to a file positioning function
16739 (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
16740 stream. The external storage corresponding to the stream is unchanged.
16741 3 One wide character of pushback is guaranteed, even if the call to the ungetwc function
16742 follows just after a call to a formatted wide character input function fwscanf,
16743 vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
16744 on the same stream without an intervening read or file positioning operation on that
16745 stream, the operation may fail.
16746 4 If the value of c equals that of the macro WEOF, the operation fails and the input stream is
16748 5 A successful call to the ungetwc function clears the end-of-file indicator for the stream.
16749 The value of the file position indicator for the stream after reading or discarding all
16750 pushed-back wide characters is the same as it was before the wide characters were pushed
16751 back. For a text or binary stream, the value of its file position indicator after a successful
16752 call to the ungetwc function is unspecified until all pushed-back wide characters are
16755 6 The ungetwc function returns the wide character pushed back, or WEOF if the operation
16757 7.28.4 General wide string utilities
16758 1 The header <wchar.h> declares a number of functions useful for wide string
16759 manipulation. Various methods are used for determining the lengths of the arrays, but in
16760 all cases a wchar_t * argument points to the initial (lowest addressed) element of the
16761 array. If an array is accessed beyond the end of an object, the behavior is undefined.
16762 2 Where an argument declared as size_t n determines the length of the array for a
16763 function, n can have the value zero on a call to that function. Unless explicitly stated
16764 otherwise in the description of a particular function in this subclause, pointer arguments
16765 on such a call shall still have valid values, as described in 7.1.4. On such a call, a
16766 function that locates a wide character finds no occurrence, a function that compares two
16767 wide character sequences returns zero, and a function that copies wide characters copies
16768 zero wide characters.
16775 7.28.4.1 Wide string numeric conversion functions
16776 7.28.4.1.1 The wcstod, wcstof, and wcstold functions
16778 1 #include <wchar.h>
16779 double wcstod(const wchar_t * restrict nptr,
16780 wchar_t ** restrict endptr);
16781 float wcstof(const wchar_t * restrict nptr,
16782 wchar_t ** restrict endptr);
16783 long double wcstold(const wchar_t * restrict nptr,
16784 wchar_t ** restrict endptr);
16786 2 The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
16787 string pointed to by nptr to double, float, and long double representation,
16788 respectively. First, they decompose the input string into three parts: an initial, possibly
16789 empty, sequence of white-space wide characters (as specified by the iswspace
16790 function), a subject sequence resembling a floating-point constant or representing an
16791 infinity or NaN; and a final wide string of one or more unrecognized wide characters,
16792 including the terminating null wide character of the input wide string. Then, they attempt
16793 to convert the subject sequence to a floating-point number, and return the result.
16794 3 The expected form of the subject sequence is an optional plus or minus sign, then one of
16796 -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
16797 character, then an optional exponent part as defined for the corresponding single-byte
16798 characters in 6.4.4.2;
16799 -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
16800 decimal-point wide character, then an optional binary exponent part as defined in
16802 -- INF or INFINITY, or any other wide string equivalent except for case
16803 -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
16804 case in the NAN part, where:
16808 n-wchar-sequence digit
16809 n-wchar-sequence nondigit
16810 The subject sequence is defined as the longest initial subsequence of the input wide
16811 string, starting with the first non-white-space wide character, that is of the expected form.
16814 The subject sequence contains no wide characters if the input wide string is not of the
16816 4 If the subject sequence has the expected form for a floating-point number, the sequence of
16817 wide characters starting with the first digit or the decimal-point wide character
16818 (whichever occurs first) is interpreted as a floating constant according to the rules of
16819 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
16820 if neither an exponent part nor a decimal-point wide character appears in a decimal
16821 floating point number, or if a binary exponent part does not appear in a hexadecimal
16822 floating point number, an exponent part of the appropriate type with value zero is
16823 assumed to follow the last digit in the string. If the subject sequence begins with a minus
16824 sign, the sequence is interpreted as negated.326) A wide character sequence INF or
16825 INFINITY is interpreted as an infinity, if representable in the return type, else like a
16826 floating constant that is too large for the range of the return type. A wide character
16827 sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
16828 in the return type, else like a subject sequence part that does not have the expected form;
16829 the meaning of the n-wchar sequences is implementation-defined.327) A pointer to the
16830 final wide string is stored in the object pointed to by endptr, provided that endptr is
16831 not a null pointer.
16832 5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
16833 value resulting from the conversion is correctly rounded.
16834 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
16836 7 If the subject sequence is empty or does not have the expected form, no conversion is
16837 performed; the value of nptr is stored in the object pointed to by endptr, provided
16838 that endptr is not a null pointer.
16839 Recommended practice
16840 8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
16841 the result is not exactly representable, the result should be one of the two numbers in the
16842 appropriate internal format that are adjacent to the hexadecimal floating source value,
16843 with the extra stipulation that the error should have a correct sign for the current rounding
16848 326) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
16849 negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
16850 methods may yield different results if rounding is toward positive or negative infinity. In either case,
16851 the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
16852 327) An implementation may use the n-wchar sequence to determine extra information to be represented in
16853 the NaN's significand.
16857 9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
16858 <float.h>) significant digits, the result should be correctly rounded. If the subject
16859 sequence D has the decimal form and more than DECIMAL_DIG significant digits,
16860 consider the two bounding, adjacent decimal strings L and U, both having
16861 DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
16862 The result should be one of the (equal or adjacent) values that would be obtained by
16863 correctly rounding L and U according to the current rounding direction, with the extra
16864 stipulation that the error with respect to D should have a correct sign for the current
16865 rounding direction.328)
16867 10 The functions return the converted value, if any. If no conversion could be performed,
16868 zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
16869 plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
16870 return type and sign of the value), and the value of the macro ERANGE is stored in
16871 errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
16872 no greater than the smallest normalized positive number in the return type; whether
16873 errno acquires the value ERANGE is implementation-defined.
16878 328) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
16879 to the same internal floating value, but if not will round to adjacent values.
16883 7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
16885 1 #include <wchar.h>
16887 const wchar_t * restrict nptr,
16888 wchar_t ** restrict endptr,
16890 long long int wcstoll(
16891 const wchar_t * restrict nptr,
16892 wchar_t ** restrict endptr,
16894 unsigned long int wcstoul(
16895 const wchar_t * restrict nptr,
16896 wchar_t ** restrict endptr,
16898 unsigned long long int wcstoull(
16899 const wchar_t * restrict nptr,
16900 wchar_t ** restrict endptr,
16903 2 The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
16904 portion of the wide string pointed to by nptr to long int, long long int,
16905 unsigned long int, and unsigned long long int representation,
16906 respectively. First, they decompose the input string into three parts: an initial, possibly
16907 empty, sequence of white-space wide characters (as specified by the iswspace
16908 function), a subject sequence resembling an integer represented in some radix determined
16909 by the value of base, and a final wide string of one or more unrecognized wide
16910 characters, including the terminating null wide character of the input wide string. Then,
16911 they attempt to convert the subject sequence to an integer, and return the result.
16912 3 If the value of base is zero, the expected form of the subject sequence is that of an
16913 integer constant as described for the corresponding single-byte characters in 6.4.4.1,
16914 optionally preceded by a plus or minus sign, but not including an integer suffix. If the
16915 value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
16916 is a sequence of letters and digits representing an integer with the radix specified by
16917 base, optionally preceded by a plus or minus sign, but not including an integer suffix.
16918 The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
16919 letters and digits whose ascribed values are less than that of base are permitted. If the
16920 value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
16921 of letters and digits, following the sign if present.
16925 4 The subject sequence is defined as the longest initial subsequence of the input wide
16926 string, starting with the first non-white-space wide character, that is of the expected form.
16927 The subject sequence contains no wide characters if the input wide string is empty or
16928 consists entirely of white space, or if the first non-white-space wide character is other
16929 than a sign or a permissible letter or digit.
16930 5 If the subject sequence has the expected form and the value of base is zero, the sequence
16931 of wide characters starting with the first digit is interpreted as an integer constant
16932 according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
16933 value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
16934 letter its value as given above. If the subject sequence begins with a minus sign, the value
16935 resulting from the conversion is negated (in the return type). A pointer to the final wide
16936 string is stored in the object pointed to by endptr, provided that endptr is not a null
16938 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
16940 7 If the subject sequence is empty or does not have the expected form, no conversion is
16941 performed; the value of nptr is stored in the object pointed to by endptr, provided
16942 that endptr is not a null pointer.
16944 8 The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
16945 value, if any. If no conversion could be performed, zero is returned. If the correct value
16946 is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
16947 LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
16948 sign of the value, if any), and the value of the macro ERANGE is stored in errno.
16949 7.28.4.2 Wide string copying functions
16950 7.28.4.2.1 The wcscpy function
16952 1 #include <wchar.h>
16953 wchar_t *wcscpy(wchar_t * restrict s1,
16954 const wchar_t * restrict s2);
16956 2 The wcscpy function copies the wide string pointed to by s2 (including the terminating
16957 null wide character) into the array pointed to by s1.
16959 3 The wcscpy function returns the value of s1.
16964 7.28.4.2.2 The wcsncpy function
16966 1 #include <wchar.h>
16967 wchar_t *wcsncpy(wchar_t * restrict s1,
16968 const wchar_t * restrict s2,
16971 2 The wcsncpy function copies not more than n wide characters (those that follow a null
16972 wide character are not copied) from the array pointed to by s2 to the array pointed to by
16974 3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
16975 wide characters are appended to the copy in the array pointed to by s1, until n wide
16976 characters in all have been written.
16978 4 The wcsncpy function returns the value of s1.
16979 7.28.4.2.3 The wmemcpy function
16981 1 #include <wchar.h>
16982 wchar_t *wmemcpy(wchar_t * restrict s1,
16983 const wchar_t * restrict s2,
16986 2 The wmemcpy function copies n wide characters from the object pointed to by s2 to the
16987 object pointed to by s1.
16989 3 The wmemcpy function returns the value of s1.
16994 329) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
16995 result will not be null-terminated.
16999 7.28.4.2.4 The wmemmove function
17001 1 #include <wchar.h>
17002 wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
17005 2 The wmemmove function copies n wide characters from the object pointed to by s2 to
17006 the object pointed to by s1. Copying takes place as if the n wide characters from the
17007 object pointed to by s2 are first copied into a temporary array of n wide characters that
17008 does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
17009 the temporary array are copied into the object pointed to by s1.
17011 3 The wmemmove function returns the value of s1.
17012 7.28.4.3 Wide string concatenation functions
17013 7.28.4.3.1 The wcscat function
17015 1 #include <wchar.h>
17016 wchar_t *wcscat(wchar_t * restrict s1,
17017 const wchar_t * restrict s2);
17019 2 The wcscat function appends a copy of the wide string pointed to by s2 (including the
17020 terminating null wide character) to the end of the wide string pointed to by s1. The initial
17021 wide character of s2 overwrites the null wide character at the end of s1.
17023 3 The wcscat function returns the value of s1.
17024 7.28.4.3.2 The wcsncat function
17026 1 #include <wchar.h>
17027 wchar_t *wcsncat(wchar_t * restrict s1,
17028 const wchar_t * restrict s2,
17031 2 The wcsncat function appends not more than n wide characters (a null wide character
17032 and those that follow it are not appended) from the array pointed to by s2 to the end of
17036 the wide string pointed to by s1. The initial wide character of s2 overwrites the null
17037 wide character at the end of s1. A terminating null wide character is always appended to
17040 3 The wcsncat function returns the value of s1.
17041 7.28.4.4 Wide string comparison functions
17042 1 Unless explicitly stated otherwise, the functions described in this subclause order two
17043 wide characters the same way as two integers of the underlying integer type designated
17045 7.28.4.4.1 The wcscmp function
17047 1 #include <wchar.h>
17048 int wcscmp(const wchar_t *s1, const wchar_t *s2);
17050 2 The wcscmp function compares the wide string pointed to by s1 to the wide string
17053 3 The wcscmp function returns an integer greater than, equal to, or less than zero,
17054 accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
17055 wide string pointed to by s2.
17056 7.28.4.4.2 The wcscoll function
17058 1 #include <wchar.h>
17059 int wcscoll(const wchar_t *s1, const wchar_t *s2);
17061 2 The wcscoll function compares the wide string pointed to by s1 to the wide string
17062 pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
17065 3 The wcscoll function returns an integer greater than, equal to, or less than zero,
17066 accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
17069 330) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
17074 wide string pointed to by s2 when both are interpreted as appropriate to the current
17076 7.28.4.4.3 The wcsncmp function
17078 1 #include <wchar.h>
17079 int wcsncmp(const wchar_t *s1, const wchar_t *s2,
17082 2 The wcsncmp function compares not more than n wide characters (those that follow a
17083 null wide character are not compared) from the array pointed to by s1 to the array
17086 3 The wcsncmp function returns an integer greater than, equal to, or less than zero,
17087 accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
17088 to, or less than the possibly null-terminated array pointed to by s2.
17089 7.28.4.4.4 The wcsxfrm function
17091 1 #include <wchar.h>
17092 size_t wcsxfrm(wchar_t * restrict s1,
17093 const wchar_t * restrict s2,
17096 2 The wcsxfrm function transforms the wide string pointed to by s2 and places the
17097 resulting wide string into the array pointed to by s1. The transformation is such that if
17098 the wcscmp function is applied to two transformed wide strings, it returns a value greater
17099 than, equal to, or less than zero, corresponding to the result of the wcscoll function
17100 applied to the same two original wide strings. No more than n wide characters are placed
17101 into the resulting array pointed to by s1, including the terminating null wide character. If
17102 n is zero, s1 is permitted to be a null pointer.
17104 3 The wcsxfrm function returns the length of the transformed wide string (not including
17105 the terminating null wide character). If the value returned is n or greater, the contents of
17106 the array pointed to by s1 are indeterminate.
17107 4 EXAMPLE The value of the following expression is the length of the array needed to hold the
17108 transformation of the wide string pointed to by s:
17113 1 + wcsxfrm(NULL, s, 0)
17115 7.28.4.4.5 The wmemcmp function
17117 1 #include <wchar.h>
17118 int wmemcmp(const wchar_t *s1, const wchar_t *s2,
17121 2 The wmemcmp function compares the first n wide characters of the object pointed to by
17122 s1 to the first n wide characters of the object pointed to by s2.
17124 3 The wmemcmp function returns an integer greater than, equal to, or less than zero,
17125 accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
17127 7.28.4.5 Wide string search functions
17128 7.28.4.5.1 The wcschr function
17130 1 #include <wchar.h>
17131 wchar_t *wcschr(const wchar_t *s, wchar_t c);
17133 2 The wcschr function locates the first occurrence of c in the wide string pointed to by s.
17134 The terminating null wide character is considered to be part of the wide string.
17136 3 The wcschr function returns a pointer to the located wide character, or a null pointer if
17137 the wide character does not occur in the wide string.
17138 7.28.4.5.2 The wcscspn function
17140 1 #include <wchar.h>
17141 size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
17143 2 The wcscspn function computes the length of the maximum initial segment of the wide
17144 string pointed to by s1 which consists entirely of wide characters not from the wide
17145 string pointed to by s2.
17152 3 The wcscspn function returns the length of the segment.
17153 7.28.4.5.3 The wcspbrk function
17155 1 #include <wchar.h>
17156 wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
17158 2 The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
17159 any wide character from the wide string pointed to by s2.
17161 3 The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
17162 no wide character from s2 occurs in s1.
17163 7.28.4.5.4 The wcsrchr function
17165 1 #include <wchar.h>
17166 wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
17168 2 The wcsrchr function locates the last occurrence of c in the wide string pointed to by
17169 s. The terminating null wide character is considered to be part of the wide string.
17171 3 The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
17172 not occur in the wide string.
17173 7.28.4.5.5 The wcsspn function
17175 1 #include <wchar.h>
17176 size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
17178 2 The wcsspn function computes the length of the maximum initial segment of the wide
17179 string pointed to by s1 which consists entirely of wide characters from the wide string
17182 3 The wcsspn function returns the length of the segment.
17187 7.28.4.5.6 The wcsstr function
17189 1 #include <wchar.h>
17190 wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
17192 2 The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
17193 the sequence of wide characters (excluding the terminating null wide character) in the
17194 wide string pointed to by s2.
17196 3 The wcsstr function returns a pointer to the located wide string, or a null pointer if the
17197 wide string is not found. If s2 points to a wide string with zero length, the function
17199 7.28.4.5.7 The wcstok function
17201 1 #include <wchar.h>
17202 wchar_t *wcstok(wchar_t * restrict s1,
17203 const wchar_t * restrict s2,
17204 wchar_t ** restrict ptr);
17206 2 A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
17207 a sequence of tokens, each of which is delimited by a wide character from the wide string
17208 pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
17209 which the wcstok function stores information necessary for it to continue scanning the
17211 3 The first call in a sequence has a non-null first argument and stores an initial value in the
17212 object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
17213 the object pointed to by ptr is required to have the value stored by the previous call in
17214 the sequence, which is then updated. The separator wide string pointed to by s2 may be
17215 different from call to call.
17216 4 The first call in the sequence searches the wide string pointed to by s1 for the first wide
17217 character that is not contained in the current separator wide string pointed to by s2. If no
17218 such wide character is found, then there are no tokens in the wide string pointed to by s1
17219 and the wcstok function returns a null pointer. If such a wide character is found, it is
17220 the start of the first token.
17221 5 The wcstok function then searches from there for a wide character that is contained in
17222 the current separator wide string. If no such wide character is found, the current token
17225 extends to the end of the wide string pointed to by s1, and subsequent searches in the
17226 same wide string for a token return a null pointer. If such a wide character is found, it is
17227 overwritten by a null wide character, which terminates the current token.
17228 6 In all cases, the wcstok function stores sufficient information in the pointer pointed to
17229 by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
17230 value for ptr, shall start searching just past the element overwritten by a null wide
17231 character (if any).
17233 7 The wcstok function returns a pointer to the first wide character of a token, or a null
17234 pointer if there is no token.
17237 static wchar_t str1[] = L"?a???b,,,#c";
17238 static wchar_t str2[] = L"\t \t";
17239 wchar_t *t, *ptr1, *ptr2;
17240 t = wcstok(str1, L"?", &ptr1); // t points to the token L"a"
17241 t = wcstok(NULL, L",", &ptr1); // t points to the token L"??b"
17242 t = wcstok(str2, L" \t", &ptr2); // t is a null pointer
17243 t = wcstok(NULL, L"#,", &ptr1); // t points to the token L"c"
17244 t = wcstok(NULL, L"?", &ptr1); // t is a null pointer
17246 7.28.4.5.8 The wmemchr function
17248 1 #include <wchar.h>
17249 wchar_t *wmemchr(const wchar_t *s, wchar_t c,
17252 2 The wmemchr function locates the first occurrence of c in the initial n wide characters of
17253 the object pointed to by s.
17255 3 The wmemchr function returns a pointer to the located wide character, or a null pointer if
17256 the wide character does not occur in the object.
17263 7.28.4.6 Miscellaneous functions
17264 7.28.4.6.1 The wcslen function
17266 1 #include <wchar.h>
17267 size_t wcslen(const wchar_t *s);
17269 2 The wcslen function computes the length of the wide string pointed to by s.
17271 3 The wcslen function returns the number of wide characters that precede the terminating
17272 null wide character.
17273 7.28.4.6.2 The wmemset function
17275 1 #include <wchar.h>
17276 wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
17278 2 The wmemset function copies the value of c into each of the first n wide characters of
17279 the object pointed to by s.
17281 3 The wmemset function returns the value of s.
17282 7.28.5 Wide character time conversion functions
17283 7.28.5.1 The wcsftime function
17285 1 #include <time.h>
17287 size_t wcsftime(wchar_t * restrict s,
17289 const wchar_t * restrict format,
17290 const struct tm * restrict timeptr);
17292 2 The wcsftime function is equivalent to the strftime function, except that:
17293 -- The argument s points to the initial element of an array of wide characters into which
17294 the generated output is to be placed.
17299 -- The argument maxsize indicates the limiting number of wide characters.
17300 -- The argument format is a wide string and the conversion specifiers are replaced by
17301 corresponding sequences of wide characters.
17302 -- The return value indicates the number of wide characters.
17304 3 If the total number of resulting wide characters including the terminating null wide
17305 character is not more than maxsize, the wcsftime function returns the number of
17306 wide characters placed into the array pointed to by s not including the terminating null
17307 wide character. Otherwise, zero is returned and the contents of the array are
17309 7.28.6 Extended multibyte/wide character conversion utilities
17310 1 The header <wchar.h> declares an extended set of functions useful for conversion
17311 between multibyte characters and wide characters.
17312 2 Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and
17313 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used
17314 to describe the current conversion state from a particular multibyte character sequence to
17315 a wide character sequence (or the reverse) under the rules of a particular setting for the
17316 LC_CTYPE category of the current locale.
17317 3 The initial conversion state corresponds, for a conversion in either direction, to the
17318 beginning of a new multibyte character in the initial shift state. A zero-valued
17319 mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
17320 valued mbstate_t object can be used to initiate conversion involving any multibyte
17321 character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
17322 been altered by any of the functions described in this subclause, and is then used with a
17323 different multibyte character sequence, or in the other conversion direction, or with a
17324 different LC_CTYPE category setting than on earlier function calls, the behavior is
17326 4 On entry, each function takes the described conversion state (either internal or pointed to
17327 by an argument) as current. The conversion state described by the referenced object is
17328 altered as needed to track the shift state, and the position within a multibyte character, for
17329 the associated multibyte character sequence.
17334 331) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
17335 mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
17340 7.28.6.1 Single-byte/wide character conversion functions
17341 7.28.6.1.1 The btowc function
17343 1 #include <wchar.h> *
17344 wint_t btowc(int c);
17346 2 The btowc function determines whether c constitutes a valid single-byte character in the
17347 initial shift state.
17349 3 The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
17350 does not constitute a valid single-byte character in the initial shift state. Otherwise, it
17351 returns the wide character representation of that character.
17352 7.28.6.1.2 The wctob function
17354 1 #include <wchar.h> *
17355 int wctob(wint_t c);
17357 2 The wctob function determines whether c corresponds to a member of the extended
17358 character set whose multibyte character representation is a single byte when in the initial
17361 3 The wctob function returns EOF if c does not correspond to a multibyte character with
17362 length one in the initial shift state. Otherwise, it returns the single-byte representation of
17363 that character as an unsigned char converted to an int.
17364 7.28.6.2 Conversion state functions
17365 7.28.6.2.1 The mbsinit function
17367 1 #include <wchar.h>
17368 int mbsinit(const mbstate_t *ps);
17370 2 If ps is not a null pointer, the mbsinit function determines whether the referenced
17371 mbstate_t object describes an initial conversion state.
17378 3 The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
17379 describes an initial conversion state; otherwise, it returns zero.
17380 7.28.6.3 Restartable multibyte/wide character conversion functions
17381 1 These functions differ from the corresponding multibyte character functions of 7.22.7
17382 (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
17383 pointer to mbstate_t that points to an object that can completely describe the current
17384 conversion state of the associated multibyte character sequence. If ps is a null pointer,
17385 each function uses its own internal mbstate_t object instead, which is initialized at
17386 program startup to the initial conversion state; the functions are not required to avoid data
17387 races in this case. The implementation behaves as if no library function calls these
17388 functions with a null pointer for ps.
17389 2 Also unlike their corresponding functions, the return value does not represent whether the
17390 encoding is state-dependent.
17391 7.28.6.3.1 The mbrlen function
17393 1 #include <wchar.h>
17394 size_t mbrlen(const char * restrict s,
17396 mbstate_t * restrict ps);
17398 2 The mbrlen function is equivalent to the call:
17399 mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
17400 where internal is the mbstate_t object for the mbrlen function, except that the
17401 expression designated by ps is evaluated only once.
17403 3 The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
17405 Forward references: the mbrtowc function (7.28.6.3.2).
17412 7.28.6.3.2 The mbrtowc function
17414 1 #include <wchar.h>
17415 size_t mbrtowc(wchar_t * restrict pwc,
17416 const char * restrict s,
17418 mbstate_t * restrict ps);
17420 2 If s is a null pointer, the mbrtowc function is equivalent to the call:
17421 mbrtowc(NULL, "", 1, ps)
17422 In this case, the values of the parameters pwc and n are ignored.
17423 3 If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
17424 the byte pointed to by s to determine the number of bytes needed to complete the next
17425 multibyte character (including any shift sequences). If the function determines that the
17426 next multibyte character is complete and valid, it determines the value of the
17427 corresponding wide character and then, if pwc is not a null pointer, stores that value in
17428 the object pointed to by pwc. If the corresponding wide character is the null wide
17429 character, the resulting state described is the initial conversion state.
17431 4 The mbrtowc function returns the first of the following that applies (given the current
17433 0 if the next n or fewer bytes complete the multibyte character that
17434 corresponds to the null wide character (which is the value stored).
17435 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
17436 character (which is the value stored); the value returned is the number
17437 of bytes that complete the multibyte character.
17438 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
17439 multibyte character, and all n bytes have been processed (no value is
17441 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
17442 do not contribute to a complete and valid multibyte character (no
17443 value is stored); the value of the macro EILSEQ is stored in errno,
17444 and the conversion state is unspecified.
17446 332) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
17447 sequence of redundant shift sequences (for implementations with state-dependent encodings).
17451 7.28.6.3.3 The wcrtomb function
17453 1 #include <wchar.h>
17454 size_t wcrtomb(char * restrict s,
17456 mbstate_t * restrict ps);
17458 2 If s is a null pointer, the wcrtomb function is equivalent to the call
17459 wcrtomb(buf, L'\0', ps)
17460 where buf is an internal buffer.
17461 3 If s is not a null pointer, the wcrtomb function determines the number of bytes needed
17462 to represent the multibyte character that corresponds to the wide character given by wc
17463 (including any shift sequences), and stores the multibyte character representation in the
17464 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
17465 wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
17466 to restore the initial shift state; the resulting state described is the initial conversion state.
17468 4 The wcrtomb function returns the number of bytes stored in the array object (including
17469 any shift sequences). When wc is not a valid wide character, an encoding error occurs:
17470 the function stores the value of the macro EILSEQ in errno and returns
17471 (size_t)(-1); the conversion state is unspecified.
17472 7.28.6.4 Restartable multibyte/wide string conversion functions
17473 1 These functions differ from the corresponding multibyte string functions of 7.22.8
17474 (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
17475 mbstate_t that points to an object that can completely describe the current conversion
17476 state of the associated multibyte character sequence. If ps is a null pointer, each function
17477 uses its own internal mbstate_t object instead, which is initialized at program startup
17478 to the initial conversion state; the functions are not required to avoid data races in this
17479 case. The implementation behaves as if no library function calls these functions with a
17480 null pointer for ps.
17481 2 Also unlike their corresponding functions, the conversion source parameter, src, has a
17482 pointer-to-pointer type. When the function is storing the results of conversions (that is,
17483 when dst is not a null pointer), the pointer object pointed to by this parameter is updated
17484 to reflect the amount of the source processed by that invocation.
17491 7.28.6.4.1 The mbsrtowcs function
17493 1 #include <wchar.h>
17494 size_t mbsrtowcs(wchar_t * restrict dst,
17495 const char ** restrict src,
17497 mbstate_t * restrict ps);
17499 2 The mbsrtowcs function converts a sequence of multibyte characters that begins in the
17500 conversion state described by the object pointed to by ps, from the array indirectly
17501 pointed to by src into a sequence of corresponding wide characters. If dst is not a null
17502 pointer, the converted characters are stored into the array pointed to by dst. Conversion
17503 continues up to and including a terminating null character, which is also stored.
17504 Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
17505 not form a valid multibyte character, or (if dst is not a null pointer) when len wide
17506 characters have been stored into the array pointed to by dst.333) Each conversion takes
17507 place as if by a call to the mbrtowc function.
17508 3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
17509 pointer (if conversion stopped due to reaching a terminating null character) or the address
17510 just past the last multibyte character converted (if any). If conversion stopped due to
17511 reaching a terminating null character and if dst is not a null pointer, the resulting state
17512 described is the initial conversion state.
17514 4 If the input conversion encounters a sequence of bytes that do not form a valid multibyte
17515 character, an encoding error occurs: the mbsrtowcs function stores the value of the
17516 macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
17517 unspecified. Otherwise, it returns the number of multibyte characters successfully
17518 converted, not including the terminating null character (if any).
17523 333) Thus, the value of len is ignored if dst is a null pointer.
17527 7.28.6.4.2 The wcsrtombs function
17529 1 #include <wchar.h>
17530 size_t wcsrtombs(char * restrict dst,
17531 const wchar_t ** restrict src,
17533 mbstate_t * restrict ps);
17535 2 The wcsrtombs function converts a sequence of wide characters from the array
17536 indirectly pointed to by src into a sequence of corresponding multibyte characters that
17537 begins in the conversion state described by the object pointed to by ps. If dst is not a
17538 null pointer, the converted characters are then stored into the array pointed to by dst.
17539 Conversion continues up to and including a terminating null wide character, which is also
17540 stored. Conversion stops earlier in two cases: when a wide character is reached that does
17541 not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
17542 next multibyte character would exceed the limit of len total bytes to be stored into the
17543 array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
17545 3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
17546 pointer (if conversion stopped due to reaching a terminating null wide character) or the
17547 address just past the last wide character converted (if any). If conversion stopped due to
17548 reaching a terminating null wide character, the resulting state described is the initial
17551 4 If conversion stops because a wide character is reached that does not correspond to a
17552 valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
17553 value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
17554 state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
17555 character sequence, not including the terminating null character (if any).
17560 334) If conversion stops because a terminating null wide character has been reached, the bytes stored
17561 include those necessary to reach the initial shift state immediately before the null byte.
17565 7.29 Wide character classification and mapping utilities <wctype.h>
17566 7.29.1 Introduction
17567 1 The header <wctype.h> defines one macro, and declares three data types and many
17569 2 The types declared are
17571 described in 7.28.1;
17573 which is a scalar type that can hold values which represent locale-specific character
17576 which is a scalar type that can hold values which represent locale-specific character
17578 3 The macro defined is WEOF (described in 7.28.1).
17579 4 The functions declared are grouped as follows:
17580 -- Functions that provide wide character classification;
17581 -- Extensible functions that provide wide character classification;
17582 -- Functions that provide wide character case mapping;
17583 -- Extensible functions that provide wide character mapping.
17584 5 For all functions described in this subclause that accept an argument of type wint_t, the
17585 value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
17586 this argument has any other value, the behavior is undefined.
17587 6 The behavior of these functions is affected by the LC_CTYPE category of the current
17593 335) See ''future library directions'' (7.30.13).
17597 7.29.2 Wide character classification utilities
17598 1 The header <wctype.h> declares several functions useful for classifying wide
17600 2 The term printing wide character refers to a member of a locale-specific set of wide
17601 characters, each of which occupies at least one printing position on a display device. The
17602 term control wide character refers to a member of a locale-specific set of wide characters
17603 that are not printing wide characters.
17604 7.29.2.1 Wide character classification functions
17605 1 The functions in this subclause return nonzero (true) if and only if the value of the
17606 argument wc conforms to that in the description of the function.
17607 2 Each of the following functions returns true for each wide character that corresponds (as
17608 if by a call to the wctob function) to a single-byte character for which the corresponding
17609 character classification function from 7.4.1 returns true, except that the iswgraph and
17610 iswpunct functions may differ with respect to wide characters other than L' ' that are
17611 both printing and white-space wide characters.336)
17612 Forward references: the wctob function (7.28.6.1.2).
17613 7.29.2.1.1 The iswalnum function
17615 1 #include <wctype.h>
17616 int iswalnum(wint_t wc);
17618 2 The iswalnum function tests for any wide character for which iswalpha or
17620 7.29.2.1.2 The iswalpha function
17622 1 #include <wctype.h>
17623 int iswalpha(wint_t wc);
17625 2 The iswalpha function tests for any wide character for which iswupper or
17626 iswlower is true, or any wide character that is one of a locale-specific set of alphabetic
17628 336) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
17629 iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
17630 (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
17631 && iswspace(wc) is true, but not both.
17635 wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
17637 7.29.2.1.3 The iswblank function
17639 1 #include <wctype.h>
17640 int iswblank(wint_t wc);
17642 2 The iswblank function tests for any wide character that is a standard blank wide
17643 character or is one of a locale-specific set of wide characters for which iswspace is true
17644 and that is used to separate words within a line of text. The standard blank wide
17645 characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
17646 locale, iswblank returns true only for the standard blank characters.
17647 7.29.2.1.4 The iswcntrl function
17649 1 #include <wctype.h>
17650 int iswcntrl(wint_t wc);
17652 2 The iswcntrl function tests for any control wide character.
17653 7.29.2.1.5 The iswdigit function
17655 1 #include <wctype.h>
17656 int iswdigit(wint_t wc);
17658 2 The iswdigit function tests for any wide character that corresponds to a decimal-digit
17659 character (as defined in 5.2.1).
17660 7.29.2.1.6 The iswgraph function
17662 1 #include <wctype.h>
17663 int iswgraph(wint_t wc);
17668 337) The functions iswlower and iswupper test true or false separately for each of these additional
17669 wide characters; all four combinations are possible.
17674 2 The iswgraph function tests for any wide character for which iswprint is true and
17675 iswspace is false.338)
17676 7.29.2.1.7 The iswlower function
17678 1 #include <wctype.h>
17679 int iswlower(wint_t wc);
17681 2 The iswlower function tests for any wide character that corresponds to a lowercase
17682 letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
17683 iswdigit, iswpunct, or iswspace is true.
17684 7.29.2.1.8 The iswprint function
17686 1 #include <wctype.h>
17687 int iswprint(wint_t wc);
17689 2 The iswprint function tests for any printing wide character.
17690 7.29.2.1.9 The iswpunct function
17692 1 #include <wctype.h>
17693 int iswpunct(wint_t wc);
17695 2 The iswpunct function tests for any printing wide character that is one of a locale-
17696 specific set of punctuation wide characters for which neither iswspace nor iswalnum
17698 7.29.2.1.10 The iswspace function
17700 1 #include <wctype.h>
17701 int iswspace(wint_t wc);
17705 338) Note that the behavior of the iswgraph and iswpunct functions may differ from their
17706 corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
17707 characters other than ' '.
17712 2 The iswspace function tests for any wide character that corresponds to a locale-specific
17713 set of white-space wide characters for which none of iswalnum, iswgraph, or
17715 7.29.2.1.11 The iswupper function
17717 1 #include <wctype.h>
17718 int iswupper(wint_t wc);
17720 2 The iswupper function tests for any wide character that corresponds to an uppercase
17721 letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
17722 iswdigit, iswpunct, or iswspace is true.
17723 7.29.2.1.12 The iswxdigit function
17725 1 #include <wctype.h>
17726 int iswxdigit(wint_t wc);
17728 2 The iswxdigit function tests for any wide character that corresponds to a
17729 hexadecimal-digit character (as defined in 6.4.4.1).
17730 7.29.2.2 Extensible wide character classification functions
17731 1 The functions wctype and iswctype provide extensible wide character classification
17732 as well as testing equivalent to that performed by the functions described in the previous
17733 subclause (7.29.2.1).
17734 7.29.2.2.1 The iswctype function
17736 1 #include <wctype.h>
17737 int iswctype(wint_t wc, wctype_t desc);
17739 2 The iswctype function determines whether the wide character wc has the property
17740 described by desc. The current setting of the LC_CTYPE category shall be the same as
17741 during the call to wctype that returned the value desc.
17742 3 Each of the following expressions has a truth-value equivalent to the call to the wide
17743 character classification function (7.29.2.1) in the comment that follows the expression:
17748 iswctype(wc, wctype("alnum")) // iswalnum(wc)
17749 iswctype(wc, wctype("alpha")) // iswalpha(wc)
17750 iswctype(wc, wctype("blank")) // iswblank(wc)
17751 iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
17752 iswctype(wc, wctype("digit")) // iswdigit(wc)
17753 iswctype(wc, wctype("graph")) // iswgraph(wc)
17754 iswctype(wc, wctype("lower")) // iswlower(wc)
17755 iswctype(wc, wctype("print")) // iswprint(wc)
17756 iswctype(wc, wctype("punct")) // iswpunct(wc)
17757 iswctype(wc, wctype("space")) // iswspace(wc)
17758 iswctype(wc, wctype("upper")) // iswupper(wc)
17759 iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
17761 4 The iswctype function returns nonzero (true) if and only if the value of the wide
17762 character wc has the property described by desc.
17763 Forward references: the wctype function (7.29.2.2.2).
17764 7.29.2.2.2 The wctype function
17766 1 #include <wctype.h>
17767 wctype_t wctype(const char *property);
17769 2 The wctype function constructs a value with type wctype_t that describes a class of
17770 wide characters identified by the string argument property.
17771 3 The strings listed in the description of the iswctype function shall be valid in all
17772 locales as property arguments to the wctype function.
17774 4 If property identifies a valid class of wide characters according to the LC_CTYPE
17775 category of the current locale, the wctype function returns a nonzero value that is valid
17776 as the second argument to the iswctype function; otherwise, it returns zero.
17783 7.29.3 Wide character case mapping utilities
17784 1 The header <wctype.h> declares several functions useful for mapping wide characters.
17785 7.29.3.1 Wide character case mapping functions
17786 7.29.3.1.1 The towlower function
17788 1 #include <wctype.h>
17789 wint_t towlower(wint_t wc);
17791 2 The towlower function converts an uppercase letter to a corresponding lowercase letter.
17793 3 If the argument is a wide character for which iswupper is true and there are one or
17794 more corresponding wide characters, as specified by the current locale, for which
17795 iswlower is true, the towlower function returns one of the corresponding wide
17796 characters (always the same one for any given locale); otherwise, the argument is
17797 returned unchanged.
17798 7.29.3.1.2 The towupper function
17800 1 #include <wctype.h>
17801 wint_t towupper(wint_t wc);
17803 2 The towupper function converts a lowercase letter to a corresponding uppercase letter.
17805 3 If the argument is a wide character for which iswlower is true and there are one or
17806 more corresponding wide characters, as specified by the current locale, for which
17807 iswupper is true, the towupper function returns one of the corresponding wide
17808 characters (always the same one for any given locale); otherwise, the argument is
17809 returned unchanged.
17810 7.29.3.2 Extensible wide character case mapping functions
17811 1 The functions wctrans and towctrans provide extensible wide character mapping as
17812 well as case mapping equivalent to that performed by the functions described in the
17813 previous subclause (7.29.3.1).
17820 7.29.3.2.1 The towctrans function
17822 1 #include <wctype.h>
17823 wint_t towctrans(wint_t wc, wctrans_t desc);
17825 2 The towctrans function maps the wide character wc using the mapping described by
17826 desc. The current setting of the LC_CTYPE category shall be the same as during the call
17827 to wctrans that returned the value desc.
17828 3 Each of the following expressions behaves the same as the call to the wide character case
17829 mapping function (7.29.3.1) in the comment that follows the expression:
17830 towctrans(wc, wctrans("tolower")) // towlower(wc)
17831 towctrans(wc, wctrans("toupper")) // towupper(wc)
17833 4 The towctrans function returns the mapped value of wc using the mapping described
17835 7.29.3.2.2 The wctrans function
17837 1 #include <wctype.h>
17838 wctrans_t wctrans(const char *property);
17840 2 The wctrans function constructs a value with type wctrans_t that describes a
17841 mapping between wide characters identified by the string argument property.
17842 3 The strings listed in the description of the towctrans function shall be valid in all
17843 locales as property arguments to the wctrans function.
17845 4 If property identifies a valid mapping of wide characters according to the LC_CTYPE
17846 category of the current locale, the wctrans function returns a nonzero value that is valid
17847 as the second argument to the towctrans function; otherwise, it returns zero.
17854 7.30 Future library directions
17855 1 The following names are grouped under individual headers for convenience. All external
17856 names described below are reserved no matter what headers are included by the program.
17857 7.30.1 Complex arithmetic <complex.h>
17858 1 The function names
17860 cerfc clog10 clgamma
17861 cexp2 clog1p ctgamma
17862 and the same names suffixed with f or l may be added to the declarations in the
17863 <complex.h> header.
17864 7.30.2 Character handling <ctype.h>
17865 1 Function names that begin with either is or to, and a lowercase letter may be added to
17866 the declarations in the <ctype.h> header.
17867 7.30.3 Errors <errno.h>
17868 1 Macros that begin with E and a digit or E and an uppercase letter may be added to the
17869 declarations in the <errno.h> header.
17870 7.30.4 Format conversion of integer types <inttypes.h>
17871 1 Macro names beginning with PRI or SCN followed by any lowercase letter or X may be
17872 added to the macros defined in the <inttypes.h> header.
17873 7.30.5 Localization <locale.h>
17874 1 Macros that begin with LC_ and an uppercase letter may be added to the definitions in
17875 the <locale.h> header.
17876 7.30.6 Signal handling <signal.h>
17877 1 Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
17878 letter may be added to the definitions in the <signal.h> header.
17879 7.30.7 Boolean type and values <stdbool.h>
17880 1 The ability to undefine and perhaps then redefine the macros bool, true, and false is
17881 an obsolescent feature.
17882 7.30.8 Integer types <stdint.h>
17883 1 Typedef names beginning with int or uint and ending with _t may be added to the
17884 types defined in the <stdint.h> header. Macro names beginning with INT or UINT
17885 and ending with _MAX, _MIN, or _C may be added to the macros defined in the
17890 7.30.9 Input/output <stdio.h>
17891 1 Lowercase letters may be added to the conversion specifiers and length modifiers in
17892 fprintf and fscanf. Other characters may be used in extensions.
17893 2 The use of ungetc on a binary stream where the file position indicator is zero prior to
17894 the call is an obsolescent feature.
17895 7.30.10 General utilities <stdlib.h>
17896 1 Function names that begin with str and a lowercase letter may be added to the
17897 declarations in the <stdlib.h> header.
17898 7.30.11 String handling <string.h>
17899 1 Function names that begin with str, mem, or wcs and a lowercase letter may be added
17900 to the declarations in the <string.h> header.
17901 7.30.12 Extended multibyte and wide character utilities <wchar.h>
17902 1 Function names that begin with wcs and a lowercase letter may be added to the
17903 declarations in the <wchar.h> header.
17904 2 Lowercase letters may be added to the conversion specifiers and length modifiers in
17905 fwprintf and fwscanf. Other characters may be used in extensions.
17906 7.30.13 Wide character classification and mapping utilities
17908 1 Function names that begin with is or to and a lowercase letter may be added to the
17909 declarations in the <wctype.h> header.
17918 Language syntax summary
17919 1 NOTE The notation is described in 6.1.
17921 A.1 Lexical grammar
17922 A.1.1 Lexical elements
17929 (6.4) preprocessing-token:
17936 each non-white-space character that cannot be one of the above
17944 (6.4.1) keyword: one of
17950 const register _Alignas
17951 continue restrict _Atomic
17952 default return _Bool
17954 double signed _Generic
17955 else sizeof _Imaginary
17956 enum static _Noreturn
17957 extern struct _Static_assert
17958 float switch _Thread_local
17961 (6.4.2.1) identifier:
17962 identifier-nondigit
17963 identifier identifier-nondigit
17965 (6.4.2.1) identifier-nondigit:
17967 universal-character-name
17968 other implementation-defined characters
17969 (6.4.2.1) nondigit: one of
17970 _ a b c d e f g h i j k l m
17971 n o p q r s t u v w x y z
17972 A B C D E F G H I J K L M
17973 N O P Q R S T U V W X Y Z
17974 (6.4.2.1) digit: one of
17975 0 1 2 3 4 5 6 7 8 9
17982 A.1.4 Universal character names
17983 (6.4.3) universal-character-name:
17985 \U hex-quad hex-quad
17987 hexadecimal-digit hexadecimal-digit
17988 hexadecimal-digit hexadecimal-digit
17993 enumeration-constant
17995 (6.4.4.1) integer-constant:
17996 decimal-constant integer-suffixopt
17997 octal-constant integer-suffixopt
17998 hexadecimal-constant integer-suffixopt
17999 (6.4.4.1) decimal-constant:
18001 decimal-constant digit
18002 (6.4.4.1) octal-constant:
18004 octal-constant octal-digit
18005 (6.4.4.1) hexadecimal-constant:
18006 hexadecimal-prefix hexadecimal-digit
18007 hexadecimal-constant hexadecimal-digit
18008 (6.4.4.1) hexadecimal-prefix: one of
18010 (6.4.4.1) nonzero-digit: one of
18012 (6.4.4.1) octal-digit: one of
18020 (6.4.4.1) hexadecimal-digit: one of
18021 0 1 2 3 4 5 6 7 8 9
18024 (6.4.4.1) integer-suffix:
18025 unsigned-suffix long-suffixopt
18026 unsigned-suffix long-long-suffix
18027 long-suffix unsigned-suffixopt
18028 long-long-suffix unsigned-suffixopt
18029 (6.4.4.1) unsigned-suffix: one of
18031 (6.4.4.1) long-suffix: one of
18033 (6.4.4.1) long-long-suffix: one of
18035 (6.4.4.2) floating-constant:
18036 decimal-floating-constant
18037 hexadecimal-floating-constant
18038 (6.4.4.2) decimal-floating-constant:
18039 fractional-constant exponent-partopt floating-suffixopt
18040 digit-sequence exponent-part floating-suffixopt
18041 (6.4.4.2) hexadecimal-floating-constant:
18042 hexadecimal-prefix hexadecimal-fractional-constant
18043 binary-exponent-part floating-suffixopt
18044 hexadecimal-prefix hexadecimal-digit-sequence
18045 binary-exponent-part floating-suffixopt
18046 (6.4.4.2) fractional-constant:
18047 digit-sequenceopt . digit-sequence
18049 (6.4.4.2) exponent-part:
18050 e signopt digit-sequence
18051 E signopt digit-sequence
18052 (6.4.4.2) sign: one of
18059 (6.4.4.2) digit-sequence:
18061 digit-sequence digit
18062 (6.4.4.2) hexadecimal-fractional-constant:
18063 hexadecimal-digit-sequenceopt .
18064 hexadecimal-digit-sequence
18065 hexadecimal-digit-sequence .
18066 (6.4.4.2) binary-exponent-part:
18067 p signopt digit-sequence
18068 P signopt digit-sequence
18069 (6.4.4.2) hexadecimal-digit-sequence:
18071 hexadecimal-digit-sequence hexadecimal-digit
18072 (6.4.4.2) floating-suffix: one of
18074 (6.4.4.3) enumeration-constant:
18076 (6.4.4.4) character-constant:
18077 ' c-char-sequence '
18078 L' c-char-sequence '
18079 u' c-char-sequence '
18080 U' c-char-sequence '
18081 (6.4.4.4) c-char-sequence:
18083 c-char-sequence c-char
18085 any member of the source character set except
18086 the single-quote ', backslash \, or new-line character
18088 (6.4.4.4) escape-sequence:
18089 simple-escape-sequence
18090 octal-escape-sequence
18091 hexadecimal-escape-sequence
18092 universal-character-name
18099 (6.4.4.4) simple-escape-sequence: one of
18101 \a \b \f \n \r \t \v
18102 (6.4.4.4) octal-escape-sequence:
18104 \ octal-digit octal-digit
18105 \ octal-digit octal-digit octal-digit
18106 (6.4.4.4) hexadecimal-escape-sequence:
18107 \x hexadecimal-digit
18108 hexadecimal-escape-sequence hexadecimal-digit
18109 A.1.6 String literals
18110 (6.4.5) string-literal:
18111 encoding-prefixopt " s-char-sequenceopt "
18112 (6.4.5) encoding-prefix:
18117 (6.4.5) s-char-sequence:
18119 s-char-sequence s-char
18121 any member of the source character set except
18122 the double-quote ", backslash \, or new-line character
18125 (6.4.6) punctuator: one of
18128 / % << >> < > <= >= == != ^ | && ||
18130 = *= /= %= += -= <<= >>= &= ^= |=
18132 <: :> <% %> %: %:%:
18140 (6.4.7) header-name:
18141 < h-char-sequence >
18142 " q-char-sequence "
18143 (6.4.7) h-char-sequence:
18145 h-char-sequence h-char
18147 any member of the source character set except
18148 the new-line character and >
18149 (6.4.7) q-char-sequence:
18151 q-char-sequence q-char
18153 any member of the source character set except
18154 the new-line character and "
18155 A.1.9 Preprocessing numbers
18160 pp-number identifier-nondigit
18172 A.2 Phrase structure grammar
18174 (6.5.1) primary-expression:
18180 (6.5.1.1) generic-selection:
18181 _Generic ( assignment-expression , generic-assoc-list )
18182 (6.5.1.1) generic-assoc-list:
18183 generic-association
18184 generic-assoc-list , generic-association
18185 (6.5.1.1) generic-association:
18186 type-name : assignment-expression
18187 default : assignment-expression
18188 (6.5.2) postfix-expression:
18190 postfix-expression [ expression ]
18191 postfix-expression ( argument-expression-listopt )
18192 postfix-expression . identifier
18193 postfix-expression -> identifier
18194 postfix-expression ++
18195 postfix-expression --
18196 ( type-name ) { initializer-list }
18197 ( type-name ) { initializer-list , }
18198 (6.5.2) argument-expression-list:
18199 assignment-expression
18200 argument-expression-list , assignment-expression
18201 (6.5.3) unary-expression:
18203 ++ unary-expression
18204 -- unary-expression
18205 unary-operator cast-expression
18206 sizeof unary-expression
18207 sizeof ( type-name )
18208 alignof ( type-name )
18212 (6.5.3) unary-operator: one of
18214 (6.5.4) cast-expression:
18216 ( type-name ) cast-expression
18217 (6.5.5) multiplicative-expression:
18219 multiplicative-expression * cast-expression
18220 multiplicative-expression / cast-expression
18221 multiplicative-expression % cast-expression
18222 (6.5.6) additive-expression:
18223 multiplicative-expression
18224 additive-expression + multiplicative-expression
18225 additive-expression - multiplicative-expression
18226 (6.5.7) shift-expression:
18227 additive-expression
18228 shift-expression << additive-expression
18229 shift-expression >> additive-expression
18230 (6.5.8) relational-expression:
18232 relational-expression < shift-expression
18233 relational-expression > shift-expression
18234 relational-expression <= shift-expression
18235 relational-expression >= shift-expression
18236 (6.5.9) equality-expression:
18237 relational-expression
18238 equality-expression == relational-expression
18239 equality-expression != relational-expression
18240 (6.5.10) AND-expression:
18241 equality-expression
18242 AND-expression & equality-expression
18243 (6.5.11) exclusive-OR-expression:
18245 exclusive-OR-expression ^ AND-expression
18252 (6.5.12) inclusive-OR-expression:
18253 exclusive-OR-expression
18254 inclusive-OR-expression | exclusive-OR-expression
18255 (6.5.13) logical-AND-expression:
18256 inclusive-OR-expression
18257 logical-AND-expression && inclusive-OR-expression
18258 (6.5.14) logical-OR-expression:
18259 logical-AND-expression
18260 logical-OR-expression || logical-AND-expression
18261 (6.5.15) conditional-expression:
18262 logical-OR-expression
18263 logical-OR-expression ? expression : conditional-expression
18264 (6.5.16) assignment-expression:
18265 conditional-expression
18266 unary-expression assignment-operator assignment-expression
18267 (6.5.16) assignment-operator: one of
18268 = *= /= %= += -= <<= >>= &= ^= |=
18269 (6.5.17) expression:
18270 assignment-expression
18271 expression , assignment-expression
18272 (6.6) constant-expression:
18273 conditional-expression
18276 declaration-specifiers init-declarator-listopt ;
18277 static_assert-declaration *
18278 (6.7) declaration-specifiers:
18279 storage-class-specifier declaration-specifiersopt
18280 type-specifier declaration-specifiersopt
18281 type-qualifier declaration-specifiersopt
18282 function-specifier declaration-specifiersopt
18283 alignment-specifier declaration-specifiersopt
18284 (6.7) init-declarator-list:
18286 init-declarator-list , init-declarator
18291 (6.7) init-declarator:
18293 declarator = initializer
18294 (6.7.1) storage-class-specifier:
18301 (6.7.2) type-specifier:
18313 _Atomic ( type-name )
18314 struct-or-union-specifier
18317 (6.7.2.1) struct-or-union-specifier:
18318 struct-or-union identifieropt { struct-declaration-list }
18319 struct-or-union identifier
18320 (6.7.2.1) struct-or-union:
18323 (6.7.2.1) struct-declaration-list:
18325 struct-declaration-list struct-declaration
18326 (6.7.2.1) struct-declaration:
18327 specifier-qualifier-list struct-declarator-listopt ;
18328 static_assert-declaration
18332 (6.7.2.1) specifier-qualifier-list:
18333 type-specifier specifier-qualifier-listopt
18334 type-qualifier specifier-qualifier-listopt
18335 (6.7.2.1) struct-declarator-list:
18337 struct-declarator-list , struct-declarator
18338 (6.7.2.1) struct-declarator:
18340 declaratoropt : constant-expression
18341 (6.7.2.2) enum-specifier:
18342 enum identifieropt { enumerator-list }
18343 enum identifieropt { enumerator-list , }
18345 (6.7.2.2) enumerator-list:
18347 enumerator-list , enumerator
18348 (6.7.2.2) enumerator:
18349 enumeration-constant
18350 enumeration-constant = constant-expression
18351 (6.7.3) type-qualifier:
18356 (6.7.4) function-specifier:
18359 (6.7.5) alignment-specifier:
18360 _Alignas ( type-name )
18361 _Alignas ( constant-expression )
18362 (6.7.6) declarator:
18363 pointeropt direct-declarator
18370 (6.7.6) direct-declarator:
18373 direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
18374 direct-declarator [ static type-qualifier-listopt assignment-expression ]
18375 direct-declarator [ type-qualifier-list static assignment-expression ]
18376 direct-declarator [ type-qualifier-listopt * ]
18377 direct-declarator ( parameter-type-list )
18378 direct-declarator ( identifier-listopt )
18380 * type-qualifier-listopt
18381 * type-qualifier-listopt pointer
18382 (6.7.6) type-qualifier-list:
18384 type-qualifier-list type-qualifier
18385 (6.7.6) parameter-type-list:
18387 parameter-list , ...
18388 (6.7.6) parameter-list:
18389 parameter-declaration
18390 parameter-list , parameter-declaration
18391 (6.7.6) parameter-declaration:
18392 declaration-specifiers declarator
18393 declaration-specifiers abstract-declaratoropt
18394 (6.7.6) identifier-list:
18396 identifier-list , identifier
18398 specifier-qualifier-list abstract-declaratoropt
18399 (6.7.7) abstract-declarator:
18401 pointeropt direct-abstract-declarator
18408 (6.7.7) direct-abstract-declarator:
18409 ( abstract-declarator )
18410 direct-abstract-declaratoropt [ type-qualifier-listopt
18411 assignment-expressionopt ]
18412 direct-abstract-declaratoropt [ static type-qualifier-listopt
18413 assignment-expression ]
18414 direct-abstract-declaratoropt [ type-qualifier-list static
18415 assignment-expression ]
18416 direct-abstract-declaratoropt [ * ]
18417 direct-abstract-declaratoropt ( parameter-type-listopt )
18418 (6.7.8) typedef-name:
18420 (6.7.9) initializer:
18421 assignment-expression
18422 { initializer-list }
18423 { initializer-list , }
18424 (6.7.9) initializer-list:
18425 designationopt initializer
18426 initializer-list , designationopt initializer
18427 (6.7.9) designation:
18429 (6.7.9) designator-list:
18431 designator-list designator
18432 (6.7.9) designator:
18433 [ constant-expression ]
18435 (6.7.10) static_assert-declaration:
18436 _Static_assert ( constant-expression , string-literal ) ;
18447 expression-statement
18448 selection-statement
18449 iteration-statement
18451 (6.8.1) labeled-statement:
18452 identifier : statement
18453 case constant-expression : statement
18454 default : statement
18455 (6.8.2) compound-statement:
18456 { block-item-listopt }
18457 (6.8.2) block-item-list:
18459 block-item-list block-item
18460 (6.8.2) block-item:
18463 (6.8.3) expression-statement:
18465 (6.8.4) selection-statement:
18466 if ( expression ) statement
18467 if ( expression ) statement else statement
18468 switch ( expression ) statement
18469 (6.8.5) iteration-statement:
18470 while ( expression ) statement
18471 do statement while ( expression ) ;
18472 for ( expressionopt ; expressionopt ; expressionopt ) statement
18473 for ( declaration expressionopt ; expressionopt ) statement
18474 (6.8.6) jump-statement:
18478 return expressionopt ;
18482 A.2.4 External definitions
18483 (6.9) translation-unit:
18484 external-declaration
18485 translation-unit external-declaration
18486 (6.9) external-declaration:
18487 function-definition
18489 (6.9.1) function-definition:
18490 declaration-specifiers declarator declaration-listopt compound-statement
18491 (6.9.1) declaration-list:
18493 declaration-list declaration
18494 A.3 Preprocessing directives
18495 (6.10) preprocessing-file:
18506 if-group elif-groupsopt else-groupopt endif-line
18508 # if constant-expression new-line groupopt
18509 # ifdef identifier new-line groupopt
18510 # ifndef identifier new-line groupopt
18511 (6.10) elif-groups:
18513 elif-groups elif-group
18515 # elif constant-expression new-line groupopt
18521 # else new-line groupopt
18524 (6.10) control-line:
18525 # include pp-tokens new-line
18526 # define identifier replacement-list new-line
18527 # define identifier lparen identifier-listopt )
18528 replacement-list new-line
18529 # define identifier lparen ... ) replacement-list new-line
18530 # define identifier lparen identifier-list , ... )
18531 replacement-list new-line
18532 # undef identifier new-line
18533 # line pp-tokens new-line
18534 # error pp-tokensopt new-line
18535 # pragma pp-tokensopt new-line
18538 pp-tokensopt new-line
18539 (6.10) non-directive:
18542 a ( character not immediately preceded by white-space
18543 (6.10) replacement-list:
18546 preprocessing-token
18547 pp-tokens preprocessing-token
18549 the new-line character
18559 B.1 Diagnostics <assert.h>
18562 void assert(scalar expression);
18563 B.2 Complex <complex.h>
18564 __STDC_NO_COMPLEX__ imaginary
18565 complex _Imaginary_I
18567 #pragma STDC CX_LIMITED_RANGE on-off-switch
18568 double complex cacos(double complex z);
18569 float complex cacosf(float complex z);
18570 long double complex cacosl(long double complex z);
18571 double complex casin(double complex z);
18572 float complex casinf(float complex z);
18573 long double complex casinl(long double complex z);
18574 double complex catan(double complex z);
18575 float complex catanf(float complex z);
18576 long double complex catanl(long double complex z);
18577 double complex ccos(double complex z);
18578 float complex ccosf(float complex z);
18579 long double complex ccosl(long double complex z);
18580 double complex csin(double complex z);
18581 float complex csinf(float complex z);
18582 long double complex csinl(long double complex z);
18583 double complex ctan(double complex z);
18584 float complex ctanf(float complex z);
18585 long double complex ctanl(long double complex z);
18586 double complex cacosh(double complex z);
18587 float complex cacoshf(float complex z);
18588 long double complex cacoshl(long double complex z);
18589 double complex casinh(double complex z);
18590 float complex casinhf(float complex z);
18591 long double complex casinhl(long double complex z);
18595 double complex catanh(double complex z);
18596 float complex catanhf(float complex z);
18597 long double complex catanhl(long double complex z);
18598 double complex ccosh(double complex z);
18599 float complex ccoshf(float complex z);
18600 long double complex ccoshl(long double complex z);
18601 double complex csinh(double complex z);
18602 float complex csinhf(float complex z);
18603 long double complex csinhl(long double complex z);
18604 double complex ctanh(double complex z);
18605 float complex ctanhf(float complex z);
18606 long double complex ctanhl(long double complex z);
18607 double complex cexp(double complex z);
18608 float complex cexpf(float complex z);
18609 long double complex cexpl(long double complex z);
18610 double complex clog(double complex z);
18611 float complex clogf(float complex z);
18612 long double complex clogl(long double complex z);
18613 double cabs(double complex z);
18614 float cabsf(float complex z);
18615 long double cabsl(long double complex z);
18616 double complex cpow(double complex x, double complex y);
18617 float complex cpowf(float complex x, float complex y);
18618 long double complex cpowl(long double complex x,
18619 long double complex y);
18620 double complex csqrt(double complex z);
18621 float complex csqrtf(float complex z);
18622 long double complex csqrtl(long double complex z);
18623 double carg(double complex z);
18624 float cargf(float complex z);
18625 long double cargl(long double complex z);
18626 double cimag(double complex z);
18627 float cimagf(float complex z);
18628 long double cimagl(long double complex z);
18629 double complex CMPLX(double x, double y);
18630 float complex CMPLXF(float x, float y);
18631 long double complex CMPLXL(long double x, long double y);
18632 double complex conj(double complex z);
18633 float complex conjf(float complex z);
18634 long double complex conjl(long double complex z);
18635 double complex cproj(double complex z);
18639 float complex cprojf(float complex z);
18640 long double complex cprojl(long double complex z);
18641 double creal(double complex z);
18642 float crealf(float complex z);
18643 long double creall(long double complex z);
18644 B.3 Character handling <ctype.h>
18645 int isalnum(int c);
18646 int isalpha(int c);
18647 int isblank(int c);
18648 int iscntrl(int c);
18649 int isdigit(int c);
18650 int isgraph(int c);
18651 int islower(int c);
18652 int isprint(int c);
18653 int ispunct(int c);
18654 int isspace(int c);
18655 int isupper(int c);
18656 int isxdigit(int c);
18657 int tolower(int c);
18658 int toupper(int c);
18659 B.4 Errors <errno.h>
18660 EDOM EILSEQ ERANGE errno
18661 __STDC_WANT_LIB_EXT1__
18663 B.5 Floating-point environment <fenv.h>
18664 fenv_t FE_OVERFLOW FE_TOWARDZERO
18665 fexcept_t FE_UNDERFLOW FE_UPWARD
18666 FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV
18667 FE_INEXACT FE_DOWNWARD
18668 FE_INVALID FE_TONEAREST
18669 #pragma STDC FENV_ACCESS on-off-switch
18670 int feclearexcept(int excepts);
18671 int fegetexceptflag(fexcept_t *flagp, int excepts);
18672 int feraiseexcept(int excepts);
18673 int fesetexceptflag(const fexcept_t *flagp,
18675 int fetestexcept(int excepts);
18679 int fegetround(void);
18680 int fesetround(int round);
18681 int fegetenv(fenv_t *envp);
18682 int feholdexcept(fenv_t *envp);
18683 int fesetenv(const fenv_t *envp);
18684 int feupdateenv(const fenv_t *envp);
18685 B.6 Characteristics of floating types <float.h>
18686 FLT_ROUNDS DBL_DIG FLT_MAX
18687 FLT_EVAL_METHOD LDBL_DIG DBL_MAX
18688 FLT_HAS_SUBNORM FLT_MIN_EXP LDBL_MAX
18689 DBL_HAS_SUBNORM DBL_MIN_EXP FLT_EPSILON
18690 LDBL_HAS_SUBNORM LDBL_MIN_EXP DBL_EPSILON
18691 FLT_RADIX FLT_MIN_10_EXP LDBL_EPSILON
18692 FLT_MANT_DIG DBL_MIN_10_EXP FLT_MIN
18693 DBL_MANT_DIG LDBL_MIN_10_EXP DBL_MIN
18694 LDBL_MANT_DIG FLT_MAX_EXP LDBL_MIN
18695 FLT_DECIMAL_DIG DBL_MAX_EXP FLT_TRUE_MIN
18696 DBL_DECIMAL_DIG LDBL_MAX_EXP DBL_TRUE_MIN
18697 LDBL_DECIMAL_DIG FLT_MAX_10_EXP LDBL_TRUE_MIN
18698 DECIMAL_DIG DBL_MAX_10_EXP
18699 FLT_DIG LDBL_MAX_10_EXP
18700 B.7 Format conversion of integer types <inttypes.h>
18702 PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
18703 PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
18704 PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
18705 PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
18706 PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
18707 PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
18708 SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
18709 SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
18710 SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
18711 SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
18712 SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
18713 intmax_t imaxabs(intmax_t j);
18714 imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
18715 intmax_t strtoimax(const char * restrict nptr,
18716 char ** restrict endptr, int base);
18720 uintmax_t strtoumax(const char * restrict nptr,
18721 char ** restrict endptr, int base);
18722 intmax_t wcstoimax(const wchar_t * restrict nptr,
18723 wchar_t ** restrict endptr, int base);
18724 uintmax_t wcstoumax(const wchar_t * restrict nptr,
18725 wchar_t ** restrict endptr, int base);
18726 B.8 Alternative spellings <iso646.h>
18727 and bitor not_eq xor
18728 and_eq compl or xor_eq
18730 B.9 Sizes of integer types <limits.h>
18731 CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX
18732 SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN
18733 SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX
18734 UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX
18735 CHAR_MIN USHRT_MAX LONG_MAX
18736 B.10 Localization <locale.h>
18737 struct lconv LC_ALL LC_CTYPE LC_NUMERIC
18738 NULL LC_COLLATE LC_MONETARY LC_TIME
18739 char *setlocale(int category, const char *locale);
18740 struct lconv *localeconv(void);
18741 B.11 Mathematics <math.h>
18742 float_t FP_INFINITE FP_FAST_FMAL
18743 double_t FP_NAN FP_ILOGB0
18744 HUGE_VAL FP_NORMAL FP_ILOGBNAN
18745 HUGE_VALF FP_SUBNORMAL MATH_ERRNO
18746 HUGE_VALL FP_ZERO MATH_ERREXCEPT
18747 INFINITY FP_FAST_FMA math_errhandling
18749 #pragma STDC FP_CONTRACT on-off-switch
18750 int fpclassify(real-floating x);
18751 int isfinite(real-floating x);
18752 int isinf(real-floating x);
18753 int isnan(real-floating x);
18754 int isnormal(real-floating x);
18755 int signbit(real-floating x);
18758 double acos(double x);
18759 float acosf(float x);
18760 long double acosl(long double x);
18761 double asin(double x);
18762 float asinf(float x);
18763 long double asinl(long double x);
18764 double atan(double x);
18765 float atanf(float x);
18766 long double atanl(long double x);
18767 double atan2(double y, double x);
18768 float atan2f(float y, float x);
18769 long double atan2l(long double y, long double x);
18770 double cos(double x);
18771 float cosf(float x);
18772 long double cosl(long double x);
18773 double sin(double x);
18774 float sinf(float x);
18775 long double sinl(long double x);
18776 double tan(double x);
18777 float tanf(float x);
18778 long double tanl(long double x);
18779 double acosh(double x);
18780 float acoshf(float x);
18781 long double acoshl(long double x);
18782 double asinh(double x);
18783 float asinhf(float x);
18784 long double asinhl(long double x);
18785 double atanh(double x);
18786 float atanhf(float x);
18787 long double atanhl(long double x);
18788 double cosh(double x);
18789 float coshf(float x);
18790 long double coshl(long double x);
18791 double sinh(double x);
18792 float sinhf(float x);
18793 long double sinhl(long double x);
18794 double tanh(double x);
18795 float tanhf(float x);
18796 long double tanhl(long double x);
18797 double exp(double x);
18798 float expf(float x);
18802 long double expl(long double x);
18803 double exp2(double x);
18804 float exp2f(float x);
18805 long double exp2l(long double x);
18806 double expm1(double x);
18807 float expm1f(float x);
18808 long double expm1l(long double x);
18809 double frexp(double value, int *exp);
18810 float frexpf(float value, int *exp);
18811 long double frexpl(long double value, int *exp);
18812 int ilogb(double x);
18813 int ilogbf(float x);
18814 int ilogbl(long double x);
18815 double ldexp(double x, int exp);
18816 float ldexpf(float x, int exp);
18817 long double ldexpl(long double x, int exp);
18818 double log(double x);
18819 float logf(float x);
18820 long double logl(long double x);
18821 double log10(double x);
18822 float log10f(float x);
18823 long double log10l(long double x);
18824 double log1p(double x);
18825 float log1pf(float x);
18826 long double log1pl(long double x);
18827 double log2(double x);
18828 float log2f(float x);
18829 long double log2l(long double x);
18830 double logb(double x);
18831 float logbf(float x);
18832 long double logbl(long double x);
18833 double modf(double value, double *iptr);
18834 float modff(float value, float *iptr);
18835 long double modfl(long double value, long double *iptr);
18836 double scalbn(double x, int n);
18837 float scalbnf(float x, int n);
18838 long double scalbnl(long double x, int n);
18839 double scalbln(double x, long int n);
18840 float scalblnf(float x, long int n);
18841 long double scalblnl(long double x, long int n);
18842 double cbrt(double x);
18846 float cbrtf(float x);
18847 long double cbrtl(long double x);
18848 double fabs(double x);
18849 float fabsf(float x);
18850 long double fabsl(long double x);
18851 double hypot(double x, double y);
18852 float hypotf(float x, float y);
18853 long double hypotl(long double x, long double y);
18854 double pow(double x, double y);
18855 float powf(float x, float y);
18856 long double powl(long double x, long double y);
18857 double sqrt(double x);
18858 float sqrtf(float x);
18859 long double sqrtl(long double x);
18860 double erf(double x);
18861 float erff(float x);
18862 long double erfl(long double x);
18863 double erfc(double x);
18864 float erfcf(float x);
18865 long double erfcl(long double x);
18866 double lgamma(double x);
18867 float lgammaf(float x);
18868 long double lgammal(long double x);
18869 double tgamma(double x);
18870 float tgammaf(float x);
18871 long double tgammal(long double x);
18872 double ceil(double x);
18873 float ceilf(float x);
18874 long double ceill(long double x);
18875 double floor(double x);
18876 float floorf(float x);
18877 long double floorl(long double x);
18878 double nearbyint(double x);
18879 float nearbyintf(float x);
18880 long double nearbyintl(long double x);
18881 double rint(double x);
18882 float rintf(float x);
18883 long double rintl(long double x);
18884 long int lrint(double x);
18885 long int lrintf(float x);
18886 long int lrintl(long double x);
18890 long long int llrint(double x);
18891 long long int llrintf(float x);
18892 long long int llrintl(long double x);
18893 double round(double x);
18894 float roundf(float x);
18895 long double roundl(long double x);
18896 long int lround(double x);
18897 long int lroundf(float x);
18898 long int lroundl(long double x);
18899 long long int llround(double x);
18900 long long int llroundf(float x);
18901 long long int llroundl(long double x);
18902 double trunc(double x);
18903 float truncf(float x);
18904 long double truncl(long double x);
18905 double fmod(double x, double y);
18906 float fmodf(float x, float y);
18907 long double fmodl(long double x, long double y);
18908 double remainder(double x, double y);
18909 float remainderf(float x, float y);
18910 long double remainderl(long double x, long double y);
18911 double remquo(double x, double y, int *quo);
18912 float remquof(float x, float y, int *quo);
18913 long double remquol(long double x, long double y,
18915 double copysign(double x, double y);
18916 float copysignf(float x, float y);
18917 long double copysignl(long double x, long double y);
18918 double nan(const char *tagp);
18919 float nanf(const char *tagp);
18920 long double nanl(const char *tagp);
18921 double nextafter(double x, double y);
18922 float nextafterf(float x, float y);
18923 long double nextafterl(long double x, long double y);
18924 double nexttoward(double x, long double y);
18925 float nexttowardf(float x, long double y);
18926 long double nexttowardl(long double x, long double y);
18927 double fdim(double x, double y);
18928 float fdimf(float x, float y);
18929 long double fdiml(long double x, long double y);
18930 double fmax(double x, double y);
18934 float fmaxf(float x, float y);
18935 long double fmaxl(long double x, long double y);
18936 double fmin(double x, double y);
18937 float fminf(float x, float y);
18938 long double fminl(long double x, long double y);
18939 double fma(double x, double y, double z);
18940 float fmaf(float x, float y, float z);
18941 long double fmal(long double x, long double y,
18943 int isgreater(real-floating x, real-floating y);
18944 int isgreaterequal(real-floating x, real-floating y);
18945 int isless(real-floating x, real-floating y);
18946 int islessequal(real-floating x, real-floating y);
18947 int islessgreater(real-floating x, real-floating y);
18948 int isunordered(real-floating x, real-floating y);
18949 B.12 Nonlocal jumps <setjmp.h>
18951 int setjmp(jmp_buf env);
18952 _Noreturn void longjmp(jmp_buf env, int val);
18953 B.13 Signal handling <signal.h>
18954 sig_atomic_t SIG_IGN SIGILL SIGTERM
18955 SIG_DFL SIGABRT SIGINT
18956 SIG_ERR SIGFPE SIGSEGV
18957 void (*signal(int sig, void (*func)(int)))(int);
18958 int raise(int sig);
18965 B.14 Alignment <stdalign.h>
18967 __alignas_is_defined
18968 B.15 Variable arguments <stdarg.h>
18970 type va_arg(va_list ap, type);
18971 void va_copy(va_list dest, va_list src);
18972 void va_end(va_list ap);
18973 void va_start(va_list ap, parmN);
18974 B.16 Atomics <stdatomic.h>
18975 ATOMIC_CHAR_LOCK_FREE atomic_uint
18976 ATOMIC_CHAR16_T_LOCK_FREE atomic_long
18977 ATOMIC_CHAR32_T_LOCK_FREE atomic_ulong
18978 ATOMIC_WCHAR_T_LOCK_FREE atomic_llong
18979 ATOMIC_SHORT_LOCK_FREE atomic_ullong
18980 ATOMIC_INT_LOCK_FREE atomic_char16_t
18981 ATOMIC_LONG_LOCK_FREE atomic_char32_t
18982 ATOMIC_LLONG_LOCK_FREE atomic_wchar_t
18983 ATOMIC_ADDRESS_LOCK_FREE atomic_int_least8_t
18984 ATOMIC_FLAG_INIT atomic_uint_least8_t
18985 memory_order atomic_int_least16_t
18986 atomic_flag atomic_uint_least16_t
18987 atomic_bool atomic_int_least32_t
18988 atomic_address atomic_uint_least32_t
18989 memory_order_relaxed atomic_int_least64_t
18990 memory_order_consume atomic_uint_least64_t
18991 memory_order_acquire atomic_int_fast8_t
18992 memory_order_release atomic_uint_fast8_t
18993 memory_order_acq_rel atomic_int_fast16_t
18994 memory_order_seq_cst atomic_uint_fast16_t
18995 atomic_char atomic_int_fast32_t
18996 atomic_schar atomic_uint_fast32_t
18997 atomic_uchar atomic_int_fast64_t
18998 atomic_short atomic_uint_fast64_t
18999 atomic_ushort atomic_intptr_t
19000 atomic_int atomic_uintptr_t
19006 atomic_size_t atomic_intmax_t
19007 atomic_ptrdiff_t atomic_uintmax_t
19008 #define ATOMIC_VAR_INIT(C value)
19009 void atomic_init(volatile A *obj, C value);
19010 type kill_dependency(type y);
19011 void atomic_thread_fence(memory_order order);
19012 void atomic_signal_fence(memory_order order);
19013 _Bool atomic_is_lock_free(atomic_type const volatile *obj);
19014 void atomic_store(volatile A *object, C desired);
19015 void atomic_store_explicit(volatile A *object,
19016 C desired, memory_order order);
19017 C atomic_load(volatile A *object);
19018 C atomic_load_explicit(volatile A *object,
19019 memory_order order);
19020 C atomic_exchange(volatile A *object, C desired);
19021 C atomic_exchange_explicit(volatile A *object,
19022 C desired, memory_order order);
19023 _Bool atomic_compare_exchange_strong(volatile A *object,
19024 C *expected, C desired);
19025 _Bool atomic_compare_exchange_strong_explicit(
19026 volatile A *object, C *expected, C desired,
19027 memory_order success, memory_order failure);
19028 _Bool atomic_compare_exchange_weak(volatile A *object,
19029 C *expected, C desired);
19030 _Bool atomic_compare_exchange_weak_explicit(
19031 volatile A *object, C *expected, C desired,
19032 memory_order success, memory_order failure);
19033 C atomic_fetch_key(volatile A *object, M operand);
19034 C atomic_fetch_key_explicit(volatile A *object,
19035 M operand, memory_order order);
19036 bool atomic_flag_test_and_set(
19037 volatile atomic_flag *object);
19038 bool atomic_flag_test_and_set_explicit(
19039 volatile atomic_flag *object, memory_order order);
19040 void atomic_flag_clear(volatile atomic_flag *object);
19041 void atomic_flag_clear_explicit(
19042 volatile atomic_flag *object, memory_order order);
19049 B.17 Boolean type and values <stdbool.h>
19053 __bool_true_false_are_defined
19054 B.18 Common definitions <stddef.h>
19055 ptrdiff_t max_align_t NULL
19057 offsetof(type, member-designator)
19058 __STDC_WANT_LIB_EXT1__
19060 B.19 Integer types <stdint.h>
19061 intN_t INT_LEASTN_MIN PTRDIFF_MAX
19062 uintN_t INT_LEASTN_MAX SIG_ATOMIC_MIN
19063 int_leastN_t UINT_LEASTN_MAX SIG_ATOMIC_MAX
19064 uint_leastN_t INT_FASTN_MIN SIZE_MAX
19065 int_fastN_t INT_FASTN_MAX WCHAR_MIN
19066 uint_fastN_t UINT_FASTN_MAX WCHAR_MAX
19067 intptr_t INTPTR_MIN WINT_MIN
19068 uintptr_t INTPTR_MAX WINT_MAX
19069 intmax_t UINTPTR_MAX INTN_C(value)
19070 uintmax_t INTMAX_MIN UINTN_C(value)
19071 INTN_MIN INTMAX_MAX INTMAX_C(value)
19072 INTN_MAX UINTMAX_MAX UINTMAX_C(value)
19073 UINTN_MAX PTRDIFF_MIN
19074 __STDC_WANT_LIB_EXT1__
19082 B.20 Input/output <stdio.h>
19083 size_t _IOLBF FILENAME_MAX TMP_MAX
19084 FILE _IONBF L_tmpnam stderr
19085 fpos_t BUFSIZ SEEK_CUR stdin
19086 NULL EOF SEEK_END stdout
19087 _IOFBF FOPEN_MAX SEEK_SET
19088 int remove(const char *filename);
19089 int rename(const char *old, const char *new);
19090 FILE *tmpfile(void);
19091 char *tmpnam(char *s);
19092 int fclose(FILE *stream);
19093 int fflush(FILE *stream);
19094 FILE *fopen(const char * restrict filename,
19095 const char * restrict mode);
19096 FILE *freopen(const char * restrict filename,
19097 const char * restrict mode,
19098 FILE * restrict stream);
19099 void setbuf(FILE * restrict stream,
19100 char * restrict buf);
19101 int setvbuf(FILE * restrict stream,
19102 char * restrict buf,
19103 int mode, size_t size);
19104 int fprintf(FILE * restrict stream,
19105 const char * restrict format, ...);
19106 int fscanf(FILE * restrict stream,
19107 const char * restrict format, ...);
19108 int printf(const char * restrict format, ...);
19109 int scanf(const char * restrict format, ...);
19110 int snprintf(char * restrict s, size_t n,
19111 const char * restrict format, ...);
19112 int sprintf(char * restrict s,
19113 const char * restrict format, ...);
19114 int sscanf(const char * restrict s,
19115 const char * restrict format, ...);
19116 int vfprintf(FILE * restrict stream,
19117 const char * restrict format, va_list arg);
19118 int vfscanf(FILE * restrict stream,
19119 const char * restrict format, va_list arg);
19120 int vprintf(const char * restrict format, va_list arg);
19121 int vscanf(const char * restrict format, va_list arg);
19125 int vsnprintf(char * restrict s, size_t n,
19126 const char * restrict format, va_list arg);
19127 int vsprintf(char * restrict s,
19128 const char * restrict format, va_list arg);
19129 int vsscanf(const char * restrict s,
19130 const char * restrict format, va_list arg);
19131 int fgetc(FILE *stream);
19132 char *fgets(char * restrict s, int n,
19133 FILE * restrict stream);
19134 int fputc(int c, FILE *stream);
19135 int fputs(const char * restrict s,
19136 FILE * restrict stream);
19137 int getc(FILE *stream);
19139 int putc(int c, FILE *stream);
19140 int putchar(int c);
19141 int puts(const char *s);
19142 int ungetc(int c, FILE *stream);
19143 size_t fread(void * restrict ptr,
19144 size_t size, size_t nmemb,
19145 FILE * restrict stream);
19146 size_t fwrite(const void * restrict ptr,
19147 size_t size, size_t nmemb,
19148 FILE * restrict stream);
19149 int fgetpos(FILE * restrict stream,
19150 fpos_t * restrict pos);
19151 int fseek(FILE *stream, long int offset, int whence);
19152 int fsetpos(FILE *stream, const fpos_t *pos);
19153 long int ftell(FILE *stream);
19154 void rewind(FILE *stream);
19155 void clearerr(FILE *stream);
19156 int feof(FILE *stream);
19157 int ferror(FILE *stream);
19158 void perror(const char *s);
19159 __STDC_WANT_LIB_EXT1__
19160 L_tmpnam_s TMP_MAX_S errno_t rsize_t
19161 errno_t tmpfile_s(FILE * restrict * restrict streamptr);
19162 errno_t tmpnam_s(char *s, rsize_t maxsize);
19168 errno_t fopen_s(FILE * restrict * restrict streamptr,
19169 const char * restrict filename,
19170 const char * restrict mode);
19171 errno_t freopen_s(FILE * restrict * restrict newstreamptr,
19172 const char * restrict filename,
19173 const char * restrict mode,
19174 FILE * restrict stream);
19175 int fprintf_s(FILE * restrict stream,
19176 const char * restrict format, ...);
19177 int fscanf_s(FILE * restrict stream,
19178 const char * restrict format, ...);
19179 int printf_s(const char * restrict format, ...);
19180 int scanf_s(const char * restrict format, ...);
19181 int snprintf_s(char * restrict s, rsize_t n,
19182 const char * restrict format, ...);
19183 int sprintf_s(char * restrict s, rsize_t n,
19184 const char * restrict format, ...);
19185 int sscanf_s(const char * restrict s,
19186 const char * restrict format, ...);
19187 int vfprintf_s(FILE * restrict stream,
19188 const char * restrict format,
19190 int vfscanf_s(FILE * restrict stream,
19191 const char * restrict format,
19193 int vprintf_s(const char * restrict format,
19195 int vscanf_s(const char * restrict format,
19197 int vsnprintf_s(char * restrict s, rsize_t n,
19198 const char * restrict format,
19200 int vsprintf_s(char * restrict s, rsize_t n,
19201 const char * restrict format,
19203 int vsscanf_s(const char * restrict s,
19204 const char * restrict format,
19206 char *gets_s(char *s, rsize_t n);
19212 B.21 General utilities <stdlib.h>
19213 size_t ldiv_t EXIT_FAILURE MB_CUR_MAX
19214 wchar_t lldiv_t EXIT_SUCCESS
19215 div_t NULL RAND_MAX
19216 double atof(const char *nptr);
19217 int atoi(const char *nptr);
19218 long int atol(const char *nptr);
19219 long long int atoll(const char *nptr);
19220 double strtod(const char * restrict nptr,
19221 char ** restrict endptr);
19222 float strtof(const char * restrict nptr,
19223 char ** restrict endptr);
19224 long double strtold(const char * restrict nptr,
19225 char ** restrict endptr);
19226 long int strtol(const char * restrict nptr,
19227 char ** restrict endptr, int base);
19228 long long int strtoll(const char * restrict nptr,
19229 char ** restrict endptr, int base);
19230 unsigned long int strtoul(
19231 const char * restrict nptr,
19232 char ** restrict endptr, int base);
19233 unsigned long long int strtoull(
19234 const char * restrict nptr,
19235 char ** restrict endptr, int base);
19237 void srand(unsigned int seed);
19238 void *aligned_alloc(size_t alignment, size_t size);
19239 void *calloc(size_t nmemb, size_t size);
19240 void free(void *ptr);
19241 void *malloc(size_t size);
19242 void *realloc(void *ptr, size_t size);
19243 _Noreturn void abort(void);
19244 int atexit(void (*func)(void));
19245 int at_quick_exit(void (*func)(void));
19246 _Noreturn void exit(int status);
19247 _Noreturn void _Exit(int status);
19248 char *getenv(const char *name);
19249 _Noreturn void quick_exit(int status);
19250 int system(const char *string);
19255 void *bsearch(const void *key, const void *base,
19256 size_t nmemb, size_t size,
19257 int (*compar)(const void *, const void *));
19258 void qsort(void *base, size_t nmemb, size_t size,
19259 int (*compar)(const void *, const void *));
19261 long int labs(long int j);
19262 long long int llabs(long long int j);
19263 div_t div(int numer, int denom);
19264 ldiv_t ldiv(long int numer, long int denom);
19265 lldiv_t lldiv(long long int numer,
19266 long long int denom);
19267 int mblen(const char *s, size_t n);
19268 int mbtowc(wchar_t * restrict pwc,
19269 const char * restrict s, size_t n);
19270 int wctomb(char *s, wchar_t wchar);
19271 size_t mbstowcs(wchar_t * restrict pwcs,
19272 const char * restrict s, size_t n);
19273 size_t wcstombs(char * restrict s,
19274 const wchar_t * restrict pwcs, size_t n);
19275 __STDC_WANT_LIB_EXT1__
19278 constraint_handler_t
19279 constraint_handler_t set_constraint_handler_s(
19280 constraint_handler_t handler);
19281 void abort_handler_s(
19282 const char * restrict msg,
19283 void * restrict ptr,
19285 void ignore_handler_s(
19286 const char * restrict msg,
19287 void * restrict ptr,
19289 errno_t getenv_s(size_t * restrict len,
19290 char * restrict value, rsize_t maxsize,
19291 const char * restrict name);
19298 void *bsearch_s(const void *key, const void *base,
19299 rsize_t nmemb, rsize_t size,
19300 int (*compar)(const void *k, const void *y,
19303 errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
19304 int (*compar)(const void *x, const void *y,
19307 errno_t wctomb_s(int * restrict status,
19311 errno_t mbstowcs_s(size_t * restrict retval,
19312 wchar_t * restrict dst, rsize_t dstmax,
19313 const char * restrict src, rsize_t len);
19314 errno_t wcstombs_s(size_t * restrict retval,
19315 char * restrict dst, rsize_t dstmax,
19316 const wchar_t * restrict src, rsize_t len);
19317 B.22 String handling <string.h>
19320 void *memcpy(void * restrict s1,
19321 const void * restrict s2, size_t n);
19322 void *memmove(void *s1, const void *s2, size_t n);
19323 char *strcpy(char * restrict s1,
19324 const char * restrict s2);
19325 char *strncpy(char * restrict s1,
19326 const char * restrict s2, size_t n);
19327 char *strcat(char * restrict s1,
19328 const char * restrict s2);
19329 char *strncat(char * restrict s1,
19330 const char * restrict s2, size_t n);
19331 int memcmp(const void *s1, const void *s2, size_t n);
19332 int strcmp(const char *s1, const char *s2);
19333 int strcoll(const char *s1, const char *s2);
19334 int strncmp(const char *s1, const char *s2, size_t n);
19335 size_t strxfrm(char * restrict s1,
19336 const char * restrict s2, size_t n);
19337 void *memchr(const void *s, int c, size_t n);
19340 char *strchr(const char *s, int c);
19341 size_t strcspn(const char *s1, const char *s2);
19342 char *strpbrk(const char *s1, const char *s2);
19343 char *strrchr(const char *s, int c);
19344 size_t strspn(const char *s1, const char *s2);
19345 char *strstr(const char *s1, const char *s2);
19346 char *strtok(char * restrict s1,
19347 const char * restrict s2);
19348 void *memset(void *s, int c, size_t n);
19349 char *strerror(int errnum);
19350 size_t strlen(const char *s);
19351 __STDC_WANT_LIB_EXT1__
19354 errno_t memcpy_s(void * restrict s1, rsize_t s1max,
19355 const void * restrict s2, rsize_t n);
19356 errno_t memmove_s(void *s1, rsize_t s1max,
19357 const void *s2, rsize_t n);
19358 errno_t strcpy_s(char * restrict s1,
19360 const char * restrict s2);
19361 errno_t strncpy_s(char * restrict s1,
19363 const char * restrict s2,
19365 errno_t strcat_s(char * restrict s1,
19367 const char * restrict s2);
19368 errno_t strncat_s(char * restrict s1,
19370 const char * restrict s2,
19372 char *strtok_s(char * restrict s1,
19373 rsize_t * restrict s1max,
19374 const char * restrict s2,
19375 char ** restrict ptr);
19376 errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
19377 errno_t strerror_s(char *s, rsize_t maxsize,
19379 size_t strerrorlen_s(errno_t errnum);
19383 size_t strnlen_s(const char *s, size_t maxsize);
19384 B.23 Type-generic math <tgmath.h>
19385 acos sqrt fmod nextafter
19386 asin fabs frexp nexttoward
19387 atan atan2 hypot remainder
19388 acosh cbrt ilogb remquo
19389 asinh ceil ldexp rint
19390 atanh copysign lgamma round
19391 cos erf llrint scalbn
19392 sin erfc llround scalbln
19393 tan exp2 log10 tgamma
19394 cosh expm1 log1p trunc
19395 sinh fdim log2 carg
19396 tanh floor logb cimag
19398 log fmax lround cproj
19399 pow fmin nearbyint creal
19400 B.24 Threads <threads.h>
19401 ONCE_FLAG_INIT mtx_plain
19402 TSS_DTOR_ITERATIONS mtx_recursive
19407 tss_dtor_t thrd_busy
19408 thrd_start_t thrd_error
19409 once_flag thrd_nomem
19411 void call_once(once_flag *flag, void (*func)(void));
19412 int cnd_broadcast(cnd_t *cond);
19413 void cnd_destroy(cnd_t *cond);
19414 int cnd_init(cnd_t *cond);
19415 int cnd_signal(cnd_t *cond);
19416 int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
19418 int cnd_wait(cnd_t *cond, mtx_t *mtx);
19419 void mtx_destroy(mtx_t *mtx);
19420 int mtx_init(mtx_t *mtx, int type);
19421 int mtx_lock(mtx_t *mtx);
19424 int mtx_timedlock(mtx_t *mtx, const xtime *xt);
19425 int mtx_trylock(mtx_t *mtx);
19426 int mtx_unlock(mtx_t *mtx);
19427 int thrd_create(thrd_t *thr, thrd_start_t func,
19429 thrd_t thrd_current(void);
19430 int thrd_detach(thrd_t thr);
19431 int thrd_equal(thrd_t thr0, thrd_t thr1);
19432 void thrd_exit(int res);
19433 int thrd_join(thrd_t thr, int *res);
19434 void thrd_sleep(const xtime *xt);
19435 void thrd_yield(void);
19436 int tss_create(tss_t *key, tss_dtor_t dtor);
19437 void tss_delete(tss_t key);
19438 void *tss_get(tss_t key);
19439 int tss_set(tss_t key, void *val);
19440 int xtime_get(xtime *xt, int base);
19441 B.25 Date and time <time.h>
19443 CLOCKS_PER_SEC clock_t struct tm
19444 clock_t clock(void);
19445 double difftime(time_t time1, time_t time0);
19446 time_t mktime(struct tm *timeptr);
19447 time_t time(time_t *timer);
19448 char *asctime(const struct tm *timeptr);
19449 char *ctime(const time_t *timer);
19450 struct tm *gmtime(const time_t *timer);
19451 struct tm *localtime(const time_t *timer);
19452 size_t strftime(char * restrict s,
19454 const char * restrict format,
19455 const struct tm * restrict timeptr);
19456 __STDC_WANT_LIB_EXT1__
19459 errno_t asctime_s(char *s, rsize_t maxsize,
19460 const struct tm *timeptr);
19466 errno_t ctime_s(char *s, rsize_t maxsize,
19467 const time_t *timer);
19468 struct tm *gmtime_s(const time_t * restrict timer,
19469 struct tm * restrict result);
19470 struct tm *localtime_s(const time_t * restrict timer,
19471 struct tm * restrict result);
19472 B.26 Unicode utilities <uchar.h>
19473 mbstate_t size_t char16_t char32_t
19474 size_t mbrtoc16(char16_t * restrict pc16,
19475 const char * restrict s, size_t n,
19476 mbstate_t * restrict ps);
19477 size_t c16rtomb(char * restrict s, char16_t c16,
19478 mbstate_t * restrict ps);
19479 size_t mbrtoc32(char32_t * restrict pc32,
19480 const char * restrict s, size_t n,
19481 mbstate_t * restrict ps);
19482 size_t c32rtomb(char * restrict s, char32_t c32,
19483 mbstate_t * restrict ps);
19484 B.27 Extended multibyte/wide character utilities <wchar.h>
19485 wchar_t wint_t WCHAR_MAX
19486 size_t struct tm WCHAR_MIN
19487 mbstate_t NULL WEOF
19488 int fwprintf(FILE * restrict stream,
19489 const wchar_t * restrict format, ...);
19490 int fwscanf(FILE * restrict stream,
19491 const wchar_t * restrict format, ...);
19492 int swprintf(wchar_t * restrict s, size_t n,
19493 const wchar_t * restrict format, ...);
19494 int swscanf(const wchar_t * restrict s,
19495 const wchar_t * restrict format, ...);
19496 int vfwprintf(FILE * restrict stream,
19497 const wchar_t * restrict format, va_list arg);
19498 int vfwscanf(FILE * restrict stream,
19499 const wchar_t * restrict format, va_list arg);
19500 int vswprintf(wchar_t * restrict s, size_t n,
19501 const wchar_t * restrict format, va_list arg);
19507 int vswscanf(const wchar_t * restrict s,
19508 const wchar_t * restrict format, va_list arg);
19509 int vwprintf(const wchar_t * restrict format,
19511 int vwscanf(const wchar_t * restrict format,
19513 int wprintf(const wchar_t * restrict format, ...);
19514 int wscanf(const wchar_t * restrict format, ...);
19515 wint_t fgetwc(FILE *stream);
19516 wchar_t *fgetws(wchar_t * restrict s, int n,
19517 FILE * restrict stream);
19518 wint_t fputwc(wchar_t c, FILE *stream);
19519 int fputws(const wchar_t * restrict s,
19520 FILE * restrict stream);
19521 int fwide(FILE *stream, int mode);
19522 wint_t getwc(FILE *stream);
19523 wint_t getwchar(void);
19524 wint_t putwc(wchar_t c, FILE *stream);
19525 wint_t putwchar(wchar_t c);
19526 wint_t ungetwc(wint_t c, FILE *stream);
19527 double wcstod(const wchar_t * restrict nptr,
19528 wchar_t ** restrict endptr);
19529 float wcstof(const wchar_t * restrict nptr,
19530 wchar_t ** restrict endptr);
19531 long double wcstold(const wchar_t * restrict nptr,
19532 wchar_t ** restrict endptr);
19533 long int wcstol(const wchar_t * restrict nptr,
19534 wchar_t ** restrict endptr, int base);
19535 long long int wcstoll(const wchar_t * restrict nptr,
19536 wchar_t ** restrict endptr, int base);
19537 unsigned long int wcstoul(const wchar_t * restrict nptr,
19538 wchar_t ** restrict endptr, int base);
19539 unsigned long long int wcstoull(
19540 const wchar_t * restrict nptr,
19541 wchar_t ** restrict endptr, int base);
19542 wchar_t *wcscpy(wchar_t * restrict s1,
19543 const wchar_t * restrict s2);
19544 wchar_t *wcsncpy(wchar_t * restrict s1,
19545 const wchar_t * restrict s2, size_t n);
19551 wchar_t *wmemcpy(wchar_t * restrict s1,
19552 const wchar_t * restrict s2, size_t n);
19553 wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
19555 wchar_t *wcscat(wchar_t * restrict s1,
19556 const wchar_t * restrict s2);
19557 wchar_t *wcsncat(wchar_t * restrict s1,
19558 const wchar_t * restrict s2, size_t n);
19559 int wcscmp(const wchar_t *s1, const wchar_t *s2);
19560 int wcscoll(const wchar_t *s1, const wchar_t *s2);
19561 int wcsncmp(const wchar_t *s1, const wchar_t *s2,
19563 size_t wcsxfrm(wchar_t * restrict s1,
19564 const wchar_t * restrict s2, size_t n);
19565 int wmemcmp(const wchar_t *s1, const wchar_t *s2,
19567 wchar_t *wcschr(const wchar_t *s, wchar_t c);
19568 size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
19569 wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
19570 wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
19571 size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
19572 wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
19573 wchar_t *wcstok(wchar_t * restrict s1,
19574 const wchar_t * restrict s2,
19575 wchar_t ** restrict ptr);
19576 wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
19577 size_t wcslen(const wchar_t *s);
19578 wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
19579 size_t wcsftime(wchar_t * restrict s, size_t maxsize,
19580 const wchar_t * restrict format,
19581 const struct tm * restrict timeptr);
19582 wint_t btowc(int c);
19583 int wctob(wint_t c);
19584 int mbsinit(const mbstate_t *ps);
19585 size_t mbrlen(const char * restrict s, size_t n,
19586 mbstate_t * restrict ps);
19587 size_t mbrtowc(wchar_t * restrict pwc,
19588 const char * restrict s, size_t n,
19589 mbstate_t * restrict ps);
19595 size_t wcrtomb(char * restrict s, wchar_t wc,
19596 mbstate_t * restrict ps);
19597 size_t mbsrtowcs(wchar_t * restrict dst,
19598 const char ** restrict src, size_t len,
19599 mbstate_t * restrict ps);
19600 size_t wcsrtombs(char * restrict dst,
19601 const wchar_t ** restrict src, size_t len,
19602 mbstate_t * restrict ps);
19603 __STDC_WANT_LIB_EXT1__
19606 int fwprintf_s(FILE * restrict stream,
19607 const wchar_t * restrict format, ...);
19608 int fwscanf_s(FILE * restrict stream,
19609 const wchar_t * restrict format, ...);
19610 int snwprintf_s(wchar_t * restrict s,
19612 const wchar_t * restrict format, ...);
19613 int swprintf_s(wchar_t * restrict s, rsize_t n,
19614 const wchar_t * restrict format, ...);
19615 int swscanf_s(const wchar_t * restrict s,
19616 const wchar_t * restrict format, ...);
19617 int vfwprintf_s(FILE * restrict stream,
19618 const wchar_t * restrict format,
19620 int vfwscanf_s(FILE * restrict stream,
19621 const wchar_t * restrict format, va_list arg);
19622 int vsnwprintf_s(wchar_t * restrict s,
19624 const wchar_t * restrict format,
19626 int vswprintf_s(wchar_t * restrict s,
19628 const wchar_t * restrict format,
19630 int vswscanf_s(const wchar_t * restrict s,
19631 const wchar_t * restrict format,
19638 int vwprintf_s(const wchar_t * restrict format,
19640 int vwscanf_s(const wchar_t * restrict format,
19642 int wprintf_s(const wchar_t * restrict format, ...);
19643 int wscanf_s(const wchar_t * restrict format, ...);
19644 errno_t wcscpy_s(wchar_t * restrict s1,
19646 const wchar_t * restrict s2);
19647 errno_t wcsncpy_s(wchar_t * restrict s1,
19649 const wchar_t * restrict s2,
19651 errno_t wmemcpy_s(wchar_t * restrict s1,
19653 const wchar_t * restrict s2,
19655 errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
19656 const wchar_t *s2, rsize_t n);
19657 errno_t wcscat_s(wchar_t * restrict s1,
19659 const wchar_t * restrict s2);
19660 errno_t wcsncat_s(wchar_t * restrict s1,
19662 const wchar_t * restrict s2,
19664 wchar_t *wcstok_s(wchar_t * restrict s1,
19665 rsize_t * restrict s1max,
19666 const wchar_t * restrict s2,
19667 wchar_t ** restrict ptr);
19668 size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
19669 errno_t wcrtomb_s(size_t * restrict retval,
19670 char * restrict s, rsize_t smax,
19671 wchar_t wc, mbstate_t * restrict ps);
19672 errno_t mbsrtowcs_s(size_t * restrict retval,
19673 wchar_t * restrict dst, rsize_t dstmax,
19674 const char ** restrict src, rsize_t len,
19675 mbstate_t * restrict ps);
19682 errno_t wcsrtombs_s(size_t * restrict retval,
19683 char * restrict dst, rsize_t dstmax,
19684 const wchar_t ** restrict src, rsize_t len,
19685 mbstate_t * restrict ps);
19686 B.28 Wide character classification and mapping utilities <wctype.h>
19687 wint_t wctrans_t wctype_t WEOF
19688 int iswalnum(wint_t wc);
19689 int iswalpha(wint_t wc);
19690 int iswblank(wint_t wc);
19691 int iswcntrl(wint_t wc);
19692 int iswdigit(wint_t wc);
19693 int iswgraph(wint_t wc);
19694 int iswlower(wint_t wc);
19695 int iswprint(wint_t wc);
19696 int iswpunct(wint_t wc);
19697 int iswspace(wint_t wc);
19698 int iswupper(wint_t wc);
19699 int iswxdigit(wint_t wc);
19700 int iswctype(wint_t wc, wctype_t desc);
19701 wctype_t wctype(const char *property);
19702 wint_t towlower(wint_t wc);
19703 wint_t towupper(wint_t wc);
19704 wint_t towctrans(wint_t wc, wctrans_t desc);
19705 wctrans_t wctrans(const char *property);
19715 1 The following are the sequence points described in 5.1.2.3:
19716 -- Between the evaluations of the function designator and actual arguments in a function
19717 call and the actual call. (6.5.2.2).
19718 -- Between the evaluations of the first and second operands of the following operators:
19719 logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17).
19720 -- Between the evaluations of the first operand of the conditional ? : operator and
19721 whichever of the second and third operands is evaluated (6.5.15).
19722 -- The end of a full declarator: declarators (6.7.6);
19723 -- Between the evaluation of a full expression and the next full expression to be
19724 evaluated. The following are full expressions: an initializer that is not part of a
19725 compound literal (6.7.9); the expression in an expression statement (6.8.3); the
19726 controlling expression of a selection statement (if or switch) (6.8.4); the
19727 controlling expression of a while or do statement (6.8.5); each of the (optional)
19728 expressions of a for statement (6.8.5.3); the (optional) expression in a return
19729 statement (6.8.6.4).
19730 -- Immediately before a library function returns (7.1.4).
19731 -- After the actions associated with each formatted input/output function conversion
19732 specifier (7.21.6, 7.28.2).
19733 -- Immediately before and immediately after each call to a comparison function, and
19734 also between any call to a comparison function and any movement of the objects
19735 passed as arguments to that call (7.22.5).
19744 Universal character names for identifiers
19745 1 This clause lists the hexadecimal code values that are valid in universal character names
19747 2 This table is reproduced unchanged from ISO/IEC TR 10176:1998, produced by ISO/IEC
19748 JTC 1/SC 22/WG 20, except for the omission of ranges that are part of the basic character
19750 Latin: 00AA, 00BA, 00C0-00D6, 00D8-00F6, 00F8-01F5, 01FA-0217,
19751 0250-02A8, 1E00-1E9B, 1EA0-1EF9, 207F
19752 Greek: 0386, 0388-038A, 038C, 038E-03A1, 03A3-03CE, 03D0-03D6,
19753 03DA, 03DC, 03DE, 03E0, 03E2-03F3, 1F00-1F15, 1F18-1F1D,
19754 1F20-1F45, 1F48-1F4D, 1F50-1F57, 1F59, 1F5B, 1F5D,
19755 1F5F-1F7D, 1F80-1FB4, 1FB6-1FBC, 1FC2-1FC4, 1FC6-1FCC,
19756 1FD0-1FD3, 1FD6-1FDB, 1FE0-1FEC, 1FF2-1FF4, 1FF6-1FFC
19757 Cyrillic: 0401-040C, 040E-044F, 0451-045C, 045E-0481, 0490-04C4,
19758 04C7-04C8, 04CB-04CC, 04D0-04EB, 04EE-04F5, 04F8-04F9
19759 Armenian: 0531-0556, 0561-0587
19760 Hebrew: 05B0-05B9, 05BB-05BD, 05BF, 05C1-05C2, 05D0-05EA,
19762 Arabic: 0621-063A, 0640-0652, 0670-06B7, 06BA-06BE, 06C0-06CE,
19763 06D0-06DC, 06E5-06E8, 06EA-06ED
19764 Devanagari: 0901-0903, 0905-0939, 093E-094D, 0950-0952, 0958-0963
19765 Bengali: 0981-0983, 0985-098C, 098F-0990, 0993-09A8, 09AA-09B0,
19766 09B2, 09B6-09B9, 09BE-09C4, 09C7-09C8, 09CB-09CD,
19767 09DC-09DD, 09DF-09E3, 09F0-09F1
19768 Gurmukhi: 0A02, 0A05-0A0A, 0A0F-0A10, 0A13-0A28, 0A2A-0A30,
19769 0A32-0A33, 0A35-0A36, 0A38-0A39, 0A3E-0A42, 0A47-0A48,
19770 0A4B-0A4D, 0A59-0A5C, 0A5E, 0A74
19771 Gujarati: 0A81-0A83, 0A85-0A8B, 0A8D, 0A8F-0A91, 0A93-0AA8,
19772 0AAA-0AB0, 0AB2-0AB3, 0AB5-0AB9, 0ABD-0AC5,
19773 0AC7-0AC9, 0ACB-0ACD, 0AD0, 0AE0
19774 Oriya: 0B01-0B03, 0B05-0B0C, 0B0F-0B10, 0B13-0B28, 0B2A-0B30,
19775 0B32-0B33, 0B36-0B39, 0B3E-0B43, 0B47-0B48, 0B4B-0B4D,
19778 0B5C-0B5D, 0B5F-0B61
19779 Tamil: 0B82-0B83, 0B85-0B8A, 0B8E-0B90, 0B92-0B95, 0B99-0B9A,
19780 0B9C, 0B9E-0B9F, 0BA3-0BA4, 0BA8-0BAA, 0BAE-0BB5,
19781 0BB7-0BB9, 0BBE-0BC2, 0BC6-0BC8, 0BCA-0BCD
19782 Telugu: 0C01-0C03, 0C05-0C0C, 0C0E-0C10, 0C12-0C28, 0C2A-0C33,
19783 0C35-0C39, 0C3E-0C44, 0C46-0C48, 0C4A-0C4D, 0C60-0C61
19784 Kannada: 0C82-0C83, 0C85-0C8C, 0C8E-0C90, 0C92-0CA8, 0CAA-0CB3,
19785 0CB5-0CB9, 0CBE-0CC4, 0CC6-0CC8, 0CCA-0CCD, 0CDE,
19787 Malayalam: 0D02-0D03, 0D05-0D0C, 0D0E-0D10, 0D12-0D28, 0D2A-0D39,
19788 0D3E-0D43, 0D46-0D48, 0D4A-0D4D, 0D60-0D61
19789 Thai: 0E01-0E3A, 0E40-0E5B
19790 Lao: 0E81-0E82, 0E84, 0E87-0E88, 0E8A, 0E8D, 0E94-0E97,
19791 0E99-0E9F, 0EA1-0EA3, 0EA5, 0EA7, 0EAA-0EAB,
19792 0EAD-0EAE, 0EB0-0EB9, 0EBB-0EBD, 0EC0-0EC4, 0EC6,
19793 0EC8-0ECD, 0EDC-0EDD
19794 Tibetan: 0F00, 0F18-0F19, 0F35, 0F37, 0F39, 0F3E-0F47, 0F49-0F69,
19795 0F71-0F84, 0F86-0F8B, 0F90-0F95, 0F97, 0F99-0FAD,
19797 Georgian: 10A0-10C5, 10D0-10F6
19798 Hiragana: 3041-3093, 309B-309C
19799 Katakana: 30A1-30F6, 30FB-30FC
19800 Bopomofo: 3105-312C
19801 CJK Unified Ideographs: 4E00-9FA5
19803 Digits: 0660-0669, 06F0-06F9, 0966-096F, 09E6-09EF, 0A66-0A6F,
19804 0AE6-0AEF, 0B66-0B6F, 0BE7-0BEF, 0C66-0C6F, 0CE6-0CEF,
19805 0D66-0D6F, 0E50-0E59, 0ED0-0ED9, 0F20-0F33
19806 Special characters: 00B5, 00B7, 02B0-02B8, 02BB, 02BD-02C1, 02D0-02D1,
19807 02E0-02E4, 037A, 0559, 093D, 0B3D, 1FBE, 203F-2040, 2102,
19808 2107, 210A-2113, 2115, 2118-211D, 2124, 2126, 2128, 212A-2131,
19809 2133-2138, 2160-2182, 3005-3007, 3021-3029
19818 Implementation limits
19819 1 The contents of the header <limits.h> are given below, in alphabetical order. The
19820 minimum magnitudes shown shall be replaced by implementation-defined magnitudes
19821 with the same sign. The values shall all be constant expressions suitable for use in #if
19822 preprocessing directives. The components are described further in 5.2.4.2.1.
19824 #define CHAR_MAX UCHAR_MAX or SCHAR_MAX
19825 #define CHAR_MIN 0 or SCHAR_MIN
19826 #define INT_MAX +32767
19827 #define INT_MIN -32767
19828 #define LONG_MAX +2147483647
19829 #define LONG_MIN -2147483647
19830 #define LLONG_MAX +9223372036854775807
19831 #define LLONG_MIN -9223372036854775807
19832 #define MB_LEN_MAX 1
19833 #define SCHAR_MAX +127
19834 #define SCHAR_MIN -127
19835 #define SHRT_MAX +32767
19836 #define SHRT_MIN -32767
19837 #define UCHAR_MAX 255
19838 #define USHRT_MAX 65535
19839 #define UINT_MAX 65535
19840 #define ULONG_MAX 4294967295
19841 #define ULLONG_MAX 18446744073709551615
19842 2 The contents of the header <float.h> are given below. All integer values, except
19843 FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing
19844 directives; all floating values shall be constant expressions. The components are
19845 described further in 5.2.4.2.2.
19846 3 The values given in the following list shall be replaced by implementation-defined
19848 #define FLT_EVAL_METHOD
19850 4 The values given in the following list shall be replaced by implementation-defined
19851 constant expressions that are greater or equal in magnitude (absolute value) to those
19852 shown, with the same sign:
19855 #define DLB_DECIMAL_DIG 10
19857 #define DBL_MANT_DIG
19858 #define DBL_MAX_10_EXP +37
19859 #define DBL_MAX_EXP
19860 #define DBL_MIN_10_EXP -37
19861 #define DBL_MIN_EXP
19862 #define DECIMAL_DIG 10
19863 #define FLT_DECIMAL_DIG 6
19865 #define FLT_MANT_DIG
19866 #define FLT_MAX_10_EXP +37
19867 #define FLT_MAX_EXP
19868 #define FLT_MIN_10_EXP -37
19869 #define FLT_MIN_EXP
19870 #define FLT_RADIX 2
19871 #define LDLB_DECIMAL_DIG 10
19872 #define LDBL_DIG 10
19873 #define LDBL_MANT_DIG
19874 #define LDBL_MAX_10_EXP +37
19875 #define LDBL_MAX_EXP
19876 #define LDBL_MIN_10_EXP -37
19877 #define LDBL_MIN_EXP
19878 5 The values given in the following list shall be replaced by implementation-defined
19879 constant expressions with values that are greater than or equal to those shown:
19880 #define DBL_MAX 1E+37
19881 #define FLT_MAX 1E+37
19882 #define LDBL_MAX 1E+37
19883 6 The values given in the following list shall be replaced by implementation-defined
19884 constant expressions with (positive) values that are less than or equal to those shown:
19885 #define DBL_EPSILON 1E-9
19886 #define DBL_MIN 1E-37
19887 #define FLT_EPSILON 1E-5
19888 #define FLT_MIN 1E-37
19889 #define LDBL_EPSILON 1E-9
19890 #define LDBL_MIN 1E-37
19899 IEC 60559 floating-point arithmetic
19901 1 This annex specifies C language support for the IEC 60559 floating-point standard. The
19902 IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
19903 microprocessor systems, second edition (IEC 60559:1989), previously designated
19904 IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic
19905 (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point
19906 Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove
19907 dependencies on radix and word length. IEC 60559 generally refers to the floating-point
19908 standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that
19909 defines __STDC_IEC_559__ shall conform to the specifications in this annex.339)
19910 Where a binding between the C language and IEC 60559 is indicated, the
19911 IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since
19912 negative and positive infinity are representable in IEC 60559 formats, all real numbers lie
19913 within the range of representable values.
19915 1 The C floating types match the IEC 60559 formats as follows:
19916 -- The float type matches the IEC 60559 single format.
19917 -- The double type matches the IEC 60559 double format.
19918 -- The long double type matches an IEC 60559 extended format,340) else a
19919 non-IEC 60559 extended format, else the IEC 60559 double format.
19920 Any non-IEC 60559 extended format used for the long double type shall have more
19921 precision than IEC 60559 double and at least the range of IEC 60559 double.341)
19926 339) Implementations that do not define __STDC_IEC_559__ are not required to conform to these
19928 340) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit
19929 and quadruple 128-bit IEC 60559 formats.
19930 341) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
19935 Recommended practice
19936 2 The long double type should match an IEC 60559 extended format.
19937 F.2.1 Infinities, signed zeros, and NaNs
19938 1 This specification does not define the behavior of signaling NaNs.342) It generally uses
19939 the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan
19940 functions in <math.h> provide designations for IEC 60559 NaNs and infinities.
19941 F.3 Operators and functions
19942 1 C operators and functions provide IEC 60559 required and recommended facilities as
19944 -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and
19946 -- The sqrt functions in <math.h> provide the IEC 60559 square root operation.
19947 -- The remainder functions in <math.h> provide the IEC 60559 remainder
19948 operation. The remquo functions in <math.h> provide the same operation but
19949 with additional information.
19950 -- The rint functions in <math.h> provide the IEC 60559 operation that rounds a
19951 floating-point number to an integer value (in the same precision). The nearbyint
19952 functions in <math.h> provide the nearbyinteger function recommended in the
19953 Appendix to ANSI/IEEE 854.
19954 -- The conversions for floating types provide the IEC 60559 conversions between
19955 floating-point precisions.
19956 -- The conversions from integer to floating types provide the IEC 60559 conversions
19957 from integer to floating point.
19958 -- The conversions from floating to integer types provide IEC 60559-like conversions
19959 but always round toward zero.
19960 -- The lrint and llrint functions in <math.h> provide the IEC 60559
19961 conversions, which honor the directed rounding mode, from floating point to the
19962 long int and long long int integer formats. The lrint and llrint
19963 functions can be used to implement IEC 60559 conversions from floating to other
19965 -- The translation time conversion of floating constants and the strtod, strtof,
19966 strtold, fprintf, fscanf, and related library functions in <stdlib.h>,
19969 342) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are
19970 sufficient for closure of the arithmetic.
19974 <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
19975 strtold function in <stdlib.h> provides the conv function recommended in the
19976 Appendix to ANSI/IEEE 854.
19977 -- The relational and equality operators provide IEC 60559 comparisons. IEC 60559
19978 identifies a need for additional comparison predicates to facilitate writing code that
19979 accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
19980 isless, islessequal, islessgreater, and isunordered) in <math.h>
19981 supplement the language operators to address this need. The islessgreater and
19982 isunordered macros provide respectively a quiet version of the <> predicate and
19983 the unordered predicate recommended in the Appendix to IEC 60559.
19984 -- The feclearexcept, feraiseexcept, and fetestexcept functions in
19985 <fenv.h> provide the facility to test and alter the IEC 60559 floating-point
19986 exception status flags. The fegetexceptflag and fesetexceptflag
19987 functions in <fenv.h> provide the facility to save and restore all five status flags at
19988 one time. These functions are used in conjunction with the type fexcept_t and the
19989 floating-point exception macros (FE_INEXACT, FE_DIVBYZERO,
19990 FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
19991 -- The fegetround and fesetround functions in <fenv.h> provide the facility
19992 to select among the IEC 60559 directed rounding modes represented by the rounding
19993 direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
19994 FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the
19995 IEC 60559 directed rounding modes.
19996 -- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in
19997 <fenv.h> provide a facility to manage the floating-point environment, comprising
19998 the IEC 60559 status flags and control modes.
19999 -- The copysign functions in <math.h> provide the copysign function
20000 recommended in the Appendix to IEC 60559.
20001 -- The fabs functions in <math.h> provide the abs function recommended in the
20002 Appendix to IEC 60559.
20003 -- The unary minus (-) operator provides the unary minus (-) operation recommended
20004 in the Appendix to IEC 60559.
20005 -- The scalbn and scalbln functions in <math.h> provide the scalb function
20006 recommended in the Appendix to IEC 60559.
20007 -- The logb functions in <math.h> provide the logb function recommended in the
20008 Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
20009 -- The nextafter and nexttoward functions in <math.h> provide the nextafter
20010 function recommended in the Appendix to IEC 60559 (but with a minor change to
20014 better handle signed zeros).
20015 -- The isfinite macro in <math.h> provides the finite function recommended in
20016 the Appendix to IEC 60559.
20017 -- The isnan macro in <math.h> provides the isnan function recommended in the
20018 Appendix to IEC 60559.
20019 -- The signbit macro and the fpclassify macro in <math.h>, used in
20020 conjunction with the number classification macros (FP_NAN, FP_INFINITE,
20021 FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
20022 function recommended in the Appendix to IEC 60559 (except that the classification
20023 macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).
20024 F.4 Floating to integer conversion
20025 1 If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised
20026 (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part
20027 of the floating value exceeds the range of the integer type, then the ''invalid'' floating-
20028 point exception is raised and the resulting value is unspecified. Otherwise, the resulting
20029 value is determined by 6.3.1.4. Conversion of an integral floating value that does not
20030 exceed the range of the integer type raises no floating-point exceptions; whether
20031 conversion of a non-integral floating value raises the ''inexact'' floating-point exception is
20033 F.5 Binary-decimal conversion
20034 1 Conversion from the widest supported IEC 60559 format to decimal with
20035 DECIMAL_DIG digits and back is the identity function.344)
20036 2 Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
20037 particular, conversion between any supported IEC 60559 format and decimal with
20038 DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
20039 rounding mode), which assures that conversion from the widest supported IEC 60559
20040 format to decimal with DECIMAL_DIG digits and back is the identity function.
20044 343) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer
20045 conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those
20046 cases where it matters, library functions can be used to effect such conversions with or without raising
20047 the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in
20049 344) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
20050 DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
20051 IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
20052 DBL_DIG are 18 and 15, respectively, for these formats.)
20056 3 Functions such as strtod that convert character sequences to floating types honor the
20057 rounding direction. Hence, if the rounding direction might be upward or downward, the
20058 implementation cannot convert a minus-signed sequence by negating the converted
20060 F.6 The return statement
20061 If the return expression is evaluated in a floating-point format different from the return
20062 type, the expression is converted to the return type of the function and the resulting value
20063 is returned to the caller.
20064 F.7 Contracted expressions
20065 1 A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed
20066 zeros, subnormals, and the rounding directions in a manner consistent with the basic
20067 arithmetic operations covered by IEC 60559.
20068 Recommended practice
20069 2 A contracted expression should raise floating-point exceptions in a manner generally
20070 consistent with the basic arithmetic operations.
20071 F.8 Floating-point environment
20072 1 The floating-point environment defined in <fenv.h> includes the IEC 60559 floating-
20073 point exception status flags and directed-rounding control modes. It includes also
20074 IEC 60559 dynamic rounding precision and trap enablement modes, if the
20075 implementation supports them.345)
20076 F.8.1 Environment management
20077 1 IEC 60559 requires that floating-point operations implicitly raise floating-point exception
20078 status flags, and that rounding control modes can be set explicitly to affect result values of
20079 floating-point operations. When the state for the FENV_ACCESS pragma (defined in
20080 <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects
20081 which respect sequence points.346)
20086 345) This specification does not require dynamic rounding precision nor trap enablement modes.
20087 346) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating-
20088 point control modes will be the default ones and the floating-point status flags will not be tested,
20089 which allows certain optimizations (see F.9).
20094 1 During translation the IEC 60559 default modes are in effect:
20095 -- The rounding direction mode is rounding to nearest.
20096 -- The rounding precision mode (if supported) is set so that results are not shortened.
20097 -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
20098 Recommended practice
20099 2 The implementation should produce a diagnostic message for each translation-time
20100 floating-point exception, other than ''inexact'';347) the implementation should then
20101 proceed with the translation of the program.
20103 1 At program startup the floating-point environment is initialized as prescribed by
20105 -- All floating-point exception status flags are cleared.
20106 -- The rounding direction mode is rounding to nearest.
20107 -- The dynamic rounding precision mode (if supported) is set so that results are not
20109 -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
20110 F.8.4 Constant expressions
20111 1 An arithmetic constant expression of floating type, other than one in an initializer for an
20112 object that has static or thread storage duration, is evaluated (as if) during execution; thus,
20113 it is affected by any operative floating-point control modes and raises floating-point
20114 exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma
20120 347) As floating constants are converted to appropriate internal representations at translation time, their
20121 conversion is subject to default rounding modes and raises no execution-time floating-point exceptions
20122 (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example
20123 strtod, provide execution-time conversion of numeric strings.
20124 348) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0
20125 are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
20126 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
20127 efficiency of translation-time evaluation through static initialization, such as
20128 const static double one_third = 1.0/3.0;
20134 #pragma STDC FENV_ACCESS ON
20137 float w[] = { 0.0/0.0 }; // raises an exception
20138 static float x = 0.0/0.0; // does not raise an exception
20139 float y = 0.0/0.0; // raises an exception
20140 double z = 0.0/0.0; // raises an exception
20143 3 For the static initialization, the division is done at translation time, raising no (execution-time) floating-
20144 point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at
20147 F.8.5 Initialization
20148 1 All computation for automatic initialization is done (as if) at execution time; thus, it is
20149 affected by any operative modes and raises floating-point exceptions as required by
20150 IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation
20151 for initialization of objects that have static or thread storage duration is done (as if) at
20155 #pragma STDC FENV_ACCESS ON
20158 float u[] = { 1.1e75 }; // raises exceptions
20159 static float v = 1.1e75; // does not raise exceptions
20160 float w = 1.1e75; // raises exceptions
20161 double x = 1.1e75; // may raise exceptions
20162 float y = 1.1e75f; // may raise exceptions
20163 long double z = 1.1e75; // does not raise exceptions
20166 3 The static initialization of v raises no (execution-time) floating-point exceptions because its computation is
20167 done at translation time. The automatic initialization of u and w require an execution-time conversion to
20168 float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations
20169 of x and y entail execution-time conversion; however, in some expression evaluation methods, the
20170 conversions is not to a narrower format, in which case no floating-point exception is raised.349) The
20171 automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating-
20172 point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to
20176 349) Use of float_t and double_t variables increases the likelihood of translation-time computation.
20177 For example, the automatic initialization
20178 double_t x = 1.1e75;
20179 could be done at translation time, regardless of the expression evaluation method.
20183 their internal representations occur at translation time in all cases.
20185 F.8.6 Changing the environment
20186 1 Operations defined in 6.5 and functions and macros defined for the standard libraries
20187 change floating-point status flags and control modes just as indicated by their
20188 specifications (including conformance to IEC 60559). They do not change flags or modes
20189 (so as to be detectable by the user) in any other cases.
20190 2 If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559
20191 valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and
20192 ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised
20193 before ''inexact''.
20195 1 This section identifies code transformations that might subvert IEC 60559-specified
20196 behavior, and others that do not.
20197 F.9.1 Global transformations
20198 1 Floating-point arithmetic operations and external function calls may entail side effects
20199 which optimization shall honor, at least where the state of the FENV_ACCESS pragma is
20200 ''on''. The flags and modes in the floating-point environment may be regarded as global
20201 variables; floating-point operations (+, *, etc.) implicitly read the modes and write the
20203 2 Concern about side effects may inhibit code motion and removal of seemingly useless
20204 code. For example, in
20206 #pragma STDC FENV_ACCESS ON
20210 for (i = 0; i < n; i++) x + 1;
20213 x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop
20214 body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of
20215 course these optimizations are valid if the implementation can rule out the nettlesome
20217 3 This specification does not require support for trap handlers that maintain information
20218 about the order or count of floating-point exceptions. Therefore, between function calls,
20219 floating-point exceptions need not be precise: the actual order and number of occurrences
20220 of floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
20223 the preceding loop could be treated as
20225 F.9.2 Expression transformations
20226 1 x/2 (<->) x x 0.5 Although similar transformations involving inexact constants
20227 generally do not yield numerically equivalent expressions, if the
20228 constants are exact then such transformations can be made on
20229 IEC 60559 machines and others that round perfectly.
20230 1 x x and x/1 (->) x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559
20231 machines, among others).350)
20232 x/x (->) 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero,
20234 x - y (<->) x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on
20235 IEC 60559 machines, among others).
20236 x - y (<->) -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1
20237 is +0 but -(1 - 1) is -0 (in the default rounding direction).351)
20238 x - x (->) 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or
20240 0 x x (->) 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN,
20242 x+0(->) x The expressions x + 0 and x are not equivalent if x is -0, because
20243 (-0) + (+0) yields +0 (in the default rounding direction), not -0.
20244 x-0(->) x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but
20245 +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the
20246 FENV_ACCESS pragma is ''off'', promising default rounding, then
20247 the implementation can replace x - 0 by x, even if x might be zero.
20248 -x (<->) 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because
20249 -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is
20252 350) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and
20253 other transformations that remove arithmetic operators.
20254 351) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
20256 1/(1/ (+-) (inf)) is (+-) (inf)
20258 conj(csqrt(z)) is csqrt(conj(z)),
20263 F.9.3 Relational operators
20264 1 x != x (->) false The expression x != x is true if x is a NaN.
20265 x = x (->) true The expression x = x is false if x is a NaN.
20266 x < y (->) isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these
20267 expressions are not equivalent because of side effects when x or y is a
20268 NaN and the state of the FENV_ACCESS pragma is ''on''. This
20269 transformation, which would be desirable if extra code were required
20270 to cause the ''invalid'' floating-point exception for unordered cases,
20271 could be performed provided the state of the FENV_ACCESS pragma
20273 The sense of relational operators shall be maintained. This includes handling unordered
20274 cases as expressed by the source code.
20276 // calls g and raises ''invalid'' if a and b are unordered
20281 is not equivalent to
20282 // calls f and raises ''invalid'' if a and b are unordered
20288 // calls f without raising ''invalid'' if a and b are unordered
20289 if (isgreaterequal(a,b))
20293 nor, unless the state of the FENV_ACCESS pragma is ''off'', to
20294 // calls g without raising ''invalid'' if a and b are unordered
20299 but is equivalent to
20311 F.9.4 Constant arithmetic
20312 1 The implementation shall honor floating-point exceptions raised by execution-time
20313 constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4
20314 and F.8.5.) An operation on constants that raises no floating-point exception can be
20315 folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a
20316 further check is required to assure that changing the rounding direction to downward does
20317 not alter the sign of the result,352) and implementations that support dynamic rounding
20318 precision modes shall assure further that the result of the operation raises no floating-
20319 point exception when converted to the semantic type of the operation.
20320 F.10 Mathematics <math.h>
20321 1 This subclause contains specifications of <math.h> facilities that are particularly suited
20322 for IEC 60559 implementations.
20323 2 The Standard C macro HUGE_VAL and its float and long double analogs,
20324 HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
20326 3 Special cases for functions in <math.h> are covered directly or indirectly by
20327 IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The
20328 other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and
20329 (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags
20330 in a manner consistent with the basic arithmetic operations covered by IEC 60559.
20331 4 The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a
20333 5 The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in
20334 subsequent subclauses of this annex.
20335 6 The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of
20336 rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value
20337 whose magnitude is too large.
20338 7 The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially
20339 subnormal or zero) and suffers loss of accuracy.353)
20342 352) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward.
20343 353) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on
20344 when the floating-point exception is raised.
20348 8 Whether or when library functions raise the ''inexact'' floating-point exception is
20349 unspecified, unless explicitly specified otherwise.
20350 9 Whether or when library functions raise an undeserved ''underflow'' floating-point
20351 exception is unspecified.354) Otherwise, as implied by F.8.6, the <math.h> functions do
20352 not raise spurious floating-point exceptions (detectable by the user), other than the
20353 ''inexact'' floating-point exception.
20354 10 Whether the functions honor the rounding direction mode is implementation-defined,
20355 unless explicitly specified otherwise.
20356 11 Functions with a NaN argument return a NaN result and raise no floating-point exception,
20357 except where stated otherwise.
20358 12 The specifications in the following subclauses append to the definitions in <math.h>.
20359 For families of functions, the specifications apply to all of the functions even though only
20360 the principal function is shown. Unless otherwise specified, where the symbol ''(+-)''
20361 occurs in both an argument and the result, the result has the same sign as the argument.
20362 Recommended practice
20363 13 If a function with one or more NaN arguments returns a NaN result, the result should be
20364 the same as one of the NaN arguments (after possible type conversion), except perhaps
20366 F.10.1 Trigonometric functions
20367 F.10.1.1 The acos functions
20368 1 -- acos(1) returns +0.
20369 -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for
20371 F.10.1.2 The asin functions
20372 1 -- asin((+-)0) returns (+-)0.
20373 -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for
20379 354) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if
20380 avoiding them would be too costly.
20384 F.10.1.3 The atan functions
20385 1 -- atan((+-)0) returns (+-)0.
20386 -- atan((+-)(inf)) returns (+-)pi /2.
20387 F.10.1.4 The atan2 functions
20388 1 -- atan2((+-)0, -0) returns (+-)pi .355)
20389 -- atan2((+-)0, +0) returns (+-)0.
20390 -- atan2((+-)0, x) returns (+-)pi for x < 0.
20391 -- atan2((+-)0, x) returns (+-)0 for x > 0.
20392 -- atan2(y, (+-)0) returns -pi /2 for y < 0.
20393 -- atan2(y, (+-)0) returns pi /2 for y > 0.
20394 -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0.
20395 -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0.
20396 -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x.
20397 -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4.
20398 -- atan2((+-)(inf), +(inf)) returns (+-)pi /4.
20399 F.10.1.5 The cos functions
20400 1 -- cos((+-)0) returns 1.
20401 -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20402 F.10.1.6 The sin functions
20403 1 -- sin((+-)0) returns (+-)0.
20404 -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20405 F.10.1.7 The tan functions
20406 1 -- tan((+-)0) returns (+-)0.
20407 -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20412 355) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise
20413 the ''divide-by-zero'' floating-point exception.
20417 F.10.2 Hyperbolic functions
20418 F.10.2.1 The acosh functions
20419 1 -- acosh(1) returns +0.
20420 -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1.
20421 -- acosh(+(inf)) returns +(inf).
20422 F.10.2.2 The asinh functions
20423 1 -- asinh((+-)0) returns (+-)0.
20424 -- asinh((+-)(inf)) returns (+-)(inf).
20425 F.10.2.3 The atanh functions
20426 1 -- atanh((+-)0) returns (+-)0.
20427 -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
20428 -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for
20430 F.10.2.4 The cosh functions
20431 1 -- cosh((+-)0) returns 1.
20432 -- cosh((+-)(inf)) returns +(inf).
20433 F.10.2.5 The sinh functions
20434 1 -- sinh((+-)0) returns (+-)0.
20435 -- sinh((+-)(inf)) returns (+-)(inf).
20436 F.10.2.6 The tanh functions
20437 1 -- tanh((+-)0) returns (+-)0.
20438 -- tanh((+-)(inf)) returns (+-)1.
20439 F.10.3 Exponential and logarithmic functions
20440 F.10.3.1 The exp functions
20441 1 -- exp((+-)0) returns 1.
20442 -- exp(-(inf)) returns +0.
20443 -- exp(+(inf)) returns +(inf).
20450 F.10.3.2 The exp2 functions
20451 1 -- exp2((+-)0) returns 1.
20452 -- exp2(-(inf)) returns +0.
20453 -- exp2(+(inf)) returns +(inf).
20454 F.10.3.3 The expm1 functions
20455 1 -- expm1((+-)0) returns (+-)0.
20456 -- expm1(-(inf)) returns -1.
20457 -- expm1(+(inf)) returns +(inf).
20458 F.10.3.4 The frexp functions
20459 1 -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp.
20460 -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object
20462 -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp
20463 (and returns a NaN).
20464 2 frexp raises no floating-point exceptions.
20465 3 When the radix of the argument is a power of 2, the returned value is exact and is
20466 independent of the current rounding direction mode.
20467 4 On a binary system, the body of the frexp function might be
20469 *exp = (value == 0) ? 0 : (int)(1 + logb(value));
20470 return scalbn(value, -(*exp));
20472 F.10.3.5 The ilogb functions
20473 1 When the correct result is representable in the range of the return type, the returned value
20474 is exact and is independent of the current rounding direction mode.
20475 2 If the correct result is outside the range of the return type, the numeric result is
20476 unspecified and the ''invalid'' floating-point exception is raised.
20483 F.10.3.6 The ldexp functions
20484 1 On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).
20485 F.10.3.7 The log functions
20486 1 -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20487 -- log(1) returns +0.
20488 -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20489 -- log(+(inf)) returns +(inf).
20490 F.10.3.8 The log10 functions
20491 1 -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20492 -- log10(1) returns +0.
20493 -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20494 -- log10(+(inf)) returns +(inf).
20495 F.10.3.9 The log1p functions
20496 1 -- log1p((+-)0) returns (+-)0.
20497 -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20498 -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for
20500 -- log1p(+(inf)) returns +(inf).
20501 F.10.3.10 The log2 functions
20502 1 -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20503 -- log2(1) returns +0.
20504 -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20505 -- log2(+(inf)) returns +(inf).
20506 F.10.3.11 The logb functions
20507 1 -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20508 -- logb((+-)(inf)) returns +(inf).
20509 2 The returned value is exact and is independent of the current rounding direction mode.
20516 F.10.3.12 The modf functions
20517 1 -- modf((+-)x, iptr) returns a result with the same sign as x.
20518 -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr.
20519 -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
20521 2 The returned values are exact and are independent of the current rounding direction
20523 3 modf behaves as though implemented by
20526 #pragma STDC FENV_ACCESS ON
20527 double modf(double value, double *iptr)
20529 int save_round = fegetround();
20530 fesetround(FE_TOWARDZERO);
20531 *iptr = nearbyint(value);
20532 fesetround(save_round);
20534 isinf(value) ? 0.0 :
20535 value - (*iptr), value);
20537 F.10.3.13 The scalbn and scalbln functions
20538 1 -- scalbn((+-)0, n) returns (+-)0.
20539 -- scalbn(x, 0) returns x.
20540 -- scalbn((+-)(inf), n) returns (+-)(inf).
20541 F.10.4 Power and absolute value functions
20542 F.10.4.1 The cbrt functions
20543 1 -- cbrt((+-)0) returns (+-)0.
20544 -- cbrt((+-)(inf)) returns (+-)(inf).
20551 F.10.4.2 The fabs functions
20552 1 -- fabs((+-)0) returns +0.
20553 -- fabs((+-)(inf)) returns +(inf).
20554 2 The returned value is exact and is independent of the current rounding direction mode.
20555 F.10.4.3 The hypot functions
20556 1 -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent.
20557 -- hypot(x, (+-)0) is equivalent to fabs(x).
20558 -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN.
20559 F.10.4.4 The pow functions
20560 1 -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception
20561 for y an odd integer < 0.
20562 -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception
20563 for y < 0 and not an odd integer.
20564 -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0.
20565 -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer.
20566 -- pow(-1, (+-)(inf)) returns 1.
20567 -- pow(+1, y) returns 1 for any y, even a NaN.
20568 -- pow(x, (+-)0) returns 1 for any x, even a NaN.
20569 -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for
20570 finite x < 0 and finite non-integer y.
20571 -- pow(x, -(inf)) returns +(inf) for | x | < 1.
20572 -- pow(x, -(inf)) returns +0 for | x | > 1.
20573 -- pow(x, +(inf)) returns +0 for | x | < 1.
20574 -- pow(x, +(inf)) returns +(inf) for | x | > 1.
20575 -- pow(-(inf), y) returns -0 for y an odd integer < 0.
20576 -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer.
20577 -- pow(-(inf), y) returns -(inf) for y an odd integer > 0.
20578 -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer.
20579 -- pow(+(inf), y) returns +0 for y < 0.
20580 -- pow(+(inf), y) returns +(inf) for y > 0.
20585 F.10.4.5 The sqrt functions
20586 1 sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value
20587 is dependent on the current rounding direction mode.
20588 F.10.5 Error and gamma functions
20589 F.10.5.1 The erf functions
20590 1 -- erf((+-)0) returns (+-)0.
20591 -- erf((+-)(inf)) returns (+-)1.
20592 F.10.5.2 The erfc functions
20593 1 -- erfc(-(inf)) returns 2.
20594 -- erfc(+(inf)) returns +0.
20595 F.10.5.3 The lgamma functions
20596 1 -- lgamma(1) returns +0.
20597 -- lgamma(2) returns +0.
20598 -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for
20599 x a negative integer or zero.
20600 -- lgamma(-(inf)) returns +(inf).
20601 -- lgamma(+(inf)) returns +(inf).
20602 F.10.5.4 The tgamma functions
20603 1 -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
20604 -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a
20606 -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20607 -- tgamma(+(inf)) returns +(inf).
20608 F.10.6 Nearest integer functions
20609 F.10.6.1 The ceil functions
20610 1 -- ceil((+-)0) returns (+-)0.
20611 -- ceil((+-)(inf)) returns (+-)(inf).
20612 2 The returned value is exact and is independent of the current rounding direction mode.
20613 3 The double version of ceil behaves as though implemented by
20621 #pragma STDC FENV_ACCESS ON
20622 double ceil(double x)
20625 int save_round = fegetround();
20626 fesetround(FE_UPWARD);
20627 result = rint(x); // or nearbyint instead of rint
20628 fesetround(save_round);
20631 F.10.6.2 The floor functions
20632 1 -- floor((+-)0) returns (+-)0.
20633 -- floor((+-)(inf)) returns (+-)(inf).
20634 2 The returned value is exact and is independent of the current rounding direction mode.
20635 3 See the sample implementation for ceil in F.10.6.1.
20636 F.10.6.3 The nearbyint functions
20637 1 The nearbyint functions use IEC 60559 rounding according to the current rounding
20638 direction. They do not raise the ''inexact'' floating-point exception if the result differs in
20639 value from the argument.
20640 -- nearbyint((+-)0) returns (+-)0 (for all rounding directions).
20641 -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions).
20642 F.10.6.4 The rint functions
20643 1 The rint functions differ from the nearbyint functions only in that they do raise the
20644 ''inexact'' floating-point exception if the result differs in value from the argument.
20645 F.10.6.5 The lrint and llrint functions
20646 1 The lrint and llrint functions provide floating-to-integer conversion as prescribed
20647 by IEC 60559. They round according to the current rounding direction. If the rounded
20648 value is outside the range of the return type, the numeric result is unspecified and the
20649 ''invalid'' floating-point exception is raised. When they raise no other floating-point
20650 exception and the result differs from the argument, they raise the ''inexact'' floating-point
20658 F.10.6.6 The round functions
20659 1 -- round((+-)0) returns (+-)0.
20660 -- round((+-)(inf)) returns (+-)(inf).
20661 2 The double version of round behaves as though implemented by
20664 #pragma STDC FENV_ACCESS ON
20665 double round(double x)
20669 feholdexcept(&save_env);
20671 if (fetestexcept(FE_INEXACT)) {
20672 fesetround(FE_TOWARDZERO);
20673 result = rint(copysign(0.5 + fabs(x), x));
20675 feupdateenv(&save_env);
20678 The round functions may, but are not required to, raise the ''inexact'' floating-point
20679 exception for non-integer numeric arguments, as this implementation does.
20680 F.10.6.7 The lround and llround functions
20681 1 The lround and llround functions differ from the lrint and llrint functions
20682 with the default rounding direction just in that the lround and llround functions
20683 round halfway cases away from zero and need not raise the ''inexact'' floating-point
20684 exception for non-integer arguments that round to within the range of the return type.
20685 F.10.6.8 The trunc functions
20686 1 The trunc functions use IEC 60559 rounding toward zero (regardless of the current
20687 rounding direction). The returned value is exact.
20688 -- trunc((+-)0) returns (+-)0.
20689 -- trunc((+-)(inf)) returns (+-)(inf).
20696 F.10.7 Remainder functions
20697 F.10.7.1 The fmod functions
20698 1 -- fmod((+-)0, y) returns (+-)0 for y not zero.
20699 -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x
20700 infinite or y zero.
20701 -- fmod(x, (+-)(inf)) returns x for x not infinite.
20702 2 When subnormal results are supported, the returned value is exact and is independent of
20703 the current rounding direction mode.
20704 3 The double version of fmod behaves as though implemented by
20707 #pragma STDC FENV_ACCESS ON
20708 double fmod(double x, double y)
20711 result = remainder(fabs(x), (y = fabs(y)));
20712 if (signbit(result)) result += y;
20713 return copysign(result, x);
20715 F.10.7.2 The remainder functions
20716 1 The remainder functions are fully specified as a basic arithmetic operation in
20718 2 When subnormal results are supported, the returned value is exact and is independent of
20719 the current rounding direction mode.
20720 F.10.7.3 The remquo functions
20721 1 The remquo functions follow the specifications for the remainder functions. They
20722 have no further specifications special to IEC 60559 implementations.
20723 2 When subnormal results are supported, the returned value is exact and is independent of
20724 the current rounding direction mode.
20731 F.10.8 Manipulation functions
20732 F.10.8.1 The copysign functions
20733 1 copysign is specified in the Appendix to IEC 60559.
20734 2 The returned value is exact and is independent of the current rounding direction mode.
20735 F.10.8.2 The nan functions
20736 1 All IEC 60559 implementations support quiet NaNs, in all floating formats.
20737 2 The returned value is exact and is independent of the current rounding direction mode.
20738 F.10.8.3 The nextafter functions
20739 1 -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions
20740 for x finite and the function value infinite.
20741 -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point
20742 exceptions for the function value subnormal or zero and x != y.
20743 2 Even though underflow or overflow can occur, the returned value is independent of the
20744 current rounding direction mode.
20745 F.10.8.4 The nexttoward functions
20746 1 No additional requirements beyond those on nextafter.
20747 2 Even though underflow or overflow can occur, the returned value is independent of the
20748 current rounding direction mode.
20749 F.10.9 Maximum, minimum, and positive difference functions
20750 F.10.9.1 The fdim functions
20751 1 No additional requirements.
20752 F.10.9.2 The fmax functions
20753 1 If just one argument is a NaN, the fmax functions return the other argument (if both
20754 arguments are NaNs, the functions return a NaN).
20755 2 The returned value is exact and is independent of the current rounding direction mode.
20756 3 The body of the fmax function might be356)
20757 { return (isgreaterequal(x, y) ||
20758 isnan(y)) ? x : y; }
20762 356) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would
20763 return +0; however, implementation in software might be impractical.
20767 F.10.9.3 The fmin functions
20768 1 The fmin functions are analogous to the fmax functions (see F.10.9.2).
20769 2 The returned value is exact and is independent of the current rounding direction mode.
20770 F.10.10 Floating multiply-add
20771 F.10.10.1 The fma functions
20772 1 -- fma(x, y, z) computes xy + z, correctly rounded once.
20773 -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point
20774 exception if one of x and y is infinite, the other is zero, and z is a NaN.
20775 -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if
20776 one of x and y is infinite, the other is zero, and z is not a NaN.
20777 -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x
20778 times y is an exact infinity and z is also an infinity but with the opposite sign.
20779 F.10.11 Comparison macros
20780 1 Relational operators and their corresponding comparison macros (7.12.14) produce
20781 equivalent result values, even if argument values are represented in wider formats. Thus,
20782 comparison macro arguments represented in formats wider than their semantic types are
20783 not converted to the semantic types, unless the wide evaluation method converts operands
20784 of relational operators to their semantic types. The standard wide evaluation methods
20785 characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert
20786 operands of relational operators to their semantic types.
20795 IEC 60559-compatible complex arithmetic
20797 1 This annex supplements annex F to specify complex arithmetic for compatibility with
20798 IEC 60559 real floating-point arithmetic. Although these specifications have been
20799 carefully designed, there is little existing practice to validate the design decisions.
20800 Therefore, these specifications are not normative, but should be viewed more as
20801 recommended practice. An implementation that defines
20802 __STDC_IEC_559_COMPLEX__ should conform to the specifications in this annex.
20804 1 There is a new keyword _Imaginary, which is used to specify imaginary types. It is
20805 used as a type specifier within declaration specifiers in the same way as _Complex is
20806 (thus, _Imaginary float is a valid type name).
20807 2 There are three imaginary types, designated as float _Imaginary, double
20808 _Imaginary, and long double _Imaginary. The imaginary types (along with
20809 the real floating and complex types) are floating types.
20810 3 For imaginary types, the corresponding real type is given by deleting the keyword
20811 _Imaginary from the type name.
20812 4 Each imaginary type has the same representation and alignment requirements as the
20813 corresponding real type. The value of an object of imaginary type is the value of the real
20814 representation times the imaginary unit.
20815 5 The imaginary type domain comprises the imaginary types.
20817 1 A complex or imaginary value with at least one infinite part is regarded as an infinity
20818 (even if its other part is a NaN). A complex or imaginary value is a finite number if each
20819 of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is
20820 a zero if each of its parts is a zero.
20828 G.4.1 Imaginary types
20829 1 Conversions among imaginary types follow rules analogous to those for real floating
20831 G.4.2 Real and imaginary
20832 1 When a value of imaginary type is converted to a real type other than _Bool,357) the
20833 result is a positive zero.
20834 2 When a value of real type is converted to an imaginary type, the result is a positive
20836 G.4.3 Imaginary and complex
20837 1 When a value of imaginary type is converted to a complex type, the real part of the
20838 complex result value is a positive zero and the imaginary part of the complex result value
20839 is determined by the conversion rules for the corresponding real types.
20840 2 When a value of complex type is converted to an imaginary type, the real part of the
20841 complex value is discarded and the value of the imaginary part is converted according to
20842 the conversion rules for the corresponding real types.
20843 G.5 Binary operators
20844 1 The following subclauses supplement 6.5 in order to specify the type of the result for an
20845 operation with an imaginary operand.
20846 2 For most operand types, the value of the result of a binary operator with an imaginary or
20847 complex operand is completely determined, with reference to real arithmetic, by the usual
20848 mathematical formula. For some operand types, the usual mathematical formula is
20849 problematic because of its treatment of infinities and because of undue overflow or
20850 underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
20851 not completely determined.
20860 G.5.1 Multiplicative operators
20862 1 If one operand has real type and the other operand has imaginary type, then the result has
20863 imaginary type. If both operands have imaginary type, then the result has real type. (If
20864 either operand has complex type, then the result has complex type.)
20865 2 If the operands are not both complex, then the result and floating-point exception
20866 behavior of the * operator is defined by the usual mathematical formula:
20869 x xu i(xv) (xu) + i(xv)
20871 iy i(yu) -yv (-yv) + i(yu)
20873 x + iy (xu) + i(yu) (-yv) + i(xv)
20874 3 If the second operand is not complex, then the result and floating-point exception
20875 behavior of the / operator is defined by the usual mathematical formula:
20882 x + iy (x/u) + i(y/u) (y/v) + i(-x/v)
20883 4 The * and / operators satisfy the following infinity properties for all real, imaginary, and
20884 complex operands:358)
20885 -- if one operand is an infinity and the other operand is a nonzero finite number or an
20886 infinity, then the result of the * operator is an infinity;
20887 -- if the first operand is an infinity and the second operand is a finite number, then the
20888 result of the / operator is an infinity;
20889 -- if the first operand is a finite number and the second operand is an infinity, then the
20890 result of the / operator is a zero;
20895 358) These properties are already implied for those cases covered in the tables, but are required for all cases
20896 (at least where the state for CX_LIMITED_RANGE is ''off'').
20900 -- if the first operand is a nonzero finite number or an infinity and the second operand is
20901 a zero, then the result of the / operator is an infinity.
20902 5 If both operands of the * operator are complex or if the second operand of the / operator
20903 is complex, the operator raises floating-point exceptions if appropriate for the calculation
20904 of the parts of the result, and may raise spurious floating-point exceptions.
20905 6 EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note
20906 that the imaginary unit I has imaginary type (see G.6).
20908 #include <complex.h>
20909 /* Multiply z * w ... */
20910 double complex _Cmultd(double complex z, double complex w)
20912 #pragma STDC FP_CONTRACT OFF
20913 double a, b, c, d, ac, bd, ad, bc, x, y;
20914 a = creal(z); b = cimag(z);
20915 c = creal(w); d = cimag(w);
20916 ac = a * c; bd = b * d;
20917 ad = a * d; bc = b * c;
20918 x = ac - bd; y = ad + bc;
20919 if (isnan(x) && isnan(y)) {
20920 /* Recover infinities that computed as NaN+iNaN ... */
20922 if ( isinf(a) || isinf(b) ) { // z is infinite
20923 /* "Box" the infinity and change NaNs in the other factor to 0 */
20924 a = copysign(isinf(a) ? 1.0 : 0.0, a);
20925 b = copysign(isinf(b) ? 1.0 : 0.0, b);
20926 if (isnan(c)) c = copysign(0.0, c);
20927 if (isnan(d)) d = copysign(0.0, d);
20930 if ( isinf(c) || isinf(d) ) { // w is infinite
20931 /* "Box" the infinity and change NaNs in the other factor to 0 */
20932 c = copysign(isinf(c) ? 1.0 : 0.0, c);
20933 d = copysign(isinf(d) ? 1.0 : 0.0, d);
20934 if (isnan(a)) a = copysign(0.0, a);
20935 if (isnan(b)) b = copysign(0.0, b);
20938 if (!recalc && (isinf(ac) || isinf(bd) ||
20939 isinf(ad) || isinf(bc))) {
20940 /* Recover infinities from overflow by changing NaNs to 0 ... */
20941 if (isnan(a)) a = copysign(0.0, a);
20942 if (isnan(b)) b = copysign(0.0, b);
20943 if (isnan(c)) c = copysign(0.0, c);
20944 if (isnan(d)) d = copysign(0.0, d);
20951 x = INFINITY * ( a * c - b * d );
20952 y = INFINITY * ( a * d + b * c );
20957 7 This implementation achieves the required treatment of infinities at the cost of only one isnan test in
20958 ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.
20960 8 EXAMPLE 2 Division of two double _Complex operands could be implemented as follows.
20962 #include <complex.h>
20963 /* Divide z / w ... */
20964 double complex _Cdivd(double complex z, double complex w)
20966 #pragma STDC FP_CONTRACT OFF
20967 double a, b, c, d, logbw, denom, x, y;
20969 a = creal(z); b = cimag(z);
20970 c = creal(w); d = cimag(w);
20971 logbw = logb(fmax(fabs(c), fabs(d)));
20972 if (isfinite(logbw)) {
20973 ilogbw = (int)logbw;
20974 c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);
20976 denom = c * c + d * d;
20977 x = scalbn((a * c + b * d) / denom, -ilogbw);
20978 y = scalbn((b * c - a * d) / denom, -ilogbw);
20979 /* Recover infinities and zeros that computed as NaN+iNaN; */
20980 /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */
20981 if (isnan(x) && isnan(y)) {
20982 if ((denom == 0.0) &&
20983 (!isnan(a) || !isnan(b))) {
20984 x = copysign(INFINITY, c) * a;
20985 y = copysign(INFINITY, c) * b;
20987 else if ((isinf(a) || isinf(b)) &&
20988 isfinite(c) && isfinite(d)) {
20989 a = copysign(isinf(a) ? 1.0 : 0.0, a);
20990 b = copysign(isinf(b) ? 1.0 : 0.0, b);
20991 x = INFINITY * ( a * c + b * d );
20992 y = INFINITY * ( b * c - a * d );
20994 else if (isinf(logbw) &&
20995 isfinite(a) && isfinite(b)) {
20996 c = copysign(isinf(c) ? 1.0 : 0.0, c);
20997 d = copysign(isinf(d) ? 1.0 : 0.0, d);
20998 x = 0.0 * ( a * c + b * d );
20999 y = 0.0 * ( b * c - a * d );
21007 9 Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than
21008 for multiplication. In the spirit of the multiplication example above, this code does not defend against
21009 overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of
21010 with division, provides better roundoff characteristics.
21012 G.5.2 Additive operators
21014 1 If both operands have imaginary type, then the result has imaginary type. (If one operand
21015 has real type and the other operand has imaginary type, or if either operand has complex
21016 type, then the result has complex type.)
21017 2 In all cases the result and floating-point exception behavior of a + or - operator is defined
21018 by the usual mathematical formula:
21021 x x(+-)u x (+-) iv (x (+-) u) (+-) iv
21023 iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v)
21025 x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v)
21026 G.6 Complex arithmetic <complex.h>
21031 are defined, respectively, as _Imaginary and a constant expression of type const
21032 float _Imaginary with the value of the imaginary unit. The macro
21034 is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
21035 the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
21037 2 This subclause contains specifications for the <complex.h> functions that are
21038 particularly suited to IEC 60559 implementations. For families of functions, the
21039 specifications apply to all of the functions even though only the principal function is
21043 shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument
21044 and the result, the result has the same sign as the argument.
21045 3 The functions are continuous onto both sides of their branch cuts, taking into account the
21046 sign of zero. For example, csqrt(-2 (+-) i0) = (+-)isqrt:2. -
21047 4 Since complex and imaginary values are composed of real values, each function may be
21048 regarded as computing real values from real values. Except as noted, the functions treat
21049 real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a
21050 manner consistent with the specifications for real functions in F.10.359)
21051 5 The functions cimag, conj, cproj, and creal are fully specified for all
21052 implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-
21054 6 Each of the functions cabs and carg is specified by a formula in terms of a real
21055 function (whose special cases are covered in annex F):
21056 cabs(x + iy) = hypot(x, y)
21057 carg(x + iy) = atan2(y, x)
21058 7 Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
21059 a formula in terms of other complex functions (whose special cases are specified below):
21060 casin(z) = -i casinh(iz)
21061 catan(z) = -i catanh(iz)
21062 ccos(z) = ccosh(iz)
21063 csin(z) = -i csinh(iz)
21064 ctan(z) = -i ctanh(iz)
21065 8 For the other functions, the following subclauses specify behavior for special cases,
21066 including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For
21067 families of functions, the specifications apply to all of the functions even though only the
21068 principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the
21069 specifications for the upper half-plane imply the specifications for the lower half-plane; if
21070 the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the
21071 specifications for the first quadrant imply the specifications for the other three quadrants.
21072 9 In the following subclauses, cis(y) is defined as cos(y) + i sin(y).
21077 359) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
21078 other part is a NaN.
21082 G.6.1 Trigonometric functions
21083 G.6.1.1 The cacos functions
21084 1 -- cacos(conj(z)) = conj(cacos(z)).
21085 -- cacos((+-)0 + i0) returns pi /2 - i0.
21086 -- cacos((+-)0 + iNaN) returns pi /2 + iNaN.
21087 -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x.
21088 -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21089 point exception, for nonzero finite x.
21090 -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y.
21091 -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y.
21092 -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf).
21093 -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf).
21094 -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
21095 result is unspecified).
21096 -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21097 point exception, for finite y.
21098 -- cacos(NaN + i (inf)) returns NaN - i (inf).
21099 -- cacos(NaN + iNaN) returns NaN + iNaN.
21100 G.6.2 Hyperbolic functions
21101 G.6.2.1 The cacosh functions
21102 1 -- cacosh(conj(z)) = conj(cacosh(z)).
21103 -- cacosh((+-)0 + i0) returns +0 + ipi /2.
21104 -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x.
21105 -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21106 floating-point exception, for finite x.
21107 -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y.
21108 -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y.
21109 -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4.
21110 -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4.
21111 -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN.
21116 -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21117 floating-point exception, for finite y.
21118 -- cacosh(NaN + i (inf)) returns +(inf) + iNaN.
21119 -- cacosh(NaN + iNaN) returns NaN + iNaN.
21120 G.6.2.2 The casinh functions
21121 1 -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
21122 -- casinh(+0 + i0) returns 0 + i0.
21123 -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x.
21124 -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21125 floating-point exception, for finite x.
21126 -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y.
21127 -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4.
21128 -- casinh(+(inf) + iNaN) returns +(inf) + iNaN.
21129 -- casinh(NaN + i0) returns NaN + i0.
21130 -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21131 floating-point exception, for finite nonzero y.
21132 -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21134 -- casinh(NaN + iNaN) returns NaN + iNaN.
21135 G.6.2.3 The catanh functions
21136 1 -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
21137 -- catanh(+0 + i0) returns +0 + i0.
21138 -- catanh(+0 + iNaN) returns +0 + iNaN.
21139 -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point
21141 -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x.
21142 -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21143 floating-point exception, for nonzero finite x.
21144 -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y.
21145 -- catanh(+(inf) + i (inf)) returns +0 + ipi /2.
21146 -- catanh(+(inf) + iNaN) returns +0 + iNaN.
21150 -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21151 floating-point exception, for finite y.
21152 -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is
21154 -- catanh(NaN + iNaN) returns NaN + iNaN.
21155 G.6.2.4 The ccosh functions
21156 1 -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
21157 -- ccosh(+0 + i0) returns 1 + i0.
21158 -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the
21159 result is unspecified) and raises the ''invalid'' floating-point exception.
21160 -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the
21161 result is unspecified).
21162 -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21163 exception, for finite nonzero x.
21164 -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21165 point exception, for finite nonzero x.
21166 -- ccosh(+(inf) + i0) returns +(inf) + i0.
21167 -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
21168 -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
21169 unspecified) and raises the ''invalid'' floating-point exception.
21170 -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN.
21171 -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the
21172 result is unspecified).
21173 -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21174 point exception, for all nonzero numbers y.
21175 -- ccosh(NaN + iNaN) returns NaN + iNaN.
21176 G.6.2.5 The csinh functions
21177 1 -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
21178 -- csinh(+0 + i0) returns +0 + i0.
21179 -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is
21180 unspecified) and raises the ''invalid'' floating-point exception.
21181 -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is
21185 -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21186 exception, for positive finite x.
21187 -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21188 point exception, for finite nonzero x.
21189 -- csinh(+(inf) + i0) returns +(inf) + i0.
21190 -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y.
21191 -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
21192 unspecified) and raises the ''invalid'' floating-point exception.
21193 -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21195 -- csinh(NaN + i0) returns NaN + i0.
21196 -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21197 point exception, for all nonzero numbers y.
21198 -- csinh(NaN + iNaN) returns NaN + iNaN.
21199 G.6.2.6 The ctanh functions
21200 1 -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
21201 -- ctanh(+0 + i0) returns +0 + i0.
21202 -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21203 exception, for finite x.
21204 -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21205 point exception, for finite x.
21206 -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
21207 -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result
21209 -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the
21210 result is unspecified).
21211 -- ctanh(NaN + i0) returns NaN + i0.
21212 -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21213 point exception, for all nonzero numbers y.
21214 -- ctanh(NaN + iNaN) returns NaN + iNaN.
21221 G.6.3 Exponential and logarithmic functions
21222 G.6.3.1 The cexp functions
21223 1 -- cexp(conj(z)) = conj(cexp(z)).
21224 -- cexp((+-)0 + i0) returns 1 + i0.
21225 -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21226 exception, for finite x.
21227 -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21228 point exception, for finite x.
21229 -- cexp(+(inf) + i0) returns +(inf) + i0.
21230 -- cexp(-(inf) + iy) returns +0 cis(y), for finite y.
21231 -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
21232 -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of
21233 the result are unspecified).
21234 -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point
21235 exception (where the sign of the real part of the result is unspecified).
21236 -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts
21237 of the result are unspecified).
21238 -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21240 -- cexp(NaN + i0) returns NaN + i0.
21241 -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21242 point exception, for all nonzero numbers y.
21243 -- cexp(NaN + iNaN) returns NaN + iNaN.
21244 G.6.3.2 The clog functions
21245 1 -- clog(conj(z)) = conj(clog(z)).
21246 -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point
21248 -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point
21250 -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x.
21251 -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21252 point exception, for finite x.
21256 -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y.
21257 -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
21258 -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4.
21259 -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4.
21260 -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN.
21261 -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21262 point exception, for finite y.
21263 -- clog(NaN + i (inf)) returns +(inf) + iNaN.
21264 -- clog(NaN + iNaN) returns NaN + iNaN.
21265 G.6.4 Power and absolute-value functions
21266 G.6.4.1 The cpow functions
21267 1 The cpow functions raise floating-point exceptions if appropriate for the calculation of
21268 the parts of the result, and may raise spurious exceptions.360)
21269 G.6.4.2 The csqrt functions
21270 1 -- csqrt(conj(z)) = conj(csqrt(z)).
21271 -- csqrt((+-)0 + i0) returns +0 + i0.
21272 -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN).
21273 -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21274 point exception, for finite x.
21275 -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y.
21276 -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
21277 -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
21278 result is unspecified).
21279 -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN.
21280 -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21281 point exception, for finite y.
21282 -- csqrt(NaN + iNaN) returns NaN + iNaN.
21287 360) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding
21288 implementations that treat special cases more carefully.
21292 G.7 Type-generic math <tgmath.h>
21293 1 Type-generic macros that accept complex arguments also accept imaginary arguments. If
21294 an argument is imaginary, the macro expands to an expression whose type is real,
21295 imaginary, or complex, as appropriate for the particular function: if the argument is
21296 imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the
21297 types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and
21298 the types of the others are complex.
21299 2 Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,
21300 sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real
21303 sin(iy) = i sinh(y)
21304 tan(iy) = i tanh(y)
21306 sinh(iy) = i sin(y)
21307 tanh(iy) = i tan(y)
21308 asin(iy) = i asinh(y)
21309 atan(iy) = i atanh(y)
21310 asinh(iy) = i asin(y)
21311 atanh(iy) = i atan(y)
21320 Language independent arithmetic
21322 1 This annex documents the extent to which the C language supports the ISO/IEC 10967-1
21323 standard for language-independent arithmetic (LIA-1). LIA-1 is more general than
21324 IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.
21326 1 The relevant C arithmetic types meet the requirements of LIA-1 types if an
21327 implementation adds notification of exceptional arithmetic operations and meets the 1
21328 unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8).
21330 1 The LIA-1 data type Boolean is implemented by the C data type bool with values of
21331 true and false, all from <stdbool.h>.
21332 H.2.2 Integer types
21333 1 The signed C integer types int, long int, long long int, and the corresponding
21334 unsigned types are compatible with LIA-1. If an implementation adds support for the
21335 LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are
21336 LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense
21337 in that overflows or out-of-bounds results silently wrap. An implementation that defines
21338 signed integer types as also being modulo need not detect integer overflow, in which case,
21339 only integer divide-by-zero need be detected.
21340 2 The parameters for the integer data types can be accessed by the following:
21341 maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,
21343 minint INT_MIN, LONG_MIN, LLONG_MIN
21344 3 The parameter ''bounded'' is always true, and is not provided. The parameter ''minint''
21345 is always 0 for the unsigned types, and is not provided for those types.
21352 H.2.2.1 Integer operations
21353 1 The integer operations on integer types are the following:
21360 absI abs(x), labs(x), llabs(x)
21367 where x and y are expressions of the same integer type.
21368 H.2.3 Floating-point types
21369 1 The C floating-point types float, double, and long double are compatible with
21370 LIA-1. If an implementation adds support for the LIA-1 exceptional values
21371 ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant
21372 with LIA-1. An implementation that uses IEC 60559 floating-point formats and
21373 operations (see annex F) along with IEC 60559 status flags and traps has LIA-1
21375 H.2.3.1 Floating-point parameters
21376 1 The parameters for a floating point data type can be accessed by the following:
21378 p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
21379 emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
21380 emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP
21381 2 The derived constants for the floating point types are accessed by the following:
21386 fmax FLT_MAX, DBL_MAX, LDBL_MAX
21387 fminN FLT_MIN, DBL_MIN, LDBL_MIN
21388 epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
21389 rnd_style FLT_ROUNDS
21390 H.2.3.2 Floating-point operations
21391 1 The floating-point operations on floating-point types are the following:
21397 absF fabsf(x), fabs(x), fabsl(x)
21398 exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
21399 scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
21400 scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
21401 intpartF modff(x, &y), modf(x, &y), modfl(x, &y)
21402 fractpartF modff(x, &y), modf(x, &y), modfl(x, &y)
21409 where x and y are expressions of the same floating point type, n is of type int, and li
21410 is of type long int.
21411 H.2.3.3 Rounding styles
21412 1 The C Standard requires all floating types to use the same radix and rounding style, so
21413 that only one identifier for each is provided to map to LIA-1.
21414 2 The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles:
21415 truncate FLT_ROUNDS == 0
21420 nearest FLT_ROUNDS == 1
21421 other FLT_ROUNDS != 0 && FLT_ROUNDS != 1
21422 provided that an implementation extends FLT_ROUNDS to cover the rounding style used
21423 in all relevant LIA-1 operations, not just addition as in C.
21424 H.2.4 Type conversions
21425 1 The LIA-1 type conversions are the following type casts:
21426 cvtI' (->) I (int)i, (long int)i, (long long int)i,
21427 (unsigned int)i, (unsigned long int)i,
21428 (unsigned long long int)i
21429 cvtF (->) I (int)x, (long int)x, (long long int)x,
21430 (unsigned int)x, (unsigned long int)x,
21431 (unsigned long long int)x
21432 cvtI (->) F (float)i, (double)i, (long double)i
21433 cvtF' (->) F (float)x, (double)x, (long double)x
21434 2 In the above conversions from floating to integer, the use of (cast)x can be replaced with
21435 (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
21436 (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer
21437 conversion functions, lrint(), llrint(), lround(), and llround(), can be
21438 used. They all meet LIA-1's requirements on floating to integer rounding for in-range
21439 values. For out-of-range values, the conversions shall silently wrap for the modulo types.
21440 3 The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,
21441 fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),
21442 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
21443 to 65535.0 which can then be cast to unsigned short int. But, the
21444 remainder() function is not useful for doing silent wrapping to signed integer types,
21445 e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the
21446 range -32767.0 to +32768.0 which is not, in general, in the range of signed short
21448 4 C's conversions (casts) from floating-point to floating-point can meet LIA-1
21449 requirements if an implementation uses round-to-nearest (IEC 60559 default).
21450 5 C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an
21451 implementation uses round-to-nearest.
21459 1 Notification is the process by which a user or program is informed that an exceptional
21460 arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C
21461 allows an implementation to cause a notification to occur when any arithmetic operation
21462 returns an exceptional value as defined in LIA-1 clause 5.
21463 H.3.1 Notification alternatives
21464 1 LIA-1 requires at least the following two alternatives for handling of notifications:
21465 setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and-
21467 2 An implementation need only support a given notification alternative for the entire
21468 program. An implementation may support the ability to switch between notification
21469 alternatives during execution, but is not required to do so. An implementation can
21470 provide separate selection for each kind of notification, but this is not required.
21471 3 C allows an implementation to provide notification. C's SIGFPE (for traps) and
21472 FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
21473 can provide LIA-1 notification.
21474 4 C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can
21475 provide trap-and-terminate behavior, except for those LIA-1 operations implemented by
21476 math library function calls. User-provided signal handlers for SIGFPE allow for trap-
21477 and-resume behavior with the same constraint.
21479 1 C's <fenv.h> status flags are compatible with the LIA-1 indicators.
21480 2 The following mapping is for floating-point types:
21481 undefined FE_INVALID, FE_DIVBYZERO
21482 floating_overflow FE_OVERFLOW
21483 underflow FE_UNDERFLOW
21484 3 The floating-point indicator interrogation and manipulation operations are:
21485 set_indicators feraiseexcept(i)
21486 clear_indicators feclearexcept(i)
21487 test_indicators fetestexcept(i)
21488 current_indicators fetestexcept(FE_ALL_EXCEPT)
21489 where i is an expression of type int representing a subset of the LIA-1 indicators.
21490 4 C allows an implementation to provide the following LIA-1 required behavior: at
21491 program termination if any indicator is set the implementation shall send an unambiguous
21494 and ''hard to ignore'' message (see LIA-1 subclause 6.1.2)
21495 5 LIA-1 does not make the distinction between floating-point and integer for ''undefined''.
21496 This documentation makes that distinction because <fenv.h> covers only the floating-
21499 1 C is compatible with LIA-1's trap requirements for arithmetic operations, but not for
21500 math library functions (which are not permitted to invoke a user's signal handler for
21501 SIGFPE). An implementation can provide an alternative of notification through
21502 termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3).
21503 2 LIA-1 does not require that traps be precise.
21504 3 C does require that SIGFPE be the signal corresponding to arithmetic exceptions, if there
21505 is any signal raised for them.
21506 4 C supports signal handlers for SIGFPE and allows trapping of arithmetic exceptions.
21507 When arithmetic exceptions do trap, C's signal-handler mechanism allows trap-and-
21508 terminate (either default implementation behavior or user replacement for it) or trap-and-
21509 resume, at the programmer's option.
21519 1 An implementation may generate warnings in many situations, none of which are
21520 specified as part of this International Standard. The following are a few of the more
21522 2 -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
21523 -- A block with initialization of an object that has automatic storage duration is jumped
21525 -- An implicit narrowing conversion is encountered, such as the assignment of a long
21526 int or a double to an int, or a pointer to void to a pointer to any type other than
21527 a character type (6.3).
21528 -- A hexadecimal floating constant cannot be represented exactly in its evaluation format
21530 -- An integer character constant includes more than one character or a wide character
21531 constant includes more than one multibyte character (6.4.4.4).
21532 -- The characters /* are found in a comment (6.4.7).
21533 -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an
21534 lvalue in one operand, and a side effect to, or an access to the value of, the identical
21535 lvalue in the other operand (6.5).
21536 -- A function is called but no prototype has been supplied (6.5.2.2).
21537 -- The arguments in a function call do not agree in number and type with those of the
21538 parameters in a function definition that is not a prototype (6.5.2.2).
21539 -- An object is defined but not used (6.7).
21540 -- A value is given to an object of an enumerated type other than by assignment of an
21541 enumeration constant that is a member of that type, or an enumeration object that has
21542 the same type, or the value of a function that returns the same enumerated type
21544 -- An aggregate has a partly bracketed initialization (6.7.8).
21545 -- A statement cannot be reached (6.8).
21546 -- A statement with no apparent effect is encountered (6.8).
21547 -- A constant expression is used as the controlling expression of a selection statement
21551 -- An incorrectly formed preprocessing group is encountered while skipping a
21552 preprocessing group (6.10.1).
21553 -- An unrecognized #pragma directive is encountered (6.10.6).
21563 1 This annex collects some information about portability that appears in this International
21565 J.1 Unspecified behavior
21566 1 The following are unspecified:
21567 -- The manner and timing of static initialization (5.1.2).
21568 -- The termination status returned to the hosted environment if the return type of main
21569 is not compatible with int (5.1.2.2.3).
21570 -- The behavior of the display device if a printing character is written when the active
21571 position is at the final position of a line (5.2.2).
21572 -- The behavior of the display device if a backspace character is written when the active
21573 position is at the initial position of a line (5.2.2).
21574 -- The behavior of the display device if a horizontal tab character is written when the
21575 active position is at or past the last defined horizontal tabulation position (5.2.2).
21576 -- The behavior of the display device if a vertical tab character is written when the active
21577 position is at or past the last defined vertical tabulation position (5.2.2).
21578 -- How an extended source character that does not correspond to a universal character
21579 name counts toward the significant initial characters in an external identifier (5.2.4.1).
21580 -- Many aspects of the representations of types (6.2.6).
21581 -- The value of padding bytes when storing values in structures or unions (6.2.6.1).
21582 -- The values of bytes that correspond to union members other than the one last stored
21584 -- The representation used when storing a value in an object that has more than one
21585 object representation for that value (6.2.6.1).
21586 -- The values of any padding bits in integer representations (6.2.6.2).
21587 -- Whether certain operators can generate negative zeros and whether a negative zero
21588 becomes a normal zero when stored in an object (6.2.6.2).
21589 -- Whether two string literals result in distinct arrays (6.4.5).
21590 -- The order in which subexpressions are evaluated and the order in which side effects
21591 take place, except as specified for the function-call (), &&, ||, ? :, and comma
21595 -- The order in which the function designator, arguments, and subexpressions within the
21596 arguments are evaluated in a function call (6.5.2.2).
21597 -- The order of side effects among compound literal initialization list expressions
21599 -- The order in which the operands of an assignment operator are evaluated (6.5.16).
21600 -- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
21601 -- Whether a call to an inline function uses the inline definition or the external definition
21602 of the function (6.7.4).
21603 -- Whether or not a size expression is evaluated when it is part of the operand of a
21604 sizeof operator and changing the value of the size expression would not affect the
21605 result of the operator (6.7.6.2).
21606 -- The order in which any side effects occur among the initialization list expressions in
21607 an initializer (6.7.9).
21608 -- The layout of storage for function parameters (6.9.1).
21609 -- When a fully expanded macro replacement list contains a function-like macro name
21610 as its last preprocessing token and the next preprocessing token from the source file is
21611 a (, and the fully expanded replacement of that macro ends with the name of the first
21612 macro and the next preprocessing token from the source file is again a (, whether that
21613 is considered a nested replacement (6.10.3).
21614 -- The order in which # and ## operations are evaluated during macro substitution
21615 (6.10.3.2, 6.10.3.3).
21616 -- The state of the floating-point status flags when execution passes from a part of the
21617 program translated with FENV_ACCESS ''off'' to a part translated with
21618 FENV_ACCESS ''on'' (7.6.1).
21619 -- The order in which feraiseexcept raises floating-point exceptions, except as
21620 stated in F.8.6 (7.6.2.3).
21621 -- Whether math_errhandling is a macro or an identifier with external linkage
21623 -- The results of the frexp functions when the specified value is not a floating-point
21625 -- The numeric result of the ilogb functions when the correct value is outside the
21626 range of the return type (7.12.6.5, F.10.3.5).
21627 -- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5).
21632 -- The value stored by the remquo functions in the object pointed to by quo when y is
21634 -- Whether a comparison macro argument that is represented in a format wider than its
21635 semantic type is converted to the semantic type (7.12.14).
21636 -- Whether setjmp is a macro or an identifier with external linkage (7.13).
21637 -- Whether va_copy and va_end are macros or identifiers with external linkage
21639 -- The hexadecimal digit before the decimal point when a non-normalized floating-point
21640 number is printed with an a or A conversion specifier (7.21.6.1, 7.28.2.1).
21641 -- The value of the file position indicator after a successful call to the ungetc function
21642 for a text stream, or the ungetwc function for any stream, until all pushed-back
21643 characters are read or discarded (7.21.7.10, 7.28.3.10).
21644 -- The details of the value stored by the fgetpos function (7.21.9.1).
21645 -- The details of the value returned by the ftell function for a text stream (7.21.9.4).
21646 -- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold
21647 functions convert a minus-signed sequence to a negative number directly or by
21648 negating the value resulting from converting the corresponding unsigned sequence
21649 (7.22.1.3, 7.28.4.1.1).
21650 -- The order and contiguity of storage allocated by successive calls to the calloc,
21651 malloc, and realloc functions (7.22.3).
21652 -- The amount of storage allocated by a successful call to the calloc, malloc, or
21653 realloc function when 0 bytes was requested (7.22.3).
21654 -- Which of two elements that compare as equal is matched by the bsearch function
21656 -- The order of two elements that compare as equal in an array sorted by the qsort
21657 function (7.22.5.2).
21658 -- The encoding of the calendar time returned by the time function (7.26.2.4).
21659 -- The characters stored by the strftime or wcsftime function if any of the time
21660 values being converted is outside the normal range (7.26.3.5, 7.28.5.1).
21661 -- The conversion state after an encoding error occurs (7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1,
21663 -- The resulting value when the ''invalid'' floating-point exception is raised during
21664 IEC 60559 floating to integer conversion (F.4).
21670 -- Whether conversion of non-integer IEC 60559 floating values to integer raises the
21671 ''inexact'' floating-point exception (F.4).
21672 -- Whether or when library functions in <math.h> raise the ''inexact'' floating-point
21673 exception in an IEC 60559 conformant implementation (F.10).
21674 -- Whether or when library functions in <math.h> raise an undeserved ''underflow''
21675 floating-point exception in an IEC 60559 conformant implementation (F.10).
21676 -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4).
21677 -- The numeric result returned by the lrint, llrint, lround, and llround
21678 functions if the rounded value is outside the range of the return type (F.10.6.5,
21680 -- The sign of one part of the complex result of several math functions for certain
21681 exceptional values in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2,
21682 G.6.2.3, G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).
21683 J.2 Undefined behavior
21684 1 The behavior is undefined in the following circumstances:
21685 -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated
21687 -- A nonempty source file does not end in a new-line character which is not immediately
21688 preceded by a backslash character or ends in a partial preprocessing token or
21690 -- Token concatenation produces a character sequence matching the syntax of a
21691 universal character name (5.1.1.2).
21692 -- A program in a hosted environment does not define a function named main using one
21693 of the specified forms (5.1.2.2.1).
21694 -- The execution of a program contains a data race (5.1.2.4).
21695 -- A character not in the basic source character set is encountered in a source file, except
21696 in an identifier, a character constant, a string literal, a header name, a comment, or a
21697 preprocessing token that is never converted to a token (5.2.1).
21698 -- An identifier, comment, string literal, character constant, or header name contains an
21699 invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
21700 -- The same identifier has both internal and external linkage in the same translation unit
21702 -- An object is referred to outside of its lifetime (6.2.4).
21708 -- The value of a pointer to an object whose lifetime has ended is used (6.2.4).
21709 -- The value of an object with automatic storage duration is used while it is
21710 indeterminate (6.2.4, 6.7.9, 6.8).
21711 -- A trap representation is read by an lvalue expression that does not have character type
21713 -- A trap representation is produced by a side effect that modifies any part of the object
21714 using an lvalue expression that does not have character type (6.2.6.1).
21715 -- The operands to certain operators are such that they could produce a negative zero
21716 result, but the implementation does not support negative zeros (6.2.6.2).
21717 -- Two declarations of the same object or function specify types that are not compatible
21719 -- A program requires the formation of a composite type from a variable length array
21720 type whose size is specified by an expression that is not evaluated (6.2.7).
21721 -- Conversion to or from an integer type produces a value outside the range that can be
21722 represented (6.3.1.4).
21723 -- Demotion of one real floating type to another produces a value outside the range that
21724 can be represented (6.3.1.5).
21725 -- An lvalue does not designate an object when evaluated (6.3.2.1).
21726 -- A non-array lvalue with an incomplete type is used in a context that requires the value
21727 of the designated object (6.3.2.1).
21728 -- An lvalue designating an object of automatic storage duration that could have been
21729 declared with the register storage class is used in a context that requires the value
21730 of the designated object, but the object is uninitialized. (6.3.2.1).
21731 -- An lvalue having array type is converted to a pointer to the initial element of the
21732 array, and the array object has register storage class (6.3.2.1).
21733 -- An attempt is made to use the value of a void expression, or an implicit or explicit
21734 conversion (except to void) is applied to a void expression (6.3.2.2).
21735 -- Conversion of a pointer to an integer type produces a value outside the range that can
21736 be represented (6.3.2.3).
21737 -- Conversion between two pointer types produces a result that is incorrectly aligned
21739 -- A pointer is used to call a function whose type is not compatible with the referenced
21746 -- An unmatched ' or " character is encountered on a logical source line during
21747 tokenization (6.4).
21748 -- A reserved keyword token is used in translation phase 7 or 8 for some purpose other
21749 than as a keyword (6.4.1).
21750 -- A universal character name in an identifier does not designate a character whose
21751 encoding falls into one of the specified ranges (6.4.2.1).
21752 -- The initial character of an identifier is a universal character name designating a digit
21754 -- Two identifiers differ only in nonsignificant characters (6.4.2.1).
21755 -- The identifier __func__ is explicitly declared (6.4.2.2).
21756 -- The program attempts to modify a string literal (6.4.5).
21757 -- The characters ', \, ", //, or /* occur in the sequence between the < and >
21758 delimiters, or the characters ', \, //, or /* occur in the sequence between the "
21759 delimiters, in a header name preprocessing token (6.4.7).
21760 -- A side effect on a scalar object is unsequenced relative to either a different side effect
21761 on the same scalar object or a value computation using the value of the same scalar
21763 -- An exceptional condition occurs during the evaluation of an expression (6.5).
21764 -- An object has its stored value accessed other than by an lvalue of an allowable type
21766 -- For a call to a function without a function prototype in scope, the number of
21767 arguments does not equal the number of parameters (6.5.2.2).
21768 -- For call to a function without a function prototype in scope where the function is
21769 defined with a function prototype, either the prototype ends with an ellipsis or the
21770 types of the arguments after promotion are not compatible with the types of the
21771 parameters (6.5.2.2).
21772 -- For a call to a function without a function prototype in scope where the function is not
21773 defined with a function prototype, the types of the arguments after promotion are not
21774 compatible with those of the parameters after promotion (with certain exceptions)
21776 -- A function is defined with a type that is not compatible with the type (of the
21777 expression) pointed to by the expression that denotes the called function (6.5.2.2).
21778 -- A member of an _Atomic-qualified structure or union is accessed (6.5.2.3).
21779 -- The operand of the unary * operator has an invalid value (6.5.3.2).
21784 -- A pointer is converted to other than an integer or pointer type (6.5.4).
21785 -- The value of the second operand of the / or % operator is zero (6.5.5).
21786 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
21787 integer type produces a result that does not point into, or just beyond, the same array
21789 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
21790 integer type produces a result that points just beyond the array object and is used as
21791 the operand of a unary * operator that is evaluated (6.5.6).
21792 -- Pointers that do not point into, or just beyond, the same array object are subtracted
21794 -- An array subscript is out of range, even if an object is apparently accessible with the
21795 given subscript (as in the lvalue expression a[1][7] given the declaration int
21797 -- The result of subtracting two pointers is not representable in an object of type
21799 -- An expression is shifted by a negative number or by an amount greater than or equal
21800 to the width of the promoted expression (6.5.7).
21801 -- An expression having signed promoted type is left-shifted and either the value of the
21802 expression is negative or the result of shifting would be not be representable in the
21803 promoted type (6.5.7).
21804 -- Pointers that do not point to the same aggregate or union (nor just beyond the same
21805 array object) are compared using relational operators (6.5.8).
21806 -- An object is assigned to an inexactly overlapping object or to an exactly overlapping
21807 object with incompatible type (6.5.16.1).
21808 -- An expression that is required to be an integer constant expression does not have an
21809 integer type; has operands that are not integer constants, enumeration constants,
21810 character constants, sizeof expressions whose results are integer constants, or
21811 immediately-cast floating constants; or contains casts (outside operands to sizeof
21812 operators) other than conversions of arithmetic types to integer types (6.6).
21813 -- A constant expression in an initializer is not, or does not evaluate to, one of the
21814 following: an arithmetic constant expression, a null pointer constant, an address
21815 constant, or an address constant for a complete object type plus or minus an integer
21816 constant expression (6.6).
21817 -- An arithmetic constant expression does not have arithmetic type; has operands that
21818 are not integer constants, floating constants, enumeration constants, character
21819 constants, or sizeof expressions; or contains casts (outside operands to sizeof
21823 operators) other than conversions of arithmetic types to arithmetic types (6.6).
21824 -- The value of an object is accessed by an array-subscript [], member-access . or ->,
21825 address &, or indirection * operator or a pointer cast in creating an address constant
21827 -- An identifier for an object is declared with no linkage and the type of the object is
21828 incomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
21829 -- A function is declared at block scope with an explicit storage-class specifier other
21830 than extern (6.7.1).
21831 -- A structure or union is defined as containing no named members, no anonymous
21832 structures, and no anonymous unions (6.7.2.1).
21833 -- An attempt is made to access, or generate a pointer to just past, a flexible array
21834 member of a structure when the referenced object provides no elements for that array
21836 -- When the complete type is needed, an incomplete structure or union type is not
21837 completed in the same scope by another declaration of the tag that defines the content
21839 -- An attempt is made to modify an object defined with a const-qualified type through
21840 use of an lvalue with non-const-qualified type (6.7.3).
21841 -- An attempt is made to refer to an object defined with a volatile-qualified type through
21842 use of an lvalue with non-volatile-qualified type (6.7.3).
21843 -- An attempt is made to refer to an object defined with an _Atomic-qualified type
21844 through use of an lvalue with non-_Atomic-qualified type (6.7.3).
21845 -- The specification of a function type includes any type qualifiers (6.7.3).
21846 -- Two qualified types that are required to be compatible do not have the identically
21847 qualified version of a compatible type (6.7.3).
21848 -- An object which has been modified is accessed through a restrict-qualified pointer to
21849 a const-qualified type, or through a restrict-qualified pointer and another pointer that
21850 are not both based on the same object (6.7.3.1).
21851 -- A restrict-qualified pointer is assigned a value based on another restricted pointer
21852 whose associated block neither began execution before the block associated with this
21853 pointer, nor ended before the assignment (6.7.3.1).
21854 -- A function with external linkage is declared with an inline function specifier, but is
21855 not also defined in the same translation unit (6.7.4).
21856 -- A function declared with a _Noreturn function specifier returns to its caller (6.7.4).
21861 -- The definition of an object has an alignment specifier and another declaration of that
21862 object has a different alignment specifier (6.7.5).
21863 -- Declarations of an object in different translation units have different alignment
21864 specifiers (6.7.5).
21865 -- Two pointer types that are required to be compatible are not identically qualified, or
21866 are not pointers to compatible types (6.7.6.1).
21867 -- The size expression in an array declaration is not a constant expression and evaluates
21868 at program execution time to a nonpositive value (6.7.6.2).
21869 -- In a context requiring two array types to be compatible, they do not have compatible
21870 element types, or their size specifiers evaluate to unequal values (6.7.6.2).
21871 -- A declaration of an array parameter includes the keyword static within the [ and
21872 ] and the corresponding argument does not provide access to the first element of an
21873 array with at least the specified number of elements (6.7.6.3).
21874 -- A storage-class specifier or type qualifier modifies the keyword void as a function
21875 parameter type list (6.7.6.3).
21876 -- In a context requiring two function types to be compatible, they do not have
21877 compatible return types, or their parameters disagree in use of the ellipsis terminator
21878 or the number and type of parameters (after default argument promotion, when there
21879 is no parameter type list or when one type is specified by a function definition with an
21880 identifier list) (6.7.6.3).
21881 -- The value of an unnamed member of a structure or union is used (6.7.9).
21882 -- The initializer for a scalar is neither a single expression nor a single expression
21883 enclosed in braces (6.7.9).
21884 -- The initializer for a structure or union object that has automatic storage duration is
21885 neither an initializer list nor a single expression that has compatible structure or union
21887 -- The initializer for an aggregate or union, other than an array initialized by a string
21888 literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9).
21889 -- An identifier with external linkage is used, but in the program there does not exist
21890 exactly one external definition for the identifier, or the identifier is not used and there
21891 exist multiple external definitions for the identifier (6.9).
21892 -- A function definition includes an identifier list, but the types of the parameters are not
21893 declared in a following declaration list (6.9.1).
21894 -- An adjusted parameter type in a function definition is not a complete object type
21899 -- A function that accepts a variable number of arguments is defined without a
21900 parameter type list that ends with the ellipsis notation (6.9.1).
21901 -- The } that terminates a function is reached, and the value of the function call is used
21902 by the caller (6.9.1).
21903 -- An identifier for an object with internal linkage and an incomplete type is declared
21904 with a tentative definition (6.9.2).
21905 -- The token defined is generated during the expansion of a #if or #elif
21906 preprocessing directive, or the use of the defined unary operator does not match
21907 one of the two specified forms prior to macro replacement (6.10.1).
21908 -- The #include preprocessing directive that results after expansion does not match
21909 one of the two header name forms (6.10.2).
21910 -- The character sequence in an #include preprocessing directive does not start with a
21912 -- There are sequences of preprocessing tokens within the list of macro arguments that
21913 would otherwise act as preprocessing directives (6.10.3).
21914 -- The result of the preprocessing operator # is not a valid character string literal
21916 -- The result of the preprocessing operator ## is not a valid preprocessing token
21918 -- The #line preprocessing directive that results after expansion does not match one of
21919 the two well-defined forms, or its digit sequence specifies zero or a number greater
21920 than 2147483647 (6.10.4).
21921 -- A non-STDC #pragma preprocessing directive that is documented as causing
21922 translation failure or some other form of undefined behavior is encountered (6.10.6).
21923 -- A #pragma STDC preprocessing directive does not match one of the well-defined
21925 -- The name of a predefined macro, or the identifier defined, is the subject of a
21926 #define or #undef preprocessing directive (6.10.8).
21927 -- An attempt is made to copy an object to an overlapping object by use of a library
21928 function, other than as explicitly allowed (e.g., memmove) (clause 7).
21929 -- A file with the same name as one of the standard headers, not provided as part of the
21930 implementation, is placed in any of the standard places that are searched for included
21931 source files (7.1.2).
21932 -- A header is included within an external declaration or definition (7.1.2).
21937 -- A function, object, type, or macro that is specified as being declared or defined by
21938 some standard header is used before any header that declares or defines it is included
21940 -- A standard header is included while a macro is defined with the same name as a
21942 -- The program attempts to declare a library function itself, rather than via a standard
21943 header, but the declaration does not have external linkage (7.1.2).
21944 -- The program declares or defines a reserved identifier, other than as allowed by 7.1.4
21946 -- The program removes the definition of a macro whose name begins with an
21947 underscore and either an uppercase letter or another underscore (7.1.3).
21948 -- An argument to a library function has an invalid value or a type not expected by a
21949 function with variable number of arguments (7.1.4).
21950 -- The pointer passed to a library function array parameter does not have a value such
21951 that all address computations and object accesses are valid (7.1.4).
21952 -- The macro definition of assert is suppressed in order to access an actual function
21954 -- The argument to the assert macro does not have a scalar type (7.2).
21955 -- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in
21956 any context other than outside all external declarations or preceding all explicit
21957 declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
21958 -- The value of an argument to a character handling function is neither equal to the value
21959 of EOF nor representable as an unsigned char (7.4).
21960 -- A macro definition of errno is suppressed in order to access an actual object, or the
21961 program defines an identifier with the name errno (7.5).
21962 -- Part of the program tests floating-point status flags, sets floating-point control modes,
21963 or runs under non-default mode settings, but was translated with the state for the
21964 FENV_ACCESS pragma ''off'' (7.6.1).
21965 -- The exception-mask argument for one of the functions that provide access to the
21966 floating-point status flags has a nonzero value not obtained by bitwise OR of the
21967 floating-point exception macros (7.6.2).
21968 -- The fesetexceptflag function is used to set floating-point status flags that were
21969 not specified in the call to the fegetexceptflag function that provided the value
21970 of the corresponding fexcept_t object (7.6.2.4).
21976 -- The argument to fesetenv or feupdateenv is neither an object set by a call to
21977 fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
21978 -- The value of the result of an integer arithmetic or conversion function cannot be
21979 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).
21980 -- The program modifies the string pointed to by the value returned by the setlocale
21981 function (7.11.1.1).
21982 -- The program modifies the structure pointed to by the value returned by the
21983 localeconv function (7.11.2.1).
21984 -- A macro definition of math_errhandling is suppressed or the program defines
21985 an identifier with the name math_errhandling (7.12).
21986 -- An argument to a floating-point classification or comparison macro is not of real
21987 floating type (7.12.3, 7.12.14).
21988 -- A macro definition of setjmp is suppressed in order to access an actual function, or
21989 the program defines an external identifier with the name setjmp (7.13).
21990 -- An invocation of the setjmp macro occurs other than in an allowed context
21992 -- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
21993 -- After a longjmp, there is an attempt to access the value of an object of automatic
21994 storage duration that does not have volatile-qualified type, local to the function
21995 containing the invocation of the corresponding setjmp macro, that was changed
21996 between the setjmp invocation and longjmp call (7.13.2.1).
21997 -- The program specifies an invalid pointer to a signal handler function (7.14.1.1).
21998 -- A signal handler returns when the signal corresponded to a computational exception
22000 -- A signal occurs as the result of calling the abort or raise function, and the signal
22001 handler calls the raise function (7.14.1.1).
22002 -- A signal occurs other than as the result of calling the abort or raise function, and
22003 the signal handler refers to an object with static storage duration other than by
22004 assigning a value to an object declared as volatile sig_atomic_t, or calls any
22005 function in the standard library other than the abort function, the _Exit function,
22006 the quick_exit function, or the signal function (for the same signal number)
22008 -- The value of errno is referred to after a signal occurred other than as the result of
22009 calling the abort or raise function and the corresponding signal handler obtained
22010 a SIG_ERR return from a call to the signal function (7.14.1.1).
22014 -- A signal is generated by an asynchronous signal handler (7.14.1.1).
22015 -- A function with a variable number of arguments attempts to access its varying
22016 arguments other than through a properly declared and initialized va_list object, or
22017 before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4).
22018 -- The macro va_arg is invoked using the parameter ap that was passed to a function
22019 that invoked the macro va_arg with the same parameter (7.16).
22020 -- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in
22021 order to access an actual function, or the program defines an external identifier with
22022 the name va_copy or va_end (7.16.1).
22023 -- The va_start or va_copy macro is invoked without a corresponding invocation
22024 of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3,
22026 -- The type parameter to the va_arg macro is not such that a pointer to an object of
22027 that type can be obtained simply by postfixing a * (7.16.1.1).
22028 -- The va_arg macro is invoked when there is no actual next argument, or with a
22029 specified type that is not compatible with the promoted type of the actual next
22030 argument, with certain exceptions (7.16.1.1).
22031 -- The va_copy or va_start macro is called to initialize a va_list that was
22032 previously initialized by either macro without an intervening invocation of the
22033 va_end macro for the same va_list (7.16.1.2, 7.16.1.4).
22034 -- The parameter parmN of a va_start macro is declared with the register
22035 storage class, with a function or array type, or with a type that is not compatible with
22036 the type that results after application of the default argument promotions (7.16.1.4).
22037 -- The member designator parameter of an offsetof macro is an invalid right
22038 operand of the . operator for the type parameter, or designates a bit-field (7.19).
22039 -- The argument in an instance of one of the integer-constant macros is not a decimal,
22040 octal, or hexadecimal constant, or it has a value that exceeds the limits for the
22041 corresponding type (7.20.4).
22042 -- A byte input/output function is applied to a wide-oriented stream, or a wide character
22043 input/output function is applied to a byte-oriented stream (7.21.2).
22044 -- Use is made of any portion of a file beyond the most recent wide character written to
22045 a wide-oriented stream (7.21.2).
22046 -- The value of a pointer to a FILE object is used after the associated file is closed
22048 -- The stream for the fflush function points to an input stream or to an update stream
22049 in which the most recent operation was input (7.21.5.2).
22052 -- The string pointed to by the mode argument in a call to the fopen function does not
22053 exactly match one of the specified character sequences (7.21.5.3).
22054 -- An output operation on an update stream is followed by an input operation without an
22055 intervening call to the fflush function or a file positioning function, or an input
22056 operation on an update stream is followed by an output operation with an intervening
22057 call to a file positioning function (7.21.5.3).
22058 -- An attempt is made to use the contents of the array that was supplied in a call to the
22059 setvbuf function (7.21.5.6).
22060 -- There are insufficient arguments for the format in a call to one of the formatted
22061 input/output functions, or an argument does not have an appropriate type (7.21.6.1,
22062 7.21.6.2, 7.28.2.1, 7.28.2.2).
22063 -- The format in a call to one of the formatted input/output functions or to the
22064 strftime or wcsftime function is not a valid multibyte character sequence that
22065 begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.26.3.5, 7.28.2.1, 7.28.2.2,
22067 -- In a call to one of the formatted output functions, a precision appears with a
22068 conversion specifier other than those described (7.21.6.1, 7.28.2.1).
22069 -- A conversion specification for a formatted output function uses an asterisk to denote
22070 an argument-supplied field width or precision, but the corresponding argument is not
22071 provided (7.21.6.1, 7.28.2.1).
22072 -- A conversion specification for a formatted output function uses a # or 0 flag with a
22073 conversion specifier other than those described (7.21.6.1, 7.28.2.1).
22074 -- A conversion specification for one of the formatted input/output functions uses a
22075 length modifier with a conversion specifier other than those described (7.21.6.1,
22076 7.21.6.2, 7.28.2.1, 7.28.2.2).
22077 -- An s conversion specifier is encountered by one of the formatted output functions,
22078 and the argument is missing the null terminator (unless a precision is specified that
22079 does not require null termination) (7.21.6.1, 7.28.2.1).
22080 -- An n conversion specification for one of the formatted input/output functions includes
22081 any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1,
22082 7.21.6.2, 7.28.2.1, 7.28.2.2).
22083 -- A % conversion specifier is encountered by one of the formatted input/output
22084 functions, but the complete conversion specification is not exactly %% (7.21.6.1,
22085 7.21.6.2, 7.28.2.1, 7.28.2.2).
22086 -- An invalid conversion specification is found in the format for one of the formatted
22087 input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2,
22091 7.26.3.5, 7.28.2.1, 7.28.2.2, 7.28.5.1).
22092 -- The number of characters transmitted by a formatted output function is greater than
22093 INT_MAX (7.21.6.1, 7.21.6.3, 7.21.6.8, 7.21.6.10).
22094 -- The result of a conversion by one of the formatted input functions cannot be
22095 represented in the corresponding object, or the receiving object does not have an
22096 appropriate type (7.21.6.2, 7.28.2.2).
22097 -- A c, s, or [ conversion specifier is encountered by one of the formatted input
22098 functions, and the array pointed to by the corresponding argument is not large enough
22099 to accept the input sequence (and a null terminator if the conversion specifier is s or
22100 [) (7.21.6.2, 7.28.2.2).
22101 -- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the
22102 formatted input functions, but the input is not a valid multibyte character sequence
22103 that begins in the initial shift state (7.21.6.2, 7.28.2.2).
22104 -- The input item for a %p conversion by one of the formatted input functions is not a
22105 value converted earlier during the same program execution (7.21.6.2, 7.28.2.2).
22106 -- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
22107 vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
22108 vwscanf function is called with an improperly initialized va_list argument, or
22109 the argument is used (other than in an invocation of va_end) after the function
22110 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,
22111 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10).
22112 -- The contents of the array supplied in a call to the fgets or fgetws function are
22113 used after a read error occurred (7.21.7.2, 7.28.3.2).
22114 -- The file position indicator for a binary stream is used after a call to the ungetc
22115 function where its value was zero before the call (7.21.7.10).
22116 -- The file position indicator for a stream is used after an error occurred during a call to
22117 the fread or fwrite function (7.21.8.1, 7.21.8.2).
22118 -- A partial element read by a call to the fread function is used (7.21.8.1).
22119 -- The fseek function is called for a text stream with a nonzero offset and either the
22120 offset was not returned by a previous successful call to the ftell function on a
22121 stream associated with the same file or whence is not SEEK_SET (7.21.9.2).
22122 -- The fsetpos function is called to set a position that was not returned by a previous
22123 successful call to the fgetpos function on a stream associated with the same file
22125 -- A non-null pointer returned by a call to the calloc, malloc, or realloc function
22126 with a zero requested size is used to access an object (7.22.3).
22130 -- The value of a pointer that refers to space deallocated by a call to the free or
22131 realloc function is used (7.22.3).
22132 -- The alignment requested of the aligned_alloc function is not valid or not
22133 supported by the implementation, or the size requested is not an integral multiple of
22134 the alignment (7.22.3.1).
22135 -- The pointer argument to the free or realloc function does not match a pointer
22136 earlier returned by a memory management function, or the space has been deallocated
22137 by a call to free or realloc (7.22.3.3, 7.22.3.5).
22138 -- The value of the object allocated by the malloc function is used (7.22.3.4).
22139 -- The value of any bytes in a new object allocated by the realloc function beyond
22140 the size of the old object are used (7.22.3.5).
22141 -- The program calls the exit or quick_exit function more than once, or calls both
22142 functions (7.22.4.4, 7.22.4.7).
22143 -- During the call to a function registered with the atexit or at_quick_exit
22144 function, a call is made to the longjmp function that would terminate the call to the
22145 registered function (7.22.4.4, 7.22.4.7).
22146 -- The string set up by the getenv or strerror function is modified by the program
22147 (7.22.4.6, 7.23.6.2).
22148 -- A command is executed through the system function in a way that is documented as
22149 causing termination or some other form of undefined behavior (7.22.4.8).
22150 -- A searching or sorting utility function is called with an invalid pointer argument, even
22151 if the number of elements is zero (7.22.5).
22152 -- The comparison function called by a searching or sorting utility function alters the
22153 contents of the array being searched or sorted, or returns ordering values
22154 inconsistently (7.22.5).
22155 -- The array being searched by the bsearch function does not have its elements in
22156 proper order (7.22.5.1).
22157 -- The current conversion state is used by a multibyte/wide character conversion
22158 function after changing the LC_CTYPE category (7.22.7).
22159 -- A string or wide string utility function is instructed to access an array beyond the end
22160 of an object (7.23.1, 7.28.4).
22161 -- A string or wide string utility function is called with an invalid pointer argument, even
22162 if the length is zero (7.23.1, 7.28.4).
22163 -- The contents of the destination array are used after a call to the strxfrm,
22164 strftime, wcsxfrm, or wcsftime function in which the specified length was
22168 too small to hold the entire null-terminated result (7.23.4.5, 7.26.3.5, 7.28.4.4.4,
22170 -- The first argument in the very first call to the strtok or wcstok is a null pointer
22171 (7.23.5.8, 7.28.4.5.7).
22172 -- The type of an argument to a type-generic macro is not compatible with the type of
22173 the corresponding parameter of the selected function (7.24).
22174 -- A complex argument is supplied for a generic parameter of a type-generic macro that
22175 has no corresponding complex function (7.24).
22176 -- At least one field of the broken-down time passed to asctime contains a value
22177 outside its normal range, or the calculated year exceeds four digits or is less than the
22178 year 1000 (7.26.3.1).
22179 -- The argument corresponding to an s specifier without an l qualifier in a call to the
22180 fwprintf function does not point to a valid multibyte character sequence that
22181 begins in the initial shift state (7.28.2.11).
22182 -- In a call to the wcstok function, the object pointed to by ptr does not have the
22183 value stored by the previous call for the same wide string (7.28.4.5.7).
22184 -- An mbstate_t object is used inappropriately (7.28.6).
22185 -- The value of an argument of type wint_t to a wide character classification or case
22186 mapping function is neither equal to the value of WEOF nor representable as a
22188 -- The iswctype function is called using a different LC_CTYPE category from the
22189 one in effect for the call to the wctype function that returned the description
22191 -- The towctrans function is called using a different LC_CTYPE category from the
22192 one in effect for the call to the wctrans function that returned the description
22200 J.3 Implementation-defined behavior
22201 1 A conforming implementation is required to document its choice of behavior in each of
22202 the areas listed in this subclause. The following are implementation-defined:
22204 1 -- How a diagnostic is identified (3.10, 5.1.1.3).
22205 -- Whether each nonempty sequence of white-space characters other than new-line is
22206 retained or replaced by one space character in translation phase 3 (5.1.1.2).
22208 1 -- The mapping between physical source file multibyte characters and the source
22209 character set in translation phase 1 (5.1.1.2).
22210 -- The name and type of the function called at program startup in a freestanding
22211 environment (5.1.2.1).
22212 -- The effect of program termination in a freestanding environment (5.1.2.1).
22213 -- An alternative manner in which the main function may be defined (5.1.2.2.1).
22214 -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
22215 -- What constitutes an interactive device (5.1.2.3).
22216 -- Whether a program can have more than one thread of execution in a freestanding
22217 environment (5.1.2.4).
22218 -- The set of signals, their semantics, and their default handling (7.14).
22219 -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a
22220 computational exception (7.14.1.1).
22221 -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
22222 program startup (7.14.1.1).
22223 -- The set of environment names and the method for altering the environment list used
22224 by the getenv function (7.22.4.6).
22225 -- The manner of execution of the string by the system function (7.22.4.8).
22233 1 -- Which additional multibyte characters may appear in identifiers and their
22234 correspondence to universal character names (6.4.2).
22235 -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).
22237 1 -- The number of bits in a byte (3.6).
22238 -- The values of the members of the execution character set (5.2.1).
22239 -- The unique value of the member of the execution character set produced for each of
22240 the standard alphabetic escape sequences (5.2.2).
22241 -- The value of a char object into which has been stored any character other than a
22242 member of the basic execution character set (6.2.5).
22243 -- Which of signed char or unsigned char has the same range, representation,
22244 and behavior as ''plain'' char (6.2.5, 6.3.1.1).
22245 -- The mapping of members of the source character set (in character constants and string
22246 literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
22247 -- The value of an integer character constant containing more than one character or
22248 containing a character or escape sequence that does not map to a single-byte
22249 execution character (6.4.4.4).
22250 -- The value of a wide character constant containing more than one multibyte character
22251 or a single multibyte character that maps to multiple members of the extended
22252 execution character set, or containing a multibyte character or escape sequence not
22253 represented in the extended execution character set (6.4.4.4).
22254 -- The current locale used to convert a wide character constant consisting of a single
22255 multibyte character that maps to a member of the extended execution character set
22256 into a corresponding wide character code (6.4.4.4).
22257 -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so,
22258 the treatment of the resulting multibyte character sequence (6.4.5).
22259 -- The current locale used to convert a wide string literal into corresponding wide
22260 character codes (6.4.5).
22261 -- The value of a string literal containing a multibyte character or escape sequence not
22262 represented in the execution character set (6.4.5).
22263 -- The encoding of any of wchar_t, char16_t, and char32_t where the
22264 corresponding standard encoding macro (__STDC_ISO_10646__,
22265 __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2).
22270 1 -- Any extended integer types that exist in the implementation (6.2.5).
22271 -- Whether signed integer types are represented using sign and magnitude, two's
22272 complement, or ones' complement, and whether the extraordinary value is a trap
22273 representation or an ordinary value (6.2.6.2).
22274 -- The rank of any extended integer type relative to another extended integer type with
22275 the same precision (6.3.1.1).
22276 -- The result of, or the signal raised by, converting an integer to a signed integer type
22277 when the value cannot be represented in an object of that type (6.3.1.3).
22278 -- The results of some bitwise operations on signed integers (6.5).
22279 J.3.6 Floating point
22280 1 -- The accuracy of the floating-point operations and of the library functions in
22281 <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
22282 -- The accuracy of the conversions between floating-point internal representations and
22283 string representations performed by the library functions in <stdio.h>,
22284 <stdlib.h>, and <wchar.h> (5.2.4.2.2).
22285 -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS
22287 -- The evaluation methods characterized by non-standard negative values of
22288 FLT_EVAL_METHOD (5.2.4.2.2).
22289 -- The direction of rounding when an integer is converted to a floating-point number that
22290 cannot exactly represent the original value (6.3.1.4).
22291 -- The direction of rounding when a floating-point number is converted to a narrower
22292 floating-point number (6.3.1.5).
22293 -- How the nearest representable value or the larger or smaller representable value
22294 immediately adjacent to the nearest representable value is chosen for certain floating
22295 constants (6.4.4.2).
22296 -- Whether and how floating expressions are contracted when not disallowed by the
22297 FP_CONTRACT pragma (6.5).
22298 -- The default state for the FENV_ACCESS pragma (7.6.1).
22299 -- Additional floating-point exceptions, rounding modes, environments, and
22300 classifications, and their macro names (7.6, 7.12).
22301 -- The default state for the FP_CONTRACT pragma (7.12.2).
22306 J.3.7 Arrays and pointers
22307 1 -- The result of converting a pointer to an integer or vice versa (6.3.2.3).
22308 -- The size of the result of subtracting two pointers to elements of the same array
22311 1 -- The extent to which suggestions made by using the register storage-class
22312 specifier are effective (6.7.1).
22313 -- The extent to which suggestions made by using the inline function specifier are
22315 J.3.9 Structures, unions, enumerations, and bit-fields
22316 1 -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an
22317 unsigned int bit-field (6.7.2, 6.7.2.1).
22318 -- Allowable bit-field types other than _Bool, signed int, and unsigned int
22320 -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
22321 -- The order of allocation of bit-fields within a unit (6.7.2.1).
22322 -- The alignment of non-bit-field members of structures (6.7.2.1). This should present
22323 no problem unless binary data written by one implementation is read by another.
22324 -- The integer type compatible with each enumerated type (6.7.2.2).
22326 1 -- What constitutes an access to an object that has volatile-qualified type (6.7.3).
22327 J.3.11 Preprocessing directives
22328 1 -- The locations within #pragma directives where header name preprocessing tokens
22329 are recognized (6.4, 6.4.7).
22330 -- How sequences in both forms of header names are mapped to headers or external
22331 source file names (6.4.7).
22332 -- Whether the value of a character constant in a constant expression that controls
22333 conditional inclusion matches the value of the same character constant in the
22334 execution character set (6.10.1).
22335 -- Whether the value of a single-character character constant in a constant expression
22336 that controls conditional inclusion may have a negative value (6.10.1).
22337 -- The places that are searched for an included < > delimited header, and how the places
22338 are specified or the header is identified (6.10.2).
22341 -- How the named source file is searched for in an included " " delimited header
22343 -- The method by which preprocessing tokens (possibly resulting from macro
22344 expansion) in a #include directive are combined into a header name (6.10.2).
22345 -- The nesting limit for #include processing (6.10.2).
22346 -- Whether the # operator inserts a \ character before the \ character that begins a
22347 universal character name in a character constant or string literal (6.10.3.2).
22348 -- The behavior on each recognized non-STDC #pragma directive (6.10.6).
22349 -- The definitions for __DATE__ and __TIME__ when respectively, the date and
22350 time of translation are not available (6.10.8.1).
22351 J.3.12 Library functions
22352 1 -- Any library facilities available to a freestanding program, other than the minimal set
22353 required by clause 4 (5.1.2.1).
22354 -- The format of the diagnostic printed by the assert macro (7.2.1.1).
22355 -- The representation of the floating-point status flags stored by the
22356 fegetexceptflag function (7.6.2.2).
22357 -- Whether the feraiseexcept function raises the ''inexact'' floating-point
22358 exception in addition to the ''overflow'' or ''underflow'' floating-point exception
22360 -- Strings other than "C" and "" that may be passed as the second argument to the
22361 setlocale function (7.11.1.1).
22362 -- The types defined for float_t and double_t when the value of the
22363 FLT_EVAL_METHOD macro is less than 0 (7.12).
22364 -- Domain errors for the mathematics functions, other than those required by this
22365 International Standard (7.12.1).
22366 -- The values returned by the mathematics functions on domain errors or pole errors
22368 -- The values returned by the mathematics functions on underflow range errors, whether
22369 errno is set to the value of the macro ERANGE when the integer expression
22370 math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow''
22371 floating-point exception is raised when the integer expression math_errhandling
22372 & MATH_ERREXCEPT is nonzero. (7.12.1).
22373 -- Whether a domain error occurs or zero is returned when an fmod function has a
22374 second argument of zero (7.12.10.1).
22378 -- Whether a domain error occurs or zero is returned when a remainder function has
22379 a second argument of zero (7.12.10.2).
22380 -- The base-2 logarithm of the modulus used by the remquo functions in reducing the
22381 quotient (7.12.10.3).
22382 -- Whether a domain error occurs or zero is returned when a remquo function has a
22383 second argument of zero (7.12.10.3).
22384 -- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call
22385 of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
22386 -- The null pointer constant to which the macro NULL expands (7.19).
22387 -- Whether the last line of a text stream requires a terminating new-line character
22389 -- Whether space characters that are written out to a text stream immediately before a
22390 new-line character appear when read in (7.21.2).
22391 -- The number of null characters that may be appended to data written to a binary
22393 -- Whether the file position indicator of an append-mode stream is initially positioned at
22394 the beginning or end of the file (7.21.3).
22395 -- Whether a write on a text stream causes the associated file to be truncated beyond that
22397 -- The characteristics of file buffering (7.21.3).
22398 -- Whether a zero-length file actually exists (7.21.3).
22399 -- The rules for composing valid file names (7.21.3).
22400 -- Whether the same file can be simultaneously open multiple times (7.21.3).
22401 -- The nature and choice of encodings used for multibyte characters in files (7.21.3).
22402 -- The effect of the remove function on an open file (7.21.4.1).
22403 -- The effect if a file with the new name exists prior to a call to the rename function
22405 -- Whether an open temporary file is removed upon abnormal program termination
22407 -- Which changes of mode are permitted (if any), and under what circumstances
22409 -- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
22410 sequence printed for a NaN (7.21.6.1, 7.28.2.1).
22414 -- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1,
22416 -- The interpretation of a - character that is neither the first nor the last character, nor
22417 the second where a ^ character is the first, in the scanlist for %[ conversion in the
22418 fscanf or fwscanf function (7.21.6.2, 7.28.2.1).
22419 -- The set of sequences matched by a %p conversion and the interpretation of the
22420 corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.28.2.2).
22421 -- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell
22422 functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4).
22423 -- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is
22424 converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold
22425 function (7.22.1.3, 7.28.4.1.1).
22426 -- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold
22427 function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.28.4.1.1).
22428 -- Whether the calloc, malloc, and realloc functions return a null pointer or a
22429 pointer to an allocated object when the size requested is zero (7.22.3).
22430 -- Whether open streams with unwritten buffered data are flushed, open streams are
22431 closed, or temporary files are removed when the abort or _Exit function is called
22432 (7.22.4.1, 7.22.4.5).
22433 -- The termination status returned to the host environment by the abort, exit,
22434 _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7).
22435 -- The value returned by the system function when its argument is not a null pointer
22437 -- The local time zone and Daylight Saving Time (7.26.1).
22438 -- The range and precision of times representable in clock_t and time_t (7.26).
22439 -- The era for the clock function (7.26.2.1).
22440 -- The replacement string for the %Z specifier to the strftime, and wcsftime
22441 functions in the "C" locale (7.26.3.5, 7.28.5.1).
22442 -- Whether the functions in <math.h> honor the rounding direction mode in an
22443 IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).
22450 J.3.13 Architecture
22451 1 -- The values or expressions assigned to the macros specified in the headers
22452 <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3).
22453 -- The result of attempting to indirectly access an object with automatic or thread
22454 storage duration from a thread other than the one with which it is associated (6.2.4).
22455 -- The number, order, and encoding of bytes in any object (when not explicitly specified
22456 in this International Standard) (6.2.6.1).
22457 -- Whether any extended alignments are supported and the contexts in which they are
22459 -- Valid alignment values other than those returned by an alignof expression for
22460 fundamental types, if any (6.2.8).
22461 -- The value of the result of the sizeof and alignof operators (6.5.3.4).
22462 J.4 Locale-specific behavior
22463 1 The following characteristics of a hosted environment are locale-specific and are required
22464 to be documented by the implementation:
22465 -- Additional members of the source and execution character sets beyond the basic
22466 character set (5.2.1).
22467 -- The presence, meaning, and representation of additional multibyte characters in the
22468 execution character set beyond the basic character set (5.2.1.2).
22469 -- The shift states used for the encoding of multibyte characters (5.2.1.2).
22470 -- The direction of writing of successive printing characters (5.2.2).
22471 -- The decimal-point character (7.1.1).
22472 -- The set of printing characters (7.4, 7.29.2).
22473 -- The set of control characters (7.4, 7.29.2).
22474 -- The sets of characters tested for by the isalpha, isblank, islower, ispunct,
22475 isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,
22476 iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
22477 7.4.1.11, 7.29.2.1.2, 7.29.2.1.3, 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, 7.29.2.1.11).
22478 -- The native environment (7.11.1.1).
22479 -- Additional subject sequences accepted by the numeric conversion functions (7.22.1,
22481 -- The collation sequence of the execution character set (7.23.4.3, 7.28.4.4.2).
22486 -- The contents of the error message strings set up by the strerror function
22488 -- The formats for time and date (7.26.3.5, 7.28.5.1).
22489 -- Character mappings that are supported by the towctrans function (7.29.1).
22490 -- Character classifications that are supported by the iswctype function (7.29.1).
22491 J.5 Common extensions
22492 1 The following extensions are widely used in many systems, but are not portable to all
22493 implementations. The inclusion of any extension that may cause a strictly conforming
22494 program to become invalid renders an implementation nonconforming. Examples of such
22495 extensions are new keywords, extra library functions declared in standard headers, or
22496 predefined macros with names that do not begin with an underscore.
22497 J.5.1 Environment arguments
22498 1 In a hosted environment, the main function receives a third argument, char *envp[],
22499 that points to a null-terminated array of pointers to char, each of which points to a string
22500 that provides information about the environment for this execution of the program
22502 J.5.2 Specialized identifiers
22503 1 Characters other than the underscore _, letters, and digits, that are not part of the basic
22504 source character set (such as the dollar sign $, or characters in national character sets)
22505 may appear in an identifier (6.4.2).
22506 J.5.3 Lengths and cases of identifiers
22507 1 All characters in identifiers (with or without external linkage) are significant (6.4.2).
22508 J.5.4 Scopes of identifiers
22509 1 A function identifier, or the identifier of an object the declaration of which contains the
22510 keyword extern, has file scope (6.2.1).
22511 J.5.5 Writable string literals
22512 1 String literals are modifiable (in which case, identical string literals should denote distinct
22520 J.5.6 Other arithmetic types
22521 1 Additional arithmetic types, such as __int128 or double double, and their
22522 appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have
22523 more range or precision than long double, may be used for evaluating expressions of
22524 other floating types, and may be used to define float_t or double_t.
22525 J.5.7 Function pointer casts
22526 1 A pointer to an object or to void may be cast to a pointer to a function, allowing data to
22527 be invoked as a function (6.5.4).
22528 2 A pointer to a function may be cast to a pointer to an object or to void, allowing a
22529 function to be inspected or modified (for example, by a debugger) (6.5.4).
22530 J.5.8 Extended bit-field types
22531 1 A bit-field may be declared with a type other than _Bool, unsigned int, or
22532 signed int, with an appropriate maximum width (6.7.2.1).
22533 J.5.9 The fortran keyword
22534 1 The fortran function specifier may be used in a function declaration to indicate that
22535 calls suitable for FORTRAN should be generated, or that a different representation for the
22536 external name is to be generated (6.7.4).
22537 J.5.10 The asm keyword
22538 1 The asm keyword may be used to insert assembly language directly into the translator
22539 output (6.8). The most common implementation is via a statement of the form:
22540 asm ( character-string-literal );
22541 J.5.11 Multiple external definitions
22542 1 There may be more than one external definition for the identifier of an object, with or
22543 without the explicit use of the keyword extern; if the definitions disagree, or more than
22544 one is initialized, the behavior is undefined (6.9.2).
22545 J.5.12 Predefined macro names
22546 1 Macro names that do not begin with an underscore, describing the translation and
22547 execution environments, are defined by the implementation before translation begins
22555 J.5.13 Floating-point status flags
22556 1 If any floating-point status flags are set on normal termination after all calls to functions
22557 registered by the atexit function have been made (see 7.22.4.4), the implementation
22558 writes some diagnostics indicating the fact to the stderr stream, if it is still open,
22559 J.5.14 Extra arguments for signal handlers
22560 1 Handlers for specific signals are called with extra arguments in addition to the signal
22562 J.5.15 Additional stream types and file-opening modes
22563 1 Additional mappings from files to streams are supported (7.21.2).
22564 2 Additional file-opening modes may be specified by characters appended to the mode
22565 argument of the fopen function (7.21.5.3).
22566 J.5.16 Defined file position indicator
22567 1 The file position indicator is decremented by each successful call to the ungetc or
22568 ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10,
22570 J.5.17 Math error reporting
22571 1 Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors
22572 instead of, or in addition to, setting errno or raising floating-point exceptions (7.3,
22582 Bounds-checking interfaces
22584 1 Traditionally, the C Library has contained many functions that trust the programmer to
22585 provide output character arrays big enough to hold the result being produced. Not only
22586 do these functions not check that the arrays are big enough, they frequently lack the
22587 information needed to perform such checks. While it is possible to write safe, robust, and
22588 error-free code using the existing library, the library tends to promote programming styles
22589 that lead to mysterious failures if a result is too big for the provided array.
22590 2 A common programming style is to declare character arrays large enough to handle most
22591 practical cases. However, if these arrays are not large enough to handle the resulting
22592 strings, data can be written past the end of the array overwriting other data and program
22593 structures. The program never gets any indication that a problem exists, and so never has
22594 a chance to recover or to fail gracefully.
22595 3 Worse, this style of programming has compromised the security of computers and
22596 networks. Buffer overflows can often be exploited to run arbitrary code with the
22597 permissions of the vulnerable (defective) program.
22598 4 If the programmer writes runtime checks to verify lengths before calling library
22599 functions, then those runtime checks frequently duplicate work done inside the library
22600 functions, which discover string lengths as a side effect of doing their job.
22601 5 This annex provides alternative library functions that promote safer, more secure
22602 programming. The alternative functions verify that output buffers are large enough for
22603 the intended result and return a failure indicator if they are not. Data is never written past
22604 the end of an array. All string results are null terminated.
22605 6 This annex also addresses another problem that complicates writing robust code:
22606 functions that are not reentrant because they return pointers to static objects owned by the
22607 function. Such functions can be troublesome since a previously returned result can
22608 change if the function is called again, perhaps by another thread.
22616 1 This annex specifies a series of optional extensions that can be useful in the mitigation of
22617 security vulnerabilities in programs, and comprise new functions, macros, and types
22618 declared or defined in existing standard headers.
22619 2 An implementation that defines __STDC_LIB_EXT1__ shall conform to the
22620 specifications in this annex.361)
22621 3 Subclause K.3 should be read as if it were merged into the parallel structure of named
22622 subclauses of clause 7.
22625 K.3.1.1 Standard headers
22626 1 The functions, macros, and types declared or defined in K.3 and its subclauses are not
22627 declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
22628 defined as a macro which expands to the integer constant 0 at the point in the source file
22629 where the appropriate header is first included.
22630 2 The functions, macros, and types declared or defined in K.3 and its subclauses are
22631 declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
22632 defined as a macro which expands to the integer constant 1 at the point in the source file
22633 where the appropriate header is first included.362)
22634 3 It is implementation-defined whether the functions, macros, and types declared or defined
22635 in K.3 and its subclauses are declared or defined by their respective headers if
22636 __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file
22637 where the appropriate header is first included.363)
22638 4 Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be
22639 defined identically for all inclusions of any headers from subclause K.3. If
22640 __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the
22641 implementation shall issue a diagnostic as if a preprocessor error directive were used.
22644 361) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these
22646 362) Future revisions of this International Standard may define meanings for other values of
22647 __STDC_WANT_LIB_EXT1__.
22648 363) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in
22649 headers. All other names are not reserved, and a conforming implementation is not permitted to use
22650 them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an
22651 unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the
22652 implementation is not conforming.
22656 K.3.1.2 Reserved identifiers
22657 1 Each macro name in any of the following subclauses is reserved for use as specified if it
22658 is defined by any of its associated headers when included; unless explicitly stated
22659 otherwise (see 7.1.4).
22660 2 All identifiers with external linkage in any of the following subclauses are reserved for
22661 use as identifiers with external linkage if any of them are used by the program. None of
22662 them are reserved if none of them are used.
22663 3 Each identifier with file scope listed in any of the following subclauses is reserved for use
22664 as a macro name and as an identifier with file scope in the same name space if it is
22665 defined by any of its associated headers when included.
22666 K.3.1.3 Use of errno
22667 1 An implementation may set errno for the functions defined in this annex, but is not
22669 K.3.1.4 Runtime-constraint violations
22670 1 Most functions in this annex include as part of their specification a list of runtime-
22671 constraints. These runtime-constraints are requirements on the program using the
22673 2 Implementations shall verify that the runtime-constraints for a function are not violated
22674 by the program. If a runtime-constraint is violated, the implementation shall call the
22675 currently registered runtime-constraint handler (see set_constraint_handler_s
22676 in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library
22677 function result in only one call to the runtime-constraint handler. It is unspecified which
22678 one of the multiple runtime-constraint violations cause the handler to be called.
22679 3 If the runtime-constraints section for a function states an action to be performed when a
22680 runtime-constraint violation occurs, the function shall perform the action before calling
22681 the runtime-constraint handler. If the runtime-constraints section lists actions that are
22682 prohibited when a runtime-constraint violation occurs, then such actions are prohibited to
22683 the function both before calling the handler and after the handler returns.
22684 4 The runtime-constraint handler might not return. If the handler does return, the library
22685 function whose runtime-constraint was violated shall return some indication of failure as
22686 given by the returns section in the function's specification.
22690 364) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still
22691 exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a
22692 runtime-constraint violation by calling the runtime-constraint handler. This license comes directly
22693 from the definition of undefined behavior.
22697 K.3.2 Errors <errno.h>
22698 1 The header <errno.h> defines a type.
22701 which is type int.365)
22702 K.3.3 Common definitions <stddef.h>
22703 1 The header <stddef.h> defines a type.
22706 which is the type size_t.366)
22707 K.3.4 Integer types <stdint.h>
22708 1 The header <stdint.h> defines a macro.
22711 which expands to a value367) of type size_t. Functions that have parameters of type
22712 rsize_t consider it a runtime-constraint violation if the values of those parameters are
22713 greater than RSIZE_MAX.
22714 Recommended practice
22715 3 Extremely large object sizes are frequently a sign that an object's size was calculated
22716 incorrectly. For example, negative numbers appear as very large positive numbers when
22717 converted to an unsigned type like size_t. Also, some implementations do not support
22718 objects as large as the maximum value that can be represented by type size_t.
22719 4 For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect
22720 programming errors. For implementations targeting machines with large address spaces,
22721 it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest
22722 object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of
22723 some legitimate, but very large, objects. Implementations targeting machines with small
22724 address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there
22726 365) As a matter of programming style, errno_t may be used as the type of something that deals only
22727 with the values that might be found in errno. For example, a function which returns the value of
22728 errno might be declared as having the return type errno_t.
22729 366) See the description of the RSIZE_MAX macro in <stdint.h>.
22730 367) The macro RSIZE_MAX need not expand to a constant expression.
22734 is no object size that is considered a runtime-constraint violation.
22735 K.3.5 Input/output <stdio.h>
22736 1 The header <stdio.h> defines several macros and two types.
22739 which expands to an integer constant expression that is the size needed for an array of
22740 char large enough to hold a temporary file name string generated by the tmpnam_s
22743 which expands to an integer constant expression that is the maximum number of unique
22744 file names that can be generated by the tmpnam_s function.
22747 which is type int; and
22749 which is the type size_t.
22750 K.3.5.1 Operations on files
22751 K.3.5.1.1 The tmpfile_s function
22753 1 #define __STDC_WANT_LIB_EXT1__ 1
22755 errno_t tmpfile_s(FILE * restrict * restrict streamptr);
22756 Runtime-constraints
22757 2 streamptr shall not be a null pointer.
22758 3 If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
22760 4 The tmpfile_s function creates a temporary binary file that is different from any other
22761 existing file and that will automatically be removed when it is closed or at program
22762 termination. If the program terminates abnormally, whether an open temporary file is
22763 removed is implementation-defined. The file is opened for update with "wb+" mode
22764 with the meaning that mode has in the fopen_s function (including the mode's effect
22765 on exclusive access and file permissions).
22770 5 If the file was created successfully, then the pointer to FILE pointed to by streamptr
22771 will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
22772 to FILE pointed to by streamptr will be set to a null pointer.
22773 Recommended practice
22774 It should be possible to open at least TMP_MAX_S temporary files during the lifetime of
22775 the program (this limit may be shared with tmpnam_s) and there should be no limit on
22776 the number simultaneously open other than this limit and any limit on the number of open
22779 6 The tmpfile_s function returns zero if it created the file. If it did not create the file or
22780 there was a runtime-constraint violation, tmpfile_s returns a nonzero value.
22781 K.3.5.1.2 The tmpnam_s function
22783 1 #define __STDC_WANT_LIB_EXT1__ 1
22785 errno_t tmpnam_s(char *s, rsize_t maxsize);
22786 Runtime-constraints
22787 2 s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX.
22788 maxsize shall be greater than the length of the generated file name string.
22790 3 The tmpnam_s function generates a string that is a valid file name and that is not the
22791 same as the name of an existing file.368) The function is potentially capable of generating
22792 TMP_MAX_S different strings, but any or all of them may already be in use by existing
22793 files and thus not be suitable return values. The lengths of these strings shall be less than
22794 the value of the L_tmpnam_s macro.
22795 4 The tmpnam_s function generates a different string each time it is called.
22796 5 It is assumed that s points to an array of at least maxsize characters. This array will be
22797 set to generated string, as specified below.
22801 368) Files created using strings generated by the tmpnam_s function are temporary only in the sense that
22802 their names should not collide with those generated by conventional naming rules for the
22803 implementation. It is still necessary to use the remove function to remove such files when their use
22804 is ended, and before program termination. Implementations should take care in choosing the patterns
22805 used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the
22806 race condition and possible conflict when multiple programs run simultaneously by the same user
22807 generate the same temporary file names.
22811 6 The implementation shall behave as if no library function except tmpnam calls the
22812 tmpnam_s function.369)
22813 Recommended practice
22814 7 After a program obtains a file name using the tmpnam_s function and before the
22815 program creates a file with that name, the possibility exists that someone else may create
22816 a file with that same name. To avoid this race condition, the tmpfile_s function
22817 should be used instead of tmpnam_s when possible. One situation that requires the use
22818 of the tmpnam_s function is when the program needs to create a temporary directory
22819 rather than a temporary file.
22821 8 If no suitable string can be generated, or if there is a runtime-constraint violation, the
22822 tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize
22823 is greater than zero) and returns a nonzero value.
22824 9 Otherwise, the tmpnam_s function writes the string in the array pointed to by s and
22826 Environmental limits
22827 10 The value of the macro TMP_MAX_S shall be at least 25.
22828 K.3.5.2 File access functions
22829 K.3.5.2.1 The fopen_s function
22831 1 #define __STDC_WANT_LIB_EXT1__ 1
22833 errno_t fopen_s(FILE * restrict * restrict streamptr,
22834 const char * restrict filename,
22835 const char * restrict mode);
22836 Runtime-constraints
22837 2 None of streamptr, filename, or mode shall be a null pointer.
22838 3 If there is a runtime-constraint violation, fopen_s does not attempt to open a file.
22839 Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the
22845 369) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming
22846 convention for temporary files), but this is not required.
22851 4 The fopen_s function opens the file whose name is the string pointed to by
22852 filename, and associates a stream with it.
22853 5 The mode string shall be as described for fopen, with the addition that modes starting
22854 with the character 'w' or 'a' may be preceded by the character 'u', see below:
22855 uw truncate to zero length or create text file for writing, default
22857 uwx create text file for writing, default permissions
22858 ua append; open or create text file for writing at end-of-file, default
22860 uwb truncate to zero length or create binary file for writing, default
22862 uwbx create binary file for writing, default permissions
22863 uab append; open or create binary file for writing at end-of-file, default
22865 uw+ truncate to zero length or create text file for update, default
22867 uw+x create text file for update, default permissions
22868 ua+ append; open or create text file for update, writing at end-of-file,
22869 default permissions
22870 uw+b or uwb+ truncate to zero length or create binary file for update, default
22872 uw+bx or uwb+x create binary file for update, default permissions
22873 ua+b or uab+ append; open or create binary file for update, writing at end-of-file,
22874 default permissions
22875 6 Opening a file with exclusive mode ('x' as the last character in the mode argument)
22876 fails if the file already exists or cannot be created.
22877 7 To the extent that the underlying system supports the concepts, files opened for writing
22878 shall be opened with exclusive (also known as non-shared) access. If the file is being
22879 created, and the first character of the mode string is not 'u', to the extent that the
22880 underlying system supports it, the file shall have a file permission that prevents other
22881 users on the system from accessing the file. If the file is being created and first character
22882 of the mode string is 'u', then by the time the file has been closed, it shall have the
22883 system default file access permissions.370)
22884 8 If the file was opened successfully, then the pointer to FILE pointed to by streamptr
22885 will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
22888 370) These are the same permissions that the file would have been created with by fopen.
22892 to FILE pointed to by streamptr will be set to a null pointer.
22894 9 The fopen_s function returns zero if it opened the file. If it did not open the file or if
22895 there was a runtime-constraint violation, fopen_s returns a nonzero value.
22896 K.3.5.2.2 The freopen_s function
22898 1 #define __STDC_WANT_LIB_EXT1__ 1
22900 errno_t freopen_s(FILE * restrict * restrict newstreamptr,
22901 const char * restrict filename,
22902 const char * restrict mode,
22903 FILE * restrict stream);
22904 Runtime-constraints
22905 2 None of newstreamptr, mode, and stream shall be a null pointer.
22906 3 If there is a runtime-constraint violation, freopen_s neither attempts to close any file
22907 associated with stream nor attempts to open a file. Furthermore, if newstreamptr is
22908 not a null pointer, fopen_s sets *newstreamptr to the null pointer.
22910 4 The freopen_s function opens the file whose name is the string pointed to by
22911 filename and associates the stream pointed to by stream with it. The mode
22912 argument has the same meaning as in the fopen_s function (including the mode's effect
22913 on exclusive access and file permissions).
22914 5 If filename is a null pointer, the freopen_s function attempts to change the mode of
22915 the stream to that specified by mode, as if the name of the file currently associated with
22916 the stream had been used. It is implementation-defined which changes of mode are
22917 permitted (if any), and under what circumstances.
22918 6 The freopen_s function first attempts to close any file that is associated with stream.
22919 Failure to close the file is ignored. The error and end-of-file indicators for the stream are
22921 7 If the file was opened successfully, then the pointer to FILE pointed to by
22922 newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE
22923 pointed to by newstreamptr will be set to a null pointer.
22925 8 The freopen_s function returns zero if it opened the file. If it did not open the file or
22926 there was a runtime-constraint violation, freopen_s returns a nonzero value.
22930 K.3.5.3 Formatted input/output functions
22931 1 Unless explicitly stated otherwise, if the execution of a function described in this
22932 subclause causes copying to take place between objects that overlap, the objects take on
22933 unspecified values.
22934 K.3.5.3.1 The fprintf_s function
22936 1 #define __STDC_WANT_LIB_EXT1__ 1
22938 int fprintf_s(FILE * restrict stream,
22939 const char * restrict format, ...);
22940 Runtime-constraints
22941 2 Neither stream nor format shall be a null pointer. The %n specifier371) (modified or
22942 not by flags, field width, or precision) shall not appear in the string pointed to by
22943 format. Any argument to fprintf_s corresponding to a %s specifier shall not be a
22945 3 If there is a runtime-constraint violation,372) the fprintf_s function does not attempt
22946 to produce further output, and it is unspecified to what extent fprintf_s produced
22947 output before discovering the runtime-constraint violation.
22949 4 The fprintf_s function is equivalent to the fprintf function except for the explicit
22950 runtime-constraints listed above.
22952 5 The fprintf_s function returns the number of characters transmitted, or a negative
22953 value if an output error, encoding error, or runtime-constraint violation occurred.
22958 371) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
22959 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
22960 format string was %%n.
22961 372) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
22962 implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
22963 constraint violation.
22967 K.3.5.3.2 The fscanf_s function
22969 1 #define __STDC_WANT_LIB_EXT1__ 1
22971 int fscanf_s(FILE * restrict stream,
22972 const char * restrict format, ...);
22973 Runtime-constraints
22974 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
22975 order to store converted input shall not be a null pointer.
22976 3 If there is a runtime-constraint violation,373) the fscanf_s function does not attempt to
22977 perform further input, and it is unspecified to what extent fscanf_s performed input
22978 before discovering the runtime-constraint violation.
22980 4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion
22981 specifiers apply to a pair of arguments (unless assignment suppression is indicated by a
22982 *). The first of these arguments is the same as for fscanf. That argument is
22983 immediately followed in the argument list by the second argument, which has type
22984 rsize_t and gives the number of elements in the array pointed to by the first argument
22985 of the pair. If the first argument points to a scalar object, it is considered to be an array of
22987 5 A matching failure occurs if the number of elements in a receiving object is insufficient to
22988 hold the converted input (including any trailing null character).
22990 6 The fscanf_s function returns the value of the macro EOF if an input failure occurs
22991 before any conversion or if there is a runtime-constraint violation. Otherwise, the
22993 373) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
22994 implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
22995 constraint violation.
22996 374) If the format is known at translation time, an implementation may issue a diagnostic for any argument
22997 used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
22998 argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
22999 the format is not known at translation time. For example, an implementation may issue a diagnostic
23000 for each argument after format that has of type pointer to one of char, signed char,
23001 unsigned char, or void that is not followed by an argument of a type compatible with
23002 rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
23003 using the hh length modifier, a length argument must follow the pointer argument. Another useful
23004 diagnostic could flag any non-pointer argument following format that did not have a type
23005 compatible with rsize_t.
23009 fscanf_s function returns the number of input items assigned, which can be fewer than
23010 provided for, or even zero, in the event of an early matching failure.
23011 7 EXAMPLE 1 The call:
23012 #define __STDC_WANT_LIB_EXT1__ 1
23015 int n, i; float x; char name[50];
23016 n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
23017 with the input line:
23018 25 54.32E-1 thompson
23019 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
23022 8 EXAMPLE 2 The call:
23023 #define __STDC_WANT_LIB_EXT1__ 1
23027 n = fscanf_s(stdin, "%s", s, sizeof s);
23028 with the input line:
23030 will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an
23031 array of six characters to store it.
23033 K.3.5.3.3 The printf_s function
23035 1 #define __STDC_WANT_LIB_EXT1__ 1
23037 int printf_s(const char * restrict format, ...);
23038 Runtime-constraints
23039 2 format shall not be a null pointer. The %n specifier375) (modified or not by flags, field
23040 width, or precision) shall not appear in the string pointed to by format. Any argument
23041 to printf_s corresponding to a %s specifier shall not be a null pointer.
23042 3 If there is a runtime-constraint violation, the printf_s function does not attempt to
23043 produce further output, and it is unspecified to what extent printf_s produced output
23044 before discovering the runtime-constraint violation.
23047 375) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23048 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23049 format string was %%n.
23054 4 The printf_s function is equivalent to the printf function except for the explicit
23055 runtime-constraints listed above.
23057 5 The printf_s function returns the number of characters transmitted, or a negative
23058 value if an output error, encoding error, or runtime-constraint violation occurred.
23059 K.3.5.3.4 The scanf_s function
23061 1 #define __STDC_WANT_LIB_EXT1__ 1
23063 int scanf_s(const char * restrict format, ...);
23064 Runtime-constraints
23065 2 format shall not be a null pointer. Any argument indirected though in order to store
23066 converted input shall not be a null pointer.
23067 3 If there is a runtime-constraint violation, the scanf_s function does not attempt to
23068 perform further input, and it is unspecified to what extent scanf_s performed input
23069 before discovering the runtime-constraint violation.
23071 4 The scanf_s function is equivalent to fscanf_s with the argument stdin
23072 interposed before the arguments to scanf_s.
23074 5 The scanf_s function returns the value of the macro EOF if an input failure occurs
23075 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23076 scanf_s function returns the number of input items assigned, which can be fewer than
23077 provided for, or even zero, in the event of an early matching failure.
23078 K.3.5.3.5 The snprintf_s function
23080 1 #define __STDC_WANT_LIB_EXT1__ 1
23082 int snprintf_s(char * restrict s, rsize_t n,
23083 const char * restrict format, ...);
23084 Runtime-constraints
23085 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23086 than RSIZE_MAX. The %n specifier376) (modified or not by flags, field width, or
23087 precision) shall not appear in the string pointed to by format. Any argument to
23090 snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
23092 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23093 than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the
23096 4 The snprintf_s function is equivalent to the snprintf function except for the
23097 explicit runtime-constraints listed above.
23098 5 The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the
23099 array pointed to by s.
23101 6 The snprintf_s function returns the number of characters that would have been
23102 written had n been sufficiently large, not counting the terminating null character, or a
23103 negative value if a runtime-constraint violation occurred. Thus, the null-terminated
23104 output has been completely written if and only if the returned value is nonnegative and
23106 K.3.5.3.6 The sprintf_s function
23108 1 #define __STDC_WANT_LIB_EXT1__ 1
23110 int sprintf_s(char * restrict s, rsize_t n,
23111 const char * restrict format, ...);
23112 Runtime-constraints
23113 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23114 than RSIZE_MAX. The number of characters (including the trailing null) required for the
23115 result to be written to the array pointed to by s shall not be greater than n. The %n
23116 specifier377) (modified or not by flags, field width, or precision) shall not appear in the
23117 string pointed to by format. Any argument to sprintf_s corresponding to a %s
23118 specifier shall not be a null pointer. No encoding error shall occur.
23122 376) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23123 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23124 format string was %%n.
23125 377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23126 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23127 format string was %%n.
23131 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23132 than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the
23135 4 The sprintf_s function is equivalent to the sprintf function except for the
23136 parameter n and the explicit runtime-constraints listed above.
23137 5 The sprintf_s function, unlike snprintf_s, treats a result too big for the array
23138 pointed to by s as a runtime-constraint violation.
23140 6 If no runtime-constraint violation occurred, the sprintf_s function returns the number
23141 of characters written in the array, not counting the terminating null character. If an
23142 encoding error occurred, sprintf_s returns a negative value. If any other runtime-
23143 constraint violation occurred, sprintf_s returns zero.
23144 K.3.5.3.7 The sscanf_s function
23146 1 #define __STDC_WANT_LIB_EXT1__ 1
23148 int sscanf_s(const char * restrict s,
23149 const char * restrict format, ...);
23150 Runtime-constraints
23151 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
23152 to store converted input shall not be a null pointer.
23153 3 If there is a runtime-constraint violation, the sscanf_s function does not attempt to
23154 perform further input, and it is unspecified to what extent sscanf_s performed input
23155 before discovering the runtime-constraint violation.
23157 4 The sscanf_s function is equivalent to fscanf_s, except that input is obtained from
23158 a string (specified by the argument s) rather than from a stream. Reaching the end of the
23159 string is equivalent to encountering end-of-file for the fscanf_s function. If copying
23160 takes place between objects that overlap, the objects take on unspecified values.
23162 5 The sscanf_s function returns the value of the macro EOF if an input failure occurs
23163 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23164 sscanf_s function returns the number of input items assigned, which can be fewer than
23165 provided for, or even zero, in the event of an early matching failure.
23169 K.3.5.3.8 The vfprintf_s function
23171 1 #define __STDC_WANT_LIB_EXT1__ 1
23172 #include <stdarg.h>
23174 int vfprintf_s(FILE * restrict stream,
23175 const char * restrict format,
23177 Runtime-constraints
23178 2 Neither stream nor format shall be a null pointer. The %n specifier378) (modified or
23179 not by flags, field width, or precision) shall not appear in the string pointed to by
23180 format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a
23182 3 If there is a runtime-constraint violation, the vfprintf_s function does not attempt to
23183 produce further output, and it is unspecified to what extent vfprintf_s produced
23184 output before discovering the runtime-constraint violation.
23186 4 The vfprintf_s function is equivalent to the vfprintf function except for the
23187 explicit runtime-constraints listed above.
23189 5 The vfprintf_s function returns the number of characters transmitted, or a negative
23190 value if an output error, encoding error, or runtime-constraint violation occurred.
23191 K.3.5.3.9 The vfscanf_s function
23193 1 #define __STDC_WANT_LIB_EXT1__ 1
23194 #include <stdarg.h>
23196 int vfscanf_s(FILE * restrict stream,
23197 const char * restrict format,
23203 378) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23204 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23205 format string was %%n.
23209 Runtime-constraints
23210 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
23211 order to store converted input shall not be a null pointer.
23212 3 If there is a runtime-constraint violation, the vfscanf_s function does not attempt to
23213 perform further input, and it is unspecified to what extent vfscanf_s performed input
23214 before discovering the runtime-constraint violation.
23216 4 The vfscanf_s function is equivalent to fscanf_s, with the variable argument list
23217 replaced by arg, which shall have been initialized by the va_start macro (and
23218 possibly subsequent va_arg calls). The vfscanf_s function does not invoke the
23221 5 The vfscanf_s function returns the value of the macro EOF if an input failure occurs
23222 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23223 vfscanf_s function returns the number of input items assigned, which can be fewer
23224 than provided for, or even zero, in the event of an early matching failure.
23225 K.3.5.3.10 The vprintf_s function
23227 1 #define __STDC_WANT_LIB_EXT1__ 1
23228 #include <stdarg.h>
23230 int vprintf_s(const char * restrict format,
23232 Runtime-constraints
23233 2 format shall not be a null pointer. The %n specifier380) (modified or not by flags, field
23234 width, or precision) shall not appear in the string pointed to by format. Any argument
23235 to vprintf_s corresponding to a %s specifier shall not be a null pointer.
23236 3 If there is a runtime-constraint violation, the vprintf_s function does not attempt to
23237 produce further output, and it is unspecified to what extent vprintf_s produced output
23238 before discovering the runtime-constraint violation.
23240 379) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23241 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23243 380) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23244 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23245 format string was %%n.
23250 4 The vprintf_s function is equivalent to the vprintf function except for the explicit
23251 runtime-constraints listed above.
23253 5 The vprintf_s function returns the number of characters transmitted, or a negative
23254 value if an output error, encoding error, or runtime-constraint violation occurred.
23255 K.3.5.3.11 The vscanf_s function
23257 1 #define __STDC_WANT_LIB_EXT1__ 1
23258 #include <stdarg.h>
23260 int vscanf_s(const char * restrict format,
23262 Runtime-constraints
23263 2 format shall not be a null pointer. Any argument indirected though in order to store
23264 converted input shall not be a null pointer.
23265 3 If there is a runtime-constraint violation, the vscanf_s function does not attempt to
23266 perform further input, and it is unspecified to what extent vscanf_s performed input
23267 before discovering the runtime-constraint violation.
23269 4 The vscanf_s function is equivalent to scanf_s, with the variable argument list
23270 replaced by arg, which shall have been initialized by the va_start macro (and
23271 possibly subsequent va_arg calls). The vscanf_s function does not invoke the
23274 5 The vscanf_s function returns the value of the macro EOF if an input failure occurs
23275 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23276 vscanf_s function returns the number of input items assigned, which can be fewer than
23277 provided for, or even zero, in the event of an early matching failure.
23282 381) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23283 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23288 K.3.5.3.12 The vsnprintf_s function
23290 1 #define __STDC_WANT_LIB_EXT1__ 1
23291 #include <stdarg.h>
23293 int vsnprintf_s(char * restrict s, rsize_t n,
23294 const char * restrict format,
23296 Runtime-constraints
23297 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23298 than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or
23299 precision) shall not appear in the string pointed to by format. Any argument to
23300 vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
23302 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23303 than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the
23306 4 The vsnprintf_s function is equivalent to the vsnprintf function except for the
23307 explicit runtime-constraints listed above.
23308 5 The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within
23309 the array pointed to by s.
23311 6 The vsnprintf_s function returns the number of characters that would have been
23312 written had n been sufficiently large, not counting the terminating null character, or a
23313 negative value if a runtime-constraint violation occurred. Thus, the null-terminated
23314 output has been completely written if and only if the returned value is nonnegative and
23320 382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23321 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23322 format string was %%n.
23326 K.3.5.3.13 The vsprintf_s function
23328 1 #define __STDC_WANT_LIB_EXT1__ 1
23329 #include <stdarg.h>
23331 int vsprintf_s(char * restrict s, rsize_t n,
23332 const char * restrict format,
23334 Runtime-constraints
23335 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23336 than RSIZE_MAX. The number of characters (including the trailing null) required for the
23337 result to be written to the array pointed to by s shall not be greater than n. The %n
23338 specifier383) (modified or not by flags, field width, or precision) shall not appear in the
23339 string pointed to by format. Any argument to vsprintf_s corresponding to a %s
23340 specifier shall not be a null pointer. No encoding error shall occur.
23341 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23342 than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the
23345 4 The vsprintf_s function is equivalent to the vsprintf function except for the
23346 parameter n and the explicit runtime-constraints listed above.
23347 5 The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array
23348 pointed to by s as a runtime-constraint violation.
23350 6 If no runtime-constraint violation occurred, the vsprintf_s function returns the
23351 number of characters written in the array, not counting the terminating null character. If
23352 an encoding error occurred, vsprintf_s returns a negative value. If any other
23353 runtime-constraint violation occurred, vsprintf_s returns zero.
23358 383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23359 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23360 format string was %%n.
23364 K.3.5.3.14 The vsscanf_s function
23366 1 #define __STDC_WANT_LIB_EXT1__ 1
23367 #include <stdarg.h>
23369 int vsscanf_s(const char * restrict s,
23370 const char * restrict format,
23372 Runtime-constraints
23373 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
23374 to store converted input shall not be a null pointer.
23375 3 If there is a runtime-constraint violation, the vsscanf_s function does not attempt to
23376 perform further input, and it is unspecified to what extent vsscanf_s performed input
23377 before discovering the runtime-constraint violation.
23379 4 The vsscanf_s function is equivalent to sscanf_s, with the variable argument list
23380 replaced by arg, which shall have been initialized by the va_start macro (and
23381 possibly subsequent va_arg calls). The vsscanf_s function does not invoke the
23384 5 The vsscanf_s function returns the value of the macro EOF if an input failure occurs
23385 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23386 vscanf_s function returns the number of input items assigned, which can be fewer than
23387 provided for, or even zero, in the event of an early matching failure.
23388 K.3.5.4 Character input/output functions
23389 K.3.5.4.1 The gets_s function
23391 1 #define __STDC_WANT_LIB_EXT1__ 1
23393 char *gets_s(char *s, rsize_t n);
23398 384) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23399 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23404 Runtime-constraints
23405 2 s shall not be a null pointer. n shall neither be equal to zero nor be greater than
23406 RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading
23407 n-1 characters from stdin.385)
23408 3 If there is a runtime-constraint violation, s[0] is set to the null character, and characters
23409 are read and discarded from stdin until a new-line character is read, or end-of-file or a
23412 4 The gets_s function reads at most one less than the number of characters specified by n
23413 from the stream pointed to by stdin, into the array pointed to by s. No additional
23414 characters are read after a new-line character (which is discarded) or after end-of-file.
23415 The discarded new-line character does not count towards number of characters read. A
23416 null character is written immediately after the last character read into the array.
23417 5 If end-of-file is encountered and no characters have been read into the array, or if a read
23418 error occurs during the operation, then s[0] is set to the null character, and the other
23419 elements of s take unspecified values.
23420 Recommended practice
23421 6 The fgets function allows properly-written programs to safely process input lines too
23422 long to store in the result array. In general this requires that callers of fgets pay
23423 attention to the presence or absence of a new-line character in the result array. Consider
23424 using fgets (along with any needed processing based on new-line characters) instead of
23427 7 The gets_s function returns s if successful. If there was a runtime-constraint violation,
23428 or if end-of-file is encountered and no characters have been read into the array, or if a
23429 read error occurs during the operation, then a null pointer is returned.
23434 385) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for
23435 a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a
23436 one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets
23437 expect such a relationship.
23441 K.3.6 General utilities <stdlib.h>
23442 1 The header <stdlib.h> defines three types.
23445 which is type int; and
23447 which is the type size_t; and
23448 constraint_handler_t
23449 which has the following definition
23450 typedef void (*constraint_handler_t)(
23451 const char * restrict msg,
23452 void * restrict ptr,
23454 K.3.6.1 Runtime-constraint handling
23455 K.3.6.1.1 The set_constraint_handler_s function
23457 1 #define __STDC_WANT_LIB_EXT1__ 1
23458 #include <stdlib.h>
23459 constraint_handler_t set_constraint_handler_s(
23460 constraint_handler_t handler);
23462 2 The set_constraint_handler_s function sets the runtime-constraint handler to
23463 be handler. The runtime-constraint handler is the function to be called when a library
23464 function detects a runtime-constraint violation. Only the most recent handler registered
23465 with set_constraint_handler_s is called when a runtime-constraint violation
23467 3 When the handler is called, it is passed the following arguments in the following order:
23468 1. A pointer to a character string describing the runtime-constraint violation.
23469 2. A null pointer or a pointer to an implementation defined object.
23470 3. If the function calling the handler has a return type declared as errno_t, the
23471 return value of the function is passed. Otherwise, a positive value of type
23478 4 The implementation has a default constraint handler that is used if no calls to the
23479 set_constraint_handler_s function have been made. The behavior of the
23480 default handler is implementation-defined, and it may cause the program to exit or abort.
23481 5 If the handler argument to set_constraint_handler_s is a null pointer, the
23482 implementation default handler becomes the current constraint handler.
23484 6 The set_constraint_handler_s function returns a pointer to the previously
23485 registered handler.386)
23486 K.3.6.1.2 The abort_handler_s function
23488 1 #define __STDC_WANT_LIB_EXT1__ 1
23489 #include <stdlib.h>
23490 void abort_handler_s(
23491 const char * restrict msg,
23492 void * restrict ptr,
23495 2 A pointer to the abort_handler_s function shall be a suitable argument to the
23496 set_constraint_handler_s function.
23497 3 The abort_handler_s function writes a message on the standard error stream in an
23498 implementation-defined format. The message shall include the string pointed to by msg.
23499 The abort_handler_s function then calls the abort function.387)
23501 4 The abort_handler_s function does not return to its caller.
23506 386) If the previous handler was registered by calling set_constraint_handler_s with a null
23507 pointer argument, a pointer to the implementation default handler is returned (not NULL).
23508 387) Many implementations invoke a debugger when the abort function is called.
23512 K.3.6.1.3 The ignore_handler_s function
23514 1 #define __STDC_WANT_LIB_EXT1__ 1
23515 #include <stdlib.h>
23516 void ignore_handler_s(
23517 const char * restrict msg,
23518 void * restrict ptr,
23521 2 A pointer to the ignore_handler_s function shall be a suitable argument to the
23522 set_constraint_handler_s function.
23523 3 The ignore_handler_s function simply returns to its caller.388)
23525 4 The ignore_handler_s function returns no value.
23526 K.3.6.2 Communication with the environment
23527 K.3.6.2.1 The getenv_s function
23529 1 #define __STDC_WANT_LIB_EXT1__ 1
23530 #include <stdlib.h>
23531 errno_t getenv_s(size_t * restrict len,
23532 char * restrict value, rsize_t maxsize,
23533 const char * restrict name);
23534 Runtime-constraints
23535 2 name shall not be a null pointer. maxsize shall neither equal zero nor be greater than
23536 RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.
23537 3 If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len
23538 is not null), and the environment list is not searched.
23540 4 The getenv_s function searches an environment list, provided by the host environment,
23541 for a string that matches the string pointed to by name.
23544 388) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in
23545 which a runtime-constraint violation occurs will return to its caller. The caller can determine whether
23546 a runtime-constraint violation occurred based on the library function's specification (usually, the
23547 library function returns a nonzero errno_t).
23551 5 If that name is found then getenv_s performs the following actions. If len is not a
23552 null pointer, the length of the string associated with the matched list member is stored in
23553 the integer pointed to by len. If the length of the associated string is less than maxsize,
23554 then the associated string is copied to the array pointed to by value.
23555 6 If that name is not found then getenv_s performs the following actions. If len is not
23556 a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than
23557 zero, then value[0] is set to the null character.
23558 7 The set of environment names and the method for altering the environment list are
23559 implementation-defined.
23561 8 The getenv_s function returns zero if the specified name is found and the associated
23562 string was successfully stored in value. Otherwise, a nonzero value is returned.
23563 K.3.6.3 Searching and sorting utilities
23564 1 These utilities make use of a comparison function to search or sort arrays of unspecified
23565 type. Where an argument declared as size_t nmemb specifies the length of the array
23566 for a function, if nmemb has the value zero on a call to that function, then the comparison
23567 function is not called, a search finds no matching element, sorting performs no
23568 rearrangement, and the pointer to the array may be null.
23569 2 The implementation shall ensure that the second argument of the comparison function
23570 (when called from bsearch_s), or both arguments (when called from qsort_s), are
23571 pointers to elements of the array.389) The first argument when called from bsearch_s
23573 3 The comparison function shall not alter the contents of either the array or search key. The
23574 implementation may reorder elements of the array between calls to the comparison
23575 function, but shall not otherwise alter the contents of any individual element.
23576 4 When the same objects (consisting of size bytes, irrespective of their current positions
23577 in the array) are passed more than once to the comparison function, the results shall be
23578 consistent with one another. That is, for qsort_s they shall define a total ordering on
23579 the array, and for bsearch_s the same object shall always compare the same way with
23585 389) That is, if the value passed is p, then the following expressions are always valid and nonzero:
23586 ((char *)p - (char *)base) % size == 0
23587 (char *)p >= (char *)base
23588 (char *)p < (char *)base + nmemb * size
23593 5 A sequence point occurs immediately before and immediately after each call to the
23594 comparison function, and also between any call to the comparison function and any
23595 movement of the objects passed as arguments to that call.
23596 K.3.6.3.1 The bsearch_s function
23598 1 #define __STDC_WANT_LIB_EXT1__ 1
23599 #include <stdlib.h>
23600 void *bsearch_s(const void *key, const void *base,
23601 rsize_t nmemb, rsize_t size,
23602 int (*compar)(const void *k, const void *y,
23605 Runtime-constraints
23606 2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
23607 zero, then none of key, base, or compar shall be a null pointer.
23608 3 If there is a runtime-constraint violation, the bsearch_s function does not search the
23611 4 The bsearch_s function searches an array of nmemb objects, the initial element of
23612 which is pointed to by base, for an element that matches the object pointed to by key.
23613 The size of each element of the array is specified by size.
23614 5 The comparison function pointed to by compar is called with three arguments. The first
23615 two point to the key object and to an array element, in that order. The function shall
23616 return an integer less than, equal to, or greater than zero if the key object is considered,
23617 respectively, to be less than, to match, or to be greater than the array element. The array
23618 shall consist of: all the elements that compare less than, all the elements that compare
23619 equal to, and all the elements that compare greater than the key object, in that order.390)
23620 The third argument to the comparison function is the context argument passed to
23621 bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison
23627 390) In practice, this means that the entire array has been sorted according to the comparison function.
23628 391) The context argument is for the use of the comparison function in performing its duties. For
23629 example, it might specify a collating sequence used by the comparison function.
23634 6 The bsearch_s function returns a pointer to a matching element of the array, or a null
23635 pointer if no match is found or there is a runtime-constraint violation. If two elements
23636 compare as equal, which element is matched is unspecified.
23637 K.3.6.3.2 The qsort_s function
23639 1 #define __STDC_WANT_LIB_EXT1__ 1
23640 #include <stdlib.h>
23641 errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
23642 int (*compar)(const void *x, const void *y,
23645 Runtime-constraints
23646 2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
23647 zero, then neither base nor compar shall be a null pointer.
23648 3 If there is a runtime-constraint violation, the qsort_s function does not sort the array.
23650 4 The qsort_s function sorts an array of nmemb objects, the initial element of which is
23651 pointed to by base. The size of each object is specified by size.
23652 5 The contents of the array are sorted into ascending order according to a comparison
23653 function pointed to by compar, which is called with three arguments. The first two
23654 point to the objects being compared. The function shall return an integer less than, equal
23655 to, or greater than zero if the first argument is considered to be respectively less than,
23656 equal to, or greater than the second. The third argument to the comparison function is the
23657 context argument passed to qsort_s. The sole use of context by qsort_s is to
23658 pass it to the comparison function.392)
23659 6 If two elements compare as equal, their relative order in the resulting sorted array is
23662 7 The qsort_s function returns zero if there was no runtime-constraint violation.
23663 Otherwise, a nonzero value is returned.
23668 392) The context argument is for the use of the comparison function in performing its duties. For
23669 example, it might specify a collating sequence used by the comparison function.
23673 K.3.6.4 Multibyte/wide character conversion functions
23674 1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
23675 of the current locale. For a state-dependent encoding, each function is placed into its
23676 initial conversion state by a call for which its character pointer argument, s, is a null
23677 pointer. Subsequent calls with s as other than a null pointer cause the internal conversion
23678 state of the function to be altered as necessary. A call with s as a null pointer causes
23679 these functions to set the int pointed to by their status argument to a nonzero value if
23680 encodings have state dependency, and zero otherwise.393) Changing the LC_CTYPE
23681 category causes the conversion state of these functions to be indeterminate.
23682 K.3.6.4.1 The wctomb_s function
23684 1 #define __STDC_WANT_LIB_EXT1__ 1
23685 #include <stdlib.h>
23686 errno_t wctomb_s(int * restrict status,
23690 Runtime-constraints
23691 2 Let n denote the number of bytes needed to represent the multibyte character
23692 corresponding to the wide character given by wc (including any shift sequences).
23693 3 If s is not a null pointer, then smax shall not be less than n, and smax shall not be
23694 greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.
23695 4 If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to
23696 by status, and if s is not a null pointer, no more than smax elements in the array
23697 pointed to by s will be accessed.
23699 5 The wctomb_s function determines n and stores the multibyte character representation
23700 of wc in the array whose first element is pointed to by s (if s is not a null pointer). The
23701 number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide
23702 character, a null byte is stored, preceded by any shift sequence needed to restore the
23703 initial shift state, and the function is left in the initial conversion state.
23704 6 The implementation shall behave as if no library function calls the wctomb_s function.
23708 393) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
23709 character codes, but are grouped with an adjacent multibyte character.
23713 7 If s is a null pointer, the wctomb_s function stores into the int pointed to by status a
23714 nonzero or zero value, if multibyte character encodings, respectively, do or do not have
23715 state-dependent encodings.
23716 8 If s is not a null pointer, the wctomb_s function stores into the int pointed to by
23717 status either n or -1 if wc, respectively, does or does not correspond to a valid
23718 multibyte character.
23719 9 In no case will the int pointed to by status be set to a value greater than the
23722 10 The wctomb_s function returns zero if successful, and a nonzero value if there was a
23723 runtime-constraint violation or wc did not correspond to a valid multibyte character.
23724 K.3.6.5 Multibyte/wide string conversion functions
23725 1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
23726 the current locale.
23727 K.3.6.5.1 The mbstowcs_s function
23729 1 #include <stdlib.h>
23730 errno_t mbstowcs_s(size_t * restrict retval,
23731 wchar_t * restrict dst, rsize_t dstmax,
23732 const char * restrict src, rsize_t len);
23733 Runtime-constraints
23734 2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
23735 neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
23736 then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
23737 zero. If dst is not a null pointer and len is not less than dstmax, then a null character
23738 shall occur within the first dstmax multibyte characters of the array pointed to by src.
23739 3 If there is a runtime-constraint violation, then mbstowcs_s does the following. If
23740 retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If
23741 dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
23742 then mbstowcs_s sets dst[0] to the null wide character.
23744 4 The mbstowcs_s function converts a sequence of multibyte characters that begins in
23745 the initial shift state from the array pointed to by src into a sequence of corresponding
23746 wide characters. If dst is not a null pointer, the converted characters are stored into the
23747 array pointed to by dst. Conversion continues up to and including a terminating null
23748 character, which is also stored. Conversion stops earlier in two cases: when a sequence of
23751 bytes is encountered that does not form a valid multibyte character, or (if dst is not a
23752 null pointer) when len wide characters have been stored into the array pointed to by
23753 dst.394) If dst is not a null pointer and no null wide character was stored into the array
23754 pointed to by dst, then dst[len] is set to the null wide character. Each conversion
23755 takes place as if by a call to the mbrtowc function.
23756 5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
23757 sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
23758 the mbstowcs_s function stores the value (size_t)(-1) into *retval.
23759 Otherwise, the mbstowcs_s function stores into *retval the number of multibyte
23760 characters successfully converted, not including the terminating null character (if any).
23761 6 All elements following the terminating null wide character (if any) written by
23762 mbstowcs_s in the array of dstmax wide characters pointed to by dst take
23763 unspecified values when mbstowcs_s returns.395)
23764 7 If copying takes place between objects that overlap, the objects take on unspecified
23767 8 The mbstowcs_s function returns zero if no runtime-constraint violation and no
23768 encoding error occurred. Otherwise, a nonzero value is returned.
23769 K.3.6.5.2 The wcstombs_s function
23771 1 #include <stdlib.h>
23772 errno_t wcstombs_s(size_t * restrict retval,
23773 char * restrict dst, rsize_t dstmax,
23774 const wchar_t * restrict src, rsize_t len);
23775 Runtime-constraints
23776 2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
23777 neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
23778 then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
23779 zero. If dst is not a null pointer and len is not less than dstmax, then the conversion
23780 shall have been stopped (see below) because a terminating null wide character was
23781 reached or because an encoding error occurred.
23786 394) Thus, the value of len is ignored if dst is a null pointer.
23787 395) This allows an implementation to attempt converting the multibyte string before discovering a
23788 terminating null character did not occur where required.
23792 3 If there is a runtime-constraint violation, then wcstombs_s does the following. If
23793 retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If
23794 dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
23795 then wcstombs_s sets dst[0] to the null character.
23797 4 The wcstombs_s function converts a sequence of wide characters from the array
23798 pointed to by src into a sequence of corresponding multibyte characters that begins in
23799 the initial shift state. If dst is not a null pointer, the converted characters are then stored
23800 into the array pointed to by dst. Conversion continues up to and including a terminating
23801 null wide character, which is also stored. Conversion stops earlier in two cases:
23802 -- when a wide character is reached that does not correspond to a valid multibyte
23804 -- (if dst is not a null pointer) when the next multibyte character would exceed the
23805 limit of n total bytes to be stored into the array pointed to by dst. If the wide
23806 character being converted is the null wide character, then n is the lesser of len or
23807 dstmax. Otherwise, n is the lesser of len or dstmax-1.
23808 If the conversion stops without converting a null wide character and dst is not a null
23809 pointer, then a null character is stored into the array pointed to by dst immediately
23810 following any multibyte characters already stored. Each conversion takes place as if by a
23811 call to the wcrtomb function.396)
23812 5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
23813 wide character that does not correspond to a valid multibyte character, an encoding error
23814 occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval.
23815 Otherwise, the wcstombs_s function stores into *retval the number of bytes in the
23816 resulting multibyte character sequence, not including the terminating null character (if
23818 6 All elements following the terminating null character (if any) written by wcstombs_s
23819 in the array of dstmax elements pointed to by dst take unspecified values when
23820 wcstombs_s returns.397)
23821 7 If copying takes place between objects that overlap, the objects take on unspecified
23825 396) If conversion stops because a terminating null wide character has been reached, the bytes stored
23826 include those necessary to reach the initial shift state immediately before the null byte. However, if
23827 the conversion stops before a terminating null wide character has been reached, the result will be null
23828 terminated, but might not end in the initial shift state.
23829 397) When len is not less than dstmax, the implementation might fill the array before discovering a
23830 runtime-constraint violation.
23835 8 The wcstombs_s function returns zero if no runtime-constraint violation and no
23836 encoding error occurred. Otherwise, a nonzero value is returned.
23837 K.3.7 String handling <string.h>
23838 1 The header <string.h> defines two types.
23841 which is type int; and
23843 which is the type size_t.
23844 K.3.7.1 Copying functions
23845 K.3.7.1.1 The memcpy_s function
23847 1 #define __STDC_WANT_LIB_EXT1__ 1
23848 #include <string.h>
23849 errno_t memcpy_s(void * restrict s1, rsize_t s1max,
23850 const void * restrict s2, rsize_t n);
23851 Runtime-constraints
23852 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23853 RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
23854 objects that overlap.
23855 3 If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first
23856 s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is
23857 not greater than RSIZE_MAX.
23859 4 The memcpy_s function copies n characters from the object pointed to by s2 into the
23860 object pointed to by s1.
23862 5 The memcpy_s function returns zero if there was no runtime-constraint violation.
23863 Otherwise, a nonzero value is returned.
23870 K.3.7.1.2 The memmove_s function
23872 1 #define __STDC_WANT_LIB_EXT1__ 1
23873 #include <string.h>
23874 errno_t memmove_s(void *s1, rsize_t s1max,
23875 const void *s2, rsize_t n);
23876 Runtime-constraints
23877 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23878 RSIZE_MAX. n shall not be greater than s1max.
23879 3 If there is a runtime-constraint violation, the memmove_s function stores zeros in the
23880 first s1max characters of the object pointed to by s1 if s1 is not a null pointer and
23881 s1max is not greater than RSIZE_MAX.
23883 4 The memmove_s function copies n characters from the object pointed to by s2 into the
23884 object pointed to by s1. This copying takes place as if the n characters from the object
23885 pointed to by s2 are first copied into a temporary array of n characters that does not
23886 overlap the objects pointed to by s1 or s2, and then the n characters from the temporary
23887 array are copied into the object pointed to by s1.
23889 5 The memmove_s function returns zero if there was no runtime-constraint violation.
23890 Otherwise, a nonzero value is returned.
23891 K.3.7.1.3 The strcpy_s function
23893 1 #define __STDC_WANT_LIB_EXT1__ 1
23894 #include <string.h>
23895 errno_t strcpy_s(char * restrict s1,
23897 const char * restrict s2);
23898 Runtime-constraints
23899 2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
23900 s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max).
23901 Copying shall not take place between objects that overlap.
23902 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
23903 greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the
23909 4 The strcpy_s function copies the string pointed to by s2 (including the terminating
23910 null character) into the array pointed to by s1.
23911 5 All elements following the terminating null character (if any) written by strcpy_s in
23912 the array of s1max characters pointed to by s1 take unspecified values when
23913 strcpy_s returns.398)
23915 6 The strcpy_s function returns zero399) if there was no runtime-constraint violation.
23916 Otherwise, a nonzero value is returned.
23917 K.3.7.1.4 The strncpy_s function
23919 1 #define __STDC_WANT_LIB_EXT1__ 1
23920 #include <string.h>
23921 errno_t strncpy_s(char * restrict s1,
23923 const char * restrict s2,
23925 Runtime-constraints
23926 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23927 RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
23928 shall be greater than strnlen_s(s2, s1max). Copying shall not take place between
23929 objects that overlap.
23930 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
23931 greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the
23934 4 The strncpy_s function copies not more than n successive characters (characters that
23935 follow a null character are not copied) from the array pointed to by s2 to the array
23936 pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null
23940 398) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
23941 any of those characters are null. Such an approach might write a character to every element of s1
23942 before discovering that the first element should be set to the null character.
23943 399) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
23944 within the array pointed to by s1 and that the result in s1 is null terminated.
23948 5 All elements following the terminating null character (if any) written by strncpy_s in
23949 the array of s1max characters pointed to by s1 take unspecified values when
23950 strncpy_s returns.400)
23952 6 The strncpy_s function returns zero401) if there was no runtime-constraint violation.
23953 Otherwise, a nonzero value is returned.
23954 7 EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result
23955 will not be null terminated or that characters will be written past the end of the destination array.
23956 #define __STDC_WANT_LIB_EXT1__ 1
23957 #include <string.h>
23959 char src1[100] = "hello";
23960 char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'};
23961 char dst1[6], dst2[5], dst3[5];
23963 r1 = strncpy_s(dst1, 6, src1, 100);
23964 r2 = strncpy_s(dst2, 5, src2, 7);
23965 r3 = strncpy_s(dst3, 5, src2, 4);
23966 The first call will assign to r1 the value zero and to dst1 the sequence hello\0.
23967 The second call will assign to r2 a nonzero value and to dst2 the sequence \0.
23968 The third call will assign to r3 the value zero and to dst3 the sequence good\0.
23970 K.3.7.2 Concatenation functions
23971 K.3.7.2.1 The strcat_s function
23973 1 #define __STDC_WANT_LIB_EXT1__ 1
23974 #include <string.h>
23975 errno_t strcat_s(char * restrict s1,
23977 const char * restrict s2);
23978 Runtime-constraints
23979 2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
23985 400) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
23986 any of those characters are null. Such an approach might write a character to every element of s1
23987 before discovering that the first element should be set to the null character.
23988 401) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
23989 within the array pointed to by s1 and that the result in s1 is null terminated.
23993 3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
23994 s1max shall not equal zero. m shall not equal zero.402) m shall be greater than
23995 strnlen_s(s2, m). Copying shall not take place between objects that overlap.
23996 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
23997 greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the
24000 5 The strcat_s function appends a copy of the string pointed to by s2 (including the
24001 terminating null character) to the end of the string pointed to by s1. The initial character
24002 from s2 overwrites the null character at the end of s1.
24003 6 All elements following the terminating null character (if any) written by strcat_s in
24004 the array of s1max characters pointed to by s1 take unspecified values when
24005 strcat_s returns.403)
24007 7 The strcat_s function returns zero404) if there was no runtime-constraint violation.
24008 Otherwise, a nonzero value is returned.
24009 K.3.7.2.2 The strncat_s function
24011 1 #define __STDC_WANT_LIB_EXT1__ 1
24012 #include <string.h>
24013 errno_t strncat_s(char * restrict s1,
24015 const char * restrict s2,
24017 Runtime-constraints
24018 2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
24020 3 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24021 RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.405) If n is not less
24024 402) Zero means that s1 was not null terminated upon entry to strcat_s.
24025 403) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
24026 any of those characters are null. Such an approach might write a character to every element of s1
24027 before discovering that the first element should be set to the null character.
24028 404) A zero return value implies that all of the requested characters from the string pointed to by s2 were
24029 appended to the string pointed to by s1 and that the result in s1 is null terminated.
24033 than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take
24034 place between objects that overlap.
24035 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24036 greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the
24039 5 The strncat_s function appends not more than n successive characters (characters
24040 that follow a null character are not copied) from the array pointed to by s2 to the end of
24041 the string pointed to by s1. The initial character from s2 overwrites the null character at
24042 the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to
24044 6 All elements following the terminating null character (if any) written by strncat_s in
24045 the array of s1max characters pointed to by s1 take unspecified values when
24046 strncat_s returns.406)
24048 7 The strncat_s function returns zero407) if there was no runtime-constraint violation.
24049 Otherwise, a nonzero value is returned.
24050 8 EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result
24051 will not be null terminated or that characters will be written past the end of the destination array.
24052 #define __STDC_WANT_LIB_EXT1__ 1
24053 #include <string.h>
24055 char s1[100] = "good";
24056 char s2[6] = "hello";
24057 char s3[6] = "hello";
24058 char s4[7] = "abc";
24059 char s5[1000] = "bye";
24060 int r1, r2, r3, r4;
24061 r1 = strncat_s(s1, 100, s5, 1000);
24062 r2 = strncat_s(s2, 6, "", 1);
24063 r3 = strncat_s(s3, 6, "X", 2);
24064 r4 = strncat_s(s4, 7, "defghijklmn", 3);
24065 After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0.
24069 405) Zero means that s1 was not null terminated upon entry to strncat_s.
24070 406) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
24071 any of those characters are null. Such an approach might write a character to every element of s1
24072 before discovering that the first element should be set to the null character.
24073 407) A zero return value implies that all of the requested characters from the string pointed to by s2 were
24074 appended to the string pointed to by s1 and that the result in s1 is null terminated.
24078 After the second call r2 will have the value zero and s2 will contain the sequence hello\0.
24079 After the third call r3 will have a nonzero value and s3 will contain the sequence \0.
24080 After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0.
24082 K.3.7.3 Search functions
24083 K.3.7.3.1 The strtok_s function
24085 1 #define __STDC_WANT_LIB_EXT1__ 1
24086 #include <string.h>
24087 char *strtok_s(char * restrict s1,
24088 rsize_t * restrict s1max,
24089 const char * restrict s2,
24090 char ** restrict ptr);
24091 Runtime-constraints
24092 2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
24093 shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
24094 The end of the token found shall occur within the first *s1max characters of s1 for the
24095 first call, and shall occur within the first *s1max characters of where searching resumes
24096 on subsequent calls.
24097 3 If there is a runtime-constraint violation, the strtok_s function does not indirect
24098 through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
24100 4 A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a
24101 sequence of tokens, each of which is delimited by a character from the string pointed to
24102 by s2. The fourth argument points to a caller-provided char pointer into which the
24103 strtok_s function stores information necessary for it to continue scanning the same
24105 5 The first call in a sequence has a non-null first argument and s1max points to an object
24106 whose value is the number of elements in the character array pointed to by the first
24107 argument. The first call stores an initial value in the object pointed to by ptr and
24108 updates the value pointed to by s1max to reflect the number of elements that remain in
24109 relation to ptr. Subsequent calls in the sequence have a null first argument and the
24110 objects pointed to by s1max and ptr are required to have the values stored by the
24111 previous call in the sequence, which are then updated. The separator string pointed to by
24112 s2 may be different from call to call.
24113 6 The first call in the sequence searches the string pointed to by s1 for the first character
24114 that is not contained in the current separator string pointed to by s2. If no such character
24115 is found, then there are no tokens in the string pointed to by s1 and the strtok_s
24116 function returns a null pointer. If such a character is found, it is the start of the first token.
24119 7 The strtok_s function then searches from there for the first character in s1 that is
24120 contained in the current separator string. If no such character is found, the current token
24121 extends to the end of the string pointed to by s1, and subsequent searches in the same
24122 string for a token return a null pointer. If such a character is found, it is overwritten by a
24123 null character, which terminates the current token.
24124 8 In all cases, the strtok_s function stores sufficient information in the pointer pointed
24125 to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
24126 value for ptr, shall start searching just past the element overwritten by a null character
24129 9 The strtok_s function returns a pointer to the first character of a token, or a null
24130 pointer if there is no token or there is a runtime-constraint violation.
24132 #define __STDC_WANT_LIB_EXT1__ 1
24133 #include <string.h>
24134 static char str1[] = "?a???b,,,#c";
24135 static char str2[] = "\t \t";
24136 char *t, *ptr1, *ptr2;
24137 rsize_t max1 = sizeof(str1);
24138 rsize_t max2 = sizeof(str2);
24139 t = strtok_s(str1, &max1, "?", &ptr1); // t points to the token "a"
24140 t = strtok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b"
24141 t = strtok_s(str2, &max2, " \t", &ptr2); // t is a null pointer
24142 t = strtok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c"
24143 t = strtok_s(NULL, &max1, "?", &ptr1); // t is a null pointer
24145 K.3.7.4 Miscellaneous functions
24146 K.3.7.4.1 The memset_s function
24148 1 #define __STDC_WANT_LIB_EXT1__ 1
24149 #include <string.h>
24150 errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
24151 Runtime-constraints
24152 2 s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n
24153 shall not be greater than smax.
24154 3 If there is a runtime-constraint violation, then if s is not a null pointer and smax is not
24155 greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an
24156 unsigned char) into each of the first smax characters of the object pointed to by s.
24163 4 The memset_s function copies the value of c (converted to an unsigned char) into
24164 each of the first n characters of the object pointed to by s. Unlike memset, any call to
24165 the memset_s function shall be evaluated strictly according to the rules of the abstract
24166 machine as described in (5.1.2.3). That is, any call to the memset_s function shall
24167 assume that the memory indicated by s and n may be accessible in the future and thus
24168 must contain the values indicated by c.
24170 5 The memset_s function returns zero if there was no runtime-constraint violation.
24171 Otherwise, a nonzero value is returned.
24172 K.3.7.4.2 The strerror_s function
24174 1 #define __STDC_WANT_LIB_EXT1__ 1
24175 #include <string.h>
24176 errno_t strerror_s(char *s, rsize_t maxsize,
24178 Runtime-constraints
24179 2 s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX.
24180 maxsize shall not equal zero.
24181 3 If there is a runtime-constraint violation, then the array (if any) pointed to by s is not
24184 4 The strerror_s function maps the number in errnum to a locale-specific message
24185 string. Typically, the values for errnum come from errno, but strerror_s shall
24186 map any value of type int to a message.
24187 5 If the length of the desired string is less than maxsize, then the string is copied to the
24188 array pointed to by s.
24189 6 Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied
24190 from the string to the array pointed to by s and then s[maxsize-1] is set to the null
24191 character. Then, if maxsize is greater than 3, then s[maxsize-2],
24192 s[maxsize-3], and s[maxsize-4] are set to the character period (.).
24194 7 The strerror_s function returns zero if the length of the desired string was less than
24195 maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s
24196 function returns a nonzero value.
24200 K.3.7.4.3 The strerrorlen_s function
24202 1 #define __STDC_WANT_LIB_EXT1__ 1
24203 #include <string.h>
24204 size_t strerrorlen_s(errno_t errnum);
24206 2 The strerrorlen_s function calculates the length of the (untruncated) locale-specific
24207 message string that the strerror_s function maps to errnum.
24209 3 The strerrorlen_s function returns the number of characters (not including the null
24210 character) in the full message string.
24211 K.3.7.4.4 The strnlen_s function
24213 1 #define __STDC_WANT_LIB_EXT1__ 1
24214 #include <string.h>
24215 size_t strnlen_s(const char *s, size_t maxsize);
24217 2 The strnlen_s function computes the length of the string pointed to by s.
24219 3 If s is a null pointer,408) then the strnlen_s function returns zero.
24220 4 Otherwise, the strnlen_s function returns the number of characters that precede the
24221 terminating null character. If there is no null character in the first maxsize characters of
24222 s then strnlen_s returns maxsize. At most the first maxsize characters of s shall
24223 be accessed by strnlen_s.
24228 408) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints
24229 along with the values returned for a null pointer or an unterminated string argument make
24230 strnlen_s useful in algorithms that gracefully handle such exceptional data.
24234 K.3.8 Date and time <time.h>
24235 1 The header <time.h> defines two types.
24238 which is type int; and
24240 which is the type size_t.
24241 K.3.8.1 Components of time
24242 1 A broken-down time is normalized if the values of the members of the tm structure are in
24243 their normal rages.409)
24244 K.3.8.2 Time conversion functions
24245 1 Like the strftime function, the asctime_s and ctime_s functions do not return a
24246 pointer to a static object, and other library functions are permitted to call them.
24247 K.3.8.2.1 The asctime_s function
24249 1 #define __STDC_WANT_LIB_EXT1__ 1
24251 errno_t asctime_s(char *s, rsize_t maxsize,
24252 const struct tm *timeptr);
24253 Runtime-constraints
24254 2 Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and
24255 shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr
24256 shall be normalized. The calendar year represented by the broken-down time pointed to
24257 by timeptr shall not be less than calendar year 0 and shall not be greater than calendar
24259 3 If there is a runtime-constraint violation, there is no attempt to convert the time, and
24260 s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is
24261 not greater than RSIZE_MAX.
24263 4 The asctime_s function converts the normalized broken-down time in the structure
24264 pointed to by timeptr into a 26 character (including the null character) string in the
24267 409) The normal ranges are defined in 7.26.1.
24272 Sun Sep 16 01:03:52 1973\n\0
24273 The fields making up this string are (in order):
24274 1. The name of the day of the week represented by timeptr->tm_wday using the
24275 following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat.
24276 2. The character space.
24277 3. The name of the month represented by timeptr->tm_mon using the following
24278 three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
24280 4. The character space.
24281 5. The value of timeptr->tm_mday as if printed using the fprintf format
24283 6. The character space.
24284 7. The value of timeptr->tm_hour as if printed using the fprintf format
24286 8. The character colon.
24287 9. The value of timeptr->tm_min as if printed using the fprintf format
24289 10. The character colon.
24290 11. The value of timeptr->tm_sec as if printed using the fprintf format
24292 12. The character space.
24293 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf
24295 14. The character new line.
24296 15. The null character.
24297 Recommended practice
24298 The strftime function allows more flexible formatting and supports locale-specific
24299 behavior. If you do not require the exact form of the result string produced by the
24300 asctime_s function, consider using the strftime function instead.
24302 5 The asctime_s function returns zero if the time was successfully converted and stored
24303 into the array pointed to by s. Otherwise, it returns a nonzero value.
24306 K.3.8.2.2 The ctime_s function
24308 1 #define __STDC_WANT_LIB_EXT1__ 1
24310 errno_t ctime_s(char *s, rsize_t maxsize,
24311 const time_t *timer);
24312 Runtime-constraints
24313 2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and
24314 shall not be greater than RSIZE_MAX.
24315 3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null
24316 pointer and maxsize is not equal zero and is not greater than RSIZE_MAX.
24318 4 The ctime_s function converts the calendar time pointed to by timer to local time in
24319 the form of a string. It is equivalent to
24320 asctime_s(s, maxsize, localtime_s(timer))
24321 Recommended practice
24322 The strftime function allows more flexible formatting and supports locale-specific
24323 behavior. If you do not require the exact form of the result string produced by the
24324 ctime_s function, consider using the strftime function instead.
24326 5 The ctime_s function returns zero if the time was successfully converted and stored
24327 into the array pointed to by s. Otherwise, it returns a nonzero value.
24328 K.3.8.2.3 The gmtime_s function
24330 1 #define __STDC_WANT_LIB_EXT1__ 1
24332 struct tm *gmtime_s(const time_t * restrict timer,
24333 struct tm * restrict result);
24334 Runtime-constraints
24335 2 Neither timer nor result shall be a null pointer.
24336 3 If there is a runtime-constraint violation, there is no attempt to convert the time.
24338 4 The gmtime_s function converts the calendar time pointed to by timer into a broken-
24339 down time, expressed as UTC. The broken-down time is stored in the structure pointed
24344 5 The gmtime_s function returns result, or a null pointer if the specified time cannot
24345 be converted to UTC or there is a runtime-constraint violation.
24346 K.3.8.2.4 The localtime_s function
24348 1 #define __STDC_WANT_LIB_EXT1__ 1
24350 struct tm *localtime_s(const time_t * restrict timer,
24351 struct tm * restrict result);
24352 Runtime-constraints
24353 2 Neither timer nor result shall be a null pointer.
24354 3 If there is a runtime-constraint violation, there is no attempt to convert the time.
24356 4 The localtime_s function converts the calendar time pointed to by timer into a
24357 broken-down time, expressed as local time. The broken-down time is stored in the
24358 structure pointed to by result.
24360 5 The localtime_s function returns result, or a null pointer if the specified time
24361 cannot be converted to local time or there is a runtime-constraint violation.
24362 K.3.9 Extended multibyte and wide character utilities <wchar.h>
24363 1 The header <wchar.h> defines two types.
24366 which is type int; and
24368 which is the type size_t.
24369 3 Unless explicitly stated otherwise, if the execution of a function described in this
24370 subclause causes copying to take place between objects that overlap, the objects take on
24371 unspecified values.
24378 K.3.9.1 Formatted wide character input/output functions
24379 K.3.9.1.1 The fwprintf_s function
24381 1 #define __STDC_WANT_LIB_EXT1__ 1
24383 int fwprintf_s(FILE * restrict stream,
24384 const wchar_t * restrict format, ...);
24385 Runtime-constraints
24386 2 Neither stream nor format shall be a null pointer. The %n specifier410) (modified or
24387 not by flags, field width, or precision) shall not appear in the wide string pointed to by
24388 format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a
24390 3 If there is a runtime-constraint violation, the fwprintf_s function does not attempt to
24391 produce further output, and it is unspecified to what extent fwprintf_s produced
24392 output before discovering the runtime-constraint violation.
24394 4 The fwprintf_s function is equivalent to the fwprintf function except for the
24395 explicit runtime-constraints listed above.
24397 5 The fwprintf_s function returns the number of wide characters transmitted, or a
24398 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24399 K.3.9.1.2 The fwscanf_s function
24401 1 #define __STDC_WANT_LIB_EXT1__ 1
24404 int fwscanf_s(FILE * restrict stream,
24405 const wchar_t * restrict format, ...);
24406 Runtime-constraints
24407 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
24408 order to store converted input shall not be a null pointer.
24411 410) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24412 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24413 example, if the entire format string was L"%%n".
24417 3 If there is a runtime-constraint violation, the fwscanf_s function does not attempt to
24418 perform further input, and it is unspecified to what extent fwscanf_s performed input
24419 before discovering the runtime-constraint violation.
24421 4 The fwscanf_s function is equivalent to fwscanf except that the c, s, and [
24422 conversion specifiers apply to a pair of arguments (unless assignment suppression is
24423 indicated by a *). The first of these arguments is the same as for fwscanf. That
24424 argument is immediately followed in the argument list by the second argument, which has
24425 type size_t and gives the number of elements in the array pointed to by the first
24426 argument of the pair. If the first argument points to a scalar object, it is considered to be
24427 an array of one element.411)
24428 5 A matching failure occurs if the number of elements in a receiving object is insufficient to
24429 hold the converted input (including any trailing null character).
24431 6 The fwscanf_s function returns the value of the macro EOF if an input failure occurs
24432 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24433 fwscanf_s function returns the number of input items assigned, which can be fewer
24434 than provided for, or even zero, in the event of an early matching failure.
24435 K.3.9.1.3 The snwprintf_s function
24437 1 #define __STDC_WANT_LIB_EXT1__ 1
24439 int snwprintf_s(wchar_t * restrict s,
24441 const wchar_t * restrict format, ...);
24442 Runtime-constraints
24443 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24444 than RSIZE_MAX. The %n specifier412) (modified or not by flags, field width, or
24446 411) If the format is known at translation time, an implementation may issue a diagnostic for any argument
24447 used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
24448 argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
24449 the format is not known at translation time. For example, an implementation may issue a diagnostic
24450 for each argument after format that has of type pointer to one of char, signed char,
24451 unsigned char, or void that is not followed by an argument of a type compatible with
24452 rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
24453 using the hh length modifier, a length argument must follow the pointer argument. Another useful
24454 diagnostic could flag any non-pointer argument following format that did not have a type
24455 compatible with rsize_t.
24459 precision) shall not appear in the wide string pointed to by format. Any argument to
24460 snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
24462 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24463 than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the
24464 null wide character.
24466 4 The snwprintf_s function is equivalent to the swprintf function except for the
24467 explicit runtime-constraints listed above.
24468 5 The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within
24469 the array pointed to by s.
24471 6 The snwprintf_s function returns the number of wide characters that would have
24472 been written had n been sufficiently large, not counting the terminating wide null
24473 character, or a negative value if a runtime-constraint violation occurred. Thus, the null-
24474 terminated output has been completely written if and only if the returned value is
24475 nonnegative and less than n.
24476 K.3.9.1.4 The swprintf_s function
24478 1 #define __STDC_WANT_LIB_EXT1__ 1
24480 int swprintf_s(wchar_t * restrict s, rsize_t n,
24481 const wchar_t * restrict format, ...);
24482 Runtime-constraints
24483 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24484 than RSIZE_MAX. The number of wide characters (including the trailing null) required
24485 for the result to be written to the array pointed to by s shall not be greater than n. The %n
24486 specifier413) (modified or not by flags, field width, or precision) shall not appear in the
24487 wide string pointed to by format. Any argument to swprintf_s corresponding to a
24488 %s specifier shall not be a null pointer. No encoding error shall occur.
24491 412) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24492 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24493 example, if the entire format string was L"%%n".
24494 413) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24495 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24496 example, if the entire format string was L"%%n".
24500 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24501 than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the
24502 null wide character.
24504 4 The swprintf_s function is equivalent to the swprintf function except for the
24505 explicit runtime-constraints listed above.
24506 5 The swprintf_s function, unlike snwprintf_s, treats a result too big for the array
24507 pointed to by s as a runtime-constraint violation.
24509 6 If no runtime-constraint violation occurred, the swprintf_s function returns the
24510 number of wide characters written in the array, not counting the terminating null wide
24511 character. If an encoding error occurred or if n or more wide characters are requested to
24512 be written, swprintf_s returns a negative value. If any other runtime-constraint
24513 violation occurred, swprintf_s returns zero.
24514 K.3.9.1.5 The swscanf_s function
24516 1 #define __STDC_WANT_LIB_EXT1__ 1
24518 int swscanf_s(const wchar_t * restrict s,
24519 const wchar_t * restrict format, ...);
24520 Runtime-constraints
24521 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
24522 to store converted input shall not be a null pointer.
24523 3 If there is a runtime-constraint violation, the swscanf_s function does not attempt to
24524 perform further input, and it is unspecified to what extent swscanf_s performed input
24525 before discovering the runtime-constraint violation.
24527 4 The swscanf_s function is equivalent to fwscanf_s, except that the argument s
24528 specifies a wide string from which the input is to be obtained, rather than from a stream.
24529 Reaching the end of the wide string is equivalent to encountering end-of-file for the
24530 fwscanf_s function.
24532 5 The swscanf_s function returns the value of the macro EOF if an input failure occurs
24533 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24534 swscanf_s function returns the number of input items assigned, which can be fewer
24535 than provided for, or even zero, in the event of an early matching failure.
24538 K.3.9.1.6 The vfwprintf_s function
24540 1 #define __STDC_WANT_LIB_EXT1__ 1
24541 #include <stdarg.h>
24544 int vfwprintf_s(FILE * restrict stream,
24545 const wchar_t * restrict format,
24547 Runtime-constraints
24548 2 Neither stream nor format shall be a null pointer. The %n specifier414) (modified or
24549 not by flags, field width, or precision) shall not appear in the wide string pointed to by
24550 format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be
24552 3 If there is a runtime-constraint violation, the vfwprintf_s function does not attempt
24553 to produce further output, and it is unspecified to what extent vfwprintf_s produced
24554 output before discovering the runtime-constraint violation.
24556 4 The vfwprintf_s function is equivalent to the vfwprintf function except for the
24557 explicit runtime-constraints listed above.
24559 5 The vfwprintf_s function returns the number of wide characters transmitted, or a
24560 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24561 K.3.9.1.7 The vfwscanf_s function
24563 1 #define __STDC_WANT_LIB_EXT1__ 1
24564 #include <stdarg.h>
24567 int vfwscanf_s(FILE * restrict stream,
24568 const wchar_t * restrict format, va_list arg);
24572 414) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24573 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24574 example, if the entire format string was L"%%n".
24578 Runtime-constraints
24579 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
24580 order to store converted input shall not be a null pointer.
24581 3 If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to
24582 perform further input, and it is unspecified to what extent vfwscanf_s performed input
24583 before discovering the runtime-constraint violation.
24585 4 The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument
24586 list replaced by arg, which shall have been initialized by the va_start macro (and
24587 possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the
24590 5 The vfwscanf_s function returns the value of the macro EOF if an input failure occurs
24591 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24592 vfwscanf_s function returns the number of input items assigned, which can be fewer
24593 than provided for, or even zero, in the event of an early matching failure.
24594 K.3.9.1.8 The vsnwprintf_s function
24596 1 #define __STDC_WANT_LIB_EXT1__ 1
24597 #include <stdarg.h>
24599 int vsnwprintf_s(wchar_t * restrict s,
24601 const wchar_t * restrict format,
24603 Runtime-constraints
24604 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24605 than RSIZE_MAX. The %n specifier416) (modified or not by flags, field width, or
24606 precision) shall not appear in the wide string pointed to by format. Any argument to
24607 vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No
24608 encoding error shall occur.
24610 415) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24611 value of arg after the return is indeterminate.
24612 416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24613 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24614 example, if the entire format string was L"%%n".
24618 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24619 than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to
24620 the null wide character.
24622 4 The vsnwprintf_s function is equivalent to the vswprintf function except for the
24623 explicit runtime-constraints listed above.
24624 5 The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit
24625 within the array pointed to by s.
24627 6 The vsnwprintf_s function returns the number of wide characters that would have
24628 been written had n been sufficiently large, not counting the terminating null character, or
24629 a negative value if a runtime-constraint violation occurred. Thus, the null-terminated
24630 output has been completely written if and only if the returned value is nonnegative and
24632 K.3.9.1.9 The vswprintf_s function
24634 1 #define __STDC_WANT_LIB_EXT1__ 1
24635 #include <stdarg.h>
24637 int vswprintf_s(wchar_t * restrict s,
24639 const wchar_t * restrict format,
24641 Runtime-constraints
24642 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24643 than RSIZE_MAX. The number of wide characters (including the trailing null) required
24644 for the result to be written to the array pointed to by s shall not be greater than n. The %n
24645 specifier417) (modified or not by flags, field width, or precision) shall not appear in the
24646 wide string pointed to by format. Any argument to vswprintf_s corresponding to a
24647 %s specifier shall not be a null pointer. No encoding error shall occur.
24648 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24649 than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the
24650 null wide character.
24652 417) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24653 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24654 example, if the entire format string was L"%%n".
24659 4 The vswprintf_s function is equivalent to the vswprintf function except for the
24660 explicit runtime-constraints listed above.
24661 5 The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the
24662 array pointed to by s as a runtime-constraint violation.
24664 6 If no runtime-constraint violation occurred, the vswprintf_s function returns the
24665 number of wide characters written in the array, not counting the terminating null wide
24666 character. If an encoding error occurred or if n or more wide characters are requested to
24667 be written, vswprintf_s returns a negative value. If any other runtime-constraint
24668 violation occurred, vswprintf_s returns zero.
24669 K.3.9.1.10 The vswscanf_s function
24671 1 #define __STDC_WANT_LIB_EXT1__ 1
24672 #include <stdarg.h>
24674 int vswscanf_s(const wchar_t * restrict s,
24675 const wchar_t * restrict format,
24677 Runtime-constraints
24678 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
24679 to store converted input shall not be a null pointer.
24680 3 If there is a runtime-constraint violation, the vswscanf_s function does not attempt to
24681 perform further input, and it is unspecified to what extent vswscanf_s performed input
24682 before discovering the runtime-constraint violation.
24684 4 The vswscanf_s function is equivalent to swscanf_s, with the variable argument
24685 list replaced by arg, which shall have been initialized by the va_start macro (and
24686 possibly subsequent va_arg calls). The vswscanf_s function does not invoke the
24692 418) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24693 value of arg after the return is indeterminate.
24698 5 The vswscanf_s function returns the value of the macro EOF if an input failure occurs
24699 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24700 vswscanf_s function returns the number of input items assigned, which can be fewer
24701 than provided for, or even zero, in the event of an early matching failure.
24702 K.3.9.1.11 The vwprintf_s function
24704 1 #define __STDC_WANT_LIB_EXT1__ 1
24705 #include <stdarg.h>
24707 int vwprintf_s(const wchar_t * restrict format,
24709 Runtime-constraints
24710 2 format shall not be a null pointer. The %n specifier419) (modified or not by flags, field
24711 width, or precision) shall not appear in the wide string pointed to by format. Any
24712 argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.
24713 3 If there is a runtime-constraint violation, the vwprintf_s function does not attempt to
24714 produce further output, and it is unspecified to what extent vwprintf_s produced
24715 output before discovering the runtime-constraint violation.
24717 4 The vwprintf_s function is equivalent to the vwprintf function except for the
24718 explicit runtime-constraints listed above.
24720 5 The vwprintf_s function returns the number of wide characters transmitted, or a
24721 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24726 419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24727 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24728 example, if the entire format string was L"%%n".
24732 K.3.9.1.12 The vwscanf_s function
24734 1 #define __STDC_WANT_LIB_EXT1__ 1
24735 #include <stdarg.h>
24737 int vwscanf_s(const wchar_t * restrict format,
24739 Runtime-constraints
24740 2 format shall not be a null pointer. Any argument indirected though in order to store
24741 converted input shall not be a null pointer.
24742 3 If there is a runtime-constraint violation, the vwscanf_s function does not attempt to
24743 perform further input, and it is unspecified to what extent vwscanf_s performed input
24744 before discovering the runtime-constraint violation.
24746 4 The vwscanf_s function is equivalent to wscanf_s, with the variable argument list
24747 replaced by arg, which shall have been initialized by the va_start macro (and
24748 possibly subsequent va_arg calls). The vwscanf_s function does not invoke the
24751 5 The vwscanf_s function returns the value of the macro EOF if an input failure occurs
24752 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24753 vwscanf_s function returns the number of input items assigned, which can be fewer
24754 than provided for, or even zero, in the event of an early matching failure.
24755 K.3.9.1.13 The wprintf_s function
24757 1 #define __STDC_WANT_LIB_EXT1__ 1
24759 int wprintf_s(const wchar_t * restrict format, ...);
24760 Runtime-constraints
24761 2 format shall not be a null pointer. The %n specifier421) (modified or not by flags, field
24763 420) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24764 value of arg after the return is indeterminate.
24765 421) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24766 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24767 example, if the entire format string was L"%%n".
24771 width, or precision) shall not appear in the wide string pointed to by format. Any
24772 argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.
24773 3 If there is a runtime-constraint violation, the wprintf_s function does not attempt to
24774 produce further output, and it is unspecified to what extent wprintf_s produced output
24775 before discovering the runtime-constraint violation.
24777 4 The wprintf_s function is equivalent to the wprintf function except for the explicit
24778 runtime-constraints listed above.
24780 5 The wprintf_s function returns the number of wide characters transmitted, or a
24781 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24782 K.3.9.1.14 The wscanf_s function
24784 1 #define __STDC_WANT_LIB_EXT1__ 1
24786 int wscanf_s(const wchar_t * restrict format, ...);
24787 Runtime-constraints
24788 2 format shall not be a null pointer. Any argument indirected though in order to store
24789 converted input shall not be a null pointer.
24790 3 If there is a runtime-constraint violation, the wscanf_s function does not attempt to
24791 perform further input, and it is unspecified to what extent wscanf_s performed input
24792 before discovering the runtime-constraint violation.
24794 4 The wscanf_s function is equivalent to fwscanf_s with the argument stdin
24795 interposed before the arguments to wscanf_s.
24797 5 The wscanf_s function returns the value of the macro EOF if an input failure occurs
24798 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24799 wscanf_s function returns the number of input items assigned, which can be fewer than
24800 provided for, or even zero, in the event of an early matching failure.
24807 K.3.9.2 General wide string utilities
24808 K.3.9.2.1 Wide string copying functions
24809 K.3.9.2.1.1 The wcscpy_s function
24811 1 #define __STDC_WANT_LIB_EXT1__ 1
24813 errno_t wcscpy_s(wchar_t * restrict s1,
24815 const wchar_t * restrict s2);
24816 Runtime-constraints
24817 2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
24818 s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max).
24819 Copying shall not take place between objects that overlap.
24820 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24821 greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the
24822 null wide character.
24824 4 The wcscpy_s function copies the wide string pointed to by s2 (including the
24825 terminating null wide character) into the array pointed to by s1.
24826 5 All elements following the terminating null wide character (if any) written by
24827 wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified
24828 values when wcscpy_s returns.422)
24830 6 The wcscpy_s function returns zero423) if there was no runtime-constraint violation.
24831 Otherwise, a nonzero value is returned.
24836 422) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
24837 if any of those wide characters are null. Such an approach might write a wide character to every
24838 element of s1 before discovering that the first element should be set to the null wide character.
24839 423) A zero return value implies that all of the requested wide characters from the string pointed to by s2
24840 fit within the array pointed to by s1 and that the result in s1 is null terminated.
24844 K.3.9.2.1.2 The wcsncpy_s function
24846 7 #define __STDC_WANT_LIB_EXT1__ 1
24848 errno_t wcsncpy_s(wchar_t * restrict s1,
24850 const wchar_t * restrict s2,
24852 Runtime-constraints
24853 8 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24854 RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
24855 shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between
24856 objects that overlap.
24857 9 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24858 greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the
24859 null wide character.
24861 10 The wcsncpy_s function copies not more than n successive wide characters (wide
24862 characters that follow a null wide character are not copied) from the array pointed to by
24863 s2 to the array pointed to by s1. If no null wide character was copied from s2, then
24864 s1[n] is set to a null wide character.
24865 11 All elements following the terminating null wide character (if any) written by
24866 wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified
24867 values when wcsncpy_s returns.424)
24869 12 The wcsncpy_s function returns zero425) if there was no runtime-constraint violation.
24870 Otherwise, a nonzero value is returned.
24871 13 EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the
24872 result will not be null terminated or that wide characters will be written past the end of the destination
24878 424) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
24879 if any of those wide characters are null. Such an approach might write a wide character to every
24880 element of s1 before discovering that the first element should be set to the null wide character.
24881 425) A zero return value implies that all of the requested wide characters from the string pointed to by s2
24882 fit within the array pointed to by s1 and that the result in s1 is null terminated.
24886 #define __STDC_WANT_LIB_EXT1__ 1
24889 wchar_t src1[100] = L"hello";
24890 wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'};
24891 wchar_t dst1[6], dst2[5], dst3[5];
24893 r1 = wcsncpy_s(dst1, 6, src1, 100);
24894 r2 = wcsncpy_s(dst2, 5, src2, 7);
24895 r3 = wcsncpy_s(dst3, 5, src2, 4);
24896 The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0.
24897 The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0.
24898 The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0.
24900 K.3.9.2.1.3 The wmemcpy_s function
24902 14 #define __STDC_WANT_LIB_EXT1__ 1
24904 errno_t wmemcpy_s(wchar_t * restrict s1,
24906 const wchar_t * restrict s2,
24908 Runtime-constraints
24909 15 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24910 RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
24911 objects that overlap.
24912 16 If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the
24913 first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
24914 s1max is not greater than RSIZE_MAX.
24916 17 The wmemcpy_s function copies n successive wide characters from the object pointed
24917 to by s2 into the object pointed to by s1.
24919 18 The wmemcpy_s function returns zero if there was no runtime-constraint violation.
24920 Otherwise, a nonzero value is returned.
24927 K.3.9.2.1.4 The wmemmove_s function
24929 19 #define __STDC_WANT_LIB_EXT1__ 1
24931 errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
24932 const wchar_t *s2, rsize_t n);
24933 Runtime-constraints
24934 20 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24935 RSIZE_MAX. n shall not be greater than s1max.
24936 21 If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the
24937 first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
24938 s1max is not greater than RSIZE_MAX.
24940 22 The wmemmove_s function copies n successive wide characters from the object pointed
24941 to by s2 into the object pointed to by s1. This copying takes place as if the n wide
24942 characters from the object pointed to by s2 are first copied into a temporary array of n
24943 wide characters that does not overlap the objects pointed to by s1 or s2, and then the n
24944 wide characters from the temporary array are copied into the object pointed to by s1.
24946 23 The wmemmove_s function returns zero if there was no runtime-constraint violation.
24947 Otherwise, a nonzero value is returned.
24948 K.3.9.2.2 Wide string concatenation functions
24949 K.3.9.2.2.1 The wcscat_s function
24951 1 #define __STDC_WANT_LIB_EXT1__ 1
24953 errno_t wcscat_s(wchar_t * restrict s1,
24955 const wchar_t * restrict s2);
24956 Runtime-constraints
24957 2 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
24959 3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
24960 s1max shall not equal zero. m shall not equal zero.426) m shall be greater than
24961 wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.
24965 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24966 greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the
24967 null wide character.
24969 5 The wcscat_s function appends a copy of the wide string pointed to by s2 (including
24970 the terminating null wide character) to the end of the wide string pointed to by s1. The
24971 initial wide character from s2 overwrites the null wide character at the end of s1.
24972 6 All elements following the terminating null wide character (if any) written by
24973 wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified
24974 values when wcscat_s returns.427)
24976 7 The wcscat_s function returns zero428) if there was no runtime-constraint violation.
24977 Otherwise, a nonzero value is returned.
24978 K.3.9.2.2.2 The wcsncat_s function
24980 8 #define __STDC_WANT_LIB_EXT1__ 1
24982 errno_t wcsncat_s(wchar_t * restrict s1,
24984 const wchar_t * restrict s2,
24986 Runtime-constraints
24987 9 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
24989 10 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24990 RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.429) If n is not less
24991 than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take
24992 place between objects that overlap.
24995 426) Zero means that s1 was not null terminated upon entry to wcscat_s.
24996 427) This allows an implementation to append wide characters from s2 to s1 while simultaneously
24997 checking if any of those wide characters are null. Such an approach might write a wide character to
24998 every element of s1 before discovering that the first element should be set to the null wide character.
24999 428) A zero return value implies that all of the requested wide characters from the wide string pointed to by
25000 s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
25001 429) Zero means that s1 was not null terminated upon entry to wcsncat_s.
25005 11 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
25006 greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the
25007 null wide character.
25009 12 The wcsncat_s function appends not more than n successive wide characters (wide
25010 characters that follow a null wide character are not copied) from the array pointed to by
25011 s2 to the end of the wide string pointed to by s1. The initial wide character from s2
25012 overwrites the null wide character at the end of s1. If no null wide character was copied
25013 from s2, then s1[s1max-m+n] is set to a null wide character.
25014 13 All elements following the terminating null wide character (if any) written by
25015 wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified
25016 values when wcsncat_s returns.430)
25018 14 The wcsncat_s function returns zero431) if there was no runtime-constraint violation.
25019 Otherwise, a nonzero value is returned.
25020 15 EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the
25021 result will not be null terminated or that wide characters will be written past the end of the destination
25023 #define __STDC_WANT_LIB_EXT1__ 1
25026 wchar_t s1[100] = L"good";
25027 wchar_t s2[6] = L"hello";
25028 wchar_t s3[6] = L"hello";
25029 wchar_t s4[7] = L"abc";
25030 wchar_t s5[1000] = L"bye";
25031 int r1, r2, r3, r4;
25032 r1 = wcsncat_s(s1, 100, s5, 1000);
25033 r2 = wcsncat_s(s2, 6, L"", 1);
25034 r3 = wcsncat_s(s3, 6, L"X", 2);
25035 r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
25036 After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0.
25037 After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0.
25038 After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0.
25039 After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0.
25044 430) This allows an implementation to append wide characters from s2 to s1 while simultaneously
25045 checking if any of those wide characters are null. Such an approach might write a wide character to
25046 every element of s1 before discovering that the first element should be set to the null wide character.
25047 431) A zero return value implies that all of the requested wide characters from the wide string pointed to by
25048 s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
25052 K.3.9.2.3 Wide string search functions
25053 K.3.9.2.3.1 The wcstok_s function
25055 1 #define __STDC_WANT_LIB_EXT1__ 1
25057 wchar_t *wcstok_s(wchar_t * restrict s1,
25058 rsize_t * restrict s1max,
25059 const wchar_t * restrict s2,
25060 wchar_t ** restrict ptr);
25061 Runtime-constraints
25062 2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
25063 shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
25064 The end of the token found shall occur within the first *s1max wide characters of s1 for
25065 the first call, and shall occur within the first *s1max wide characters of where searching
25066 resumes on subsequent calls.
25067 3 If there is a runtime-constraint violation, the wcstok_s function does not indirect
25068 through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
25070 4 A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1
25071 into a sequence of tokens, each of which is delimited by a wide character from the wide
25072 string pointed to by s2. The fourth argument points to a caller-provided wchar_t
25073 pointer into which the wcstok_s function stores information necessary for it to
25074 continue scanning the same wide string.
25075 5 The first call in a sequence has a non-null first argument and s1max points to an object
25076 whose value is the number of elements in the wide character array pointed to by the first
25077 argument. The first call stores an initial value in the object pointed to by ptr and
25078 updates the value pointed to by s1max to reflect the number of elements that remain in
25079 relation to ptr. Subsequent calls in the sequence have a null first argument and the
25080 objects pointed to by s1max and ptr are required to have the values stored by the
25081 previous call in the sequence, which are then updated. The separator wide string pointed
25082 to by s2 may be different from call to call.
25083 6 The first call in the sequence searches the wide string pointed to by s1 for the first wide
25084 character that is not contained in the current separator wide string pointed to by s2. If no
25085 such wide character is found, then there are no tokens in the wide string pointed to by s1
25086 and the wcstok_s function returns a null pointer. If such a wide character is found, it is
25087 the start of the first token.
25092 7 The wcstok_s function then searches from there for the first wide character in s1 that
25093 is contained in the current separator wide string. If no such wide character is found, the
25094 current token extends to the end of the wide string pointed to by s1, and subsequent
25095 searches in the same wide string for a token return a null pointer. If such a wide character
25096 is found, it is overwritten by a null wide character, which terminates the current token.
25097 8 In all cases, the wcstok_s function stores sufficient information in the pointer pointed
25098 to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
25099 value for ptr, shall start searching just past the element overwritten by a null wide
25100 character (if any).
25102 9 The wcstok_s function returns a pointer to the first wide character of a token, or a null
25103 pointer if there is no token or there is a runtime-constraint violation.
25105 #define __STDC_WANT_LIB_EXT1__ 1
25107 static wchar_t str1[] = L"?a???b,,,#c";
25108 static wchar_t str2[] = L"\t \t";
25109 wchar_t *t, *ptr1, *ptr2;
25110 rsize_t max1 = wcslen(str1)+1;
25111 rsize_t max2 = wcslen(str2)+1;
25112 t = wcstok_s(str1, &max1, "?", &ptr1); // t points to the token "a"
25113 t = wcstok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b"
25114 t = wcstok_s(str2, &max2, " \t", &ptr2); // t is a null pointer
25115 t = wcstok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c"
25116 t = wcstok_s(NULL, &max1, "?", &ptr1); // t is a null pointer
25118 K.3.9.2.4 Miscellaneous functions
25119 K.3.9.2.4.1 The wcsnlen_s function
25121 1 #define __STDC_WANT_LIB_EXT1__ 1
25123 size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
25125 2 The wcsnlen_s function computes the length of the wide string pointed to by s.
25127 3 If s is a null pointer,432) then the wcsnlen_s function returns zero.
25128 4 Otherwise, the wcsnlen_s function returns the number of wide characters that precede
25129 the terminating null wide character. If there is no null wide character in the first
25130 maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first
25134 maxsize wide characters of s shall be accessed by wcsnlen_s.
25135 K.3.9.3 Extended multibyte/wide character conversion utilities
25136 K.3.9.3.1 Restartable multibyte/wide character conversion functions
25137 1 Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the
25138 conversion state) to be a null pointer.
25139 K.3.9.3.1.1 The wcrtomb_s function
25141 2 #include <wchar.h>
25142 errno_t wcrtomb_s(size_t * restrict retval,
25143 char * restrict s, rsize_t smax,
25144 wchar_t wc, mbstate_t * restrict ps);
25145 Runtime-constraints
25146 3 Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax
25147 shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer,
25148 then smax shall be not be less than the number of bytes to be stored in the array pointed
25149 to by s. If s is a null pointer, then smax shall equal zero.
25150 4 If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is
25151 not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then
25152 wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then
25153 wcrtomb_s sets *retval to (size_t)(-1).
25155 5 If s is a null pointer, the wcrtomb_s function is equivalent to the call
25156 wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
25157 where retval and buf are internal variables of the appropriate types, and the size of
25158 buf is greater than MB_CUR_MAX.
25159 6 If s is not a null pointer, the wcrtomb_s function determines the number of bytes
25160 needed to represent the multibyte character that corresponds to the wide character given
25161 by wc (including any shift sequences), and stores the multibyte character representation
25162 in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are
25163 stored. If wc is a null wide character, a null byte is stored, preceded by any shift
25164 sequence needed to restore the initial shift state; the resulting state described is the initial
25167 432) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints
25168 along with the values returned for a null pointer or an unterminated wide string argument make
25169 wcsnlen_s useful in algorithms that gracefully handle such exceptional data.
25173 7 If wc does not correspond to a valid multibyte character, an encoding error occurs: the
25174 wcrtomb_s function stores the value (size_t)(-1) into *retval and the
25175 conversion state is unspecified. Otherwise, the wcrtomb_s function stores into
25176 *retval the number of bytes (including any shift sequences) stored in the array pointed
25179 8 The wcrtomb_s function returns zero if no runtime-constraint violation and no
25180 encoding error occurred. Otherwise, a nonzero value is returned.
25181 K.3.9.3.2 Restartable multibyte/wide string conversion functions
25182 1 Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not
25183 permit the ps parameter (the pointer to the conversion state) to be a null pointer.
25184 K.3.9.3.2.1 The mbsrtowcs_s function
25186 2 #include <wchar.h>
25187 errno_t mbsrtowcs_s(size_t * restrict retval,
25188 wchar_t * restrict dst, rsize_t dstmax,
25189 const char ** restrict src, rsize_t len,
25190 mbstate_t * restrict ps);
25191 Runtime-constraints
25192 3 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
25193 then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
25194 pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
25195 not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null
25196 character shall occur within the first dstmax multibyte characters of the array pointed to
25198 4 If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If
25199 retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1).
25200 If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
25201 then mbsrtowcs_s sets dst[0] to the null wide character.
25203 5 The mbsrtowcs_s function converts a sequence of multibyte characters that begins in
25204 the conversion state described by the object pointed to by ps, from the array indirectly
25205 pointed to by src into a sequence of corresponding wide characters. If dst is not a null
25206 pointer, the converted characters are stored into the array pointed to by dst. Conversion
25207 continues up to and including a terminating null character, which is also stored.
25208 Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
25209 not form a valid multibyte character, or (if dst is not a null pointer) when len wide
25212 characters have been stored into the array pointed to by dst.433) If dst is not a null
25213 pointer and no null wide character was stored into the array pointed to by dst, then
25214 dst[len] is set to the null wide character. Each conversion takes place as if by a call
25215 to the mbrtowc function.
25216 6 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
25217 pointer (if conversion stopped due to reaching a terminating null character) or the address
25218 just past the last multibyte character converted (if any). If conversion stopped due to
25219 reaching a terminating null character and if dst is not a null pointer, the resulting state
25220 described is the initial conversion state.
25221 7 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
25222 sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
25223 the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the
25224 conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into
25225 *retval the number of multibyte characters successfully converted, not including the
25226 terminating null character (if any).
25227 8 All elements following the terminating null wide character (if any) written by
25228 mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take
25229 unspecified values when mbsrtowcs_s returns.434)
25230 9 If copying takes place between objects that overlap, the objects take on unspecified
25233 10 The mbsrtowcs_s function returns zero if no runtime-constraint violation and no
25234 encoding error occurred. Otherwise, a nonzero value is returned.
25235 K.3.9.3.2.2 The wcsrtombs_s function
25237 11 #include <wchar.h>
25238 errno_t wcsrtombs_s(size_t * restrict retval,
25239 char * restrict dst, rsize_t dstmax,
25240 const wchar_t ** restrict src, rsize_t len,
25241 mbstate_t * restrict ps);
25246 433) Thus, the value of len is ignored if dst is a null pointer.
25247 434) This allows an implementation to attempt converting the multibyte string before discovering a
25248 terminating null character did not occur where required.
25252 Runtime-constraints
25253 12 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
25254 then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
25255 pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
25256 not equal zero. If dst is not a null pointer and len is not less than dstmax, then the
25257 conversion shall have been stopped (see below) because a terminating null wide character
25258 was reached or because an encoding error occurred.
25259 13 If there is a runtime-constraint violation, then wcsrtombs_s does the following. If
25260 retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1).
25261 If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
25262 then wcsrtombs_s sets dst[0] to the null character.
25264 14 The wcsrtombs_s function converts a sequence of wide characters from the array
25265 indirectly pointed to by src into a sequence of corresponding multibyte characters that
25266 begins in the conversion state described by the object pointed to by ps. If dst is not a
25267 null pointer, the converted characters are then stored into the array pointed to by dst.
25268 Conversion continues up to and including a terminating null wide character, which is also
25269 stored. Conversion stops earlier in two cases:
25270 -- when a wide character is reached that does not correspond to a valid multibyte
25272 -- (if dst is not a null pointer) when the next multibyte character would exceed the
25273 limit of n total bytes to be stored into the array pointed to by dst. If the wide
25274 character being converted is the null wide character, then n is the lesser of len or
25275 dstmax. Otherwise, n is the lesser of len or dstmax-1.
25276 If the conversion stops without converting a null wide character and dst is not a null
25277 pointer, then a null character is stored into the array pointed to by dst immediately
25278 following any multibyte characters already stored. Each conversion takes place as if by a
25279 call to the wcrtomb function.435)
25280 15 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
25281 pointer (if conversion stopped due to reaching a terminating null wide character) or the
25282 address just past the last wide character converted (if any). If conversion stopped due to
25283 reaching a terminating null wide character, the resulting state described is the initial
25287 435) If conversion stops because a terminating null wide character has been reached, the bytes stored
25288 include those necessary to reach the initial shift state immediately before the null byte. However, if
25289 the conversion stops before a terminating null wide character has been reached, the result will be null
25290 terminated, but might not end in the initial shift state.
25294 16 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
25295 wide character that does not correspond to a valid multibyte character, an encoding error
25296 occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval
25297 and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores
25298 into *retval the number of bytes in the resulting multibyte character sequence, not
25299 including the terminating null character (if any).
25300 17 All elements following the terminating null character (if any) written by wcsrtombs_s
25301 in the array of dstmax elements pointed to by dst take unspecified values when
25302 wcsrtombs_s returns.436)
25303 18 If copying takes place between objects that overlap, the objects take on unspecified
25306 19 The wcsrtombs_s function returns zero if no runtime-constraint violation and no
25307 encoding error occurred. Otherwise, a nonzero value is returned.
25312 436) When len is not less than dstmax, the implementation might fill the array before discovering a
25313 runtime-constraint violation.
25321 1 This annex specifies optional behavior that can aid in the analyzability of C programs.
25322 2 An implementation that defines __STDC_ANALYZABLE__ shall conform to the
25323 specifications in this annex.437)
25326 1 out-of-bounds store
25327 an (attempted) access (3.1) that, at run time, for a given computational state, would
25328 modify (or, for an object declared volatile, fetch) one or more bytes that lie outside
25329 the bounds permitted by this Standard.
25331 1 bounded undefined behavior
25332 undefined behavior (3.4.3) that does not perform an out-of-bounds store.
25333 2 NOTE 1 The behavior might perform a trap.
25335 3 NOTE 2 Any values produced or stored might be indeterminate values.
25338 1 critical undefined behavior
25339 undefined behavior that is not bounded undefined behavior.
25340 2 NOTE The behavior might perform an out-of-bounds store or perform a trap.
25345 437) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these
25351 1 If the program performs a trap (3.19.5), the implementation is permitted to invoke a
25352 runtime-constraint handler. Any such semantics are implementation-defined.
25353 2 All undefined behavior shall be limited to bounded undefined behavior, except for the
25354 following which are permitted to result in critical undefined behavior:
25355 -- An object is referred to outside of its lifetime (6.2.4).
25356 -- An lvalue does not designate an object when evaluated (6.3.2.1).
25357 -- A pointer is used to call a function whose type is not compatible with the referenced
25359 -- The operand of the unary * operator has an invalid value (6.5.3.2).
25360 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
25361 integer type produces a result that points just beyond the array object and is used as
25362 the operand of a unary * operator that is evaluated (6.5.6).
25363 -- An argument to a library function has an invalid value or a type not expected by a
25364 function with variable number of arguments (7.1.4).
25365 -- The value of a pointer that refers to space deallocated by a call to the free or realloc
25366 function is used (7.22.3).
25367 -- A string or wide string utility function is instructed to access an array beyond the end
25368 of an object (7.23.1, 7.28.4).
25377 1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was
25378 published in The C Programming Language by Brian W. Kernighan and Dennis
25379 M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T.
25380 2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara,
25381 California, USA, November 1984.
25382 3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information
25383 Processing Systems, Information Processing Systems Technical Report.
25384 4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point
25386 5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent
25387 Floating-Point Arithmetic.
25388 6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems,
25389 second edition (previously designated IEC 559:1989).
25390 7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and
25391 symbols for use in the physical sciences and technology.
25392 8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for
25393 information interchange.
25394 9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1:
25396 10. ISO 4217:1995, Codes for the representation of currencies and funds.
25397 11. ISO 8601:1988, Data elements and interchange formats -- Information
25398 interchange -- Representation of dates and times.
25399 12. ISO/IEC 9899:1990, Programming languages -- C.
25400 13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1.
25401 14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2.
25402 15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity.
25403 16. ISO/IEC 9899:1999, Programming languages -- C.
25404 17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1.
25405 18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2.
25406 19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3.
25412 20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System
25413 Interface (POSIX) -- Part 2: Shell and Utilities.
25414 21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the
25415 preparation of programming language standards.
25416 22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet
25417 Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane.
25418 23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to
25419 ISO/IEC 10646-1:1993.
25420 24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to
25421 ISO/IEC 10646-1:1993.
25422 25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993
25423 Transformation Format for 16 planes of group 00 (UTF-16).
25424 26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS
25425 Transformation Format 8 (UTF-8).
25426 27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993.
25427 28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993.
25428 29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul
25430 30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993
25432 31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33
25433 additional characters.
25434 32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993.
25435 33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993
25436 Identifiers for characters.
25437 34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993
25439 35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993
25440 Unified Canadian Aboriginal Syllabics.
25441 36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993
25443 37. ISO/IEC 10967-1:1994, Information technology -- Language independent
25444 arithmetic -- Part 1: Integer and floating point arithmetic.
25449 38. ISO/IEC TR 19769:2004, Information technology -- Programming languages,
25450 their environments and system software interfaces -- Extensions for the
25451 programming language C to support new character data types.
25452 39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages,
25453 their environments and system software interfaces -- Extensions to the C library
25454 -- Part 1: Bounds-checking interfaces.
25467 [^ x ^], 3.20 , (comma operator), 5.1.2.4, 6.5.17
25468 , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
25469 [_ x _], 3.21 6.7.2.3, 6.7.9
25470 ! (logical negation operator), 6.5.3.3 - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2
25471 != (inequality operator), 6.5.9 - (unary minus operator), 6.5.3.3, F.3
25472 # operator, 6.10.3.2 -- (postfix decrement operator), 6.3.2.1, 6.5.2.4
25473 # preprocessing directive, 6.10.7 -- (prefix decrement operator), 6.3.2.1, 6.5.3.1
25474 # punctuator, 6.10 -= (subtraction assignment operator), 6.5.16.2
25475 ## operator, 6.10.3.3 -> (structure/union pointer operator), 6.5.2.3
25476 #define preprocessing directive, 6.10.3 . (structure/union member operator), 6.3.2.1,
25477 #elif preprocessing directive, 6.10.1 6.5.2.3
25478 #else preprocessing directive, 6.10.1 . punctuator, 6.7.9
25479 #endif preprocessing directive, 6.10.1 ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3
25480 #error preprocessing directive, 4, 6.10.5 / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1
25481 #if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, /* */ (comment delimiters), 6.4.9
25482 6.10.1, 7.1.4 // (comment delimiter), 6.4.9
25483 #ifdef preprocessing directive, 6.10.1 /= (division assignment operator), 6.5.16.2
25484 #ifndef preprocessing directive, 6.10.1 : (colon punctuator), 6.7.2.1
25485 #include preprocessing directive, 5.1.1.2, :> (alternative spelling of ]), 6.4.6
25486 6.10.2 ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3,
25487 #line preprocessing directive, 6.10.4 6.8.5, 6.8.6
25488 #pragma preprocessing directive, 6.10.6 < (less-than operator), 6.5.8
25489 #undef preprocessing directive, 6.10.3.5, 7.1.3, <% (alternative spelling of {), 6.4.6
25490 7.1.4 <: (alternative spelling of [), 6.4.6
25491 % (remainder operator), 6.2.6.2, 6.5.5 << (left-shift operator), 6.2.6.2, 6.5.7
25492 %: (alternative spelling of #), 6.4.6 <<= (left-shift assignment operator), 6.5.16.2
25493 %:%: (alternative spelling of ##), 6.4.6 <= (less-than-or-equal-to operator), 6.5.8
25494 %= (remainder assignment operator), 6.5.16.2 <assert.h> header, 7.2
25495 %> (alternative spelling of }), 6.4.6 <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2,
25496 & (address operator), 6.3.2.1, 6.5.3.2 7.3, 7.24, 7.30.1, G.6, J.5.17
25497 & (bitwise AND operator), 6.2.6.2, 6.5.10 <ctype.h> header, 7.4, 7.30.2
25498 && (logical AND operator), 5.1.2.4, 6.5.13 <errno.h> header, 7.5, 7.30.3, K.3.2
25499 &= (bitwise AND assignment operator), 6.5.16.2 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F,
25500 ' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, H
25501 7.4.1.10, 7.29.2.1.3 <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
25502 ( ) (cast operator), 6.5.4 7.28.4.1.1
25503 ( ) (function-call operator), 6.5.2.2 <inttypes.h> header, 7.8, 7.30.4
25504 ( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5 <iso646.h> header, 4, 7.9
25505 ( ){ } (compound-literal operator), 6.5.2.5 <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10
25506 * (asterisk punctuator), 6.7.6.1, 6.7.6.2 <locale.h> header, 7.11, 7.30.5
25507 * (indirection operator), 6.5.2.1, 6.5.3.2 <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,
25508 * (multiplication operator), 6.2.6.2, 6.5.5, F.3, F.10, J.5.17
25509 G.5.1 <setjmp.h> header, 7.13
25510 *= (multiplication assignment operator), 6.5.16.2 <signal.h> header, 7.14, 7.30.6
25511 + (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2, <stdalign.h> header, 4, 7.15
25512 6.5.6, F.3, G.5.2 <stdarg.h> header, 4, 6.7.6.3, 7.16
25513 + (unary plus operator), 6.5.3.3 <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17
25514 ++ (postfix increment operator), 6.3.2.1, 6.5.2.4 <stdbool.h> header, 4, 7.18, 7.30.7, H
25515 ++ (prefix increment operator), 6.3.2.1, 6.5.3.1 <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
25516 += (addition assignment operator), 6.5.16.2
25519 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \x hexadecimal digits (hexadecimal-character
25520 <stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, escape sequence), 6.4.4.4
25521 7.20, 7.30.8, K.3.3, K.3.4 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11
25522 <stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F, ^= (bitwise exclusive OR assignment operator),
25524 <stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F, __alignas_is_defined macro, 7.15
25525 K.3.1.4, K.3.6 __bool_true_false_are_defined
25526 <string.h> header, 7.23, 7.30.11, K.3.7 macro, 7.18
25527 <tgmath.h> header, 7.24, G.7 __cplusplus macro, 6.10.8
25528 <threads.h> header, 6.10.8.3, 7.1.2, 7.25 __DATE__ macro, 6.10.8.1
25529 <time.h> header, 7.26, K.3.8 __FILE__ macro, 6.10.8.1, 7.2.1.1
25530 <uchar.h> header, 6.4.4.4, 6.4.5, 7.27 __func__ identifier, 6.4.2.2, 7.2.1.1
25531 <wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28, __LINE__ macro, 6.10.8.1, 7.2.1.1
25532 7.30.12, F, K.3.9 __STDC_, 6.11.9
25533 <wctype.h> header, 7.29, 7.30.13 __STDC__ macro, 6.10.8.1
25534 = (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1
25535 = (simple assignment operator), 6.5.16.1 __STDC_HOSTED__ macro, 6.10.8.1
25536 == (equality operator), 6.5.9 __STDC_IEC_559__ macro, 6.10.8.3, F.1
25537 > (greater-than operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro,
25538 >= (greater-than-or-equal-to operator), 6.5.8 6.10.8.3, G.1
25539 >> (right-shift operator), 6.2.6.2, 6.5.7 __STDC_ISO_10646__ macro, 6.10.8.2
25540 >>= (right-shift assignment operator), 6.5.16.2 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2
25541 ? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_MB_MIGHT_NEQ_WC__ macro,
25542 ?? (trigraph sequences), 5.2.1.1 6.10.8.2, 7.19
25543 [ ] (array subscript operator), 6.5.2.1, 6.5.3.2 __STDC_NO_COMPLEX__ macro, 6.10.8.3,
25544 [ ] (brackets punctuator), 6.7.6.2, 6.7.9 7.3.1
25545 \ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 __STDC_NO_THREADS__ macro, 6.10.8.3,
25546 \ (escape character), 6.4.4.4 7.17.1, 7.25.1
25547 \" (double-quote escape sequence), 6.4.4.4, __STDC_NO_VLA__ macro, 6.10.8.3
25548 6.4.5, 6.10.9 __STDC_UTF_16__ macro, 6.10.8.2
25549 \\ (backslash escape sequence), 6.4.4.4, 6.10.9 __STDC_UTF_32__ macro, 6.10.8.2
25550 \' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_VERSION__ macro, 6.10.8.1
25551 \0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1
25552 padding of binary stream, 7.21.2 __TIME__ macro, 6.10.8.1
25553 \? (question-mark escape sequence), 6.4.4.4 __VA_ARGS__ identifier, 6.10.3, 6.10.3.1
25554 \a (alert escape sequence), 5.2.2, 6.4.4.4 _Alignas, 6.7.5
25555 \b (backspace escape sequence), 5.2.2, 6.4.4.4 _Atomic type qualifier, 6.7.2, 6.7.3
25556 \f (form-feed escape sequence), 5.2.2, 6.4.4.4, _Atomic-qualified type, 6.2.5, 6.2.6.1, 6.5.2.3,
25557 7.4.1.10 6.5.2.4, 6.5.16.2, 6.7.2, 6.7.3
25558 \n (new-line escape sequence), 5.2.2, 6.4.4.4, _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1,
25560 \octal digits (octal-character escape sequence), _Bool type conversions, 6.3.1.2
25561 6.4.4.4 _Complex types, 6.2.5, 6.7.2, 7.3.1, G
25562 \r (carriage-return escape sequence), 5.2.2, _Complex_I macro, 7.3.1
25563 6.4.4.4, 7.4.1.10 _Exit function, 7.22.4.5, 7.22.4.7
25564 \t (horizontal-tab escape sequence), 5.2.2, _Imaginary keyword, G.2
25565 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3 _Imaginary types, 7.3.1, G
25566 \U (universal character names), 6.4.3 _Imaginary_I macro, 7.3.1, G.6
25567 \u (universal character names), 6.4.3 _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
25568 \v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, _IOLBF macro, 7.21.1, 7.21.5.6
25569 7.4.1.10 _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
25573 _Noreturn, 6.7.4 alignment specifier, 6.7.5
25574 _Pragma operator, 5.1.1.2, 6.10.9 alignof operator, 6.5.3, 6.5.3.4
25575 _Static_assert, 6.7.10, 7.2 allocated storage, order and contiguity, 7.22.3
25576 _Thread_local storage-class specifier, 6.2.4, and macro, 7.9
25577 6.7.1 AND operators
25578 { } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, bitwise (&), 6.2.6.2, 6.5.10
25579 6.8.2 bitwise assignment (&=), 6.5.16.2
25580 { } (compound-literal operator), 6.5.2.5 logical (&&), 5.1.2.4, 6.5.13
25581 | (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 and_eq macro, 7.9
25582 |= (bitwise inclusive OR assignment operator), anonymous structure, 6.7.2.1
25583 6.5.16.2 anonymous union, 6.7.2.1
25584 || (logical OR operator), 5.1.2.4, 6.5.14 ANSI/IEEE 754, F.1
25585 ~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 ANSI/IEEE 854, F.1
25586 argc (main function parameter), 5.1.2.2.1
25587 abort function, 7.2.1.1, 7.14.1.1, 7.21.3, argument, 3.3
25588 7.22.4.1, 7.25.3.6, K.3.6.1.2 array, 6.9.1
25589 abort_handler_s function, K.3.6.1.2 default promotions, 6.5.2.2
25590 abs function, 7.22.6.1 function, 6.5.2.2, 6.9.1
25591 absolute-value functions macro, substitution, 6.10.3.1
25592 complex, 7.3.8, G.6.4 argument, complex, 7.3.9.1
25593 integer, 7.8.2.1, 7.22.6.1 argv (main function parameter), 5.1.2.2.1
25594 real, 7.12.7, F.10.4 arithmetic constant expression, 6.6
25595 abstract declarator, 6.7.7 arithmetic conversions, usual, see usual arithmetic
25596 abstract machine, 5.1.2.3 conversions
25597 access, 3.1, 6.7.3, L.2.1 arithmetic operators
25598 accuracy, see floating-point accuracy additive, 6.2.6.2, 6.5.6, G.5.2
25599 acos functions, 7.12.4.1, F.10.1.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12
25600 acos type-generic macro, 7.24 increment and decrement, 6.5.2.4, 6.5.3.1
25601 acosh functions, 7.12.5.1, F.10.2.1 multiplicative, 6.2.6.2, 6.5.5, G.5.1
25602 acosh type-generic macro, 7.24 shift, 6.2.6.2, 6.5.7
25603 acquire fence, 7.17.4 unary, 6.5.3.3
25604 acquire operation, 5.1.2.4 arithmetic types, 6.2.5
25605 active position, 5.2.2 arithmetic, pointer, 6.5.6
25606 actual argument, 3.3 array
25607 actual parameter (deprecated), 3.3 argument, 6.9.1
25608 addition assignment operator (+=), 6.5.16.2 declarator, 6.7.6.2
25609 addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, initialization, 6.7.9
25610 6.5.6, F.3, G.5.2 multidimensional, 6.5.2.1
25611 additive expressions, 6.5.6, G.5.2 parameter, 6.9.1
25612 address constant, 6.6 storage order, 6.5.2.1
25613 address operator (&), 6.3.2.1, 6.5.3.2 subscript operator ([ ]), 6.5.2.1, 6.5.3.2
25614 address-free, 7.17.5 subscripting, 6.5.2.1
25615 aggregate initialization, 6.7.9 type, 6.2.5
25616 aggregate types, 6.2.5 type conversion, 6.3.2.1
25617 alert escape sequence (\a), 5.2.2, 6.4.4.4 variable length, 6.7.6, 6.7.6.2, 6.10.8.3
25618 aliasing, 6.5 arrow operator (->), 6.5.2.3
25619 alignas macro, 7.15 as-if rule, 5.1.2.3
25620 aligned_alloc function, 7.22.3, 7.22.3.1 ASCII code set, 5.2.1.1
25621 alignment, 3.2, 6.2.8, 7.22.3.1 asctime function, 7.26.3.1
25622 pointer, 6.2.5, 6.3.2.3 asctime_s function, K.3.8.2, K.3.8.2.1
25623 structure/union member, 6.7.2.1 asin functions, 7.12.4.2, F.10.1.2
25627 asin type-generic macro, 7.24, G.7 atomic_is_lock_free generic function,
25628 asinh functions, 7.12.5.2, F.10.2.2 7.17.5.1
25629 asinh type-generic macro, 7.24, G.7 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
25630 asm keyword, J.5.10 atomic_load generic functions, 7.17.7.2
25631 assert macro, 7.2.1.1 ATOMIC_LONG_LOCK_FREE macro, 7.17.1
25632 assert.h header, 7.2 ATOMIC_SHORT_LOCK_FREE macro, 7.17.1
25633 assignment atomic_signal_fence function, 7.17.4.2
25634 compound, 6.5.16.2 atomic_store generic functions, 7.17.7.1
25635 conversion, 6.5.16.1 atomic_thread_fence function, 7.17.4.1
25636 expression, 6.5.16 ATOMIC_VAR_INIT macro, 7.17.2.1
25637 operators, 6.3.2.1, 6.5.16 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1
25638 simple, 6.5.16.1 atomics header, 7.17
25639 associativity of operators, 6.5 auto storage-class specifier, 6.7.1, 6.9
25640 asterisk punctuator (*), 6.7.6.1, 6.7.6.2 automatic storage duration, 5.2.3, 6.2.4
25641 at_quick_exit function, 7.22.4.2, 7.22.4.3,
25642 7.22.4.4, 7.22.4.5, 7.22.4.7 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
25643 atan functions, 7.12.4.3, F.10.1.3 backslash escape sequence (\\), 6.4.4.4, 6.10.9
25644 atan type-generic macro, 7.24, G.7 backspace escape sequence (\b), 5.2.2, 6.4.4.4
25645 atan2 functions, 7.12.4.4, F.10.1.4 basic character set, 3.6, 3.7.2, 5.2.1
25646 atan2 type-generic macro, 7.24 basic types, 6.2.5
25647 atanh functions, 7.12.5.3, F.10.2.3 behavior, 3.4
25648 atanh type-generic macro, 7.24, G.7 binary streams, 7.21.2, 7.21.7.10, 7.21.9.2,
25649 atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, 7.21.9.4
25650 7.22.4.5, 7.22.4.7, J.5.13 bit, 3.5
25651 atof function, 7.22.1, 7.22.1.1 high order, 3.6
25652 atoi function, 7.22.1, 7.22.1.2 low order, 3.6
25653 atol function, 7.22.1, 7.22.1.2 bit-field, 6.7.2.1
25654 atoll function, 7.22.1, 7.22.1.2 bitand macro, 7.9
25655 atomic lock-free macros, 7.17.1, 7.17.5 bitor macro, 7.9
25656 atomic operations, 5.1.2.4 bitwise operators, 6.5
25657 atomic types, 5.1.2.3, 6.10.8.3, 7.17.6 AND, 6.2.6.2, 6.5.10
25658 atomic_address type, 7.17.1, 7.17.6 AND assignment (&=), 6.5.16.2
25659 ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3
25660 atomic_bool type, 7.17.1, 7.17.6 exclusive OR, 6.2.6.2, 6.5.11
25661 ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR assignment (^=), 6.5.16.2
25662 7.17.1 inclusive OR, 6.2.6.2, 6.5.12
25663 ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR assignment (|=), 6.5.16.2
25664 7.17.1 shift, 6.2.6.2, 6.5.7
25665 ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 blank character, 7.4.1.3
25666 atomic_compare_exchange generic block, 6.8, 6.8.2, 6.8.4, 6.8.5
25667 functions, 7.17.7.4 block scope, 6.2.1
25668 atomic_exchange generic functions, 7.17.7.3 block structure, 6.2.1
25669 atomic_fetch and modify generic functions, bold type convention, 6.1
25670 7.17.7.5 bool macro, 7.18
25671 atomic_flag type, 7.17.1, 7.17.8 boolean type, 6.3.1.2
25672 atomic_flag_clear functions, 7.17.8.2 boolean type conversion, 6.3.1.1, 6.3.1.2
25673 ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8 bounded undefined behavior, L.2.2
25674 atomic_flag_test_and_set functions, braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9,
25676 atomic_init generic function, 7.17.2.2 brackets operator ([ ]), 6.5.2.1, 6.5.3.2
25677 ATOMIC_INT_LOCK_FREE macro, 7.17.1 brackets punctuator ([ ]), 6.7.6.2, 6.7.9
25681 branch cuts, 7.3.3 type-generic macro for, 7.24
25682 break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4
25683 broken-down time, 7.26.1, 7.26.2.3, 7.26.3, type-generic macro for, 7.24
25684 7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5, ceil functions, 7.12.9.1, F.10.6.1
25685 K.3.8.2.1, K.3.8.2.3, K.3.8.2.4 ceil type-generic macro, 7.24
25686 bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.30.1
25687 bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.30.1
25688 btowc function, 7.28.6.1.1 cexp functions, 7.3.7.1, G.6.3.1
25689 BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5 type-generic macro for, 7.24
25690 byte, 3.6, 6.5.3.4 cexp2 function, 7.30.1
25691 byte input/output functions, 7.21.1 cexpm1 function, 7.30.1
25692 byte-oriented stream, 7.21.2 char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2,
25694 C program, 5.1.1.1 char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
25695 c16rtomb function, 7.27.1.2 6.3.1.8
25696 c32rtomb function, 7.27.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
25697 cabs functions, 7.3.8.1, G.6 char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
25698 type-generic macro for, 7.24 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1
25699 cacos functions, 7.3.5.1, G.6.1.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
25700 type-generic macro for, 7.24 CHAR_MIN macro, 5.2.4.2.1
25701 cacosh functions, 7.3.6.1, G.6.2.1 character, 3.7, 3.7.1
25702 type-generic macro for, 7.24 character array initialization, 6.7.9
25703 calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, character case mapping functions, 7.4.2
25704 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, wide character, 7.29.3.1
25705 K.3.8.2.3, K.3.8.2.4 extensible, 7.29.3.2
25706 call by value, 6.5.2.2 character classification functions, 7.4.1
25707 call_once function, 7.25.1, 7.25.2.1 wide character, 7.29.2.1
25708 calloc function, 7.22.3, 7.22.3.2 extensible, 7.29.2.2
25709 carg functions, 7.3.9.1, G.6 character constant, 5.1.1.2, 5.2.1, 6.4.4.4
25710 carg type-generic macro, 7.24, G.7 character display semantics, 5.2.2
25711 carriage-return escape sequence (\r), 5.2.2, character handling header, 7.4, 7.11.1.1
25712 6.4.4.4, 7.4.1.10 character input/output functions, 7.21.7, K.3.5.4
25713 carries a dependency, 5.1.2.4 wide character, 7.28.3
25714 case label, 6.8.1, 6.8.4.2 character sets, 5.2.1
25715 case mapping functions character string literal, see string literal
25716 character, 7.4.2 character type conversion, 6.3.1.1
25717 wide character, 7.29.3.1 character types, 6.2.5, 6.7.9
25718 extensible, 7.29.3.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6
25719 casin functions, 7.3.5.2, G.6 cimag type-generic macro, 7.24, G.7
25720 type-generic macro for, 7.24 cis function, G.6
25721 casinh functions, 7.3.6.2, G.6.2.2 classification functions
25722 type-generic macro for, 7.24 character, 7.4.1
25723 cast expression, 6.5.4 floating-point, 7.12.3
25724 cast operator (( )), 6.5.4 wide character, 7.29.2.1
25725 catan functions, 7.3.5.3, G.6 extensible, 7.29.2.2
25726 type-generic macro for, 7.24 clearerr function, 7.21.10.1
25727 catanh functions, 7.3.6.3, G.6.2.3 clgamma function, 7.30.1
25728 type-generic macro for, 7.24 clock function, 7.26.2.1
25729 cbrt functions, 7.12.7.1, F.10.4.1 clock_t type, 7.26.1, 7.26.2.1
25730 cbrt type-generic macro, 7.24 CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1
25731 ccos functions, 7.3.5.4, G.6 clog functions, 7.3.7.2, G.6.3.2
25735 type-generic macro for, 7.24 string, 7.23.3, K.3.7.2
25736 clog10 function, 7.30.1 wide string, 7.28.4.3, K.3.9.2.2
25737 clog1p function, 7.30.1 concatenation, preprocessing, see preprocessing
25738 clog2 function, 7.30.1 concatenation
25739 CMPLX macros, 7.3.9.3 conceptual models, 5.1
25740 cnd_broadcast function, 7.25.3.1, 7.25.3.5, conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3,
25741 7.25.3.6 7.1.2, F.1, G.1, K.2, L.1
25742 cnd_destroy function, 7.25.3.2 conditional inclusion, 6.10.1
25743 cnd_init function, 7.25.3.3 conditional operator (? :), 5.1.2.4, 6.5.15
25744 cnd_signal function, 7.25.3.4, 7.25.3.5, conflict, 5.1.2.4
25745 7.25.3.6 conformance, 4
25746 cnd_t type, 7.25.1 conj functions, 7.3.9.4, G.6
25747 cnd_timedwait function, 7.25.3.5 conj type-generic macro, 7.24
25748 cnd_wait function, 7.25.3.3, 7.25.3.6 const type qualifier, 6.7.3
25749 collating sequences, 5.2.1 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
25750 colon punctuator (:), 6.7.2.1 constant expression, 6.6, F.8.4
25751 comma operator (,), 5.1.2.4, 6.5.17 constants, 6.4.4
25752 comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, as primary expression, 6.5.1
25753 6.7.2.3, 6.7.9 character, 6.4.4.4
25754 command processor, 7.22.4.8 enumeration, 6.2.1, 6.4.4.3
25755 comment delimiters (/* */ and //), 6.4.9 floating, 6.4.4.2
25756 comments, 5.1.1.2, 6.4, 6.4.9 hexadecimal, 6.4.4.1
25757 common extensions, J.5 integer, 6.4.4.1
25758 common initial sequence, 6.5.2.3 octal, 6.4.4.1
25759 common real type, 6.3.1.8 constraint, 3.8, 4
25760 common warnings, I constraint_handler_t type, K.3.6
25761 comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, consume operation, 5.1.2.4
25762 K.3.6.3, K.3.6.3.1, K.3.6.3.2 content of structure/union/enumeration, 6.7.2.3
25763 string, 7.23.4 contiguity of allocated storage, 7.22.3
25764 wide string, 7.28.4.4 continue statement, 6.8.6.2
25765 comparison macros, 7.12.14 contracted expression, 6.5, 7.12.2, F.7
25766 comparison, pointer, 6.5.8 control character, 5.2.1, 7.4
25767 compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control wide character, 7.29.2
25768 compl macro, 7.9 conversion, 6.3
25769 complement operator (~), 6.2.6.2, 6.5.3.3 arithmetic operands, 6.3.1
25770 complete type, 6.2.5 array argument, 6.9.1
25771 complex macro, 7.3.1 array parameter, 6.9.1
25772 complex numbers, 6.2.5, G arrays, 6.3.2.1
25773 complex type conversion, 6.3.1.6, 6.3.1.7 boolean, 6.3.1.2
25774 complex type domain, 6.2.5 boolean, characters, and integers, 6.3.1.1
25775 complex types, 6.2.5, 6.7.2, 6.10.8.3, G by assignment, 6.5.16.1
25776 complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2, by return statement, 6.8.6.4
25777 7.3, 7.24, 7.30.1, G.6, J.5.17 complex types, 6.3.1.6
25778 compliance, see conformance explicit, 6.3
25779 components of time, 7.26.1, K.3.8.1 function, 6.3.2.1
25780 composite type, 6.2.7 function argument, 6.5.2.2, 6.9.1
25781 compound assignment, 6.5.16.2 function designators, 6.3.2.1
25782 compound literals, 6.5.2.5 function parameter, 6.9.1
25783 compound statement, 6.8.2 imaginary, G.4.1
25784 compound-literal operator (( ){ }), 6.5.2.5 imaginary and complex, G.4.3
25785 concatenation functions implicit, 6.3
25789 lvalues, 6.3.2.1 csinh functions, 7.3.6.5, G.6.2.5
25790 pointer, 6.3.2.1, 6.3.2.3 type-generic macro for, 7.24
25791 real and complex, 6.3.1.7 csqrt functions, 7.3.8.3, G.6.4.2
25792 real and imaginary, G.4.2 type-generic macro for, 7.24
25793 real floating and integer, 6.3.1.4, F.3, F.4 ctan functions, 7.3.5.6, G.6
25794 real floating types, 6.3.1.5, F.3 type-generic macro for, 7.24
25795 signed and unsigned integers, 6.3.1.3 ctanh functions, 7.3.6.6, G.6.2.6
25796 usual arithmetic, see usual arithmetic type-generic macro for, 7.24
25797 conversions ctgamma function, 7.30.1
25798 void type, 6.3.2.2 ctime function, 7.26.3.2
25799 conversion functions ctime_s function, K.3.8.2, K.3.8.2.2
25800 multibyte/wide character, 7.22.7, K.3.6.4 ctype.h header, 7.4, 7.30.2
25801 extended, 7.28.6, K.3.9.3 current object, 6.7.9
25802 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
25803 multibyte/wide string, 7.22.8, K.3.6.5
25804 restartable, 7.28.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6,
25805 numeric, 7.8.2.3, 7.22.1 7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3,
25806 wide string, 7.8.2.4, 7.28.4.1 7.28.6.4
25807 single byte/wide character, 7.28.6.1 data stream, see streams
25808 time, 7.26.3, K.3.8.2 date and time header, 7.26, K.3.8
25809 wide character, 7.28.5 Daylight Saving Time, 7.26.1
25810 conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2
25811 7.28.2.2 DBL_DIG macro, 5.2.4.2.2
25812 conversion state, 7.22.7, 7.27.1, 7.27.1.1, DBL_EPSILON macro, 5.2.4.2.2
25813 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2
25814 7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2
25815 7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4, DBL_MAX macro, 5.2.4.2.2
25816 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
25817 K.3.9.3.2.2 DBL_MAX_EXP macro, 5.2.4.2.2
25818 conversion state functions, 7.28.6.2 DBL_MIN macro, 5.2.4.2.2
25819 copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2
25820 string, 7.23.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2
25821 wide string, 7.28.4.2, K.3.9.2.1 DBL_TRUE_MIN macro, 5.2.4.2.2
25822 copysign functions, 7.3.9.5, 7.12.11.1, F.3, decimal constant, 6.4.4.1
25823 F.10.8.1 decimal digit, 5.2.1
25824 copysign type-generic macro, 7.24 decimal-point character, 7.1.1, 7.11.2.1
25825 correctly rounded result, 3.9 DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1,
25826 corresponding real type, 6.2.5 7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5
25827 cos functions, 7.12.4.5, F.10.1.5 declaration specifiers, 6.7
25828 cos type-generic macro, 7.24, G.7 declarations, 6.7
25829 cosh functions, 7.12.5.4, F.10.2.4 function, 6.7.6.3
25830 cosh type-generic macro, 7.24, G.7 pointer, 6.7.6.1
25831 cpow functions, 7.3.8.2, G.6.4.1 structure/union, 6.7.2.1
25832 type-generic macro for, 7.24 typedef, 6.7.8
25833 cproj functions, 7.3.9.5, G.6 declarator, 6.7.6
25834 cproj type-generic macro, 7.24 abstract, 6.7.7
25835 creal functions, 7.3.9.6, G.6 declarator type derivation, 6.2.5, 6.7.6
25836 creal type-generic macro, 7.24, G.7 decrement operators, see arithmetic operators,
25837 critical undefined behavior, L.2.3 increment and decrement
25838 csin functions, 7.3.5.5, G.6 default argument promotions, 6.5.2.2
25839 type-generic macro for, 7.24 default initialization, 6.7.9
25843 default label, 6.8.1, 6.8.4.2 elif preprocessing directive, 6.10.1
25844 define preprocessing directive, 6.10.3 ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3
25845 defined operator, 6.10.1, 6.10.8 else preprocessing directive, 6.10.1
25846 definition, 6.7 else statement, 6.8.4.1
25847 function, 6.9.1 empty statement, 6.8.3
25848 dependency-ordered before, 5.1.2.4 encoding error, 7.21.3, 7.27.1.1, 7.27.1.2,
25849 derived declarator types, 6.2.5 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,
25850 derived types, 6.2.5 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,
25851 designated initializer, 6.7.9 K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1,
25852 destringizing, 6.10.9 K.3.9.3.2.2
25853 device input/output, 5.1.2.3 end-of-file, 7.28.1
25854 diagnostic message, 3.10, 5.1.1.3 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1,
25855 diagnostics, 5.1.1.3 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2,
25856 diagnostics header, 7.2 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1,
25857 difftime function, 7.26.2.2 7.28.3.10
25858 digit, 5.2.1, 7.4 end-of-file macro, see EOF macro
25859 digraphs, 6.4.6 end-of-line indicator, 5.2.1
25860 direct input/output functions, 7.21.8 endif preprocessing directive, 6.10.1
25861 display device, 5.2.2 enum type, 6.2.5, 6.7.2, 6.7.2.2
25862 div function, 7.22.6.2 enumerated type, 6.2.5
25863 div_t type, 7.22 enumeration, 6.2.5, 6.7.2.2
25864 division assignment operator (/=), 6.5.16.2 enumeration constant, 6.2.1, 6.4.4.3
25865 division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enumeration content, 6.7.2.3
25866 do statement, 6.8.5.2 enumeration members, 6.7.2.2
25867 documentation of implementation, 4 enumeration specifiers, 6.7.2.2
25868 domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration tag, 6.2.3, 6.7.2.3
25869 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumerator, 6.7.2.2
25870 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, environment, 5
25871 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, environment functions, 7.22.4, K.3.6.2
25872 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 environment list, 7.22.4.6, K.3.6.2.1
25873 dot operator (.), 6.5.2.3 environmental considerations, 5.2
25874 double _Complex type, 6.2.5 environmental limits, 5.2.4, 7.13.1.1, 7.21.2,
25875 double _Complex type conversion, 6.3.1.6, 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2,
25876 6.3.1.7, 6.3.1.8 7.22.4.3, 7.28.2.1, K.3.5.1.2
25877 double _Imaginary type, G.2 EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2,
25878 double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11,
25879 7.28.2.2, F.2 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4,
25880 double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9,
25881 6.3.1.8 7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4,
25882 double-precision arithmetic, 5.1.2.3 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12,
25883 double-quote escape sequence (\"), 6.4.4.4, 7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7,
25884 6.4.5, 6.10.9 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2,
25885 double_t type, 7.12, J.5.6 K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12,
25887 EDOM macro, 7.5, 7.12.1, see also domain error equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9
25888 effective type, 6.5 equal-to operator, see equality operator
25889 EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2, equality expressions, 6.5.9
25890 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, equality operator (==), 6.5.9
25891 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1,
25892 see also encoding error 7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see
25893 element type, 6.2.5 also range error, pole error
25897 erf functions, 7.12.8.1, F.10.5.1 exp type-generic macro, 7.24
25898 erf type-generic macro, 7.24 exp2 functions, 7.12.6.2, F.10.3.2
25899 erfc functions, 7.12.8.2, F.10.5.2 exp2 type-generic macro, 7.24
25900 erfc type-generic macro, 7.24 explicit conversion, 6.3
25901 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
25902 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, expm1 type-generic macro, 7.24
25903 7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1, exponent part, 6.4.4.2
25904 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1, exponential functions
25905 7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2, complex, 7.3.7, G.6.3
25906 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17, real, 7.12.6, F.10.3
25907 K.3.1.3, K.3.7.4.2 expression, 6.5
25908 errno.h header, 7.5, 7.30.3, K.3.2 assignment, 6.5.16
25909 errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, cast, 6.5.4
25910 K.3.7, K.3.8, K.3.9 constant, 6.6
25911 error evaluation, 5.1.2.3
25912 domain, see domain error full, 6.8
25913 encoding, see encoding error order of evaluation, see order of evaluation
25914 pole, see pole error parenthesized, 6.5.1
25915 range, see range error primary, 6.5.1
25916 error conditions, 7.12.1 unary, 6.5.3
25917 error functions, 7.12.8, F.10.5 expression statement, 6.8.3
25918 error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended alignment, 6.2.8
25919 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
25920 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended characters, 5.2.1
25921 7.28.3.1, 7.28.3.3 extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
25922 error preprocessing directive, 4, 6.10.5 7.20
25923 error-handling functions, 7.21.10, 7.23.6.2, extended multibyte/wide character conversion
25924 K.3.7.4.2, K.3.7.4.3 utilities, 7.28.6, K.3.9.3
25925 escape character (\), 6.4.4.4 extensible wide character case mapping functions,
25926 escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 7.29.3.2
25927 evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12 extensible wide character classification functions,
25928 evaluation method, 5.2.4.2.2, 6.5, F.8.5 7.29.2.2
25929 evaluation of expression, 5.1.2.3 extern storage-class specifier, 6.2.2, 6.7.1
25930 evaluation order, see order of evaluation external definition, 6.9
25931 exceptional condition, 6.5 external identifiers, underscore, 7.1.3
25932 excess precision, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, external linkage, 6.2.2
25933 6.8.6.4 external name, 6.4.2.1
25934 excess range, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4 external object definitions, 6.9.2
25935 exclusive OR operators
25936 bitwise (^), 6.2.6.2, 6.5.11 fabs functions, 7.12.7.2, F.3, F.10.4.2
25937 bitwise assignment (^=), 6.5.16.2 fabs type-generic macro, 7.24, G.7
25938 executable program, 5.1.1.1 false macro, 7.18
25939 execution character set, 5.2.1 fclose function, 7.21.5.1
25940 execution environment, 5, 5.1.2, see also fdim functions, 7.12.12.1, F.10.9.1
25941 environmental limits fdim type-generic macro, 7.24
25942 execution sequence, 5.1.2.3, 6.8 FE_ALL_EXCEPT macro, 7.6
25943 exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4, FE_DFL_ENV macro, 7.6
25944 7.22.4.5, 7.22.4.7 FE_DIVBYZERO macro, 7.6, 7.12, F.3
25945 EXIT_FAILURE macro, 7.22, 7.22.4.4 FE_DOWNWARD macro, 7.6, F.3
25946 EXIT_SUCCESS macro, 7.22, 7.22.4.4 FE_INEXACT macro, 7.6, F.3
25947 exp functions, 7.12.6.1, F.10.3.1 FE_INVALID macro, 7.6, 7.12, F.3
25951 FE_OVERFLOW macro, 7.6, 7.12, F.3 float _Complex type, 6.2.5
25952 FE_TONEAREST macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6,
25953 FE_TOWARDZERO macro, 7.6, F.3 6.3.1.7, 6.3.1.8
25954 FE_UNDERFLOW macro, 7.6, F.3 float _Imaginary type, G.2
25955 FE_UPWARD macro, 7.6, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
25956 feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
25957 fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 6.3.1.8
25958 fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
25959 fegetround function, 7.6, 7.6.3.1, F.3 7.28.4.1.1
25960 feholdexcept function, 7.6.4.2, 7.6.4.3, float_t type, 7.12, J.5.6
25961 7.6.4.4, F.3 floating constant, 6.4.4.2
25962 fence, 5.1.2.4 floating suffix, f or F, 6.4.4.2
25963 fences, 7.17.4 floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
25964 fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H F.3, F.4
25965 FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9, floating types, 6.2.5, 6.11.1
25966 F.10 floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5,
25967 fenv_t type, 7.6 7.22.1.3, F.5, see also contracted expression
25968 feof function, 7.21.10.2 floating-point arithmetic functions, 7.12, F.10
25969 feraiseexcept function, 7.6.2, 7.6.2.3, F.3 floating-point classification functions, 7.12.3
25970 ferror function, 7.21.10.3 floating-point control mode, 7.6, F.8.6
25971 fesetenv function, 7.6.4.3, F.3 floating-point environment, 7.6, F.8, F.8.6
25972 fesetexceptflag function, 7.6.2, 7.6.2.4, F.3 floating-point exception, 7.6, 7.6.2, F.10
25973 fesetround function, 7.6, 7.6.3.2, F.3 floating-point number, 5.2.4.2.2, 6.2.5
25974 fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point rounding mode, 5.2.4.2.2
25975 feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point status flag, 7.6, F.8.6
25976 fexcept_t type, 7.6, F.3 floor functions, 7.12.9.2, F.10.6.2
25977 fflush function, 7.21.5.2, 7.21.5.3 floor type-generic macro, 7.24
25978 fgetc function, 7.21.1, 7.21.3, 7.21.7.1, FLT_DECIMAL_DIG macro, 5.2.4.2.2
25979 7.21.7.5, 7.21.8.1 FLT_DIG macro, 5.2.4.2.2
25980 fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3 FLT_EPSILON macro, 5.2.4.2.2
25981 fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1 FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12,
25982 fgetwc function, 7.21.1, 7.21.3, 7.28.3.1, F.10.11
25983 7.28.3.6 FLT_HAS_SUBNORM macro, 5.2.4.2.2
25984 fgetws function, 7.21.1, 7.28.3.2 FLT_MANT_DIG macro, 5.2.4.2.2
25985 field width, 7.21.6.1, 7.28.2.1 FLT_MAX macro, 5.2.4.2.2
25986 file, 7.21.3 FLT_MAX_10_EXP macro, 5.2.4.2.2
25987 access functions, 7.21.5, K.3.5.2 FLT_MAX_EXP macro, 5.2.4.2.2
25988 name, 7.21.3 FLT_MIN macro, 5.2.4.2.2
25989 operations, 7.21.4, K.3.5.1 FLT_MIN_10_EXP macro, 5.2.4.2.2
25990 position indicator, 7.21.1, 7.21.2, 7.21.3, FLT_MIN_EXP macro, 5.2.4.2.2
25991 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10, FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3,
25992 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2, 7.28.2.1, 7.28.4.1.1
25993 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1, FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3
25994 7.28.3.3, 7.28.3.10 FLT_TRUE_MIN macro, 5.2.4.2.2
25995 positioning functions, 7.21.9 fma functions, 7.12, 7.12.13.1, F.10.10.1
25996 file scope, 6.2.1, 6.9 fma type-generic macro, 7.24
25997 FILE type, 7.21.1, 7.21.3 fmax functions, 7.12.12.2, F.10.9.2
25998 FILENAME_MAX macro, 7.21.1 fmax type-generic macro, 7.24
25999 flags, 7.21.6.1, 7.28.2.1, see also floating-point fmin functions, 7.12.12.3, F.10.9.3
26000 status flag fmin type-generic macro, 7.24
26001 flexible array member, 6.7.2.1 fmod functions, 7.12.10.1, F.10.7.1
26005 fmod type-generic macro, 7.24 fscanf_s function, K.3.5.3.2, K.3.5.3.4,
26006 fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 K.3.5.3.7, K.3.5.3.9
26007 FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10,
26008 K.3.5.1.1 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10
26009 fopen_s function, K.3.5.1.1, K.3.5.2.1, fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10,
26010 K.3.5.2.2 7.21.9.1, 7.21.9.3, 7.28.3.10
26011 for statement, 6.8.5, 6.8.5.3 ftell function, 7.21.9.2, 7.21.9.4
26012 form-feed character, 5.2.1, 6.4 full declarator, 6.7.6
26013 form-feed escape sequence (\f), 5.2.2, 6.4.4.4, full expression, 6.8
26014 7.4.1.10 fully buffered stream, 7.21.3
26015 formal argument (deprecated), 3.16 function
26016 formal parameter, 3.16 argument, 6.5.2.2, 6.9.1
26017 formatted input/output functions, 7.11.1.1, 7.21.6, body, 6.9.1
26018 K.3.5.3 call, 6.5.2.2
26019 wide character, 7.28.2, K.3.9.1 library, 7.1.4
26020 fortran keyword, J.5.9 declarator, 6.7.6.3, 6.11.6
26021 forward reference, 3.11 definition, 6.7.6.3, 6.9.1, 6.11.7
26022 FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see designator, 6.3.2.1
26023 also contracted expression image, 5.2.3
26024 FP_FAST_FMA macro, 7.12 inline, 6.7.4
26025 FP_FAST_FMAF macro, 7.12 library, 5.1.1.1, 7.1.4
26026 FP_FAST_FMAL macro, 7.12 name length, 5.2.4.1, 6.4.2.1, 6.11.3
26027 FP_ILOGB0 macro, 7.12, 7.12.6.5 no-return, 6.7.4
26028 FP_ILOGBNAN macro, 7.12, 7.12.6.5 parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1
26029 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,
26030 FP_NAN macro, 7.12, F.3 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12
26031 FP_NORMAL macro, 7.12, F.3 prototype scope, 6.2.1, 6.7.6.2
26032 FP_SUBNORMAL macro, 7.12, F.3 recursive call, 6.5.2.2
26033 FP_ZERO macro, 7.12, F.3 return, 6.8.6.4, F.6
26034 fpclassify macro, 7.12.3.1, F.3 scope, 6.2.1
26035 fpos_t type, 7.21.1, 7.21.2 type, 6.2.5
26036 fprintf function, 7.8.1, 7.21.1, 7.21.6.1, type conversion, 6.3.2.1
26037 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6, function specifiers, 6.7.4
26038 7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1 function type, 6.2.5
26039 fprintf_s function, K.3.5.3.1 function-call operator (( )), 6.5.2.2
26040 fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3, function-like macro, 6.10.3
26041 7.21.7.7, 7.21.8.2 fundamental alignment, 6.2.8
26042 fputs function, 7.21.1, 7.21.7.4 future directions
26043 fputwc function, 7.21.1, 7.21.3, 7.28.3.3, language, 6.11
26044 7.28.3.8 library, 7.30
26045 fputws function, 7.21.1, 7.28.3.4 fwide function, 7.21.2, 7.28.3.5
26046 fread function, 7.21.1, 7.21.8.1 fwprintf function, 7.8.1, 7.21.1, 7.21.6.2,
26047 free function, 7.22.3.3, 7.22.3.5 7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5,
26048 freestanding execution environment, 4, 5.1.2, 7.28.2.11, K.3.9.1.1
26049 5.1.2.1 fwprintf_s function, K.3.9.1.1
26050 freopen function, 7.21.2, 7.21.5.4 fwrite function, 7.21.1, 7.21.8.2
26051 freopen_s function, K.3.5.2.2 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2,
26052 frexp functions, 7.12.6.4, F.10.3.4 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10,
26053 frexp type-generic macro, 7.24 K.3.9.1.2
26054 fscanf function, 7.8.1, 7.21.1, 7.21.6.2, fwscanf_s function, K.3.9.1.2, K.3.9.1.5,
26055 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2 K.3.9.1.7, K.3.9.1.14
26059 gamma functions, 7.12.8, F.10.5 name spaces, 6.2.3
26060 general utilities, 7.22, K.3.6 reserved, 6.4.1, 7.1.3, K.3.1.2
26061 wide string, 7.28.4, K.3.9.2 scope, 6.2.1
26062 general wide string utilities, 7.28.4, K.3.9.2 type, 6.2.5
26063 generic parameters, 7.24 identifier list, 6.7.6
26064 generic selection, 6.5.1.1 identifier nondigit, 6.4.2.1
26065 getc function, 7.21.1, 7.21.7.5, 7.21.7.6 IEC 559, F.1
26066 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,
26067 getenv function, 7.22.4.6 7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G,
26068 getenv_s function, K.3.6.2.1 H.1
26069 gets function, K.3.5.4.1 IEEE 754, F.1
26070 gets_s function, K.3.5.4.1 IEEE 854, F.1
26071 getwc function, 7.21.1, 7.28.3.6, 7.28.3.7 IEEE floating-point arithmetic standard, see
26072 getwchar function, 7.21.1, 7.28.3.7 IEC 60559, ANSI/IEEE 754,
26073 gmtime function, 7.26.3.3 ANSI/IEEE 854
26074 gmtime_s function, K.3.8.2.3 if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
26075 goto statement, 6.2.1, 6.8.1, 6.8.6.1 6.10.1, 7.1.4
26076 graphic characters, 5.2.1 if statement, 6.8.4.1
26077 greater-than operator (>), 6.5.8 ifdef preprocessing directive, 6.10.1
26078 greater-than-or-equal-to operator (>=), 6.5.8 ifndef preprocessing directive, 6.10.1
26079 ignore_handler_s function, K.3.6.1.3
26080 happens before, 5.1.2.4 ilogb functions, 7.12, 7.12.6.5, F.10.3.5
26081 header, 5.1.1.1, 7.1.2, see also standard headers ilogb type-generic macro, 7.24
26082 header names, 6.4, 6.4.7, 6.10.2 imaginary macro, 7.3.1, G.6
26083 hexadecimal constant, 6.4.4.1 imaginary numbers, G
26084 hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4 imaginary type domain, G.2
26085 hexadecimal prefix, 6.4.4.1 imaginary types, G
26086 hexadecimal-character escape sequence imaxabs function, 7.8.2.1
26087 (\x hexadecimal digits), 6.4.4.4 imaxdiv function, 7.8, 7.8.2.2
26088 high-order bit, 3.6 imaxdiv_t type, 7.8
26089 horizontal-tab character, 5.2.1, 6.4 implementation, 3.12
26090 horizontal-tab escape sequence (\r), 7.29.2.1.3 implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1,
26091 horizontal-tab escape sequence (\t), 5.2.2, 6.7.6, 6.8.4.2, E, see also environmental
26092 6.4.4.4, 7.4.1.3, 7.4.1.10 limits
26093 hosted execution environment, 4, 5.1.2, 5.1.2.2 implementation-defined behavior, 3.4.1, 4, J.3
26094 HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3, implementation-defined value, 3.19.1
26095 7.28.4.1.1, F.10 implicit conversion, 6.3
26096 HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3, implicit initialization, 6.7.9
26097 7.28.4.1.1, F.10 include preprocessing directive, 5.1.1.2, 6.10.2
26098 HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3, inclusive OR operators
26099 7.28.4.1.1, F.10 bitwise (|), 6.2.6.2, 6.5.12
26100 hyperbolic functions bitwise assignment (|=), 6.5.16.2
26101 complex, 7.3.6, G.6.2 incomplete type, 6.2.5
26102 real, 7.12.5, F.10.2 increment operators, see arithmetic operators,
26103 hypot functions, 7.12.7.3, F.10.4.3 increment and decrement
26104 hypot type-generic macro, 7.24 indeterminate value, 3.19.2
26105 indeterminately sequenced, 5.1.2.3, 6.5.2.2,
26106 I macro, 7.3.1, 7.3.9.5, G.6 6.5.2.4, 6.5.16.2, see also sequenced before,
26107 identifier, 6.4.2.1, 6.5.1 unsequenced
26108 linkage, see linkage indirection operator (*), 6.5.2.1, 6.5.3.2
26109 maximum length, 6.4.2.1 inequality operator (!=), 6.5.9
26113 infinitary, 7.12.1 extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20
26114 INFINITY macro, 7.3.9.5, 7.12, F.2.1 inter-thread happens before, 5.1.2.4
26115 initial position, 5.2.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3
26116 initial shift state, 5.2.1.2 internal linkage, 6.2.2
26117 initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal name, 6.4.2.1
26118 F.8.5 interrupt, 5.2.3
26119 in blocks, 6.8 INTMAX_C macro, 7.20.4.2
26120 initializer, 6.7.9 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
26121 permitted form, 6.6 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
26122 string literal, 6.3.2.1 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
26123 inline, 6.7.4 7.28.2.1, 7.28.2.2
26124 inner scope, 6.2.1 INTN_C macros, 7.20.4.1
26125 input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, INTN_MAX macros, 7.20.2.1
26126 K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MIN macros, 7.20.2.1
26127 K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5, intN_t types, 7.20.1.1
26128 K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 INTPTR_MAX macro, 7.20.2.4
26129 input/output functions INTPTR_MIN macro, 7.20.2.4
26130 character, 7.21.7, K.3.5.4 intptr_t type, 7.20.1.4
26131 direct, 7.21.8 inttypes.h header, 7.8, 7.30.4
26132 formatted, 7.21.6, K.3.5.3 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
26133 wide character, 7.28.2, K.3.9.1 isalpha function, 7.4.1.1, 7.4.1.2
26134 wide character, 7.28.3 isblank function, 7.4.1.3
26135 formatted, 7.28.2, K.3.9.1 iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7,
26136 input/output header, 7.21, K.3.5 7.4.1.11
26137 input/output, device, 5.1.2.3 isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5,
26138 int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 7.4.1.7, 7.4.1.11, 7.11.1.1
26139 int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isfinite macro, 7.12.3.2, F.3
26140 6.3.1.8 isgraph function, 7.4.1.6
26141 INT_FASTN_MAX macros, 7.20.2.3 isgreater macro, 7.12.14.1, F.3
26142 INT_FASTN_MIN macros, 7.20.2.3 isgreaterequal macro, 7.12.14.2, F.3
26143 int_fastN_t types, 7.20.1.3 isinf macro, 7.12.3.3
26144 INT_LEASTN_MAX macros, 7.20.2.2 isless macro, 7.12.14.3, F.3
26145 INT_LEASTN_MIN macros, 7.20.2.2 islessequal macro, 7.12.14.4, F.3
26146 int_leastN_t types, 7.20.1.2 islessgreater macro, 7.12.14.5, F.3
26147 INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5 islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
26148 INT_MIN macro, 5.2.4.2.1, 7.12 7.4.2.2
26149 integer arithmetic functions, 7.8.2.1, 7.8.2.2, isnan macro, 7.12.3.4, F.3
26150 7.22.6 isnormal macro, 7.12.3.5
26151 integer character constant, 6.4.4.4 ISO 31-11, 2, 3
26152 integer constant, 6.4.4.1 ISO 4217, 2, 7.11.2.1
26153 integer constant expression, 6.3.2.3, 6.6, 6.7.2.1, ISO 8601, 2, 7.26.3.5
26154 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1, ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2
26155 7.1.4 ISO/IEC 10976-1, H.1
26156 integer conversion rank, 6.3.1.1 ISO/IEC 2382-1, 2, 3
26157 integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, ISO/IEC 646, 2, 5.2.1.1
26158 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3, ISO/IEC 9945-2, 7.11
26159 7.21.6.1, 7.28.2.1 ISO/IEC TR 10176, D
26160 integer suffix, 6.4.4.1 iso646.h header, 4, 7.9
26161 integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isprint function, 5.2.2, 7.4.1.8
26162 F.3, F.4 ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
26163 integer types, 6.2.5, 7.20 7.4.1.11
26167 isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9, Latin alphabet, 5.2.1, 6.4.2.1
26168 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
26169 7.22.1.4, 7.28.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3,
26170 isunordered macro, 7.12.14.6, F.3 7.28.4.4.2
26171 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,
26172 7.4.2.2 7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2,
26173 iswalnum function, 7.29.2.1.1, 7.29.2.1.9, 7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5
26174 7.29.2.1.10, 7.29.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
26175 iswalpha function, 7.29.2.1.1, 7.29.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
26176 7.29.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5
26177 iswblank function, 7.29.2.1.3, 7.29.2.2.1 lconv structure type, 7.11
26178 iswcntrl function, 7.29.2.1.2, 7.29.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2
26179 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_DIG macro, 5.2.4.2.2
26180 iswctype function, 7.29.2.2.1, 7.29.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2
26181 iswdigit function, 7.29.2.1.1, 7.29.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2
26182 7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2
26183 iswgraph function, 7.29.2.1, 7.29.2.1.6, LDBL_MAX macro, 5.2.4.2.2
26184 7.29.2.1.10, 7.29.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2
26185 iswlower function, 7.29.2.1.2, 7.29.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2
26186 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 LDBL_MIN macro, 5.2.4.2.2
26187 iswprint function, 7.29.2.1.6, 7.29.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2
26188 7.29.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2
26189 iswpunct function, 7.29.2.1, 7.29.2.1.2, LDBL_TRUE_MIN macro, 5.2.4.2.2
26190 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, ldexp functions, 7.12.6.6, F.10.3.6
26191 7.29.2.1.11, 7.29.2.2.1 ldexp type-generic macro, 7.24
26192 iswspace function, 7.21.6.2, 7.28.2.2, ldiv function, 7.22.6.2
26193 7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6, ldiv_t type, 7.22
26194 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, leading underscore in identifiers, 7.1.3
26195 7.29.2.1.11, 7.29.2.2.1 left-shift assignment operator (<<=), 6.5.16.2
26196 iswupper function, 7.29.2.1.2, 7.29.2.1.11, left-shift operator (<<), 6.2.6.2, 6.5.7
26197 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 length
26198 iswxdigit function, 7.29.2.1.12, 7.29.2.2.1 external name, 5.2.4.1, 6.4.2.1, 6.11.3
26199 isxdigit function, 7.4.1.12, 7.11.1.1 function name, 5.2.4.1, 6.4.2.1, 6.11.3
26200 italic type convention, 3, 6.1 identifier, 6.4.2.1
26201 iteration statements, 6.8.5 internal name, 5.2.4.1, 6.4.2.1
26202 length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1,
26203 jmp_buf type, 7.13 7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1
26204 jump statements, 6.8.6 length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,
26206 keywords, 6.4.1, G.2, J.5.9, J.5.10 less-than operator (<), 6.5.8
26207 kill_dependency macro, 5.1.2.4, 7.17.3.1 less-than-or-equal-to operator (<=), 6.5.8
26208 known constant size, 6.2.5 letter, 5.2.1, 7.4
26209 lexical elements, 5.1.1.2, 6.4
26210 L_tmpnam macro, 7.21.1, 7.21.4.4 lgamma functions, 7.12.8.3, F.10.5.3
26211 L_tmpnam_s macro, K.3.5, K.3.5.1.2 lgamma type-generic macro, 7.24
26212 label name, 6.2.1, 6.2.3 library, 5.1.1.1, 7, K.3
26213 labeled statement, 6.8.1 future directions, 7.30
26214 labs function, 7.22.6.1 summary, B
26215 language, 6 terms, 7.1.1
26216 future directions, 6.11 use of functions, 7.1.4
26217 syntax summary, A lifetime, 6.2.4
26221 limits long double _Complex type conversion,
26222 environmental, see environmental limits 6.3.1.6, 6.3.1.7, 6.3.1.8
26223 implementation, see implementation limits long double _Imaginary type, G.2
26224 numerical, see numerical limits long double suffix, l or L, 6.4.4.2
26225 translation, see translation limits long double type, 6.2.5, 6.4.4.2, 6.7.2,
26226 limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2
26227 line buffered stream, 7.21.3 long double type conversion, 6.3.1.4, 6.3.1.5,
26228 line number, 6.10.4, 6.10.8.1 6.3.1.7, 6.3.1.8
26229 line preprocessing directive, 6.10.4 long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,
26230 lines, 5.1.1.2, 7.21.2 7.21.6.2, 7.28.2.1, 7.28.2.2
26231 preprocessing directive, 6.10 long int type conversion, 6.3.1.1, 6.3.1.3,
26232 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
26233 6.11.2 long integer suffix, l or L, 6.4.4.1
26234 llabs function, 7.22.6.1 long long int type, 6.2.5, 6.3.1.1, 6.7.2,
26235 lldiv function, 7.22.6.2 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2
26236 lldiv_t type, 7.22 long long int type conversion, 6.3.1.1,
26237 LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.3.1.3, 6.3.1.4, 6.3.1.8
26238 7.28.4.1.2 long long integer suffix, ll or LL, 6.4.4.1
26239 LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4, LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
26240 7.28.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
26241 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,
26242 llrint type-generic macro, 7.24 7.22.4.7
26243 llround functions, 7.12.9.7, F.10.6.7 loop body, 6.8.5
26244 llround type-generic macro, 7.24 low-order bit, 3.6
26245 local time, 7.26.1 lowercase letter, 5.2.1
26246 locale, 3.4.2 lrint functions, 7.12.9.5, F.3, F.10.6.5
26247 locale-specific behavior, 3.4.2, J.4 lrint type-generic macro, 7.24
26248 locale.h header, 7.11, 7.30.5 lround functions, 7.12.9.7, F.10.6.7
26249 localeconv function, 7.11.1.1, 7.11.2.1 lround type-generic macro, 7.24
26250 localization, 7.11 lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16
26251 localtime function, 7.26.3.4
26252 localtime_s function, K.3.8.2.4 macro argument substitution, 6.10.3.1
26253 log functions, 7.12.6.7, F.10.3.7 macro definition
26254 log type-generic macro, 7.24 library function, 7.1.4
26255 log10 functions, 7.12.6.8, F.10.3.8 macro invocation, 6.10.3
26256 log10 type-generic macro, 7.24 macro name, 6.10.3
26257 log1p functions, 7.12.6.9, F.10.3.9 length, 5.2.4.1
26258 log1p type-generic macro, 7.24 predefined, 6.10.8, 6.11.9
26259 log2 functions, 7.12.6.10, F.10.3.10 redefinition, 6.10.3
26260 log2 type-generic macro, 7.24 scope, 6.10.3.5
26261 logarithmic functions macro parameter, 6.10.3
26262 complex, 7.3.7, G.6.3 macro preprocessor, 6.10
26263 real, 7.12.6, F.10.3 macro replacement, 6.10.3
26264 logb functions, 7.12.6.11, F.3, F.10.3.11 magnitude, complex, 7.3.8.1
26265 logb type-generic macro, 7.24 main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4,
26266 logical operators 7.21.3
26267 AND (&&), 5.1.2.4, 6.5.13 malloc function, 7.22.3, 7.22.3.4, 7.22.3.5
26268 negation (!), 6.5.3.3 manipulation functions
26269 OR (||), 5.1.2.4, 6.5.14 complex, 7.3.9
26270 logical source lines, 5.1.1.2 real, 7.12.11, F.10.8
26271 long double _Complex type, 6.2.5 matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10,
26275 K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modification order, 5.1.2.4
26276 math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, modulus functions, 7.12.6.12
26277 F.10, J.5.17 modulus, complex, 7.3.8.1
26278 MATH_ERREXCEPT macro, 7.12, F.10 mtx_destroy function, 7.25.4.1
26279 math_errhandling macro, 7.1.3, 7.12, F.10 mtx_init function, 7.25.1, 7.25.4.2
26280 MATH_ERRNO macro, 7.12 mtx_lock function, 7.25.4.3
26281 max_align_t type, 7.19 mtx_t type, 7.25.1
26282 maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.25.4.4
26283 MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.25.4.5
26284 7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3, mtx_unlock function, 7.25.4.3, 7.25.4.4,
26285 K.3.6.4.1, K.3.9.3.1.1 7.25.4.5, 7.25.4.6
26286 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
26287 mblen function, 7.22.7.1, 7.28.6.3 multibyte conversion functions
26288 mbrlen function, 7.28.6.3.1 wide character, 7.22.7, K.3.6.4
26289 mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1 extended, 7.28.6, K.3.9.3
26290 mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
26291 mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2, wide string, 7.22.8, K.3.6.5
26292 7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2, restartable, 7.28.6.4, K.3.9.3.2
26293 7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1 multibyte string, 7.1.1
26294 mbsinit function, 7.28.6.2.1 multibyte/wide character conversion functions,
26295 mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2 7.22.7, K.3.6.4
26296 mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1 extended, 7.28.6, K.3.9.3
26297 mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1, restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
26298 7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1, multibyte/wide string conversion functions,
26299 7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3, 7.22.8, K.3.6.5
26300 7.28.6.3.1, 7.28.6.4 restartable, 7.28.6.4, K.3.9.3.2
26301 mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4 multidimensional array, 6.5.2.1
26302 mbstowcs_s function, K.3.6.5.1 multiplication assignment operator (*=), 6.5.16.2
26303 mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2, multiplication operator (*), 6.2.6.2, 6.5.5, F.3,
26304 7.22.8.1, 7.28.6.3 G.5.1
26305 member access operators (. and ->), 6.5.2.3 multiplicative expressions, 6.5.5, G.5.1
26306 member alignment, 6.7.2.1
26307 memchr function, 7.23.5.1 n-char sequence, 7.22.1.3
26308 memcmp function, 7.23.4, 7.23.4.1 n-wchar sequence, 7.28.4.1.1
26309 memcpy function, 7.23.2.1 name
26310 memcpy_s function, K.3.7.1.1 external, 5.2.4.1, 6.4.2.1, 6.11.3
26311 memmove function, 7.23.2.2 file, 7.21.3
26312 memmove_s function, K.3.7.1.2 internal, 5.2.4.1, 6.4.2.1
26313 memory location, 3.14 label, 6.2.3
26314 memory management functions, 7.22.3 structure/union member, 6.2.3
26315 memory_order type, 7.17.1, 7.17.3 name spaces, 6.2.3
26316 memset function, 7.23.6.1, K.3.7.4.1 named label, 6.8.1
26317 memset_s function, K.3.7.4.1 NaN, 5.2.4.2.2
26318 minimum functions, 7.12.12, F.10.9 nan functions, 7.12.11.2, F.2.1, F.10.8.2
26319 minus operator, unary, 6.5.3.3 NAN macro, 7.12, F.2.1
26320 miscellaneous functions NDEBUG macro, 7.2
26321 string, 7.23.6, K.3.7.4 nearbyint functions, 7.12.9.3, 7.12.9.4, F.3,
26322 wide string, 7.28.4.6, K.3.9.2.4 F.10.6.3
26323 mktime function, 7.26.2.3 nearbyint type-generic macro, 7.24
26324 modf functions, 7.12.6.12, F.10.3.12 nearest integer functions, 7.12.9, F.10.6
26325 modifiable lvalue, 6.3.2.1 negation operator (!), 6.5.3.3
26329 negative zero, 6.2.6.2, 7.12.11.1 operator, 6.4.6
26330 new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operators, 6.5
26331 new-line escape sequence (\n), 5.2.2, 6.4.4.4, additive, 6.2.6.2, 6.5.6
26332 7.4.1.10 alignof, 6.5.3.4
26333 nextafter functions, 7.12.11.3, 7.12.11.4, F.3, assignment, 6.5.16
26334 F.10.8.3 associativity, 6.5
26335 nextafter type-generic macro, 7.24 equality, 6.5.9
26336 nexttoward functions, 7.12.11.4, F.3, F.10.8.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1
26337 nexttoward type-generic macro, 7.24 postfix, 6.5.2
26338 no linkage, 6.2.2 precedence, 6.5
26339 no-return function, 6.7.4 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
26340 non-stop floating-point control mode, 7.6.4.2 relational, 6.5.8
26341 nongraphic characters, 5.2.2, 6.4.4.4 shift, 6.5.7
26342 nonlocal jumps header, 7.13 sizeof, 6.5.3.4
26343 norm, complex, 7.3.8.1 unary, 6.5.3
26344 normalized broken-down time, K.3.8.1, K.3.8.2.1 unary arithmetic, 6.5.3.3
26345 not macro, 7.9 optional features, see conditional features
26346 not-equal-to operator, see inequality operator or macro, 7.9
26347 not_eq macro, 7.9 OR operators
26348 null character (\0), 5.2.1, 6.4.4.4, 6.4.5 bitwise exclusive (^), 6.2.6.2, 6.5.11
26349 padding of binary stream, 7.21.2 bitwise exclusive assignment (^=), 6.5.16.2
26350 NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1, bitwise inclusive (|), 6.2.6.2, 6.5.12
26351 7.26.1, 7.28.1 bitwise inclusive assignment (|=), 6.5.16.2
26352 null pointer, 6.3.2.3 logical (||), 5.1.2.4, 6.5.14
26353 null pointer constant, 6.3.2.3 or_eq macro, 7.9
26354 null preprocessing directive, 6.10.7 order of allocated storage, 7.22.3
26355 null statement, 6.8.3 order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3,
26356 null wide character, 7.1.1 see also sequence points
26357 number classification macros, 7.12, 7.12.3.1 ordinary identifier name space, 6.2.3
26358 numeric conversion functions, 7.8.2.3, 7.22.1 orientation of stream, 7.21.2, 7.28.3.5
26359 wide string, 7.8.2.4, 7.28.4.1 out-of-bounds store, L.2.1
26360 numerical limits, 5.2.4.2 outer scope, 6.2.1
26361 over-aligned, 6.2.8
26363 object representation, 6.2.6.1 padding
26364 object type, 6.2.5 binary stream, 7.21.2
26365 object-like macro, 6.10.3 bits, 6.2.6.2, 7.20.1.1
26366 observable behavior, 5.1.2.3 structure/union, 6.2.6.1, 6.7.2.1
26367 obsolescence, 6.11, 7.30 parameter, 3.16
26368 octal constant, 6.4.4.1 array, 6.9.1
26369 octal digit, 6.4.4.1, 6.4.4.4 ellipsis, 6.7.6.3, 6.10.3
26370 octal-character escape sequence (\octal digits), function, 6.5.2.2, 6.7, 6.9.1
26371 6.4.4.4 macro, 6.10.3
26372 offsetof macro, 7.19 main function, 5.1.2.2.1
26373 on-off switch, 6.10.6 program, 5.1.2.2.1
26374 once_flag type, 7.25.1 parameter type list, 6.7.6.3
26375 ONCE_FLAG_INIT macro, 7.25.1 parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5
26376 ones' complement, 6.2.6.2 parenthesized expression, 6.5.1
26377 operand, 6.4.6, 6.5 parse state, 7.21.2
26378 operating system, 5.1.2.1, 7.22.4.8 perform a trap, 3.19.5
26379 operations on files, 7.21.4, K.3.5.1 permitted form of initializer, 6.6
26383 perror function, 7.21.10.4 PRIcLEASTN macros, 7.8.1
26384 phase angle, complex, 7.3.9.1 PRIcMAX macros, 7.8.1
26385 physical source lines, 5.1.1.2 PRIcN macros, 7.8.1
26386 placemarker, 6.10.3.3 PRIcPTR macros, 7.8.1
26387 plus operator, unary, 6.5.3.3 primary expression, 6.5.1
26388 pointer arithmetic, 6.5.6 printf function, 7.21.1, 7.21.6.3, 7.21.6.10,
26389 pointer comparison, 6.5.8 K.3.5.3.3
26390 pointer declarator, 6.7.6.1 printf_s function, K.3.5.3.3
26391 pointer operator (->), 6.5.2.3 printing character, 5.2.2, 7.4, 7.4.1.8
26392 pointer to function, 6.5.2.2 printing wide character, 7.29.2
26393 pointer type, 6.2.5 program diagnostics, 7.2.1
26394 pointer type conversion, 6.3.2.1, 6.3.2.3 program execution, 5.1.2.2.2, 5.1.2.3
26395 pointer, null, 6.3.2.3 program file, 5.1.1.1
26396 pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, program image, 5.1.1.2
26397 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
26398 7.12.8.3, 7.12.8.4 program parameters, 5.1.2.2.1
26399 portability, 4, J program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
26400 position indicator, file, see file position indicator program structure, 5.1.1.1
26401 positive difference, 7.12.12.1 program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3,
26402 positive difference functions, 7.12.12, F.10.9 5.1.2.3
26403 postfix decrement operator (--), 6.3.2.1, 6.5.2.4 program, conforming, 4
26404 postfix expressions, 6.5.2 program, strictly conforming, 4
26405 postfix increment operator (++), 6.3.2.1, 6.5.2.4 promotions
26406 pow functions, 7.12.7.4, F.10.4.4 default argument, 6.5.2.2
26407 pow type-generic macro, 7.24 integer, 5.1.2.3, 6.3.1.1
26408 power functions prototype, see function prototype
26409 complex, 7.3.8, G.6.4 pseudo-random sequence functions, 7.22.2
26410 real, 7.12.7, F.10.4 PTRDIFF_MAX macro, 7.20.3
26411 pp-number, 6.4.8 PTRDIFF_MIN macro, 7.20.3
26412 pragma operator, 6.10.9 ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1,
26413 pragma preprocessing directive, 6.10.6, 6.11.8 7.21.6.2, 7.28.2.1, 7.28.2.2
26414 precedence of operators, 6.5 punctuators, 6.4.6
26415 precedence of syntax rules, 5.1.1.2 putc function, 7.21.1, 7.21.7.7, 7.21.7.8
26416 precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1 putchar function, 7.21.1, 7.21.7.8
26417 excess, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4 puts function, 7.21.1, 7.21.7.9
26418 predefined macro names, 6.10.8, 6.11.9 putwc function, 7.21.1, 7.28.3.8, 7.28.3.9
26419 prefix decrement operator (--), 6.3.2.1, 6.5.3.1 putwchar function, 7.21.1, 7.28.3.9
26420 prefix increment operator (++), 6.3.2.1, 6.5.3.1
26421 preprocessing concatenation, 6.10.3.3 qsort function, 7.22.5, 7.22.5.2
26422 preprocessing directives, 5.1.1.2, 6.10 qsort_s function, K.3.6.3, K.3.6.3.2
26423 preprocessing file, 5.1.1.1, 6.10 qualified types, 6.2.5
26424 preprocessing numbers, 6.4, 6.4.8 qualified version of type, 6.2.5
26425 preprocessing operators question-mark escape sequence (\?), 6.4.4.4
26426 #, 6.10.3.2 quick_exit function, 7.22.4.3, 7.22.4.4,
26427 ##, 6.10.3.3 7.22.4.7
26428 _Pragma, 5.1.1.2, 6.10.9 quiet NaN, 5.2.4.2.2
26430 preprocessing tokens, 5.1.1.2, 6.4, 6.10 raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1
26431 preprocessing translation unit, 5.1.1.1 rand function, 7.22, 7.22.2.1, 7.22.2.2
26432 preprocessor, 6.10 RAND_MAX macro, 7.22, 7.22.2.1
26433 PRIcFASTN macros, 7.8.1 range
26437 excess, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4 rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5,
26438 range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1, 7.28.3.10
26439 7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, right-shift assignment operator (>>=), 6.5.16.2
26440 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
26441 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
26442 7.12.11.3, 7.12.12.1, 7.12.13.1 rint type-generic macro, 7.24
26443 rank, see integer conversion rank round functions, 7.12.9.6, F.10.6.6
26444 read-modify-write operations, 5.1.2.4 round type-generic macro, 7.24
26445 real floating type conversion, 6.3.1.4, 6.3.1.5, rounding mode, floating point, 5.2.4.2.2
26446 6.3.1.7, F.3, F.4 RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2,
26447 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,
26448 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,
26449 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,
26450 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,
26451 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,
26452 recommended practice, 3.17 K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4,
26453 recursion, 6.5.2.2 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2,
26454 recursive function call, 6.5.2.2 K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1,
26455 redefinition of macro, 6.10.3 K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1,
26456 reentrancy, 5.1.2.3, 5.2.3 K.3.9.3.2.1, K.3.9.3.2.2
26457 library functions, 7.1.4 rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2,
26458 referenced type, 6.2.5 K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
26459 register storage-class specifier, 6.7.1, 6.9 runtime-constraint, 3.18
26460 relational expressions, 6.5.8 Runtime-constraint handling functions, K.3.6.1
26461 relaxed atomic operations, 5.1.2.4 rvalue, 6.3.2.1
26462 release fence, 7.17.4
26463 release operation, 5.1.2.4 same scope, 6.2.1
26464 release sequence, 5.1.2.4 save calling environment function, 7.13.1
26465 reliability of data, interrupted, 5.1.2.3 scalar types, 6.2.5
26466 remainder assignment operator (%=), 6.5.16.2 scalbln function, 7.12.6.13, F.3, F.10.3.13
26467 remainder functions, 7.12.10, F.10.7 scalbln type-generic macro, 7.24
26468 remainder functions, 7.12.10.2, 7.12.10.3, F.3, scalbn function, 7.12.6.13, F.3, F.10.3.13
26469 F.10.7.2 scalbn type-generic macro, 7.24
26470 remainder operator (%), 6.2.6.2, 6.5.5 scanf function, 7.21.1, 7.21.6.4, 7.21.6.11
26471 remainder type-generic macro, 7.24 scanf_s function, K.3.5.3.4, K.3.5.3.11
26472 remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2 scanlist, 7.21.6.2, 7.28.2.2
26473 remquo functions, 7.12.10.3, F.3, F.10.7.3 scanset, 7.21.6.2, 7.28.2.2
26474 remquo type-generic macro, 7.24 SCHAR_MAX macro, 5.2.4.2.1
26475 rename function, 7.21.4.2 SCHAR_MIN macro, 5.2.4.2.1
26476 representations of types, 6.2.6 SCNcFASTN macros, 7.8.1
26477 pointer, 6.2.5 SCNcLEASTN macros, 7.8.1
26478 rescanning and replacement, 6.10.3.4 SCNcMAX macros, 7.8.1
26479 reserved identifiers, 6.4.1, 7.1.3, K.3.1.2 SCNcN macros, 7.8.1
26480 restartable multibyte/wide character conversion SCNcPTR macros, 7.8.1
26481 functions, 7.27.1, 7.28.6.3, K.3.9.3.1 scope of identifier, 6.2.1, 6.9.2
26482 restartable multibyte/wide string conversion search functions
26483 functions, 7.28.6.4, K.3.9.3.2 string, 7.23.5, K.3.7.3
26484 restore calling environment function, 7.13.2 utility, 7.22.5, K.3.6.3
26485 restrict type qualifier, 6.7.3, 6.7.3.1 wide string, 7.28.4.5, K.3.9.2.3
26486 restrict-qualified type, 6.2.5, 6.7.3 SEEK_CUR macro, 7.21.1, 7.21.9.2
26487 return statement, 6.8.6.4, F.6 SEEK_END macro, 7.21.1, 7.21.9.2
26491 SEEK_SET macro, 7.21.1, 7.21.9.2 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7
26492 selection statements, 6.8.4 signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
26493 self-referential structure, 6.7.2.3 signal handling functions, 7.14.1
26494 semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, signal.h header, 7.14, 7.30.6
26495 6.8.5, 6.8.6 signaling NaN, 5.2.4.2.2, F.2.1
26496 separate compilation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1
26497 separate translation, 5.1.1.1 signbit macro, 7.12.3.6, F.3
26498 sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2,
26499 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, 7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2
26500 7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3 signed character, 6.3.1.1
26501 sequenced after, see sequenced before signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
26502 sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
26503 6.5.16, see also indeterminately sequenced, 6.3.1.8
26504 unsequenced signed types, 6.2.5, 6.7.2
26505 sequencing of statements, 6.8 significand part, 6.4.4.2
26506 set_constraint_handler_s function, SIGSEGV macro, 7.14, 7.14.1.1
26507 K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3 SIGTERM macro, 7.14
26508 setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5 simple assignment operator (=), 6.5.16.1
26509 setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1 sin functions, 7.12.4.6, F.10.1.6
26510 setjmp.h header, 7.13 sin type-generic macro, 7.24, G.7
26511 setlocale function, 7.11.1.1, 7.11.2.1 single-byte character, 3.7.1, 5.2.1.2
26512 setvbuf function, 7.21.1, 7.21.3, 7.21.5.1, single-byte/wide character conversion functions,
26513 7.21.5.5, 7.21.5.6 7.28.6.1
26514 shall, 4 single-precision arithmetic, 5.1.2.3
26515 shift expressions, 6.5.7 single-quote escape sequence (\'), 6.4.4.4, 6.4.5
26516 shift sequence, 7.1.1 singularity, 7.12.1
26517 shift states, 5.2.1.2 sinh functions, 7.12.5.5, F.10.2.5
26518 short identifier, character, 5.2.4.1, 6.4.3 sinh type-generic macro, 7.24, G.7
26519 short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, SIZE_MAX macro, 7.20.3
26520 7.21.6.2, 7.28.2.1, 7.28.2.2 size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1,
26521 short int type conversion, 6.3.1.1, 6.3.1.3, 7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27,
26522 6.3.1.4, 6.3.1.8 7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4,
26523 SHRT_MAX macro, 5.2.4.2.1 K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
26524 SHRT_MIN macro, 5.2.4.2.1 sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
26525 side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4, snprintf function, 7.21.6.5, 7.21.6.12,
26526 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5, K.3.5.3.5
26527 7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1, snprintf_s function, K.3.5.3.5, K.3.5.3.6
26528 F.9.3 snwprintf_s function, K.3.9.1.3, K.3.9.1.4
26529 SIG_ATOMIC_MAX macro, 7.20.3 sorting utility functions, 7.22.5, K.3.6.3
26530 SIG_ATOMIC_MIN macro, 7.20.3 source character set, 5.1.1.2, 5.2.1
26531 sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1, source file, 5.1.1.1
26532 7.20.3 name, 6.10.4, 6.10.8.1
26533 SIG_DFL macro, 7.14, 7.14.1.1 source file inclusion, 6.10.2
26534 SIG_ERR macro, 7.14, 7.14.1.1 source lines, 5.1.1.2
26535 SIG_IGN macro, 7.14, 7.14.1.1 source text, 5.1.1.2
26536 SIGABRT macro, 7.14, 7.22.4.1 space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
26537 SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17 7.4.1.10, 7.29.2.1.3
26538 SIGILL macro, 7.14, 7.14.1.1 sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6
26539 SIGINT macro, 7.14 sprintf_s function, K.3.5.3.5, K.3.5.3.6
26540 sign and magnitude, 6.2.6.2 sqrt functions, 7.12.7.5, F.3, F.10.4.5
26541 sign bit, 6.2.6.2 sqrt type-generic macro, 7.24
26545 srand function, 7.22.2.2 expression, 6.8.3
26546 sscanf function, 7.21.6.7, 7.21.6.14 for, 6.8.5.3
26547 sscanf_s function, K.3.5.3.7, K.3.5.3.14 goto, 6.8.6.1
26548 standard error stream, 7.21.1, 7.21.3, 7.21.10.4 if, 6.8.4.1
26549 standard headers, 4, 7.1.2 iteration, 6.8.5
26550 <assert.h>, 7.2 jump, 6.8.6
26551 <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, labeled, 6.8.1
26552 7.24, 7.30.1, G.6, J.5.17 null, 6.8.3
26553 <ctype.h>, 7.4, 7.30.2 return, 6.8.6.4, F.6
26554 <errno.h>, 7.5, 7.30.3, K.3.2 selection, 6.8.4
26555 <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H sequencing, 6.8
26556 <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3, switch, 6.8.4.2
26557 7.28.4.1.1 while, 6.8.5.1
26558 <inttypes.h>, 7.8, 7.30.4 static assertions, 6.7.10
26559 <iso646.h>, 4, 7.9 static storage duration, 6.2.4
26560 <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10 static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
26561 <locale.h>, 7.11, 7.30.5 static, in array declarators, 6.7.6.2, 6.7.6.3
26562 <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10, static_assert declaration, 6.7.10
26563 J.5.17 static_assert macro, 7.2
26564 <setjmp.h>, 7.13 stdalign.h header, 4, 7.15
26565 <signal.h>, 7.14, 7.30.6 stdarg.h header, 4, 6.7.6.3, 7.16
26566 <stdalign.h>, 4, 7.15 stdatomic.h header, 6.10.8.3, 7.1.2, 7.17
26567 <stdarg.h>, 4, 6.7.6.3, 7.16 stdbool.h header, 4, 7.18, 7.30.7, H
26568 <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17 STDC, 6.10.6, 6.11.8
26569 <stdbool.h>, 4, 7.18, 7.30.7, H stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
26570 <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3
26571 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 stderr macro, 7.21.1, 7.21.2, 7.21.3
26572 <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4,
26573 7.30.8, K.3.3, K.3.4 7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4,
26574 <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 K.3.5.4.1, K.3.9.1.14
26575 <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F, stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,
26576 K.3.1.4, K.3.6 7.30.8, K.3.3, K.3.4
26577 <string.h>, 7.23, 7.30.11, K.3.7 stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5
26578 <tgmath.h>, 7.24, G.7 stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F,
26579 <threads.h>, 6.10.8.3, 7.1.2, 7.25 K.3.1.4, K.3.6
26580 <time.h>, 7.26, K.3.8 stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3,
26581 <uchar.h>, 6.4.4.4, 6.4.5, 7.27 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9
26582 <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, storage duration, 6.2.4
26583 F, K.3.9 storage order of array, 6.5.2.1
26584 <wctype.h>, 7.29, 7.30.13 storage unit (bit-field), 6.2.6.1, 6.7.2.1
26585 standard input stream, 7.21.1, 7.21.3 storage-class specifiers, 6.7.1, 6.11.5
26586 standard integer types, 6.2.5 strcat function, 7.23.3.1
26587 standard output stream, 7.21.1, 7.21.3 strcat_s function, K.3.7.2.1
26588 standard signed integer types, 6.2.5 strchr function, 7.23.5.2
26589 state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4 strcmp function, 7.23.4, 7.23.4.2
26590 statements, 6.8 strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5
26591 break, 6.8.6.3 strcpy function, 7.23.2.3
26592 compound, 6.8.2 strcpy_s function, K.3.7.1.3
26593 continue, 6.8.6.2 strcspn function, 7.23.5.3
26594 do, 6.8.5.2 streams, 7.21.2, 7.22.4.4
26595 else, 6.8.4.1 fully buffered, 7.21.3
26599 line buffered, 7.21.3 strtoumax function, 7.8.2.3
26600 orientation, 7.21.2 struct hack, see flexible array member
26601 standard error, 7.21.1, 7.21.3 struct lconv, 7.11
26602 standard input, 7.21.1, 7.21.3 struct tm, 7.26.1
26603 standard output, 7.21.1, 7.21.3 structure
26604 unbuffered, 7.21.3 arrow operator (->), 6.5.2.3
26605 strerror function, 7.21.10.4, 7.23.6.2 content, 6.7.2.3
26606 strerror_s function, K.3.7.4.2, K.3.7.4.3 dot operator (.), 6.5.2.3
26607 strerrorlen_s function, K.3.7.4.3 initialization, 6.7.9
26608 strftime function, 7.11.1.1, 7.26.3, 7.26.3.5, member alignment, 6.7.2.1
26609 7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2 member name space, 6.2.3
26610 stricter, 6.2.8 member operator (.), 6.3.2.1, 6.5.2.3
26611 strictly conforming program, 4 pointer operator (->), 6.5.2.3
26612 string, 7.1.1 specifier, 6.7.2.1
26613 comparison functions, 7.23.4 tag, 6.2.3, 6.7.2.3
26614 concatenation functions, 7.23.3, K.3.7.2 type, 6.2.5, 6.7.2.1
26615 conversion functions, 7.11.1.1 strxfrm function, 7.11.1.1, 7.23.4.5
26616 copying functions, 7.23.2, K.3.7.1 subnormal floating-point numbers, 5.2.4.2.2
26617 library function conventions, 7.23.1 subscripting, 6.5.2.1
26618 literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9 subtraction assignment operator (-=), 6.5.16.2
26619 miscellaneous functions, 7.23.6, K.3.7.4 subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2
26620 numeric conversion functions, 7.8.2.3, 7.22.1 suffix
26621 search functions, 7.23.5, K.3.7.3 floating constant, 6.4.4.2
26622 string handling header, 7.23, K.3.7 integer constant, 6.4.4.1
26623 string.h header, 7.23, 7.30.11, K.3.7 switch body, 6.8.4.2
26624 stringizing, 6.10.3.2, 6.10.9 switch case label, 6.8.1, 6.8.4.2
26625 strlen function, 7.23.6.3 switch default label, 6.8.1, 6.8.4.2
26626 strncat function, 7.23.3.2 switch statement, 6.8.1, 6.8.4.2
26627 strncat_s function, K.3.7.2.2 swprintf function, 7.28.2.3, 7.28.2.7,
26628 strncmp function, 7.23.4, 7.23.4.4 K.3.9.1.3, K.3.9.1.4
26629 strncpy function, 7.23.2.4 swprintf_s function, K.3.9.1.3, K.3.9.1.4
26630 strncpy_s function, K.3.7.1.4 swscanf function, 7.28.2.4, 7.28.2.8
26631 strnlen_s function, K.3.7.4.4 swscanf_s function, K.3.9.1.5, K.3.9.1.10
26632 stronger, 6.2.8 symbols, 3
26633 strpbrk function, 7.23.5.4 synchronization operation, 5.1.2.4
26634 strrchr function, 7.23.5.5 synchronize with, 5.1.2.4
26635 strspn function, 7.23.5.6 syntactic categories, 6.1
26636 strstr function, 7.23.5.7 syntax notation, 6.1
26637 strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3, syntax rule precedence, 5.1.1.2
26638 7.28.2.2, F.3 syntax summary, language, A
26639 strtof function, 7.12.11.2, 7.22.1.3, F.3 system function, 7.22.4.8
26640 strtoimax function, 7.8.2.3
26641 strtok function, 7.23.5.8 tab characters, 5.2.1, 6.4
26642 strtok_s function, K.3.7.3.1 tag compatibility, 6.2.7
26643 strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tag name space, 6.2.3
26644 7.22.1.4, 7.28.2.2 tags, 6.7.2.3
26645 strtold function, 7.12.11.2, 7.22.1.3, F.3 tan functions, 7.12.4.7, F.10.1.7
26646 strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4 tan type-generic macro, 7.24, G.7
26647 strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tanh functions, 7.12.5.6, F.10.2.6
26648 7.22.1.4, 7.28.2.2 tanh type-generic macro, 7.24, G.7
26649 strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4 temporary lifetime, 6.2.4
26653 tentative definition, 6.9.2 towlower function, 7.29.3.1.1, 7.29.3.2.1
26654 terms, 3 towupper function, 7.29.3.1.2, 7.29.3.2.1
26655 text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 translation environment, 5, 5.1.1
26656 tgamma functions, 7.12.8.4, F.10.5.4 translation limits, 5.2.4.1
26657 tgamma type-generic macro, 7.24 translation phases, 5.1.1.2
26658 tgmath.h header, 7.24, G.7 translation unit, 5.1.1.1, 6.9
26659 thrd_create function, 7.25.1, 7.25.5.1 trap, see perform a trap
26660 thrd_current function, 7.25.5.2 trap representation, 3.19.4, 6.2.6.1, 6.2.6.2,
26661 thrd_detach function, 7.25.5.3, 7.25.5.6 6.3.2.3, 6.5.2.3
26662 thrd_equal function, 7.25.5.4 trigonometric functions
26663 thrd_exit function, 7.25.5.5 complex, 7.3.5, G.6.1
26664 thrd_join function, 7.25.5.3, 7.25.5.6 real, 7.12.4, F.10.1
26665 thrd_sleep function, 7.25.5.7 trigraph sequences, 5.1.1.2, 5.2.1.1
26666 thrd_start_t type, 7.25.1 true macro, 7.18
26667 thrd_t type, 7.25.1 trunc functions, 7.12.9.8, F.10.6.8
26668 thrd_yield function, 7.25.5.8 trunc type-generic macro, 7.24
26669 thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6 truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3
26670 thread storage duration, 6.2.4, 7.6 truncation toward zero, 6.5.5
26671 threads header, 7.25 tss_create function, 7.25.6.1
26672 threads.h header, 6.10.8.3, 7.1.2, 7.25 tss_delete function, 7.25.6.2
26673 time TSS_DTOR_ITERATIONS macro, 7.25.1
26674 broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1, tss_dtor_t type, 7.25.1
26675 7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1, tss_get function, 7.25.6.3
26676 K.3.8.2.3, K.3.8.2.4 tss_set function, 7.25.6.4
26677 calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, tss_t type, 7.25.1
26678 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, two's complement, 6.2.6.2, 7.20.1.1
26679 K.3.8.2.3, K.3.8.2.4 type category, 6.2.5
26680 components, 7.26.1, K.3.8.1 type conversion, 6.3
26681 conversion functions, 7.26.3, K.3.8.2 type definitions, 6.7.8
26682 wide character, 7.28.5 type domain, 6.2.5, G.2
26683 local, 7.26.1 type names, 6.7.7
26684 manipulation functions, 7.26.2 type punning, 6.5.2.3
26685 normalized broken down, K.3.8.1, K.3.8.2.1 type qualifiers, 6.7.3
26686 time function, 7.26.2.4 type specifiers, 6.7.2
26687 time.h header, 7.26, K.3.8 type-generic macro, 7.24, G.7
26688 time_t type, 7.26.1 typedef declaration, 6.7.8
26689 TIME_UTC macro, 7.25.7.1 typedef storage-class specifier, 6.7.1, 6.7.8
26690 tm structure type, 7.26.1, 7.28.1, K.3.8.1 types, 6.2.5
26691 TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4 _Atomic qualified, 6.2.5, 6.2.6.1, 6.5.2.3,
26692 TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2 6.5.2.4, 6.5.16.2, 6.7.2, 6.7.3
26693 tmpfile function, 7.21.4.3, 7.22.4.4 atomic, 5.1.2.3, 6.10.8.3, 7.17.6
26694 tmpfile_s function, K.3.5.1.1, K.3.5.1.2 character, 6.7.9
26695 tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4, compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6
26696 K.3.5.1.2 complex, 6.2.5, G
26697 tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2 composite, 6.2.7
26698 token, 5.1.1.2, 6.4, see also preprocessing tokens const qualified, 6.7.3
26699 token concatenation, 6.10.3.3 conversions, 6.3
26700 token pasting, 6.10.3.3 imaginary, G
26701 tolower function, 7.4.2.1 restrict qualified, 6.7.3
26702 toupper function, 7.4.2.2 volatile qualified, 6.7.3
26703 towctrans function, 7.29.3.2.1, 7.29.3.2.2
26707 uchar.h header, 6.4.4.4, 6.4.5, 7.27 universal character name, 6.4.3
26708 UCHAR_MAX macro, 5.2.4.2.1 unnormalized floating-point numbers, 5.2.4.2.2
26709 UINT_FASTN_MAX macros, 7.20.2.3 unqualified type, 6.2.5
26710 uint_fastN_t types, 7.20.1.3 unqualified version of type, 6.2.5
26711 uint_least16_t type, 7.27 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also
26712 uint_least32_t type, 7.27 indeterminately sequenced, sequenced
26713 UINT_LEASTN_MAX macros, 7.20.2.2 before
26714 uint_leastN_t types, 7.20.1.2 unsigned char type, K.3.5.3.2, K.3.9.1.2
26715 UINT_MAX macro, 5.2.4.2.1 unsigned integer suffix, u or U, 6.4.4.1
26716 UINTMAX_C macro, 7.20.4.2 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1
26717 UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 unsigned type conversion, 6.3.1.1, 6.3.1.3,
26718 uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, 6.3.1.4, 6.3.1.8
26719 7.28.2.1, 7.28.2.2 unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2,
26720 UINTN_C macros, 7.20.4.1 7.28.2.1, 7.28.2.2
26721 UINTN_MAX macros, 7.20.2.1 unspecified behavior, 3.4.4, 4, J.1
26722 uintN_t types, 7.20.1.1 unspecified value, 3.19.3
26723 UINTPTR_MAX macro, 7.20.2.4 uppercase letter, 5.2.1
26724 uintptr_t type, 7.20.1.4 use of library functions, 7.1.4
26725 ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, USHRT_MAX macro, 5.2.4.2.1
26726 7.28.4.1.2 usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6,
26727 ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
26728 7.28.4.1.2 UTF-16, 6.10.8.2
26729 unary arithmetic operators, 6.5.3.3 UTF-32, 6.10.8.2
26730 unary expression, 6.5.3 UTF-8 string literal, see string literal
26731 unary minus operator (-), 6.5.3.3, F.3 utilities, general, 7.22, K.3.6
26732 unary operators, 6.5.3 wide string, 7.28.4, K.3.9.2
26733 unary plus operator (+), 6.5.3.3
26734 unbuffered stream, 7.21.3 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2,
26735 undef preprocessing directive, 6.10.3.5, 7.1.3, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
26736 7.1.4 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
26737 undefined behavior, 3.4.3, 4, J.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
26738 underscore character, 6.4.2.1 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
26739 underscore, leading, in identifier, 7.1.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
26740 ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2, va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1,
26741 7.21.9.3 7.16.1.2, 7.16.1.3
26742 ungetwc function, 7.21.1, 7.28.3.10 va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3,
26743 Unicode, 7.27, see also char16_t type, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
26744 char32_t type, wchar_t type 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
26745 Unicode required set, 6.10.8.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
26746 union 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
26747 arrow operator (->), 6.5.2.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
26748 content, 6.7.2.3 va_list type, 7.16, 7.16.1.3
26749 dot operator (.), 6.5.2.3 va_start macro, 7.16, 7.16.1, 7.16.1.1,
26750 initialization, 6.7.9 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8,
26751 member alignment, 6.7.2.1 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12,
26752 member name space, 6.2.3 7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6,
26753 member operator (.), 6.3.2.1, 6.5.2.3 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10,
26754 pointer operator (->), 6.5.2.3 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7,
26755 specifier, 6.7.2.1 K.3.9.1.10, K.3.9.1.12
26756 tag, 6.2.3, 6.7.2.3 value, 3.19
26757 type, 6.2.5, 6.7.2.1 value bits, 6.2.6.2
26761 variable arguments, 6.10.3, 7.16 vswscanf function, 7.28.2.8
26762 variable arguments header, 7.16 vswscanf_s function, K.3.9.1.10
26763 variable length array, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11
26764 variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf_s function, K.3.9.1.11
26765 vertical-tab character, 5.2.1, 6.4 vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10
26766 vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, vwscanf_s function, K.3.9.1.12
26768 vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8 warnings, I
26769 vfprintf_s function, K.3.5.3.8, K.3.5.3.9, wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,
26770 K.3.5.3.11, K.3.5.3.14 F, K.3.9
26771 vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9 WCHAR_MAX macro, 7.20.3, 7.28.1
26772 vfscanf_s function, K.3.5.3.9, K.3.5.3.11, WCHAR_MIN macro, 7.20.3, 7.28.1
26773 K.3.5.3.14 wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19,
26774 vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1,
26775 vfwprintf_s function, K.3.9.1.6 7.28.2.1, 7.28.2.2
26776 vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10 wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2,
26777 vfwscanf_s function, K.3.9.1.7 7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1,
26778 visibility of identifier, 6.2.1 K.3.9.3.2.2
26779 visible sequence of side effects, 5.1.2.4 wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1
26780 visible side effect, 5.1.2.4 wcscat function, 7.28.4.3.1
26781 VLA, see variable length array wcscat_s function, K.3.9.2.2.1
26782 void expression, 6.3.2.2 wcschr function, 7.28.4.5.1
26783 void function parameter, 6.7.6.3 wcscmp function, 7.28.4.4.1, 7.28.4.4.4
26784 void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2, wcscoll function, 7.28.4.4.2, 7.28.4.4.4
26785 K.3.9.1.2 wcscpy function, 7.28.4.2.1
26786 void type conversion, 6.3.2.2 wcscpy_s function, K.3.9.2.1.1
26787 volatile storage, 5.1.2.3 wcscspn function, 7.28.4.5.2
26788 volatile type qualifier, 6.7.3 wcsftime function, 7.11.1.1, 7.28.5.1
26789 volatile-qualified type, 6.2.5, 6.7.3 wcslen function, 7.28.4.6.1
26790 vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10, wcsncat function, 7.28.4.3.2
26791 K.3.5.3.10 wcsncat_s function, K.3.9.2.2.2
26792 vprintf_s function, K.3.5.3.9, K.3.5.3.10, wcsncmp function, 7.28.4.4.3
26793 K.3.5.3.11, K.3.5.3.14 wcsncpy function, 7.28.4.2.2
26794 vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11 wcsncpy_s function, K.3.9.2.1.2
26795 vscanf_s function, K.3.5.3.9, K.3.5.3.11, wcsnlen_s function, K.3.9.2.4.1
26796 K.3.5.3.14 wcspbrk function, 7.28.4.5.3
26797 vsnprintf function, 7.21.6.8, 7.21.6.12, wcsrchr function, 7.28.4.5.4
26798 K.3.5.3.12 wcsrtombs function, 7.28.6.4.2, K.3.9.3.2
26799 vsnprintf_s function, K.3.5.3.9, K.3.5.3.11, wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2
26800 K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcsspn function, 7.28.4.5.5
26801 vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9 wcsstr function, 7.28.4.5.6
26802 vsprintf function, 7.21.6.8, 7.21.6.13, wcstod function, 7.21.6.2, 7.28.2.2
26803 K.3.5.3.13 wcstod function, 7.28.4.1.1
26804 vsprintf_s function, K.3.5.3.9, K.3.5.3.11, wcstof function, 7.28.4.1.1
26805 K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcstoimax function, 7.8.2.4
26806 vsscanf function, 7.21.6.8, 7.21.6.14 wcstok function, 7.28.4.5.7
26807 vsscanf_s function, K.3.5.3.9, K.3.5.3.11, wcstok_s function, K.3.9.2.3.1
26808 K.3.5.3.14 wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2,
26809 vswprintf function, 7.28.2.7, K.3.9.1.8, 7.28.4.1.2
26810 K.3.9.1.9 wcstold function, 7.28.4.1.1
26811 vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.28.4.1.2
26815 wcstombs function, 7.22.8.2, 7.28.6.4 7.29.1
26816 wcstombs_s function, K.3.6.5.2 wmemchr function, 7.28.4.5.8
26817 wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2, wmemcmp function, 7.28.4.4.5
26818 7.28.4.1.2 wmemcpy function, 7.28.4.2.3
26819 wcstoull function, 7.8.2.4, 7.28.4.1.2 wmemcpy_s function, K.3.9.2.1.3
26820 wcstoumax function, 7.8.2.4 wmemmove function, 7.28.4.2.4
26821 wcsxfrm function, 7.28.4.4.4 wmemmove_s function, K.3.9.2.1.4
26822 wctob function, 7.28.6.1.2, 7.29.2.1 wmemset function, 7.28.4.6.2
26823 wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3 wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11,
26824 wctomb_s function, K.3.6.4.1 K.3.9.1.13
26825 wctrans function, 7.29.3.2.1, 7.29.3.2.2 wprintf_s function, K.3.9.1.13
26826 wctrans_t type, 7.29.1, 7.29.3.2.2 wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12,
26827 wctype function, 7.29.2.2.1, 7.29.2.2.2 7.28.3.10
26828 wctype.h header, 7.29, 7.30.13 wscanf_s function, K.3.9.1.12, K.3.9.1.14
26829 wctype_t type, 7.29.1, 7.29.2.2.2
26830 weaker, 6.2.8 xor macro, 7.9
26831 WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6, xor_eq macro, 7.9
26832 7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10, xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7,
26833 7.28.6.1.1, 7.29.1 7.25.7.1
26834 while statement, 6.8.5.1 xtime_get function, 7.25.7.1
26835 white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
26837 white-space characters, 6.4
26838 wide character, 3.7.3
26839 case mapping functions, 7.29.3.1
26840 extensible, 7.29.3.2
26841 classification functions, 7.29.2.1
26842 extensible, 7.29.2.2
26844 formatted input/output functions, 7.28.2,
26846 input functions, 7.21.1
26847 input/output functions, 7.21.1, 7.28.3
26848 output functions, 7.21.1
26849 single-byte conversion functions, 7.28.6.1
26851 wide string comparison functions, 7.28.4.4
26852 wide string concatenation functions, 7.28.4.3,
26854 wide string copying functions, 7.28.4.2, K.3.9.2.1
26855 wide string literal, see string literal
26856 wide string miscellaneous functions, 7.28.4.6,
26858 wide string numeric conversion functions, 7.8.2.4,
26860 wide string search functions, 7.28.4.5, K.3.9.2.3
26861 wide-oriented stream, 7.21.2
26863 WINT_MAX macro, 7.20.3
26864 WINT_MIN macro, 7.20.3
26865 wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1,
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